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ABSTRACT The atmospheric state and synoptic situation associated with widespread summer June, July, and August temperature extremes in southern Alaska is explored. Using ERA-Interim data and a self-organizing map framework, the evolution of the atmospheric state leading up to days that are defined as experiencing extreme surface temperature are compared with the evolution for non-extreme days. The variables evaluated include circulation at the surface and aloft and surface radiative fluxes. For warm extremes, blocking evident in the 500 hPa flow combined with anomalously large surface downward shortwave radiation allowed surface temperatures to become extreme. For cold extremes, an upper level trough and cold air advection aloft coupled with a more minor role of anomalously negative surface downward shortwave radiation were important. The self-organizing map framework allowed an investigation of these details beyond a composite analysis of all extremes. [ABSTRACT FROM AUTHOR]

The article focuses on a study which analyzed the relationship between near-surface atmospheric circulation and precipitation in the Mackenzie and Yukon River basins. Using self-organizing maps, a climatology of sea level pressure patterns based on ERA40 reanalysis was developed. Near-surface atmospheric patterns in the region and low-pressure patterns over land areas and the Beaufort/Chuckchi Seas in the summer was analyzed.

This paper describes work to improve the understanding of the broad range of factors affecting the occurrence of flooding in Barrow, Alaska, using as a basis the series of extreme events that have affected the community over the past 50 years. A numerical weather prediction model and a storm surge inundation model have been applied to the 21 case studies identified in National Weather Service data as high wind events. Based on this simulation work flow, a reduced-form model that adequately describes the flooding response has been developed. Specifically, it was found that when wind is forecast to be greater than 13 m s-1 (30 mph) for at least 20 h, this is the most accurate predictor of the possibility of damaging flood. It was found that wind direction, the magnitude of fetch to the sea ice edge (when present), and maximum wind speed were in contrast relatively small contributors to the likelihood of flooding. [ABSTRACT FROM AUTHOR]

The coastal geography of Barrow, Alaska, makes the city vulnerable to weather events that cause flooding and erosion. This study uses the self-organizing map (SOM) algorithm, an unsupervised learning process that codifies large, multivariate datasets onto a 2-dimensional array, or map, to study large-scale circulation patterns associated with temperature and high wind extremes at Barrow. The analysis first uses the SOM algorithm to produce an automated 55 yr synoptic climatology of daily sea level pressure patterns for the western Arctic for August to November, when the area is potentially ice free. The results are in agreement with previous Arctic climatologies, showing the Aleutian Low to be dominant in southern Alaska, and high pressure prevalent over the Beaufort and Chukchi Seas. The SOM algorithm is then used to study circulation patterns associated with temperature and high wind extremes at Barrow. These results show that high winds are associated with patterns containing a strong pressure gradient between the Aleutian Low and the Beaufort and Chukchi Seas and also with patterns that contain a low pressure system to the north of Barrow. High (low) air temperature extreme anomalies are associated with patterns that produce strong, southerly (northerly) air flow at Barrow. This study demonstrates the utility of using SOMs to investigate the relationship between local weather conditions and large-scale patterns. This approach can be applied to future global climate model (GCM) simulations to investigate the impact of changes in large-scale circulation patterns to local extreme events. [ABSTRACT FROM AUTHOR]

The Beaufort–Chukchi cyclones of October 1963 and August 2000 produced the highest winds ever recorded in Barrow, Alaska. In both cases, winds of 25 m s[sup -1] were observed with gusts unofficially reported at 33 m s[sup -1] . The October 1963 storm caused significant flooding, contaminated drinking water, and interrupted power supplies. The August 2000 storm caused the wreck of a $6 million dredge, and removed roofs from 40 buildings. Both storms were unusual in that they tracked eastward from the East Siberian Sea into the Chukchi and Beaufort Seas, rather than following a more typical northward track into the Arctic Ocean. This paper addresses, through modeling and analysis, the development processes of these two storms. The October 1963 system was a long-lived, warm core, zonally elongated cyclone that traversed around the Arctic basin through the Canadian Archipelago. The August 2000 system was an open-wave cyclone that dissipated rapidly into a weak, cold core eddy in the Alaskan sector of the Beaufort Sea. Approximating the contributions to development using terms in a quasigeostrophic omega equation, it was found that both storms were characterized by the increasing importance of the convergence of the Q vector (representing differential vorticity advection and thermal advection) in the midtroposphere, at the expense of forcing by the turbulent fluxes of heat, moisture, and momentum in the boundary layer. However, the influence of surface turbulent fluxes in the early stages of development was important, particularly for the August 2000 cyclone, which passed over an extensive coastal lead in the East Siberian Sea. This study concludes that the observed retreat in western Arctic ice cover is unlikely to be an important contributor to increasing cyclonic activity in the region, but that ice retreat north of Eurasia could have an impact. [ABSTRACT FROM AUTHOR]