Global analysis of cloud phase and ice crystal orientation from Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) data using attenuated backscattering and depolarization ratio

Abstract

[1] A method for discriminating cloud particle types was developed using lidar backscattering copolarization and cross-polarization channel measurements from Cloud-Aerosol Lidar With Orthogonal Polarization (CALIOP) on board Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO). In spaceborne lidar measurements, significant multiple scattering effects discriminate between cloud water and ice difficult using the depolarization ratio (d). We theoretically estimated the relationship between d and cloud extinction on the basis of the backward Monte Carlo method. Cloud particle type was determined by the combined use of d and the ratio of attenuated backscattering coefficients for two vertically consecutive layers. Ice particles were further classified into two categories: randomly oriented ice crystals (3-D ice) and horizontally oriented plates (2-D plate). The method was applied to CALIOP data for September-November 2006. We found that 3-D ice generally occurred colder than −20°C, whereas 2-D plate occurred between −10°C and −20°C, with high-occurrence frequency in high-latitude regions. We compared the results to those obtained using the vertical feature mask (VFM). The VFM tended to show a homogeneous cloud type through the entire cloud layer in vertical directions and misclassified 2-D plate as water. The ratio of water particles relative to ice particles decreased with decreasing temperature. By the proposed method, water cloud occurrence in subtropical and high-latitude regions was greater (up to 20%) than in the other regions below −10°C; however, the VFM results did not show such dependence on latitude. Comparison of ice and water cloud between our results and Moderate Resolution Imaging Spectroradiometer (MODIS) products showed better agreement for water cloud than for ice cloud.Citation: Yoshida, R., H. Okamoto, Y. Hagihara, and H. Ishimoto (2010), Global analysis of cloud phase and ice crystal orientation from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) data using attenuated backscattering and depolarization ratio,

Depolarization Ratio of Clouds Measured by Multiple-Field of view Multiple Scattering Polarization Lidar

“…That is, the footprint size of conventional groundbased lidar with FOV of 1 mrad is about 1m at the altitude of 1km while that of CALIPSO lidar was 90m. Analysis of CALIPSO lidar data showed depolarization ratio of water clouds tended to increase as estimated extinction of the layer increased [2]. The characteristics were reproduced by the results of numerical simulations by Monte Carlo method.…”

“…Due to these characteristics, the discrimination of cloud particle phase was not possible by depolarization information alone in case of space borne lidar observations. Thus it was necessary to take into account the combination of attenuation of backscattered lidar signals and depolarization to discriminate between randomly oriented ice, horizontally oriented ice particles and water particles [2]. It is also worth to note that there is no global product of three-dimensional distribution of water cloud microphysics using CALIPSO data.…”

Improved rain rate and drop size retrievals from airborne Doppler radar

“…First all targets detected by radar are classified as containing ice due to the sensitivity of that instrument to the largest particles. Then liquid and ice as detected by lidar are distinguished based on the vertical gradient of lidar backscatter, which is higher in liquid cloud (Ceccaldi et al, 2013); this method of distinguishing liquid cloud is consistent with the method of Yoshida et al (2010) using the lidar depolarization ratio. Where radar detects ice and lidar detects liquid, mixed-phase cloud is diagnosed.…”

Interpreting an evaluation of the ECMWF global model with CloudSat observations: ambiguities due to radar reflectivity forward operator uncertainties

“…As noted in section 3, an additional sensitivity experiment using the 'hexagonal plates' shape instead increases the reflectivity, which leads to a higher discrepancy with observations in the extratropics (not shown). Observational evidence shows the existence of plates is confined to a temperature range between −10 • C and −20 • C (Yoshida et al, 2010) and is therefore of limited applicability across a wider temperature range.…”