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Abstract
The transport of passive tracers observed by the Upper Atmosphere Research Satellite is simulated using computed three-dimensional trajectories of ≈ 100 000 air parcels initialized on a stratosphere grid, with horizontal winds provided by the United Kingdom Meteorological Office data assimilation system, and vertical (cross isentropic) velocities computed using a fast radiation code. The conservative evolution of trace constituent fields is estimated over 20–30-day periods by assigning to each parcel the observed mixing ratio of the long-lived trace gases N20 and CH4 observed by the Cryogenic Limb Army Etalon Spectrometer (CLAES) and H2O observed by the Microwave Limb Sounder (MLS) on the initialization date. Agreement between calculated and observed fields is best inside the polar vortex and is better in the Arctic than in the Antarctic. Although there is not always detailed agreement outside the vortex, the trajectory calculations still reproduce the average large-scale characteristics of passive tracer evolution in midlatitudes. In late winter, synoptic maps from trajectory calculations reproduce all major features of the observations, including large tongues or blobs of material drawn from low latitudes into the region of the anticyclone during February–March 1993. Comparison of lower-stratospheric observations of the CLAES tracers with the calculations suggests that discontinuities seen in CLAES data in the Antarctic late winter lower stratosphere are inconsistent with passive tracer behavior. In the Arctic, and in the Antarctic late winter, MLS H20 observations show behavior that is inconsistent with calculations and with that expected for passive tracers inside the polar vortex in the middle-to-upper stratosphere. Diabatic descent rates in the Arctic lower stratosphere deduced from data are consistent with those from the calculations. In the Antarctic lower stratosphere, the calculations appear to underestimate the diabatic descent. The agreement between large-scale features of calculated and observed tracer fields supports the utility of these calculations in diagnosing trace species transport in the winter polar vortex.
Abstract
The transport of passive tracers observed by the Upper Atmosphere Research Satellite is simulated using computed three-dimensional trajectories of ≈ 100 000 air parcels initialized on a stratosphere grid, with horizontal winds provided by the United Kingdom Meteorological Office data assimilation system, and vertical (cross isentropic) velocities computed using a fast radiation code. The conservative evolution of trace constituent fields is estimated over 20–30-day periods by assigning to each parcel the observed mixing ratio of the long-lived trace gases N20 and CH4 observed by the Cryogenic Limb Army Etalon Spectrometer (CLAES) and H2O observed by the Microwave Limb Sounder (MLS) on the initialization date. Agreement between calculated and observed fields is best inside the polar vortex and is better in the Arctic than in the Antarctic. Although there is not always detailed agreement outside the vortex, the trajectory calculations still reproduce the average large-scale characteristics of passive tracer evolution in midlatitudes. In late winter, synoptic maps from trajectory calculations reproduce all major features of the observations, including large tongues or blobs of material drawn from low latitudes into the region of the anticyclone during February–March 1993. Comparison of lower-stratospheric observations of the CLAES tracers with the calculations suggests that discontinuities seen in CLAES data in the Antarctic late winter lower stratosphere are inconsistent with passive tracer behavior. In the Arctic, and in the Antarctic late winter, MLS H20 observations show behavior that is inconsistent with calculations and with that expected for passive tracers inside the polar vortex in the middle-to-upper stratosphere. Diabatic descent rates in the Arctic lower stratosphere deduced from data are consistent with those from the calculations. In the Antarctic lower stratosphere, the calculations appear to underestimate the diabatic descent. The agreement between large-scale features of calculated and observed tracer fields supports the utility of these calculations in diagnosing trace species transport in the winter polar vortex.
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.
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.
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.
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.
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.
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.
