New perspectives on thermosphere tides: 1. Lower thermosphere spectra and seasonal-latitudinal structures

Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry (TIMED/SABER) temperature measurements at 110 km and between ±50° latitude extending from 2002 through 2010 are analyzed to reveal the tidal spectrum entering the ionosphere-thermosphere (IT) system. Seasonal-latitudinal structures are presented for the most prominent spectral components which include DE3, DE2, D0, DW1, DW2, SE1 to SE4, SW1 to SW4, SW6, TE1, TW4, TW5, and TW7. Referring to recent calculations of lower atmosphere heat sources as well as vertical structure characteristics of these waves anticipated from classical tidal theory, we analyze the likely origins of these waves and the nature of their seasonal-latitudinal structures. Several waves are likely to arise through nonlinear wave-wave interactions, and in some cases, this appears to be the sole viable mechanism leading to their existence. The tidal spectrum quantified here is especially relevant to the dynamo generation of electric fields which then impose the tidal variability on the overlying F-region ionosphere. Part 2 of this 2-part study examines penetration of the tidal spectrum to the upper thermosphere.