The South Atlantic Anomaly and its influence on the total electron content distribution

One of the more significant space weather effects that occurs during geomagnetic storms is a disturbance that moves plasma from the equatorial region of Earth's ionosphere into the mid-latitudes. This effect is manifested when the peaks in the total electron content (TEC), associated with the Appleton anomaly, are observed to move further north and south in latitude. During large geomagnetic storms, greatly enhanced TEC values have been observed as far north as Florida. Recently there has been evidence that the longitude sector associated with the South Atlantic Anomaly (SAA) shows more significant effects in the TEC distribution than other longitude sectors during geomagnetic storms. Using global GPS total electron content (TEC) data, we have examined the TEC distribution at different longitude sectors for a variety of background conditions, to investigate the possible influence of the SAA. Here we present the preliminary results of this study. We obtained GPS TEC values from both hemispheres and from quiet and storm time conditions using MIT Haystack Observatory's MADRIGAL data base. Over the course of the study we processed 74 days worth of GPS TEC data. These days occurred across all seasons in primarily three separate years: 2001, 2002, and 2005. These years were selected based on the solar cycle: 2001 and 2002 represent solar maximum conditions, and 2005 represents solar minimum. Data from a series of five longitude sectors were collected. Each longitude sector contained TEC data averaged over 15 degrees of longitude and 5 degrees of latitude. Of the five longitude sectors, three covered the SAA region (the Brazilian sector of South America) and two regions were unaffected by the SAA (central Africa and central Australia). Our data shows that the absolute value of the maximum observed TEC at local noon in the longitude sectors associated with the SAA is greater than that observed in the sectors not associated with the SAA. One caveat to our finding is that there are limitations in the current availability of GPS TEC measurements in many of these longitude sectors. Because of this, in future work, we hope to incorporate TEC observations from other data sources such as the new COSMIC data set.