Sources of the traveling ionospheric disturbances observed by the ionospheric TIDDBIT sounder near Wallops Island on 30 October 2007

We model the gravity waves (GWs) excited by Tropical Storm (TS) Noel at 0432 UT on 30 October 2007. Using forward ray tracing, we calculate the body forces which result from the saturation and dissipation of these GWs. We then analyze the 59 traveling ionospheric disturbances (TIDs) observed by the TIDDBIT ionospheric sounder at 0400-1000 UT near Wallops Island. These TIDs were located at the bottomside of the F layer at z = 230-290 km, had periods of tau(r) = 15 to 90 min, horizontal wavelengths of lambda(H) = 100 to 3000 km, and horizontal phase speeds of c(H) = 140 to 650 m/s. 33 (similar to 60%) of the TIDs were propagating northwest(NW) and north(N) ward, from the direction of TS Noel 1700-2000 km away. We show that these TIDs were likely GWs. 40% of these GWs had phase speeds larger than 280m/s. This precluded a tropospheric source and suggested mesospheric and thermospheric sources instead. Using reverse ray tracing, we compare the GW locations with the regions of convective overshoot, mesospheric body forces, and thermospheric body forces. We identify 27 of the northwest/northward propagating GWs as likely being secondary GWs excited by thermospheric body forces. Three may have originated from mesospheric body forces, although this is much less likely. None are identified as primary GWs excited directly by TS Noel. 11 of these GWs with c(H) < 205 m/s likely reflected near the tropopause prior to detection. This secondary GW spectrum peaks at lambda(H) similar to 100-300 km and c(H) similar to 100-300 m/s. To our knowledge, this is the first identification and quantification of secondary GWs from thermospheric body forces.