Statistical Study Of The Effects Of Cross Polar Cap Potential And Its Temporal Variation Rate On Equatorial F Region Vertical Drift During Magnetic Disturbances

The electric field penetration has been one of the hot topics during recent years. It is important to study the electric field penetration effect during geomagnetic periods in order to understand the energy coupling process in the low latitude ionosphere from the solar wind to the magnetosphere. However, many researches on this subject have been carried out in the past40years, some problems still being unsolved and the most important one is under what circumstances the electric field penetration likely to occur.Solar wind which brings the inpterplanetary magnetic field interacts with the Earth's magnetosphere during geomagnetic storms. Large amounts of solar wind energy impinge into the inner magnetosphere through magnetic reconnection or other mechanisms. Large-scale interplanetary electric field can penetrate into the magnetosphere and the mid-and low-latitude ionosphere and it can obviously change the magnitude or even polarity of the ion drift and electric field.This dissertation investigates the effect of cross polar cap potential and its temporal variation rate on the vertical ion drift of equatorial F region and polar cap potential saturation phenomenon as well during geomagnetic disturbances. Firstly, we present ion drift data of DMSP/ROCSAT-1and cross polar cap potential output by AMIE (Assimilative Mapping of Ionospheric Electrodynamics) model. Special attention has been paid to to the effect of?cpc and its temporal variation rate (??cpc) on the disturbed ion velocity (?Vx) in118magnetic disturbed cases (Kp>4) during2001-2003. Statistical studies have been carried out to obtain the most probable time delay and penetration efficiency of electric field penetration from magnetopause to the low latitude ionospehere. Secondly, we use the solar wind data from OMNI and cross polar cap potential from AMIE to study the saturation effect during magnetic disturbances. Quantitative equation between the dawn-dusk component of interplanetary electric field (Ey) and cross polar cap potential has obtained.The main results obtained and studies performed in this dissertation can be concluded as follows:1. Using DMSP ion drift data at the dawn-dusk sector and day-night sector, the effect of?cpc and its temporal variation rate (??cpc) on the disturbed ion velocity (?Vx) have been studied. The results show that?Vx correlates better with??cpc than with?cpc at the four local times which the DMSP satellites cover, indicating that rapidly varied electric field is more likely to penetrate into low latitude. The penetration efficiency and linear equation between??cpc and?Vx are obtained.2. Using ROCSAT-1ion drift data of six years from1999-2004, quiet-time ion drift pattern at equatorial ionospehere have been analyzed systematically. The result shows an evidently seasonal, local time and longitudinal dependence of quiet-time (Kp<2) equatorial vertical ion drift. The main characteristics of vertical ion drift can be concluded as follows:Upward at daytime and downward at nighttime. The peak value of vertical ion drift varies evidently with longitude and local time, particularly during equinox. The daytime peak is more likely to occur before noon (0900-1100LT) and before sunrise (0400-0500LT) at nighttime. Large prereversal enhancements occur over a broad range of longitudes near dusk during equinox and close to dawn during June solstice. The prereversal times do not change much with longitude.3. Using ROCSAT-1ion drift data from2001-2003, statistical study has been made to investigate the effect of?cpc and??cpc on?Vx. It can be found that?Vx correlates better with??cpc than with?cpc at nearly all local times4. Using solar wind data from OMNI and cross polar cap potential output by AMIE model, we define a characteristic parameter AEmax which is the maximum magnitude of AE index in each case and the saturation events in different AEmax region have been studied. AEmax correlates well with saturation value of cross polar cap potential (?sat). The correlation coefficiency is0.81.5. The statistical study shows that while1000?AEmax?2000nT and-2?Ey?3mV/m,?cpc varies linearly with Ey, the slope is about6.5.?cpc appears to saturate and?sat is about90kV while Ey>3mV/m. The slope of the linear fit is1/7.?cpc varies slowly with Ey and the smallest magnitude of?sat is about54kV while Ey<-2mV/m. The slope of the linear fit is about0.5. The threshold of Ey is above4mV/m corresponding to the saturation of?cpc while2000<AEmax?3000nT. The threshold of Ey will exceed10mV/m in the superstorms while AEmax>3000nT,The innovation of this dissertation can be concluded as follows:1. Correlation analysis reveals that?Vx has a better relationship with??cpc than?cpc, indicating that rapidly varied solar wind is more effective to cause electric field penetration.2. Statistical studies show a threshold of Ey. The cross polar cap potential appears to saturate if Ey exceed this threshold;?sat is about90kV and the slope of linear fit is1/7; AEmax has an evidently positive relationship with?sat,3. Large prereversal enhancements occur over a broad range of longitudes near dawn during June solstice. The prereversal times do not change much with longitude.