Height distribution of Joule heating and its influence on the thermosphere

Abstract

The National Center for Atmospheric Research Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (NCAR TIE‐GCM) is employed to quantify the influence of Joule heating at different altitudes on the neutral temperature and density at 400 km for solar minimum and maximum conditions. The results show that high‐altitude Joule heating is more efficient than low‐altitude heating in affecting the upper thermosphere. Most of the Joule heating is deposited under 150 km, and the largest Joule heating deposition per scale height happens at about 125 km, independent of solar activity. However, the temperature and density changes at 400 km are largest for heat deposited at ∼140 km for solar minimum and ∼263 km for solar maximum. The timescale for the thermospheric response varies with the altitude of heating. Joule heating deposited at lower heights needs more time to conduct upward, and it takes more time for the thermosphere at 400 km to approach a steady state. A simple one‐dimensional model is utilized to explain how the amplitude and characteristic timescale of the upper‐thermosphere response to Joule heating depends on the height of heat input. The characteristic response timescale for heat deposited around 135 km is ∼6 hours, while that for heat deposited around 238 km is ∼0.5 hours. The initial temperature response at 400 km to the high‐altitude heating is much stronger than the response to the low‐altitude heating, but the responses become comparable after about 4 days.