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- Author or Editor: S. K. Avery x
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Abstract
A steady-state, linear, quasi-geostrophic model of stationary waves on a sphere is employed to study the lower boundary forcing of airflow over topography and the internal forcing that results from the geographical distribution of diabatic heating. The lower boundary vertical motions forced by airflow over topography are shown to depend on the following: 1) whether or not consideration is made of the horizontal deflection of airflow around topographic features; 2) the level of the wind profile at which flow over topography is assumed to take place; and 3) the topographic data set that was used in the forcing formulation. Different methods of calculating the lower boundary vertical motions give rise to sizeable differences in the calculated planetary waves. Large uncertainties are also found in the modeled results depending on the choices made as to the vertical distribution of the forcing by diabatic heating. Given these uncertainties, the relative roles of topographic forcing and diabatic heating in forcing stationary planetary waves are explored in an alternative manner. The lower boundary forcing is taken to be given by the observed stationary planetary wave in lower boundary (900 mb) geopotential height, and the internal forcing is computed using the planetary wave propagation equation on the observed wave structure. Using this method, it is found that the lower boundary forcing generally accounts for the phase structure of the stationary planetary waves, and the response to the internal forcing generally acts to destructively interfere with the response from the lower boundary forcing. This interference is larger for wavenumber 2 in the stratosphere than for wavenumber 1.
Abstract
A steady-state, linear, quasi-geostrophic model of stationary waves on a sphere is employed to study the lower boundary forcing of airflow over topography and the internal forcing that results from the geographical distribution of diabatic heating. The lower boundary vertical motions forced by airflow over topography are shown to depend on the following: 1) whether or not consideration is made of the horizontal deflection of airflow around topographic features; 2) the level of the wind profile at which flow over topography is assumed to take place; and 3) the topographic data set that was used in the forcing formulation. Different methods of calculating the lower boundary vertical motions give rise to sizeable differences in the calculated planetary waves. Large uncertainties are also found in the modeled results depending on the choices made as to the vertical distribution of the forcing by diabatic heating. Given these uncertainties, the relative roles of topographic forcing and diabatic heating in forcing stationary planetary waves are explored in an alternative manner. The lower boundary forcing is taken to be given by the observed stationary planetary wave in lower boundary (900 mb) geopotential height, and the internal forcing is computed using the planetary wave propagation equation on the observed wave structure. Using this method, it is found that the lower boundary forcing generally accounts for the phase structure of the stationary planetary waves, and the response to the internal forcing generally acts to destructively interfere with the response from the lower boundary forcing. This interference is larger for wavenumber 2 in the stratosphere than for wavenumber 1.
Abstract
The effects of the zonal mean circulation and planetary-wave winds on the distribution of nitric oxide in the 55–120 km height region is investigated. A time-dependent numerical model is used to investigate the interaction between planetary waves and the zonal mean circulation, and the effect of the circulation on the nitric oxide distribution is determined. The initial nitric oxide (NO) distribution is obtained by using a simple source/sink chemistry, vertical eddy diffusion, and advective transport by the zonal mean circulation. Changes in the initial NO distribution which result from the addition of planetary-wave winds are described. Planetary waves are found to induce a wave-like structure in the nitric oxide distribution which resembles that derived from observational data. Planetary waves can affect the nitric oxide concentration in two ways: first,through the wave-induced changes in the mean meridional circulation, and second, through the nitric oxide perturbation induced by wave winds themselves. The changes in total nitric oxide are due primarily to the zonal asymmetries in nitric oxide induced by the planetary waves. Implications of this result for explaining the winter anomaly are discussed.
Abstract
The effects of the zonal mean circulation and planetary-wave winds on the distribution of nitric oxide in the 55–120 km height region is investigated. A time-dependent numerical model is used to investigate the interaction between planetary waves and the zonal mean circulation, and the effect of the circulation on the nitric oxide distribution is determined. The initial nitric oxide (NO) distribution is obtained by using a simple source/sink chemistry, vertical eddy diffusion, and advective transport by the zonal mean circulation. Changes in the initial NO distribution which result from the addition of planetary-wave winds are described. Planetary waves are found to induce a wave-like structure in the nitric oxide distribution which resembles that derived from observational data. Planetary waves can affect the nitric oxide concentration in two ways: first,through the wave-induced changes in the mean meridional circulation, and second, through the nitric oxide perturbation induced by wave winds themselves. The changes in total nitric oxide are due primarily to the zonal asymmetries in nitric oxide induced by the planetary waves. Implications of this result for explaining the winter anomaly are discussed.
Abstract
Satellite-radiance data (Nimbus 5, 6; ≤80 km) and the MSIS-83 model have been used to prepare global zonal-mean gradient winds (30–120 km) for the new CIRA-1986. Here these are supplemented by planetary-wave morphology from the same Nimbus data to provide local gradient winds—the zonal wind and the eddy portion of the meridional wind are calculated by this method. These data are then compared with radar-derived wind contours (∼60–110 km), extending the comparisons done earlier (Manson et al.) for heights below 80 km. Overall the agreement for the zonal winds is good, especially below 80 km; differences are shown so the user can evaluate each product. The comparison of meridional winds is particularly valuable and unique as it reveals considerable ageostrophy, particularly in summer months near the height of the zonal wind's reversal from west- to eastward flow. Coriolis torques due to this meridional flow are available from Saskatoon (52°), Poker Flat (65°), and Tromsö (70°) in the Northern Hemisphere, and Adelaide (35°), Christchurch (44°), and Mawson (68°) in the Southern Hemisphere. Values of 60–100 m s−1 day−1 are generally consistent with estimates of the balancing gravity wave momentum deposition made by direct methods at the same locations.
Abstract
Satellite-radiance data (Nimbus 5, 6; ≤80 km) and the MSIS-83 model have been used to prepare global zonal-mean gradient winds (30–120 km) for the new CIRA-1986. Here these are supplemented by planetary-wave morphology from the same Nimbus data to provide local gradient winds—the zonal wind and the eddy portion of the meridional wind are calculated by this method. These data are then compared with radar-derived wind contours (∼60–110 km), extending the comparisons done earlier (Manson et al.) for heights below 80 km. Overall the agreement for the zonal winds is good, especially below 80 km; differences are shown so the user can evaluate each product. The comparison of meridional winds is particularly valuable and unique as it reveals considerable ageostrophy, particularly in summer months near the height of the zonal wind's reversal from west- to eastward flow. Coriolis torques due to this meridional flow are available from Saskatoon (52°), Poker Flat (65°), and Tromsö (70°) in the Northern Hemisphere, and Adelaide (35°), Christchurch (44°), and Mawson (68°) in the Southern Hemisphere. Values of 60–100 m s−1 day−1 are generally consistent with estimates of the balancing gravity wave momentum deposition made by direct methods at the same locations.
