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Abstract
The horizontal structure of the balances of kinetic energy and total energy simulated by the Oregon State University (OSU) two-level atmospheric general circulation model are studied for January and July on the basis of a three-year simulation with prescribed seasonally-varying solar radiation and sea-surface temperature. The various mechanisms responsible for the local energy changes are identified, and the fulfillment of the energy balance requirement is examined.
In the upper level of the model atmosphere, the horizontal convergence of the kinetic energy flux and the production of kinetic energy through ageostrophic motion tend to balance each other. Thus an upper-level southerly (northerly) ageostrophic flow is induced in the entrance (exit) region of the middle latitude jet stream. In the lower level of the model, the corresponding energy flux convergence and ageostrophic flow are more complicated for different jet stream regions.
In January, the vertical integral of the total energy shows large external heating over the North Pacific and North Atlantic oceans, and cooling over most of the land area of the Northern Hemisphere. In July, an overall seasonal reversal is found. In general, horizontal energy flux convergence is such that energy gained from strong local heating is transported to areas of local heal sinks. Both seasons are also characterized by strong energy flux divergence in the tropics, which is associated with the poleward transport of heat (and momentum). On the global annual average the net frictional dissipation is about 2 W m−2, which is comparable to estimates of the numerical sink of energy within the model as a result of data sampling and inconsistency in the diagnostic schemes.
Abstract
The horizontal structure of the balances of kinetic energy and total energy simulated by the Oregon State University (OSU) two-level atmospheric general circulation model are studied for January and July on the basis of a three-year simulation with prescribed seasonally-varying solar radiation and sea-surface temperature. The various mechanisms responsible for the local energy changes are identified, and the fulfillment of the energy balance requirement is examined.
In the upper level of the model atmosphere, the horizontal convergence of the kinetic energy flux and the production of kinetic energy through ageostrophic motion tend to balance each other. Thus an upper-level southerly (northerly) ageostrophic flow is induced in the entrance (exit) region of the middle latitude jet stream. In the lower level of the model, the corresponding energy flux convergence and ageostrophic flow are more complicated for different jet stream regions.
In January, the vertical integral of the total energy shows large external heating over the North Pacific and North Atlantic oceans, and cooling over most of the land area of the Northern Hemisphere. In July, an overall seasonal reversal is found. In general, horizontal energy flux convergence is such that energy gained from strong local heating is transported to areas of local heal sinks. Both seasons are also characterized by strong energy flux divergence in the tropics, which is associated with the poleward transport of heat (and momentum). On the global annual average the net frictional dissipation is about 2 W m−2, which is comparable to estimates of the numerical sink of energy within the model as a result of data sampling and inconsistency in the diagnostic schemes.
Abstract
The heat and moisture budgets associated with five large nonsquall cloud clusters observed during Phase 3 of the Global Atmospheric Research Program's Atlantic Tropical Experiment (GATE) are investigated. The input data for the budget computations are objectively analyzed fields of wind, temperature and relative humidity that were based on conventional upper-air soundings. Estimates of the radiative heating rate were obtained from Cox and Griffith. A compositing technique is used to summarize the budget results for the growing, mature and dissipating stages of the clusters.
The budgets in the growing stage are characterized by a very large low-level, apparent moisture sink separated in height from the region where the apparent heating is realized. In the mature stage, the apparent heating maximum shifts upward, accompanied by the development of a corresponding secondary maximum of apparent drying. A composite of radiative heating estimates from Cox and Griffith shows that the horizontal radiative heating gradients reach their maximum strength during the mature stage. In the dissipating stage, the apparent heat source is approximately balanced by the apparent moisture sink above the freezing level; below the freezing level, the implied vertical convective flux of sensible and latent heat is approximately constant with height.
The time-dependent behavior of the budgets gives support to the hypothesis of Leary and Houze that the widespread upper-level cloud decks associated with cloud clusters play an active and important role in determining large-scale beat and moisture budgets in the tropics.
Abstract
The heat and moisture budgets associated with five large nonsquall cloud clusters observed during Phase 3 of the Global Atmospheric Research Program's Atlantic Tropical Experiment (GATE) are investigated. The input data for the budget computations are objectively analyzed fields of wind, temperature and relative humidity that were based on conventional upper-air soundings. Estimates of the radiative heating rate were obtained from Cox and Griffith. A compositing technique is used to summarize the budget results for the growing, mature and dissipating stages of the clusters.
The budgets in the growing stage are characterized by a very large low-level, apparent moisture sink separated in height from the region where the apparent heating is realized. In the mature stage, the apparent heating maximum shifts upward, accompanied by the development of a corresponding secondary maximum of apparent drying. A composite of radiative heating estimates from Cox and Griffith shows that the horizontal radiative heating gradients reach their maximum strength during the mature stage. In the dissipating stage, the apparent heat source is approximately balanced by the apparent moisture sink above the freezing level; below the freezing level, the implied vertical convective flux of sensible and latent heat is approximately constant with height.
The time-dependent behavior of the budgets gives support to the hypothesis of Leary and Houze that the widespread upper-level cloud decks associated with cloud clusters play an active and important role in determining large-scale beat and moisture budgets in the tropics.
The South China Sea Monsoon Experiment (SCSMEX) is an international field experiment with the objective to better understand the key physical processes for the onset and evolution of the summer monsoon over Southeast Asia and southern China aiming at improving monsoon predictions. In this article, a description of the major meteorological observation platforms during the intensive observing periods of SCSMEX is presented. In addition, highlights of early results and discussions of the role of SCSMEX in providing valuable in situ data for calibration of satellite rainfall estimates from the Tropical Rainfall Measuring Mission are provided. Preliminary results indicate that there are distinctive stages in the onset of the South China Sea monsoon including possibly strong influences from extratropical systems as well as from convection over the Indian Ocean and the Bay of Bengal. There is some tantalizing evidence of complex interactions between the supercloud cluster development over the Indian Ocean, advancing southwest monsoon flow over the South China Sea, midlatitude disturbances, and the western Pacific subtropical high, possibly contributing to the disastrous flood of the Yangtze River Basin in China during June 1998.
The South China Sea Monsoon Experiment (SCSMEX) is an international field experiment with the objective to better understand the key physical processes for the onset and evolution of the summer monsoon over Southeast Asia and southern China aiming at improving monsoon predictions. In this article, a description of the major meteorological observation platforms during the intensive observing periods of SCSMEX is presented. In addition, highlights of early results and discussions of the role of SCSMEX in providing valuable in situ data for calibration of satellite rainfall estimates from the Tropical Rainfall Measuring Mission are provided. Preliminary results indicate that there are distinctive stages in the onset of the South China Sea monsoon including possibly strong influences from extratropical systems as well as from convection over the Indian Ocean and the Bay of Bengal. There is some tantalizing evidence of complex interactions between the supercloud cluster development over the Indian Ocean, advancing southwest monsoon flow over the South China Sea, midlatitude disturbances, and the western Pacific subtropical high, possibly contributing to the disastrous flood of the Yangtze River Basin in China during June 1998.
