Orographic Modifications to Heavy Mei-Yu Rainfall in Taiwan

Taiwan regularly receives heavy rainfall, including from the seasonal Mei-yu front, a shallow, quasi-stationary front characterized by prefrontal moist, monsoonal southwesterlies and postfrontal drier northeasterlies. As these fronts progress south through Taiwan during May and June, the modification of the frontal structure, progression, and orientation by the island’s steep topography are not well understood and require further analysis. With this gap in knowledge, a challenge remains in predicting the impact of complex topography in controlling Mei-yu front rainfall intensity and duration.

To investigate the influence of topography on Mei-yu fronts, multiple Mei-yu events characterized by varying rainfall intensities and durations relative to the mountains are simulated using the Weather Research and Forecasting (WRF) model. By modeling these Mei-yu fronts, a slowing of Mei-yu front propagation speed is found to decrease the rainfall duration. Topography can modify the front’s propagation speed by altering the prefrontal and postfrontal winds through barrier jets and orographic deformation in proximity to the frontal wind shift line. This presentation describes these model-based results and highlights ongoing analysis of Mei-yu heavy rainfall events using observations collected during the 2022 Prediction of Rainfall Extremes Campaign in the Pacific (PRECIP) field campaign in Taiwan