This study presents initial results of the ionospheric scintillation in the F layer using the S4 index derived from the radio occultation experiment (RO‐S4) on FORMOSAT‐7/COSMIC‐2 (F7/C2), and a global map of equatorial plasma bubbles (EPBs) is constructed by using the RO-S4. The F7/C2 RO‐S4 during August 2019 to April 2020 show clear scintillation distributions around American and the Atlantic Ocean longitudes and compared with Jicamarca range‐time‐intensity (RTI) maps of the 50 MHz radar. Result shows that the occurrence of intense RO‐S4 in the range 0.125–0.5 is co‐located with the bottomside of the spread‐F patterns. The increase of RO‐S4 at the upward phase of bottom‐side oscillations is consistent with the theory that EPB seeding by the large‐scale wave. The locations and occurrences of the RO‐S4 greater than 0.5 are consistent with airglows depletions from the NASA GOLD mission. Climatology analyses show that monthly occurrences of RO‐S4 > 0.5 agree well with the monthly EPB occurrences in the GOLD 135.6 nm image, and show a similar longitudinal distribution to in‐situ measurements. The results suggest that the RO‐S4 intensities can be utilized to identify EPBs of specific scales.

Non-migrating atmospheric tides are evident throughout Earth’s upper atmosphere. Features corresponding to these non-migrating tides are also found in observations of the ionosphere, and especially in the location and strength of the equatorial ionization anomaly. It is widely accepted that the primary mechanism responsible for imprinting this signature of the atmospheric waves on the ionosphere involves the E-region dynamo. However, both theory and modeling suggest that other mechanisms should also contribute to the longitudinal modulation of the equatorial ionization anomaly. Providing observational confirmation of these various mechanisms was one of the primary goals for NASA’s Ionospheric Connection Explorer (ICON) mission. Utilizing data from multiple ICON instruments at once, we provide observational constraints on the effectiveness of various mechanisms by which non-migrating tides can produce longitudinal variations in the equatorial ionization anomaly.

The neutral wind dynamo plays an important role in generating low-latitude ionospheric variability and is associated with creating favorable conditions for space weather effects. The neutral wind in the lower thermosphere is highly variable due to its influence from lower atmospheric upward propagating waves and tides. In addition, observational and modelling studies have indicated large variability of the plasma drift on time scales from days to seasons associated with the wind dynamo at low and middle latitudes. The relationship of the ionospheric drift variability to the neutral wind variations is still not fully understood. The Ionospheric Connection explorer (ICON) mission is designed to focus on the low to middle latitude region and measures key parameters, such as the plasma drift and density and neutral temperatures and winds, to examine the vertical coupling of the lower to upper atmosphere. In this presentation, we will focus on the ICON observations and compare to Whole Atmosphere Community Climate Model-Extended (WACCM-X) simulations to examine the daytime low latitude ion drift and neutral wind variations. We investigate the variation of ion drift and neutral wind on different time scales. We compare WACCM-X simulations with the observations to shed light on what variability can be captured by this whole atmosphere model. We conclude with discussing possible reasons for disagreement.

Atmospheric tides play important roles in the dynamics of the upper atmosphere. The sources of atmospheric tides can be from convection in the troposphere, solar heating throughout the atmosphere, or generated by nonlinear wave-tide interactions locally. The Michelson Interferometer for Global High-resolution Thermosphereic Imaging (MIGHTI) onboard the Ionospheric Connection Explorer (ICON) is designed to measure the neutral winds and temperatures in the thermosphere. During day of year 85 to 105 in 2020, in the fixed local time frame, zonal wavenumber 3 and 4 are observed in the neutral wind from 95 km to 300 km. This event provides the opportunity to study the vertical evolution of the zonal wave structure, and the response in the ionosphere.  In this study, we focus on the vertical variation of the wave structure in neutral wind.  The possible atmospheric non-migrating tides propagating from lower to higher altitudes will be discussed based on theory and comparison of MIGHTI measurements with several TIE-GCM runs.

This study examines the ionospheric response during a minor magnetic storm under deep solar minimum conditions using the Global Ionospheric Specification (GIS) electron density constructed by using the radio occultation (RO) slant total electron content (TEC) measurements of the FORMOSAT-7/COSMIC-2 (F7/C2) constellation and ground-based global navigation satellite system (GNSS) TEC. The equatorial ionization anomaly (EIA) crest density increased by about ~300%, with a localized region of more intense enhancements over the European sector. These enhancements are validated with global ionosphere map (GIM) TEC data product and ground based GNSS observations. The vertically resolved electron density structures reconstructed by the GIS help us to understand the physical processes giving rise to such unexpectedly intense ionosphere responses during the storm.  The altitude distribution and poleward shift of the EIA crests indicate that prompt penetration electric fields (PPEF) play an important role in producing the observed positive storm responses, with the storm-induced equatorward circulations likely contributing to an accumulation of plasma that is competing against recombination losses. In addition, storm-time thermosphere composition changes, which appear to be more effective under deep solar minimum conditions, might also play a crucial role in producing these large low-latitude enhancements during a relatively minor storm.

The FORMOSAT‐7/COSMIC‐2 (F7/C2) satellite mission was launched on 25 June 2019 with six low‐Earth‐orbit satellites and can provide thousands of daily radio occultation (RO) soundings in the low‐latitude and midlatitude regions. This study shows the preliminary results of space weather data products based on F7/C2 RO sounding: global ionospheric specification (GIS) electron density and Ne‐aided Abel and Abel electron density profiles. GIS is the ionospheric data assimilation product based on the Gauss‐Markov Kalman filter, assimilating the ground‐based Global Positioning System and space‐based F7/C2 RO slant total electron content, providing continuous global three‐dimensional electron density distribution. The Ne‐aided Abel inversion implements four‐dimensional climatological electron density constructed from previous RO observations, which has the advantage of providing altitudinal information on the horizontal gradient to reduce the retrieval error due to the spherical symmetry assumption of the Abel inversion. The comparisons show that climatological structures are consistent with each other above 300 km altitude. Both the Abel electron density profiles and GIS detect electron density variations during a minor geomagnetic storm that occurred within the study period. Moreover, GIS is further capable of reconstructing the variation of equatorial ionization anomaly crests. Detailed validations of all the three products are carried out using manually scaled digisonde NmF2 (hmF2), the results show that both GIS and Ne‐aided Abel are reliable products in studying ionosphere climatology, with the additional advantage of GIS for space weather research and day‐to‐day variations.

In recent years, geomagnetically induced currents (GIC) in national power networks by space weather have been widely recognised as a serious threat to global socio-economic stability; with extreme geomagnetic storms likely to cause the widespread collapse of national power grids, both predicting and mitigating these currents is of major international importance. New Zealand is fortunate to have a significant amount of dense, high-quality GIC measurements from the national power-grid, which provides us with a unique opportunity to not only study the impact of GIC on the electricity network, but the potential to forecast the occurrence of GIC and protect the network from GIC-related damage through mitigation protocols. In this presentation we will outline the aims and objectives of our current project to investigate GIC from a New Zealand context. The primary scientific questions have been developed in consultation with the New Zealand energy industry, spanning both electrical power networks and gas distribution pipelines. Our actvities include the creation of a national magnetometer array and the execution of a dense magnetotelluric survey, both of which will feed into a state-of-the-art induction model allowing us to estimate the impact of an extreme solar storm. From this modelling, we hope to develop GIC prediction and mitigation techniques applicable not only to New Zealand, but to other mid- and low-latitude countries at risk of GIC.

Taking into account the recently discovered response of seismicity to artificial electromagnetic impacts on the Earth crust [1,2], a hypothesis is proposed on a possibility of earthquake triggering by severe space weather conditions that is currently under discussion [3]. One of the most significant manifestations of space weather on the Earth is geomagnetically-induced electric currents (GIC), excited in the surface layers of the Earth and conductors during sharp changes in the geomagnetic field. Practically unexplored are GIT in the conductive fault zones of the Earth crust, as well as their impact on deformation processes in the earthquake sources. It should be noted that, due to the saturation of crustal faults with highly mineralized fluids or graphitization of the fault, its electrical conductivity may exceed the conductivity of the host rocks by several orders of magnitude. The numerical estimations demonstrated that under strong disturbances of the geomagnetic field of ~ 10² nT during strong solar flares or geomagnetic storms the GIC density in a conductive fault can reach 10^-6 A/m² that is an order of magnitude higher than the current density generated in earthquake source by artificial pulsed power systems [1]. Thus, under certain conditions (the level of the stress-strain state of a fault, its conductivity and orientation), telluric currents (GIC) excited in faults by sharp variations of geomagnetic field can trigger earthquakes. The results obtained were confirmed by observation of sharp increase of global seismicity after the strong solar flare of X9.3 class on September 6, 2017 followed by strong magnetic storm (Kp>8). The reported study was funded by RFBR and NSFC, project number 21-55-53053. References: [1]. Zeigarnik V. et al (2018) Geoph Res Abstr 20: EGU2018-15436-1. [2]. Novikov V.A. et al (2017) Earthq. Sci. 30, 4, 167-172. [3]. Sorokin V.M. et al ( 2019) Earthq. Sci., 32, 1, 26-34.

Thanks to recent advances in radio interferometric instrumentation, we’ve entered a new era of solar radio observations—broadband dynamic imaging spectroscopy. In this talk, I will first introduce the history of solar radio observations based on either dynamic spectral measurements radiation integrated over the Sun or imaging at a few discrete frequencies, then review some recent progress based on dynamic imaging spectroscopy over a wide frequency range that has placed us in a strong position to make revolutionary breakthroughs in measuring the coronal magnetic fields. Future perspectives will also be briefly discussed.

Magnetic flux ropes are the centerpiece of solar eruptions. Direct measurements for the magnetic field of flux ropes are crucial for understanding the triggering and energy release processes, yet they remain heretofore elusive. Here we report microwave imaging spectroscopy observations of an M1.4-class solar flare occurred on 2017 September 6, using data obtained by the Expanded Owens Valley Solar Array. This flare event is associated with a failed eruption of a twisted filament observed in Hɑ by the Goode Solar Telescope at the Big Bear Solar Observatory. The filament, initially located along the magnetic polarity inversion line prior to the event, undergoes a failed eruption during the course of the flare. The upper portion of the erupting filament has a counterpart in microwaves, whose spectral properties indicate gyrosynchrotron radiation from flare-accelerated nonthermal electrons. Using spatially resolved microwave spectral analysis, we derive the magnetic field strength along the filament spine, which ranges from 600--1400 Gauss from its apex to the legs. The results agree well with the non-linear force-free magnetic model extrapolated from the pre-flare photospheric magnetogram. The multi-wavelength signatures of the event are consistent with the standard scenario of eruptive flares, except that the eruption failed to fully develop and escape as a coronal mass ejection. We conclude that the failed eruption is likely due to the strong strapping coronal magnetic field above the filament.

In the standard model of solar flares, a large-scale reconnection current sheet is postulated to be the central engine for powering the flare energy release and accelerating particles. However, where and how the energy release and particle acceleration occur remain unclear owing to the lack of measurements of the magnetic properties of the current sheet. Here we report the measurement of the spatially resolved magnetic field and flare-accelerated relativistic electrons along a current-sheet feature in a solar flare. The measured magnetic field profile shows a local maximum where the reconnecting field lines of opposite polarities closely approach each other, known as the reconnection X point. The measurements also reveal a local minimum near the bottom of the current sheet above the flare loop-top, referred to as a "magnetic bottle". This spatial structure agrees with theoretical predictions and numerical modeling results. A strong reconnection electric field of about 4,000 V m^-1 is inferred near the X point. This location, however, shows a local depletion of microwave-emitting relativistic electrons. These electrons instead concentrate at or near the magnetic bottle structure, where more than 99% of them reside at each instant. Our observations suggest that the loop-top magnetic bottle is probably the primary site for accelerating and confining the relativistic electrons.

The interaction between the magnetic field and an atom/ion breaks the symmetry of an atomic system allowing atomic states with the same magnetic quantum number and parity to mix and gives rise to a magnetic-field-induced transition (MIT) to appear in spectra. The intensities of these lines have a strong, to first order quadratic dependence on the external field strength and therefore can be used for magnetic field diagnostics. It was found that a pseudo-degeneracy of the 3p⁴3d ⁴D_7/2,5/2 occurred in Fe X, and an external magnetic field could induce a mixing of these two levels and thereby cause an MIT at 257.26 Å from the ⁴D_7/2 to the ²P^o_3/2 level. The pseudo-degeneracy of the two levels for Fe X causes this MIT to be sensitive to the relatively small magnetic fields expected in the solar corona. Recent studies have illustrated the potential of this method that allows the measurement of the coronal magnetic field strength utilizing spectra lines observed by the Hinode/EIS satellite. This new method can provide 2D and temporal resolution maps of the magnetic field from the solar disk to the limb, complementing the DKIST and CoMP ground-based observatories, and extending our reach to the disk for which the only measurements are done using radio measurements.

Coronal magnetic field diagnostics plays a crucial role in advancing our understanding on the mechanisms of a variety of solar activities, including solar flares and coronal mass ejections (CME). Here we report results from the microwave spectral imaging observation from the Expanded Owens Valley Solar Array (EOVSA) of a C1.4 flare occurring on 2017 July 14^th. We obtained information on the evolving coronal magnetic field in the flare region using the microwave spectra fitting technique. We also examined the temporal and spatial correspondence between the magnetic field evolution and atmospheric dynamics observed by the Atmospheric Imaging Assembly on board the Solar Dynamic Observatory (SDO/AIA) and the Interface Region Imaging Spectrograph (IRIS). The analysis result suggests that the energy released during the decay of magnetic field directly contributes to the particle acceleration and plasma heating in the active region. Our study demonstrates that microwave spectral imaging observations are capable of determining the evolving coronal magnetic field during small-scale solar flares, thus shedding new light on the details of magnetic reconnection and particle acceleration in these eruptive events.

Magnetic field is the key to understand extreme activities, such as flares and coronal mass ejections, in the solar and stellar coronae. However, measurements of the coronal magnetic fields are limited. Recently, it was proposed that the intensity ratios of some EUV spectral lines from the Fe X ion can be used to measure the magnetic field in the solar corona based on the theory of magnetic field induced transitions (MIT). In order to test the validity of this method, we performed forward modeling with different 3D MHD models of the solar atmosphere. We first synthesized emissions of the Fe X lines from each model, then calculated a magnetic field based on the line ratios. Finally, we compared the magnetic field derived from the Fe X line pairs to that in each model to evaluate the accuracy of magnetic field measurements based on the MIT theory. We also compared the results using different atomic databases and different Fe X line pairs. Moreover, we also performed forward modeling with a series of 3D stellar MHD models that correspond to different levels of stellar activity, and discussed the possibility of magnetic field measurements of the stellar coronae based on the MIT theory.

The external magnetic field introduced as an additional Hamiltonian will cause additional mixing of some adjacent energy levels. This will produce some new transition channels, namely magnetic field induced transition. By observing the intensities of these spectral lines whose intensity is proportional to the square of the external magnetic field, it is expected to realize more comprehensive real-time detection of the coronal magnetic field. However, in order to achieve this method, we need to calibrate the relationship between the magnetic field and the actual spectral line intensity, while there were many theoretical calculations already, but we found some inconsistencies between the calculation and the astrophysical observation. In this work, we use the electron beam ion trap device which can simulate the coronal plasma environment to observe the spectral line intensity under controllable plasma parameters. We find that there is an obvious systematic deviation between the observation results and the theoretical expectation and with a same trend. So more extensive experiments for this deviation is arranged accordingly, which possibly achieve a more reliable and experimental evaluated method to measure the coronal magnetic field.