Movement and vertical coupling of adiabatic baroclinic tropical cyclones

The vertical coupling and movement of an adiabatic baroclinic tropical cycl one (TC) are investigated through two numerical experiments in which the TC is affected by either a vertical environmental shear or a differential bet a drift. In both cases, the initial response of the symmetric vortex is to tilt in the vertical. In response to the vertical tilt, a three-dimensional asymmetric circulation with a typical radius of 100 km develops within the TC core region. In addition, the wavenumber-one potential vorticity (PV) a nomalies develop with positive anomalies downtilt (uptilt) above (below) th e maximum PV level in order to maintain a balanced state between the therma l and dynamical fields. On a beta plane, in contrast to the beta gyres, the mesoscale asymmetric circulation is a pair of counterrotating inner gyres centered at the radius of maximum wind. As a result, the resulting three-di mensional mesoscale asymmetric circulation, not the penetration flow, plays an important role in the vertical coupling of adiabatic baroclinic vortice s. In both cases, the TC motion is not simply due to the advection of the s ymmetric PV component by the asymmetric (ventilation) flow. The horizontal advection of the asymmetric PV anomalies by the symmetric cyclonic flow and the vertical PV advection associated with the asymmetric vertical motion a lso considerably contribute to the TC motion. The latter two processes also play a critical role in the vertical coupling of the baroclinic TC due to the presence of the vertical PV gradient.