The effect of optically thin cirrus clouds on solar radiation in Camaguey, Cuba
- ISSN: 1680-7316
- DOI: 10.5194/acp-11-8625-2011
The effect of optically thin cirrus clouds on solar radiation is\nanalyzed by numerical simulation, using lidar measurements of cirrus\nconducted at Camaguey, Cuba. Sign and amplitude of the cirrus clouds\neffect on solar radiation is evaluated. There is a relation between the\nsolar zenith angle and solar cirrus cloud radiative forcing (SCRF)\npresent in the diurnal cycle of the SCRF. Maximums of SCRF out of noon\nlocated at the cirrus cloud base height are found for the thin and\nopaque cirrus clouds. The cirrus clouds optical depth (COD) threshold\nfor having double SCRF maximum out of noon instead of a single one at\nnoon was 0.083. In contrast, the heating rate shows a maximum at noon in\nthe location of cirrus clouds maximum extinction values. Cirrus clouds\nhave a cooling effect in the solar spectrum at the Top of the Atmosphere\n(TOA) and at the surface (SFC). The daily mean value of SCRF has an\naverage value of -9.1 W m(-2) at TOA and -5.6 W m(-2) at SFC. The cirrus\nclouds also have a local heating effect on the atmospheric layer where\nthey are located. Cirrus clouds have mean daily values of heating rates\nof 0.63 K day(-1) with a range between 0.35 K day(-1) and 1.24 K\nday(-1). The principal effect is in the near-infrared spectral band of\nthe solar spectrum. There is a linear relation between SCRF and COD,\nwith -30 W m(-2) COD(-1) and -26 W m(-2) COD(-1), values for the slopes\nof the fits at the TOA and SFC, respectively, in the broadband solar\nspectrum.