Seasonal climate variability and predictability issues associated with recurving tropical cyclones, an extreme Arctic ridge, and a land-falling atmospheric river from 27 November to 5 December 2007

A noteworthy aspect of the Northern Hemisphere (NH) October–December 2007 climate was the existence of 90-day positive tropospheric geopotential height and temperature anomalies poleward of the Arctic Circle to the north of Alaska. A tropospheric-deep ridge that existed in this region between 27 November and 5 December, however, accounted for 30-50% of the 90-day geopotential height and temperature anomalies and suggests a linkage between the multiscale singular event and the NH climate of late 2007.

Ridge development appeared to be related to the complex evolution of a 100+ m s-1 North Pacific jet stream (NPJ) that 1) supported the poleward transport of anomalously high (+10 to +20 mm) precipitable water values within the NPJ-exit region to over the Arctic Ocean, 2) was accelerated by the recurvature of, and potentially warm outflow from, western Pacific typhoons Hagibis and Mitag and tropical depression (TD) 26W, and 3) influenced the rapid extratropical intensification of the merged remnants of Mitag and TD 26W. The latter cyclone, in association with a land-falling atmospheric river, impacted the Pacific Northwest from 1-4 December with rainfall amounts exceeding 100 mm (per day) and widespread wind gusts greater than 45 m s-1.

The presented research will focus on the synoptic-scale evolution and predictability of the tropical and midlatitude North Pacific flow. Further emphasis will be given to quantifying the role of potential vorticity, vorticity, heat, and moisture fluxes in the support of Arctic ridge development and identifying a climatology of similar Arctic ridge events.