Atmospheric Chemistry and Physics
www.atmos-chem-phys.net
1680-7316
1680-7324
10
14
2010
10.5194/acp-10-6527-2010
http://www.atmos-chem-phys.net/10/6527/2010/
http://www.atmos-chem-phys.net/10/6527/2010/acp-10-6527-2010.html
http://www.atmos-chem-phys.net/10/6527/2010/acp-10-6527-2010.pdf
6527
6536
2010-07-16
A comparison of ship and satellite measurements of cloud properties with global climate model simulations in the southeast Pacific stratus deck
M. A. Brunke
brunke@atmo.arizona.edu
S. P. de Szoeke
P. Zuidema
X. Zeng
The University of Arizona, Department of Atmospheric Sciences, Tucson, Arizona, USA
Oregon State University, College of Oceanic and Atmospheric Sciences, Corvallis, Oregon, USA
University of Miami, Rosentiel School of Marine and Atmospheric Science, Miami, Florida, USA
Here, liquid water path (LWP), cloud fraction, cloud top height, and cloud
base height retrieved by a suite of A-train satellite instruments (the CPR
aboard CloudSat, CALIOP aboard CALIPSO, and MODIS aboard Aqua) are compared
to ship observations from research cruises made in 2001 and 2003–2007 into
the stratus/stratocumulus deck over the southeast Pacific Ocean. It is found
that CloudSat radar-only LWP is generally too high over this region and the
CloudSat/CALIPSO cloud bases are too low. This results in a relationship
(LWP~<i>h</i><sup>9</sup>) between CloudSat LWP and CALIPSO cloud thickness (<i>h</i>)
that is very different from the adiabatic relationship (LWP~<i>h</i><sup>2</sup>)
from in situ observations. Such biases can be reduced if LWPs
suspected to be contaminated by precipitation are eliminated, as determined
by the maximum radar reflectivity <i>Z</i><sub>max</sub>>−15 dBZ in the apparent lower
half of the cloud, and if cloud bases are determined based upon the
adiabatically-determined cloud thickness (<i>h</i>~LWP<sup>1/2</sup>).
Furthermore, comparing results from a global model (CAM3.1) to ship
observations reveals that, while the simulated LWP is quite reasonable, the
model cloud is too thick and too low, allowing the model to have LWPs that
are almost independent of <i>h</i>. This model can also obtain a reasonable diurnal
cycle in LWP and cloud fraction at a location roughly in the centre of this
region (20° S, 85° W) but has an opposite diurnal cycle to those
observed aboard ship at a location closer to the coast (20° S, 75° W).
The diurnal cycle at the latter location is slightly improved in the newest
version of the model (CAM4). However, the simulated clouds remain too thick
and too low, as cloud bases are usually at or near the surface.
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