Observation and Comparison of Cloud-base Heights by Ground-based Millimeter-wave Cloud Radar

As cloud automatic observation achieved breakthrough progress, a long-term comparison test on different devices is needed to select the suitable cloud observation equipment for regular operation of China. A Ka-band millimeter-wave (35 GHz) cloud radar (KaCR) and a vaisala laser ceilometer (VCEIL) are installed in Meteorological Observation Center of CMA, and data are compared with L-band rawinsonde observations (LRAOBS) in Beijing Weather Observatory from 20 Nov to 31 Dec in 2014. Among these instruments, the KaCR observes the echo power value and its temporal resolution is from 1 s to 60 s, the VCEIL measures the back scattering intense data with the same temporal resolution of KaCR, and the LRAOBS works twice every day. Data acquisition ratio measured by KaCR and VCEIL under different visibility conditions are compared. A comparison test of cloud base heights and cloud top heights measured by KaCR and VCEIL is also carried out. A comparison test of cloud base height and cloud top height measured by KaCR and LRAOBS and a real example is analyzed. And the cloud base heights and cloud top heights measured by KaCR, VCEIL and LRAOBS during a precipitation process are compared too.
    The result indicates that the detection ability of KaCR is better than VCEIL under low visibility condition, and their difference of detection ability reduces with the visibility increasing. The cloud base heights measured by KaCR and VCEIL are well consistent, with the correlation coefficient reaching 0.92. The correlation coefficient of cloud base height between KaCR and LRAOBS is about 0.93, and that between KaCR and LRAOBS is about 0.78. Cloud base height measured by KaCR is slightly lower than that measured by VCEIL and LRAOBS, and cloud top height measured by KaCR is slightly lower than that measured by LRAOBS. KaCR can clearly show the process of cloud formation and dissipation and the structure changes of cloud compared with VCEIL and LRAOBS, but cannot accurately identify the cloud base position when it rains.