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- Author or Editor: M. SANKAR-RAO x
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Abstract
A finite difference procedure is utilized for the solution of a coupled system of two ordinary differential equations governing the time averaged quasi-geostrophic perturbations in the atmosphere. The seasonal changes in the latitudinal mean state are found to introduce important phase changes and reversals in the asymmetric meridional circulation. A hypothetical latitudinal mean stability profile, which resembles many of the latitudinal mean stability profiles generally used in analytical studies, is found to give acceptable results in many cases. Barographic models for the zonal mean state are found to be incapable of giving acceptable quantitative results
Abstract
A finite difference procedure is utilized for the solution of a coupled system of two ordinary differential equations governing the time averaged quasi-geostrophic perturbations in the atmosphere. The seasonal changes in the latitudinal mean state are found to introduce important phase changes and reversals in the asymmetric meridional circulation. A hypothetical latitudinal mean stability profile, which resembles many of the latitudinal mean stability profiles generally used in analytical studies, is found to give acceptable results in many cases. Barographic models for the zonal mean state are found to be incapable of giving acceptable quantitative results
Abstract
Within the framework of a quasi-geostrophic model, the influence of different kinds of vertical profiles of diabatic heating on a stationary harmonic of the atmosphere is studied. Except in the cases in which there is a diabatic heating reversal in the upper layers of the atmosphere, the results show qualitative similarity, especially in phase. This lends support to the somewhat arbitrarily selected vertical profiles of diabatic heating used in many previous studies.
Abstract
Within the framework of a quasi-geostrophic model, the influence of different kinds of vertical profiles of diabatic heating on a stationary harmonic of the atmosphere is studied. Except in the cases in which there is a diabatic heating reversal in the upper layers of the atmosphere, the results show qualitative similarity, especially in phase. This lends support to the somewhat arbitrarily selected vertical profiles of diabatic heating used in many previous studies.
Abstract
Computations for the northward local eddy flux of heat are presented for twelve Indian stations, for a period of one year. Over India the local eddy flux term appears to contribute little towards the total flux required by the hemispheric radiative imbalance. The seasonal changes of the local eddy flux of latent heat are related to the monsoon pattern.
Abstract
Computations for the northward local eddy flux of heat are presented for twelve Indian stations, for a period of one year. Over India the local eddy flux term appears to contribute little towards the total flux required by the hemispheric radiative imbalance. The seasonal changes of the local eddy flux of latent heat are related to the monsoon pattern.
Abstract
No abstract available.
Abstract
No abstract available.
Abstract
An observational analysis is made of the magnitudes of individual terms in the potential vorticity equation applied to the normal January and July maps for the Northern Hemisphere. From the measurements along 45N an estimate is made of the total “forcing function” for the asymmetric disturbances. Cross sections along 30, 45, and 6ON of the mean meridional velocity and mean temperature and hemispheric distributions of a measure of the normal static stability are also shown.
Abstract
An observational analysis is made of the magnitudes of individual terms in the potential vorticity equation applied to the normal January and July maps for the Northern Hemisphere. From the measurements along 45N an estimate is made of the total “forcing function” for the asymmetric disturbances. Cross sections along 30, 45, and 6ON of the mean meridional velocity and mean temperature and hemispheric distributions of a measure of the normal static stability are also shown.
Abstract
Kurihara and Holloway have proposed an integration scheme that offers advantages in the problems of geophysical fluid dynamics by rigorously conserving mass and energy. We have attempted to investigate the accuracy of the Kurihara and Holloway method by numerical experiments, applying it to a problem for which an approximate analytic solution is available.
For the case in which the planetary wave number is 4, we find that with the equal-area grid and with a latitude grid spacing of 4.5°, the planetary wave is destroyed by truncation errors within 5 days. In order to achieve a solution with acceptable accuracy, in which the planetary wave character is retained for a minimum of 10 days, the grid spacing near the Pole has to be decreased by a factor of 9.
Abstract
Kurihara and Holloway have proposed an integration scheme that offers advantages in the problems of geophysical fluid dynamics by rigorously conserving mass and energy. We have attempted to investigate the accuracy of the Kurihara and Holloway method by numerical experiments, applying it to a problem for which an approximate analytic solution is available.
For the case in which the planetary wave number is 4, we find that with the equal-area grid and with a latitude grid spacing of 4.5°, the planetary wave is destroyed by truncation errors within 5 days. In order to achieve a solution with acceptable accuracy, in which the planetary wave character is retained for a minimum of 10 days, the grid spacing near the Pole has to be decreased by a factor of 9.
Abstract
Two smoothing techniques are tested as a practical means of allowing a larger time step in the numerical integration of a primitive equation free-surface model. The numerical integration uses a finite-difference grid and operators based on the method of Kurihara and Holloway.
A time step six times larger can be used with a corresponding six-fold decrease in computer time, by implementing the weighted averaging procedure given by Langlois and Kwok in their description of the Mintz-Arakawa general circulation model. A Fourier filtering scheme permits the use of a time step 10 times larger, and results in a five-fold improvement in computer time. After 10 days, the geopotential and wind fields obtained with these techniques still closely resemble the unsmoothed fields, the closest correspondence being found with the Fourier filtering technique.
In another set of experiments, steady-state solutions to special cases of the governing analytic equations are used as initial conditions in a test of the accuracy of the grid and operators. These steady-state solutions are preserved satisfactorily for the 10-day integration period.
Abstract
Two smoothing techniques are tested as a practical means of allowing a larger time step in the numerical integration of a primitive equation free-surface model. The numerical integration uses a finite-difference grid and operators based on the method of Kurihara and Holloway.
A time step six times larger can be used with a corresponding six-fold decrease in computer time, by implementing the weighted averaging procedure given by Langlois and Kwok in their description of the Mintz-Arakawa general circulation model. A Fourier filtering scheme permits the use of a time step 10 times larger, and results in a five-fold improvement in computer time. After 10 days, the geopotential and wind fields obtained with these techniques still closely resemble the unsmoothed fields, the closest correspondence being found with the Fourier filtering technique.
In another set of experiments, steady-state solutions to special cases of the governing analytic equations are used as initial conditions in a test of the accuracy of the grid and operators. These steady-state solutions are preserved satisfactorily for the 10-day integration period.
Abstract
In this work, the interannual variability of the Asian summer monsoon is studied by analyzing outputs of the Atmospheric Model Intercomparison Project integration using the Goddard Laboratory for Atmospheres general circulation model. The main effort is devoted to exploring and understanding precursory signals associated with the interannual variability of the Asian monsoon and deciphering possible physical mechanisms responsible for the signals.
It is found that strong precursory signals of highly anomalous Asian summer monsoon appear over the subtropical Asian region during the previous winter-spring seasons. Prior to a strong summer monsoon, the westerlies over subtropical Asia are weaker than normal, and vice versa. Dynamically consistent changes are found in other fields such as atmospheric temperature, geopotential height, and surface temperature. These precursory signals seem to have a barotropic structure in the troposphere. They exist over a broad region and last for two to three seasons. The robustness of the signals is important for improving seasonal prediction of the Asian summer monsoon.
It is hypothesized that the above-described precursory signals of the Asian summer monsoon are linked to land-surface hydrologic processes, such as changes in snow mass and soil moisture in the Asian continent, as well as anomalous sea surface temperature forcing in the Pacific and Indian Oceans. Evidence in support of the above hypothesis can be found in the variability of a variety of parameters from both model simulation and observations.
Abstract
In this work, the interannual variability of the Asian summer monsoon is studied by analyzing outputs of the Atmospheric Model Intercomparison Project integration using the Goddard Laboratory for Atmospheres general circulation model. The main effort is devoted to exploring and understanding precursory signals associated with the interannual variability of the Asian monsoon and deciphering possible physical mechanisms responsible for the signals.
It is found that strong precursory signals of highly anomalous Asian summer monsoon appear over the subtropical Asian region during the previous winter-spring seasons. Prior to a strong summer monsoon, the westerlies over subtropical Asia are weaker than normal, and vice versa. Dynamically consistent changes are found in other fields such as atmospheric temperature, geopotential height, and surface temperature. These precursory signals seem to have a barotropic structure in the troposphere. They exist over a broad region and last for two to three seasons. The robustness of the signals is important for improving seasonal prediction of the Asian summer monsoon.
It is hypothesized that the above-described precursory signals of the Asian summer monsoon are linked to land-surface hydrologic processes, such as changes in snow mass and soil moisture in the Asian continent, as well as anomalous sea surface temperature forcing in the Pacific and Indian Oceans. Evidence in support of the above hypothesis can be found in the variability of a variety of parameters from both model simulation and observations.
