Delayed response of low latitudes TEC during thirty-six geomagnetic storms from 2014 to 2017

Abstract

Ionospheric response to the onset of geomagnetic storms is an important aspect for developing models towards better understanding and prediction of ionospheric parameters, particularly over the equatorial and low latitude sectors that are associated with several complexities. Our paper discusses the time response of the ionosphere (Δtiono), where Δtiono is the time elapsed from the onset of sudden storm commencement (SSC) of a magnetic storm to the absolute maximum value of DVTEC (TEC: total electron content). Over the period 2014 to 2017, thirty-six storms are reviewed, and their Δtiono are analyzed along with the magnetic and solar parameters. We defined a threshold value of TEC to be 8 TECU. Three storms are studied in detail as a reference for the entire range of storms (March 2015, June 2015, and September 2015). The stations used are Kourou (KOUR; 5.25°N/52.80°W) in the American longitude sector, Addis Ababa (AAE; 9.03N°/38.76°E) in the African longitude, Port Blair (PBRI; 11.63°N/92.71°E) and Patumwan (CUSV; 13.73°N/100.53°E) in the Asian longitude sector. In the Asian and American sectors, for all storms combined, there is no significant correlation (0.44 for the Asian sector and 0.22 for the American sector) between the delay (SSC time/time of maximum DVTEC) and the minimum of the Dst as found by previous studies. Instead, we considered geomagnetic storms satisfying the criteria: a) SSC occurs on the day side, and b) the origin of the magnetic storm on the solar disk must be far from the limb or does not belong to the far side, to obtain a much better correlation. The highest correlation value is observed at Thailand (0.84), followed by India (0.79) and South America (0.759), and the minimum value at Africa (0.641). The average response time in our study was found to be about 27.2 h. We observed positive and negative ionospheric storms, five negative storms in South America followed by two in Asia and a single negative storm in Africa from which it is realized that the most negative storms are in the time range of 9–15 LT. Nevertheless, there is hardly any relationship between the strength of DVTEC amplitude and the intensity of magnetic storms irrespective of longitude sectors.