Statistical Study of Band-Shaped Rainfall Systems, the Koshikijima and Nagasaki Lines, Observed around Kyushu Island, Japan

Abstract

The favorable environmental low-level wind condition under which band-shaped rainfall systems form around Kyushu Island, located in the western part of Japan, was statistically examined using upper-air sounding data at Kagoshima and meteorological radar data. The representative rainbands extending northeastward from the Koshikijima Islands (the Koshikijima line), and the Nagasaki Peninsula (the Nagasaki line), are discussed in this study. The favorable conditions for their formation and maintenance are that the southwesterly low-level wind field persists for longer than 12 hours, and that the wind speed at an 850 hPa level is between 5 m s À1 and 25 m s À1 . When the Koshikijima line stagnates for a long time to cause heavy rainfall, other disturbances are usually found around the Koshikijima Islands. Meanwhile, the Nagasaki line forms more frequently than the Koshikijima line, and it often stagnates for a long time without other disturbance.

A Role of Environmental Shear on the Organization Mode of Quasi-Stationary Convective Clusters during the Warm Season in Japan

“…and in the Tohoku region (i.e., the northern part of the main island of Japan). This distribution of the orientation features seems to be consistent with the previous studies; the southwest-northeast rainbands over the western part of Kyushu Island (Kato 2005) and over Shikoku Island (Unuma and Murata 2012). Figure 4 shows the relationships between orientations of the QSCCs and environmental shear directions.…”

“…Low-and/or middle-level environmental shears play important roles in controlling convective organization mode over tropical, sub-tropical (Barnes and Sieckman 1984;Alexander and Young 1992;LeMone et al 1998;Johnson et al 2005;Cetrone and Houze 2006), and midlatitude regions (Bluestein and Jain 1985;Blanchard 1990;Houze et al 1990;Rotunno et al 1988;Parker and Johnson 2000;Seko 2001;Weisman and Rotunno 2004;Schumacher and Johnson 2005;Kato 2005;Takemi 2006Takemi , 2007Seko 2010). Because the vertical shears vary under background synoptic conditions, the mode of convective organization is considered to be modulated by the regional features of the synoptic conditions.…”

“…Kato (2005) examined the frequency distributions of the precipitation and found that the elongated convective systems tend to occur when the wind direction at 925− 850 hPa levels is southwest. A similar analysis except for the wind direction at the 850-hPa level was conducted by Unuma and Murata (2012).…”

Decrease in Baiu Precipitation and Heavy Rainfall Days in Late June of the 2000s in Northwestern Kyushu, Western Japan

“…These facts suggest that the decrease in precipitation at Nagasaki might be partly a reflection of the rainfall area's narrow meridional extension, which contains the heavy rainfall area (≥ 50 mm day −1 ). Conversely, heavy rainfall sometimes occurs in the warm sector of BF (Ninomiya 1978;Kato 2005). An example would be the significant precipitation at Nagasaki when the surface front was located just to its north in 1971−2000.…”

Seasonal Migration of the Baiu Frontal Zone over the East China Sea: Sea Surface Temperature Effect

“…The East China Sea is a key region of the Baiu frontal rainfall because the accumulative precipitation for June in the Baiu frontal zone is the largest in Kyushu, which is located at the eastern edge of the East China Sea and regularly suffers heavy rainfall disasters (e.g., Nagata and Ogura 1991;Kato 1998;Kato 2005). During several of these heavy rainfall events, a localized cold high over the Yellow Sea has been confirmed on the surface weather map (Moteki et al 2004a(Moteki et al , 2004b.…”