Ionospheric response to the geomagnetic storm of 15 May 2005 over midlatitudes in the day and night sectors simultaneously

Abstract

The ionospheric response to the geomagnetic storm of 15 May 2005 has been studied over midlatitude stations in the dayside and nightside, simultaneously. In the day side the ionospheric response has been studied using the ground-based GPS and ionosonde measurements from the stations POL2 and Alma-Ata, respectively. The dayside total electron content (TEC) and f o F 2 variations are characterized by two well-separated enhancements. Of which the first enhancement in both the parameters is attributed to the episode of prompt penetration electric field caused by the sudden southward turning of interplanetary magnetic field (IMF) B z around 0600 UT. The second enhancement which was also superposed by wave like modulations has been attributed to the storm-induced winds. The maximum peak-to-peak amplitude of modulation in TEC is found to be 5 TECU (total electron content unit, 1 TECU = 10 16 el m À2). The enhanced plasma density observed during the daytime at midlatitudes is found to be locally produced and not transported from the equatorial ionization anomaly region because the time of enhanced plasma density at midlatitude is earlier than that observed at low latitudes. During the storm main phase, the nightside GPS observations from the midlatitude station ALGO (Algonquin Park, Canada) show moderate to large TEC fluctuations and short duration depletions that occur in a narrow latitude zone. These fluctuations and depletions in TEC have been attributed to the combined effect of storm-induced equatorward movement of the midlatitude ionospheric trough due to the expansion of auroral oval and the storm time-enhanced density. The maximum amplitude of the TEC depletions is found to be of the order of 20 TECU. Rate of TEC Index is also found to be high with a maximum value of 2.

Positive and negative ionospheric storms occurring during the 15 May 2005 geomagnetic superstorm

“…northern EIA crest occurred at lower latitudes and (2) the midlatitude trough was seen in the ALGO GPS data (e.g., the trough detected by PRN 11 at~0600 UT in the study of Galav et al [2014] correlates well with this study's map in Figure 2c). However, our global GPS TEC map (see Figure 2c) reveal also that the GPS POL2 and ALGO observations of Galav et al [2014] depict individual and local daytime and nighttime ionospheric features that are not representative of other regions in the daytime and nighttime sectors, respectively.…”

“…Our correlations reveal that the polar cap substorm related perturbation E field of the initial phase and the undershielding PPEF of the main phase triggered the development of sunward or westward progressing SED plume plasma in the Asian region, close to the POL2 GPS station employed by Galav et al [2014] in their study, causing locally some positive storms there (see Figures 4a and 4b). Meanwhile, the midlatitude trough appeared across the North American continent and also over the ALGO GPS station, utilized by Galav et al [2014], creating a strong negative storm in the narrow (~5 latitude degree) trough region.…”

“…However, our global GPS TEC map (see Figure 2c) reveal also that the GPS POL2 and ALGO observations of Galav et al [2014] depict individual and local daytime and nighttime ionospheric features that are not representative of other regions in the daytime and nighttime sectors, respectively.…”

“…Meanwhile, the midlatitude trough appeared across the North American continent and also over the ALGO GPS station, utilized by Galav et al [2014], creating a strong negative storm in the narrow (~5 latitude degree) trough region. Consequently, our correlation and observational results add to the study of Galav et al [2014] by providing further observations and verifying their interpretations. Our global GPS TEC map (see Figure 2c) serve as evidence and thus verify that (1) the GPS TEC increase seen in the POL2 GPS data was due to the SED plume plasma and the Figure 8.…”

“…More recently, Galav et al [2014] detected midlatitude daytime (nighttime) TEC increases (decreases) occurring simultaneously over the Northern Hemisphere during the main phase of the 15 May 2005 geomagnetic superstorm. While the TEC time series constructed for Poligan (POL2; 33.72°N, geomagnetic) tracked daytime increases that were due to both storm time PPEF and storm-induced equatorward neutral winds, the TEC time series constructed for Algonquin (ALGO; 55.93°N) detected depletions that were attributed to the midlatitude trough [Galav et al, 2014]. Some earlier studies covering this geomagnetic superstorm focused on the low-latitude regions of the Indian zone [Dashora et al, 2009] and Southeast Asia [Sharma et al, 2011].…”