A Physically Based Algorithm for Non-Blackbody Correction of Cloud-Top Temperature and Application to Convection Study

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  • Chunpeng Wang
    Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor, Michigan
  • Zhengzhao Johnny Luo
    Department of Earth and Atmospheric Sciences, and NOAA Cooperative Remote Sensing Science and Technology Center, City College of New York, New York, New York
  • Xiuhong Chen
    Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor, Michigan
  • Xiping Zeng
    Mesoscale Atmospheric Processes Laboratory, NASA Goddard Space Flight Center, Greenbelt, Maryland
  • Wei-Kuo Tao
    Mesoscale Atmospheric Processes Laboratory, NASA Goddard Space Flight Center, Greenbelt, Maryland
  • Xianglei Huang
    Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor, Michigan

Description

<jats:title>Abstract</jats:title><jats:p>Cloud-top temperature (CTT) is an important parameter for convective clouds and is usually different from the 11-<jats:italic>μ</jats:italic>m brightness temperature due to non-blackbody effects. This paper presents an algorithm for estimating convective CTT by using simultaneous passive [Moderate Resolution Imaging Spectroradiometer (MODIS)] and active [<jats:italic>CloudSat</jats:italic> + <jats:italic>Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations</jats:italic> (<jats:italic>CALIPSO</jats:italic>)] measurements of clouds to correct for the non-blackbody effect. To do this, a weighting function of the MODIS 11-<jats:italic>μ</jats:italic>m band is explicitly calculated by feeding cloud hydrometer profiles from <jats:italic>CloudSat</jats:italic> and <jats:italic>CALIPSO</jats:italic> retrievals and temperature and humidity profiles based on ECMWF analyses into a radiation transfer model. Among 16 837 tropical deep convective clouds observed by <jats:italic>CloudSat</jats:italic> in 2008, the averaged effective emission level (EEL) of the 11-<jats:italic>μ</jats:italic>m channel is located at optical depth ~0.72, with a standard deviation of 0.3. The distance between the EEL and cloud-top height determined by <jats:italic>CloudSat</jats:italic> is shown to be related to a parameter called cloud-top fuzziness (CTF), defined as the vertical separation between −30 and 10 dB<jats:italic>Z</jats:italic> of <jats:italic>CloudSat</jats:italic> radar reflectivity. On the basis of these findings a relationship is then developed between the CTF and the difference between MODIS 11-<jats:italic>μ</jats:italic>m brightness temperature and physical CTT, the latter being the non-blackbody correction of CTT. Correction of the non-blackbody effect of CTT is applied to analyze convective cloud-top buoyancy. With this correction, about 70% of the convective cores observed by <jats:italic>CloudSat</jats:italic> in the height range of 6–10 km have positive buoyancy near cloud top, meaning clouds are still growing vertically, although their final fate cannot be determined by snapshot observations.</jats:p>

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