Georgia Codato

Radiation balance at the surface in the city of São Paulo, Brazil: diurnal and seasonal variations

The main goal of this work is to describe the diurnal and seasonal variations of the radiation balance components at the surface in the city of São Paulo based on observations carried out during 2004. Monthly average hourly values indicate that the amplitudes of the diurnal cycles of net radiation (Q*), downwelling and upwelling shortwave radiation (SWDW, SWUP), and longwave radiations (LWDW, LWUP) in February were, respectively, 37%, 14%, 19%, 11%, and 5% larger than they were in August. The monthly average daily values indicate a variation of 60% for Q*, with a minimum in June and a maximum in December; 45% for SWDW, with a minimum in May and a maximum in September; 50% for SWUP, with a minimum in June and a maximum in September; 13% for LWDW, with a minimum in July and a maximum in January; and 9% for LWUP, with a minimum in July and a maximum in February. It was verified that the atmospheric broadband transmissivity varied from 0.36 to 0.57; the effective albedo of the surface varied from 0.08 to 0.10; and the atmospheric effective emissivity varied from 0.79 to 0.92. The surface effective emissivity remained approximately constant and equal to 0.96. The albedo and surface effective emissivity for São Paulo agreed with those reported for urban areas in Europe and North America cities. This indicates that material and geometric effects on albedo and surface emissivity in São Paulo are similar to ones observed in typical middle latitudes cities. On the other hand, it was found that São Paulo city induces an urban heat island with daytime maximum intensity varying from 2.6°C in July (16:00 LT) to 5.5°C in September (15:00 LT). The analysis of the radiometric properties carried out here indicate that this daytime maximum is a primary response to the seasonal variation of daily values of net solar radiation at the surface.

Observational Characterization of the Downward Atmospheric Longwave Radiation at the Surface in the City of São Paulo

This work describes the seasonal and diurnal variations of downward longwave atmospheric irradiance (LW) at the surface in Sao Paulo, Brazil, using 5-min-averaged values of LW, air temperature, relative hu- midity, and solar radiation observed continuously and simultaneously from 1997 to 2006 on a micrometeo- rological platform, located at the top of a 4-story building. An objective procedure, including 2-step filtering and dome emission effect correction, was used to evaluate the quality of the 9-yr-long LW dataset. The comparison between LW values observed and yielded by the Surface Radiation Budget project shows spatial and temporal agreement, indicating that monthly and annual average values of LW observed in one point of Sao Paulo can be used as representative of the entire metropolitan region of Sao Paulo. The maximum monthly averaged value of the LW is observed during summer (389 6 14 W m 22 ; January), and the minimum is observed during winter (332 6 12 W m 22 ; July). The effective emissivity follows the LW and shows a maximum in summer (0.907 6 0.032; January) and a minimum in winter (0.818 6 0.029; June). The mean cloud effect, identified objectively by comparing the monthly averaged values of the LW during clear-sky days and all-sky conditions, intensified the monthly average LW by about 32.0 6 3.5 W m 22 and the atmospheric effective emissivity by about 0.088 6 0.024. In August, the driest month of the year in Sao Paulo, the diurnal evolution of the LW shows a minimum (325 6 11 W m 22 ) at 0900 LT and a maximum (345 6 12 W m 22 )a t 1800 LT, which lags behind (by 4 h) the maximum diurnal variation of the screen temperature. The diurnal evolution of effective emissivity shows a minimum (0.781 6 0.027) during daytime and a maximum (0.842 6 0.030) during nighttime. The diurnal evolution of all-sky condition and clear-sky day differences in the ef- fective emissivity remain relatively constant (7% 6 1%), indicating that clouds do not change the emissivity diurnal pattern. The relationship between effective emissivity and screen air temperature and between ef- fective emissivity and water vapor is complex. During the night, when the planetary boundary layer is shal- lower, the effective emissivity can be estimated by screen parameters. During the day, the relationship be- tween effective emissivity and screen parameters varies from place to place and depends on the planetary boundary layer process. Because the empirical expressions do not contain enough information about the diurnal variation of the vertical stratification of air temperature and moisture in Sao Paulo, they are likely to fail in reproducing the diurnal variation of the surface emissivity. The most accurate way to estimate the LW for clear-sky conditions in Sao Paulo is to use an expression derived from a purely empirical approach.

Energy Balance at the Surface in King George Island - Preliminary Results of Eta Project

In this work the diurnal evolution of the energy balance at the surface is estimated for the King George Island, based on in situ observations of net radiation, soil heat ux and vertical pro les of wind speed, air temperature and speci c humidity measured at the South Tower in the Brazilian Antarctic Station Comandante Ferraz. e turbulent uxes were estimated by adjusting vertical pro les expressions based on the Monin-Obukhov Similarity eory. e diurnal evolution of the energy balance components at the surface indicates, during this period, that the large input of energy causes large imbalance in the surface energy balance. e imbalanced term, estimated also for other periods, seems to be related mainly to the heterogeneity of the land use and topography.

Balanço de Radiação em Superfície na Região Metropolitana do rio de janeiro

The radiation budget at the surface of the Metropolitan Region of Rio de Janeiro was obtained from measurements collected on the radiometric platform located...