An intense tropical cyclone, Typhoon Rusa (2002), passed over the Korea Peninsula in late August 2002. It made landfall on the south coast of the peninsula and crossed over the central-east coast. The coastal areas of the central-eastern peninsula were devastated by this storm, mainly due to heavy rainfall, especially in the area located on the eastern side of the Taebaek Mountains. In August 31, 2002 Gangneung, located in that area, reported a record-breaking rainfall of 870.5 mm in 24 hrs. Daegwallyeong, located on the eastern slope of the same mountains, recorded a 24-hr accumulated rainfall of 712.5 mm. In contrast, the western side of the mountains had relatively small rainfall totals. This strongly suggests that the rainfall associated with Rusa was enhanced by the pornographic convective rain induced by the easterly winds from the storm.

In this study, the orographic effect on this heavy rainfall event is investigated using the PSU/NCAR MM5. A triple nesting procedure is employed at the standard horizontal resolutions of 27km, 9km and 3km, respectively. A control experiment (with terrain) exhibited an excellent forecast of the heavy rainfall highly localized in the eastern coastal area on the foot of the Mountains. An experiment removing the model terrain produced less localized rainfall over a relatively broad area in the central-eastern part of the peninsula. The simulation results confirm that strong easterly flow over the northern part of Rusa resulted in orographically-induced convective rainfall and greatly increased the amount of rainfall that would have occurred over flat terrain. The model predicted rainfall amounts were sufficient to produce flooding over the eastern foothills of the Taebaek Mountains.