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Abstract
The residual mean circulation (rmc) has been calculated from the transformed thermodynamic equation using LIMS (Limb Infrared Monitor of the Stratosphere) data for the 100–0.1 mb region. For discussion, it has been divided into two components: the diabatic circulation, associated with the diabatic heating, and the transient circulation, more directly connected to eddy activity. The slowly varying diabatic circulation reveals an equator-to-pole circulation at lower levels in the stratosphere, usually overlain by a summer-to-winter pole circulation. However, there are strong seasonal variations, so that the pole-to-pole circulation fills the entire region at the December solstice, while the equator-to-pole circulation extends to above 0.1 mb at the equinoxes. The transient circulation is characterized by rapid variations and small vertical and horizontal scales. Though generally smaller than the diabatic circulation, it can dominate in the lower stratosphere during disturbed conditions.
This circulation is consistent with the transformed momentum equation in the lower stratosphere (where drag is expected to be small) during undisturbed periods. It suggests a large drag due to small-scale waves (such as gravity waves) in the mesosphere, although the magnitudes are uncertain. The downward propagation of the semiannual oscillation causes the rmc in the tropics to vary, and it is capable of creating the equatorial water vapor maximum above 10 mb.
Abstract
The residual mean circulation (rmc) has been calculated from the transformed thermodynamic equation using LIMS (Limb Infrared Monitor of the Stratosphere) data for the 100–0.1 mb region. For discussion, it has been divided into two components: the diabatic circulation, associated with the diabatic heating, and the transient circulation, more directly connected to eddy activity. The slowly varying diabatic circulation reveals an equator-to-pole circulation at lower levels in the stratosphere, usually overlain by a summer-to-winter pole circulation. However, there are strong seasonal variations, so that the pole-to-pole circulation fills the entire region at the December solstice, while the equator-to-pole circulation extends to above 0.1 mb at the equinoxes. The transient circulation is characterized by rapid variations and small vertical and horizontal scales. Though generally smaller than the diabatic circulation, it can dominate in the lower stratosphere during disturbed conditions.
This circulation is consistent with the transformed momentum equation in the lower stratosphere (where drag is expected to be small) during undisturbed periods. It suggests a large drag due to small-scale waves (such as gravity waves) in the mesosphere, although the magnitudes are uncertain. The downward propagation of the semiannual oscillation causes the rmc in the tropics to vary, and it is capable of creating the equatorial water vapor maximum above 10 mb.
Abstract
Using satellite data from the Nimbus 7 LIMS instrument, a previous study by Smith showed that interactions among planetary waves 1, 2 and 3 in the stratosphere were significant during January 1979. That month was characterized by an exceptionally large wave 1 amplitude in the stratosphere. The present study extends the analysis to the period November 1978–March 1979 to determine the conditions under which wave–wave interactions have a significant effect on variations in wave activity and on wave-mean flow interactions. A quantitative measure of how wave–wave interactions affect the wave activity of zonal waves 1 and 2 is obtained from the potential enstrophy budget.
The results demonstrate that the relative importance of wave–wave versus wave-mean flow interactions depends on the magnitude of the eddy mean wind and potential vorticity relative to the zonal means. When the zonal mean wind is weak, a relatively small amplitude wave tends to behave nonlinearly, whereas when the mean wind is strong, only large amplitude waves are significantly nonlinear. In the 1978–79 winter, the zonal mean wind was weaker and wave–wave interactions were more important in middle and late winter than during November–December.
Further evidence is presented that the vacillation between waves 1 and 2, which has been observed in the winter stratosphere of both hemispheres, is as strongly influenced by wave–wave interactions in the stratosphere as by variations in the forcing from the troposphere.
Abstract
Using satellite data from the Nimbus 7 LIMS instrument, a previous study by Smith showed that interactions among planetary waves 1, 2 and 3 in the stratosphere were significant during January 1979. That month was characterized by an exceptionally large wave 1 amplitude in the stratosphere. The present study extends the analysis to the period November 1978–March 1979 to determine the conditions under which wave–wave interactions have a significant effect on variations in wave activity and on wave-mean flow interactions. A quantitative measure of how wave–wave interactions affect the wave activity of zonal waves 1 and 2 is obtained from the potential enstrophy budget.
The results demonstrate that the relative importance of wave–wave versus wave-mean flow interactions depends on the magnitude of the eddy mean wind and potential vorticity relative to the zonal means. When the zonal mean wind is weak, a relatively small amplitude wave tends to behave nonlinearly, whereas when the mean wind is strong, only large amplitude waves are significantly nonlinear. In the 1978–79 winter, the zonal mean wind was weaker and wave–wave interactions were more important in middle and late winter than during November–December.
Further evidence is presented that the vacillation between waves 1 and 2, which has been observed in the winter stratosphere of both hemispheres, is as strongly influenced by wave–wave interactions in the stratosphere as by variations in the forcing from the troposphere.
Abstract
Observational evidence is presented for planetary scale (zonal wave number 1–2) mixed Rossby–gravity (MRG) waves in the equatorial upper stratosphere (35–50 km). These waves are detected in Limb Infrared Monitor of the Stratosphere (LIMS) measurements as coherently propagating temperature maxima of amplitude 0.1–0.3 K, which are antisymmetric (out of phase) about the equator, centered near 10°–15° north and south latitude. These features have vertical wavelengths of order 10–15 km, periods near 2–3 days, and zonal phase velocities close to 200 m s−1. Both eastward and westward propagating waves are found, and the observed vertical wavelengths and meridional structures are in good agreement with the MRG dispersion relation. Theoretical estimates of the zonal accelerations attributable to these waves suggest they do not contribute substantially to the zonal momentum balance in the middle atmosphere.
Abstract
Observational evidence is presented for planetary scale (zonal wave number 1–2) mixed Rossby–gravity (MRG) waves in the equatorial upper stratosphere (35–50 km). These waves are detected in Limb Infrared Monitor of the Stratosphere (LIMS) measurements as coherently propagating temperature maxima of amplitude 0.1–0.3 K, which are antisymmetric (out of phase) about the equator, centered near 10°–15° north and south latitude. These features have vertical wavelengths of order 10–15 km, periods near 2–3 days, and zonal phase velocities close to 200 m s−1. Both eastward and westward propagating waves are found, and the observed vertical wavelengths and meridional structures are in good agreement with the MRG dispersion relation. Theoretical estimates of the zonal accelerations attributable to these waves suggest they do not contribute substantially to the zonal momentum balance in the middle atmosphere.
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.
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.
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.
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.
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.
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.
Abstract
An examination of satellite-derived temperatures reveals that the winter polar stratopause is usually elevated and warmer than the adjacent midlatitude stratopause. This “separated stratopause” occurs in both hemispheres, but is more pronounced and persistent in the southern winter. It descends with time towards spring and exhibits week to week variability. Observational diagnostics and results from a two dimensional (2-D) model suggest that gravity wave driving can account for this separated polar stratopause by driving a meridional circulation with downwelling over the winter pole. In the model, the solar heating pattern induces stronger winter westerlies than summer easterlies, which leads to a stronger gravity wave driven circulation in the winter hemisphere. Spherical geometry and the high latitude location of the winter westerly jet combine to yield a concentrated region of downwelling. Model results suggest that descent of the temperature maximum with time is probably caused by wave–mean flow interaction.
Abstract
An examination of satellite-derived temperatures reveals that the winter polar stratopause is usually elevated and warmer than the adjacent midlatitude stratopause. This “separated stratopause” occurs in both hemispheres, but is more pronounced and persistent in the southern winter. It descends with time towards spring and exhibits week to week variability. Observational diagnostics and results from a two dimensional (2-D) model suggest that gravity wave driving can account for this separated polar stratopause by driving a meridional circulation with downwelling over the winter pole. In the model, the solar heating pattern induces stronger winter westerlies than summer easterlies, which leads to a stronger gravity wave driven circulation in the winter hemisphere. Spherical geometry and the high latitude location of the winter westerly jet combine to yield a concentrated region of downwelling. Model results suggest that descent of the temperature maximum with time is probably caused by wave–mean flow interaction.
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.
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.
Abstract
The Measurement of Pollution in the Troposphere (MOPITT) instrument is an eight-channel gas correlation radiometer selected for the Earth Observing System (EOS) Terra spacecraft launched in December 1999. Algorithms for the retrieval of tropospheric carbon monoxide (CO) profiles from MOPITT measurements have been developed. In this paper, validation studies of the MOPITT CO retrieval algorithm using observations by the Interferometric Monitor for greenhouse Gases (IMG) during the Winter Clouds Experiment (WINCE) conducted from 23 January to 13 February 1997 are described. Synthetic radiance spectra calculated by a line-by-line radiative transfer model, FASCOD3, using the retrieved CO profile agrees well with IMG-measured radiance spectra. Observations by the Moderate Resolution Imaging Spectrometer (MODIS) Airborne Simulator (MAS) from the NASA ER-2 platform during WINCE were successfully used to assist in the identification of clear and cloudy IMG observations.
Abstract
The Measurement of Pollution in the Troposphere (MOPITT) instrument is an eight-channel gas correlation radiometer selected for the Earth Observing System (EOS) Terra spacecraft launched in December 1999. Algorithms for the retrieval of tropospheric carbon monoxide (CO) profiles from MOPITT measurements have been developed. In this paper, validation studies of the MOPITT CO retrieval algorithm using observations by the Interferometric Monitor for greenhouse Gases (IMG) during the Winter Clouds Experiment (WINCE) conducted from 23 January to 13 February 1997 are described. Synthetic radiance spectra calculated by a line-by-line radiative transfer model, FASCOD3, using the retrieved CO profile agrees well with IMG-measured radiance spectra. Observations by the Moderate Resolution Imaging Spectrometer (MODIS) Airborne Simulator (MAS) from the NASA ER-2 platform during WINCE were successfully used to assist in the identification of clear and cloudy IMG observations.
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.
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.
