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- Author or Editor: Miguel A. Gaertner x
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Abstract
A new method for vertical interpolation of the mass field, starting from data on standard p levels, has been devised. The method extracts information about vertical temperature profiles from geopotential values on these levels, thus recovering part of the relevant details about atmospheric thermal stratification that get lost in this widely used type of representation. Through the proposed procedure, a vertical temperature profile with a piece-wise linear dependence on height is obtained. It conserves original geopotential thicknesses while maintaining the initial temperature values on standards p levels. By statistically comparing the method with usual interpolations of T and ϕ, it is shown that the proposed method provides a clearly better reproduction of internal and potential energy of atmospheric columns. This feature may be important, for example, in the assignment of initial and boundary values for numerical simulations, where a correct model reproduction of thermal stratification is essential.
Abstract
A new method for vertical interpolation of the mass field, starting from data on standard p levels, has been devised. The method extracts information about vertical temperature profiles from geopotential values on these levels, thus recovering part of the relevant details about atmospheric thermal stratification that get lost in this widely used type of representation. Through the proposed procedure, a vertical temperature profile with a piece-wise linear dependence on height is obtained. It conserves original geopotential thicknesses while maintaining the initial temperature values on standards p levels. By statistically comparing the method with usual interpolations of T and ϕ, it is shown that the proposed method provides a clearly better reproduction of internal and potential energy of atmospheric columns. This feature may be important, for example, in the assignment of initial and boundary values for numerical simulations, where a correct model reproduction of thermal stratification is essential.
Abstract
The forcing mechanisms of the diurnal thermal depression formed over the Iberian Peninsula in the summer and the typical air circulation induced over the Northern Plateau are analyzed by a two-dimensional hydrostatic, high-resolution, primitive equation model applied in a vertical plane perpendicular to the coastline of the Bay of Biscay. Such circulation is characterized by a low-level flow of relatively cold air that progresses inward over the elevated central plateau throughout the afternoon and evening, reaching inland distances up to 150 km at dawn, which tends to fill up the already formed thermal depression. Despite the simplicity of the model, the results obtained show a satisfactory agreement with observations. Finally, a comparison is made between results obtained from a set of simulations with different combinations of land-use types, topographic profiles, thermal stability, and synoptic wind, keeping the other conditions fixed, in order to analyze the individual effects of different terrain and atmospheric-related forcings.
Abstract
The forcing mechanisms of the diurnal thermal depression formed over the Iberian Peninsula in the summer and the typical air circulation induced over the Northern Plateau are analyzed by a two-dimensional hydrostatic, high-resolution, primitive equation model applied in a vertical plane perpendicular to the coastline of the Bay of Biscay. Such circulation is characterized by a low-level flow of relatively cold air that progresses inward over the elevated central plateau throughout the afternoon and evening, reaching inland distances up to 150 km at dawn, which tends to fill up the already formed thermal depression. Despite the simplicity of the model, the results obtained show a satisfactory agreement with observations. Finally, a comparison is made between results obtained from a set of simulations with different combinations of land-use types, topographic profiles, thermal stability, and synoptic wind, keeping the other conditions fixed, in order to analyze the individual effects of different terrain and atmospheric-related forcings.
Abstract
Thirteen regional climate model (RCM) simulations of June–July 1993 were compared with each other and observations. Water vapor conservation and precipitation characteristics in each RCM were examined for a 10° × 10° subregion of the upper Mississippi River basin, containing the region of maximum 60-day accumulated precipitation in all RCMs and station reports.
All RCMs produced positive precipitation minus evapotranspiration (P − E > 0), though most RCMs produced P − E below the observed range. RCM recycling ratios were within the range estimated from observations. No evidence of common errors of E was found. In contrast, common dry bias of P was found in the simulations.
Daily cycles of terms in the water vapor conservation equation were qualitatively similar in most RCMs. Nocturnal maximums of P and C (convergence) occurred in 9 of 13 RCMs, consistent with observations. Three of the four driest simulations failed to couple P and C overnight, producing afternoon maximum P. Further, dry simulations tended to produce a larger fraction of their 60-day accumulated precipitation from low 3-h totals.
In station reports, accumulation from high (low) 3-h totals had a nocturnal (early morning) maximum. This time lag occurred, in part, because many mesoscale convective systems had reached peak intensity overnight and had declined in intensity by early morning. None of the RCMs contained such a time lag. It is recommended that short-period experiments be performed to examine the ability of RCMs to simulate mesoscale convective systems prior to generating long-period simulations for hydroclimatology.
Abstract
Thirteen regional climate model (RCM) simulations of June–July 1993 were compared with each other and observations. Water vapor conservation and precipitation characteristics in each RCM were examined for a 10° × 10° subregion of the upper Mississippi River basin, containing the region of maximum 60-day accumulated precipitation in all RCMs and station reports.
All RCMs produced positive precipitation minus evapotranspiration (P − E > 0), though most RCMs produced P − E below the observed range. RCM recycling ratios were within the range estimated from observations. No evidence of common errors of E was found. In contrast, common dry bias of P was found in the simulations.
Daily cycles of terms in the water vapor conservation equation were qualitatively similar in most RCMs. Nocturnal maximums of P and C (convergence) occurred in 9 of 13 RCMs, consistent with observations. Three of the four driest simulations failed to couple P and C overnight, producing afternoon maximum P. Further, dry simulations tended to produce a larger fraction of their 60-day accumulated precipitation from low 3-h totals.
In station reports, accumulation from high (low) 3-h totals had a nocturnal (early morning) maximum. This time lag occurred, in part, because many mesoscale convective systems had reached peak intensity overnight and had declined in intensity by early morning. None of the RCMs contained such a time lag. It is recommended that short-period experiments be performed to examine the ability of RCMs to simulate mesoscale convective systems prior to generating long-period simulations for hydroclimatology.
