[1] Recent observations and model simulations demonstrate unequivocally that non-Sunsynchronous (nonmigrating) tides due to deep tropical convection produce large longitudinal and local time variations in bulk ionosphere-thermosphere-mesosphere properties. We thus stand at an exciting research frontier: understanding how persistent, large-scale tropospheric weather systems affect the geospace environment. Science challenge questions include: (1) How much of the tropospheric influence is due to tidal propagation directly into the upper thermosphere? (2) How large is the interannual and the solar cycle variability of the tides and what causes them? These questions are addressed using solar maximum to solar minimum tidal wind and temperature analyses from the Thermosphere Ionosphere Mesosphere Electrodynamics and Dynamics (TIMED) satellite in the mesosphere/lower thermosphere (MLT), and from the Challenging Minisatellite Payload (CHAMP) satellite at $400 km. A physics-based empirical fit model is used to connect the TIMED with the CHAMP tides, i.e., to close the ''thermospheric gap'' of current spaceborne observations. Temperature, density, and horizontal and vertical wind results are presented for the important diurnal, eastward, wave number 3 (DE3) tide and may be summarized as follows. (1) Upper thermospheric DE3 tidal winds and temperatures are fully attributable to troposphere forcing. (2) A quasi-2-year 15-20% amplitude modulation in the MLT is presumably caused by the QBO. No perceivable solar cycle dependence is found in the MLT region. DE3 amplitudes in the upper thermosphere can increase by a factor of 3 in the zonal wind, by $60% in temperature and by a factor of 5 in density, caused by reduced dissipation above 120 km during solar minimum.

[1] The climatological model of the equatorial electrojet, EEJM-1, derived from Ørsted, CHAMP and SAC-C satellite measurements provides the opportunity to investigate the longitudinal variation of the current strength in detail. Special emphasis is put in this study on the effect of nonmigrating tides. We have found that the influence of the diurnal eastward-propagating mode with wavenumber-3, DE3, is particularly strong. In polar orbiting satellite observations the DE3 tidal signal appears as a four-peaked longitudinal structure. We have put special emphasis in our analysis to isolate the DE3 contribution from other sources contributing to the wavenumber-4 structure in satellite data. The amplitude of the DE3 signature in the EEJ not only peaks during equinox seasons, but is also strong around the June solstice. When looking at the modulation of the EEJ intensity the DE3 accounts for about 25% during the months of April through September. It is thus the dominant cause for longitudinal variations. During December solstice months the influence of DE3 is negligible. A secondary three-peaked longitudinal pattern emerges during solstice seasons when the DE3 influence is removed.

Abstract. The accelerometer onboard CHAMP enables us to derive the thermospheric zonal wind at orbit altitudes (∼400 km). Numerous equatorial overflights (∼45 250) are used to investigate the influence of nonmigrating tides on the thermospheric zonal wind. In a previous study a so called "wave-4" longitudinally signal observed in the satellite frame was identified in the zonal wind residuals during equinox. Using four years of data (2002-2005), we determine the annual variation of this prominent feature which is strongest during the months of July through October and has a smaller second maximum during March/April. Due to the large data set we were able to separate the observed wavenumbers into the tidal components. Thereby, we can identify the eastward propagating diurnal tide with zonal wavenumber s=3 (DE3) as the prime cause for the observed wave-4 pattern in the zonal wind. Analyzing the zonal wind along the geographic and the dip equator revealed that the largest amplitudes of DE3 are found along the dip equator. Besides DE3 we present the full spectrum of nonmigrating tides in the upper thermosphere.

Simultaneous observations of the electron density and the zonal wind obtained by the CHAMP satellite at 400 km are used to study systematic longitudinal variations. The time period selected is August–September 2004 allowing observations at pre‐noon and post‐sunset hours. The equatorial ionization anomaly (EIA) and the zonal delta‐wind (deviation from zonal average) show a persistent and dominant 4‐peaked longitudinal variation. We interpret this structure as caused by the wavenumber‐3 nonmigrating diurnal tide (DE3). The EIA and the zonal delta‐wind exhibit extrema at about the same longitudes. But, while the intensifications of the EIA and the delta‐wind are in phase during the evening hours, they are out of phase in the morning. Possible coupling mechanisms are investigated.

Abstract. Measurements of the CHAMP accelerometer are utilized to investigate the average thermospheric wind distribution in the polar regions at altitudes around 400 km. This study puts special emphasis on the seasonal differences in the wind patterns. For this purpose 131 days centered on the June solstice of 2003 are considered. Within that period CHAMP's orbit is precessing once through all local times. The cross-track wind estimates of all 2030 passes are used to construct mean wind vectors for 918 equal-area cells. These bin averages are presented in corrected geomagnetic coordinates. Both hemispheres are considered simultaneously providing summer and winter responses for the same prevailing geophysical conditions. The period under study is characterized by high magnetic activity (Kp=4−) but moderate solar flux level (F10.7=124). Our analysis reveals clear wind features in the summer (Northern) Hemisphere. Over the polar cap there is a fast day-to-night flow with mean speeds surpassing 600 m/s in the dawn sector. At auroral latitudes we find strong westward zonal winds on the dawn side. On the dusk side, however, an anti-cyclonic vortex is forming. The dawn/dusk asymmetry is attributed to the combined action of Coriolis and centrifugal forces. Along the auroral oval the sunward streaming plasma causes a stagnation of the day-to-night wind. This effect is particularly clear on the dusk side. On the dawn side it is evident only from midnight to 06:00 MLT. The winter (Southern) Hemisphere reveals similar wind features, but they are less well ordered. The mean day-to-night wind over the polar cap is weaker by about 35%. Otherwise, the seasonal differences are mainly confined to the dayside (06:00–18:00 MLT). In addition, the larger offset between geographic and geomagnetic pole in the south also causes hemispheric differences of the thermospheric wind distribution.

structures. These tides are prominent during solstices and generally weak during equinoxes. 33 34 35

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[1] Using 2 years of coordinated CHAMP and DMSP observations we have investigated for the first time the relationship between subauroral polarization streams (SAPS), ionospheric Hall current (electrojet), upper thermospheric zonal wind, and mass density at subauroral regions in the dusk and premidnight sectors, separately for both hemispheres. For comparison, we have also analyzed the same parameters as a function of magnetic latitude (30°-80°magnetic latitude) during non-SAPS periods. During periods of non-SAPS, the neutral wind exhibits similar features as during SAPS events in the dusk to premidnight sector, streaming westward in the same direction as the plasma drift. Both neutral and plasma velocities peak at the same latitude regardless of SAPS occurrence. For higher geomagnetic activity both velocities are faster and the peaks shift equatorward. During non-SAPS periods, the ratio between plasma and neutral wind velocity is on average 2.75 ± 0.4 in both hemispheres irrespective of geomagnetic activity. The neutral wind during SAPS events gets enhanced by a factor of 1.5/1.2 for Kp < 4 and 1.3/1.9 for Kp ≥ 4 in the Northern/Southern Hemisphere, respectively, as compared to non-SAPS time. The velocity difference between SAPS and neutral wind is also larger during SAPS period than during non-SAPS period, and the difference tends to increase with increasing geomagnetic activity. The peak latitude of the eastward auroral electrojet appears 1.5°poleward of the plasma drift during SAPS events, confirming the formation of SAPS equatorward of the high-conductivity channel. These SAPS-induced large winds can heat the upper thermosphere. As a result we observe a 10% enhanced mass density at 400 km altitude with respect to periods without SAPS. In addition a density anomaly peak occurs collocated with the SAPS, displaced from the electrojet peak. We regard this as an indication for efficient thermospheric heating by ion neutral friction.Citation: Wang, H., H. Lühr, K. Häusler, and P. Ritter (2011), Effect of subauroral polarization streams on the thermosphere: A statistical study,