Warm Season Afternoon Thunderstorm Characteristics under Weak Synoptic-Scale Forcing over Taiwan Island

Abstract

The spatial and temporal characteristics and distributions of thunderstorms in Taiwan during the warm season (May-October) from 2005 to 2008 and under weak synoptic-scale forcing are documented using radar reflectivity, lightning, radiosonde, and surface data. Average hourly rainfall amounts peaked in midafternoon (1500-1600 local solar time, LST). The maximum frequency of rain was located in a narrow strip, parallel to the orientation of the mountains, along the lower slopes of the mountains. Significant diurnal variations were found in surface wind, temperature, and dewpoint temperature between days with and without afternoon thunderstorms (TS A and non-TS A days). Before thunderstorms occurred, on TS A days, the surface temperature was warmer (about 0.58-1.58C) and the surface dewpoint temperature was moister (about 0.58-28C) than on non-TS A days. Sounding observations from northern Taiwan also showed warmer and higher moisture conditions on TS A days relative to non-TS A days. The largest average difference was in the 750-550-hPa layer where the non-TS A days averaged 2.58-3.58C drier. These preconvective factors associated with the occurrences of afternoon thunderstorms could be integrated into nowcasting tools to enhance warning systems and decision-making capabilities in real-time operations.

Summer Convective Afternoon Rainfall Simulation and Projection Using WRF Driven by Global Climate Model. Part I: Over Taiwan

“…Among these weather systems, convective afternoon rainfall (hereafter, CAR) is the most frequently observed pattern (Wang and Chen 2008). Because of its importance to local residents, the characteristics and causes of CAR have been examined in many studies (Chen et al 1991;Johnson and Bresch 1991;Kerns et al 2010;Lin et al 2011;Huang and Chan 2012;Wang et al 2013). Studies have noted that CAR generally occurs on a day associated with a stronger sea breeze circulation during the daytime (e.g., Lin et al 2012).…”

Diurnal Circulations and Rainfall in Taiwan during SoWMEX/TiMREX (2008)

“…In the mountainous subtropical island of Taiwan, rainfall is controlled throughout the year by such circulations, which cause a pronounced diurnal oscillation in island-averaged low-level divergence (Johnson and Bresch 1991;Chen et al 1999;Kishtawal and Krishnamurti 2001;Kerns et al 2010;Lin et al 2011). Great complexity is added to this system in the presence of monsoon flow, which interacts with Taiwan's main topographic barrier, the Central Mountain Range (CMR), to generate enhanced upstream convergence, barrier jets, offshore rainbands, and lee vortices (Sun and Chern 1993;Li and Chen 1998;Yeh and Chen 2002;Chen et al 2004;Alpers et al 2007;Yu and Lin 2008;Yu and Hsieh 2009).…”

Initiation and Maintenance Mechanisms for Heavy Precipitation System over a Mountainous Island under a Prevailing Monsoon Current

“…1) (Chen & Chen, 2003;Kerns et al, 2010). Since the prevailing monsoon current is from southwest, the maximum accumulated rainfall associated with local rainshowers is over the western windward slopes of the north northeast-south southwest oriented mountain (Chen & Chen, 2003;Kerns et al, 2010;Wang & Chen, 2008;Lin et al, 2011).…”

“…The frequency of occurrence of radar echoes over the western and southwestern coast of Taiwan reaches their maximum during 1700-1800 LST (Fig. 5 of Lin et al, 2011). Over the adjacent oceans in southern Taiwan Strait, the estimated rainfall by the Tropical Rainfall Measuring Mission (TRMM) for May-September 1988 also has a diurnal cycle with a late-night to early-morning maximum (Krishtawal & Krishnamurti, 2001).…”