[1] The Student Nitric Oxide Explorer (SNOE) satellite made near-continuous measurements of nitric oxide in the lower thermosphere (97.5 km to 150 km) between March 1998 and September 2000. Using eigenanalysis, this daily nitric oxide data set is represented as a time mean plus the sum of orthogonal functions of space multiplied by time-varying coefficients. The functions, typically called empirical orthogonal functions (EOFs), are ordered by the amount of variance they capture from the original data set. While this analysis in no way guarantees that the modes of variability identified by the EOFs are associated with physical processes, we show that it is clearly so for the first three EOFs of the SNOE data set. The dominant mode of variability is associated with auroral activity, followed by a seasonal effect, and then a response to varying solar EUV flux. As a result, it is possible to construct a compact, three-dimensional nitric oxide empirical model (NOEM) in the lower thermosphere that takes as input a planetary magnetic index, day of year, and 10.7 cm solar radio flux. Since it is possible that changes in lower thermospheric nitric oxide could lead to changes in stratospheric ozone, the model presented here can be utilized in climate simulations without the need to incorporate many thermospheric processes.

ΣO/N2 ratios in the Earth's thermosphere are measured by the Global Ultraviolet Imager (GUVI) on the TIMED satellite, and demonstrate strong 9 and 7 day oscillations in 2005 and 2006, respectively, that are well correlated with the solar wind speed and Kp index. This work builds on the recently discovered connection between rotating solar coronal holes and thermospheric mass density variations. The work described here is the first description of geomagnetically forced periodicities in neutral composition. Furthermore, these observations provide the first definitive proof that the processes creating neutral composition changes during geomagnetic storms occur continuously at all activity levels and all over the world. The ΣO/N2 response versus the mass density response indicates the important role of vertical winds at high latitudes while thermal expansion dominates at lower latitudes.

[1] The evolution of the pre-reversal enhancement in the vertical ion drift in the equatorial F region is described via an examination of the current systems determined from a coupled ionosphere thermosphere model. We find that the pre-reversal enhancement is produced by a reversal in the F region zonal wind that results in an additional upward current where the E region Pedersen conductivity is declining across the dusk sector. The continuity of the total current is maintained through an enhancement in the eastward zonal current and an associated upward drift of the ions.Citation: Heelis, R. A., G. Crowley, F. Rodrigues, A. Reynolds, R. Wilder, I. Azeem, and A. Maute (2012), The role of zonal winds in the production of a pre-reversal enhancement in the vertical ion drift in the low latitude ionosphere,

[1] It has already been shown that the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM) is capable of reproducing the pre-reversal enhancement (PRE) of the equatorial zonal electric field. However, the ability of TIE-GCM to reproduce the post-sunset plasma vortex, an important feature of the evening equatorial ionosphere closely related to the PRE, has been overlooked and had yet to be addressed. In order to address the ability of TIE-GCM to reproduce the vortex, we examined model simulations of the plasma flow pattern in the geomagnetic equatorial plane and compared the simulations with ground-based radar observations. We found that TIE-GCM is indeed capable of reproducing the overall features of the post-sunset equatorial plasma vortex pattern. We also found that both E and F region dynamos in TIE-GCM dictate the main features of the vertical shear in the zonal plasma drifts that is part of the evening vortex. The contribution of vertical currents to the shear, however, is not negligible. Comparison of simulation results with radar measurements of the vortex indicates that the model can still be improved to better match the observations.

Traveling ionospheric disturbances (TIDs) have been detected using various measurement techniques, including HF sounders, incoherent scatter radars, in situ measurements, and optical techniques. However, observations of TIDs have tended to be sparse and there is a need for additional observations to provide new scientific insight into the geophysical source phenomenology and wave propagation physics. The dense network of GPS receivers around the globe offers a relatively new data source to observe and monitor TIDs. In this paper, we use total electron content (TEC) measurements from ~4000 GPS receivers throughout the continental United States to observe TIDs associated with the 11 March 2011 Tohoku tsunami. The tsunami propagated across the Pacific to the U.S. west coast over several hours, and we show that corresponding TIDs were observed in the US. Using this network of GPS receivers we present a 2D imaging of TEC perturbations and calculate various TID parameters, including horizontal wavelength, speed, and period. Well‐formed, planar TIDs were detected over the west coast of the U.S. ~10 h after the earthquake. Fast Fourier transform analysis of the observed waveforms revealed that the period of the wave was 15.1 min with a horizontal wavelength of 194.8 km, phase velocity of 233.0 m/s, and an azimuth of 105.2° (propagating nearly due east in the direction of the tsunami wave). These results are consistent with the TID observations in airglow measurements from Hawaii earlier in the day and with other GPS TEC observations.