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On the twilight zone between clouds and aerosols
Author(s) -
Koren Ilan,
Remer Lorraine A.,
Kaufman Yoram J.,
Rudich Yi,
Martins J. Vanderlei
Publication year - 2007
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2007gl029253
Subject(s) - aerosol , atmosphere (unit) , twilight , atmospheric sciences , environmental science , aeronet , meteorology , geology , physics , astronomy
Cloud and aerosols interact and form a complex system leading to high uncertainty in understanding climate change. To simplify this non‐linear system it is customary to distinguish between “cloudy” and “cloud‐free” areas and measure them separately. However, we find that clouds are surrounded by a “twilight zone” – a belt of forming and evaporating cloud fragments and hydrated aerosols extending tens of kilometers from the clouds into the so‐called cloud‐free zone. The gradual transition from cloudy to dry atmosphere is proportional to the aerosol loading, suggesting an additional aerosol effect on the composition and radiation fluxes of the atmosphere. Using AERONET data, we find that the measured aerosol optical depth is higher by 13% ± 2% in the visible and 22% ± 2% in the NIR in measurements taken near clouds relative to its value in the measurements taken before or after, and that 30%−60% of the free atmosphere is affected by this phenomenon.