Theor Appl Climatol (2010) 102:43–60 DOI 10.1007/s00704-009-0235-5 ORIGINAL PAPER Diurnal and spatial variabilities of monsoonal CG lightning and precipitation and their association with the synoptic weather conditions over South Korea Yu-Kyung Hyun & S. K. Kar & Kyung-Ja Ha & J. H. Lee Received: 25 November 2008 /Accepted: 9 November 2009 /Published online: 20 December 2009 # The Author(s) 2009. This article is published with open access at Springerlink.com Abstract The spatial and temporal variations in cloud-to- summer, mainly due to the northward transportation of ground (CG) lightning and precipitation during the summer moisture to the Korean Peninsula. Conversely, the strong monsoon months in Korea have been analyzed in relation to afternoon peak for the southern region was confronted with the regional synoptic weather conditions. The lightning data early morning peaks in the midwestern region during 2001. used in this study were collected from a lightning detection The eastward transport of moisture has been analyzed and network installed by the Korean Meteorological Adminis- was considered to be dominant in 2001. The study of tration, while the precipitation data were collected from 386 several warm and cold type fronts in 2000 and 2001 Automatic Weather Stations spread over the entire Korean indicate that the warm type fronts in 2000 were associated Peninsula during 2000 to 2001. A distinctive morning peak with very little lightning, while the cold type fronts of precipitation is observed over the midwest region of appeared to be responsible for the occurrence of abundant Korea. Along the east coast, little precipitation and CG lightning in 2001, thereby, indicating that the warm and flash counts are found. Despite the strong afternoon peaks cold type fronts were representative of the local lightning of convective rainfall due to the high elevation over the distribution in the respective years. southern inland region, the south coast shows nocturnal or early morning peaks, which represents a common oceanic pattern of flash counts. In 2000, the nighttime peak for 1 Introduction lightning counts dominates over the southern area, while the afternoon peak was strong in the midland during the Convective activity is an important meteorological event. It has been found that the lightning activity associated to convective systems can be a useful indicator of their rain Y.-K. Hyun yield. The connection between lightning and rainfall has Climate Research Lab., National Institute of Meteorological Research, Korean Meteorological Administration, been documented by various researchers (Molinie et al. Seoul 156-720, South Korea 1999; MacGorman and Rust 1998; Uman 1987; Latham 1981; Shackford 1960; Marshall and Radhakant 1978; S. K. Kar Petersen et al. 1999; Carey and Rutledge 2000; Latham et Center for Space and Remote Sensing Research, National Central University, al. 2004; Zhou et al. 2002). The higher correlation between Chung-Li, Taiwan, Republic of China cloud-to-ground (CG) lightning and rainfall than that between total lightning and rainfall has been reported by * K.-J. Ha ( ) Cheze and Sauvageot (1997). The connection between Division of Earth Environmental System, Pusan National University, lightning and convective precipitation has been documented Busan 609-735, South Korea both for individual thunderstorms (Piepgrass and Krider e-mail: [email protected] 1982; Cheze and Sauvageot 1997; Soula and Chauzy 2001) and also for large spatial and long temporal domains J. H. Lee Weather Radar Division, Korean Meteorological Administration, (Sheridan et al. 1997; Petersen and Rutledge 1998). Seoul 156-720, South Korea Moreover, their spatial distribution would be a useful 44 Y.-K. Hyun et al. quantitative indicator of different rainfall regimes, as low-level convergence between the local land–sea breeze indicated by Zipser (1994) and Petersen and Rutledge and the predominant monsoon wind. (1998).AninvestigationconductedbyPetersenand The goal of this study is to investigate the variations in Rutledge (1998) examined the relationship between the the lightning and precipitation activity over the Korean precipitation and lightning on a large spatial and temporal Peninsula during two synoptically different years. The scale for several different parts of the globe using the seasonal, diurnal, and spatial variabilities in CG lightning total rain mass and CG flash density. Direct estimation of have been analyzed; the results were compared with rainfall from CG lightning observations has also been precipitation information. This study will be useful in explored by various researchers (Piepgrass and Krider understanding the role of lightning in the monsoon rain 1982;Buechleretal.1990; Chronis et al. 2004). Despite band over Korea, and this improved understanding could similar synoptic conditions, the actual lightning distribu- eventually result in enhanced proficiency for predicting tion varies day by day due to the random nature of the convective rainfall in similar situations. initiation of thunderstorms. However, many common features are found in the structure of lighting distribution. Moreover, orography and 2 Data and methodology local synoptic conditions have a great influence on the initiation of local lightning and production of precipitation. The lightning data used in this study were collected from a Rainfall, especially when influenced by terrain, is often lightning detection network installed by the Korean Meteoro- highly episodic in time and space. Therefore, because of the logical Administration (KMA; open circle in Fig. 1). The complex topography of the Korean Peninsula, a study of network consisted of eight IMProved Accuracy from the rainfall and lightning activity is needed. The relation- Combined Technology Enhanced Sensitivity and Perfor- ships of lightning and precipitation to certain orographic mance (IMPACT ESP) sensors. The detection efficiency and features (Watson et al. 1994; Finke and Hauf 1996)ortoa position accuracy was obtained by combining time of arrival synoptic pattern (Reap 1994) have been used in this study. and magnetic direction finding technology in the IMPACT Thunderstorms are quite frequent in the Korean Penin- ESP sensor, with the time motivated by GPS. For the sula and have been considered relevant by meteorologists accurate detection of lightning events, three IMPACT sensors for characterizing the meteorology of Korea (Lim and Lee are needed. The flash detection efficiency was greater than 2005; Kar and Ha 2003). In the middle latitudes, the rainfall 90%, with ground strike location accuracy better than 1 km variability during the day is more complex due to the over South Korea as shown in Fig. 1. The lightning detection interaction of regional and synoptic circulations with local efficiency of this type of network has been summarized by flows and convergence zones. These circulations are Cummins et al. (1998). To determine the total (both negative determined by regular and predictable forcing by solar and positive) monthly number of CG lightning flash counts, heating and topographic effects, such as orographic clouds a temporal scale of one month and a spatial scale of 0.05 and sea breeze, of which the Korean Peninsula is an latitude×0.05 longitude were used. example. Nonetheless, the number of studies related to the Korean Peninsula is limited. These studies have not shed any light on the time–space variability of lightning with the regional synoptic weather conditions. For total precipita- tion, Ramage (1952) suggested that most coastal stations around the Yellow Sea had a distinctive morning peak in precipitation based on observed precipitation in East Asia, including China, Korea, and Japan. Stations in the interior land region of East Asia have shown either two peaks of comparable magnitude or no well-defined variation. To explain the early morning peak, the author suggested that warm air advection, which is favorable for the monsoon circulation, plays a crucial role over that region. Ramage (1952) also commented on the intensified diurnal variation in precipitation, which was influenced by land–sea breezes, topography, and nocturnal radiation from cloud tops. Lim and Kwon (1998) have also shown two peaks in the early Fig. 1 Observation stations, lightning detection efficiency (percent), morning and late afternoon for the Korean Peninsula. Oki and system accuracy (kilometer). The thick black and gray lines and Musiake (1994) reported morning peaks in Japan with indicate the system accuracy and detection efficiency, respectively Diurnal and spatial variabilities of monsoonal CG lightning and precipitation and their association 45 Precipitation data were obtained from 386 Automatic for 2000 and the lower two for 2001. The precipitation Weather Stations (AWS) spread over the entire Korean varied from 0 to about 70 mm per day and the number of Peninsula (closed circles in Fig. 1). For simplicity, the CG flashes from 0 to more than 1.0 count per 0.05 precipitation was assumed to be uniformly distributed latitude×0.05 longitude per day. In 2000, the monsoon within 0.25 latitude×0.25 longitude block. Blocks not precipitation started to increase in late June and continued including a station are marked by shaded rectangles in through the end of August. In late August, the precipitation Fig. 1, where the precipitation has been interpolated. Our significantly increased. For 6 days in August, from the 23rd selection of a small spatial scale helped to maintain the to the 28th, heavy rainfall was observed