Identification and Analysis of Long-Lived Storm Enhanced Density

Abstract:

The Earth’s upper atmosphere can be altered by geomagnetic storms via the solar wind-magnetosphere-ionosphere interaction. This research is to understand the response of the ionosphere, a layer in the upper atmosphere dominated by a population of electrons and ions called a plasma, during geomagnetic storm activity. The storms can modulate the plasma density in the ionosphere, i.e., cause an increase (positive storm) or a decrease (negative storm). Studying the global GPS-derived total electron content (TEC) data can reveal to us the impact of these geomagnetic storms on the ionosphere.

Geomagnetic data gathered from NASA’s CDAWeb allowed us to categorize the storms by their strength using the SYM-H index, a high-resolution proxy of the Disturbance Storm-Time (DST) index. GPS-data from the CEDAR Madrigal database of the World-wide GNSS Receiver Network at MIT’s Haystack Observatory was used to download TEC data for analysis. To more accurately understand the storm-time ionospheric response, residual TEC data obtained by subtracting quiet time TEC from storm-time TEC was studied.

By looking at the statistics of 664 storms between 2000 and 2018, there were 296 minor storms (SYM-H ≥ -60 ≤ -30), 231 moderate storms (SYM-H ≥ -100 ≤ -60 ), 109 major storms (SYM-H ≥-250 ≤ -100), and 13 superstorms (SYM-H ≤ -250). The strongest TEC enhancement was associated with the major storms and superstorms. We see a strong dependence on solar cycle and local time.

The biggest level of enhancement is related to geomagnetic conditions in the superstorm category. However, a majority of the enhancements are associated with minor to moderate storm conditions. Mechanisms for this occurrence are yet to be determined. This research aids existing work in classification of LLSED.