ST3.5

In this work, the effect of disturbance dynamo electric field (DDEF) induced by subauroral polarization streams (SAPS) on the variations of the equatorial electrojet (EEJ) and its counter electrojet (CEJ) during the geomagnetic storm on June 1, 2013 is analyzed in detail for the first time. Observations from ground-based magnetometers showed that the SAPS-induced EEJ flows westward and eastward in the daytime and dawn/dusk sectors, respectively. The effects of SAPS on EEJ are mainly associated with the changes of zonal ionospheric electric field, while the changes in the ionospheric conductivity play a secondary role. By using Thermosphere Ionosphere Electrodynamic General Circulation Model simulations, the zonal electric field induced by SAPS associated with the DDEF is examined. The results of the simulations show that the DDEF has a significant impact on the EEJ variability. The daytime westward EEJ at the dip equator is mainly driven by disturbance zonal wind, with secondary contributions from disturbance meridional wind. A similar mechanism can be observed in the dawn/dusk sector when the eastward EEJ is produced; however, it has a much weaker intensity than that during the daytime.

How to cite: Zhang, K., Yamazaki, Y., and Xiong, C.: Effects of Subauroral Polarization Streams on the Equatorial Electrojet During the Geomagnetic Storm on June 1, 2013, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-21, https://doi.org/10.5194/egusphere-egu22-21, 2022.

Using ground-based magnetic field measurements and numerical simulations from the Thermosphere-Ionosphere Electrodynamic General Circulation Model (TIEGCM), a first paper (Zhang et al., 2021b, under review) introduced the potential roles of disturbance dynamo electric field due to subauroral polarization streams (SAPS) on the equatorial electrojet (EEJ) during a moderate geomagnetic storm on June 1, 2013. Our second study investigated the temporal responses of equatorial electrojet to SAPS. At noon, the residual EEJ (ΔEEJ) owing to SAPS flows westward, that is, counter equatorial electrojet (CEJ). The temporal variation of CEJ excited by the dynamo electric field was basically consistent with that by SAPS, and the effects of zonal wind were larger than those of meridional wind. The relative time delay of CEJ and SAPS was related to the propagation time of disturbance wind from mid-latitudes to low-latitudes. It took 2-3 h for SAPS-related disturbance wind to propagate to the equatorial region and change the polarity of EEJ. The influence of meridional winds on the temporal variations of ΔEEJ is related to the generation of eastward currents at mid-latitudes, which can accumulate the positive charges at dusk terminator and then generate a westward electric field at lower latitudes.

How to cite: Qian, C. and Zhang, K.: Effects of Subauroral Polarization Streams on the Equatorial Electrojet During the Geomagnetic Storm on June 1, 2013. Part II: the temporal variations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-984, https://doi.org/10.5194/egusphere-egu22-984, 2022.

Based on Thermosphere-Ionosphere Electrodynamics General Circulation Model simulation and CHAllenging Minisatellite Payload observations, the effects of the geomagnetic field intensity and solar activity on the thermospheric zonal wind and the related physical mechanisms are investigated. The weakening of the magnetic field results in an increase in the westward wind during the daytime and a decrease in the eastward wind at night, and leading to a decreasing superrotation. The weakening solar activity causes a reduction in the zonal wind and superrotation. The theoretical term analysis shows that when the magnetic field is weakened, the vertical upward drift velocity of the plasma increases, resulting in a decrease in the electron density and ion drag in the F layer. The weakening of eastward acceleration of the viscous force and ion drag results in an enhanced westward wind. The downward drift velocity of ions increases at night, resulting in an increase in the electron density at the F layer, while the ion-neutral velocity difference decreases. The weakening of eastward acceleration of the pressure gradient and viscous force at night are the main reasons for the decreased eastward wind. The reduced solar activity leads to a decrease in the pressure gradient and ion drag. Combined with the change of viscous force, these processes cause the decrease in the superrotation. The geomagnetic field configuration is the main reason for the variation in the superrotation with UT. When the magnetic field is weakened, although the average neutral wind decreases, the Pedersen conductivity of the F-layer is quadrupled. Therefore, the meridional current system driven by the F-layer dynamo is enhanced accordingly. Due to obvious longitudinal difference in the magnetic field intensity, the longitudinal variation of superrotation is expected.

How to cite: Gao, J. and Zhang, K.: Influence of the Magnetic Field Strength and Solar Activity on the Thermospheric Zonal Wind, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-985, https://doi.org/10.5194/egusphere-egu22-985, 2022.

The auroral electrojet plays an important role in the ionosphere-magnetosphere coupling progress. Based on ten years of DMSP and CHAMP coordinated observations, we investigate the local time variations of the auroral electrojets during storm periods. The results show that the auroral electrojets respond obviously to the sudden change of solar wind inputs (merging electric field, substorm, and interplanetary shock) in all local time. The local time asymmetry of the response time and strength of the electrojets to these three types of disturbances are investigated. The auroral electrojets respond to the shock faster than the sudden change of merging electric field. The disturbed auroral electrojet strength peaks at different local times during different kinds of solar wind input events. The different features of eastward and westward electrojets during storm periods are studied during the disturbance periods. The physical mechanisms for the local time variations of auroral electrojets in response to the disturbance are discussed in detail. 

How to cite: Zhong, Y., Xia, H., and Qian, C.: Local time variations of auroral electrojet during storm time: DMSP and CHAMP coordinated observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-998, https://doi.org/10.5194/egusphere-egu22-998, 2022.

        The high-resolution Vector Field Magnetometer and Langmuir Probe onboard the Swarm satellites provide us an opportunity to observe both EMIC wave and plasma density oscillation. A total of 102 plasma density oscillation events were found during storm time from 2014 to 2018. The temporal and spatial distribution of these oscillation events is roughly consistent with the EMIC wave. The longitudinal distribution and related mechanism are studied. There are obvious magnetic local time (MLT) differences in the peak occurrence rate of plasma density oscillation during storm phases and distinct geomagnetic activity. As the geomagnetic disturbance intensifies，the plasma density oscillations show a trend of westward drift and are more likely to occur at lower latitudes. For all plasma density oscillation events, the phase of these oscillation with EMIC wave is different. Most plasma density oscillation have a relative amplitude ratio of 100 to 1000 to the compressional wave, the possible mechanism is discussed in detail.

How to cite: He, Y. and Sun, L.: A Stastistical study of plasmas density oscillation induced from pc1 wave by Swarm Satellites during storm time from 2014 to 2018, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1000, https://doi.org/10.5194/egusphere-egu22-1000, 2022.

 Based on the magnetic field observation of Swarm satellite from 2015 to 2019, the variation of ionospheric radial current (IRC) with local time and geographic longitude at March equinox, June solstice and December solstice are analyzed, respectively. The observations are compared with the simulation results of thermosphere ionosphere electrodynamics general circulation model (TIE-GCM). The observed IRC are mainly downward in the noon section and upward in the evening section, which is reproduced well by the model. The zonal distribution of IRC shows obvious local time asymmetry. The downward IRC in the eastern hemisphere in the noon section is greater than that in the western hemisphere, while the upward IRC in the western hemisphere in the evening section is greater than that in the eastern hemisphere. This zonal variation in the evening sector is more obvious at March equinox and less obvious at June solstice. The simulation results of TIE-GCM also show similar zonal characteristics, especially on the nightside. The physical mechanisms of the local time and geographic longitude distribution of IRC are discussed in details.

How to cite: Xia, H. and Qian, C.: Zonal variation of ionospheric radial current (IRC) as observed by Swarm and simulated by TIE-GCM, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1412, https://doi.org/10.5194/egusphere-egu22-1412, 2022.

Total electron content (TEC) observations can provide insights into electron density variations in the ionosphere. Such variations are associated with many aspects of ionospheric dynamics, including traveling ionospheric disturbances. In the present work we assimilate observations of TEC and horizontal TEC gradients into the SAMI3 (SAMI3 is Another Model of the Ionosphere 3D) ionosphere model. Assimilation into SAMI3 is accomplished using an ensemble Kalman filter implemented within LightDA, an extensible data assimilation library. Our TEC gradient observations are obtained from the Very Large Array Low-band Ionosphere and Transient Experiment (VLITE) and the TEC measurements are derived from GNSS receiver data. VLITE provides high precision and high spatial resolution TEC gradient observations over a small area, while GNSS observations supplement these with global coverage. By leveraging TEC observations in a physics-based model through data assimilation, we aim to improve our understanding of ionospheric processes and develop tools for improved ionospheric forecasting capabilities.

How to cite: Haiducek, J., Helmboldt, J., and Huba, J.: Assimilation of total electron content in a SAMI3 simulation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1511, https://doi.org/10.5194/egusphere-egu22-1511, 2022.

Thermospheric density is essential for the calculation of atmospheric drag, which is the main cause of the orbit decay for low-Earth-orbit (LEO) satellites. During geomagnetic storms, the Joule heating has a strong impact on neutral mass density. In this work, we statistically investigate 265 geomagnetic storms to explore the response of thermospheric density to Joule heating from 2002 to 2008. We obtain the density enhancements from Challenging Minisatellite Payload (CHAMP) and the Gravity Recovery and Climate Experiment (GRACE) satellites, and we also calculate Joule heating from the Defense Meteorological Satellite Program (DMSP) spacecraft and the Weimer electric potential model. The results show that the thermospheric density delays Joule heating during geomagnetic storms. The time lag is about 0-2 hrs during weak and moderate storms, while it is 3-5 hrs for intense storms. In addition, Joule heating can affect the density enhancement at higher latitude regions. The latitudinal difference between thermospheric density and Joule heating is about 0°-10° during weak and moderate geomagnetic storms, while it increases to 10°-15° for intense storms. Besides, we use the temporal relationship of thermospheric density with geomagnetic activity indices and Joule heating as calibration for the NRLMSISE-00 model during geomagnetic storms. The calibrated NRLMSISE-00 model results can better simulate the storm-time thermospheric density, with the Mean Relative Error (MRE) between observation and model decreasing from 40% to 10%.

How to cite: Wang, X., Liu, S., Miao, J., Lu, X., Aa, E., and Luo, B.: Thermospheric density variation and its response to Joule heating during geomagnetic storms, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3034, https://doi.org/10.5194/egusphere-egu22-3034, 2022.

The interaction between the Sun and the Earth defines the space environment of the Earth. This interaction is complex and exhibits various time scales ranging from a  few seconds to years. The High-Intensity Long-Duration Continuous AE Activity (HILDCAA) events are mainly the manifestations of the interactions of the corotating interaction regions (CIRs) with the terrestrial magnetosphere which continues for several days. The responses of two HILDCAA events are investigated by using solar wind observations at the L1 point, magnetospheric measurements at geosynchronous orbit, and changes in the global ionosphere. This study provides evidence of the existence of quasi-periodic oscillations (1.5-2hr) in the ionospheric electric field over low latitude, total electron content at high latitude, the magnetic field over the globe, energetic electron flux and magnetic field at geosynchronous orbit, geomagnetic indices (SYM-H, AE, and PC) and the Y-component of the interplanetary electric field (IEFy) during the HILDCAA events at all local times. Based on detailed wavelet and cross-spectrum analyses, it is shown that the periodic oscillations of 1.5-2hr in IEFy are the most effective one that controls the solar wind-magnetosphere-ionosphere coupling process during the  HILDCAA events for several days. Therefore, this investigation for the first time, shows that the  HILDCAA event affects the global magnetosphere-ionosphere system with a “resonant” mode of oscillation. These results are important not only to evaluate the solar wind-magnetosphere-ionosphere coupling process during the HILDCAA events but can also help to build up a forecasting strategy in the future.

How to cite: Rout, D., Singh, R., Pandey, K., Pant, T., Stolle, C., Chakrabarty, D., Thampi, S., and Bag, T.: Evidence for Presence of a Global Resonant Mode of Oscillations During High-Intensity Long-Duration Continuous AE Activity (HILDCAA) events, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5961, https://doi.org/10.5194/egusphere-egu22-5961, 2022.

Magnetic storms are caused by the interactions between the solar wind and the Earth’s magnetosphere. Many studies have been carried out for strong magnetic storms. However, moderate or weak storms and their impacts on the ionosphere are less explored. This study investigates the large-scale and mesoscale structures in ionospheric total electron content (TEC) during a moderate storm (Sym-H index minimum: -63 nT) driven by two interacting solar wind high-speed streams (HSSs) and associated co-rotating interaction regions (CIRs) during 14-21 March 2016. For the solar wind, the IMF Bz minimum is -20 nT and the solar wind speed maximum 612 km/s. The long storm starts with a strong storm sudden commencement (SSC) with a peak close to 19 UT on 14 March 2016. The GNSS/TEC maps are obtained from the Madrigal database. The associated field-aligned currents (FACs) from AMPERE, ionospheric convection maps from SuperDARN, and the O/N₂ ratio from TIMED/GUVI are also studied for understanding the physics behind.

The focus of the study is on the changes of TEC at high and middle latitudes and the possible coupling between the two. To better characterize the changes, we subtract from the TEC maps the quiet time background (13 March 2016). Our analysis shows the different responses of TEC changes during the storm initial, main, and recovery phases. During the initial phase, TEC enhancements and depletions are found mainly at high latitudes within the auroral oval and close to the cusp, plausibly associated with auroral precipitation and variations in the upward and downward field-aligned currents (FACs). After the onset of the main phase, the TEC is enhanced at mid-latitudes with a maximum of ~10 TECU. During the main phase, we observe the evolution of a storm-enhanced-density (SED) plume and a transient enhancement of TEC in the polar cap. During the late main and the recovery phases, a strong TEC depletion at high and middle latitudes is found on the dayside and in the evening sector. The depletion is associated with the decrease of the O/N₂ ratio indicating upwelling of the neutral atmosphere. The possible physical mechanisms associated with the observed TEC variations will be discussed.

How to cite: Geethakumari, G. P. P., Aikio, A., Cai, L., Vanhamaki, H., Pedersen, M., Coster, A., Marchaudon, A., Blelly, P.-L., Haberle, V., Maute, A., Ellahouny, N., Virtanen, I., Norberg, J., Soyama, S.-I., and Grandin, M.: Total Electron Content Variations during an HSS/CIR driven storm at high and middle latitudes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8194, https://doi.org/10.5194/egusphere-egu22-8194, 2022.

Modelling the whole atmosphere from the surface to the ionosphere allows us to better forecast and understand our weather and climate. It is a scientific and computational challenge to model this complex system numerically with its many drivers and feedback loops. Recent efforts to improve whole atmosphere models include raising the altitude to incorporate improved representations of the ionosphere and thermosphere. The Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM-X) is one of the most comprehensive numerical models, spanning the range of altitude from the Earth’s surface to the upper thermosphere (~700 km). WACCM-X can model the global ionosphere and thermosphere, whilst providing coupling between atmosphere layers through chemical, physical and dynamical processes. Using WACCM-X, we can explore the implications of this coupling for the climate and for the near space environment. 

The high-latitude ionosphere-thermosphere behaves dynamically during geomagnetically active times due to time-varying solar wind driving and internal magnetospheric dynamics. We present high- and mid-latitude observations from the Super Dual Auroral Radar Network, Incoherent Scatter Radars and Fabry-Perot Interferometers which observe the ionosphere-thermosphere system. We investigate observed plasma flows, which respond directly to solar wind driving, alongside WACCM-X model simulations which are nudged to a meteorological reanalysis dataset in the troposphere and stratosphere during a variety of solar storm conditions. We discuss these in the context of time-varying dynamics due to solar wind driving and investigate the expansion of the high-latitude convection to lower latitudes during geomagnetic storms. Our results show that the latitudinal expansion is not yet fully captured in WACCM-X and we discuss how this may be mitigated. We further show that during a geomagnetic storm, the differences between the WACCM-X ionospheric data and the observations by SuperDARN at high- to mid-latitudes may vary by up to ~20 kV for the electrostatic potential during a geomagnetic storm. This translates to an electric field difference of 25 mV/m and differences in the plasma drift velocities in excess of ~800 m/s.

How to cite: Walach, M.-T., Grocott, A., Orr, L., Feng, W., Marsh, D., and Aruliah, A.: Ionosphere and Thermosphere Observations in the Context of Whole Atmosphere Modelling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8322, https://doi.org/10.5194/egusphere-egu22-8322, 2022.