Developing spin-up time framework for WRF extreme precipitation simulations

Despite the wide application of the Weather Research and Forecasting (WRF) model in extreme precipitation simulations, there is a lack of consensus and clear guidance on identifying the suitable length of spin-up time. In this study, the WRF model was used to simulate the extreme precipitation events that happened on the 4 November 2015 at Alexandria of the Nile Delta. According to the observation from the Integrated Multi-satellitE Retrievals for Global Precipitation Measurement (IMERG), 21 spin-up time experiments of the 3-level-nested domain scenario and 21 spin-up time experiments of the 2-level-nested domain scenario were designed to explore the relationship between model required spin-up time and initial conditions. The simulation perfor-mances were evaluated by seven verification metrics and one overall performance score. Here we try to provide guidelines on how to determine the optimal spin-up time through satellite data without too many trial-and-error tests. An Optimal Spin-up Time Identifying (OSTI) framework with possible weather situations and spin-up time determining steps is proposed to help future work. It is found that the occurrences of disturbing weather events strengthen the influence of initial conditions on simulation outputs and increase model requirements for spin-up time lengths. Moreover, this framework is more useful for precipitation events with strong synoptic backgrounds because their simulation performances depend largely on the development of appropriate atmospheric circula-tions and physical equilibrium states in the model.