1.Chengdu University of Information Technology;2.Chinese Academy of Meteorological Sciences
The National Natural Science Foundation of China (91837310), supported by the National Key Research and Development Program of China (2018YFC1505702) , Beijige foundation of Jiangsu Institute of Meteorological Sciences (BJG201901), and Scientific Research Foundation of Chengdu University of Information Technology (KYTZ201728)
Abstract: Supercooled water in convective clouds has always been a difficult point in meteorological detection. In this paper, based on Doppler spectra of a Ka-band millimeter-wave radar used in the third Tibetan Plateau Atmospheric Experiment and relevant radiosonde data, an algorithm for identifying and retrieving supercooled water in convective clouds over Nagqu of the Tibetan Plateau was proposed. Subsequently, retrieval effects of the algorithm were analyzed using two convective cases (including stratocumulus, cumulus humilis, and altocumulus clouds), and verified by comparing with measurements from a co-located microwave radiometer (MWR). Finally, two useful empirical relations of effective radius–radar reflectivity (R_e–Z_e) and liquid water content–radar reflectivity (LWC–Z_e) for the supercooled water in convective clouds over Nagqu were presented. The main findings are as follows: The stratocumulus, cumulus congestus, and altocumulus clouds over Nagqu are dominated by updrafts with rapid changes on the hydrometeor phase in the vertical orientation, resulting widely distributions of the formed supercooled particles in terms of both their Z_e, R_e, and LWC. Supercooled particles in different convective cloud types also locate at different cloud body positions. The velocity of the in-cloud updraft is highly and positively correlated with the supercooled water Z_e, R_e, and LWC. They possess similar temporal variations and coincident spatial distributions. The retrieved spatial positions and microphysical parameters of the cloud supercooled water are consistent with the conclusions of previous studies and observations. The radar-derived LWP are also proved to agree well with the counterparts of MWR with similar temporal variations and value peaks. Their correlation coefficients can approach 0.63–0.79. For convective clouds of the Tibetan Plateau, R_e and Z_e of the supercooled water exhibit a confident power empirical relations, namely, R_e=195.4Z_e^1.78+8 for cloud droplets and R_e=67.8Z_e^0.3 for raindrops, respectively. Supercooled raindrops also possess a certain LWC–Z_e, that is LWC=0.024Z_e^0.82, whereas, the power-form relation for the cloud droplets is inapparent.