Yanshi Huang

Energy input into the upper atmosphere associated with high‐speed solar wind streams in 2005

A 9 day periodic oscillation in solar wind properties, geomagnetic activity, andupper atmosphere has been reported for the year 2005. To understand the energytransfer processes from the high‐speed solar wind streams into the upper atmosphere, weexamined Joule heating and hemispheric power (HP) from the assimilative mapping ofionospheric electrodynamics (AMIE) outputs for 2005. There are clear 9 day periodvariations in all AMIE outputs, and the 9 day periodic oscillation in the global integratedJoule heating is presented for the first time. The band‐pass filter centered at 9 dayperiod shows that both Joule heating and HP variations are correlated very well to theneutral density variation. It indicates that the energy transfer process into the upperatmosphere associated with high‐speed solar wind streams is a combination of Jouleheating and particle precipitation, while Joule heating plays a dominant role. Thesensitivities of Joule heating and HP to the solar wind speed are close to 0.40 and0.15 GW/(km/s), respectively.

Ionization due to electron and proton precipitation during the August 2011 storm

The parameterizations of monoenergetic particle impact ionization in Fang et al. (2010) (Fang2010) and Fang et al. (2013) (Fang2013) are applied to the complex energy spectra measured by DMSP F16 satellite to calculate the ionization rates from electron and ion precipitations for a Northern Hemisphere pass from 0030 UT to 0106 UT on 6 August 2011. Clear enhancement of electron flux is found in the polar cap. The mean electron energy in the polar cap is mostly above 100 eV, while the mean energy in the auroral zone is typically above 1 keV. At the same time, F16 captures a strong Poynting flux enhancement in the polar cap, which is comparable to those in the auroral zone. The particle impact ionization rates using Fang2010 and Fang2013 parameterizations show clear enhancement at F region altitudes mainly due to the low-energy precipitating electrons, peaking probably in the cusp but also showing enhanced levels throughout most of the polar cap region. The general circulation models (GCMs), National Center for Atmospheric Research Thermosphere-Ionosphere-Electrodynamics General Circulation Model, and Global Ionosphere-Thermosphere Model, using their default empirical formulations of particle impact ionization, do not capture the observed features shown in the total particle ionization rate applying the Fang2010 and Fang2013 parameterizations to DMSP measurements. The difference between GCM simulations and Fang2010 and Fang2013 applied to DMSP data is due to the difference of both the inputs to the models and the parameterization of the ionization rates.

Comparison of the neutral wind seasonal variation from midlatitude conjugate observations

The seasonal variation of F region neutral wind from the midlatitude conjugate Fabry-Perot interferometer observations has been studied. The meridional wind at Palmer station (64°S,64°W) has a significant local time dependence with strong equatorward wind at midnight and polarward wind at dawn and dusk. The zonal wind switches from eastward to westward in the early morning section. From the June solstice (austral winter) to equinox, the maximum meridional wind increases from 90 m/s to 130 m/s, and the zonal wind switches direction at an earlier local time. The neutral winds from Palmer have been compared with those from the geomagnetic conjugate location, Millstone Hill (MH). At equinox, the local time variation of neutral wind shows a very good conjugacy between these two locations. But at June solstice, the similarity in the zonal wind becomes less clear. This seasonal dependence can be attributed to the seasonal variation of solar and geomagnetic forcings. The annual variation of daily average neutral wind from Palmer and MH has also been compared. The meridional wind shows a clear offset of season, and the magnitude at Palmer is averagely 40 m/s more equatorward than that at MH. The zonal wind is dominantly westward at Palmer and eastward at MH. The annual variation of neutral wind, especially the zonal component, is much less symmetric between the two sites than the local time variation. The empirical horizontal wind model shows a good agreement with the observations in both local time and annual variations.