Outgoing longwave radiation at the top of the atmosphere: preliminary assessment using GOES-8 imager data

Abstract

GOES-8 Imager radiances in water vapor and infrared channels 3, 4 and 5 were used for assessing outgoing longwave radiation (OLR) at the top of the atmosphere. Estimation by ITPP5 software applied to HIRS/NOAA 14 passes over Brazil was considered as true reference. Imagery from both satellites is currently acquired and processed at CPTEC/INPE. GOES full-resolution imagery allows assessment of mean irradiance for sets of GOES pixels contained within the area of a single HIRS pixel. Additional GOES variables were estimated, such as: an equivalent channel at 8 mm and a longwave tail for l>15 mm (this one is not detected neither by HIRS nor GOES sensors). Isotropic outgoing radiance was assumed. Multivariate regression of GOES irradiances on OLR ITPP estimates provided a GOES estimator with accuracy comparable with others already published and based on AVHRR/NOAA information. It was found that a regression based only on channel 4 and the longwave tail yielded estimates with the same accuracy: mean deviation of 3 W.m -2 and standard deviation of 11 W.m -2. The application for another period in the year, averaged over 1°´1° grid cells, yielded similar mean deviation and standard deviation of 7 W.m -2. These results suggest that the algorithm applied in this work has physical rather than purely statistical meaning and could be used for OLR monitoring in daily and seasonal scales.Keywords: Outgoing Longwave Radiation (OLR), GOES 8 Imager, NOAA 14, Terrestrial Radiation RESUMO Radiâncias obtidas do satélite GOES 8 nos canais de vapor dágua e infravermelho termal (2, 4 e 5) foram utilizadas para estimar Radiação de Onda Longa (ROL) emergente no topo da atmosfera. As estimativas de ROL pelo utilitário ITPP5, aplicadas à informação do sensor HIRS/NOAA, foram consideradas como verdade de referência. Imagens dos dois satélites são continuamente recebidas e processadas no CPTEC/INPE. As imagens GOES de alta resolução permitiram considerar grupos de pixels (e a irradiância média correspondente) contidos na área de um único pixel HIRS. Variáveis adicionais foram elaboradas, como por exemplo: um canal equivalente em 8 mm e uma cauda espectral de onda longa para l>15 mm (esta última, não detectada nem pelo HIRS nem pelo GOES). Assumiu-se a hipótese de isotropia para a radiância emergente. Regressão multivariada das irradiâncias GOES com relação à estimativa ITPP da ROL forneceu um estimador GOES com precisão comparável à de outros já publicados e baseados na informação de AVHRR/NOAA. Verificou-se que uma regressão baseada apenas nas irradiâncias do canal 4 e da cauda de onda longa fornece estimativas com a mesma precisão: erro médio de 3 W.m -2 e desvio padrão de 11 W.m -2. A aplicação do algoritmo para outra época do ano, avaliando médias em células de 1°´1°, produz um desvio médio similar e um desvio padrão de 7 W.m -2. Estes resultados sugerem que o algoritmo resgatou propriedades físicas e não simplesmente estatísticas da ROL, e poderia ser aplicado para monitoramento de ROL em escala diária e sazonal.

Dynamic Characteristics of the Circulation and Diurnal Spatial Cycle of Outgoing Longwave Radiation in the Different Phases of the Madden–Julian Oscillation during the Formation of the South Atlantic Convergence Zone

“…Thus, OLR data from the DSA of very high temporal resolution (3 h) were used to verify the diurnal space cycle in the SA and, consequently, the SACZ events in the different phases of the MJO. The estimated OLR data are based on the works of Ceballos et al [42], which show consistency with the National Center for Environmental Prediction's (NCEP) data, having high-quality and mainly covering extensive areas of SA every 3 h.…”

“…The spatial diurnal cycle of the estimated OLR data [42] presented values above those found in the NOAA data [59] but coherent in the resolution, which can be used for studying the temporal evolution of convective processes in the South American continent. The beginning of intense convective activity started at 18 UTC, intensified at 21 UTC, and dissipated at 15 UTC.…”