Comparisons of global cloud ice from MLS, CloudSat, and correlative data sets

AMS Citation:
Wu, D. L., and Coauthors, 2009: Comparisons of global cloud ice from MLS, CloudSat, and correlative data sets. Journal of Geophysical Research-Atmospheres, 114, D00A24, doi:10.1029/2008JD009946.
Resource Type:article
Title:Comparisons of global cloud ice from MLS, CloudSat, and correlative data sets
Abstract: Aura Microwave Limb Sounder (MLS) version 2.2 (V2.2) and CloudSat R04 (release 4) ice water content (IWC) and partial - column ice water path (pIWP) measurements are analyzed and compared to other correlative data sets. The MLS IWC, representing an average over ∼300 × 7 × 4 km³ volume, is retrieved at 215–268 hPa with precision varying between 0.06 and 1 mg/m³. The MLS pIWP products, representing the partial columns over ∼100 × 7 km2 area with the bottom at ∼8, ∼6, and ∼11 km for 115, 240, and 640 GHz, have estimated precisions of 5, 1.5, and 0.8 g/m², respectively. CloudSat, on the other hand, shows a minimum detectable sensitivity of −31 dBZ in the reflectivity measurement at 94 GHz. CloudSat IWC is an average over ∼1.8 × 1.4 × 0.5 km³ volume, and its precision varies from 0.4 mg/m³ at 8 km to 1.6 mg/m³ at 12 km. The estimated single‐profile precision for CloudSat IWP is ∼9 g/m². However, these measurements are associated with relatively large systematic error, mostly due to uncertainties in the retrieval assumptions about microphysics, which lead to relatively poor accuracy compared to measurement precision. To characterize systematic differences among various observations and those derived from models, we employ the normalized probability density function (pdf) in the comparisons. CloudSat IWC shows generally consistent slopes of pdf distribution with in situ observations, particularly at ∼12 km where the in situ data come mostly from long‐leg flights. Despite similar IWC morphology found between MLS and CloudSat observations, CloudSat R04 IWC retrieval is higher compared to MLS, especially at 14-17 km where the MLS technique is not limited by sensitivity saturation. The MLS and CloudSat IWC pdf's agree well in the overlapped sensitivity range with relative difference <50%, but the difference appears to increase with IWC. MLS and CloudSat cloud ice measurements are compared with other data sets in terms of monthly map and pdf. Comparisons with European Center for Medium range Weather Forecasting (ECMWF) analyses show that grid box averages of monthly ECMWF IWC are much smaller (by ∼5× and ∼20×) than the same MLS and CloudSat averages. Comparisons of pIWP data from CloudSat and passive sensors reveal large uncertainties associated with passive techniques, such as penetration depth and sensitivity limitation. In particular, retrievals from Moderate Resolution Imaging Spectroradiometer (MODIS) and Advanced Microwave Sounding Unit-B (AMSU-B) differ largely in IWP pdf from the CloudSat R04 retrieval, showing CloudSat values generally lower (by ∼5× and ∼8×, respectively) at IWP = 10-500 g/m² but higher at IWP > 500 g/m².
Peer Review:Refereed
Copyright Information:An edited version of this paper was published by AGU. Copyright [2009] American Geophysical Union.
OpenSky citable URL: ark:/85065/d7wh2r1p
Publisher's Version: 10.1029/2008JD009946
  • D. Wu
  • R. Austin
  • M. Deng
  • S. Durden
  • Andrew Heymsfield - NCAR/UCAR
  • J. Jiang
  • A. Lambert
  • J.-L Li
  • N. Livesey
  • G. McFarquhar
  • J. Pittman
  • G. Stephens
  • S. Tanelli
  • D. Vane
  • D. Waliser
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