GPS-based Imaging of Traveling Ionospheric Disturbances

Traveling Ionospheric Disturbances (TIDs) are perturbations in ionospheric electron density caused by Atmospheric gravity waves (AGWs) via ion-neutral collisions as they travel through the thermosphere/ionosphere from their source region.  At ionospheric heights, the motion of the neutral gas in the AGW sets the ionosphere into motion through collisional coupling.  As a result, the signature of the AGW is manifested as variations of electron density in the ionosphere and identified as TIDs. Therefore, simultaneous observations of TIDs and AGWs can provide a unique perspective on neutral ionosphere-atmosphere coupling. There are many mechanisms that generate AGWs. Several studies have suggested that convective storms, and tropospheric deep convection cells [Fovell et al., 1992; Alexander et al., 1995; Lane et al. 2001]  are one of the primary drivers for AGWs that propagate upward into the mesopause region [Alexander, 1996; Holton and Alexander, 1999; Walterscheid et al., 2001].  In this paper, we use Total Electron Content (TEC) measurements from over 4000 GPS receivers distributed throughout the continental United States to observe TIDs associated with several events including a tornado outbreak on May 25, 2015 in Kansas, Hurricane Irene, the 2011 Tohoku tsunami, and geomagnetic storms. The network of GPS receivers used in the study in effect provides a 2D spatial map of TEC perturbations, which can be used to calculate TID parameters, including horizontal wavelength, speed, and period. The work presented in this paper demonstrates a new technique for studying atmosphere-ionosphere coupling and for monitoring ionospheric space weather.