Quantifying Aurora Driven Gravity Waves in the Thermosphere During Low Geomagnetic Activity.

In this study, we quantify thermospheric gravity waves due to aurora during low geomagnetic conditions (Kp<3) using the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM). Auroral inputs in TIEGCM are specified using maps produced through a Lattice Kriging data assimilation approach, which combines auroral electron flux and characteristic energy from DMSP satellite with the Kp-dependent empirical auroral model. Two simulations are performed with identical electric-field forcing from SuperDARN spherical-harmonic fitting but with different auroral forcing: one using empirical aurora with a Kp=0 condition and the other using assimilated auroral maps with realistic Kp, allowing the effect of auroral forcing to be isolated. We identified 36 gravity wave events by analyzing vertical wind perturbations from 10- 16 July 2021, near 200km using a two-dimensional Fourier transform method. The dominant waves exhibit periods of 2–4 hours, horizontal wavelengths of 1500–4,000 km, and phase speeds of 200–600 m/s, propagating primarily in the meridional direction. These wave properties closely match those reported during the Global-Scale Observations of the Limb and Disk (GOLD) gravity wave campaigns. Wave amplitudes show significant positive correlations with auroral number flux (r = 0.77) and characteristic energy (r = 0.67), indicating a strong connection between aurora and wave activity. Overall, we show that data-assimilated auroral forcing used in TIEGCM can generate large-scale thermospheric gravity waves even during quiet geomagnetic conditions, with characteristics consistent with those reported in observational studies from GOLD.