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Abstract The diurnal cycle of precipitation plays a crucial role in regulating Earth's water cycle, energy balance, and regional climate patterns. However, the diurnal precipitation across mainland Southeast Asia (MSEA) and the factors influencing its spatial variations are not fully understood. In this study, we investigated diurnal precipitation patterns in summertime (June–August) from 2002 to 2005 over MSEA using ground‐based observations, satellite products, the global ERA5 reanalysis, and high‐resolution simulations from the Weather Research and Forecasting (WRF) Model at 9‐ and 3‐km grid spacing forced by ERA5 hourly data on ∼0.25° grids. Various observation‐based data sets including GHCN‐Daily, Multi‐Source Weighted‐Ensemble Precipitation (MSWEP), Asian Precipitation ‐ Highly‐Resolved Observational Data Integration Towards Evaluation of Water Resources (APHRODITE), and Integrated Multi‐satellite Retrievals for Global Precipitation Measurement (IMERG) were used. In evaluating daily precipitation over MSEA, MSWEP, and APHRODITE data sets show similar patterns in precipitation amount, frequency, and intensity, while IMERG tends to produce higher amounts but with less frequency. ERA5 overestimates light precipitation compared to the other data sets. The WRF simulations generally produce heavier but less frequent light precipitation, with the 3‐km simulation producing less intense precipitation than the 9‐km simulation. A k‐means classification of IMERG data revealed five distinct spatial regimes with varying diurnal precipitation cycles. The WRF simulations closely match these regimes, capturing key diurnal cycles missed by ERA5 over mountainous regions and coastlines. Additionally, convective activities and near‐surface winds influence these cycles, with WRF simulations better representing coastal and mountain precipitation patterns than ERA5. High‐resolution WRF simulations, especially the 3‐km simulation, capture diurnal precipitation more accurately than ERA5, highlighting the importance of employing convection‐permitting models to simulate precipitation diurnal cycles over complex terrain. 

Abstract The Tibetan Plateau is regarded as the Earth's Third Pole, which is the source region of several major rivers that impact more 20% the world population. This high‐altitude region is reported to have been undergoing much greater rate of weather changes under global warming, but the existing reanalysis products are inadequate for depicting the state of the atmosphere, particularly with regard to the amount of precipitation and its diurnal cycle. An ensemble Kalman filter (EnKF) data assimilation system based on the limited‐area Weather Research and Forecasting (WRF) model was evaluated for use in developing a regional reanalysis over the Tibetan Plateau and the surrounding regions. A 3‐month prototype reanalysis over the summer months (June−August) of 2015 using WRF‐EnKF at a 30‐km grid spacing to assimilate nonradiance observations from the Global Telecommunications System was developed and evaluated against independent sounding and satellite observations in comparison to the ERA‐Interim and fifth European Centre for Medium‐Range Weather Forecasts Reanalysis (ERA5) global reanalysis. Results showed that both the posterior analysis and the subsequent 6‐ to 12‐hr WRF forecasts of the prototype regional reanalysis compared favorably with independent sounding observations, satellite‐based precipitation versus those from ERA‐Interim and ERA5 during the same period. In particular, the prototype regional reanalysis had clear advantages over the global reanalyses of ERA‐Interim and ERA5 in the analysis accuracy of atmospheric humidity, as well as in the subsequent downscale‐simulated precipitation intensity, spatial distribution, diurnal evolution, and extreme occurrence.