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Major Achievements in 2020


1. Papers and Conference Presentations in 2020

     Papers of the FST Team Members: 17

        (8 papers have been published, and additional 9 papers have been submitted for publication) .

     Conference Presentations of the FST Team Members: 25

     Special Sessions Convened by the FST Team Members in National and International Conferences: 22


2. Major Accomplishments in 2020

Equatorial Westward Ion Drifts during Severe Magnetic Storms
         Equatorial zonal ion drifts measured by the Defense Meteorological Satellite Program satellites during ten severe magnetic storms with a minimum Dst < -200 nT in the solar maximum years of 2000-2003 are analyzed. Strong westward plasma drifts (200-400 m/s) are observed in the dusk-evening sector. The westward drifts occur immediately after the storm onset and are well correlated with the Dst index. The features and variations of the equatorial westward ion drifts cannot be explained with storm-time disturbance winds, and a new mechanism is proposed. This new mechanism is that the poleward electric fields associated with the subauroral polarization stream penetrate or extend to low latitudes, producing the westward plasma drifts in the equatorial region.
         Huang, C.-S. (2020). Westward plasma drifts in the nighttime equatorial ionosphere during severe magnetic storms: A new type of penetration electric fields caused by subauroral polarization stream. Journal of Geophysical Research: Space Physics, 125, 2020JA028300. https://doi.org/10.1029/2020JA028300.

Rapid Establishment of Ionospheric Disturbance Current System
         A rapid re-construction of global ionospheric disturbance currents in response to a sudden enhancement in the solar wind dynamic pressure, measured by ~180 ground magnetometers, is identified. The time scale of 1 minute for global ionospheric current system to fully establish or reconstruct is identified for the first time. This new current system remains stable for 20-30 minutes. The equivalent current system is characterized by a large, single counterclockwise vortex at middle and low latitudes (below ~60o MLat) and a much smaller clockwise vortex at high latitudes. A scenario is proposed to explain the global distribution and fast reconstruction of the ionospheric current systems.
         Huang, C.-S. (2020). Systematical analyses of global ionospheric disturbance current systems caused by multiple processes: Penetration electric fields, solar wind pressure impulses, magnetospheric substorms, and ULF waves. Journal of Geophysical Research: Space Physics, 125, 2020JA027942. https://doi.org/10.1029/2020JA027942.

Global Ionospheric Currents Systems Caused by Multiple Processes
         Global ionospheric disturbance current systems caused by multiple solar wind and magnetospheric processes, including penetration and shielding electric fields, sudden enhancement and decrease in the solar wind dynamic pressure, magnetospheric sawtooth substorms, and ultra-low frequency (ULF) waves, are systematically identified for the first time. A surprising result is that the equivalent disturbance current systems are very similar, although the driving processes are completely different. The similar disturbance current systems caused by different solar wind and magnetospheric processes suggest that the global distribution of the ionospheric currents is determined by the intrinsic property of the ionosphere.
         Huang, C.-S. (2020). Systematical analyses of global ionospheric disturbance current systems caused by multiple processes: Penetration electric fields, solar wind pressure impulses, magnetospheric substorms, and ULF waves. Journal of Geophysical Research: Space Physics, 125, 2020JA027942. https://doi.org/10.1029/2020JA027942.

Multimodel Ensemble Prediction System for Specifying and Predicting Space Weather
         Multimodel Ensemble Prediction System (MEPS) of data assimilation models are used to elucidate the similarities and differences in the individual data assimilation model reconstructions of the mid-low latitude ionosphere. Ensemble model averages are also obtained. Five data assimilation models and one physics-based model were used to produce an ensemble mean output for multiple ionospheric parameters. The data assimilated included ground-based Global Positioning Satellite TEC and topside plasma densities near 800 km altitude derived from the COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate) satellites. The MEPS system we have constructed will be delivered to the NASA Community Coordinated Modeling Center.
         Schunk, R. W., Scherliess, L., Eccles, V., Gardner, L. C., Sojka, J. J., Zhu, L., et al. (2021). Challenges in specifying and predicting space weather. Space Weather, 19, 2019SW002404. https://doi.org/10.1029/2019SW002404.

Polar Topside TEC Enhancement Revealed by Jason-2 Measurements
         Significant polar topside total electron content (topTEC) enhancement (PTTE) above 1,336 km altitude, observed by the Jason-2 satellite, is reported for the first time. PTTE mostly occurs on the dayside, with a seasonal preference of southern summer, and preferentially during geomagnetically disturbed days but can also occur during quiet days. Our case analysis indicates that PTTE is observed simultaneously with the effect of tongue of ionization. This suggests that the during storms, dayside F region plasma moving poleward following the antisunward plasma convection may also be part of the PTTE source, and the plasma upflow driven by the polar wind may act to cause PTTE.
         Pi, X., Mannucci, A. J., & Verkhoglyadova, O. (2021). Polar topside TEC enhancement revealed by Jason-2 measurements. Earth and Space Science, 8, 2020EA001429. https://doi.org/10.1029/2020EA001429.

New Empirical Model for High-Latitude Electron Precipitation and Electric Field
         A new high-latitude empirical model, named for Auroral energy Spectrum and High-Latitude Electric field variabilitY (ASHLEY), is developed to improve specifications of soft electron precipitations and electric field variability that are not well represented in existing high-latitude empirical models. This new model is developed based on the electron precipitation and bulk ion drift measurements from the Defense Meteorological Satellite Program (DMSP) satellites during the most recent solar cycle. ASHLEY provides consistent mean electric field and electric field variability under different geophysical conditions. This is different from most existing electric field models which only focus on the large-scale mean electric field and ignore the electric field variability.
         Zhu, Q., Deng, Y., Maute, A., Kilcommons, L., Knipp, D., & Hairston, M. (2021). ASHLEY: A new empirical model for the high-latitude electron precipitation and electric field. Space Weather, 19, 2020SW002671. https://doi.org/10.1029/2020SW002671.

New Observations of Postsunset OI 135.6 nm Radiance by the GOLD Mission
         The Global-scale Observation of Limb and Disk (GOLD) mission, for the first time, provides synoptic two-dimensional maps of OI 135.6 nm observations. These maps describe the unambiguous and dynamic evolution of nighttime ionospheric F2-peak electron densities (NmF2) as the 135.6 nm airglow emission radiance correlates well with NmF2 at night. The equatorial ionization anomaly hemispheric asymmetry, which included both different densities and movement of two crests in a short time period (&<2h), is captured. Equatorial plasma bubbles (EPBs) and third peaks of electron density poleward of the southern EIA crests are evident in GOLD nighttime OI 135.6 radiance.
         Cai, X., Burns, A. G., Wang, W., Qian, L., Liu, J., Solomon, S. C., et al. (2021). Observation of postsunset OI 135.6 nm radiance enhancement over South America by the GOLD mission. Journal of Geophysical Research: Space Physics, 126, 2020JA028108. https://doi.org/10.1029/2020JA028108.

Statistical Results of Equatorial Plasma Irregularities Retrieved From Swarm 20132019 Observations
         In situ plasma density measurements of the Swarm constellation from 2013 to 2019 are used for a statistical analysis of equatorial plasma irregularities (EPIs). The occurrence patterns for both postsunset and postmidnight EPIs with respect to longitude, season, local time, latitude, solar activity, and geomagnetic activity level are investigated. It is found that the postsunset and postmidnight EPIs occurrence rates exhibit different longitudinal and seasonal dependence and solar activity dependence. The EPIs occurrence rate increases with increasing geomagnetic activity level. The main controlling factors for the distribution of postsunset EPIs are the magnetic declination angle, equatorial vertical E B drift, and thermospheric zonal wind.
         Aa, E., Zou, S., & Liu, S. (2020). Statistical analysis of equatorial plasma irregularities retrieved from Swarm 20132019 observations. Journal of Geophysical Research: Space Physics, 125, 2019JA027022. https://doi.org/10.1029/2019JA027022.