Observations of the Early Evolution of an Explosive Oceanic Cyclone during ERICA IOP 5. Part II: Airborne Doppler Analysis of the Mesoscale Circulation and Frontal Structure

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  • 1 Department of Atmospheric Sciences, University of California at Los Angeles, Los Angeles, California
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Abstract

Using airborne Doppler radar data collected onboard the NOAA P-3 aircraft during ERICA IOP 5, the three-dimensional wind field of the circulation center of an explosive extratropical cyclone is shown. The cyclone was entering its rapid intensification stage at the time of the analysis. The circulation formed along a frontal boundary and was characterized by mean vertical velocity, vorticity, and divergence values comparable to those derived for mature hurricanes. In addition, the circulation at this early stage of cyclone development was relatively shallow (>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 circulation is the preexisting, shallow low that has been shown to form in association 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 extreme examples of intense cold fronts.

Abstract

Using airborne Doppler radar data collected onboard the NOAA P-3 aircraft during ERICA IOP 5, the three-dimensional wind field of the circulation center of an explosive extratropical cyclone is shown. The cyclone was entering its rapid intensification stage at the time of the analysis. The circulation formed along a frontal boundary and was characterized by mean vertical velocity, vorticity, and divergence values comparable to those derived for mature hurricanes. In addition, the circulation at this early stage of cyclone development was relatively shallow (>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 circulation is the preexisting, shallow low that has been shown to form in association 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 extreme examples of intense cold fronts.

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