标题：Energetics characteristics accounting for the low-level wind’s rapid enhancement associated with an extreme explosive extratropical cyclone over the western North Pacific Ocean
摘要：During mid-January 2011, a rarely seen twin-extratropical-cyclone event appeared over the western North Pacific Ocean. One of the twin cyclones developed into an extreme explosive extratropical cyclone (EEC), which was comparable to the intensity of a typhoon. Rotational and divergent wind kinetic energy (KE) analyses were applied to understand the low-level wind’s rapid enhancement associated with the cyclone. It was found that: (i) the total wind KE associated with the EEC showed a remarkable enhancement in the lower troposphere during the cyclone’s maximum development stage, with the maximum/minimum wind acceleration appearing in the southeastern/northwestern quadrant of the EEC; (ii) the rotational wind KE experienced an obvious increase, which corresponded to the total wind KE enhancement, whereas the divergent wind KE, which was much smaller than the rotational wind, mainly featured a decreasing trend; (iii) the rotational wind KE enhancement showed variational features consistent with the horizontal enlargement and upward stretching of the EEC; (iv) the nonorthogonal wind KE enhanced the total wind KE in regions with strong rotational wind, which resulted in the maximum lower-tropospheric maximum wind, whereas in regions with strong divergent wind it mainly reduced the total wind KE; (v) the northward transport of total wind KE and the rotational wind KE production due to the work done by pressure gradient force were dominant factors for the enhancement of winds associated with the EEC, particularly in its southeastern section. In contrast, an overall conversion from rotational wind KE to divergent wind KE decelerated the rotational wind enhancement.
