Observation of scintillation enhancements and large-scale structures
within the equatorial ionization anomaly during a Sudden Stratospheric
Warming event
Abstract
Total Electron Content (TEC) and L-band scintillations measured by
several networks of GPS and GNSS receivers that operate in South and
Central America and the Caribbean region are used to observe the
morphology of the equatorial ionization anomaly (EIA), examine the
evolution of plasma bubbles, and investigate the enhancement of L-band
scintillations that occurred on February 12 and 13, 2016. A few weak and
short magnetic storms developed these days, and a minor Sudden
Stratosphere Warming (SSW) event was initiated a few days before. During
these unusual conditions, TEC maps reported a split of the otherwise
continuous crests of the EIA and the formation of a large-scale
(thousands of kilometers) almost-circular structure. The western part of
the southern crest faded, and a north-south aligned segment developed
near the center of the South American continent, joining the north and
south crests of the EIA, forming an anomaly that resembled a closed loop
on the eastern side of the continent. Concurrently with the anomaly
events, several GPS stations reported increases in the L-band
scintillation index from 0.4 to values greater than one. We analyzed TEC
values from receivers between ±6° from the magnetic equator to identify
and follow TEC depletions associated with plasma bubbles when they reach
different stations. Although the magnetic activity was moderate
(kp=30), we believe that the anomaly
redistribution and the scintillation enhancements are not related to a
prompt penetration electric field but to enhancing the semidiurnal lunar
tide propitiated by the onset of the minor SSW event.