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- Author or Editor: John C. Gille x
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Abstract
An analysis based on radiative decay times allows the quantitative calculation of the effects of thermal radiation on acoustic wave propagation in an infinite non-gray atmosphere. Computations for the earth's troposphere, Mars, Venus, and ammonia in the laboratory show that in no case is measurable alteration of the propagation velocity predicted, but radiation is the main damping mechanism at low frequencies. Calculated damping is consistent with atmospheric observations. Laboratory demonstration of this effect is probably not possible in air, but appears feasible in low pressure ammonia. Acoustic wave propagation at high altitudes (low pressures) is shown to be adiabatic, contrary to a suggestion by Golitsyn. An approximate treatment to include the effects of the finite depth of the atmosphere shows that the results are somewhat altered in detail. An important finding is that for this problem a non-gray atmosphere cannot be usefully approximated by one or more gray coefficients. A simple approximation to the effective absorption coefficient is suggested.
Abstract
An analysis based on radiative decay times allows the quantitative calculation of the effects of thermal radiation on acoustic wave propagation in an infinite non-gray atmosphere. Computations for the earth's troposphere, Mars, Venus, and ammonia in the laboratory show that in no case is measurable alteration of the propagation velocity predicted, but radiation is the main damping mechanism at low frequencies. Calculated damping is consistent with atmospheric observations. Laboratory demonstration of this effect is probably not possible in air, but appears feasible in low pressure ammonia. Acoustic wave propagation at high altitudes (low pressures) is shown to be adiabatic, contrary to a suggestion by Golitsyn. An approximate treatment to include the effects of the finite depth of the atmosphere shows that the results are somewhat altered in detail. An important finding is that for this problem a non-gray atmosphere cannot be usefully approximated by one or more gray coefficients. A simple approximation to the effective absorption coefficient is suggested.
Inversion of satellite radiometer measurements to yield values of atmospheric parameters is expected to be an important source of data within the next few years. A review of inversion methods, based in part on a recent workshop, is presented to outline their present status. General considerations indicate that fine structure will not be resolved, and that the number of parameters determined may be less than the number of measurements. Using infrared data, temperature profiles appear to be inferable with an accuracy of about ±3K, and water vapor distributions may be obtained, over clear skies or broken cloud. Microwave measurements appear to allow temperature determinations with similar accuracy which are less affected by underlying cloud. Water vapor and cloud liquid water content can also be determined, although there are engineering problems. Inversion of visible and ultraviolet data is not as far advanced, but may yield ozone distributions, cloud top heights and information on aerosols. A few of the present problem areas are mentioned.
Inversion of satellite radiometer measurements to yield values of atmospheric parameters is expected to be an important source of data within the next few years. A review of inversion methods, based in part on a recent workshop, is presented to outline their present status. General considerations indicate that fine structure will not be resolved, and that the number of parameters determined may be less than the number of measurements. Using infrared data, temperature profiles appear to be inferable with an accuracy of about ±3K, and water vapor distributions may be obtained, over clear skies or broken cloud. Microwave measurements appear to allow temperature determinations with similar accuracy which are less affected by underlying cloud. Water vapor and cloud liquid water content can also be determined, although there are engineering problems. Inversion of visible and ultraviolet data is not as far advanced, but may yield ozone distributions, cloud top heights and information on aerosols. A few of the present problem areas are mentioned.
Abstract
Zonal-mean gravity wave variance in the Limb Infrared Monitor of the Stratosphere (LIMS) temperature data is seen to correlate strongly with the residual term in the LIMS zonal-mean momentum budget throughout much of the observed mesosphere. This momentum residual is attributed to gravity wave momentum transport at scales that cannot be directly sampled by the LIMS instrument Correlation is highest in the vicinity of the fall and winter mesospheric jets, where both gravity wave variance and momentum residual reach their largest values. Correlation is also high in the Southern Hemisphere subtropical mesophere, where gravity wave variance and the momentum residual have broad temporal maxima during the easterly acceleration of the stratopause semi-annual oscillation (SAO). This subtropical correlation has important implications for the SAO eastward acceleration, which several studies suggest is forced by gravity wave momentum flux divergence. Correlation between gravity wave variance and inferred gravity wave momentum flux divergence is unexpected because variance is dominated by large scales and long periods (inertio–gravity waves), while both theoretical arguments and ground-based observations indicate that momentum transport is dominated by periods under 1 h. The results of this study suggest a broadband gravity wave field experiencing forcing and loss processes, which are largely independent of frequency.
Abstract
Zonal-mean gravity wave variance in the Limb Infrared Monitor of the Stratosphere (LIMS) temperature data is seen to correlate strongly with the residual term in the LIMS zonal-mean momentum budget throughout much of the observed mesosphere. This momentum residual is attributed to gravity wave momentum transport at scales that cannot be directly sampled by the LIMS instrument Correlation is highest in the vicinity of the fall and winter mesospheric jets, where both gravity wave variance and momentum residual reach their largest values. Correlation is also high in the Southern Hemisphere subtropical mesophere, where gravity wave variance and the momentum residual have broad temporal maxima during the easterly acceleration of the stratopause semi-annual oscillation (SAO). This subtropical correlation has important implications for the SAO eastward acceleration, which several studies suggest is forced by gravity wave momentum flux divergence. Correlation between gravity wave variance and inferred gravity wave momentum flux divergence is unexpected because variance is dominated by large scales and long periods (inertio–gravity waves), while both theoretical arguments and ground-based observations indicate that momentum transport is dominated by periods under 1 h. The results of this study suggest a broadband gravity wave field experiencing forcing and loss processes, which are largely independent of frequency.
Abstract
A new model has been developed for calculating vertical profiles of longwave irradiance and heating rates. The infrared active bands taken into account include the pure rotational water vapor, the 6.3 µm water vapor, the 15 µm carbon dioxide, the 14 and 9.6 µm ozone, the 7.66 µm methane and the 7.78 µm nitrous oxide band systems. Nimbus 3 IRIS radiance spectra obtained on clear days near the BOMEX array were compared with theoretically calculated spectra to test the spectral and frequency integrated quality of the calculations for the 400 to 1400 cm−1 region. These comparisons combined with pessimistic estimates of errors in spectral regions not observed indicate that the clear-sky upward flux at the top of the atmosphere may be calculated to within 3%.
Abstract
A new model has been developed for calculating vertical profiles of longwave irradiance and heating rates. The infrared active bands taken into account include the pure rotational water vapor, the 6.3 µm water vapor, the 15 µm carbon dioxide, the 14 and 9.6 µm ozone, the 7.66 µm methane and the 7.78 µm nitrous oxide band systems. Nimbus 3 IRIS radiance spectra obtained on clear days near the BOMEX array were compared with theoretically calculated spectra to test the spectral and frequency integrated quality of the calculations for the 400 to 1400 cm−1 region. These comparisons combined with pessimistic estimates of errors in spectral regions not observed indicate that the clear-sky upward flux at the top of the atmosphere may be calculated to within 3%.
Abstract
The theory and data for calculating the positions, intensifies, and half-widths of the spectral lines of ammonia with frequencies <1400 cm−1 are described. The ground state rotation, μ2, 2ν2− ν2, and the rotation-inversion bands of ν2 and 2ν2 were included. The quantities necessary to fit a random-exponential band model are tabulated in 25 cm−1 intervals for temperatures from 100 to 225K at 25K intervals. Temperature and pressure corrections to the half-widths for application to the Jovian atmosphere are given. Consideration of the line shape suggests that opacity in the 200–700 cm−1, interval will be due to local lines, except possibly at very low temperatures and high pressures.
Abstract
The theory and data for calculating the positions, intensifies, and half-widths of the spectral lines of ammonia with frequencies <1400 cm−1 are described. The ground state rotation, μ2, 2ν2− ν2, and the rotation-inversion bands of ν2 and 2ν2 were included. The quantities necessary to fit a random-exponential band model are tabulated in 25 cm−1 intervals for temperatures from 100 to 225K at 25K intervals. Temperature and pressure corrections to the half-widths for application to the Jovian atmosphere are given. Consideration of the line shape suggests that opacity in the 200–700 cm−1, interval will be due to local lines, except possibly at very low temperatures and high pressures.
Abstract
A detailed numerical integration of the equation of radiative transfer over the 62 µ line of atomic oxygen is described. The results show that the cooling rate h in the lower thermosphere is appreciably lower than the value (hB ) given by Bates’ approximate expression, and may even be negative near the mesopause. For the CIRA atmosphere, h hB = 0.02, 0.21 and 0.50 at altitudes 100, 110 and 120 km, respectively, and reaches 0.88 above 200 km. In relating cooling rates to temperature changes, a calculation of cp is performed which includes the effects of dissociation and accessibility of vibrational levels. The latter leads to an increase of the same order as the former.
Abstract
A detailed numerical integration of the equation of radiative transfer over the 62 µ line of atomic oxygen is described. The results show that the cooling rate h in the lower thermosphere is appreciably lower than the value (hB ) given by Bates’ approximate expression, and may even be negative near the mesopause. For the CIRA atmosphere, h hB = 0.02, 0.21 and 0.50 at altitudes 100, 110 and 120 km, respectively, and reaches 0.88 above 200 km. In relating cooling rates to temperature changes, a calculation of cp is performed which includes the effects of dissociation and accessibility of vibrational levels. The latter leads to an increase of the same order as the former.
Abstract
The calculation of limb radiance as a function of tangent height is shown to require the vertical distribution of temperature and the pressure at one level. Conversely, given the limb radiance curve and the pressure corresponding to one tangent point, it is possible to determine the temperature profile as a function of height relative to the given level, using an iterative technique. If the given pressure is incorrect, there will be systematic errors in the inferred temperatures. This feature may he used to determine the correct pressure by requiring that temperatures inferred from measurements in two spectral regions of differing opacities agree. Results of inverting synthesized realistic data are presented. The data include the effects of water vapor and ozone contamination of the carbon dioxide signal, instrument field of view, and random and systematic noise for real atmospheres having small-scale vertical structure. Results indicate that the temperature may be obtained from the tropopause to 60 km with an rms error <3K. The thickness between the 10- and 1-mb surfaces may also he determined to ±50 m. For measurements spaced 1000 km apart in mid-latitudes, this will yield thermal winds to ±7 m sec−1. Contemplated improvements in the alogrithm and the likelihood of achieving smaller noise figures than those used in the study indicate that better temperature and thickness accuracies and inferences to higher altitudes should he attainable with a real instrument.
Abstract
The calculation of limb radiance as a function of tangent height is shown to require the vertical distribution of temperature and the pressure at one level. Conversely, given the limb radiance curve and the pressure corresponding to one tangent point, it is possible to determine the temperature profile as a function of height relative to the given level, using an iterative technique. If the given pressure is incorrect, there will be systematic errors in the inferred temperatures. This feature may he used to determine the correct pressure by requiring that temperatures inferred from measurements in two spectral regions of differing opacities agree. Results of inverting synthesized realistic data are presented. The data include the effects of water vapor and ozone contamination of the carbon dioxide signal, instrument field of view, and random and systematic noise for real atmospheres having small-scale vertical structure. Results indicate that the temperature may be obtained from the tropopause to 60 km with an rms error <3K. The thickness between the 10- and 1-mb surfaces may also he determined to ±50 m. For measurements spaced 1000 km apart in mid-latitudes, this will yield thermal winds to ±7 m sec−1. Contemplated improvements in the alogrithm and the likelihood of achieving smaller noise figures than those used in the study indicate that better temperature and thickness accuracies and inferences to higher altitudes should he attainable with a real instrument.
Abstract
Small-scale features in temperature data from the Limb Infrared Monitor of the Stratosphere satellite experiment are isolated by subtracting profiles of globally mapped temperatures (containing zonal waves 0—6) from inverted temperature profiles. These features are interpreted as internal gravity waves. The preponderance of the variance is associated with the longest wavelengths, corresponding to the lowest frequencies (inertio-gravity waves). The data include approximately 2000 daily soundings between late October 1978 and late May 1979, all longitudes, latitudes from about 65°S to 85°N, and altitudes from the tropopause to the middle mesosphere (pressures from 100 to 0.1 mb). Zonal-mean gravity wave variance is compared with background winds, and variance maps are presented for five one-week periods: early November, early January, early February, late March, and early May. Time-height plots of zonal mean wave variance and background winds in the latitude bands 45°–55°S, 5°S–5°N, and 45°–55°N are also presented. Variance ranges from about 2.0 K2 in the northern late spring lower stratosphere to about 315 K2 in the northern late fall mesosphere. The Northern Hemisphere gravity wave variance field undergoes an approximate twofold increase between fall and early winter, but the maximum remains quasi-stationary; during the same period the mesospheric jet moves by several thousand kilometers. The Northern Hemisphere gravity wave field is strongly distorted by the late January minor warming, and decreases gradually between early March and late May. The tropical gravity wave variance is approximately constant with time below 40 km, but shows an increasingly strong semiannual signal above 40 km. The tropical maximum extends through January and February but is confined in altitude near 60 km. Southern Hemisphere variance decreases toward a broad minimum in January and February, but climbs rapidly after the autumnal equinox. The gravity wave variance fields during autumn in the two hemispheres are compared and seen to be quite similar, while large interhemispheric differences exist during spring. Background winds in the autumn hemispheres are also similar, while spring winds are different.
Abstract
Small-scale features in temperature data from the Limb Infrared Monitor of the Stratosphere satellite experiment are isolated by subtracting profiles of globally mapped temperatures (containing zonal waves 0—6) from inverted temperature profiles. These features are interpreted as internal gravity waves. The preponderance of the variance is associated with the longest wavelengths, corresponding to the lowest frequencies (inertio-gravity waves). The data include approximately 2000 daily soundings between late October 1978 and late May 1979, all longitudes, latitudes from about 65°S to 85°N, and altitudes from the tropopause to the middle mesosphere (pressures from 100 to 0.1 mb). Zonal-mean gravity wave variance is compared with background winds, and variance maps are presented for five one-week periods: early November, early January, early February, late March, and early May. Time-height plots of zonal mean wave variance and background winds in the latitude bands 45°–55°S, 5°S–5°N, and 45°–55°N are also presented. Variance ranges from about 2.0 K2 in the northern late spring lower stratosphere to about 315 K2 in the northern late fall mesosphere. The Northern Hemisphere gravity wave variance field undergoes an approximate twofold increase between fall and early winter, but the maximum remains quasi-stationary; during the same period the mesospheric jet moves by several thousand kilometers. The Northern Hemisphere gravity wave field is strongly distorted by the late January minor warming, and decreases gradually between early March and late May. The tropical gravity wave variance is approximately constant with time below 40 km, but shows an increasingly strong semiannual signal above 40 km. The tropical maximum extends through January and February but is confined in altitude near 60 km. Southern Hemisphere variance decreases toward a broad minimum in January and February, but climbs rapidly after the autumnal equinox. The gravity wave variance fields during autumn in the two hemispheres are compared and seen to be quite similar, while large interhemispheric differences exist during spring. Background winds in the autumn hemispheres are also similar, while spring winds are different.
Abstract
The signatures of equatorially trapped Kelvin waves in the upper stratosphere are analyzed in Solar Backscatter Ultraviolet (SBUV) ozone data over the years 1979–86. Comparisons are first made with contemporaneous Limb Infrared Monitor of the Stratosphere (LIMS) ozone data to validate the SBUV Kelvin wave signatures. SBUV and LIMS data both show coherent Kelvin wave oscillations in the upper stratosphere, where ozone is photochemically controlled, and mirrors the temperature fluctuations associated with Kelvin waves; however, SBUV data underestimate wave amplitudes by 20%–60%. Furthermore, transport-induced Kelvin wave patterns in the lower stratosphere are not observed in SBUV data. The eight years of SBUV data reveal the regular occurrence of eastward-propagating zonal wave 1–2 Kelvin waves with periods in the range of 5–15 days. These data show a strong semiannual modulation of Kelvin wave activity, as documented previously in rocketsonde observations. Eight-year-average ensemble spectra are compared to the semiannual oscillation (SAO) in stratospheric zonal winds; a seasonal asymmetry in the strength of Kelvin waves is found, which mimics that observed in the zonal winds. There is a near exact phasing of maxima in wave variance with the strongest easterly zonal winds, i.e., when the wind acceleration is near zero; this argues that Kelvin waves are not a determining factor in the westerly acceleration phase. An exception is found near the stratopause in January when Kelvin wave maxima coincide with strong westerly acceleration. Interannual variability of Kelvin waves is studied in relation to that of the stratospheric zonal winds. No consistent relationship with the quasi-biennial oscillation (QBO) in the lower stratosphere is observed, and con-correlations with upper stratospheric winds are weak or nonexistent.
Abstract
The signatures of equatorially trapped Kelvin waves in the upper stratosphere are analyzed in Solar Backscatter Ultraviolet (SBUV) ozone data over the years 1979–86. Comparisons are first made with contemporaneous Limb Infrared Monitor of the Stratosphere (LIMS) ozone data to validate the SBUV Kelvin wave signatures. SBUV and LIMS data both show coherent Kelvin wave oscillations in the upper stratosphere, where ozone is photochemically controlled, and mirrors the temperature fluctuations associated with Kelvin waves; however, SBUV data underestimate wave amplitudes by 20%–60%. Furthermore, transport-induced Kelvin wave patterns in the lower stratosphere are not observed in SBUV data. The eight years of SBUV data reveal the regular occurrence of eastward-propagating zonal wave 1–2 Kelvin waves with periods in the range of 5–15 days. These data show a strong semiannual modulation of Kelvin wave activity, as documented previously in rocketsonde observations. Eight-year-average ensemble spectra are compared to the semiannual oscillation (SAO) in stratospheric zonal winds; a seasonal asymmetry in the strength of Kelvin waves is found, which mimics that observed in the zonal winds. There is a near exact phasing of maxima in wave variance with the strongest easterly zonal winds, i.e., when the wind acceleration is near zero; this argues that Kelvin waves are not a determining factor in the westerly acceleration phase. An exception is found near the stratopause in January when Kelvin wave maxima coincide with strong westerly acceleration. Interannual variability of Kelvin waves is studied in relation to that of the stratospheric zonal winds. No consistent relationship with the quasi-biennial oscillation (QBO) in the lower stratosphere is observed, and con-correlations with upper stratospheric winds are weak or nonexistent.
Abstract
One of the limitations to the accurate calculation of radiative heating and cooling rates in the stratosphere and mesosphere has been the lack of accurate data on the atmospheric temperature and composition. Data from the LIMS experiment on Nimbus-7 have been extended to the South Pole with the aid of other observations. The data have been used as input to codes developed by Ramanathan and Dickinson to calculate the individual components and the net radiative heating rates from 100–0.1 mb. Solar heating due to ozone, nitrogen dioxide, carbon dioxide, water vapor and oxygen is shown to be nearly balanced by cooling in the thermal infrared spectral region due to carbon dioxide, ozone and water vapor. In the lower stratosphere, infrared transfer by ozone leads to heating that is sensitive to the distribution of tropospheric ozone, clouds and water vapor.
The heating and cooling rates are adjusted slightly in order to satisfy the global mass balance. The results are in qualitative agreement with earlier calculations, but show additional detail. There is as strong temporal and vertical variation of cooling in the tropics. Radiative relaxation times are as short as 7 days or less at the stratopause.
Abstract
One of the limitations to the accurate calculation of radiative heating and cooling rates in the stratosphere and mesosphere has been the lack of accurate data on the atmospheric temperature and composition. Data from the LIMS experiment on Nimbus-7 have been extended to the South Pole with the aid of other observations. The data have been used as input to codes developed by Ramanathan and Dickinson to calculate the individual components and the net radiative heating rates from 100–0.1 mb. Solar heating due to ozone, nitrogen dioxide, carbon dioxide, water vapor and oxygen is shown to be nearly balanced by cooling in the thermal infrared spectral region due to carbon dioxide, ozone and water vapor. In the lower stratosphere, infrared transfer by ozone leads to heating that is sensitive to the distribution of tropospheric ozone, clouds and water vapor.
The heating and cooling rates are adjusted slightly in order to satisfy the global mass balance. The results are in qualitative agreement with earlier calculations, but show additional detail. There is as strong temporal and vertical variation of cooling in the tropics. Radiative relaxation times are as short as 7 days or less at the stratopause.
