Assessment of longwave radiative effect of nighttime cirrus based on CloudSat and CALIPSO measurements and single-column radiative transfer simulations

摘要

Cirrus clouds strongly influence weather and climate processes due to their effects on the radiative balance of the Earth-atmosphere system. In this work, longwave radiative forcing of nighttime cirrus was studied at grid-cell scales covering the regions between 60 degrees S and 60 degrees N. The measurements of CloudSat and CALIPSO were used to obtain the occurrence frequencies of cirrus clouds with different optical thickness, and then the SBDART radiative transfer model was employed to compute the radiative forcing. For the study region, the occurrence frequencies at night time for subvisual (tau = 0.03), thin (0.03 = tau 0.3), opaque (0.3 = tau 3), and thick (tau 3) cirrus types are found to be 7.43%, 9.83%, 8.62%, and 1%; the average occurrence frequency can reach similar to 26.89%. Moreover, the mean effective radii are similar to 22.87, 19.23, 19.82, 27.6 and 39.18 mu m corresponding to total, subvisual, thin, opaque and thick cirrus clouds. We found that average longwave (4-50 mu m) radiative effect (LWRE) for nighttime cirrus clouds is similar to 17.38W.m(-2) at the top of the atmosphere (TOA) and similar to 1.14W.m(-2) at the Earth surface. Finally, the LWRF of opaque cirrus is identified to be the largest contribution to the warming effects at nighttime (similar to 7.76W.m(-2) at the TOA, 0.68W.m(-2) at the surface), primarily due to their high fractions and optical thickness, appearing simultaneously. These findings provide valuable references to understanding the role of nighttime cirrus in regulating the radiation field. (C) 2018 Elsevier Ltd. All rights reserved.