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- Author or Editor: Tatiana A. Tarasova x
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Abstract
Accurate parameterizations for calculating solar radiation absorption in the atmospheric column due to water vapor lines and continuum are proposed for use in broadband shortwave radiative transfer codes. The error in the absorption values is less than 1.5 W m−2 as compared with the values obtained by the line-by-line method for the three standard atmospheres and solar zenith angles of 30° and 75°. The error in the heating rates is less than 0.1 K day−1 at most of the atmospheric levels.
The additional absorption of solar radiation due to the water vapor continuum was also estimated. Its magnitude in the total near-infrared region of the solar spectrum is noticeable and reaches 13.0 W m−2 (6.4% from the water vapor absorption in lines) for the tropical atmosphere and solar zenith angle of 30°. Therefore, using of the proposed parameterizations can help to obtain better agreements between the solar radiative fluxes calculated and measured at the earth’s surface.
Abstract
Accurate parameterizations for calculating solar radiation absorption in the atmospheric column due to water vapor lines and continuum are proposed for use in broadband shortwave radiative transfer codes. The error in the absorption values is less than 1.5 W m−2 as compared with the values obtained by the line-by-line method for the three standard atmospheres and solar zenith angles of 30° and 75°. The error in the heating rates is less than 0.1 K day−1 at most of the atmospheric levels.
The additional absorption of solar radiation due to the water vapor continuum was also estimated. Its magnitude in the total near-infrared region of the solar spectrum is noticeable and reaches 13.0 W m−2 (6.4% from the water vapor absorption in lines) for the tropical atmosphere and solar zenith angle of 30°. Therefore, using of the proposed parameterizations can help to obtain better agreements between the solar radiative fluxes calculated and measured at the earth’s surface.
Abstract
The incident solar radiative fluxes, simulated by an atmospheric general circulation model over South America for the period 1986–88, are compared with the satellite-derived surface fluxes provided by the Surface Radiation Budget (SRB) datasets. The comparison shows that the model systematically overestimates both all-sky and clear-sky SRB fluxes while representing well their latitudinal variations. In order to analyze the reasons for the bias, the shortwave radiation code employed in the model is tested with more comprehensive techniques in a stand-alone mode. The results of testing demonstrate that the code underestimates solar radiation absorption in the clear-sky atmosphere due to trace gases and aerosols. The underestimation of the absorption due to aerosols contributes noticeably to the surface flux bias. The impact of clouds on the surface fluxes is estimated by calculating cloud radiative forcing, defined as the difference between the net surface fluxes in all-sky and clear-sky conditions. The comparison of model-simulated and satellite-derived values of cloud radiative forcing over South America demonstrates that the model simulates fairly well its latitudinal variations and annual cycles as compared with SRB data. However, the model overestimates the SRB surface cloud radiative forcing over the tropical region of South America and underestimates it over the extratropical region in both January and July. The comparisons of the incident surface fluxes simulated by the model at the grid points with those measured at three Amazonian observational sites show good agreement at one site and large discrepancies at the other two sites.
Abstract
The incident solar radiative fluxes, simulated by an atmospheric general circulation model over South America for the period 1986–88, are compared with the satellite-derived surface fluxes provided by the Surface Radiation Budget (SRB) datasets. The comparison shows that the model systematically overestimates both all-sky and clear-sky SRB fluxes while representing well their latitudinal variations. In order to analyze the reasons for the bias, the shortwave radiation code employed in the model is tested with more comprehensive techniques in a stand-alone mode. The results of testing demonstrate that the code underestimates solar radiation absorption in the clear-sky atmosphere due to trace gases and aerosols. The underestimation of the absorption due to aerosols contributes noticeably to the surface flux bias. The impact of clouds on the surface fluxes is estimated by calculating cloud radiative forcing, defined as the difference between the net surface fluxes in all-sky and clear-sky conditions. The comparison of model-simulated and satellite-derived values of cloud radiative forcing over South America demonstrates that the model simulates fairly well its latitudinal variations and annual cycles as compared with SRB data. However, the model overestimates the SRB surface cloud radiative forcing over the tropical region of South America and underestimates it over the extratropical region in both January and July. The comparisons of the incident surface fluxes simulated by the model at the grid points with those measured at three Amazonian observational sites show good agreement at one site and large discrepancies at the other two sites.
Abstract
The Center for Weather Forecasting and Climate Studies–Center for Ocean–Land–Atmosphere Studies (CPTEC–COLA) atmospheric general circulation model (AGCM) is integrated with nine initial conditions for 10 yr to obtain the model climate in an ensemble mode. The global climatological characteristics simulated by the model are compared with observational data, and emphasis is given to the Southern Hemisphere and South America. Evaluation of the model's performance is presented by showing systematic errors of several variables, and anomaly correlation and reproducibility are applied to precipitation. The model is able to simulate the main features of the global climate, and the results are consistent with analyses of other AGCMs. The seasonal cycle is reproduced well in all analyzed variables, and systematic errors occur at the same regions in different seasons. The Southern Hemisphere convergence zones are simulated reasonably well, although the model overestimates precipitation in the southern portions and underestimates it in the northern portions of these systems. The high- and low-level main circulation features such as the subtropical highs, subtropical jet streams, and storm tracks are depicted well by the model, albeit with different intensities from the reanalysis. The stationary waves of the Northern and Southern Hemispheres are weaker in the model; however, the dominant wavenumbers are similar to the observations. The energy budget analysis shows values of some radiative fluxes that are close to observations, but the unbalanced fluxes in the atmosphere and at the surface indicate that the radiation and cloud scheme parameterizations need to be improved. Besides these improvements, changes in the convection scheme and higher horizontal resolution to represent orographic effects better are being planned to improve the model's performance.
Abstract
The Center for Weather Forecasting and Climate Studies–Center for Ocean–Land–Atmosphere Studies (CPTEC–COLA) atmospheric general circulation model (AGCM) is integrated with nine initial conditions for 10 yr to obtain the model climate in an ensemble mode. The global climatological characteristics simulated by the model are compared with observational data, and emphasis is given to the Southern Hemisphere and South America. Evaluation of the model's performance is presented by showing systematic errors of several variables, and anomaly correlation and reproducibility are applied to precipitation. The model is able to simulate the main features of the global climate, and the results are consistent with analyses of other AGCMs. The seasonal cycle is reproduced well in all analyzed variables, and systematic errors occur at the same regions in different seasons. The Southern Hemisphere convergence zones are simulated reasonably well, although the model overestimates precipitation in the southern portions and underestimates it in the northern portions of these systems. The high- and low-level main circulation features such as the subtropical highs, subtropical jet streams, and storm tracks are depicted well by the model, albeit with different intensities from the reanalysis. The stationary waves of the Northern and Southern Hemispheres are weaker in the model; however, the dominant wavenumbers are similar to the observations. The energy budget analysis shows values of some radiative fluxes that are close to observations, but the unbalanced fluxes in the atmosphere and at the surface indicate that the radiation and cloud scheme parameterizations need to be improved. Besides these improvements, changes in the convection scheme and higher horizontal resolution to represent orographic effects better are being planned to improve the model's performance.
