Dependence of tropical cirrus clouds on sea surface temperature and consequences for the Archean climate

In this thesis, we study observationally the variation of upper level cloud fraction with sea surface temperature in tropical oceanic regions. We also explore the consequences of a cloud feedback, arising from variations in the coverage of thin upper level clouds, in the climate of the Archean using a simple radiative-convective model that includes the effect of the variations in the area of thin cirrus clouds. First, we look at the variation in area of upper level clouds using TRMM VIRS (Tropical Rainfall Measuring Mission, Visible Infrared Sounder) data. We quantify the effect of methodological choices on the magnitude of the observed correlations between upper level cloud cover and SST. We discuss several methodological choices that might contribute to the relatively small signals found by previous researchers (- 0%/K to 2%/K) , namely, the classification of cloudy regions into convective updrafts and anvil, the use of cloud weighted SST, and the truncation and sampling error with respect to the evolution of mesoscale convective systems. All of these contribute to some extent to the weakness of signal. We show that the coarse sampling of orbital satellites can introduce biases in the estimation of the signal. Our observational evidence shows a negative correlation between the upper level cloud fraction normalized by convection and sea surface temperatures. We also study the relation between local sea surface temperature (SST) and convective precipitation fraction and stratiform rainfall area from radar observations of precipitation, using data from the Kwajalein atoll ground-based radar as well as the precipitation radar on board of the Tropical Rainfall Measurement Mission (TRMM satellite).

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Earth, Atmospheric, and Planetary Sciences.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2009

Author dc:creator

• Rondanelli, Roberto F

Advisor dc:contributor.advisor

• Richard S. Lindzen.

• Earth, Atmospheric, and Planetary Sciences.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/55161

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/55161