Impact of Meiyu Front on the Diurnal Variations of Precipitation over East Asia

The Meiyu front, also called Baiyu in Japan, situated at the leading (northern) edge of summer monsoon, is the most prolific rain producer over East Asia. This study explores the diurnal variations of the Meiyu precipitation during the early summer monsoon period (June 1-15 from 1998-2015) over East Asia using the high-resolution NOAA/Climate Prediction Center morphing technique (CMORPH) precipitation data and the ECMWF interim reanalysis. Complementary to past studies on the diurnal variations of warm-season East Asian rainfall, this work focuses on the diurnal variations of the rainfall over the east Asia during the early summer (the “pre-Meiyu period” in South China) across a broad region including mountains, plains, oceans, as well as islands and straits. The 18-year climatological mean rainfall during this period is maximized along a long but rather narrow east-west-oriented quasi-stationary Meiyu frontal region just inland of South China coast but extends across the Taiwan Strait and Taiwan Island to south Japan islands. The precipitation diurnal cycles along this monsoonal frontal zone differ substantially from regions with different bottom terrain primarily due to the impact of the solar isolation cycle: A diurnal peak is found between 02 and 04 LST for the open ocean and between 06 and 08 LST for the offshore precipitation near the coast; the diurnal peak over land usually occurs in the afternoon and early evening though there is large difference in peak times between mainland and island and there is apparently overlapping propagating diurnal precipitation peaks. It is worth noting that the Taiwan Strait region between Mainland China and the Taiwan Island is a relatively rain free along the path of the Meiyu front. We hypothesize that several competing thermally driven diurnal varying circulation, along with the blocking of the high Taiwan topography, are likely response for this region of “rain hole”.