Numerical Study of Explosively Developing Extratropical Cyclones in the Northwestern Pacific Region

Abstract

Numerical simulations of six explosively developing extratropical cyclones in the northwestern Pacific Ocean region are conducted using a regional mesoscale numerical model [the fifth-generation Pennsylvania State University-National Center for Atmospheric Research Mesoscale Model (MM5)]. Cyclones are categorized according to the locations where they form and develop: Okhotsk-Japan Sea (OJ) cyclones originate over the eastern Asian continent and develop over the Sea of Japan or the Sea of Okhotsk, Pacific Ocean-land (PO-L) cyclones also form over the Asian continent and develop over the northwestern Pacific Ocean, and Pacific Ocean-ocean (PO-O) cyclones form and develop over the northwestern Pacific Ocean. Two cases (the most extreme and normal deepening rate cases for each cyclone type) are selected and simulated. Simulations show that the extreme cyclone of each type is characterized by a different mesoscale structure and evolutionary path, which strongly reflect the larger-scale environment: an OJ cyclone has the smallest deepening rates, associated with a distinct upper-level shortwave trough, a clear lower-level cold front, and a precipitation area that is far from the cyclone center; a PO-L cyclone has moderate deepening rates with high propagation speeds under zonally stretched upper-level jets; and a PO-O cyclone has the strongest deepening rates associated with large amounts of precipitation near its center. Sensitivity experiments involving the latent heat release associated with water vapor condensation show that PO-O cyclones rarely develop without a release of latent heat and their structures are drastically different from the control runs, while OJ cyclones exhibit almost the same developments and have similar structures to the control runs. These tendencies can be seen in both extreme and normal deepening rate cases. These results reveal that the importance of latent heat release to explosive cyclone development varies among the cyclone types, as is reflected by the cyclone origin, frontal structure, moisture distribution, and jet stream configuration.

Influences of the Kuroshio/Oyashio Extensions on Air–Sea Heat Exchanges and Storm-Track Activity as Revealed in Regional Atmospheric Model Simulations for the 2003/04 Cold Season*

“…The moist processes are important for the amplification of individual cyclones (e.g., Kuo et al 1991;Kuwano-Yoshida and Asuma 2008), since their heat exchanges with the underlying ocean via SHF, on one hand, acts to restore the SAT gradient but, on the other hand, it acts as thermal damping for SAT anomalies associated with them (Nakamura et al 2004). In this section, we discuss the relationship between LHF, precipitation, and storm activity in our simulations.…”

Accelerating two-stage explosive development of an extratropical cyclone over the northwestern Pacific Ocean: a piecewise potential vorticity diagnosis

“…Additionally, for POÁO cyclones, latent heat release (LHR) was also a very important factor (Chen and Dell'Osso, 1987). In order to investigate the role of LHR, Kuwano- Yoshida and Asuma (2008) removed LHR from simulations of OJ, POÁL and POÁO cyclones and, based on sensitivity experiments, proposed that LHR affects cyclone development mainly through nonlinear interactions with the upper-level trough and jet.…”

The Role of Latent and Sensible Heat Fluxes in an Explosive Cyclogenesis over the South American East Coast

“…Kuwano-Yoshida and Asuma (2008) showed that the moisture advection from the equator to the cyclone center is important for explosive cyclogenesis over the northwestern Pacific Ocean. In our case, the advection appears to be important because the largest specific humidity differences were observed close to the anticyclone.…”