Numerical Simulation of the Development of the Intermediate-Scale Cyclone in a Moist Model Atmosphere

T. Nitta Laboratory for A itnosphffic Research, University of Illionois, Urbana 61801

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Y. Ogura Laboratory for A itnosphffic Research, University of Illionois, Urbana 61801

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Abstract

The genesis and development of an intermediate-scale cyclone in middle latitudes was simulated numerically and its three-dimensional structure analysed.

A six-level moist primitive equation model was run for a channel flow with an initial weak baroclinicity. The motion was initiated in the flow by introducing wave motion with wavelength of 6000 km. As the initial disturbance was intensified, an extended front developed and, after several days in real time, an intermediate-scale disturbance was formed on the extended front. The analysis indicates that this secondary cyclone has a longitudinal wavelength of about 1500 km and a latitudinal half-wavelength of about 600 km. The depression is observed most strongly below 700 mb with a vertical or slightly eastward tilted trough axis. A sharp concentration of isotherms is situated in the northern part of the cyclone. In the lower troposphere, the warm air is observed on the cast side of the low center and the cold air on the west side. This thermal contrast is reversed in the middle troposphere. A remarkable accumulation of water vapor assumes a pear-like shape over the depression area. The thermal structure of the simulated depression was compared with the observed data and some agreement was noted. The effect of the water vapor was also examined in the evolution of the simulated intermediate-scale cyclone.

Abstract

The genesis and development of an intermediate-scale cyclone in middle latitudes was simulated numerically and its three-dimensional structure analysed.

A six-level moist primitive equation model was run for a channel flow with an initial weak baroclinicity. The motion was initiated in the flow by introducing wave motion with wavelength of 6000 km. As the initial disturbance was intensified, an extended front developed and, after several days in real time, an intermediate-scale disturbance was formed on the extended front. The analysis indicates that this secondary cyclone has a longitudinal wavelength of about 1500 km and a latitudinal half-wavelength of about 600 km. The depression is observed most strongly below 700 mb with a vertical or slightly eastward tilted trough axis. A sharp concentration of isotherms is situated in the northern part of the cyclone. In the lower troposphere, the warm air is observed on the cast side of the low center and the cold air on the west side. This thermal contrast is reversed in the middle troposphere. A remarkable accumulation of water vapor assumes a pear-like shape over the depression area. The thermal structure of the simulated depression was compared with the observed data and some agreement was noted. The effect of the water vapor was also examined in the evolution of the simulated intermediate-scale cyclone.

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