Fukuoka, Japan—In a paper published in Geophysical Research Letters , researchers from Kyushu University report on the activity of sporadic E layers—about 90-120 km above sea level—during the Mother's Day geomagnetic storm. The team found that the E layers were significantly enhanced during the recovery phase of the geomagnetic storm. Sporadic E layer, as the name suggests, is a phenomenon in which thin—about 1-5 km thick—but dense patches of ionized metals suddenly appear in the E layer of the ionosphere.
Moreover, the team found that these series of sporadic E layers occurred mainly over Southeast Asia, Australia, the South Pacific, and the East Pacific. They also observed a propagation characteristic of the phenomenon wherein the clouds were first detected around high latitude areas of the poles and then detected successively in lower latitude areas over time.
"When studying the Mother's Day geomagnetic storm, many researchers looked at what happened in the F layer of the ionosphere. It is about 150-500 km above sea level and is where the most ionization occurs," explains Professor Huixin Liu of Kyushu University's Faculty of Science , who led the study. "The sporadic E layer hasn't been studied very much during the storm because it appeared unaffected by solar storms. But we wanted to see if something as powerful as the Mother's Day geomagnetic storm did anything to the E layer. What we found was very interesting."
To track sporadic Es across the globe the team collected data both from the ground, using 37 ground-based radars called ionosodes, and from space, using the COSMiC-2 satellite network. This vast amount of data gave the researchers an unprecedented global map of sporadic Es activity during and after the solar storm.
"This large amount of data was critical for both detecting the presence of sporadic Es and tracking where they formed as time went by," continues Liu. "In our analysis, we found that sporadic Es formed after the main phase of the solar storm, during what we call the recovery phase. Sporadic Es were also detected first in the higher latitude regions, around the Earth's poles. They were then detected gradually in lower latitudes over time. This propagation characteristic from high to low latitudes suggests that sporadic E layers are most likely caused by the disturbed neutral winds in the E region."
Understanding the activity of the E layer is vital due to its potential to disrupt radio communications in the HF and VHF bands. The research team hopes that their new findings will lead to better insights on Es layer activity and how such unique phenomena are created in the ionosphere.
"We now know that sporadic Es enhance during the recovery phase of a solar storm, so perhaps we can forecast more accurately sporadic Es using the propagation characteristics found in our study and mitigate potential communication disruptions," concludes Liu. "We also plan to re-examine the data from other solar storms to see if we can better understand these phenomena."
