Nighttime Medium-Scale Traveling Ionospheric Disturbance (MSTID) in GPS TEC measurements

We report observations of nighttime Medium-Scale Traveling Ionospheric Disturbances (MSTIDs) in Total Electron Content (TEC) measurements from ASTRA's CASES GPS receivers in Boulder, CO. CASES stands for Connected Autonomous Space Environment Sensor and is being produced by ASTRA as a low-cost, stand-alone, and autonomous dual frequency GPS space-weather monitoring station capable of providing fully processed outputs such as scintillation severity indicators S₄, τ_o, σ_φ, the Scintillation Power Ration (SPR), and TEC with a relative accuracy of a few 0.01 TECU. MSTIDs are perturbations in ionospheric electron density caused by gravity waves travelling through the thermosphere from their source region, which is generally in the lower atmosphere. General characteristic of MSTIDs include horizontal velocities of 100-300 m/s, horizontal wavelengths of several hundred km, and perturbation periods of 10-30 minutes. In this paper, we present observations of MSTIDs in TEC measurements from multiple CASES sites in Colorado on July 27, 2012. These observations of MSTIDs are corroborated by TEC measurements from multiple Continuously Operating Reference Station (CORS) GPS sites in Colorado. The observed MSTID signature in TEC consists of a perturbation of ionospheric TEC of ~1 TECU corresponding to ~54 ns (16.2 cm) delay at the GPS L1 signal with a wave period of 20-40 minutes. This paper will describe the propagation characteristics of the observed MSTID and its spatial morphology as observed in TEC measurements from Colorado, and from distributed GPS receivers across the US.