A Numerical Study of the Effect of a Mountain Range on a Landfalling Tropical Cyclone

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  • 1 Geophysical Fluid Dynamics Laboratory/N0AA, Princeton University, Princeton, NJ 08542
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Abstract

A triply-nested, movable mesh model was used to study the effects of a mountain range on a landfalling tropical cyclone embedded in an easterly flow of ∼10 m s−1. The integration domain consisted of a 37° wide and 45° long channel, with an innermost mesh resolution of 1/6°. An idealized mountain range with maximum height of ∼958 meters was placed parallel to the shoreline. The mountain range, which spanned 19° in the north–south direction and 5° in the east–west direction, was centered in the middle of the channel. Results obtained were compared with a previous landfall simulation, performed without the effect of the mountain range included. In particular, comparison was made of the total storm rainfall, maximum wind distribution and storm decay rate. It was found that the storm filled much more rapidly in the simulation run with the mountain included. The mountain range affected the decay rate through reduction in the supply of latent and kinetic energy into the storm circulation during, as well as after, passage of the storm over the mountain. It was found that a low-level, warm and dry region was produced where the storm winds descended the mountain slope.

In order to better isolate the effect of the mountain on the basic easterly flow, a supplemental integration was performed for the flow without the storm. It revealed that the mountain range caused a significant change in the basic flow over the mountain as well as up to several hundred kilometers downstream and extending considerably above the mountain top. A low-level southerly jet was observed to the west of the mountain base.

Abstract

A triply-nested, movable mesh model was used to study the effects of a mountain range on a landfalling tropical cyclone embedded in an easterly flow of ∼10 m s−1. The integration domain consisted of a 37° wide and 45° long channel, with an innermost mesh resolution of 1/6°. An idealized mountain range with maximum height of ∼958 meters was placed parallel to the shoreline. The mountain range, which spanned 19° in the north–south direction and 5° in the east–west direction, was centered in the middle of the channel. Results obtained were compared with a previous landfall simulation, performed without the effect of the mountain range included. In particular, comparison was made of the total storm rainfall, maximum wind distribution and storm decay rate. It was found that the storm filled much more rapidly in the simulation run with the mountain included. The mountain range affected the decay rate through reduction in the supply of latent and kinetic energy into the storm circulation during, as well as after, passage of the storm over the mountain. It was found that a low-level, warm and dry region was produced where the storm winds descended the mountain slope.

In order to better isolate the effect of the mountain on the basic easterly flow, a supplemental integration was performed for the flow without the storm. It revealed that the mountain range caused a significant change in the basic flow over the mountain as well as up to several hundred kilometers downstream and extending considerably above the mountain top. A low-level southerly jet was observed to the west of the mountain base.

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