Characteristics Of Ionospheric Plasma Drifts In The Low Latitude (Hainan) Region

The ionospheric electrodynamics plays a significant role in the morphological and variations of the ionosphere,and plasma drifts are essential parameters for the understanding of dynamics of the ionosphere.The ionospheric plasma drifts result from the interaction of the electric fields and the neutral wind field,which are mainly affected by the neutral wind in mid-latitude and are more controlled by the electric field in low-latitude.At low latitudes,the quiet-time ionospheric electric fields are generated by E-region tides and at night also by F-region polarization effects.Also,the electric fields can also be obviously affected by magnetospheric dynamo and ionospheric disturbance dynamo during magnetically disturbed periods.Therefore,the more in-depth study of plasma drifts will help to understand the coupling of mid-upper atmosphere-ionosphere-magnetosphere dynamics.The averages variations of low-latitude Hainan F region plasma drifts were determined using extensive DPS-4 drifts data from 2003 to 2016,including the daily and seasonal variation both during quiet and disturbed periods.The solar cycle variation and the dynamics of the plasma drifts are also analyzed during quiet-time.Based on multi-observations such as SWARM satellite and VHF radar,the ionospheric plasma blob and drifts were comparative carried through case study and statistical analysis,respectively.The main results are as follows:1.Average variation of quiet-time ionospheric plasma drifts over HainanThe late afternoon and nighttime plasma drifts are strongly dependent on season and solar activities.The daytime dominant westward drifts are bigger in winter and independent of solar flux;the nighttime eastward drifts increase with solar flux and are more significant in equinox,less in summer.The solar flux and seasonal effects on meridian drifts are much small during the daytime than at night.The nighttime southward drifts decrease with solar flux and the least is winter.The daytime weakly upward drifts do not change much with solar activities and seasons;the enhanced sunset upward and nighttime downward drifts increase with the enhancement of solar activities,which is most pronounced in equinox and summer respectively.During solar flux descending and minimum years,there have clear day-to-night variations for zonal drifts,but the vertical drifts are dominated upward;while during solar flux ascending and maximum years,the vertical drifts have distinct day-to-night changes,but the zonal drifts are mainly eastward.The meridian drifts are strongly southward through the day during solar ascending years,and the rest of the years have weak southward drifts at sunrise and sunset periods.The PRE velocities/near sunset pre-reversal enhancement of vertical drifts increase with the flux and decrease with magnetic activities during,but saturated for large flux values in winter.The E-region tidal and F-region polarization electric field can be an explanation for zonal drifts.The ambipolar diffusion and other kinetic factors such as parallel electric field explain the distribution of the field-aligned drifts better than the wind.By combining the vertical velocities and the north-south wind,the northward E×B drifts and the zonal electric fields were given.2.Average variation of disturbed ionospheric plasma drifts over HainanThe geomagnetic effects on Hainan plasma drifts are more pronounced during the nighttime for all the three seasons.The daytime dominant westward drifts do not change much with magnetic activities in all seasons;the nighttime eastward drifts decrease with the increase of magnetic activities and are more significant in equinox,less in summer.The daytime weakly magnetic activity corresponds to large southward drifts,while the nighttime is just the opposite.The daytime weakly upward drifts are independent of magnetic activities and seasons;the enhanced sunset upward decrease with magnetic activities only in equinox;the before midnight downward drifts are suppressed in equinox and reversed in winter for magnetic disturbance,but have no obvious response in summer;the downward drifts from midnight to sunrise are basically reduced with the increase of the magnetic activities in all seasons.3.Comparative study of Hainan ionospheric plasma drifts based onsatellite and ground-based instrumentsFor the August 8^th 2016 study,the simultaneous density enhancement blob observed by SWARM and the ground-based TEC and VHF radar demonstrated the attenuation,splitting,and northward drift process of the blob.The drifts,MSF and ionospheric parameters such as layer height recorded by DPS-4 indicate that there may be different drift states in upper and lower regions of the ionosphere.The comparative observation between SWARM and the DPS-4 Digisonde in low-latitude?Hainan?is quite different,and the nighttime zonal drifts show the best correlation.New findings of this dissertation:the long-term characteristics of ionospheric plasma drifts are analyzed by using the complete solar cycle data;the response of low-latitude ionospheric drifts to geomagnetic activities study could be a significant supplement to the global distribution and previous results.By combining the vertical velocities and the north-south wind,the northward E×B drifts and the zonal electric fields were given;The dynamics of low-latitude plasma blob was studied based on the comparative observations of satellite and ground-based results.