Mesoscale Structures of Air Flow in a Mei-yu Front Leading Edge Observed by Aircraft off the East Coast of Taiwan during TAMEX IOP 9

Abstract

In order to investigate the mesoscale structures and appropriate mechanisms for their maintenance in the Mei-yu front leading edge during the TAMEX (Taiwan Area Mesoscale EXperiment) TOP 9 (15 June 1987) off the east coast of Taiwan, we measured the fine-scale in-situ data by different sensors and sensed radar data by two airborne radars mounted on the NOAA P-3 research aircraft traversing the frontal system at six different altitudes. Based upon the sudden increase of the turbulence intensities, the position of the frontal leading edge at each flight level was identified exactly and, after deducting the propagating distance of the frontal system, the composited vertical cross sections of the system in kinematics, dynamics and thermodynamics was feasible.The significant findings are: the frontal edge was parallel to the isolines of horizontal component of wind and perturbed air density and the frontal edge demonstrated a well-defined density current, the variation of thermodynamic parameters was not obvious, but the pattern of potential temperature revealed a cold core in the lower level behind the frontal edge, which coincided with the position of the heaviest air density. The probable mechanisms for the propagation of the density current and the maintenance of the frontal system were proposed to be the intense horizontal pressure gradient force from rear to front in the cold core region and the moderate convective instability at the head of the system as well as the kinetic energy transport from the mean flow.