Reduced Wet-Season Length Detected by Satellite Retrievals of Cloudiness over Brazilian Amazonia: A New Methodology

Autor(es)

Sena, Elisa T. ^{[1, 2]} ; Silva Dias, M. A. F. ^[1] ; Carvalho, L. M. V. ^[3] ; Silva Dias, P. L. ^[1]

Afiliação do(s) autor(es)

^[1] Univ Sao Paulo, Inst Astron Geofis & Ciencias Atmosfer, Sao Paulo - Brazil

^[2] Univ Fed Sao Paulo, Escola Paulista Polit Econ & Negocios, Dept Multidisciplinar, Osasco - Brazil

^[3] Univ Calif Santa Barbara, Santa Barbara, CA 93106 - USA

• Tipo de documento: Artigo Científico
• Fonte: Journal of Climate; v. 31, n. 24, p. 9941-9964, DEC 2018.
• Citações Web of Science: 3

Resumo

This study investigates the variability of the seasonal cycle of convection in the Brazilian Amazon basin during the last decades, and examines physical mechanisms that potentially trigger these modifications. A new methodology to evaluate the onset and length of the rainy season using long-term cloud fraction observations from geostationary satellites is proposed and the connection between cloud cycle variability, surface properties, and thermodynamic and dynamic conditions is explored. The results show that cloud cover has significantly decreased over the last decades. The decline in cloudiness is steeper at 1200 UTC (0800 LT), when a trend of up to -6% decade(-1) is observed over the central and eastern Amazon. High-cloud-cover reduction is the major contributor to the observed decline in total cloud fraction. Delayed onsets and a reduction of up to 4 days yr(-1) in the northern and central Amazon wet-season length are observed. Correlation analyses indicate that the El Nino phenomenon affects the interannual variability of cloudiness in the Amazon, leading to delayed onset and early demise of the rainy season. The tropical South Atlantic, the Pacific warm pool, and the North Atlantic tripole also play a small, but significant, role in the Amazon's cloudiness variability. The decrease in cloudiness over the Amazon basin reduces the amount of solar radiation reflected back to space while increasing irradiance at the surface. This local warming alters surface heat fluxes and the atmospheric thermodynamic profile, further affecting cloud development. The strong tendencies reported here indicate a significant shift in the Amazonian hydroclimate during the last few decades. (AU)

• Processo FAPESP: 16/12342-1 - Observações das variações do ciclo de vida de nuvens na Amazônia e seus impactos no balanço radiativo
• Beneficiário: Elisa Thome Sena
• Linha de fomento: Bolsas no Brasil - Pós-Doutorado
• Processo FAPESP: 17/17047-0 - O ciclo de vida de aerossóis e nuvens na Amazônia: emissões biogênicas, emissões de queimadas e impactos no ecossistema
• Beneficiário: Paulo Eduardo Artaxo Netto
• Linha de fomento: Auxílio à Pesquisa - Programa de Pesquisa sobre Mudanças Climáticas Globais - Temático