Abstract
Based on the hourly gauge-satellite merged precipitation data with the spatial resolution of 0.1° × 0.1° during 2013 ~ 2018, we have evaluated the performance of the convection-permitting Weather Research and Forecasting model at Nanjing University (WRF_NJU) in forecasting the precipitation diurnal variation and the associated atmospheric circulation over the eastern Tibetan Plateau and its surrounding regions during summer. Results indicate that WRF_NJU model can well reproduce the diurnal cycle of the summer precipitation in terms of the diurnal peak time, duration and magnitude. In addition, the eastward propagation of rainfall systems with long duration along the eastern Tibetan Plateau (ETP) and its adjacent areas can also be properly captured. The WRF_NJU model can reasonably reproduce the relevant atmospheric circulation during summer as well. However, the model tends to underestimate the summer precipitation amount (PA) and precipitation frequency (PF) over most time of a day. Relatively larger biases in the occurring time and magnitude of PA and PF diurnal peaks can be noted over the ETP and Sichuan Basin. Further analysis suggests that the underestimation of PA over the ETP is attributed to the much lower moisture supply, weaker low-level southwesterly winds and less convective available potential energy (CAPE) in the WRF_NJU model than in ERA5. Over Sichuan Basin, the underestimated PA is related to the weaker upward motion, which is corresponding to the cold biases of surface air temperature in WRF_NJU. Findings of this study provide the basic model biases and may be helpful to further improve the model physical processes.
Highlights
The diurnal variation of precipitation can modify the temporal averaged energy budget of the earth’s climate system (Dai et al 2004; Chakraborty et al 2008)
The standardized precipitation amount (PA), precipitation frequency (PF) and precipitation intensity (PI) are derived according to the formula D(h) = (R(h) − Rm)/Rm (Yu et al 2007), in which h is the hour of a day and varies from 00:00 to 23:00 Beijing time (BJT)
The spatial distribution of the precipitation diurnal peak times over most areas of the eastern Tibetan Plateau (ETP) and its surrounding regions in summer can be well captured by the model, the predicted diurnal peak times of PA and PF are about 1 ~ 2 h earlier than the observation over most ETP (Sichuan Basin)
Summary
The diurnal variation of precipitation can modify the temporal averaged energy budget of the earth’s climate system (Dai et al 2004; Chakraborty et al 2008). Under the influences of the summer monsoon, the convective systems and the land surface inhomogeneity over the vast area of TP, the performance of WRF_CPM models may differ from those in the previous studies. Previous studies have proven that the WRF model with convection-permitting resolution show good accuracy in simulating the seasonal or diurnal cycle of precipitation over TP (Maussion et al 2011; Lin et al 2018; Li et al 2020a; Ou et al 2020). Using 6-years real-time forecasts of the convective-permitting WRF model at Nanjing University (WRF_NJU), this study evaluates the predicted precipitation features over and around the TP in summer, which is the main rainy season with active meso-and micro-scale systems affected by the monsoonal circulation (Lin et al 2014). 3, the summer mean and the diurnal cycle of precipitation from the observation and the WRF_NJU model forecast product will be systematically compared.
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