Characteristics of an Explosive Cyclone over Northeast China Revealed by Satellite Water Vapor Imagery

In this paper, an explosive cyclone (EC) that occurred over Northeast China in the spring of 2016 is studied by using 6.7 μm FY satellite water vapor (WV) imagery and NCEP (1°×1°) reanalysis data. Moreover, the evolutions of the upper-level jet stream (ULJ), the vertical motions, and the potential vorticity (PV) are analyzed in detail. Results show that different shapes of the WV image dark zones could reflect different stages of the EC. At the pre-explosion stage, a small dark zone and an S-shaped baroclinic leaf cloud can be found on the WV imagery. Then the dark zone expands and the leaf cloud grows into a comma-shaped cloud at the explosively developing stage. At the post-explosion stage, the dark zone brightens, and the spiral cloud forms. The whole process can be well described by the WV imagery. The dynamic dry band associated with the sinking motion and the ULJ can develop into the dry intrusion later, which is an important signal in forecasting the EC and should be paid attention to when analyzing the WV imagery. Furthermore, the mechanism is also analyzed in detail in this article. EC usually occurs in the left-exit region of the 200-hPa jet and the region ahead of the 500-hPa trough where there is significant positive vorticity advection (PVA). When the EC moves onto the sea surface, the decreased friction would favour the development of the EC. The upper-level PVA, the strong convergence at low level, and the divergence at high levels can maintain the strong updraft. Meanwhile, the high PV zone from the upper levels extends downward, approaching the cyclone. Together, they keep the cyclone deepening continuously.