Item

Abstract

An auto-detection technique is developed to find equatorial plasma depletions (EPDs) and their amplitudes base on the in situ electron density profiles measured by Swarm satellites, which can also be applied to the measurements of other spacecraft. For the first time, three different parameters derived from Swarm satellites, the GPS receiver signal loss events, the Ionospheric Bubble Index (IBI) of L2 product, and the occurrence and amplitudes of EPDs are taken in comparison. The EPDs are found with largest occurrence rate between 2200-0000 magnetic local time (MLT) and show a similar pattern with IBI but with a larger magnitude, while largest depletion amplitudes of EPDs appear earlier between 1900-2100 MLT correspond to higher background electron density and stronger effects on the Swarm GPS receivers. Similar features are also identified from a longitudinal perspective. The occurrence rate of post-midnight EPDs is generally reduced compare to pre-midnight; however, during June solstice months even more post-midnight EPDs are observed at African longitudes. CHAMP observations confirm this point regardless to high or low solar activity conditions. Besides, evidence also shows that solar minimum is preferred for the occurrence of post-midnight EPDs over Pacific region, especially for southeast Pacific during Dec. S. months. Further by comparing with the plasma vertical drift velocity from ROCSAT-1, we suggest that the F-region vertical plasma drift plays a key role in dominating the occurrence of EPDs during pre-midnight hours, while the post-midnight EPDs are the combined results from the continuing of former EPDs and newborn EPDs, especially during June solstice. And these newborn EPDs during post-midnight hours seem less related to the plasma vertical drift.