An innovative algorithm for retrieving microwave land surface emissivity (MLSE) over China was developed using measurements of recalibrated microwave brightness temperatures (Tbs) from Fengyun-3B Microwave Radiation Imager (FY-3B MWRI) combined with cloud properties derived from Himawari 8 Advanced Himawari Imager (AHI) observations. The contributions from cloud particles and atmospheric gases to the upwelling Tbs at the top of atmosphere were fully taken into account. This method can retrieve MLSE under both clear sky condition and cloudy sky condition. The MLSEs at horizontal polarizations at 10.65GHz, 18.7GHz and 36.5GHz during July 7^th 2015 to 30^th June 2019 over China showed high values in southeast vegetated area and low values in northwest barren or sparsely vegetated area. The maximum values of MLSEs are located in the southwest-northeast oriented belt area composite of Qinglin-Taihang Mountains and the eastern edge of the Qinghai-Tibet Plateau which also is the dividing belt between high and low MLSE in China. This spatial pattern is highly consistent with that derived from AMSR-E. It demonstrates the measurements of Tbs by FY-3B MWRI, including its calibration and validation, are reliable, and the retrieving algorithm developed in this study works well. Seasonal variations of MLSE in China are mainly driven by the combined effects of vegetation, rainfall and snow cover. In tropical and south forest regions, seasonal variation of MLSE is small due to the enhancement from vegetation and the suppression from rainfall. In boreal area, snow causes significant decrease of MLSE at 36.5GHz in winter. Meanwhile, the MLSE at lower frequencies received less suppression. In desert region in Xinjiang, an increase of MLSEs at all frequencies with snow cover were observed.  The results widened our understanding of the response of land surface to environmental controlling factors. Great potential of applications of this product in multiple fields are expected.  

Optical properties of aerosols and ice particles fundamentally impact atmospheric radiative transfer. Thus, an accurate determination of their optical properties plays a key role in improving aerosol and cloud remote sensing and relevant climate simulations. In this talk, we review aerosol (dust and sea salt) and ice crystal optical modeling progress in a super-spheroid shape space with applications in radiative transfer simulations, remote sensing and relevant climate simulations. We first present current status in calculating the single-scattering properties of nonspherical particles by using the invariant imbedding T-matrix method, and then evaluate the applicability of super-spheroidal aerosol and ice models and the dust refractive index uncertainties related to dust sources at both shortwave and longwave bands. As application examples, we will present simulations related to LiDAR, POLDER (POLarization and Directionality of the Earth's Reflectances)/PARASOL (Polarization and Anisotropy of Reflectances for Atmospheric Sciences coupled with Observations from a Lidar), and HIRAS (High-spectral Resolution Infrared Atmospheric Sounder) observations. In addition to remote sensing applications, the impact of dust aerosol absorbility on regional climate in the East Asia will be also discussed. 

Aerosol analyses with a geostationary satellite can advance our understanding of the rapid spatiotemporal evolution of aerosols, which is especially critical for studies of air pollution and its mechanisms. To assimilate asynchronous observations and avoid frequent switching between the assimilation and ensemble aerosol forecasts, the Local Ensemble Transform Kalman Filter (LETKF) is extended to the four-dimensional LETKF (4D-LETKF). The hourly aerosol analyses are evaluated with both the assimilated Himawari-8 AOTs and independent Moderate Resolution Imaging Spectroradiometer (MODIS)- and AErosol RObotic NETwork (AERONET)-retrieved AOTs. All evaluations show that the assimilations positively affect the model performances and produce simulated AOTs that are closer to the observations. The analyses correctly reduce the significantly positive biases and root mean square errors (RMSEs) of the control experiment, especially over East China and Australia. The performance of the 4D-LETKF, even with an assimilation window time of 24 hours (4D-LETKF-24H), is generally comparable to that of the LETKF.

Dust aerosol, a major component of the atmospheric aerosol system, not only plays an important role in the global biogeochemical cycle system, but also has a significant impact on the global radiative energy budget and climate change. Quantitative assessment of the dust mass concentration (DMC) or dust flux is the key to understand the dust transport, sedimentation, and recycling processes in dust source and transported regions. Satellite-based estimation of the DMC is essential for accurately evaluating global biogeochemical cycle of the dust aerosols. As for the uncertainties in estimating DMC caused by mixing dust and pollutants and assuming a fixed value for the mass extinction efficiency (MEE), a classic lidar-photometer method is employed to identify and separate the dust from pollutants, obtain the dust MEE, and evaluate the effect of the above uncertainties, during five dust field experiments in Northwest China. Our results show that this method is effective for continental aerosol mixtures consisting of dust and pollutants. It is also seen that the dust loading mainly occurred in the free troposphere (< 6 km), and the average DMC trapped in the boundary layer is up to 600 ± 460 µg m-³. The dust MEE is ranging from 0.30 to 0.60 m² g⁻¹ and has a significantly negative relationship with the size of dust particles. With the assumption of the dust MEE of 0.37 (0.60) m² g⁻¹, the DMC is shown to be underestimated (overestimated) by 15-30% (20-40%). In other words, our results suggest that the change of MEE with the size of dust particles should be considered in the estimation of DMC.

The impact of radiative transfer scheme on global climate model (GCM) simulation is presented in this paper by comparing the difference between two δ-two-stream adding methods (two-stream discrete-ordinate-method (DOM) and Eddington approximation) and an adding algorithm of the δ-four-stream discrete ordinates method (δ-4DDA) radiation schemes in the Atmospheric General Circulation Model of the Beijing Climate Center (BCC_AGCM). It is found that compared to the two-stream DOM, the Eddington approximation can enhance the fraction of low cloud, and this increased cloud fraction can affect the differences in radiative fluxes between these schemes. Only consider the effects of the calculation method itself, the δ-4DDA reduces the negative shortwave cloud radiative effect (CRE) in the areas with a significant fraction of low cloud, while enhances the negative shortwave CRE in the areas with the large fraction of high cloud. For the longwave CRE, the δ-4DDA enhances the longwave CRE drastically in the regions with a significant fraction of the high cloud. The change of radiation scheme affects the simulation of other meteorological variables. The simulation of global humidity by δ-4DDA is improved obviously. The δ-4DDA simulates more accurate temperature in continents of the northern hemisphere and precipitation in North America, Africa, northern Indian Ocean and western Pacific. Although the improvement of every physical process is required to develop the models, implementing δ-4DDA scheme into GCM and evaluating the effect of it are necessary and meaningful. Reference： Yang Quan, Zhang Feng*, Zhang Hua, Wang Zhili, Li Jiangnan, Wu Kun, Shi Yining, Peng Yiran (2019) Assessment of two-stream approximations in a climate model. Journal of Quantitative Spectroscopy & Radiative Transfer, 225: 25-34 Yang Quan, Zhang Feng*, Zhang Hua, Wang Zhili, Iwabuchi Hironobu, Li Jiangnan (2020) Impact of δ-Four-Stream Radiative Transfer Scheme on global climate model simulation. Journal of Quantitative Spectroscopy & Radiative Transfer, 243: 106800

The contribution of different aerosol types to radiative forcing over distinct environments of South Asia inferred from AERONET and Model data.Rehana Khan^a,b, Tianliang Zhao^a,*, ^aCollaborative Innovation Centre on Forecast and Evaluation of Meteorological Disasters, Key Laboratory of Meteorological Disaster, Ministry of Education (KLME), International Joint Laboratory on Climate and Environment Change (ILCEC), Key Laboratory for Aerosol-Cloud-Precipitation of China Meteorological Administration, School of Atmospheric Physics, Nanjing University of Information Science and Technology, Nanjing 210044, Jiangsu, China.^bDepartment of Physics, Higher Education, Government of Khyber Pakhtunkhwa Peshawar 25000, Pakistan. *Corresponding authors Email: rehana.khan@nuist.edu.cn (R. Khan); tlzhao@nuist.edu.cn (T. L. Zhao) Abstract: To quantitatively estimate and analyze the contribution of different aerosol types to radiative forcing, we thoroughly investigated their optical and radiative properties using the Aerosol Robotic Network (AERONET) data (2007-2018) and modelling tools over distinct sites of Indo Gangetic Plain (IGP) and North China Plain (NCP) by following the threshold (FMF₅₀₀ versus SSA₄₄₀) and (AANG_440-870 versus EANG_440-870) and found the highest values for Black Carbon  (BC) type (>90%, & 65%) in (Kathmandu and Kanpur) followed by Dust, (49.55%, & 40.90%) in (Lanzhou and Karachi), with moderate contribution was recorded for Non absorbing (44%, 25.92%), in (Taihu & Beijing) and the lowest for the mixed (22.3%) aerosol type in (Karachi), respectively. Annually, the mean (±SD)  (AOT₄₄₀) was found maximum (0.73±0.36) for Dust type in Karachi and minimum for BCA (0.25±0.04) at Lanzhou, however, found varied from 0.85±0.25 to 0.57±0.30 at Taihu and Kanpur, respectively. Further, the intensive optical properties showed significant temporal and spectral changes and are well substantiated with the model analysis  (CWT and SBDART), revealed the strong presence of BC aerosol type led to a surface (BOA) and atmosphere (TOA) forcing of -60.12, -94.78 Wm⁻² and -9.60, -19.74, with an heating rate of 2.10,2.34 Kday⁻¹, respectively at Kanpur,and Kathmandu sites.

China has established a systematic institutional framework to deal with climate change, including the top-down design guides, government agency administrative orders, carbon emission data statistics and monitoring system, carbon market, and so on. In addition, an excellent low carbon development policy guarantee system also has been developed, these policies are all-round and multi-level, involving different regions and industries in China. The effects of same policy may achieve different results at different time period depending on what stage of industrial development the province or city finds itself, and additional costs are required for economically underdeveloped areas (such as Chongqing). Large-scale changes in the low-carbon development system and mechanism are needed for long-term carbon emission reduction, and emission reduction needs to gradually shift from production to consumption.

A high-resolution inversion is performed to quantify the CO₂ fluxes over Paris during the spring season (March-May) of 2019-2020, based on a network of six ground-based stations. 5-day mean daytime budgets of the fossil fuel CO₂ emissions and biogenic fluxes are estimated using the hourly CO₂ mixing ratio gradients between the station Saclay, located in the south-west of Paris region and five other sites in the urban area. The inversion relies on the transport model simulations using the Weather Research and Forecasting model at 1 km × 1 km horizontal resolution, combined with 1-km fossil fuel CO₂ emissions from the Origins inventory, and biogenic CO₂ fluxes from the VPRM model. The methodology is based on a Lagrangian particle dispersion model approach that could efficiently determine the sensitivity of downwind mixing ratio changes to upwind sources. The emission map shows noticeable changes in the central Paris region, whereas the biogenic fluxes do not show any noticeable change after inversion. An uncertainty reduction of 20% is observed for the fossil fuel emission but none for the biogenic fluxes. The rate of increase in fossil fuel emission was considerably reduced for 2020 (up to 30%). The same pattern is observed in the 5-day total flux time series where the magnitude of posterior fluxes falls below prior fluxes except for the first few days of March, before the lockdown period. A comparison of diurnal mixing ratios generated from prior and posterior fluxes shows that the mixing ratio gradient of all the sites shows a similar pattern, but the direct observations show an offset in the diurnal pattern. The study also aims to show a multisystem comparison between LPDM and Eulerian WRF-CO₂ to quantify the changes in the CO₂ emission pattern over the Paris region during the recent COVID19 lockdown during 2020.

In order to reliably monitor greenhouse gas emissions using atmospheric observations and top-down methods, it is imperative that these methods not only deliver accurate and transparent emissions estimates, but also provide realistic uncertainties on the derived emissions. Here we use two data assimilation systems to systematically quantify and study the uncertainties in the different components of the inverse modeling chain. The first system is the Carbon Cycle Fossil Fuel Data Assimilation System (CCFFDAS), which is a global system that includes process-based models for the natural carbon cycle and fossil fuel emissions. We operated CCFFDAS in Quantitative Network Design mode to quantify how the observational coverage, observation errors, and uncertainties in the prior information affect the uncertainties in the derived national-scale fossil fuel emissions. The second system is the TRACE Regional Atmosphere-Carbon Ensemble (TRACE) system, which is a regional coupled atmosphere-carbon data assimilation system capable of simultaneously constraining the atmospheric transport of CO₂ and CO₂ surface fluxes. The coupling to an atmospheric mesoscale data assimilation system allows us to use TRACE to quantify how uncertainties in mesoscale and long-range transport of CO₂, combined with observation and representation errors, contribute to the uncertainties in the top-down flux estimates. These results provide important insights into the potential capabilities and uncertainties in future greenhouse gas monitoring systems.

Accurate quantification of the sources and sinks of atmospheric CO2 is crucial for understanding the global carbon cycle. In this study, we followed the work of Liu, 2019, and improved the LETKF-Carbon data assimilation system that can assimilate multi-sources real-world observations include the surface GLOBALVIEW-CO2 observations and two carbon satellites, OCO-2 and GOSAT. We conduct three experiments using the different combinations of observations.  The different experiments showed great consistency and the main difference came from the tropical land region. The experiment assimilating only the surface observations are more resemble the prior in the tropical. Further, we compared our results with CarbonTracker-2019, CAMS, and Jena, and evaluating by using aircraft observations.

Wutaishan (WTS) Station on Wutai Mountain (2208 m a.s.l.), which is also known as the “North China Roof,” in Shanxi Province, is surrounded by lush forest vegetation and situated far (30 km) from industrial emission sources. This study filtered online observation data of the atmospheric CO₂ (G2301; Picarro) at WTS Station from March 2017 till February 2018 using both robust extraction of the baseline signal (REBS), and meteorological data (MET) in order to obtain the average background concentration, which is representative of the region (Shanxi Province and the surrounding areas). The background concentration of CO₂ averaged (410.9 ± 6.4) × 10^–6 (mole ratio, the same below), and the daily variation ranged from 2.4 × 10^–6 to 4.8 × 10^–6 , which is relatively low, across the four seasons. The concentration and the surface wind speed displayed negative correlations during spring and winter, with R being –0.44 and –0.46, respectively. Analyzing the backward trajectories, we concluded that wind from the SE–S–SW sector noticeably increased the local CO₂ concentration by transporting from high altitudes (i.e., high air masses) or along the surface.

The Nitrous oxide (N2O) is an important, potent and long-lived greenhouse gas (GHG) that contributes to global warming and the depletion of stratospheric ozone. Long-term in-situ measurements by GC-ECD have been conducted at five background Stations in China for ten years. The methods show comparable precisions at around 1% and all the measurements were calibrated by standards linked to the WMO/GAW reference scale for N2O. Mixing ratios for both “background” and “polluted” conditions are reported. The seasonal and annual variations of N₂O mole fraction are shown. These trajectories are estimated using the TrajStat based on HYSPLIT model and then clustered for the measurement period. The spatial distribution and seasonal variations of trajectories and the corresponding mean concentrations of N₂O for different clusters are analyzed.

Precise and detailed monitoring of atmospheric concentrations of greenhouse gases in urban areas is important to accurately understand anthropogenic influences in the atmosphere as well as the regional carbon cycle. In this study we use a combination of ground, aircraft, and satellite measurements of CO₂, CO, and CH₄ during a campaign from 19-21 February 2021 over the Seoul metropolitan area. We use ground concentration data of CO₂ from Seoul National University CO₂ Measurement (SNUCO₂M) and CO and CH₄ from AirKorea. In addition, we use column-averaged abundances of CO₂, CO and CH₄ measured from the ground using two portable Fourier transform infrared (FTIR) spectrometer EM27/SUNs and measured from space using the Orbiting Carbon Observatory-2 (OCO-2) and Sentinel-5P TROPOspheric Monitoring Instrument (TROPOMI). Lastly, we use aircraft measurements to quantify greenhouse gas concentrations across Seoul along the south of the Han River. Using this unique opportunity, we analyze the atmospheric concentrations using various measurements as well as combustion efficiency across the Seoul metropolitan area using ratios of CO/CO₂ and CH₄/CO₂.This study was supported by the National Research Foundation of Korea (NRF) grant funded by the Government of Korea (NRF-2019R1A2C3002868). J.-S. Park, J.-S. Choi, and H. Kim were supported by the National Institute of Environmental Research (NIER-RP2020-267).  

As one of the main components of the East Asian winter monsoon, the winter Siberian High (SH) plays an important role in the variability of East Asian climate. However, the Climate Forecast System version 2 (CFSv2), shows limited prediction skill for the winter SH. To improve the prediction skill, a hybrid ensemble canonical correlation (ECC) prediction model is established for the winter SH and SH intensity index (SHI) basing the year‐to‐year increment method and an efficient downscaling approach. Hence, three preceding predictors from observation/reanalysis [sea‐ice concentration (SIC), snow‐cover extent (SCE), and sea surface temperature (SST)] and one integrated current predictor from CFSv2 [surface air temperature and sea level pressure (SAT&SLP)] are selected based on their fundamental physical roles. Considering these individual predictors, four separate downscaling schemes are constructed. The regional‐mean temporal anomaly correlation coefficient (ACC) of the winter SH for each scheme is 0.54 (SIC‐scheme‐SH), 0.50 (SCE‐scheme‐SH), 0.72 (SST‐scheme‐SH) and 0.42 (SAT&SLP‐scheme‐SH) [four schemes exceed significant at the 1% level]. However, the skill of each scheme differs in regional and temporal distribution. Thus, a hybrid ECC prediction model is proposed by employing multiple linear regression. The regional‐mean temporal ACC of the winter SH between the observed and predicted results increases from −0.12 (CFSv2; not significant at the 10% level) to 0.85 (significant at the 1% level). Besides, the correlation coefficient between the observation and hybrid ECC scheme for winter SHI is 0.90 (significant at the 1% level). Furthermore, the strongest winter SH in 2012 is reproduced well by ECC‐scheme‐SH.

The interannual variability of heatwaves over the southeastern edge of the Tibetan Plateau (SETP) is explored. Due to the high mountains to the west and north of the plateau, and the control by westerly mean flow in spring, hot and dry conditions are often observed over the SETP, and the maximum centers of heatwave duration (about half a month per year) and its increasing trend (4 days per decade) are discussed in this study. Springtime heatwaves over the SETP also exhibit strong interannual variability and are mainly driven by a spring-type circum-global teleconnection (SCGT) pattern, which is the second leading mode of 200-hPa meridional wind over the North Hemisphere in spring. This SCGT shows distinctive features from the traditional circum-global teleconnection patterns found in boreal summer and winter. It emanates from the mid-high latitudes of the North Pacific and propagates eastward to the North Atlantic, and then splits to a north branch along the polar jet and a south branch along the subtropical jet over Eurasia. The two branches eventually reach the SETP, forming an anomalous anticyclonic circulation over the region. Hence, the SETP is controlled by significant anomalous subsidence and a clearer sky, resulting in below-normal rainfall and above-normal air temperature, in favor of more heatwaves in the region. Such a SCGT-like pattern is also responsible for the interannual variability of the SETP heatwaves in April and May, but not in March. In addition, the SCGT pattern also significantly affects the climate anomalies along its route.

The heatwave is a topic of major concern due to its disastrous effect on various sectors such as health, agriculture, infrastructure, environment. It is also one of the major climate extremes causing more death than any other climate extremes. In a warming climate scenario, heat waves are considered to be one of the major weather extremes being affected. Hence it is essential to explore all the factors that might influence this phenomenon. Also, the extended range prediction in the scales of few weeks to a month is essential for decision making in the allocation of resources and prior warning and preparedness of society for such extreme events. As tropical weather is dominated by intraseasonal variability, this extended range prediction of heatwaves can be achieved by understanding the role of intraseasonal variations on these events. In this study, we present the long-term changes in characteristics of Indian heatwaves in relation to different convectively coupled equatorial waves (CCEWs) such as Equatorial Rossby (ER) wave, Kelvin, Mixed Rossby Gravity waves, Tropical depressions (MT) wave, and Madden Julian oscillation (MJO). Our finding shows that there is a significant role of CCEWs and MJO in modulating the heatwave parameters. The extent of modulation depends on the type, phase, and location of the oscillations. The highest probability of occurrence of the heatwave was observed during the presence of ER dry phase, almost increasing the frequency of heatwave events twice that of the climatological value. While the wet phase of ER suppresses the formation of a heatwave. The MJO shows the dual nature in the formation of the heatwave, increasing heatwave formation over southeast/northwest region and suppressing heatwave over northwest/southeast India during the presence of dry/wet phase. The Kelvin and MT wave reduces the formation of the heatwaves over major parts of the country.

Tropical cyclone (TC) forecasting is crucial for disaster prevention and mitigation of hazards for many tropical and subtropical coastal locations. However, capturing TC intensity change remains a great challenge for most state-of-the-art operational forecasting systems. Recent studies found the TC intensity forecasts are sensitive to three-dimensional ocean dynamics and air-sea interface processes beneath extreme winds. By performing a series of numerical simulations based on hierarchical Atmosphere–Wave–Ocean (AWO) coupling configurations, we showed how atmosphere-ocean and atmosphere-sea wave coupling can affect the intensity of super typhoon Mangkhut (2018). The AWO coupled model can simulate TC-related strong winds, oceanic cold wake, and wind waves with high fidelity. With atmosphere-ocean (AO) coupling implemented, the simulated maximum surface wind speed is reduced by 7 m/s compared to the atmosphere-only run, due to TC-induced oceanic cold wakes in the former experiment. In the fully coupled AWO simulations, the wind speed deficit can be completely compensated by the wave-air coupling. For the central pressure, only coupled runs can capture the weakening trend consistent with observation before landfall. Further analyses showed that, in the AWO experiment, two mechanisms contribute to the improvement of TC intensity. First, in the high wind scenario (>28m/s), the surface drag coefficient reaches an asymptotic level, assisting extreme wind speed to be maintained within the eyewall. As a result, the wind speed distribution is modified and becomes broader; higher wind within the TC area helps to offset the negative effect due to leveling off of the heat exchange coefficient as wind speed increases. The simulated TC in the AWO run is able to extract 8-9% more total heat from the ocean to maintain its strength. Implications of these results on meteorological and sea-state forecasts over marine and coastal locations during TC passages are discussed.

In the CESM2 Large Ensemble data set we explore the seasonality of climatological mean and extreme monsoon precipitation at a daily and gridpoint-level resolution. The forced changes are evaluated in a linear LSQ and quantile regression framework, respectively, both in the 20th and 21st century. The high resolution, afforded by the considerable ensemble size, allows us to rigorously evaluate also the monsoon onset and retreat times. We showcase, furthermore, the value of a large ensemble dataset by demonstrating that the statistical significance of e.g. extreme quantile trends determined from single realisations do not correspond to the forced response.

This study investigates the influence of external forcings on the various summer hot drought events over northeastern China (NEC). Hot drought events are represented by the probability-based index (PI), which simultaneously considers precipitation and temperature anomalies. The results show that hot drought events over NEC increased from 1961 to 2005, and the experiments induced by the historical forcing (ALL), the increased greenhouse gases (GHG) emission forcing, and anthropogenic forcing (ANT) can well reproduce the spatial and temporal features of summer hot drought events over NEC. Based on the optimal fingerprinting method, the impact of increased anthropogenic activities can be detected at the 90% confidence level based on the residual consistency test. In addition, the attributable changes of PI in response to GHG and ANT forcings resemble the observation, implying that the increasing trends of summer hot drought events over NEC are primarily attributed to the increased anthropogenic activity. Furthermore, the occurrence probability of summer hot drought events over NEC could be further increased with the continued emissions of greenhouse gases in the future. Additional strict control regulations on GHG emissions are thus suggested to mitigate its impact on regional climate changes.

Summer monsoonal rainfall over East Asia is dominated by precipitation associated with the East Asian summer monsoonal front (EASMF). A Community Atmospheric Model (CAM5.1) with a high horizontal resolution of 50 km is employed in this study to investigate the projected future trends in the EASMF under the Representative Concentration Pathway 8.5 scenario. Based upon a suite of objectively-defined daily indices of the EASMF, we show that the EASMF in the late twenty-first century will be more intense and displaced eastward and southward from its present-day mean location. Moreover, EASMF events will exhibit a wider meridional expansion and a longer duration. Monsoonal precipitation over East Asia is particularly sensitive to the meridional displacements of EASMF. In conjunction with the projected southward shift of EASMF, an enhanced rain band is seen to extend northeastward from southern China to the northwestern Pacific south of Japan. This precipitation feature is associated with strengthened and southward-shifted westerly jet streams at 250 and 700 hPa, which are respectively linked to tropical warming in the upper troposphere and warming over the South China Sea in the lower troposphere. Within the latitudinal “gap” south of the upper-level jet and north of the lower-level jet, the local vorticity tendencies are maintained by upper-level divergence and lower-level convergence, thus accompanied by strong EASMF, enhanced upward motion, and precipitation. The role of such a “jet stream-front-precipitation” relationship on the extreme Meiyu over the Yangtze River Valley in 2020 will also be discussed.

We report on the characteristics of precipitation associated with three types of landfalling atmospheric rivers (ARs) over western North America in the winter season from 1980 to 2004. The ARs are classified according to three landfalling region as southern, middle and northern types. Two main centers of precipitation are associated with the contribution by the ARs: one over Baja California linked to the southern type of the ARs, and the other over Washington State correlated with the northern and middle types of the ARs. ARs are seen to play a dominant role in the occurrences of extreme precipitation events, with a proportionately greater impact on more extreme events. Moisture flux convergence is the dominant source of moisture for precipitation when ARs and extreme precipitation occur simultaneously in the areas studied. Moisture flux convergence in these cases is, in turn, dominated by the mean and transient moisture transported by the transient wind, with greater contributions from the latter, which are mainly concentrated in certain areas. Vertically integrated vapor transport (IVT) magnitude and direction also play a role in determining the amount of precipitation received in the three regions considered. Larger IVT magnitude corresponds to more precipitation, while an IVT direction of about 220° (0° indicating east wind) is most favorable for high precipitation amounts, which is especially obvious for the northern type of the ARs.

During the intensification of a tropical cyclone (TC), the radius of maximum tangential wind (RMW) often contracts due to the spin-up of tangential wind being much faster inside the RMW than at the RMW itself. However, rapid RMW contractions prior to rapid intensification (RI) of TCs are observed.  Statistical analysis of best track data for the North Atlantic between 2000 and 2017 indicates that rapid RMW contraction (≥20 nmi within 24 h) does not necessarily cause RI (≥30 kt within 24 h) of a TC. An efficient TC RI is generally seen if the RMW contracts to 30 nmi. The change (contraction or expansion) of the RMW is prevalent for weak storms, and RMW contraction is found to be at its most rapid for TC initial intensities ≤60 kt. Rapid RMW contraction and simultaneous RI generally occurs when the initial RMW is >30 nmi. Convective heating associated with very deep convective clouds with infrared brightness temperatures <208 K appearing towards the storm center is important for RMW contraction and sufficient amounts of the convective heating are important for intensification. Less convective heating is required to have the same intensification rate for a storm with an initially smaller RMW. A storm is more likely to experience RI with relatively less convective heating after the RMW contracts to a smaller size. This study demonstrates the role of convective heating on RMW contraction and storm spinup through different processes in the early stages of a TC.

The El Niño-Southern Oscillation (ENSO) can significantly affect the rapid intensification of tropical cyclones over the western North Pacific (WNP). However, ENSO events have various durations, which can lead to different atmospheric and oceanic conditions. Here we show that during short duration El Niño events, the WNP tropical cyclone rapid-intensification mean occurrence position migrates westward by ~8.0° longitude, which is caused by reduced vertical wind shear, increased mid-tropospheric humidity, and enhanced tropical cyclone heat potential over the westernmost WNP. The changes in these factors are caused by westward advected upper ocean heat during the decaying phase of a short duration El Niño. As super El Niño events tend to have short durations and their frequency is projected to increase under global warming, our findings have important implications for future projections of WNP tropical cyclone activity.

The accuracy of tropical cyclone (TC) track forecast has been improved year by years, on the other hand, the forecast of tropical cyclone intensity still has a difficulty of improvement. Recently the relationship between lightning activity and tropical cyclone intensity has been investigated. Lightning tends to increase during the rapid intensification of the TC. Therefore, monitoring the lightning activity becomes important for a TC intensity forecast. Lightning observation network are deployed over the western north Pacific by five very long frequency events trigger measurements called V-POTEKA at Palau, Guam, Manila Philippines, Okinawa Japan and Serpong Indonesia under the ULAT (Understanding Lightning and Thunderstorm) of SATREPS (Science and Technology Research Partnership for Sustainable Development) in the Philippines. Lightning activity was drastically increased around the TC during the TC genesis stage of tropical storm Maysak on 28 August 2020. Numbers of lightning reached the maximum during the life cycle of the TC. Location of lightnings were concentrated near the center of TC in about 100 to 200 km radius. Convective clouds reached less than 190K of blackbody temperature near the center of the TC. We called this phenomenon as “lightning burst”. Lightning burst indicates cumulonimbus was most active during the TC genesis stage. About 60% of TCs observed lightning bursts during the TC genesis stage over the Philippine Sea in 2020. We will investigate further what kind of structure occurred during the lightning burst and what kind of mechanism responsible for the lightning burst.

In this study, the secondary circulations and warm cores of tropical cyclones (TC) Fanapi (2010) and Lekima (2019) near Taiwan are examined using the idealized axisymmetric TC model and full-physics WRF model. Tangential flow, radial and vertical velocities are first obtained using the axisymmetric TC model, and then compared with those from the three-dimensional WRF model. For the axisymmetric model, the secondary circulations are obtained by solving the Sawyer-Eliassen equation with the environmental static stability, baroclinicity, inertial stability under the given radial distribution of diabatic heating (directly outputted from the WRF model). Effects of diabatic heating and environmental static stability, baroclinicity, and inertial stability are examined. Results show that differences between the axisymmetric model and WRF model at lower and upper levels are found, because effects of friction, turbulence, and radiation are not included in the idealized axisymmetric model. Baroclinic environment in the axisymmetric model produces stronger low-level inflow, upper-level outflow, eyewall updraft, but weaker temperature tendency in the eyewall than those under barotropic environment for TC Fanapi. However, for TC Lekima with double eyewalls, baroclinic environment obtains weaker downdrafts in the eye and moat region. In static stability experiments, the temperature tendency and the secondary circulation are weaker when the static stability becomes larger for both TCs. When the inertial stability increases, the low-level inflow becomes weaker and the eye downdraft is stronger for both TCs. The upper-level outflow and the eyewall updraft decrease obviously as the latent heating from the primary rainband for TC Fanapi is decreased. For TC Lekima, the secondary circulation and the temperature tendency for the eye and inner eyewall are decreased with the decreasing latent heating of the inner eyewall; similar but greater responses of secondary circulation and temperature tendency are found for the decreasing latent heating of the outer eyewall.

The prediction of the tropical cyclones (TC) genesis remains a great challenge. In recent years, the critical role of radiation feedback on TC genesis has been gradually revealed. This study shows that both in idealized RCE framework and in the real world, radiation (mostly cloud-radiation) feedback brings forward the formation of tropical cyclones by first accelerating the development of the mid-level circulation. The radiation heating anomaly in the disturbance region induces a secondary circulation that transports more water vapor up to high levels. As a result, a stratiform heating structure is enhanced, leading to a positive mid-level potential vorticity anomaly and promoting TC genesis. Comparing with previous ideas on the pathways of radiation feedback accelerates TC genesis, the results here emphasize the key role of the mid-level circulation and the vertical structure of the cloud-radiation-induced thermodynamical and dynamic responses.

Rapid intensification and rapid weakening (RW) of tropical cyclones (TCs) are challenges for operational forecasting. DeMaria et al. (2012) and Wood and Ritchie (2015) defined RW as the maximum wind reduction more than 20 and 30 knots in 24 hours, respectively. A number of factors are involved in TC’s RW, such as higher vertical wind shear, dry air intrusion (usually occurring in a sheared environment) and lower sea surface temperature (SST). The objective of this work is to investigate the RW processes of Typhoon Trami (2018) in relation to which the satellite data documented a substantial sea surface temperature (SST) cooling during passage of the typhoon. This cold wake and Trami’s RW occurred as the storm was moving at very slow translation speed. A marked structure change of Trami is found in the three-dimensional ocean-coupled model (C3D) experiment during the RW stage, in which the convective clouds (CC) and convective burst (CB) within 1.5 times radius of maximum wind (RMW) in C3D experiment dramatically decrease, resulting in the loss of diabatic heating and leading to the TC weakening. In the 3D simulation, the enthalpy flux dramatically decreases in the inner core due to the SST cooling during the RW period, while the stable boundary layer (SBL) is formed in the TC’s inner-core region. The expanding SBL coverage stabilizes the atmosphere and suppresses the convection in the inner core, leading to weakening of the storm. SBL is also identified in our analyses of the inner-core dropsonde data from the field program of T-PARCII (Tropical cyclones-Pacific Asian Research Campaign for Improvement of Intensity estimations/forecasts).

Tropical cyclone (TC) and trough interaction, having both beneficial and detrimental impacts on TC intensity, remains challenging for operational forecasts. It is noted that the Upper-tropospheric Cold Low (UTCL) is also an evident upper-level forcing that could interact with TCs in the Western North Pacific (WNP) region, particularly during the early TC season. The objective of this study is to propose more comprehensive conceptual model for the TC and upper-level forcing interaction, and identify the specific TC-UTCL configurations leading to favorable or unfavorable interaction in tropical WNP. The Weather Research and Forecasting (WRF) model is used to examine the impact of UTCL on intensity and structural change of Typhoon Nepartak (2016), conducted as the control simulation (CTL). To highlight the impacts of upper-level eddy forcing, the simulation by removing UTCL (noCL) is also performed, with the initial field modified by piecewise potential vorticity inversion (PPVI) method. Results demonstrate that higher intensification rate of TC in the CTL simulation is attributed to the response of stronger secondary circulation associated with additional upper-level eddy forcing in the downshear-left (DL) and upshear-left (UL) quadrants. The forcing involves the reduction of inertial stability and work done in the outflow layer, as well as the enhancement of eddy flux convergence of angular momentum. Stronger upward motion and therefore, larger diabatic heating contributed from inner-core convections in the critical UL quadrants are beneficial to the axisymmetrization process and the development of TC. For the noCL simulation, however, stronger secondary circulation is located in the downshear-right (DR) and DL quadrants, which is detrimental to the axisymmetrization process despite lower environmental vertical wind shear. In general, the TC-UTCL interaction in the CTL simulation is favorable to TC intensification. Sensitivity experiments are still undergoing to evaluate the specific distance and relative direction favorable or unfavorable for TC-UTCL interaction.

This study investigated the representation of surface winds in complex terrain during the passage of Typhoon Sondga (2004) in downscaling simulations with the horizontal grid spacing of 200 m. The mountainous areas in Hokkaido where forest damages occurred in the typhoon event were chosen for the present analysis. The 200-m-grid simulations were compared with the simulations with the grid spacing of 1 km. The 200-m-grid simulations clearly indicated more enhanced and more frequent extremes both in the stronger and weaker ranges of surface winds than the 1-km-grid case. Both in the 200-m grid and 1-km grid cases the mean and maximum winds in the analysis areas during the simulated time period increase with the increase in the terrain slope angle, but in the 200-m grid case the relationships of the mean and maximum winds against the terrain slope angle includes wide scatter. In this way, the response of the wind representations to the grid spacing appears differently between the 200-m and 1-km grid cases. A parameter characterized subgrid-scale orography was used to quantify the influences of the terrain complexity on surface winds, demonstrating that the area-maxima and spatial variance of surface winds are more enhanced with the increase in the subgrid-scale orography in the higher-resolution case. It is suggested that the high-resolution simulations at the 200-m grid highlight the fluctuating nature of surface winds in complex terrain, because of the better representation of the model terrain at 200 m. Benefits of the representation of surface winds in simulations at the resolution on the order of 100 m are due to the better representation of complex terrain, which enables to quantitatively assess the impacts of strong winds on forest and natural vegetation in complex terrain.

This study uses scanning Doppler lidars, automatic weather stations, wind profiler, sounding observations and high resolution reanalysis datasets to document a strong wind event in Pyeongchang, Korea. The primary objective of this study is to investigate possible mechanisms and the fine-scale structural evolution of strong winds over the complex terrain associated with the movement of a low-pressure system (LPS). The analysis results shows that the surface winds have different patterns as wind speed is increased in the lee side and a persistent strong wind in mountainous areas with the approaching LPS. The adiabatic warming would play an important role to reduce the surface pressure and the winds are accelerated by pressure gradient force (PGF) in the lee side of the TMR through the budget analysis of horizontal and vertical momentum equation. In the mountainous area, the wind speed was increasing (decreasing) when estimated acceleration (calculated by above mentioned budget analysis) is positive (negative) but it had less relations with the changes of temperature between selected surface stations along valley. Further analysis indicates that the PGF is also the key to dominate the acceleration of winds in mountainous area, but relatively lower pressure at narrower segment along the valley is related to channeling effect by checking fine-scale retrieved 3D wind patterns. The observational evidence shows that the different mechanisms are important references to determine the strength and persistence of the orographically strong winds in the same underlaying LPS under clear-air condition.
Acknowledgments. This study was funded by the Korea Environmental Industry & Technology Institute (KEITI) of the Korea Ministry of Environment (MOE) as “Advanced Water Management Research Program”. (79615). This work was funded by the Korea Meteorological Administration Research and Development Program “Enhancement of Convergence Technology of Analysis and Forecast on Severe Weather” under Grant (KMA2018-00121)

This study uses a dense rain gauge network, radar observations, and a newly developed orographic precipitation model to explore the physical mechanisms responsible for the orographic precipitation over Da-Tun Mountain (DT) associated with Typhoon Meari (2011). DT is located adjacent to the northern coast of Taiwan, with a size of ~15 km and a terrain peak of ~1 km (MSL, Mean Sea Level). Typhoon Meari brought strong northwesterly winds (20-25 m s^-1) to the DT and caused significant precipitation as it was located ~300 km northeast of Taiwan. The observational analysis shows that the accumulated rainfall over DT can exceed 260 mm within 10 h. The rainfall maximum was found along the first northwestern mountain crest of DT and its leeward side. The simulations of the orographic precipitation model show that the rainfall generated by the upslope lifting mechanism exhibits spatial distributions similar to the observations, but the accumulated rainfall is underestimated. Radar observations showed that during the analysis period, DT was significantly affected by the approach/landfall of both stratiform and convective precipitation associated with typhoon circulations. This indicates that the typhoon background precipitation may play a potential role in modulating precipitation over DT. When the microphysical effects of the background precipitation are considered in this orographic precipitation model, the simulated precipitation intensity is closer to that of the observed rainfall. These research results quantitatively demonstrate the importance of the seeder-feeder mechanism on the precipitation enhancement in the typhoon environment over DT.

During the International Collaborative Experiments for Pyeongchang 2018 Olympic and Paralympic winter games (ICE-POP 2018), a strong windstorm occurred on the lee side of the Taebaek Mountain on 14 Feb 2018 as a low-pressure system passed through the northern part of the Korean Peninsula. At that time, there was a prevailing westerly wind accompanying warm advection and inversion layers on high mountainous areas, creating favorable conditions for downslope windstorms. With the aim to investigate the generation mechanisms responsible for the downslope windstorm, numerical simulations using the Weather and Research Forecast (WRF) model with a finest horizontal resolution of 300 m are performed. The model reasonably well reproduces the passage of low-pressure system, upstream sounding, and downslope winds, but overestimates surface winds at some local points in the lee side. The adiabatic warming associated with the low pressure and the presence of the inversion intensified surface winds in the lee side. Analysis of vertical cross-sections showed a steep descend of potential temperature on the lee slope and rapid recovery on the leeward side, showing an evidence of hydraulic jump. During the windstorm event, mountain waves are generated in the lee side with horizontal wavelengths that are varying with time due to the change of background wind and stability with movement of low-pressure system. Using the dispersion relationship of internal gravity wave, the scorer parameters for mountain waves showed that waves with horizontal wavelength of 20 km or less are trapped below the altitude of 6 – 9 km. These findings suggest that the downslope windstorm is generated by mechanisms of hydraulic jump and partial reflection. *Acknowledgement: This research is supported by the Korean Meteorological Administration Research and Development Program (KMI2020-01910), and by the National Research Foundation of Korea Research and Development Program (NRF- 2019R1I1A2A1060035). 

In this study, we performed a series of tracer transport simulations using Taiwan VVM to evaluate the effects of the local leeside vortex circulation and mountain-valley circulation on the transport and accumulation of the pollutants on a diurnal time scale. The wind directions of crucial synoptic weather northeast monsoon are idealized as the initial conditions of the simulations. The major local non-traffic emission sources on the western plain Taiwan, which are Taichung Power Plant (TPP) and Sixth Naphtha Cracker (SNC), are taken as the tracer emission sites so that the experiment results could be a good proxy of the realistic scenarios. With the local circulation over complex topography being resolved explicitly, the impact of the boundary layer development on the tracer transport of Puli basin is discussed. The simulation results clarify the tracer transport mechanisms across multiple scales and we conclude that: 1) On the island-scale, the leeside vortex and its evolution could decide the distribution scenarios of the tracer emitted from the coastal areas. 2) The high tracer concentration at Puli during the night is due to the tracer being trapped by the thinning of the mixing layer in the evening. 3) The sensitivity of the local tracer transport to the change of the synoptic wind direction shows that under north-easterly due east (due north) environment, the pollutant transports from SNC (TPP) are most likely to induce high concentration in Puli at night. The evaluation of the sensitivity could also serve as a framework to understand the change of local pollution over Taiwan in the future climate. 

In the winter season of the Gangwon region, where is located in the mid-eastern part of the Korean Peninsula, easterly wind that is induced by Siberian-high frequently causes heavy snowfall. When dry and cold air mass from continent is advected over the East sea of Korea that is relatively warmer than the continental air mass, thermal instability in the lower troposphere increases, which can induce convective cloud rolls. The clouds accompanied by the snowfall are penetrated to inland by the prevailing easterly wind. The Korean Peninsula has the geographical characteristics that mountain ranges exist along the eastern coastline, that can block easterly wind and induce upward motion over the upstream region. Previous studies presented key factors which can affect the snowfall are air-sea temperature difference, wind turning layer, Froud number (FN), and the horizontal temperature contrast between land and sea. In this study, the idealized experiment is conducted by utilizing the Weather Research and Forecasting (WRF) model to examine effects of each key factor on the snowfall structure. The individual impact of each key factor is investigated by changing the variables while other factors were controlled. When the height of the wind turning layer is higher than the mountain, the maximum snowfall is located over the mountain ridge in the large FN, whereas the snowfall is limited to the windward area in the small FN. On the other hand, when the wind turning layer is lower than the mountain, it shows that the snowfall cannot cross the mountain regardless of the FN. The larger the air-sea temperature difference, the precipitation is increased and concentrated in the sea. When the horizontal temperature contrast between the land and the sea is large enough, the snowfall is limited to the seaward area off the coastal line.

Lake-air interaction plays an important role in controlling local weather and climate. This study aims to reveal the dynamical effect of water-land roughness contrast on precipitation during a summer rainfall event, which was detected by rain gauge and remote sensing observations around Lake Selin Co (a large Tibetan lake). During this event, precipitation amount to the west (downwind) of the lake was much higher than that to the east (upwind). Numerical experiments based on Weather Research and Forecasting model (WRF) were conducted to investigate this phenomenon. High-resolution WRF simulations can reproduce the precipitation contrast between downwind and upwind of the lake, but fails with the lake aerodynamic surface roughness enhanced by either enlarging the length directly or replacing the lake with adjacent land cover. Further analyses indicate that the water-land surface friction contrast directly leads to acceleration of wind above the water surface and deceleration over the land surface, enhancing the air convergence and precipitation over land area downwind of the lake. By contrast, the heat flux and evaporation from the lake are small in summer and hardly show important effects on precipitation around the lake. Therefore, the dynamical effect of the lake surface plays a dominant role in the precipitation enhancement downwind of the lake during the summer. Further analysis on a winter lake-enhanced-snowfall event shows that the dynamical effect also shows evident influence, though with a weaker magnitude than the heat flux and evaporation effect does, which has not been well addressed in previous studies. 

Hydrometeors suspended in atmosphere are a valid source of both pollution as well as several atmospheric phenomena. Much of the prediction capacities in regards to forecasting the hydrometeorological disasters rely on appropriate monitoring of the available hydrometeors at the atmosphere. Weather stations measure some parameters and indices that are good for this purpose, but the true essence could better be understood with the help of NWP models. This research attempts to find a way for monitoring the hydrometeors available at the atmosphere over Dhaka city through WRF-Chem model. The preliminary results have been promising. The RMSE results for observed aerosols are below 0.5. However, the PBIAS scores for the same are less than 10%. Although more rigorous studies are required to obtain a synthesized finding, yet the early results are showing positive vibes towards selecting the WRF-Chem model as a good alternative to monitor the available hydrometeors at different levels of the atmosphere.

Prediction of extreme precipitating events has become very important on the backdrop of increasing trend on extreme precipitation events on various parts of globe. It is also well  known that the GCMs face major challenge in simulating them. At IITM we run a  deterministic and a 21 member ensemble of NCEP Global Forecasting System (GFS) at 12 km resolution. It has been observed with these high resolution models it is possible to predict  these events in 3 to 5 days in advance over Indian region. It has been also noticed that the simulation of actual observed rainfall amount is also been a great challenge for any GCM. To  overcome this issue the percentile based extreme forecast technique has been introduced  (Based on deterministic version, GFS). Advantage of these method is, model decides whether  a particular event is extreme or not based on it’s own climatological history of rainfall. In this  way it has been possible to extract more information from the model forecast. Another  important aspect of extreme rainfall events is flood. To address this issue we have started  issuing river basin forecast for various river basins across India. The forecast haven issued  everyday with 10days lead time. This enables authorities to take necessary actions before any catastrophy.

East Asia is one of the regions predicted to be impacted the most by climate change by the end of century. As the regional effects of climate change do not follow global levels linearly, the need for dynamical downscaling is greatly emphasized. This study used the data from several GCM-RCMN chains participating in the CORDEX-East Asia phase 2 to assess changes in temperature and heat stress under RCP8.5 scenario. The net effective temperature, an index that includes the effects of temperature, humidity, and wind, was used along with temperature itself to quantify the heat impact. To define the heat stress, weather stress index WSI was used. Model performance in current climate was assessed first. Temperature bias was positive during day and negative during night, while humidity showed negative, and wind positive bias during whole day. Due to these combined factors, the bias in NET during night-time was relatively large, while the bias during daytime was negligible. This study used the maximum NET and temperature values, which occur during daytime for analysis, and therefore all models performed sufficiently. Both WSI95 (95th percentile) and WSI99 (99th percentile) distributions were also simulated well in the models. All models showed rise in both temperature and NET for both WSI95 and WSI99 indices, with some of the models showing more uniform rises over whole domain than others.

This work was funded by the Korea Meteorological Administration Research and Development Program under Grant KMI2020-01411.
The main calculations were performed by using the supercomputing resource of the Korea Meteorological Administration (National Center for Meteorological Supercomputer)

Solar power resources can make a significant contribution to electricity generation in the Philippines' low-carbon future. However, this future will also experience significant climate change that could affect future photovoltaic (PV) output due to irradiance and temperature changes. Here we examine potential future changes in solar radiation at the surface and temperature and its effect on future PV output using data from the SEACLID/CORDEX Southeast Asia simulations. For this purpose, projections for the near-future and mid-future periods under RCP4.5 and RCP8.5 scenarios are analyzed over the Philippines. Results show that most of the models agree on the projected changes in temperature but with noticeable uncertainties in the projected changes in irradiance over the country. From the first-order estimation of the impact of solar radiation and temperature changes on potential PV output, the solar energy output is estimated to slightly increase by a few percent over the country, except for a slight decrease over Mindanao in the near-future period under the RCP4.5 scenario. However, there are uncertainties in these projected changes, which may be due to the models' difficulty to robustly simulate cloud cover, thus affecting the resulting irradiance and subsequently the estimated solar energy output. Fractional contribution analysis shows that changes in potential PV output are mostly attributed to changes in irradiance rather than temperature. However, in some instances, a small decrease in PV output is also noted due to larger fractional contributions from temperature.

This study examines potential impacts of climate change on wind energy in the Philippines using the SEACLID/CORDEX Southeast Asia climate projections. Future changes in wind energy variables, such as wind speed at 80-m (based on installed wind turbines in the country) and wind power density (WPD), are derived for the near-future (2016-2035) and mid-future (2046-2065) under the Representative Concentration Pathway (RCP) scenarios, RCP4.5 and RCP8.5, relative to the baseline period 1986-2005. Initial results from the analysis of ensemble projections of the anomalies show a general decrease in WPD in both RCP4.5 and RCP8.5 in the mid-future, and in some parts of the near-future at the annual scale. However, projected increases in WPD are noted in the near-future period in the Palawan islands and the Visayas region under RCP4.5, and including Mindanao region under RCP8.5. Seasonal variations are noted in the changes especially in the June-August and September-November seasons. Results from this study can contribute in efforts to identify potential sites for renewable energy development.