UARS MLS 63 GHz radiance fluctuations have been used to study global activities and distributions of meso-scale GWs in the stratosphere and mesosphere [Wu and Waters, 1996a,b].  UARS MLS GW variances are available at 8 altitudes (28, 33, 38, 43, 48, 53, 61, and 80km) and contributed mostly by waves of vertical wavelengths > ~10km due to the instrument field-of-view filtering . Depending on the truncation length used in the analysis, the derived GW variances can represent waves of horizontal wavelengths from 30km to 1000s km. For limb-scan observations, the radiances are often truncated by 3-6 measurement points to meet the saturation criteria, which yields a horizontal scale of 50-100km. For limb-tracking observations, where the radiance sequences can be orbit-long, the truncation lengths can be as long as 1000s km. UARS MLS results revealed good correlations of GW activities with stratospheric jetstreams, surface topography, and tropospheric deep convection zones. The background mean winds play a dominant role in enhancing and filtering GWs observed in the stratosphere by satellite sensors like MLS. Over the wave conducting regions, longitudianl variations of wave activity contain valuable information on GW sources [McLandress et at, 2000; Jiang et al., 2002]. The GWs survived from the filtering in the troposphere and lower lower stratosphere are believed to have important impacts on the dynamics in the upper atmosphere.

       Aura MLS has been observing gravity waves since July 2004 with better vertical resolution and coverage over UARS MLS. The radiance measurements around the 118 GHz O2 lines have similar properties to UARS 63 GHz ones except the new instrument can penetrates deep into the upper troposphere and lower stratosphere, the region key to understanding of GW sources and excitation mechanisms. Radiative transfer calculations show that the Aura MLS radiance measurements are sensitive to waves of vertical wavelengths > 5 km and propagating in the south-north direction. The saturated radiances in limb-viewing geometry have better sensitity to wave propagation structures than nadir sounders, showing larger variances when the line-of-sight (LOS) aligns with wave fronts .

       Many GW features in satellite measurements remain unexplored. Joint data analyses and observations with different techniques and with gravity wave models are essential to understand wave properties and their roles in dynamical and chemical processes.

MLS GW observations and instrument properties:

Other Satellite Observations

Advanced satellite techniques have great potential for global gravity wave observations. Some initial results have been made with both limb (MLS, GPS, LIMS, CLAES and SABER) and nadir (AMSU-A, AIRS, MSX) instruments. Nadir instruments like AIRS have superior horizontal resolution that can resolve waves of >30 km wavelength. As a complementary technique, limb sounding instruments like CRISTA, CLAES, and GPS have advantages in vertical resolution. Because of broad gravity wave spectra, both limb and nadir techniques are needed to untangle complicated 3D wave structures. With the improved resolutions from spaceborne sensors, we begin to obtain more quantitative characterizations about wave sources and propagation properties.

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