Improved stratospheric and mesospheric sounder validation: General approach and in-flight radiometric calibration
Journal of Geophysical Research Atmospheres 101:D6 (1996) 9775-9793
Abstract:
This paper introduces a series of papers describing the validation of data products from the improved stratospheric and mesospheric sounder (ISAMS) on the Upper Atmosphere Research Satellite. ISAMS is a limb-sounding infrared gas-correlation radiometer, measuring thermal emission from a range of constituents. The constituents measured are ozone, water vapor, methane, nitrous oxide, nitric oxide, nitrogen dioxide, nitrogen pentoxide, nitric acid, carbon monoxide, and aerosol. Atmospheric temperature and composition data were obtained for approximately 180 days between September 26, 1991, and July 29, 1992, with near-global coverage. The instrument and the retrieval process are briefly described, together with aspects of the validation process relevant to all data products, including the radiometric calibration and the analysis of the calibrated radiances to produce data on a standard time-altitude grid. Copyright 1996 by the American Geophysical Union.Residual circulation in the stratosphere and lower mesosphere as diagnosed from Microwave Limb Sounder data
Journal of the Atmospheric Sciences 53:2 (1996) 217-240
Abstract:
Results for the residual circulation in the stratosphere and lower mesosphere between September 1991 and August 1994 are reported. This circulation is diagnosed by applying an accurate radiative transfer code to temperature, ozone, and water vapor measurements acquired by the Microwave Limb Sounder (MLS) onboard the Upper Atmosphere Research Satellite (UARS), augmented by climatological distributions of methane, nitrous oxide, nitrogen dioxide, surface albedo, and cloud cover. The sensitivity of the computed heating rates to the presence of Mt. Pinatubo aerosols is explored by utilizing aerosol properties derived from the measurements obtained by the Improved Stratospheric and Mesospheric Sounder instrument, also onboard UARS. The computed vertical velocities exhibit a semiannual oscillation (SAO) around the tropical stratopause, with the region of downward velocities reaching maximum spatial extent in February and August. This behavior reflects the semiannual oscillation in temperature and ozone and mimics that seen in past studies of the October 1978-May 1979 period based on data from the Limb Infrared Monitor of the Stratosphere onboard the Nimbus 7 satellite. The SAO vertical velocities are stronger during the northern winter phase, as expected if planetary waves from the winter hemisphere are involved in driving the SAO. A possible quasi-biennial oscillation (QBO) signal extending from the middle into the upper stratosphere is also hinted at, with the equatorial vertical velocities in the region 10-1 hPa significantly smaller (or even negative) in 1993/94 than in 1992/93. Despite the short data record, the authors believe that this pattern reflects a QBO signal rather than a coincidental interannual variability, since the time-height section of vertical velocity at the equator resembles that of the zonal wind. Wintertime high-latitude descent rates are usually greater in the Northern Hemisphere, but they also exhibit significant variability there. In the three northern winters analyzed in this study, strong downward velocities are diagnosed in the lower stratosphere during stratospheric warmings and are associated with enhanced wave forcing (computed as the momentum residual) in the mid- and upper stratosphere. The implications of the computed circulation for the distribution of tracers are illustrated by the example of the "double-peaked" structure in the water vapor distribution measured by MLS. © 1996 American Meteorological Society.The H2 so4 component of stratospheric aerosols derived from satellite infrared extinction measurements: Application to stratospheric transport studies
Geophysical Research Letters 23:17 (1996) 2219-2222
Abstract:
The ambient water vapour and temperature conditions of stratospheric sulphate aerosol particles govern their composition and thereby influence their infrared extinction properties. This causes problems in the use of the infrared aerosol extinction as a tracer because variations in the aerosol composition modify the changes in extinction that may arise from the transport of aerosols. An improved tracer which can be derived from measurements of the infrared aerosol extinction, temperature and water vapour abundance, is the H2SO4 component of aerosols. The application of this tracer to studies of stratospheric transport is demonstrated using data from instruments on the Upper Atmosphere Research Satellite and the results are compared to a contour advection calculation. Copyright 1996 by the American Geophysical Union.Use of volcanic aerosols to study the tropical stratospheric reservoir
Journal of Geophysical Research Atmospheres 101:D2 (1996) 3973-3988
Abstract:
Aerosol data obtained by the advanced very high resolution radiometer on NOAA 11, the improved stratospheric and mesospheric sounder on the upper atmospheric research satellite, one airborne lidar system, and several ground-based lidar systems up to 2-1/2 years after the eruption of Mount Pinatubo are used to study stratospheric dynamics. In particular, this study focuses on the tropical stratospheric reservoir and transport from it to northern midlatitudes following the eruption of Mount Pinatubo. This includes: The build-up and removal rates for sulfate aerosol, the position and motion of the center of the reservoir, and the position and width of its boundaries at altitudes of the volcanic aerosols. Ozone data from the total ozone mapping spectrometer were also used to study the position and width of the reservoir boundaries. In addition, ground-based lidar stratospheric aerosol data are used to study aerosol transport from the reservoir to the northern hemisphere as it relates to winds in the tropical stratosphere. Finally, historical in situ and satellite data were used to examine how the time and location of volcanic injections into the stratosphere affect the aerosol decay rates and seasonal variations of aerosol optical depth in the midlatitude stratosphere. Copyright 1996 by the American Geophysical Union.Validation of temperature measurements from the improved stratospheric and mesospheric sounder
Journal of Geophysical Research Atmospheres 101:D6 (1996) 9795-9809