Concentric Secondary Gravity Waves in the Thermosphere and Ionosphere over the Continental United States on 25-26 March 2015 from Deep Convection

Abstract:

We examine the total electron content (TEC) from GPS receivers over the United States on 25-26 March 2015. We observe partial to nearly fully concentric rings of travelling ionospheric disturbances (TIDs) with centers close to deep convection. Many of these TIDs have observed horizontal phase speeds c_H>300 m/s, suggesting they are induced by gravity waves (GWs) created in the thermosphere. We investigate the TIDs at 23:00 UT on 25 March and 01:20 UT on 26 March. We find that c_H and the GW period tau_r increase linearly with radius from the ring centers, and the horizontal wavelength, lambda_H, increases quadratically with radius. These are the expected results if the underlying GWs are excited by point sources. For these GWs, c_H= 150-530 m/s, tau_r ~ 10-40 min and lambda_H ~ 50-450 km. Using reverse ray-tracing, we find that no GW with c_H>230 m/s propagates below z=100 km, that the minimum altitude most GWs can propagate from is z~100 km, and that the inferred thermospheric point sources are ~2-4 degrees from deep convection. Because all TIDs for each case are excited by a point source, and because most are from GWs created in the thermosphere, we find that all these TIDs must be induced by GWs generated in the thermosphere, including those with c_H=150-230 m/s. Their close proximity to deep convection and the TEC map asymmetries suggest that these concentric TIDs are likely induced by secondary GWs generated by local horizontal body forces created by the dissipation of primary GWs from deep convection