skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Tropical thermostats and low cloud clover

Abstract

The ability of subtropical stratus low cloud cover to moderate amplify the tropical response to climate forcing such as increased CO{sub 2} is considered. Cloud radiative forcing over the subtropics is parameterized using an empirical relation between stratus cloud cover and the difference in potential temperature between 700 mb (a level that is above the trade inversion) and the surface. This relation includes the empirical negative correlation between SST and low cloud cover and is potentially a positive feedback to climate forcing. Since potential temperature above the trade inversion varies in unison across the Tropics as a result of the large-scale circulation and because moist convection relates tropospheric temperature within the convecting region to variations in surface temperature and moisture, the subtropical potential temperature at 700 mb depends upon surface conditions within the convecting region. As a result, subtropical stratus cloud cover and the associated feedback depend upon the entire tropical climate and not just the underlying SST. A simple tropical model is constructed, consisting of separate budgets of dry static energy and moisture for the convecting region (referred to as the {open_quotes}warm{close_quotes} pool) and the subtropical descending region (the {open_quotes}cold{close_quotes} pool). The cold pool is the location of stratusmore » low clouds in the model. Dynamics is implicitly included through the assumption that temperature above the boundary layer is horizontally uniform as a result of the large-scale circulation. The tropropause and warm pool surface are shown to be connected by a moist adiabat in the limit of vanishingly narrow convective updrafts. Stratus low cloud cover is found to be a negative feedback, increasing in response to doubled CO{sub 2} and reducing the tropically averaged warming in comparison to the warming with low cloud cover held fixed. 72 refs., 13 figs., 2 tabs.« less

Authors:
 [1]
  1. Columbia Univ., New York, NY (United States)
Publication Date:
OSTI Identifier:
467822
Resource Type:
Journal Article
Journal Name:
Journal of Climate
Additional Journal Information:
Journal Volume: 10; Journal Issue: 3; Other Information: PBD: Mar 1997
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; CLOUD COVER; CORRELATIONS; CARBON DIOXIDE; ENVIRONMENTAL EFFECTS; MOISTURE; CLIMATIC CHANGE; TROPICAL REGIONS

Citation Formats

Miller, R L. Tropical thermostats and low cloud clover. United States: N. p., 1997. Web. doi:10.1175/1520-0442(1997)010<0409:TTALCC>2.0.CO;2.
Miller, R L. Tropical thermostats and low cloud clover. United States. https://doi.org/10.1175/1520-0442(1997)010<0409:TTALCC>2.0.CO;2
Miller, R L. 1997. "Tropical thermostats and low cloud clover". United States. https://doi.org/10.1175/1520-0442(1997)010<0409:TTALCC>2.0.CO;2.
@article{osti_467822,
title = {Tropical thermostats and low cloud clover},
author = {Miller, R L},
abstractNote = {The ability of subtropical stratus low cloud cover to moderate amplify the tropical response to climate forcing such as increased CO{sub 2} is considered. Cloud radiative forcing over the subtropics is parameterized using an empirical relation between stratus cloud cover and the difference in potential temperature between 700 mb (a level that is above the trade inversion) and the surface. This relation includes the empirical negative correlation between SST and low cloud cover and is potentially a positive feedback to climate forcing. Since potential temperature above the trade inversion varies in unison across the Tropics as a result of the large-scale circulation and because moist convection relates tropospheric temperature within the convecting region to variations in surface temperature and moisture, the subtropical potential temperature at 700 mb depends upon surface conditions within the convecting region. As a result, subtropical stratus cloud cover and the associated feedback depend upon the entire tropical climate and not just the underlying SST. A simple tropical model is constructed, consisting of separate budgets of dry static energy and moisture for the convecting region (referred to as the {open_quotes}warm{close_quotes} pool) and the subtropical descending region (the {open_quotes}cold{close_quotes} pool). The cold pool is the location of stratus low clouds in the model. Dynamics is implicitly included through the assumption that temperature above the boundary layer is horizontally uniform as a result of the large-scale circulation. The tropropause and warm pool surface are shown to be connected by a moist adiabat in the limit of vanishingly narrow convective updrafts. Stratus low cloud cover is found to be a negative feedback, increasing in response to doubled CO{sub 2} and reducing the tropically averaged warming in comparison to the warming with low cloud cover held fixed. 72 refs., 13 figs., 2 tabs.},
doi = {10.1175/1520-0442(1997)010<0409:TTALCC>2.0.CO;2},
url = {https://www.osti.gov/biblio/467822}, journal = {Journal of Climate},
number = 3,
volume = 10,
place = {United States},
year = {1997},
month = {3}
}