| Abstract: | Structural changes during the intensification of a tropical storm into a hurricane in a numerical simulation are examined. A 10 layer primitive equation model that employs a horizontal grid spacing of 20 km over 4400 × 4400 km area is integrated. An elongated band in vertical motion over the storm area intensifies slowly during the first few hours. In the upper troposphere high pressures arise due to condensational heating. Between 8–12 h strong outflow winds develop in the upper troposphere due to the increased pressure gradients. Strong divergence occurs in the outflow wind region, and a large increase in the vertical motion, condensational heating and intensification rate of the storm ensues. Between 12–24 h the elongated band of the storm stage transforms into an eye-wall like structure, and the tropical storm intensifies into a hurricane. Regions with negative moist potential vorticity appear in the high troposphere. Widening of area of condensation and slanting of the convergence area occurs with height in the high level negative moist potential vorticity regions. Results suggest that the formation of anvil clouds in some cases may be due to the development of slantwise convection on the outer periphery of a hurricane's eye-wall. |
