SA52A-01 INVITED
Inter-annual variability of mesosphere and lower thermosphere tides
Waves that originate in the troposphere grow in amplitude as they travel upwards into decreasing density at higher altitudes where they become prominent dynamical features. The momentum deposition from upward propagating waves is thought to generate the quasi-biennial oscillation (QBO) and semiannual oscillation (SAO) in the zonal circulation of the stratosphere and mesosphere. These zonal wind oscillations, in turn, modulate the waves as they propagate upwards, including the migrating and nonmigrating tides. Understanding the behavior of the tides is not only crucial to characterizing mesopause variability but also transport in the region. Momentum deposition by the diurnal tide at low latitudes in the lower thermosphere produces indirect circulations that will transport neutral and ionized constituents both vertically and horizontally to higher latitudes. Five years of measurements by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument onboard the Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) satellite and longer time series from the Super Dual Auroral Radar Network (SuperDARN) HF radars are analyzed to examine the seasonal and inter-annual variations of the diurnal, semidiurnal and terdiurnal tides in the mesosphere and lower thermosphere. We present estimates of both the migrating and nonmigrating of these tides from the lower stratosphere to the lower thermosphere and discuss evidence of nonlinear interaction between the tides and other wave modes. We also examine the inter-relationship the tides may have with lower and middle atmosphere variability (e.g., QBO, SAO, and stratospheric warmings) and tidal impacts on the zonal mean structure of the upper atmosphere and ionosphere.
SA52A-02
Tides in a whole atmosphere model
The upper atmosphere and ionosphere clearly exhibit variability on global scales with periods from several hours to several days, characteristic of lower-atmospheric planetary waves and tides. To study the origin, vertical propagation, and possible effects of these planetary-scale perturbations on the coupled thermosphere- ionosphere-electrodynamics system, a new model of Integrated Dynamics through Earth Atmosphere (IDEA) is being developed under a NASA sponsored collaborative project between the University of Colorado and National Weather Service's (NWS) Environmental Modeling and Space Environment Centers. The IDEA model interactively couples a Whole Atmosphere Model (WAM) with Global Ionosphere-Plasmasphere (GIP) and electrodynamics models. WAM is a 150-layer general circulation model based on NWS's operational weather prediction Global Forecast System (GFS), extended from its nominal top altitude of about 60 km to over 600 km. It incorporates relevant physical processes in the extended domain, ranging from the hydrological cycle, cloud physics, and atmosphere-surface exchanges in the troposphere, to solar and Joule heating and mutual diffusion of major species in the thermosphere. Preliminary simulations reveal strong tidal waves in the upper atmosphere with a substantial contribution from non-migrating modes. The structure and variability of tides in WAM will be presented and discussed.
SA52A-03
Mesosphere and Lower Thermosphere (MLT) Temporal and Spatial Climatology and Variabilities
The Mesosphere and Lower Thermosphere (MLT) is a region of the Earth atmosphere that is very sensitive to external influences from the sun above and atmospheric layers below it. Its chemical, momentum and thermal balance, thus basic states (i.e. pressure, density, and temperature, and winds) can change in different time scales due to naturally-occurring and/or human-induced changes to the composition and energy contained within this region. The NASA Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) mission, since its successful launch in December 2001, has provided for the first time a global climatological view of the basic structure of the MLT system during the descreasing phase of this current solar cycle. It has documented the impacts on MLT structures by the tropospheric and stratospheric weather, varying solar EUV radiation and x- ray flares, geomagnetic storms powered by solar corona mass ejections, and the powerful high speed streams of energetic particles. This paper gives a 5-year climatological view of the MLT system as observed by the TIMED spacecraft and reports the characteristics and magnitudes of its temporal and spatial variabilities.
SA52A-04 INVITED
TIDAL FEATURES IN THE ARCTIC AND ANTARCTIC HIGH-LATITUDE MESOSPHERIC TEMPERATURE OBSERVATIONS
OH ariglow temperature measurements have been monitored from Resolute Bay (74.68º N, 94.90º W), Canada in the Arctic high latitude and South Pole (90º S) in the Antarctic high latitude region. Temperature measurements at both locations are derived from identical Michelson interferometer (MI) instruments operating continuously (24 hours) during winter season. For this study, we have used multi-year data base for the two sites and performed spectral analysis to retrieve wave characteristics (amplitude and phase information). From the Lomb-Scargle spectral analysis to the measured temperatures, dominant oscillations are found at various periods near tidal frequency, i.e. 8, 12, and 24 hour. Because of periods and persistence, the observed oscillations in temperature are most likely of tidal origin. Results will be discussed in the context of short variability and long term modulation of these tidal components.
SA52A-05 INVITED
Global Distribution and Inter-annual Variations of Mesospheric and Lower Thermospheric Neutral Wind Diurnal Tide
Using the TIMED Doppler interferometer (TIDI) mesospheric and lower thermospheric neutral wind multiyear data set (2002 - 2005) and NCAR TIME-GCM 1.2 annual run results at the TIDI sampling points, we study the migrating diurnal tide global distribution, interannual, and seasonal variations in connection with the mean zonal wind interannual and seasonal variations. Strong quasi-biennial oscillation (QBO) effect on the diurnal tide was observed in the TIDI data and reproduced to a less degree in the TIME-GCM run. The migrating diurnal tide amplitude is larger during the eastward phase of the stratosphere QBO and weaker during the westward phase. Westward mesosphere mean zonal winds appeared during the eastward phase of the stratosphere QBO (2002 and 2004). The strongest QBO effect on both the migrating diurnal tide and mean zonal winds were observed during the northern spring equinox. We believe that is because both the stratosphere winds and diurnal tide amplitude reach their maximum magnitudes during northern spring equinox. The stratospheric QBO winds apply the maximum filtering effect on the gravity waves, which in turn strongly modulate the diurnal and mean zonal winds. The TIDI data also exhibit large inter-hemispheric asymmetry. While in most cases, westward mean zonal winds in the mesosphere are associated with the enhanced diurnal tide, but not always. The results seem to imply that mean zonal wind is not the only factor controlling the diurnal tide amplitude. The TIME-GCM 1.2 diurnal tide amplitudes are in general smaller than that observed by TIDI. Limited vertical spatial resolution for the TIME-CGM 1.2 is suggested as the cause. Future improvements are expected with higher spatial resolution in the model. QBO effects on nonmigrating tides will also be examined.
SA52A-06
New Results on the Midnight Temperature Maximum Near Equatorial Latitudes
New observations of the equatorial thermospheric dynamics observed from Arequipa, Peru (16.2 S, 72.4 W) obtained with an imaging Fabry-Perot interferometer during the southern hemisphere winter of 2005 (June- August) show an interesting correlation of the formation of the midnight temperature maximum (MTM) with the strength of the semi-diurnal tidal meridional wind. The observations are obtained in eight azimuthal directions at 60 degree zenith angle. Each direction represents an exposure of 120 s and the Doppler shifts and Doppler broadening are analyzed with uncertainties of 8-10 m/s and 30-35 K, respectively. These results are used to prepare horizontal wind maps. When the amplitude of the meridional flow is weak, there is generally not observed any temperature enhancement near midnight. When the meridional flow equatorward is strong, 50-100 m/s, then there is observed about two hours later a significant increase in temperature of typically 100 K. This time delay between the northward component of the thermospheric wind vector and the peak of the MTM structure is observed to be about 30 minutes for two nights obtained during the spring equinox. These results suggest that the semi-diurnal tidal mode forms the MTM by convergence upon the geographical equator to the north of Arequipa. After the compressional heating has taken place, then there is a return "wave" formed that transports the heated air to the region of Arequipa. The decrease of the time delay between winter and the spring equinox is a result of the convergence region forming closer to Arequipa than during the winter. Observations of the horizontal wind maps over successive nights in early July show that the thermospheric wind structure varies considerably from night to night with a variation in the appearance of the meridional wind structure by several hours from night to night. It is tempting to suggest a relationship between this variability and the production of the equatorial spread-F phenomenon.