Application of Ground-Based Microwave Radiometers to Optimize the Estimation Method of Cloud Liquid Water on the Tibetan Plateau

The cloud liquid water content (LWC) of the Tibetan Plateau (TP) is crucial for cloud water conversion. There are very few accurate observations of the LWC on the TP. This makes our estimation of the LWC and precipitation inaccurate on the TP. This paper introduces an indirect estimation scheme for the LWC profile obtained using a monochromatic radiative transfer model (MonoRTM) and microwave radiometers (MWRs) on the TP. The LWC estimation method was improved using an optimization of the difference between the simulated and observed brightness temperature (TB) at specific microwave channels that are sensitive to liquid water. The accuracy of the LWC estimation method depends heavily on the value of the cloud-base environment humidity criterion (CBEHC). Our experiment confirmed that the default CBEHC value of 95% is unsuitable for the TP. For the rainfall scenarios, the optimization method suggested the use of CBEHC values of 81%, 76%, and 83% for Mangya, Nagqu, and Qamdo stations, respectively. The new CBEHC values produced a 30 K improvement in the TB simulation when compared to that of 95% CBEHC under rainfall conditions. This demonstrates the robustness of the LWC estimation scheme and its significant improvement in LWC estimation on the TP. For no-rainfall scenarios, the original Karstens model remained suitable for Nagqu station. An adjustment of the CBEHC to 94% for Mangya station resulted in a 1 K improvement of its TB simulation. Qamdo station had a 2.5 K improvement when the CBEHC was adjusted to 98%. The relationship between the simulated TB simulation error and the maximum relative humidity of the radiosonde profiles weakened after CBEHC optimization. Thus, the innovative method proposed in this article provides a practical estimation method for LWC in the TP region. This LWC estimation method has a higher potential for rainfall days than no-rainfall days. Under no-rainfall conditions, the accuracy of the proposed LWC estimation method is sensitive to TB errors included in its measurement and simulation. An accurate estimation of LWC for no-rainfall conditions relies more on the equipment and radiation model.