Quan Gan

Short‐term variability in the ionosphere due to the nonlinear interaction between the 6 day wave and migrating tides

Using the Thermosphere-Ionosphere-Mesosphere Electrodynamics General Circulation Model simulations, we investigate the short-term ionospheric variability due to the child waves and altered tides produced by the nonlinear interaction between the 6-day wave and migrating tides. Via the Fourier spectral diagnostics and least-square fittings, the [21hr, W2] and [13hr, W1] child waves, generated by the interaction of the 6-day wave with the DW1 and SW2, respectively, are found to play the leading roles on the sub-diurnal variability (e.g., ±10 m/s in the ion drift and ~ 50% in the NmF2) in the F-region vertical ion drift changes through the dynamo modulation induced by the low-latitude zonal wind as well as the meridional wind at higher latitudes. The relatively minor contribution of the [11hr, W3] child wave is explicit as well. Although the [29hr, W0] child wave has the largest magnitude in the E-region, its effect is totally absent in the vertical ion drift due to the zonally uniform structure. But, the [29hr, W0] child wave shows up in the NmF2. It is found that the NmF2 short-term variability is attributed to the wave modulations on both E-region dynamo and in-situ F-region composition. Also, the altered migrating tides due to the interaction will not contribute to the ionospheric changes significantly.

A numerical study of the effects of migrating tides on thermosphere midnight density maximum

In this study, we employed the National Center for Atmospheric Research Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) and the extended Canadian Middle Atmosphere Model (eCMAM) to investigate the role of the migrating terdiurnal tide on the formation and variation of the thermosphere midnight temperature maximum (MTM) and midnight mass density maximum (MDM). The migrating terdiurnal tide from the eCMAM was applied at the TIEGCMs lower boundary, along with the migrating diurnal and semidiurnal tides from the Global-Scale Wave Model. Several numerical experiments with different combinations of tidal forcing at the TIEGCMs lower boundary were carried out to determine the contribution of each tide to MTM/MDM. We found that the interplay between diurnal, semidiurnal, and terdiurnal tides determines the formation of MTM/MDM and their structure in the upper thermosphere. The decrease of thermospheric mass density after MDM reaches its maximum at ~02:00 local time is mainly controlled by the terdiurnal tide. Furthermore, we examined the generation mechanisms of the migrating terdiurnal tide in the upper thermosphere and found that they come from three sources: upward propagation from the lower thermosphere, in situ generation via nonlinear interaction, and thermal excitation.

Numerical simulation of the 6 day wave effects on the ionosphere: Dynamo modulation

The Thermosphere-Ionosphere-Mesosphere Electrodynamics General Circulation Model (TIME-GCM) is used to theoretically study the 6-day wave effects on the ionosphere. By introducing a 6-day perturbation with zonal wavenumber 1 at the model lower boundary, the TIME-GCM reasonably reproduces the 6-day wave in temperature and horizontal winds in the mesosphere and lower thermosphere (MLT) region during the vernal equinox. The E-region wind dynamo exhibits a prominent 6-day oscillation that is directly modulated by the 6-day wave. Meanwhile, significant local time variability (diurnal and semi-diurnal) is also seen in wind dynamo as a result of altered tides due to the nonlinear interaction between the 6-day wave and migrating tides. More importantly, the perturbations in the E-region neutral winds (both the 6-day oscillation and tidal-induced short-term variability) modulate the polarization electric fields, thus leading to the perturbations in vertical ion drifts and ionospheric F2-region peak electron density (NmF2). Our modeling work shows that the 6-day wave couples with the ionosphere via both the direct neutral wind modulation and the interaction with atmospheric tides.

First Results From the Ionospheric Extension of WACCM-X During the Deep Solar Minimum Year of 2008: WACCM-X Simulated Ionosphere

New ionosphere and electrodynamics modules have been incorporated in the thermosphere and ionosphere eXtension of the Whole Atmosphere Community Climate Model (WACCM‐X), in order to self‐consistently simulate the coupled atmosphere‐ionosphere system. The first specified dynamics WACCM‐X v.2.0 results are compared with several data sets, and with the Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIE‐GCM), during the deep solar minimum year. Comparisons with Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite of temperature and zonal wind in the lower thermosphere show that WACCM‐X reproduces the seasonal variability of tides remarkably well, including the migrating diurnal and semidiurnal components and the nonmigrating diurnal eastward propagating zonal wavenumber 3 component. There is overall agreement between WACCM‐X, TIE‐GCM, and vertical drifts observed by the Communication/Navigation Outage Forecast System (C/NOFS) satellite over the magnetic equator, but apparent discrepancies also exist. Both model results are dominated by diurnal variations, while C/NOFS observed vertical plasma drifts exhibit strong temporal variations. The climatological features of ionospheric peak densities and heights (NmF2 and hmF2) from WACCM‐X are in general agreement with the results derived from Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) data, although the WACCM‐X predicted NmF2 values are smaller, and the equatorial ionization anomaly crests are closer to the magnetic equator compared to COSMIC and ionosonde observations. This may result from the excessive mixing in the lower thermosphere due to the gravity wave parameterization. These data‐model comparisons demonstrate that WACCM‐X can capture the dynamic behavior of the coupled atmosphere and ionosphere in a climatological sense.