The whole atmosphere response to changes in the earth’s magnetic field from 1900 to 2000: An example of “top-down” vertical coupling

We study the effects of changes in the Earth’s magnetic field between 1900 and 2000 on the whole atmosphere (0-500 km altitude), based on simulations with the Whole Atmosphere Community Climate Model eXtension. Magnetic field changes directly affect the temperature and wind in the upper atmosphere (> ~110 km) via Joule heating and the ion drag force. However, we also find significant responses in zonal mean temperature and zonal wind in the Southern Hemisphere (SH) middle- to high-latitude troposphere, stratosphere, and mesosphere of up to ±2 K and ±2 m/s, as well as regionally significant changes in Northern Hemisphere (NH) polar surface temperatures of up to ±1.3 K, in December-January-February. In the SH, changes in gravity wave filtering in the thermosphere induce a change in the residual circulation that extends down into the upper mesosphere, where further changes in the mean windclimatology are generated, together withchangesin local planetarywavegeneration and/or amplification and gravity wave filtering. This induces further changes to a residual circulation cell extending down into the troposphere. However, inaccuracies in the simulated SH upper mesospheric wind climatology probably mean that the simulated temperatureandwindresponses in theSHlowerandmiddle atmosphereare also inaccurate. TheNHmiddle atmosphere response is zonally asymmetric, consisting of a significantchangein the positioning andshape of the upper stratospheric polar vortex, which is dynamically consistent with the surface temperature response. However, the downward coupling mechanism in the NH is generally less clear.