A Simulation Study of the Formation of Large-Scale Cyclonic and Anticyclonic Vortices in the Vicinity of the Intertropical Convergence Zone

Abstract

A regional nonhydrostatic mathematical model of the wind system of the lower atmosphere, developed recently in the Polar Geophysical Institute, is utilized to investigate the initial stage of the origin of large-scale vortices at tropical latitudes. The model produces three-dimensional distributions of the atmospheric parameters in the height range from 0 to 15 km over a limited region of the Earth’s surface. Time-dependent modeling is performed for the cases when, at the initial moment, the simulation domain is intersected by the intertropical convergence zone (ITCZ). Calculations are made for various cases in which the initial forms of the intertropical convergence zone are different and contained convexities with distinct shapes, which are consistent with the results of satellite microwave monitoring of the Earth’s atmosphere. The results of modeling indicate that the origin of convexities in the form of the intertropical convergence zone, having distinct configurations, can lead to the formation of different large-scale vortices, in particular, a cyclonic vortex, a pair of cyclonic-anticyclonic vortices, and a pair of cyclonic vortices, during a period not longer than three days. The radii of these large-scale vortices are about 400–600 km. The horizontal wind velocity in these vortices can achieve values of 15–20 m/s in the course of time.

Numerical Modeling of the Initial Formation of Cyclonic Vortices at Tropical Latitudes

“…The present study is the continuation of the investigations of the initial stage of the origin of large-scale vortices in the vicinity of an intertropical convergence zone, fulfilled earlier [23] [24]. It is known that an intertropical convergence zone may be considered as a fluid stream, having enhanced zonal velocities, in the ambient atmospheric gas, with a zonal flow of air being westward.…”

“…This idea has been confirmed with the help of mathematical modeling [23] [24]. In particular, it was shown that the origin of a convexity in the configuration of the intertropical convergence zone can lead to the formation of a single cyclonic vortex during the period of about one day, with the cyclonic center being close to the southern edge of the initial intertropical convergence zone [23].…”

“…In particular, it was shown that the origin of a convexity in the configuration of the intertropical convergence zone can lead to the formation of a single cyclonic vortex during the period of about one day, with the cyclonic center being close to the southern edge of the initial intertropical convergence zone [23]. Moreover, the results of mathematical modeling have indicated that the origin of a convexity of the intertropical convergence zone, having the specific forms, can lead to the formation of not only a single cyclonic vortex but also a cyclonic-anticyclonic pair [23] and pair of cyclonic vortices [24], during the period not longer than three days. It can be noted that the results of observation of the Earth's atmosphere indicated a simultaneous origin of twin tropical cyclones sometimes [30].…”

“…This regional model was applied to investigate the formation mechanism of polar lows [21] [22], too. Also, this regional model was applied to verify the hypothesis of the influence of the shape of the intertropical convergence zone (ITCZ) on the process of the formation of tropical cyclones [23] [24]. In these investigations, it was shown that the origin of convexities in the form of the intertropical convergence zone, having the specific configurations, can lead to the formation of different large-scale vortices, in particular, a single cyclonic vortex, pair of cyclonic-anticyclonic vortices, and pair of cyclonic vortices, during the period not longer than three days.…”

A Modeling Study of the Initial Formation of Polar Lows in the Vicinity of the Arctic Front

“…This regional model has been utilized in order to investigate numerically the mechanisms responsible for the formation of large-scale vortices over the ocean surface at tropical latitudes [31][32][33]. In these investigations, it was shown that the origin of convexities in the form of the intertropical convergence zone (ITCZ), having distinct configurations, can lead to the formation of different large-scale vortices, in particular, a 2 Advances in Meteorology cyclonic vortex, pair of cyclonic-anticyclonic vortices, and pair of cyclonic vortices, during the period not longer than three days.…”