Abstract
Abstract. 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~h9) between CloudSat LWP and CALIPSO cloud thickness (h) that is very different from the adiabatic relationship (LWP~h2) 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 Zmax>−15 dBZ in the apparent lower half of the cloud, and if cloud bases are determined based upon the adiabatically-determined cloud thickness (h~LWP1/2). 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 h. 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.
Highlights
Clouds cover a large portion of the Earth while having a profound impact on the Earth’s radiative balance and on the climate system’s sensitivity to climate forcing
A direct comparison of the CloudSat retrievals and those from Advanced Microwave Scanning Radiometer-EOS (AMSR-E) and Sensor Microwave Imager (SSM/I) is facilitated by averaging all good-quality CloudSat liquid water path (LWP) that fall within an AMSRE or SSM/I 0.25◦×0.25◦ grid box for each individual pass
The large differences between CloudSat LWPs and those from the other products are due to the fact that, while all satellites have the most LWPs in the lowest bin (
Summary
Clouds cover a large portion of the Earth while having a profound impact on the Earth’s radiative balance and on the climate system’s sensitivity to climate forcing. While we anticipate that the 2B-CWC-RO product would be highly influenced because of radar reflectivity’s increased sensitivity to droplet size (as described in more detail ), the single-measurement retrieval is more homogenous than that from another product, the 2B-CWC-RVOD The latter combines LWP based on the CPR and on MODIS-derived visible cloud optical depths which are unavailable in many situations, most notably at night. CloudSat LWP from 2B-CWC-RO is further intercompared to passive microwave satellite products retrieved from the AMSR-E on Aqua and the Special Sensor Microwave Imager (SSM/I) aboard the Defense Meteorological Satellite Programme (DMSP) satellites during October–December 2006–2008 The latter data is from the version 6 ocean algorithm from Remote Sensing Systems The AMSR-E data is derived from version 2 of the level 2B global swath ocean products (available at http://nsidc.org/ daac/index.html) which have been interpolated to the same 0.25◦×0.25◦ regular grid as SSM/I
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