Snow Clouds Observation Using the Airborne

Identification of cloud water phase, such as liquid water or ice water is important for the Earth radiation budget (Brown et al. 1995). Multiparameter radar data, such as LDR (Linear Depolarization Ratio) and ρHV(0) (correlation between both horizontal and vertical polarization with zero time lag) are useful. Meanwhile satelliteborne cloud profiling radar (CloudSAT) can measure Z factor only, and other radar (EarthCARE/CPR) can measure Doppler Velocity in addition to Z factor. Under this situation, algorithm development to identify cloud water phase is preferred. The National Institute of Information and Communications Technology (NICT) has been conducted various airborne experiments using the 95GHz cloud radar (named SPIDER) (Horie et al. 2000). SPIDER is dual polarized radar using linear polarization and has dual receivers for both polarizations. The pulse-pair processing capability is also provided. Therefore, multi-parameter data, such as Doppler velocity, LDR, ρHV(0), in addition to Z factor can be obtained. The sea surface return data were also obtained because the difference between expected and received surface returns was caused by attenuation of the atmosphere and cloud liquid (or snow/rain). The sea surface is considered useful calibration target for spaceborne cloud radar (Horie 2004) and has stable scattering property as the others results by lower frequency (Masuko et al. 1986, Jackson et al. 1992, Okamoto et al. 2002, Freilich and Vanhoff 2003). The observations of snow clouds were performed as part of Winter MCSs (Mesoscale Convective Systems) Observation over the Japan Sea in 2001, 2002 and 2003 (named WMO-01, WMO-02 and WMO-03). SPIDER was carried by Gulfstream II airplane, which was also mounted Microwave Radiometer (WVR-1100) and "in-situ" cloud particle measurement sensor (FSSP, 2DC, and 2DP probe) operated by Meteorological Research Institute, Japan. During observation, the developmental stages of snow clouds were observed. At the initial stage of developing snow, updraft at the lower altitude is found and little attenuation is occurred. At the mature stage, both strong updraft and down draft at middle altitude are found and strong attenuation is occurred. At decaying stage, only down drafts at the low and middle altitude are found and little attenuation is occurred. It is considered that the attenuation is caused by not cloud ice water but cloud liquid water. The temperature at the cloud bottom was below zero degrees, then cloud particles contained super-cooled droplet in clouds. The cloud water detection using received power only is applied to the data during airborne experiments by SPIDER. The comparison with the result of Doppler velocity is also applied. The detected cloud water is agreed with the result of Doppler measurement.