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J. W. Waters
,
K. F. Kunzi
,
R. L. Pettyjohn
,
R. K. L. Poon
, and
D. H. Staelin

Abstract

This article discusses remote sensing of atmospheric temperatures with the NEMS microwave spectrometer on the Nimbus 5 satellite, and the accuracy with which atmospheric temperatures can be determined by NEMS. The sensitivity of the NEMS instrument allows measurement of temperature profiles having vertical resolution of the respective NEMS weighting functions (∼10 km) with an rms accuracy of a few tenths of a degree Kelvin for a 16 s integration time. The accuracy of NEMS in estimating atmospheric temperatures at the discrete levels (∼2 km vertical resolution in the lower troposphere) used in the operational numerical model of the National Meteorological Center (NMC) is ∼2 K rms, as determined by comparing NEMS results with ground truth data obtained from the NMC operational analysis and from coincident radiosondes. These accuracies are consistent with the theoretical accuracies expected for NEMS.

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W. A. Lahoz
,
A. O'Neill
,
E. S. Carr
,
R. S. Harwood
,
L. Froidevaux
,
W. G. Read
,
J. W. Waters
,
J. B. Kumer
,
J. L. Mergenthaler
,
A. E. Roche
,
G. E. Peckham
, and
R. Swinbank

Abstract

The three-dimensional evolution of stratospheric water vapor distributions observed by the Microwave Limb Sounder (MLS) during the period October 1991–July 1992 is documented. The transport features inferred from the MLS water vapor distributions are corroborated using other dynamical fields, namely, nitrous oxide from the Cryogenic Limb Array Etalon Spectrometer instrument, analyzed winds from the U.K. Meteorological Office (UKMO), UKMO-derived potential vorticity, and the diabatic heating field. By taking a vortex-centered view and an along-track view, the authors observe in great detail the vertical and horizontal structure of the northern winter stratosphere. It is demonstrated that the water vapor distributions show clear signatures of the effects of diabatic descent through isentropic surfaces and quasi-horizontal transport along isentropic surfaces, and that the large-scale winter flow is organized by the interaction between the westerly polar vortex and the Aleutian high.

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J. W. Waters
,
W. G. Read
,
L. Froidevaux
,
R. F. Jarnot
,
R. E. Cofield
,
D. A. Flower
,
G. K. Lau
,
H. M. Pickett
,
M. L. Santee
,
D. L. Wu
,
M. A. Boyles
,
J. R. Burke
,
R. R. Lay
,
M. S. Loo
,
N. J. Livesey
,
T. A. Lungu
,
G. L. Manney
,
L. L. Nakamura
,
V. S. Perun
,
B. P. Ridenoure
,
Z. Shippony
,
P. H. Siegel
,
R. P. Thurstans
,
R. S. Harwood
,
H. C. Pumphrey
, and
M. J. Filipiak

Abstract

The Microwave Limb Sounder (MLS) experiments obtain measurements of atmospheric composition, temperature, and pressure by observations of millimeter- and submillimeter-wavelength thermal emission as the instrument field of view is scanned through the atmospheric limb. Features of the measurement technique include the ability to measure many atmospheric gases as well as temperature and pressure, to obtain measurements even in the presence of dense aerosol and cirrus, and to provide near-global coverage on a daily basis at all times of day and night from an orbiting platform. The composition measurements are relatively insensitive to uncertainties in atmospheric temperature. An accurate spectroscopic database is available, and the instrument calibration is also very accurate and stable. The first MLS experiment in space, launched on the (NASA) Upper Atmosphere Research Satellite (UARS) in September 1991, was designed primarily to measure stratospheric profiles of ClO, O3, H2O, and atmospheric pressure as a vertical reference. Global measurement of ClO, the predominant radical in chlorine destruction of ozone, was an especially important objective of UARS MLS. All objectives of UARS MLS have been accomplished and additional geophysical products beyond those for which the experiment was designed have been obtained, including measurement of upper-tropospheric water vapor, which is important for climate change studies. A follow-on MLS experiment is being developed for NASA’s Earth Observing System (EOS) and is scheduled to be launched on the EOS CHEMISTRY platform in late 2002. EOS MLS is designed for many stratospheric measurements, including HO x radicals, which could not be measured by UARS because adequate technology was not available, and better and more extensive upper-tropospheric and lower-stratospheric measurements.

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