OBSERVATIONS OF THE EARLY EVOLUTION OF AN EXPLOSIVE OCEANIC CYCLONE DURING ERICA IOP-5 .2. AIRBORNE DOPPLER ANALYSIS OF THE MESOSCALE CIRCULATION AND FRONTAL STRUCTURE

Using airborne Doppler radar data collected onboard the NOAA P-3 aircr aft during ERICA IOP 5, the three-dimensional wind field of the circul ation center of an explosive extratropical cyclone shown. The cyclone was is entering its rapid intensification stage at the time of the ana lysis. The circulation formed along a frontal boundary and was charact erized by mean vertical velocity, vorticity, and divergence values com parable to those derived for mature hurricanes. In, addition, the circ ulation at this early stage of cyclone development was relatively shal low (<2.5 km AGL). Intense convection occurred within and surrounding the center of the circulation suggesting that diabatic effects played a role in its development. It is believed that the mesoscale circulati on is the preexisting, shallow low that has-been shown to form in asso ciation with explosive cyclogenesis. The wind synthesis also revealed the structure of the bent-back warm front, which had undergone a scale contraction. The intensity of this warm front, based on the kinematic depiction of the strength of the secondary circulation and the small spatial scale of the frontal discontinuity, may have been greater than any other case documented in the literature and was comparable to ext reme examples of incense cold fronts.