A noteworthy aspect of the Northern Hemisphere (NH) October–December 2007 climate was the existence of 90- and 30-day positive tropospheric geopotential height, thickness, and temperature anomalies poleward of the Arctic Circle to the north of Alaska. While significant (approximately one standard deviation above the mean) on inter-seasonal timescales, these positive anomalies were influenced by an extreme tropospheric-deep ridging event from 30 November to 3 December that was associated with a major reconfiguration of the North Pacific atmospheric circulation in late November. The purpose of this presentation is to illustrate the structure and hemispheric impact of a multiscale singular event that evolved over a time scale of 10–15 days and greatly contributed to the 2007 autumnal season climatic variability at high latitudes in the NH.

A signature of the extreme ridging event was that four-day positive 300-hPa geopotential height (850-hPa temperature) anomalies exceeded 80 dam (20.0 °C) to the north of Alaska and represented values approximately four standard deviations above the mean. The lower tropospheric (850-hPa) warmth at Barrow, Alaska, derived from an analysis of 50+ years of radiosonde data, exceeded the previous December maximum of 4.2 °C by 4.6 °C, setting a new monthly temperature maximum of +8.8 °C.

The initial ridge eruption was related to the multiscale evolution and interactions among western Pacific typhoons Hagibis and Mitag, tropical depression 26W, equatorial tropical wave activity in the form of convection coupled to an oceanic Kelvin wave, and the midlatitude atmospheric flow. The energetic tropical activity, in conjunction with deep tropospheric meridional flow established by midlatitude cyclone activity, supported the transport of high (~20 mm) precipitable water values and the aforementioned warm temperatures poleward from near Hawaii across Alaska and over the Arctic Ocean. The amplified flow pattern later produced a series of strong extratropical cyclones that impacted the Pacific Northwest US from 1–3 December with heavy rain, snow, and widespread wind gusts greater than 45 m s-1.

The presented research will focus on 1) a brief climatology of similar extreme Arctic ridging events, 2) the synoptic-scale evolution of the tropical and midlatitude North Pacific flow that supported the Arctic ridge development and strong extratropical cyclones, and 3) quantifying the role of potential vorticity, vorticity, heat, and moisture fluxes in the support of Arctic ridge development.