Retrievals of vertical profiles of ice cloud microphysics from radar and IR measurements using tuned regressions between reflectivity and cloud parameters

A new approach is suggested for retrieving vertical profiles of radiatively important microphysical parameters of ice clouds from measurements of radar reflectivity and estimates of cloud optical thickness. This approach is applicable to ground-based, vertical-mode measurements of pure ice phase clouds observed without blockage from low-liquid water clouds. It involves "tuning" the coefficient of the power law reflectivity- ice water content (Ze-IWC) relations for each individual profile of radar measurements. This tuning is done based on the independent estimates of cloud ice water path obtained from layer-mean values of radar reflectivity and cloud optical thickness. After a vertical profile of IWC is retrieved using this approach, a corresponding vertical profile of cloud particle median sizes, Dm, can be easily calculated for an assumed type of the particle size distribution. By assuming that the exponent in the tuned Z e-IWC relations changes linearly within a small dynamic range, better results are obtained compared with the case when it is assumed to be constant. The accuracy of the tuned regression approach is assessed by comparing the retrieval results for several high-quality observational cases with data from the "reference" method, which uses additional measurements of Doppler velocities. This method was verified by earlier comparisons with simultaneous in situ data. The specifics of using Doppler information, however, limit the applicability of this method and prevent its real-time applications. It is shown that the relative standard deviations of IWC and Dm retrievals using the tuned regression approach compared with the reference method are about 35% and 20%, respectively. These accuracies are much better than those that can be attained by any a priori chosen fixed regression between reflectivity and cloud microphysical parameters. At the same time, these accuracies are comparable to uncertainties of estimates of cloud parameters from direct in situ sampling. The suggested tuned regression approach is easy to implement and can be used for routine processing of ground-based, and, potentially, satellite-aircraft-based radar measurements of ice clouds.

[1]  Graeme L. Stephens,et al.  Microwave radiative transfer through clouds composed of realistically shaped ice crystals , 1995 .

[2]  Brooks E. Martner,et al.  An Unattended Cloud-Profiling Radar for Use in Climate Research , 1998 .

[3]  K. Sassen,et al.  Investigation of relationships between Ka-band radar reflectivity and ice and liquid water contents , 1994 .

[4]  S. Matrosov.  Variability of Microphysical Parameters in High-Altitude Ice Clouds: Results of the Remote Sensing Method , 1997 .

[5]  Patrick Minnis,et al.  Cirrus layer microphysical properties derived from surface-based millimeter radar and infrared interferometer data , 1998 .

[6]  Mark A. Miller,et al.  An Evaluation of a 94-GHz Radar for Remote Sensing of Cloud Properties , 1995 .

[7]  Taneil Uttal,et al.  A Method for Determining Cirrus Cloud Particle Sizes Using Lidar and Radar Backscatter Technique , 1993 .

[8]  Taneil Uttal,et al.  On cloud radar and microwave radiometer measurements of stratus cloud liquid water profiles , 1998 .

[9]  L. Radke,et al.  A Summary of the Physical Properties of Cirrus Clouds , 1990 .

[10]  Qingyuan Han,et al.  Validation of Satellite Retrievals of Cloud Microphysics and Liquid Water Path Using Observations from FIRE. , 1995 .

[11]  Sergey Y. Matrosov,et al.  Radar and Radiation Properties of Ice Clouds , 1995 .

[12]  S. M. Sekelsky,et al.  Cloud observations with a polarimetric 33 GHz and 95 GHz radar , 1996 .

[13]  S. Matrosov,et al.  Cloud physics studies with 8 mm wavelength radar , 1995 .

[14]  Greg Michael McFarquhar,et al.  The role of spaceborne millimetre-wave radar in the global monitoring of ice cloud , 1995 .

[15]  John M. Firda,et al.  Particle Size Estimation in Ice-Phase Clouds Using Multifrequency Radar Reflectivity Measurements at 95, 33, and 2.8 GHz , 1999 .

[16]  Andrew J. Heymsfield,et al.  Ice crystal terminal velocities. , 1972 .

[17]  Graeme L. Stephens,et al.  Microweve Radiative Transfer through Clouds Composed of Realistically Shaped Ice Crystals. Part II. Remote Sensing of Ice Clouds. , 1995 .

[18]  C. Platt,et al.  Remote Sounding of High Clouds. IV: Observed Temperature Variations in Cirrus Optical Properties , 1981 .

[19]  K. Liou,et al.  Remote Sounding of Multilayer Cirrus Cloud Systems Using AVHRR Data Collected during FIRE-II-IFO , 1998 .

[20]  R. Kropfli,et al.  A Method for Estimating Particle Fall Velocities from Vertically Pointing Doppler Radar , 1999 .

[21]  A study of composite cirrus morphology using data from a 94-GHz radar and correlations with temperature and large-scale vertical motion , 1997 .

[22]  Sergey Y. Matrosov,et al.  Comparisons of Ice Cloud Parameters Obtained by Combined Remote Sensor Retrievals and Direct Methods , 1998 .

[23]  Kenneth Sassen,et al.  Estimation of Cloud Content by W-Band Radar , 1996 .

[24]  S. Matrosov,et al.  Ground-Based Remote Sensing of Cloud Particle Sizes during the 26 November 1991 FIRE II Cirrus Case: Comparisons with In Situ Data , 1995 .

[25]  P. Francis,et al.  Improved Measurements of the Ice Water Content in Cirrus Using a Total-Water Probe , 1995 .

[26]  V. Ramanathan,et al.  Thermodynamic regulation of ocean warming by cirrus clouds deduced from observations of the 1987 El Niño , 1991, Nature.

[27]  R. D. Kelly,et al.  Meteorological research applications of MM-wave radar , 1996 .

[28]  Paul W. Stackhouse,et al.  The Relevance of the Microphysical and Radiative Properties of Cirrus Clouds to Climate and Climatic Feedback , 1990 .

[29]  Greg Michael McFarquhar,et al.  The Role of Spaceborne Millimeter-Wave Radar in the Global Monitoring of Ice Cloud , 1995 .

[30]  I. P. Mazin,et al.  An empirical model of the physical structure of upper-layer clouds , 1991 .

[31]  Sergey Y. Matrosov,et al.  Retrieval of Vertical Profiles of Cirrus Cloud Microphysical Parameters from Doppler Radar and Infrared Radiometer Measurements , 1994 .

[32]  Sergey Y. Matrosov,et al.  Estimation of ice cloud parameters from ground‐based infrared radiometer and radar measurements , 1992 .

[33]  K. Sassen,et al.  Radar probing of cirrus and contrails: Insights from 2D model simulations , 1998 .

[34]  J. Mead,et al.  Detection of Ice Hydrometeor Alignment Using an Airborne W-band Polarimetric Radar , 1997 .

[35]  Yong Han,et al.  Multiwavelength Observations of a Developing Cloud System: The FIRE II 26 November 1991 Case Study , 1995 .