Conjugate and Non-conjugate Structures Observed in South and Central America Using Networks of GPS Receivers

Abstract:

This paper presents results based on TEC values measured by the low-latitude ionospheric sensor network (LISN) GPS receivers and others that belong to several other networks that exist in South and Central America. We have developed numerical algorithms to study the characteristics of MSTIDs as indicated by their phase velocities, their propagation directions, and their scale-sizes. We have also constructed a method to automatically detect plasma depletions that exist in South and Central America. These two methods allow us to study the day-to-day variability and the conjugate characteristics of MSTIDs and depletions at low and mid-latitudes. We found that mid-latitude (magnetic latitude > 25°) TEC depletions occur mainly during magnetically active conditions, exhibit conjugate characteristics, persist for very long periods, and last up to afternoon hours when the K_p index is high (K_p > 5o). However, we have also detected some cases of mid-latitude TEC depletions that occur during quiet magnetic conditions. These events preferentially develop during the June solstice and do not map to the opposite hemisphere. MSTIDs occur in Central America and the Caribbean region quite often. They are defined to be conjugate when the peaks and valleys of their TEC distributions closely coincide in opposite hemispheres, their scale sizes are equal and their phase velocities are mirror images with respect to the magnetic equator. We also describe the statistics of MSTIDs that show conjugate properties.