We investigated the effect of increased spring (April–May) dust aerosol over the Arabian Peninsula (AP) on the subseasonal- to-seasonal (S2S) variability of the Asian summer monsoon (ASM) using MERRA-2 re-analysis data (1980–2018). Result shows that abundant AP spring dust leads to more dust covering the AP and Pakistan northwestern India (PNWI) during May–June, causing a cooler land surface and a warmer lower and middle atmosphere with enhanced local atmospheric stabil- ity. However, the warmer atmosphere increases the meridional temperature gradient, boosting moisture transport from the Arabian Sea to PNWI, causing increased convective potential energy in PNWI region. As season advances, the accumulated convection potential energy eventually breaks through the local stability, via the elevated heat pump (EHP) effect, increas- ing precipitation over PNWI. In July and August, cloud radiation-circulation feedback further enhances the warming of the upper troposphere, strengthening precipitation in PNWI. Dynamical adjustments of large-scale circulations induced by the feedback strongly modulate ASM precipitation. Over southern and central China, precipitation is reduced, in conjunction with a contraction of South Asian High, and the development of an anomalous east-to-west oriented upper-level wavetrain in July. In August, the upper level wavetrain undergoes strong wave-mean flow interaction, culminating in the development of an anticyclonic center with drought conditions over northeast China, Korea and Japan. Over the Indian subcontinent, increased precipitation in PNWI plays an important role in initiating the EHP feedback leading to increased precipitation over the Indian subcontinent, and in modulating the jetstream-wave interaction in downstream East Asian regions in July–August

The Asian Tropopause Aerosol Layer (ATAL) has emerged over recent decades to play an increasingly prominent role in the upper troposphere and lower stratosphere above the Asian monsoon region. Although the effects of the ATAL on the surface and top-of-atmosphere radiation budget have been examined by several studies, the processes and effects by which the ATAL alters radiative transfer within the tropopause layer have been much less discussed. We have used a conditional composite approach to investigate aerosol mixing ratios and their impacts on radiative heating rates in the Asian monsoon tropopause layer in MERRA-2. We have subsampled based on the evolution of emission and data assimilation inputs to the MERRA-2 aerosol analysis to isolate the ATAL contribution and compare it to radiative heating signatures in the monsoon anticyclone region after volcanic eruptions. The results indicate that the ATAL impact on radiative heating rates in this region is on the order of 0.1 K/day, similar to that associated with ozone variability in MERRA-2 but weaker than cloud radiative effects at these altitudes. We have validated these results and tested their sensitivity to variations in the vertical structure and composition of ATAL aerosols using offline radiative transfer simulations. The idealized simulations produce similar but slightly stronger responses of radiative heating rates to the ATAL. Although the ATAL perturbations inferred from MERRA-2 are only about 10% of mean heating rates at these levels, their spatial distribution suggests potential implications for both isentropic and diabatic transport within the monsoon anticyclone, which should be examined in future work. Our results are limited by uncertainties in the composition and spatiotemporal variability of the ATAL, and reflect only the conditions in this layer as represented by MERRA-2, targeted observations and model simulations are needed to adequately constrain the uncertainties.

The precipitation variability is subject to impacts of both ocean and land surface condition changes. The influence of sea surface temperature (SST) anomalies in the tropical Indo-Pacific region on the Indochina Peninsular precipitation variability has been shown in previous studies. The present talk presents evidence for the role of land surface condition in the interannual variation of the early rainy season (May-June) precipitation over the Indochina Peninsula. A precursory signal is identified in surface air temperature (SAT) during March-April over central Asia after the late 1970s. The air temperature anomalies extend to middle troposphere and persist to early summer (May-June) and modulate the land-sea thermal contrast and lower-level and upper-level winds over the North Indian Ocean and thus affect the early rainy season precipitation over the Indochina Peninsula. The maintenance of SAT anomalies over central Asia is related to that of surface heat flux anomalies that in turn is attributed to the persisting atmospheric wind anomalies. The precursory signal is weak before the late 1970s due to the lack of persisting atmospheric wind anomalies. The interdecadal change in the persistence of central Asian SAT anomalies is associated with a difference in the distribution of the North Atlantic SST anomalies. After the late 1970s, the North Atlantic SST anomalies with a southwest-northeast distribution excite a wave train that extends from the North Atlantic to central Asia during May-June. Before the late 1970s, the wave train associated the North Atlantic SST anomalies with a south-north distribution is confined to the North Atlantic region. The role of the North Atlantic SST anomalies is illustrated using numerical model experiments.

Future change in summertime rainfall under a warmer climate will impact the lives of more than two-thirds of the world’s population. However, the future changes in the duration of the rainy season affected by regional characteristics are not yet entirely understood. We try to understand changes in the length of the rainy season as well as the amounts of the future summertime precipitation, and the related processes over regional monsoon domains using phase six of the Coupled Model Intercomparison Project archive. Projections reveal extensions of the rainy season over the most of monsoon domains, except over the American monsoon. Enhancing the precipitation in the future climate has various increasing rates depending on the subregional monsoon, and it is mainly affected by changes in thermodynamic factors. This study promotes awareness for the risk of unforeseen future situations by showing regional changes in precipitation according to future scenarios.

A reliable projection of future South Asian summer monsoon (SASM) benefits a large population in Asia. Using a 100-member ensemble of simulations by the Max Planck Institute Earth System Model (MPI-ESM) and a 50-member ensemble of simulations by the Canadian Earth System Model (CanESM2), we find that internal variability can overshadow the forced SASM rainfall trend, leading to large projection uncertainties for the next 15 to 30 years. We further identify that the Interdecadal Pacific Oscillation (IPO) is, in part, responsible for the uncertainties. Removing the IPO-related rainfall variations reduces the uncertainties in the near-term projection of the SASM rainfall by 13 to 15% and 26 to 30% in the MPI-ESM and CanESM2 ensembles, respectively. Our results demonstrate that the uncertainties in near-term projections of the SASM rainfall can be reduced by improving prediction of near-future IPO and other internal modes of climate variability.

Linkages between the variability of the Antarctic Sea Ice Extent (AnSIE) and the tropical climate has been extensively investigated. The study examines the interannual relationship between the variability of sea ice extent in the Indian Ocean (SIEIO) sector (20º–90ºE) and Indian summer monsoon rainfall (ISMR) under the influence of the Mascarene High (MH). SIEIO in high (HIP) and low (LIP) ice phase years during April-May-June (AMJ) appeared to have a significant correlation to ISMR in the Peninsula India region during June-July-August-September (JJAS), with correlation coefficients of 0.51 and 0.71, respectively. Composites of mean sea level pressure (MSLP), 500 hPa geopotential height, and 850 hPa wind anomalies during HIP and LIP also showed that there was a relationship between the SIEIO and the MH, revealing that HIP and LIP correspond respectively to the strengthening and weakening of the MH as well as increases/decreases in ISMR. During the respective HIP and LIP years, positive and negative MSLP anomalies were found respectively, particularly over the MH region associated with the eastwards and westwards shifts of its center from the normal locations. Similar features were also observed at 500 hPa geopotential height anomalies. In addition, 850 hPa wind flow illustrated strong anti-cyclonic and cyclonic anomalies in the MH region, which lead to corresponding strong and weak southwesterlies and thus respective positive and negative ISMR anomalies. Hence, a positive MH anomaly was associated with more ISMR.

The summer monsoon 2020 (June through September 2020) has been very erratic with episodes of heavy and devastating rains, landslides, catastrophic winds over South Asia (India, Pakistan, Nepal, Bangladesh), over East Asia (China, Korea, and Japan), and Southeast Asia (Singapore, Thailand, Vietnam, Laos, Cambodia, Philippines, Indonesia). The Korean Peninsula has experienced back-to-back severe typhoons during the 2020 monsoon period. Post the monsoon period the South China Sea / the Philippines Sea experienced super typhoons. China recorded a Dam burst. The withdrawal of the summer monsoon over India was delayed by more than a month. In fact India has experienced two consecutive excess monsoons 2019 and 2020. Monsoon season over South Korea has been the longest during 2020 season. Even the river Nile reached its highest level for more than a century due to torrential rains. Could the lockdown activities initiated to control the COVID-19 spread a possible cause for these major episodes?   The lockdown activities resulted in the practical standstill of the Travel Industry (Air, Rail, and Road) and the Construction industry. Even shopping malls and restaurants were closed, vehicle and human movements were restricted. These activities may have resulted in a considerable decrease in air pollutants – dust and aerosols. Reduced use of diesel and petrol may have also resulted in reduced CO2 emissions. Recent studies on the variation of air quality have documented a considerable reduction in air pollutants over East Asia as well as South Asia. It has been well documented that dust particles, aerosols can modulate the atmospheric circulation and precipitation distribution through alteration of the solar and terrestrial radiation.  Details of these episodes over the Asian domain as well over other parts of globe are planned to be discussed at the Virtual AOGS21 meeting in Singapore      

During autumn season, typhoons located far away from Japan sometimes cause large amounts of precipitation in Japan. The mechanism of remote precipitation is not clearly understood and only a few case studies have been conducted in Japan. A phenomenon like remote precipitation over North American continent is called Predecessor Rain Event (PRE), and many cases have been conducted. However, remote precipitation occurs mainly over the sea, while PRE occurs over land, so the environmental fields are quite different, and not all cases in Japan can be explained by the characteristics of PRE. In this study, we extracted and statistically analyzed the cases which remote precipitation occurred and didn’t occur when typhoons were approaching Japan in September for 40 years from 1980 to 2019. The characteristics of remote precipitation are as follows: the distribution of typhoons center at the time of occurrence is widely distributed from east to west between 120E and 150E, and the proportion of typhoons causing remote precipitation in September is about 24%. In more than 90% of the cases, remote precipitation tends to occur in the north to northeast direction of the typhoon. In most of the cases, the path of the typhoons was northward or approaching while recurving to Japan. The composite analysis of remote precipitation showed that the extending change of the subtropical high was weakening tendency from day-2 to day0. The positional relationship between the 200hPa isotach and the precipitation area showed that the precipitation area is located to the right of the jet streak entrance, like the PRE. On the other hand, in the cases of not remote precipitation, the subtropical high extended westward from day-2 to day0, which is opposite to remote precipitation. 

Typhoon Haiyan crossed the Philippines on November 8, 2013. It is estimated to be the lowest pressure ever recorded, and one of the largest tropical cyclones to hit there in recent years (Hoarau et al., 2017). The typhoon caused economic damage amounted to about US$2 billion, with the loss of at least 6,300 lives, 28,689 injured and 1,061 missing. The devastated area seemed to be suffered by the storm surge rather than the winds. Particularly, the interaction between the surface winds and the funnel-shaped coast along San Pedro Bay caused a storm surge of 6m in Tacloban (Galvin et al., 2014). As for this disaster, we analyzed the cloud properties of typhoon Haiyan using thermal infrared imagery of MTSAT-1R, i.e. IR1<10.3-11.3µm>, IR2<11.5-12.5µm>, IR3<6.2-7.3µm> and IR4<3.3-4.2µm, hourly from 1830UTC on November 3, 2013 to 0430UTC on November 11, 2013. The brightness temperature difference (BTD) among the four infrared bands, i.e. SPL<IR1-IR2>, DIW<IR1-IR3>, DIN<IR4-IR1>, were also analyzed. The area of analyses was defined within the radius of 1,600km from the center of typhoon Haiyan, and the time variations of the brightness temperature and BTD were investigated. Then the center position was obtained by interpolating the Typhoon Best Track Data, prepared every six-hour by Japan Meteorological Agency. The results revealed that the clouds which made up Haiyan were developing before landfall in the Philippines. The IR1 images showed that the cloud top temperature started to decrease after the afternoon of November 6. At the same time, the water vapor content within Haiyan increased according to IR3 images. In addition, the area of the brightness temperature differences between IR1 and IR3 to be lower than the threshold indicating cumulonimbus (typically 1.5 degrees) enlarged during the same period, suggesting the extraordinary intensity of typhoon Haiyan before hitting Philippines. 

Korea AirForce (KAF) has been retaining the numerical weather prediction model to forecast the daily weather conditions and to produce customized disaster information for aiding the military operation early and for minimizing the damage from the severe weather conditions. Along with the development of KAF’s numerical weather prediction models and the increasing number of computational resources, the need for the study to develop the operational numerical model to make it for the better prediction to the severe/local weather conditions that occurred in a short time was increased. Thus, the numerical weather prediction model for typhoon forecasting was newly developed based on the KAF's operational high-resolution regional model (KAF-WRF) to improve its performance of the original typhoon forecast model (KAF-TWRF) through the research service project in 2019. The newly developed model for typhoon forecasting (KAF-NTWRF) is consisted of three domains with 12km (601x451), 4km (301x301), and 1.33km (301x301) horizontal resolutions (grid points), respectively. We used the two-way moving nesting technique for domain 2 and 3 to resolve the inner core structure of typhoons realistically. To compare the sensitivity of physics settings to typhoon forecasting and their dissimilar reaction to the synoptic-scale weather phenomena, we selected three cumulus parameterization schemes (CPS) of Kain-Fritsch (KF), Betts-Miller-Janjic (BMJ), modified Tiedtke (TDK), and also three microphysics schemes (MPS) of WRF-single-moment-microphysics class 3 (WSM3), WRF-single-moment-microphysics class 6 (WSM6), Predicted Particle Properties (P3). We selected three TCs that recently affected South Korea and suffered rapid intensification while they moved to the mid-latitudes. The results show that there was a significant difference in simulated typhoon intensity and track performances depending on the physics schemes. Generally, the typhoon forecast skills were improved in sensitivity experiments with KF for CPS and P3 or WSM6 for MPS than others, which related to the better performances in the typhoon intensification process. 

We conducted an ensemble simulation with 1000 members on the Supercomputer Fugaku by using a nonhydrostatic icosahedral atmospheric model (NICAM) with a 14-km mesh, which was targeted to Typhoon Faxai (2019). Ensemble members started from different initial dates from 26 August 2019 to 4 September (10 days). NICAM-LETKF JAXA Research Analysis (NEXRA) was used as the initial atmospheric condition of the ensemble experiment. The NEXRA provided 100 perturbed atmospheric conditions for each initial date. The total number of ensemble members was 1000 in this study. The sea surface temperature was calculated by a slab ocean model, which was nudged to NOAA OI SST V2.1. The ensemble simulations ran for about 30 days. As a Faxai-like typhoon in an ensemble member, we regarded a tropical cyclone that met the following two conditions. 1) The tropical cyclone must pass over an area within 10 degrees of the Faxai genesis location (156.7E, 18.6N) and within 5 days of the Faxai genesis time (18UTC 4 Sep. 2019). 2) The tropical cyclone must pass an area within 10 degrees from a location (139.7E, 35.3N) within 5 days before or after 18UTC 8 Sep. 2019. Fewer number of ensemble members with the short lead time reproduced the Faxai-like typhoon than that of members with the long lead time. This is a possible reason why the short lead time is insufficient for a vortex being intensified, which may become a typhoon. As for tracks of the Faxai-like typhoon, these tracks differed between members of which even experiments started from the same initial date. The variations were more prominent in the long lead time experiments than those of the short lead time experiments. We will investigate a reason why the genesis and track of the Faxai-like typhoon substantially differ between the members.

This study develops a seasonal prediction model based on the statistical correlation between East Asia (EA) tropical cyclone (TC) landfall and atmospheric circulation, and its predictability is verified. The developed model is called statistical-dynamical seasonal typhoon forecast model (SDTFM) and uses the atmospheric circulation predicted by a coupled general circulation model as a predictor. A total of 40 ensemble members produced through different data assimilation and time-lag methods introduced as a way to reduce the initial condition error and model uncertainty enabled the development of the new SDTFM. According to the results, the SDTFM developed in this study shows a significant predictability in TC landfall prediction, when using the month of May for the initial conditions for the entire East Asia (EEA) and Northern East Asia (NEA), including the Korean Peninsula and Japan. Also, for Middle East Asia (MEA), including Taiwan, Fujian, Zhejiang, Jiangsu, and Shanghai, and Southern East Asia (SEA), which includes the south of China, the Philippines, and Vietnam, predictions using February for the initial conditions are better. The annual variability of EA TCs that make landfall is significantly predicted at the 99% confidence level, except for SEA, where the results are still significant at the 95% confidence level, even after cross-validation. The reason for the relatively low predictability in SEA seems to be a lack of outstanding steering flow in the region.
Acknowledgement
This work was carried out with the support of Cooperative Research Program for Agriculture Science and Technology Development (Project No. PJ01475503)" Rural Development Administration, Republic of Korea.

Understanding the impact of transit-oriented development (TOD) on the urban thermal environment is essential to guide the effective urban design at the neighborhood scale. TOD has a direct impact on urban mobility, lifestyle thus modifying the thermal environment. However, the level of the impact is unknown which requires additional investigation. This study numerically assesses the impact of urban development along with the Tsukuba Express (TX) railway, Tokyo, Japan on the change in thermal environment and human comfort. The TX is selected because the railway connects the high, mid-urban and suburban areas in-around the Tokyo Metropolitan region. Thus, the impact of TX on the urban environment could be evaluated separately for each type of urban area. The Weather Research and Forecasting (WRF) model with a 250-m horizontal resolution is used to simulate the area along the entire railway line including the three representative stations from 05 to 08 of August. The study uses two simulation cases: 2005 and 2015, before and after the construction of the TX, respectively. First, the results from the control simulation were verified against observations. The WRF model reproduced well the diurnal temperature variation in 2005 and 2015 along the TX railway. The mean model bias is from -0.3 C to 0.1 ºC in 2005 and 2015. Second, the impact of urbanization on the surface air temperature distribution along the TX railways is evaluated. The results show that the most significant temperature increase (2.3ºC) is simulated in Kenkyu-gakuen station between Cases 2005 and 2015 at 1900 JST. In this area, after the development of the TX railway, the anthropogenic heat release from buildings and traffic rapidly increase by around 80 W m^2, and the land-use cover changes from non-urban (Case 2005) to urban (Case 2015) by more than 80%.

The Kingdom of Saudi Arabia is characterized by a hot and arid desert climate. Occasionally, however, extreme precipitation has led to flooding events that caused extensive damage in terms of human life and infrastructure. The 25 November 2009 and 30 December 2010 flash floods in the city Jeddah have for instance caused heavy damages in urban areas. Mesoscale convective systems associated with strong moisture convergence ahead of an upper-level trough that merge with the Red Sea Trough are the major initial features triggering the intense rain events. This study investigates the effect of incorporating an urban canopy model and urban land cover within the Jeddah simulating severe weather events with the Weather Research and Forecasting model (WRF) at a convective-permitting scale (1.5 km grid spacing). Using 150 most heavy rain events (99th percentile) over 40 years (1980-2019) to setup an atmospheric climatology, we perform 3 experiments varying land surface conditions: (1) pre-settlement land surface (PRESET), (2) Low-density residential urban surface, 20 W/m² anthropogenic heating (LU.1985), and (3) High-density residential urban surface, 70 W/m² anthropogenic heating (LU.2018). Results show that LU.1985 and LU.2018 produces 5% and 18% more rainfall compared to PRESET, respectively. Tripling the urban surface area combined with higher population density may cause about threefold rise in rainfall. The results of this study have important implications on surface hydroclimatology and urban flooding. Climatologically, expanding the urban area and increasing energy usage will intensify rainfall from extreme events over the city of Jeddah, Saudi Arabia.

Cities, home to more than half of the human population, are becoming increasingly vulnerable to extreme rainfall occurrences caused by global warming and urbanization. Understanding future changes in heavy rainfall patterns is essential to derive effective urban design to save human life and maintain sustainable development. However, projecting city-scale extreme rainfall is challenging because coarse-resolution global climate models (GCMs) not adequate to represent the localized processes of urban precipitation as well as the interactions between urban areas and other mesoscale mechanisms such as sea-land and mountain-valley breezes explicitly. This study investigates the future change in extreme precipitation patterns over Tokyo, Japan in response to the warming climate caused by greenhouse gas emissions. The convection-permitting Weather Research and Forecast (WRF) simulations are employed for dynamically downscaling the future August rainfall climate up to the 2050s and 2090s from CMIP5 GCMs outcomes with two emission scenarios RCP4.5 and 8.5 considered. The pseudo-global warming (PGW) approach is used to generate future initial and boundary conditions to force the WRF by adding climate anomalies obtained from GCMs ensemble mean in the future to the present climate in the reanalysis data ERA-Interim. The response of short-term rainfall occurrences and its extremes to the future warming climate is analyzed to answer two questions: is there a robust signal of global warming on the change in extreme localized rainfall at the scale of the city; how will urban-induced modification in extreme rainfall patterns change in the future warming climate. The physical mechanisms behind such changes are also discussed here.

This study presents the first results to project the future change in extreme convection rainfall in a tropical large city such as Singapore. The convection-permitting WRF model is employed for dynamical downscaling the future change in rainfall considering 2050s and 2090s from the ensemble mean of CMIP5 GCMs outcomes with two scenarios RCP4.5 and RCP8.5. Pseudo Global Warming (PGW) approach is used for creating initial and boundary atmosphere conditions to force the WRF. The response of extreme rainfall occurrences in terms of both frequency and intensity are analyzed to answer two critical questions: (i) is there a robust signature of global warming on localized heavy rain at a city-scale; (ii) how will the urban effect on future rainfall change when background climate becomes warmer?  The physical mechanisms behind these changes are also analyzed here. This study adds value to the ongoing discussion about urban extreme precipitation, focusing on how it will change in future. The study will benefit urban planners to prepare appropriate plans to handle the challenge caused by global climate change. 

Study of shallow precipitating system remains a critical source of uncertainty in satellite based remote sensing, especially in regions of complex mountain terrain region. To solve this problem, we studied the vertical structure of shallow clouds and precipitation using the unique recent in-situ observations data sets from Braemore (8.75°N, 77.08°E), mid altitude region of the Western Ghats (WG) over the Indian Peninsula during the period 1 June 2019 to September 2019. The observed precipitation systems are classified into four categories: shallow-convective, shallow, stratiform and mixed convective-stratiform based on by vertical profile of radar reflectivity (Z) at and above the melting level from Micro rain radar and rain rate (R) from Disdrometer. The shallow precipitation is identified if the vertical extention of radar reflectivity is below the melting layer (below 4 km). From the rain rate analysis, it is found that the shallow convective system with low cloud base height has crucial role in the rain occurrence frequency over Braemore compared to other precipitating systems. The shallow-precipitation raindrop size distributions (DSDs) have small drop mass-weighted diameter (Dm) compared to other precipitating system. The averaged vertical profile of precipitable liquid water content shows that liquid water content (LWC) gradually increases with height and reach its peak value at 1.8 km then it is decreases with height. Minimum LWC value 0.1 gm^-3 observed at 4km and maximum LWC value 1.5 gm^-3 observed at 1.8 km. systematic and comprehensive study of characteristics of Shallow clouds and precipitation over a region is important to improve the understanding on rain microphysics and rainfall estimation from in-situ observations. 

Information about the raindrop size distribution (RSD) is vital to comprehend the precipitation microphysics, improve the rainfall estimation algorithms, and appraise the rainfall erosivity. Previous research has revealed that the RSD exhibits diversity with geographical location and weather type, which perpetrates to assess the region and weather-specific RSDs. Based on long-term (2004 to 2016) disdrometer measurements in north Taiwan, this study pursued to demonstrate the RSD aspects of summer seasons that were bifurcated into two weather conditions, namely typhoon (TY) and non-typhoon (NTY) rainfall. The results show a higher concentration of small drops and a lower concentration of big-size drops in TY compared to NTY rainfall, and this behavior persisted even after characterizing the RSDs into different rainfall rate classes. RSDs expressed in gamma parameters show higher mass-weighted mean diameter (D_m) and lower normalized intercept parameter (N_w) values in NTY than TY rainfall. Forbye, sorting of these two weather conditions (TY and NTY rainfall) into stratiform and convective regimes did reveal a large D_m in NTY than the TY rainfall. The RSD empirical relations used in the valuation of rainfall rate (Z –R, D_m–R, and N_w–R) and rainfall kinetic energy (KE–R, and KE–D_m) were enumerated for TY and NTY rainfall, and they exhibited profound diversity between these two weather conditions. Attributions of RSD variability between the TY and NTY rainfall to the thermo-dynamical and microphysical processes are elucidated with the aid of reanalysis, remote-sensing, and ground-based datasets. 

In the past few decades, extremely severe rainfall events have become more frequent and intense. Most of them are due to the afternoon thunderstorms in summer. Afternoon thunderstorm causes floods and landslides, which not only hurts the sociality of humans, but also the biosphere. Hence, the most important topic is to understand the detail of rainfall changes in the future.In this study, WRF model will be used to simulate the long-term projection of precipitation. First, we divide the 21^st Century into four parts, which are 2011-2015, 2046-2050, 2071-2075 and 2096-2100. By using CMIP5 under RCP8.5 scenario, a standard of changes of the weather conditions, we utilize GFDL model’s results as WRF input. The results show that the intensity of the afternoon thunderstorm in Taipei will increase. There are five main reasons that cause changes in afternoon thunderstorm: (1) Stronger southwesterly, (2) stronger sea breeze from Tamsui River, (3) stronger convergence in the daytime in Taipei basin, (4) higher mixing ratio at 850hPa, (5) higher equivalent potential temperature from surface to 500hPa. The difference between the present and the future will become larger as time approaches the end of the 21^st century. Furthermore, the strongest 10% afternoon thunderstorm cases have been selected. After rearranging all the cases sorted by rainfall amount, we find out that the median will increase by 25% and the rainfall of the most extreme case will double. The extreme afternoon thunderstorm rainfall will become more intense in the future. The change in dynamic conditions, thermal conditions, and water vapor can lead to the intensity change of the afternoon thunderstorms over Taipei basin in the future. 

From the time series of Climate Forecast System Reanalysis (CFSR), rain gauge data, and case studies, two widespread heavy rainfall (> 80 mm day^-1) periods over Taiwan during the South China Sea Two Island Monsoon Experiment (SCSTIMX) (1 to 4 June and 14 to 18 June 2017) are found to be closely related to the large moisture transport within the marine boundary layer (MBL) from the northern South China Sea [integrated vapor transport (IVT) between surface and 900-hPa level > 220 kg m^-1 s^-1] to the Taiwan area. With most of the moisture confined within the boundary layer, the moisture transport to the Taiwan area mainly occurs in the marine boundary layer jet (MBLJ). For both periods, the synoptic system-related low-level jet (SLLJ) coexists with the MBLJ, which is a subsynoptic feature. The MBLJ develops and intensifies when the mei-yu trough over southern China deepens and/or the western Pacific subtropical high strengthens and extends westward. With significant upstream moisture transport within the MBL (IVT ~300 - 315 kg m^-1 s^-1), extreme torrential rain (> 500 mm day^-1) occurs over Taiwan during 2 to 3 June of the first widespread heavy rainfall period. During the second widespread heavy rainfall period, there are two sub-periods of MBLJs and rainfall peaks (> 300 mm day^-1) on 14 and 17 June with lower moisture transport by MBLJs (IVT ~220 - 280 kg m^-1 s^-1) than during the first heavy rainfall period. For both periods, the moisture-laden MBLJs lifted by terrain and/or mei-yu jet/front systems produce heavy rainfall. The moisture transport within the MBL from the northern South China Sea to Taiwan provides a useful guide to predict heavy rainfall over Taiwan.

In summer 2020, South Korea experienced record-breaking rainfall. There were 11 consecutive heavy rainfall events (HREs) for 48 days from 29 June to 15 August. These HREs had two distinct synoptic structures depending on the occurrence periods. All HREs in 29 June–27 July (P1) were triggered by extratropical cyclones, while those in 28 July–15 August (P2) were mainly caused by monsoon rainband over the Korean Peninsula. Their transition was quite rapid. We argue that this transition is driven by the meridional teleconnection from the South China Sea (SCS) and the zonal teleconnection from the North Atlantic Ocean. In P1, the western North Pacific subtropical high (WNPSH) was significantly extended westward, but its northward expansion was delayed due to the meridional wave train from the suppressed convection over the SCS and the zonal wave induced by the negative summer North Atlantic Oscillation (SNAO). This condition prevented a northward migration of the monsoon rainband but allowed more extratropical cyclones to pass over the Korean Peninsula, resulting in four HREs. In P2, the meridional and zonal wave trains changed their phases due to the enhanced convection over the SCS and the positive SNAO, respectively, prompting an abrupt northward expansion of the WNPSH. This allowed strong southwesterly moisture transport along the northwestern boundary of the WNPSH, forming a monsoon rainband over the Korean Peninsula. As a result, seven HREs occurred, including one affected by an extratropical transition. This result demonstrates that the nature of summertime HREs in East Asia can be significantly influenced by remote forcings by determining regional synoptic conditions.

Using severe weather reports, precipitation observations, and composite Doppler radar reflectivity data, a 7-year climatology of the initiation, decay, and organization of severe convective storms (SCSs), as well as the associated severe convective weather, namely, short-duration heavy rainfall (SDHR), hail, and thunderstorm high winds (THWs), during the warm seasons (May–September) of 2011–2018 (except 2014) over North China was established. A total of 371 SCSs were identified. SCSs primarily initiated around noon with the highest frequency in the middle section of Mount Taihang. SCSs mostly decayed over the plains at night. The storm morphologies were classified into three types of cellular systems [individual cells (ICs), clusters of cells (CCs), and broken lines (BLs)], six types of linear systems [convective lines with no stratiform (NSs), with trailing stratiform (TSs), leading stratiform (LSs), parallel stratiform (PSs), embedded lines (ELs), and bow echoes (BEs)], and nonlinear systems (NLs). NLs were the most frequent morphology, followed by CCs. TSs were the most frequent linear morphology. A total of 1,429 morphologies of the 371 SCSs were found to be responsible for 15,966 severe convective weather reports. Linear (nonlinear) systems produced the most SDHR (hail and THW) reports. BEs were most efficient in producing both SDHR and THW reports whereas BLs had the highest efficiency for hail production. 

Typhoon Rammasun (2014) experienced a rapid intensification (RI) before its landfall in South China. The track, structure and intensity changes of Rammasun were reproduced reasonably in a simulation using the Weather Research and Forecasting Model (WRF-ARW). In this study, kinetic energy budget during the rapid intensification (RI) of the modeled Rammasun were analyzed to examine the dominant dynamic and thermodynamic processes associated with the RI.The winds were partitioned into environmental and tropical-cyclone winds, and the tropical-cyclone winds were further separated into rotational and divergent components. The results show that the environmental circulations tend to reduce rotational kinetic energy and divergent kinetic energy during the RI. Divergent kinetic energy is converted to rotational kinetic energy, which mainly enhances the rotational kinetic energy and leads to RI. The divergent kinetic energy comes mainly from the conversion of the available potential energy. Since the RI is defined as the increase in symmetric rotational energy, the further analysis will be conducted in a cylindrical coordinate where rotational and divergent winds are separated into symmetric and asymmetric components. The results of budget analysis of Rammasun during the RI will be reported during the session AS14 of AOGS.

Sea salt aerosols were assumed to be homogeneous spheres in WRF models. However, observations show that sea salt particles are inhomogeneous with different RHs. Using a two‐layer sphere model, we found that backscattering of solar radiation associated with sea salts is underestimated in homogeneous sea salt models. The Weather Research and Forecasting (WRF) model V3.7 is used to assess the inhomogeneity effect on typhoon Fitow, the No. 23 typhoon in 2013. To distinguish the effects of inhomogeneous sea salt on precipitation of the landfalling storm, Force (remove sea salt aerosol in radiative transfer in the WRF), control (no change in the WRF) and sensible (replace optical properties of sea salt at RH=70% in the WRF) experiments were conducted with different effects on radiative transfer. The results show that the inhomogeneous of sea salt aerosol has little effect on the track and intensity of typhoon. The main impact is concentrated on typhoon precipitation. The inhomogeneity of sea salt decreases the asymmetry factor and increases backscattering of solar radiation. Thus, the ground cooling effect is enhanced, and the atmospheric stability is increased. As a result, total accumulated precipitation in the typhoon main body is decreased. Keywords Typhoon, Precipitation, sea salt aerosols, WRF model

Over the complex terrain of the Maritime Continent (MC), it is challenging to produce accurate numerical analyses and forecasts of convection. To make matters worse, convection evolves on time scales of an hour. Since atmospheric motion vectors (AMV) and local in-situ observations are made every 3 hours or more, it is difficult for these observations to resolve convection. One solution to this challenge is to supplement in-situ observation with modern geostationary satellite infrared (GeoIR) observations. Modern GeoIR observations are frequently available (> 1 scan/hour) at high resolution (< 5-km pixel width), meaning that GeoIR observation can resolve the rapid evolution of meso-γ, or larger, convective systems. The assimilation of these GeoIR observations, on top of existing in-situ and atmospheric motion vector observations, can thus potentially improve the analyses and forecasts of MC mesoscale convective systems.In this talk, we will use an MC tropical squall event to explore the impacts of assimilating varying amounts of GeoIR observations (none at all, 3-hourly and half-hourly), on top of AMV and in-situ observations. Specifically, we employed GeoIR brightness temperature (BT) observations made by the upper tropospheric tropospheric water vapor channel (channel 8; ch08-BT) of the Advanced Himawari Imager, on board the Himawari-8 satellite. Both clear-sky and cloud-affected ch08-BT observations were assimilated. Without ch08-BT observations, the analyzed squall line propagated too quickly. While the addition of 3-hourly ch08-BT observations was found to improve the analyzed cloud fields, the addition did not noticeably improve the analyzed positions of the gust front and cold pool. In contrast, the use of half-hourly ch08-BT observations resulted in improved analyzed cloud fields, gust front position and cold pool position. These results motivate further study into using GeoIR observations to improve the analyses and forecasts to MC mesoscale convective systems.

Based on the hourly meteorological data of Zhejiang Province from 2014 to 2019,  the spatial distribution characteristics of summertime afternoon precipitation (14:00-19:00) without the influence of typhoon were analyzed. OLR (Ordinary linear region), GWR (Geographically weighted region) and GNNWR (Geographically neural network weighted region) models were used to estimate the afternoon precipitation considering geographical (latitude, longitude), topographic (altitude, slope, aspect) and meteorological (wind) factors, and the prediction effects of the three models were compared. The results show that: (1) the summertime afternoon precipitation in Zhejiang Province shows a decreasing trend from southwest to northeast, there is a wet tongue of precipitation, and there is an obvious high value area in the southern mountainous area. (2) GWR and GNNWR models considering spatial weights are superior to OLR model in both magnitude and spatial pattern. (3) GWR Model and GNNWR model with neural network have good prediction effects, the absolute error is less than 0.06, R² can reach 0.97. Compared with GWR model, GNNWR model is closer to the observed precipitation in spatial pattern, the prediction effect of local area is better. (4) The weight distribution of different factors can well explain the spatial distribution of observed and predicted precipitation in the afternoon.

For tropical cyclones (TCs) over the western North Pacific, the interaction between dry air and TC is extensive and significant since the dry air can come from not only the high-pressure system but also the dry mid-to-high-latitude continent. However, the question of how the dry-air intrusion influences the vertical structure of TC circulation and precipitation from observation has not been studied yet. In this study, we adopt several datasets from TRMM and NCEP FNL reanalysis data to explore both the vertical structure of precipitation and its variation for landfalling TCs over China. The study suggests that the process of environmental dry-air intrusion has an important regulation effect on the vertical structure and precipitation of TC, especially in the outer region of TC. 

Black carbon (BC) and dust impart significant effects on the south-Asian monsoon (SAM), which is responsible for ~80% of the region’s annual precipitation. This study implements a variable-resolution (VR) version of Community Earth System Model (CESM) to quantify two radiative effects of absorbing BC and dust on the SAM. Specifically, this study focuses on the snow darkening effect (SDE), as well as how these aerosols interact with incoming and outgoing radiation to facilitate an atmospheric response (i.e., aerosol radiation interactions; ARI). By running sensitivity experiments, the individual effects of SDE and ARI are quantified. It is found that ARI of absorbing aerosols warm the atmospheric column in a belt coincident with the May-June averaged location of the subtropical jet, bringing forth anomalous upper-tropospheric (lower-tropospheric) anticyclogenesis (cyclogenesis) and divergence (convergence). This anomalous arrangement in the mass fields brings forth enhanced rising vertical motion across south Asia and a stronger westerly low-level jet, the latter of which furnishes the Indian subcontinent with enhanced Arabian Gulf moisture. Precipitation increases of 2 mm d^-1 or more (a 60% increase in June) result across much of northern India from May through August, with larger anomalies (+5 to +10 mm d^-1) in the western Indian mountains and southern TP mountain ranges due to orographic and anabatic enhancement. Across the Tibetan Plateau foothills, SDE by BC aerosols drives large precipitation anomalies of >6 mm d^-1 (a 21 - 26% increase in May and June), comparable to ARI of absorbing aerosols from April through August. Runoff changes accompany BC SDE-induced snow changes across Tibet, while runoff changes across India result predominantly from dust ARI.

Coupling between the atmosphere and the heterogenous land surface can play an important role in the climate system. Traditional global climate models (GCMs) have coarse horizontal grid resolutions on the order of 100 km that poorly capture mesoscale processes in the atmosphere or the heterogenous land surface properties. To overcome this limitation, we have implemented a Multiple Atmosphere Multiple Land (MAML) framework in the Super-Parameterized Energy Exascale Earth System Model (SP-E3SM). In the standard SP-E3SM, all subgrid-scale atmospheric processes (e.g., radiation, clouds, and precipitation) are represented by a nonhydrostatic Cloud Resolving Model (CRM) embedded in each E3SM grid. As each atmospheric column of the CRM interacts with the same land surface represented by the E3SM Land Model (ELM), this configuration is called Multiple Atmosphere Single Land (MASL). In contrast, in the MAML framework, each atmospheric column of the CRM interacts with its own underlying land surface simulated by the ELM so that non-linear effects of land-atmosphere interactions can be better represented. To investigate the impact of the MAML approach, we perform two simulation experiments: one with the MASL approach and the other with the MAML approach. Preliminary results show that while total precipitation patterns are similar between these two simulations, regional precipitation shows some interesting difference:  MAML simulation produces less precipitation in the Amazon region worsening the dry bias, but more realistic precipitation over the Indian Monsoon region. Analysis of the results focusing particularly on the soil moisture-precipitation feedback in the two simulations and future development to improve modeling of land-atmosphere interactions in the MAML framework will be discussed.

Superparameterization means that conventional convective parameterization in a general circulation model (GCM) is replaced by a cloud-resolving model (CRM) in each GCM grid. One of the models is the superparameterized community atmosphere model (SPCAM). Although this framework can simulate deep convection directly, a previous study shows that slopes of fitting lines of precipitation as a function of column water vapor (CWV) over tropical oceans are flatter than observation. However, the study only examines a GCM scale; the CWV-precipitation relationship is not examined on a CRM scale. Our result shows that slopes of fitting lines are sharper in the CRM scale compared with observation. The inconsistency between the GCM scale and the CRM scale indicates that SPCAM cannot exhibit the CWV-precipitation relationship properly from the CRMs to the GCM. Because the precipitation of each grid in SPCAM is from an average value of its CRM, there will be moderate precipitation if wet and dry environments exist in a CRM simultaneously. Wet columns would tend to produce stronger precipitation, while dry columns tend to produce weaker precipitation. This wet-dry separation sometimes does not reflect the real distribution of convection in that scale which could be due to the periodic boundary condition in the CRM. This bias may get worse when the model simulates large convective systems like tropical cyclones. To improve SPCAM performance, one possible method is partially choosing CRM columns to feedback tendency to GCM grids. This method tries to decrease the effects of the periodic boundary condition. Sensitivity tests of domain sizes and resolution are conducted to find out the best combination.

The scaling exponents of the distributions of cluster rain amount, R, and cluster size, A, for oceanic rain clusters over the Indian and Pacific warm pools, and the intertropical convergence zones over the eastern Pacific and the tropical Atlantic, were obtained from a set of regional climate model downscaling products. The main aim of the investigation is to compare the model cluster’s scaling characteristics with those obtained from observations that have been reported previously. The scaling exponents for the model were found to be different across the ocean basins indicating the lack of universality in the modelled rain cluster distributions. The scaling exponent for the conditional mean of R given A = a, E(R|a), was found to be the same across the different ocean basins, and the estimated value of the exponent agrees with that obtained from satellite observed rain clusters. However, no crossover in the scaling of E(R|a) in the model for cluster size larger than mesoscale was seen, unlike those reported elsewhere. The implication is that in the model the intensification of rain with cluster size continues up to synoptic scale. Through simple scaling arguments it is believed that the model simulates the fundamental mesoscale dynamics well and thus estimated the E(R|a) in agreement with observations.

Air quality prediction is usually performed with regional climate models (RCMs) but also relies on global climate models (GCMs) for boundary and initial conditions, which can induce uncertainties to the simulation. Conventional RCMs and GCMs still also have some limitations in simulating multi-scale interactions between air pollution (aerosols) and large-scale processes. The development of variable resolution GCMs models provide a great opportunity to achieve two-way interactions at multi-scales and explore the physical and chemical processes in refined regional scales. In this study, multiple observation and MICS-Asia Phase III Regional Models datasets are applied to assess the performance of Community Atmosphere Model with Chemistry (CAM-chem) based on Spectral Element dynamical core (CAM-Chem-SE) with regional refined over East Asia at resolutions of 0.25 degree in the ozone pollution simulation. Our results show that, the regional refined CAM-Chem-SE model can generally reproduce the significant seasonal cycle, spatial distribution characteristics, and the vertical distribution patterns of ozone. However, ozone concentrations over China are slightly underestimated in the simulations, which may be related to the inaccurate description of pollutant emissions over China in CMIP6. A further modification of the emissions over China in CMIP6 will be needed in our evaluations. Analysis about the long-range transport of air pollutants, as well as the multiscale interactions between air pollution and climate change, will be further explored in this study.

The non-hydrostatic global variable-resolution model (MPAS-Atmosphere) is first time used to attempt at simulating the Mei-yu rainfall in 2015 over East China. Convection-permitting simulations with regional refinement at 4 km resolution (V4km) and uniform 60km resolution simulations (U60km) are compared, focusing on the diurnal variation of precipitation amount (PA), intensity (PI), and frequency (PF). Both simulations reasonably reproduce the spatial distribution of PA. V4km is more skillful in simulating the spatial distributions and magnitudes of PF and PI. The diurnal cycle of Mei-yu rainfall shows a major early morning peak and a minor afternoon peak, contributed by precipitation during two sub-periods with distinct large-scale circulations. With strong Mei-yu in the first sub-period, the diurnal variation of PA is controlled by nocturnal southwesterly jet. V4km overestimates the morning peak mainly due to its bias in simulating boundary layer inertial oscillation. Although U60km overestimates PF and underestimates PI, differences in PA between the simulations are small. With weak Mei-yu in the second sub-period, the diurnal variation of PA is controlled by both large-scale circulation and local convection. At both resolutions, deviations in the large-scale circulation modulated by a few typhoons lead to positive biases in the morning peak of PA. After removing the typhoon impacts, V4km captures the observed diurnal cycle of PA well, while U60km significantly underestimates the magnitudes of PA and PI particularly in the afternoon. Future studies focusing on advancing modeling of the southwesterly jet and typhoons may further improve the convection permitting simulations of Mei-yu rainfall.

The World Climate Research Programme (WCRP) has an international initiative called the COordinated Regional climate Downscaling EXperiment (CORDEX). The goal of the initiative is to provide regionally downscaled climate projections for most land regions of the globe, as a compliment to the global climate model projections performed within the Coupled Model Intercomparison Projects (CMIP). CORDEX includes data from both dynamical and statistical downscaling. It is anticipated that the CORDEX dataset will provide a link to the impacts and adaptation community through its better resolution and regional focus. Participation in CORDEX is open and any researchers performing climate downscaling are encourage to engage with the initiative. Here I present the current status, evaluation and future projections for the CORDEX-Australasia ensemble. The CORDEX-Australasia ensemble is the largest regional climate projection ensemble ever created for the region. It is a 20-member ensemble made by 6 regional climate models downscaling 11 global climate models. Overall the ensemble produces a good representation of recent climate. Consistent biases within the ensemble include an underestimation of the diurnal temperature range and an underestimation of precipitation across much of southern Australia. Under a high emissions scenario projected temperature changes by the end of the twenty-first century reach ~ 5 K in the interior of Australia with smaller increases found toward the coast. Projected precipitation changes are towards drying, particularly in the most populated areas of the southwest and southeast of the continent. The projected precipitation change is very seasonal with summer projected to see little change leaning toward an increase. These results provide a foundation enabling future studies of regional climate changes, climate change impacts, and adaptation options for Australia.

Coarse resolution global climate models (GCM) cannot resolve fine-scale drivers of regional climate, which is the scale where climate adaptation decisions are made. Regional climate models (RCMs) generate high-resolution projections by dynamically downscaling GCM outputs. However, evidence of where and when downscaling provides new information about both the current climate (added value, AV) and projected climate change signals, relative to driving data, is lacking. Seasons and locations where CORDEX-Australasia ERA-Interim and GCM-driven RCMs show AV for mean and extreme precipitation and temperature are identified. A new concept is introduced, ‘realised added value’, that identifies where and when RCMs simultaneously add value in the present climate and project a different climate change signal, thus suggesting plausible improvements in future climate projections by RCMs. ERA-Interim-driven RCMs add value to the simulation of summer-time mean precipitation, especially over northern and eastern Australia. GCM-driven RCMs show AV for precipitation over complex orography in south-eastern Australia during winter and widespread AV for mean and extreme minimum temperature during both seasons, especially over coastal and high-altitude areas. RCM projections of decreased winter rainfall over the Australian Alps and decreased summer rainfall over northern Australia are collocated with notable realised added value. Realised added value averaged across models, variables, seasons and statistics is evident across the majority of Australia and shows where plausible improvements in future climate projections are conferred by RCMs. This assessment of varying RCM capabilities to provide realised added value to GCM projections can be applied globally to inform climate adaptation and model development.

Highly industrialized East Asia, with its high greenhouse gas emissions, must inevitably increase renewable energy production to achieve the goals of the Paris Agreement. Photovoltaics (PV), a widely utilized renewable energy source, is directly affected by the weather and climate. This study conducted a first analysis of current and future PV potential (PVpot) changes over East Asia using the ERA5 reanalysis and multiple high-resolution regional climate model simulations. The recent PVpot over East Asia did not exhibit any notable changes, but the future PVpot is predicted to decrease by −4.0 % (winter) to −1.6 % (summer) on average. It was found that the widespread increase in near-surface air temperature leads to the overall PVpot decrease (around −2.0 %) over East Asia across all seasons. Interestingly, surface down-welling shortwave radiation increases in summer, offsetting temperature-induced PVpot decreases (by about 0.7%) while it decreases in winter and spring, intensifying the warming-driven PVpot decrease (by about -1.4% to -2.3%). Further, the changes in the number of rainy days are found to be associated with the changing patterns of surface down-welling shortwave radiation, indicating the importance of reliable projections of precipitation. Wind speed exerts a negligible effect.

In the mid-latitudes, synoptic-scale phenomena like high and low-pressure systems generate the variability of the regional-scale weather system. To identify the weather variability of extra-tropical region storm track activity has been analyzed based on observations since the mid-nineteenth century. After early-stage research that directly counted the movement of cyclones, it has been used that time filtering method based on grid analysis to an isolated disturbance with periods of 2~7 days. This bandpass filtering method has the advantage of being able to examine the distribution and the variability of the storm track spatially in vertical and horizontal space. In this study, we confirm the storm track activity in the East Asia region using the dynamical down-scale results from CORDEX (COordinated Regional climate Downscaling EXperiment) projects. Based on the analysis of reanalysis data, GCM (Global Climate Model) data which used for forcing in RCM (Regional Climate Model), and RCM data, it verifies the reproducibility and confirms the temporal change in the storm track activity. The role of added value from RCM is discussed, also.

Regional Climate Models (RCMs), including the RegCM4, are good tools for producing added climate information at a small scale (e.g., extreme precipitation) that the Global Circulation Model (GCM) cannot resolve. However, the results of RCM simulations forced by GCM have errors and uncertainties. To reduce these drawbacks, the Spectral Nudging Technique (SNT) has been applied as an alternative method for boundary conditions. To understand the impact of the SNT on the dynamical downscaling of RCM, in this study, we conducted the sensitivity experiments to the SNT using the RegCM4 forced by the United Kingdom Earth System Model (UKESM). The SNT studies in RegCM4 are considerably meaningful in the CORDEX East Asian region due to the insufficiency of previous studies. We focused on the impact of the SNT on mean and extreme precipitation. The sensitivity experiment showed that the SNT could improve the simulations of mean and extreme precipitation compared with GCM and RCM without the SNT. The impact of the SNT was significant in JJA as well as DJF, especially on extreme precipitation. Additionally, we analyzed the synoptic field related to mean and extreme precipitation to examine why the SNT improved the simulation of the RegCM4.

The Asian Precipitation Experiment (AsiaPEX) was launched in 2019 and is developing its Science Plan. It defined the objectives of AsiaPEX as "understanding of Asian land precipitation over diverse hydroclimatological conditions and multiple time scales for better prediction, disaster reduction, and sustainable development." Now is the time to finalize the Science Plan. In the AsiaPEX, we will not pursue a geographical region-oriented strategy, but a research approach-oriented strategy. Based on our six approaches, 1) observation and estimation of variation and extremes in Asian land precipitation and important variables, 2) process studies of Asian land precipitation focusing on diverse land-atmosphere coupling, 3) understanding and prediction of the variability of Asian monsoon from subseasonal to interdecadal time scales, 4) high-resolution land surface hydrological modeling and monitoring incorporating impacts of human water withdrawal, agriculture, vegetation and cryosphere, 5) coordinated observation and modeling initiatives, 6) detection and projection of the climate change impact on regional precipitation in Asia, we will review the recent development of the AsiaPEX activity. The AsiaPEX is the successor of the GAME and the MAHASRI projects under the GHP/GEWEX/WCRP, which had led the joint activity of the Asian hydroclimatological research community. These projects planned and conducted observational initiatives. The GAME project conducted its Intensive Observation Period in 1998. From 2007 to 2012, the Asian Monsoon Year (AMY) was conducted to improve Asian monsoon prediction for societal benefits through improving understanding of the variability and predictability of the Asian-Australian monsoon system. Following these achievements, one of the focuses of the discussion in the present session will be the discussion on the observational and modeling initiative of the AMY-II. We will present a plan for the AMY-II in this presentation.

Monsoons have always been of great interest to the World Climate Research Programme (WCRP), particularly to its core projects CLIVAR (Climate and Ocean: Variability, Predictability and Change) and GEWEX (Global Energy and Water EXchanges), which have jointly established a Monsoon Panel to coordinate the various monsoon related research activities with individual attention to regional monsoons around the world. Monsoons, as the primary source of water in the affected regions, have long attracted scientific attention to understand and predict their variability both in the weather and climate context. Although significant progress has been made in understanding the drivers of the monsoon processes including the complex ocean-atmosphere-land interactions, particularly during the last decade, monsoons remain a scientific challenge to model and reliably predict anomalies in their spatio-temporal patterns as well as intensity. This is crucial for a large part of the global population that are dependent on the monsoons for their annually recurring large-scale moisture transport that determines the water availability for the entire year. Furthermore, the various regional monsoon phenomena that can be found around the world share many commonalities and can be linked to large scale atmospheric and oceanic circulation. By facilitating monsoon research on local, regional as well as global scales, the WCRP aims to significantly advance our understanding and predictive capabilities, which have immense societal applications. In this presentation we introduce the objectives and structure of the Monsoon Panel and its activities including future perspectives in the light of the new WCRP Strategic Plan unfolding. A new initiative to establish an International Monsoons Project Office in collaboration with the World Weather Research Programme (WWRP) will be highlighted.  We will also showcase several examples of international collaborative monsoonal studies undertaken in the various parts of the world, and their potential implications for further advances in Asian monsoon research.

The Tibetan Plateau (TP), as a whole, has undergone a moistening process since the late 1990s. However, the southern Tibetan Plateau (STP) is an exception, where summer monsoon precipitation amount has decreased, and lakes have shrunk. The cause for the precipitation decrease is not clear yet. Here we show that the monsoon (June to September) mean precipitation changes in the STP from 1979 to 2018 features a decadal variation component with a peak of around ten years that is superposed on an upward ‘trend’ from 1979 to 1998 and a downward ‘trend’ afterward. We find that the decadal variation of the STP precipitation is associated with a large-scale dipolar sea surface temperature (SST) pattern between the equatorial central Pacific and the Indo-Pacific warm pool. A wet STP corresponds to negative SST anomaly in the equatorial central Pacific and positive SST anomaly in the Indo-Pacific warm pool. This equatorial SST gradient in the western Pacific generates pronounced easterly anomalies and a dipolar rainfall anomaly (i.e., a positive rainfall anomaly over the Maritime Continent and a negative anomaly in the equatorial western and central Pacific). Due to less precipitation over the equatorial western Pacific, the suppressed heat source appears to excite an anomalous anticyclonic band along 15-20°N extending from the Philippine Sea to the Bay of Bengal by emanating westward propagating descending transient Rossby waves. The low-level anticyclonic circulation over the Bay of Bengal further enhances northward moisture transport toward the STP and promote upward motion in the STP through changing local meridional circulation. Besides, the linearized atmospheric general circulation model experiments demonstrate that the dipole heating source can generate a high-pressure zone under the control of anticyclone over the western Pacific, which can extend westward to the Indian monsoon region.

The relation between extreme precipitation events and intraseasonal variation in Assam state, India has been investigated. First, the regional characteristics of extreme rainfall analyzed using in-situ observation data from 15 rain gauges in Assam from 2007 to 2016. The results show that the frequency of highest rainfall-rank (>50 mm d^-1) contributes significantly to the total frequency in western Assam and northern bank of the Brahmaputra. In Kokrajhar, located on the northern bank of Brahmaputra River in the western Assam, the highest rainfall rank accounts for about 20%. On the other hand, the lowest rainfall ranks (< 5 mm d^-1) are largely contributed by the south-central and central parts of Assam. Also, in Lumding and Diphu, about 60% of the rainfall is classified as the lowest rainfall rank. Based on the 99^th percentile values for each station, the maximum value is 175.1mm d^-1 in Kokrajhar and the minimum value is 68.5mm d^-1 in Nagaon. At Kokrajhar, 60% of the extreme rainfall events occur during the monsoon season (June–September). And the composite analysis of the 90^th percentile cases indicates that the extreme heavy rainfall over the northern bank of the Brahmaputra is associated with anomalies in the anticyclonic circulation over the Gangetic plain. Over the northeastern Indian subcontinent, convergence anomalies of water vapor fluxes are associated with the intensification of westerly water vapor fluxes. These cases correspond well with the break phase of the intraseasonal variation in the Bay of Bengal. 

Future greenhouse warming is expected to influence the characteristics of global monsoon systems. However, large regional uncertainties still remain. Here we use 16 Coupled Model Intercomparison Project Phase 6 (CMIP6) models to determine how the length of the summer rainy season and precipitation extremes over the Asian summer monsoon domain will change in response to greenhouse warming. Over East Asia the models simulate on average on the earlier onset and later retreat; whereas over India, the retreat will occur later. The model simulations also show an intensification of extreme rainfall events, as well as an increase of seasonal drought conditions. These results demonstrate the high volatility of the Asian summer monsoon systems and further highlight the need for improved water management strategies in this densely populated part of the world.

This study examines the characteristics of the diurnal variations of heavy rainfall episodes (≥ 110 mm in 12 h) in Korea and the related atmospheric circulation during the Changma rainy seasons of 1980-2020, aming at understanding what synoptic/mesoscale circulations were responsible for a series of long-lasting heavy rainfall events occurred in Korea during the summer of 2020. Focusing on July, the wettest period of the Changma season, the characteristics of the heavy-rainfall systems in 2020 are compared with their climatology. Two dominant pattens of diurnal variation of the heavy rainfall emerged over Korea: all-day heavy rainfall (AD) and morning only heavy rainfall (MO) types. For the AD type, the heavy rainfall is caused by abundant moisture content in conjunction with active convection in the morning (0-12 local time, LT) and the afternoon hours (12-24 LT). These systems are related to the enhanced moisture inflow and upward motion induced by the strengthening of the western North Pacific subtropical high and upper-tropospheric jet. The MO-type heavy rainfall events occur mostly in the morning hours; the associated atmospheric patterns are similar to the climatology. The 2020 heavy-rainfall system is considered a typical AD-type event and resembles the 1991 Changma in its overall atmospheric circulation. The present results suggest that extremely heavy rainfall episodes in Korea during the 2020 Changma rainy season would recur in the future if the AD-type’s conditions would be met. 

To clarify the past local characteristics of the Asian monsoon, this paper will focus on monsoonal climate events, especially from spring to autumn that effectively affected agricultural production in Takahama, a village in the Amakusa islands of Kyushu, Japan, in the pre-statistical area especially from 1793 to 1818. Nature-induced disasters such as earthquakes and storms were recorded in the diary of a village head, Shoya, at the top of his every day’s records for the village administration, because the village head briefly recorded the weather of the day after the date description using terms such as ‘fine’, ‘cloudy’, ‘rainy’, ‘storm’, ‘north wind’, ‘south wind’, ‘severe wind’, ‘earthquake in the afternoon’, and so on. To quantify these weather statements, 2 points for rain, 1 point for cloudy, 0 point for sunny day, 2.5 points for heavy rain and 1.5 points for weak rain are weighted. The difference in rainfall change from May to August is analysed based on monthly average points. There were strongholds of typhoons and heavy rains putting harvesting constraints against on an organic economy in Takahama. It was able to confirm that flooding did not occur during the peak season of typhoons, but that heavy rain, especially during the rainy season, caused enormous flood damage. Furthermore, it was understood that concern about the lack of rainfall all the time, suggested by rain-seeking rituals, was worried because the number of years for which such rituals were performed exceeded 70 percent of the years within the observed years. Sunshine was expected in July and prompt rainfall was also expected at the same time as securing the amount of solar radiation accompanied by fine weather in August. It was confirmed that the rhythm and balance of rainfall volume and solar radiation amount are important for rice growth.