Extratropical Transformation of Typhoon Vicki (9807): Structural Change and the Role of Upper-tropospheric Disturbances.

Abstract

Extratropical transformation of Typhoon Vicki (9807) is diagnosed in relation to its environment, particularly with respect to interactions with upper tropospheric disturbances, using the gridded dataset of global analysis (GANAL) produced by the Japan Meteorological Agency. TY Vicki made landfall on Japan with its maximum intensity on 22 September 1998, causing damage with strong winds. Vicki lost the diabatically generated potential vorticity (PV) anomaly at 00UTC 23 September 1998, when it was supposed to complete the extratropical transformation. It still had a considerable diabatic PV anomaly during passage over Japan, which is consistent with the cyclone intensity. At 06UTC 22 September, Vicki was located in the lower-baroclinic zone, and strong horizontal divergence directly above the cyclone center was dissipated in the upper troposphere, which suggest that was already beginning extratropical transformation. Regarding the upper tropospheric environment, Vicki was moving northward to the right entrance of the jet streak, and a trough, i.e., mesoscale PV anomaly, approached to the west of Vicki.To the north of the cyclone, mid-tropospheric warm frontogenesis and the associated northward outflow were induced. To the west of the cyclone, the upper-tropospheric frontogenesis associated with the jet entrance and the trough contributed to upper-tropospheric outflow from the cyclone and midtropospheric dry-air inflow. These contributed to organizing a wide rainfall region in the northern semicircle of the cyclone and to limiting the rainfall region in the southwest of the cyclone center. It is also suggested that interactions between upper-and mid-tropospheric outflow, and the midlatitude jet streak to the north of the cyclone contributed to a deepened layer of horizontal divergence that delayed the weakening of the cyclone during the start of the extratropical transformation.

Excitation of Deep Convection to the North of Tropical Storm Bebinca (2006)

“…As described in Section 1, the effect of an upperlevel trough in an extratropical cyclone is a key issue in studies of ETs (e.g., Sinclair 1993;Kitabatake 2002). In the case of Bebinca, an upper-level trough was also located near the storm.…”

Observation and numerical prediction of torrential rainfall over Korea caused by Typhoon Rusa (2002)

“…In particular, as a typhoon approaches the midlatitudes, the rainfall resulting from the direct and indirect influence of the typhoon is closely related to the interactions between the synoptic-scale environment and the topography. Kitabatake [2002] found that an organized rainfall region was induced in the northern semicircle of a typhoon by an extratropical transformation of the typhoon related to upper troposphere disturbances; the rainfall region was limited southwest of the cyclone center. Atallah and Bosart [2003] showed that the baroclinic zone between the juxtaposition of a cold-core potential vorticity (PV) anomaly associated with the midlatitude trough and a warm-core PV anomaly associated with a tropical cyclone provided sufficient precipitation in a region favorable for deep isentropic ascent.…”

Intense Rainfalls on August 17, 1968 over the Kiso-Hida and Nagara River Basin in Japan Associated with Intrusion of Middle Tropospheric Dry Airs over the Low-level Moist Belt

“…He also described the cold-front generation to the southwest of the transformed cyclone. Kitabatake (2002) described, in a case study on the extratropical transformation of TY Vicki in 1998, that ''to the west of the cyclone, middle tropospheric dry air, which was accompanied by the approaching upper tropospheric disturbance, descended into the cyclone and induced active convection to just west of the cyclone eye.' ' Suzuki (2000) described the characteristics of the extratropical transition of tropical cyclones in satellite imagery for 22 cases.…”