Attribution of ionospheric vertical plasma drift perturbations to large‐scale waves and the dependence on solar activity

Abstract

In this study, we quantify the contribution of individual large‐scale waves to ionospheric electrodynamics and examine the dependence of the ionospheric perturbations on solar activity. We focus on migrating diurnal tide (DW1) plus mean winds, migrating semidiurnal tide (SW2), quasi‐stationary planetary wave one (QSPW1), and nonmigrating semidiurnal westward wave one (SW1) under northern winter conditions, when QSPW1 and SW1 are climatologically strong. From thermosphere‐ionosphere‐mesosphere electrodynamics general circulation model simulations under solar minimum conditions, it is found that the mean winds and DW1 produce a wave two pattern in equatorial vertical E×Bdrift that is upward in the morning and around dusk. The modeled SW2 also produces a wave two pattern in the ionospheric vertical drift that is nearly a half wave cycle out of phase with that due to mean winds and DW1. SW1 can cause large vertical drifts around dawn, while QSPW1 does not have any direct impact on the vertical drift. Wind components of both SW2 and SW1 become large at middle to high latitudes in the E‐region, and kernel functions obtained from numerical experiments reveal that they can significantly affect the equatorial ion drift, likely through modulating the E‐region wind dynamo. The most evident changes of total ionospheric vertical drift when solar activity is increased are seen around dawn and dusk, reflecting the more dominant role of large F‐region Pedersen conductivity and of the F‐region dynamo under high solar activity. Therefore, the lower atmosphere driving of the ionospheric variability is more evident under solar minimum conditions, not only because variability is more identifiable in a quieter background but also because the E‐region wind dynamo is more significant. These numerical experiments also demonstrate that the amplitudes, phases, and latitudinal and vertical structures of large‐scale waves are important in quantifying the ionospheric responses.