Tropical Cyclone Propagation.
Final rept. 1 Nov 91-31 Oct 94,
COLORADO STATE UNIV FORT COLLINS DEPT OF ATMOSPHERIC SCIENCE
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This paper discusses the question of tropical cyclone propagation or why the average tropical cyclone moves 1-2 ms faster and usually 10-20 deg to the left of its surrounding or 5-7 deg radius deep layer 850-300 mb steering current. It is shown that the primary factor causing tropical cyclones to propagate faster and to the left of their steering flow is their location within a baroclinic environment. Irrespective of direction to which it moves or of the latitude it exists, the tropical cyclone has an environment of warm tropospheric air on its right side and cold tropospheric air on its left side. The vertical wind shear and the slope to cold air resulting from this baroclinic environment lead to a reduction in the component of surrounding wind in the direction of cyclone movement. Hydrostatics dictate that the vertical slope of anticyclones, monsoon troughs, and frontal systems be towards the cold air side. The faster movement of the cyclone center creates a forward minus rear wind asymmetry which inturn causes the inner cyclone circulation to move 10-20 deg to the left of the broader steering current flow.