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Murry L. Salby, Dennis L. Hartmann, Paul L. Bailey, and John C. Gille

Abstract

Eastward propagating disturbances over the equator are diagnosed in two independent Nimbus-7 LIMS (Limb Infrared Monitor of the Stratosphere) data sets. They are evident consistently at several pressure levels throughout the stratosphere and account for much of the temperature variance in the tropics. The disturbances, which can be seen in wavenumbers 1–3, are in phase and symmetric about the equator, latitudinally evanescent, and have short-moderate vertical phase structure, 10–40 km, which progresses downward.

Wavenumber 1 has spectral components which propagate eastward at periods of 6.7–8.6 days (54–69 m s−1) and 3.5–4.0 days (115–135 m s−1). Wavenumber 2 exhibits eastward propagating variance at periods of 6.0–7.5 days (31–39 m s−1) and 3.8–4.3 days (55–62 m s−1). The faster waves appear principally in the upper stratosphere. These features are in reasonable agreement with the structure and dispersion characteristics of simple, quasi-separable Kelvin modes. With the exception of the slower wavenumber 1 feature, reported earlier by Hirota, these components are newly documented for the middle and upper stratosphere.

Interpretations of wave structure in terms of refractive properties of the basic flow are supported by the zonal-mean winds for the period. Power structures exhibit several maxima and minima in height, with phase variations across the maxima slower than across the minima. This behavior, supported by the longer vertical wavelengths, suggests that some reflection may be occurring.

A rapid phase variation is evident in both wavenumbers 1 and 2 near the stratopause, overlying a region of magnified amplitude. The latitudinal structure at this level, can be seen to contract as well. Such behavior is suggestive of disturbance focusing, due to Doppler shifting to small intrinsic frequencies, and attendant wave absorption. Coincident with this region of enhanced power and steep phase tilt, is a layer of sharp westerly shear, which, as reported by Leovy and others, descends over a period of weeks. The concurrent observation of the two phenomena supports earlier suggestions that Kelvin waves are instrumental in the westerly acceleration of the semiannual oscillation.

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Ellis Remsberg, James M. Russell III, Larry L. Gordley, John C. Gille, and Paul L. Bailey

Abstract

The LIMS experiment on Nimbus 7 has provided new results on the stratospheric water vapor distribution. The data show 1) a latitudinal gradient with mixing ratios that increase by a factor of 2 from equator to ±60 degrees at 50 mb, 2) most of the time there is a fairly uniform mixing ratio of 5 ppmv at high latitudes, but more variation exists during winter, 3) a well-developed hygropause at low to midlatitudes of the lower stratosphere 4) a source region of water vapor in the upper stratosphere to lower mesosphere that is consistent with methane oxidation chemistry, at least within the uncertainties of the data, 5) an apparent zonal mean H2O distribution that is consistent with the circulation proposed by Brewer in 1949, and 6) a zonal mean distribution in the lower stratosphere that is consistent with the idea of quasi-isentropic transport by eddies in the meridional direction. Limits to the use of the data in the refinement of our understanding of the stratospheric water vapor budget are noted.

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Jinxue Wang, John C. Gille, Paul L. Bailey, Liwen Pan, David Edwards, and James R. Drummond

Abstract

Global tropospheric carbon monoxide (CO) distributions can be retrieved from observations by spaceborne gas correlation radiometers and high-resolution interferometers. The Measurement of Pollution in the Troposphere (MOPITT) is a gas correlation radiometer designed for tropospheric CO and CH4 remote sensing. It is being developed at the University of Toronto and the National Center for Atmospheric Research for launch on the EOS/AM-1 platform in 1999. Spaceborne high-resolution interferometers with troposphere CO remote sensing capability include the Interferometric Monitor for Greenhouse gases (IMG) instrument and the Troposphere Emission Spectrometer (TES). IMG was developed by the Ministry of International Trade and Industry (MITI) of Japan. It was on the ADEOS-1 spacecraft launched in October 1996. TES is being developed by the Jet Propulsion Laboratory for launch on the EOS/CHEM-1 platform in 2002.

For the purpose of testing the MOPITT data processing algorithms before launch, a new digital gas correlation (DGC) method was developed. This method makes it possible to use existing IMG observations to validate the MOPITT retrieval algorithms. The DGC method also allows the retrieval of global troposphere CO from MOPITT, IMG, and TES observations with a consistent algorithm. The retrieved CO profiles can be intercompared, and a consistent long time series of tropospheric CO measurements can be created. In this paper, the DGC method is described. The procedures for using the DGC method to retrieve atmospheric trace species profiles are discussed. As an example, CO profiles from IMG observations have been retrieved with the DGC method as a demonstration of its feasibility and application in MOPITT retrieval algorithm validation.

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Matthew H. Hitchman, Conway B. Leovy, John C. Gille, and Paul L. Bailey

Abstract

Data from the Limb Infrared Monitor of the Stratosphere (LIMS) are used to identify a new type of planetary scale disturbance in the equatorial lower mesosphere during northern winter 1978/79. The disturbances consist of two or three vertically stacked temperature extrema of alternating sign. They persist for as long as two weeks and do not propagate. Their occurrence is confined to regions of very weak or negative inertial stability, and their meridional to vertical aspect ratio, meridional structure and zonal spectrum are consistent with disturbances predicted by inertial instability theory. However, they are found only when there is strong forcing of the subtropical mesosphere by zonal wavenumber one and two Rossby waves. This fact, together with the absence of zonal propagation, suggests that stationary Rossby waves determine their occurrence and longitudinal structure. These structures can significantly modify the zonal mean flow and should be taken into account in dynamical models of the equatorial mesosphere.

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Jinxue Wang, John C. Gille, Paul L. Bailey, James R. Drummond, and Liwen Pan

Abstract

Measurement of Pollution in the Troposphere (MOPITT) is an eight-channel gas correlation radiometer selected for the Earth Observing System AM-1 platform to be launched in 1999. Its primary objectives are the measurement of tropospheric carbon monoxide (CO) and methane (CH4). In this paper, the sensitivities of instrument signals and CO retrieval errors to various instrument parameters, especially the gas cell pressure and temperature variations, instrument radiometric noise, and ancillary data errors (such as atmospheric temperature and water vapor profile errors), are presented and discussed. In the MOPITT pressure modulator cell pressure sensitivity study, the instrument calibration process is considered, which leads to the relaxation of previous stringent requirements on the accuracy of in-orbit cell pressure monitoring. The approach of MOPITT CO retrieval error analysis is described, and the error analysis results are compared with retrieval simulation statistics. The error analysis results indicate that tropospheric CO distributions can be retrieved with a precision of 10% for most of the troposphere.

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William J. Randel, Byron A. Boville, John C. Gille, Paul L. Bailey, Steven T. Massie, J. B. Kumer, J. L. Mergenthaler, and A. E. Roche

Abstract

Global variability and budgets of stratospheric nitrous oxide (N2O) are studied using output from a stratospheric version of the NCAR Community Climate Model. The model extends over 0–80 km, incorporating an N2O-like tracer with tropospheric source and upper-stratospheric photochemical sink, the latter parameterized using linear damping rates obtained from detailed two-dimensional model calculations. Results from the model over several seasonal cycles are compared with observations of N2O from the Cryogenic Limb Array Etalon Spectrometer instrument on the Upper Atmosphere Research Satellite. The model produces N2O structure and variability that is in reasonable agreement with the observations. Global budgets of stratospheric N2O are furthermore analyzed using model output, based on the transformed Eulerian-mean, zonal-mean framework. These budgets are used to quantify the importance of planetary wave constituent transport in the stratosphere, for both slow seasonal variations and fast planetary wave events. These results demonstrate that such wave fluxes act to form and sharpen the strong subtropical N2O gradients observed in satellite measurements.

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