Numerical experiments using a mesoscale meteorological model (MM5) are performed to evaluate the mountainous orographical effects on the heavy rainfalls brought by Typhoon 0514 (NABI), which caused the flood disaster in the southeast Kyushu area of Japan. The terrain conditions considered in the numerical model are three folds: first, a flat terrain with the altitude 1m above mean sea level; second, an idealized line-shaped mountain terrain; third, a complex terrain using GTOPO30. Although an accumulated rainfall due to Typhoon 0514 is recorded higher than 1,000 mm, a calculated one using the flat terrain is 250-300 mm. The calculated rainfall using the complex terrain becomes 200-300% (500-900 mm) in comparison to flat terrain case. This discrepancy is found to cause by blocking and evolving the convective cells, which are generated by lifting up the water vapor along the mountain slope in the windward areas. A ratio of the forecasted rainfall with/without orography provided an important index for the risk of the heavy rain in the tropical cyclone.
Numerical experiments using a mesoscale meteorological model MM5 were performed to evaluate the mountainous orographical
effects on heavy rainfalls brought by Typhoon 0514 NABI, which caused a flooding disaster in the southeast Kyushu area of
Japan. The numerical modeling studies examined three terrain conditions using a numerical model: A flat terrain with altitude 1 m above
mean sea level; an idealized, line-shaped mountain terrain; and a complex terrain using topography data from the U.S. Geological Survey.
Although the total observed rainfall due to Typhoon 0514 was greater than 1,000 mm, the rainfall value calculated using the flat terrain
conditions was 250–300 mm; and the value calculated using the complex terrain conditions was 500–900 mm. This discrepancy was
found to result from the evolution of convective cells, generated by water vapor lifted along the mountain slope in the windward areas.
The ratio of forecasted rainfall with and without orography provides an important index for evaluating the risk of heavy rain in a tropical
cyclone.
Orographical Effects of Heavy Rainfall by Typhoon 0514 (NABI)
NHR-22441.pdf
(1.16MB)
