A Synoptic-Dynamic Analysis of the Intense Arctic Cyclone of Early August 2012

A surface cyclone formed along an anomalously strong baroclinic zone over north-central Russia on 2-3 August 2012. This cyclone moved northeastward, intensified slowly, crossed the northeastern coast of Russia on 4 August, and strengthened rapidly as it moved poleward over the Arctic Ocean on 5-6 August. By 1200 UTC 6 August, this intense Arctic Ocean cyclone had achieved a minimum sea level pressure of < 965 hPa near 83°N and 170°W. This presentation is motivated by the likelihood that this cyclone was arguably the most intense storm system to impact the Arctic Ocean in the modern data record going back to the International Geophysical Year in 1957-1958. The purpose of this presentation will be to present the results of a synoptic-dynamic analysis of this intense early August cyclone to help gain a better understanding of why such intense cyclones are so rare over the Arctic Ocean.

Anticyclonic wave breaking in the upper troposphere across Russia in late July and very early August 2012 created an anomalously strong baroclinic zone between 60-80°N. Between 90°E and the Dateline, negative 850 hPa temperature anomalies between -2° and -4°C were found poleward of 70-75°N over the Arctic Ocean in the 1-5 August time mean. Likewise, positive time-mean 850 hPa temperature anomalies upwards of 8-9°C were situated over eastern Russia near 60°N. In response to this observed temperature anomaly pattern, an anomalously strong 850 hPa temperature gradient of ~10°C (2000 km)-1 between 60-80°N helped to sustain an anomalously strong (20-25 m s-1) 250 hPa jet along the coast of northeastern Russia. A local wind speed maxima along this 250 hPa jet corridor reached 40-50 m s-1 immediately upstream of the surface cyclone.

Because the surface cyclone intensified most rapidly over the relatively ice free Arctic Ocean in the poleward exit region of the aforementioned jet streak, the question arises as to how much sensible and latent heat fluxes from the relatively ice free Arctic Ocean contributed to destabilizing the lower troposphere and augmenting the dynamically driven component of the observed cyclogenesis. Likewise, unusually high observed 1000-500 hPa thickness values between 564-570 dam in the warm sector of the developing cyclone over north-central Russia were indicative of the strength of the cyclone warm sector and the ability of warm-air advection to sustain deep ascent. We will attempt to distinguish the relative importance of dynamical versus thermodynamical forcing to the cyclogenesis process in our presentation.