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Satellite Observed Sensitivity of Tropical Clouds and Moisture to Sea Surface Temperature on Various Time and Space Scales: 1. Focus on High Level Cloud Situations Over Ocean
This study examines variations in high cloud properties and relative humidity (RH) with sea surface temperature (SST) over tropical oceans (30°N–30°S) using spaceborne lidar and microwave radiometer observations. The mean values over the tropics indicate that middle‐tropospheric RH increases, high c...
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Published in: | Journal of geophysical research. Atmospheres 2022-03, Vol.127 (6), p.n/a |
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Main Authors: | , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | This study examines variations in high cloud properties and relative humidity (RH) with sea surface temperature (SST) over tropical oceans (30°N–30°S) using spaceborne lidar and microwave radiometer observations. The mean values over the tropics indicate that middle‐tropospheric RH increases, high cloud covers decrease and cloud altitudes rise with SST. These signatures are consistent with the hypotheses proposed in the literature. The analysis of this same data set but at the scale of local processes shows different behaviors for SSTs 302 K. Between 299 and 302 K, middle‐tropospheric RH, opaque cloud cover, and cloud top altitude increase together with SST, while optically thin cloud cover decreases. Over SSTs >302 K, middle‐tropospheric RH, opaque cloud cover, and opaque cloud top altitude decrease with SST, while the cover of optically thin clouds increases. Interestingly, the altitude of high clouds (not the cloud top) increases monotonically with SST from 299 to 305 K on a range of space and time scales, and the altitude of optically thin clouds remains higher than that of opaque clouds. The observed relationships on different time and space scales are compared to simulations of a global atmospheric model. Despite systematic biases, the model reproduces the sensitivity of the middle‐tropospheric RH and cloud altitude to SST rather well but fails to reproduce the variations of the balance between high opaque cloud cover and high optically thin cloud cover.
Plain Language Summary
High tropical clouds both cool and warm the planet by simultaneously reflecting incoming solar radiation and trapping energy that would have been emitted to space in cloud‐free skies. It is unclear how these clouds will evolve when the climate warms. We use satellite observations over the tropical oceans and find that tropical mean variations show that the high clouds associated with thunderstorms rise and stay at about the same temperature, while their horizontal extent decrease. On the short and small scales where cloud and moisture processes occur, we find however that these high clouds become more opaque to radiation with sea surface temperature (SST) when it is colder than 302 K, and less opaque to radiation over waters warmer than 302 K. Simultaneously, the temperature of these clouds slightly decreases when they rise. Because models are the only tool to predict future climate change, we then compare the observed results to a global atmospheric model. The |
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ISSN: | 2169-897X 2169-8996 |
DOI: | 10.1029/2021JD035438 |