SA34A-01 16:00h
Nonmigrating Diurnal Tidal Variability in Mesopause Region Winds: TIDI, TIME-GCM and GSWM Comparisons
We compare nonmigrating diurnal wind estimates determined from measurements made by the TIMED Doppler Inteferometer (TIDI) instrument on the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite with predictions from the NCAR Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (TIME-GCM) and the Global-Scale Wave Model (GSWM). The models account for two different nonmigrating tidal sources. The GSWM includes tropospheric latent heat release associate with deep tropical convection, while the TIME-GCM includes nonlinear interactions between quasi-stationary planetary waves and migrating tides. The model and measurement comparisons suggest that both sources are important to the interpretation of the TIDI tidal winds. We contrast the true model tidal results with estimates that we determine from the subsets of model wind predictions that represent what TIDI would observe if it flew through the model atmospheres. These contrasts allow us to quantify the sampling issues associated determining tidal signatures from the slowly precessing TIMED TIDI satellite data.
SA34A-02 16:15h
The 2-day wave in the mesosphere observed by SABER
A large-scale oscillation with period near 2 days is a ubiquitous feature of the summer mesosphere; it has been detected in ground-based and satellite observations, and reproduced with a variety of numerical models. The current consensus is that the 2-day oscillation is forced through baroclinic instability of the summertime stratospheric jet and takes the form of the gravest Rossby-gravity normal mode of zonal wavenumber k=3. We present SABER observations for 2002-2004 that strongly support this view, and show further that the 2-day wave is part of a set of normal modes excited in the vicinity of the region of strong curvature of the summer jet. Besides the k=3, RG mode, these include the k=4 RG mode (~1.8 days), and Rossby modes at k=2 (2.5-3 days) and k=1 (~5 days). SABER observations also reveal that the wavenumber composition of this 2-day ``complex" is different in southern and northern summer, at least in the data currently available from SABER.
SA34A-03 16:30h
The Climatology of the 5-Day Wave in the Mesosphere
In the upper mesosphere, westward propagating waves are sometimes observed with periods between 5 and 7 days. These motions are usually attributed to the so-called 5-day wave, a wavenumber 1, Rossby planetary wave that has been extensively studied in the stratosphere. A survey was carried out of planetary wave signatures in SABER temperatures over the three years of the mission. We find that 5-day wave events are relatively infrequent in the upper mesosphere. However, during May of 2003, an exceptionally strong outbreak of 5-day wave activity was observed by SABER with an amplitude of 15 K at mesopause heights. The wave penetrated well into the thermosphere. Although the period of this wave was longer than 5 days ($\sim$6 days), its global structure was consistent with that of the 5-day normal mode. The May 2003 event also showed up strongly in a year-long run of the NCAR TIME-GCM model that was forced at the 10 hPa lower boundary with NCEP reanalyses. The model output is used to study the relationship of mesospheric 5-day wave activity to perturbations in the lower atmosphere and diagnose the background conditions that determine wave propagation and amplification.
SA34A-04 16:45h
Analysis of temperature and wind measurements from the TIMED Mission: Comparison with UARS data
We report on an analysis of temperature and wind data based respectively on measurements with the SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) and TIDI (TIMED Doppler Interferometer) instruments on the TIMED (Thermosphere-Ionosphere-Mesosphere-Energetics and Dynamics) mission. Comparisons are made with corresponding results obtained from the HRDI (High Resolution Doppler Imager), MLS (Microwave Limb Sounder) and CLAES (Cryogenic Limb Array Etalon Spectrometer) instruments on the UARS (Upper Atmosphere Research Satellite) spacecraft. The TIMED and UARS instruments sample the atmosphere in a similar way as a function local solar time. Comparison of data from the two satellite missions is presented in terms of derived diurnal tidal and zonal-mean variations of temperature and winds, obtained as functions of season, latitude, and altitude. The observations are also compared with results from the Numerical Spectral Model (NSM).
SA34A-05 17:00h
Interpretation of subplanetary-scale diurnal variance in the middle atmosphere
Numerical studies indicate that diurnal waves of intermediate scale (zonal wavenumbers between 4 and 15) are significant momentum sources for the stratopause and mesopause semiannual oscillations. This paper presents observational support for such waves in the middle atmosphere. Day-night differences from the Limb Infrared Monitor of the Stratosphere (LIMS) temperatures are analyzed as proxies for the diurnal tide. The variance in zonal wavenumber 9-16 is weakest in the mesosphere when the underlying zonal mean winds are directed westward in the lower stratosphere, and eastward in the upper stratosphere and lower mesosphere. This behavior is consistent with critical level filtering of diurnal subplanetary scale waves by the zonal mean winds. However, this mechanism cannot be verified without information about the propagation directions of the diurnal waves. SABER sampling patterns enable such definitions. Preliminary analyses of SABER diurnal temperatures show further support for the existence of intermediate- scale waves, and filtering by the mean winds in the upper stratosphere. The westward-propagating waves dominate their eastward counterparts between zonal wavenumbers 7 and 11.
SA34A-06 17:15h
Global Occurrence Statistics of Mesospheric Inversion Layers Obtained From SABER Temperature Profiles
We examine the global morphology of mesospheric inversion layers (MILs) using the unprecedented temperature database derived from the SABER instrument on the TIMED satellite which so far covers the period 2002 to mid 2004. The 100 percent duty cycle of the SABER instrument allows us to get nearly global coverage of temperature profiles from 52S-83N (or 83S-52N in the opposite phase of the yaw cycle). With this data we have catalogued the occurrence and amplitude of inversion layers as a function of local time and latitude for equinox and solstice. For each season we use data from an entire yaw cycle (about 62 days) in order to cover all local times. Preliminary results show a large occurrence frequency of MILs with amplitudes of greater than 20K (at equinox) with the largest amplitudes and highest occurrence rates in the equatorial region. We correlate the occurrence of MILs and their amplitude with the expected tidal phase and amplitude and map the horizontal extent of the larger MILs.
SA34A-07 17:30h
Observations and modeling of stratospheric warmings and mesospheric coolings by the TIMED/SABER instrument and the NOGAPS forecast system
We used temperature data from the Sounding of the Atmosphere with Broadband Emission Radiometry (SABER) experiment on the TIMED satellite to quantify the connection between temperatures in the mesosphere and lower thermosphere with the stratosphere. Specifically, we studied three winter periods where stratospheric temperatures were dynamically disturbed: February 2002 in the Northern Hemisphere; August, 2002 in the Southern Hemisphere; and Jan/Feb 2003 in the Northern Hemisphere. The SABER temperatures show a clear signature of mesospheric coolings in concert with stratospheric warmings. Mesospheric temperatures between 0.7 mb and 0.01 mb show a clear and significant anticorrelation with stratospheric temperatures with no phase lag or lead. For pressures $<$ 0.01 mb, this anticorrelation breaks down suggesting that mesospheric cooling events do not extend to altitudes higher than 80 km. We have compared the August 2002 observations with hindcasts using the Navy Operational Global Atmospheric Prediction System (NOGAPS) which has been recently extended up to 85-100 km. Good agreement is seen between SABER and NOGAPS over a 5-10 day period, although the model appears to underestimate the depth of the mesospheric cooling. This likely suggests the need for greater gravity wave drag in the model. Finally, the lack of a clear correlation between stratospheric temperatures and those at 83-90 km suggests that measurements of the OH Meinel band temperatures at those altitudes may not be representative of the entire mesosphere.
SA34A-08 17:45h
Thermospheric Composition Changes in the Morning Sector near Local Midnight in Association with Substorm Activity and IMF Orientation
Repeated observations with DE-1 and other spacecraft have established that transient decreases in the far-ultraviolet (FUV) terrestrial OI emissions at subauroral latitudes in the morning sector are associated with decreases in the O/N2 ratio at thermospheric altitudes. These decreases are observed following onset of intense auroral activity and, at northern latitudes near the autumnal equinox, the greater spatial extent and depth of decrease are associated with a positive IMF By component. These changes in thermospheric composition directly affect F-region electron densities. It is believed that the altered composition is driven by aurorally related heating and the antisunward polar jet, which transports heated air to subauroral latitudes in the very early hours of local time and then into the morning sector. FUV observations of this altered composition close to local midnight and in the early morning hours are lacking, due in part to the need for FUV observations in the sunlit hemisphere (i.e., local summer), but are necessary to support this general expectation. Other important influences are also present. The GUVI/TIMED observations at FUV wavelengths are providing an extensive new set of unambiguous thermospheric composition measurements over a wide range of local times and latitudes in both auroral hemispheres as the orbit of the near-polar-orbiting TIMED spacecraft processes rapidly in local time. These data are being scanned in a search for the requisite combination of sampling at the right local times and season in periods of auroral substorms to provide answers to the question of composition changes near local midnight and the early morning hours. A further report on this search and its findings are presented in this paper.