Simulation of summer precipitation diurnal cycles over the Tibetan Plateau at the gray-zone grid spacing for cumulus parameterization

Tinghai Ou,Xingchao Chen,Changgui Lin,Kun Yang,Deliang Chen,Hui-Wen Lai,Fuqing Zhang

doi:10.1007/s00382-020-05181-x

Abstract

The Tibetan Plateau (TP) is often referred to as the “water tower of Asia” or the “Third Pole”. It remains a challenge for most global and regional models to realistically simulate precipitation, especially its diurnal cycles, over the TP. This study focuses on evaluating the summer (June–August) precipitation diurnal cycles over the TP simulated by the Weather Research and Forecasting (WRF) model. The horizontal resolution used in this study is 9 km, which is within the gray-zone grid spacing that a cumulus parameterization scheme (CU) may or may not be used. We conducted WRF simulations with different cumulus schemes (CU experiments) and a simulation without CU (No_CU experiment). The selected CUs include the Grell-3D Ensemble (Grell), New Simplified Arakawa-Schubert (NSAS), and Multiscale Kain-Fritsch (MSKF). These simulations are compared with both the in-situ observations and satellite products. Results show that the scale-aware MSKF outperforms the other CUs in simulating precipitation in terms of both the mean intensity and diurnal cycles. In addition, the peak time of precipitation intensity is better captured by all the CU experiments than by the No_CU experiment. However, all the CU experiments tend to overestimate the mean precipitation and simulate an earlier peak of precipitation frequency when compared to observations. The frequencies and initiation timings for short-duration (1–3 h) and long-duration (> 6 h) precipitation events are well captured by the No_CU experiment, while these features are poorly reproduced by the CU experiments. The results demonstrate simulation without a CU outperforms those with a CU at the gray-zone spatial resolution in regard to the precipitation diurnal cycles.

Highlights

As a fundamental cycle in the Earth’s climate system, diurnal cycles of precipitation considerably affect surface radiation, temperature, and in particular the surface hydrology (Dai et al 1999a, b)
The mean of Center morphing method (CMORPH) and Global Precipitation Measurement (GPM) averaged over the whole Tibetan Plateau (TP) agrees well with the gauge observation (Fig. 3) and is adopted as a reference for further evaluations of the model simulations with and without a cumulus parameterization scheme (CU), while the differences between satellite and gauge data are taken to indicate the uncertainty in the satellite-based reference
The simulated mean and diurnal cycles of summer precipitation using different CU options have been assessed by comparing with in-situ and satellite precipitation observations

Summary

Introduction

As a fundamental cycle in the Earth’s climate system, diurnal cycles of precipitation considerably affect surface radiation, temperature, and in particular the surface hydrology (Dai et al 1999a, b). The diurnal cycle of precipitation is driven by solar forcing and affected by complicated interactions between the atmosphere and surface processes, where convection plays an important role (Jeong et al 2011; Mooney et al 2017; Zhang et al 2017b; Zhou et al 2008). Due to the small size of convective clouds, only very fine resolution (less than a few kilometers) models can explicitly resolve the convective-scale processes. Most global and regional climate models, rely on cumulus schemes (CUs) to parameterize convective activities. Several CUs for weather/climate models have been developed, which have different assumptions on cloud feedbacks such as the formation of cirrus clouds

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Conclusion