Publication Abstracts

Miller 1997

Miller, R.L., 1997: Tropical thermostats and low cloud cover. J. Climate, 10, 409-440, doi:10.1175/1520-0442(1997)010<0409:TTALCC>2.0.CO;2.

The ability of subtropical stratus low cloud to moderate or amplify the tropical response to climate forcing such as increased CO2 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 which 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 version varies in unison across the tropics as a result of the large-scale circulation, and because moist convection related tropospheric temperature within the convecting region to variations in surface temperature and moisture, the subtropical potential temperature at 700 mb depends upon surface condtions 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 'warm' pool) and the subtropical descending region (the 'cold' pool). The cold pool is the lcoation 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 tropopause 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 CO2, and reducing the tropically-averaged warming in comparison to the warming with low cloud cover held fixed. The low cloud cover is shown to result from the increased difference in surface temperature between the warm and cold pools, and the increased low-level static stability over the warm pool, equal to the increase in potential temperature along the moist adiabat originating in the warm pool mixed layer.

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BibTeX Citation

@article{mi02800o,
  author={Miller, R. L.},
  title={Tropical thermostats and low cloud cover},
  year={1997},
  journal={J. Climate},
  volume={10},
  pages={409--440},
  doi={10.1175/1520-0442(1997)010<0409:TTALCC>2.0.CO;2},
}

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RIS Citation

TY  - JOUR
ID  - mi02800o
AU  - Miller, R. L.
PY  - 1997
TI  - Tropical thermostats and low cloud cover
JA  - J. Climate
VL  - 10
SP  - 409
EP  - 440
DO  - 10.1175/1520-0442(1997)010<0409:TTALCC>2.0.CO;2
ER  -

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