Global Impacts of Ultra-Low-Frequency Waves: 1. Thermospheric Responses and Travelling Atmosphere Disturbances

Ultra-Low-Frequency (ULF) waves cause local Thermosphere-Ionosphere (T-I) perturbations, but their impacts on the global T-I system including the generation of Travelling Atmospheric Disturbances (TADs) have never been evaluated. The main mechanisms responsible for the TAD generation and propagation, whether through dynamic or thermal process, are not clear either. We present a model study of ULF wave impacts on the thermosphere using the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM). The model results indicate that ULF waves can trigger globally propagating TADs. Thermal processes are the main driver for the TAD generation and propagation, with Joule heating and adiabatic processes taking effects inside the TAD source region, and adiabatic processes and heat conduction being the dominant processes outside. Model results also show that TAD propagation is almost symmetric in two hemispheres and independent of seasonal effects. This study reveals the physical connections between magnetospheric ULF waves and thermospheric disturbances for the first time.