A 6‐year climatology of cloud occurrence frequency from Stratospheric Aerosol and Gas Experiment II observations (1985–1990)

Abstract

A 6‐year climatology of subvisual and opaque cloud occurrence frequencies is established using observations from the Stratospheric Aerosol and Gas Experiment (SAGE) II between 1985 and 1990. The subvisual clouds are observed mostly at high altitudes near the tropopause. The opaque clouds terminate the profiling, reducing the measurement frequency of the SAGE II instrument in the troposphere. With its 1‐km vertical resolution, the climatology shows many interesting features, including (1) the seasonal expansion and migration behavior of the subvisual and opaque cloud systems; (2) the association of the zonal mean cloud frequency distributions with the tropospheric mean circulation (Hadley and Ferrel cells); (3) the tropical cloud occurrence that follows the equatorial circulation, including the Walker circulation over the Pacific Ocean; and (4) the overall higher cloud occurrence in the northern hemisphere than in the southern hemisphere. The radiative impact of subvisual clouds is estimated to be a 1‐W m−2 reduction in outgoing longwave radiation. The maximum overall effect is a net positive cloud forcing of 0.5–1 W m−2 in the tropics. During the 1987 El Niño‐Southern Oscillation (ENSO), cloud frequency was generally enhanced in the tropics and midlatitudes and reduced in the subtropics and high latitudes. The present study shows a distinct negative correlation between the high‐altitude cloud occurrence and the lower stratospheric water vapor mixing ratio in the tropics, providing intrinsic evidence on the delicate connection between the stratospheric‐tropospheric exchange and dehydration processes and the high‐altitude cloud activities.

A 6-year global cloud climatology from the Atmospheric InfraRed Sounder AIRS and a statistical analysis in synergy with CALIPSO and CloudSat

“…In the tropics, the difference can be as large as 20%, suggesting that these regions are covered by more thin cirrus (e.g. Wang et al, 1996;Winker and Trepte, 1998). For all three cloud types AIRS-LMD and TOVS Path-B agree quite well with CALIPSO clouds when excluding subvisible cirrus.…”

Seasonal ozone variations in the isentropic layer between 330 and 380 K as observed by SAGE II: Implications of extratropical cross‐tropopause transport

“…As a result, the data density in each grid is generally reduced by a factor of 15 in comparison with that used in the zonal mean distribution study. The blank regions (mostly in the tropics) in Plates 3 and 4 are the consequence of missing data due to the high occurrence of opaque clouds [Wang et al, 1996] and the less frequent SAGE II sampling coverage in the tropics [Wang et al, 1992]. Because of the sparse SAGE II coverage when used to resolve the longitudinal structure of the ozone column distribution, the results presented in this subsection should be regarded as qualitative only.…”

Cryogenic Limb Array Etalon Spectrometer observations of tropical cirrus

“…The most complete data sat describing the seasonal variability and geographical distribution of high-altitude tropical cirrus has come from the limb-viewing occultation observations of the Stratosphcric Aerosol and Gas Experiment (SAGE) II [Wang et al, 1996]. These data show that the most frequently occurring cirrus are sufficiently tenuous to be invisible to ground observers and the nadir-viewing satellite-borne instruments that gather operational meteorological data.…”