The Properties and Origins of Corotating Plasmaspheric Irregularities: Part II—Tomography With Compact Arrays of GPS Receivers

Abstract

AbstractThis paper describes insights into the nature of corotating plasmaspheric irregularities (CPIs) enabled by a newly developed method for range‐ and time‐resolved tomographic images of these structures. This was originally developed using high‐precision measurements of total electron content (TEC) gradients toward cosmic radio sources using an interferometric radio telescope, the Very Large Array (VLA). Here, the method has been adapted to work with TEC measurements from compact arrays of Global Positioning System (GPS) receivers in California and Hawaii. Because the VLA is much more sensitive to line‐of‐sight density fluctuations and the background density within the plasmasphere drops quickly with radial distance, the GPS‐based analysis has a much more limited range (maximum of ∼5,000 km with GPS versus ∼15,000 with the VLA). However, because the GPS arrays collect data continuously, they offer much more complete temporal coverage and range resolution. This enabled a thorough comparison between CPI behavior near solar maximum and that near solar minimum, which was not possible with the VLA. The solar minimum data largely agree with previously reported VLA‐based data, which were mostly confined to times near solar minimum. These indicated that the primary drivers of CPIs during these conditions are perturbations within the background electric field associated with so‐called electro‐buoyancy waves within the midlatitude ionosphere. However, the detection rates of and properties of CPIs were often markedly different near solar maximum. This points to different CPI drivers related to solar/geomagnetic activity such as substorms and/or the interchange instability at lower L‐shells (∼3–4).