The impacts of increased open water on Arctic summer storms

Of all Arctic regions, Canada Basin has the highest frequency of summer storms (Serreze and Barry 1988). On average, there were about 14 storms per storm season (June-November inclusive). October has the highest storm frequency, whereas July has the lowest (Hudak and Young, 2002). Cyclonic systems move into this region primarily from the Siberian coast and subsequently tend to stall over the Beaufort Sea (Serreze and Barry 1988). In the upper ocean, intense Arctic storms play an important role in determining the variations of the heat and salt budgets. In the winter and spring, when stratification is relatively weak in the Beaufort Sea, the deep mixing associated with an intense storm can penetrate through the halocline and thermocline layers (Yang et al. 2004). Moreover, Arctic storms can fracture the large ice floes into smaller foes and therefore increase the surface heat exchange between air and water (Holt and Martin 2001). In the Beaufort Sea, coastal erosion is often related to coastal ocean processes such as waves and nearshore currents, driven by strong surface winds generated by intense storms. For example, during single storms in 1970 and 1985, more than 3m of coastal retreat occurred near Tuktoyaktuk (Solomon et al., 1994). Therefore, it is important to understand the impacts of increased open water on storm intensity, storm tracks, and the surface winds that drive coastal ocean processes. In this study, a coupled model system consisting of the Canadian Regional Climate Model (CRCM) and an ice-ocean model (CIOM) is implemented for the Arctic basin to simulate an intense storm that moved into the Beaufort Sea during the period from 28 July to 4 August 2008. We focus on the air-sea interactions and their role on the life cycle of the storm. In particular, we try to understand the impacts of increased open water in the Chukchi and Beaufort Seas on storm intensity and the surface winds. The coupled model system is shown to simulate the storm track, intensity, maximum wind speed and the ice cover well, compared to CMC analyses and QSCAT-NCEP data. Significant ocean surface responses were simulated over the open water of the Chuckchi and Beaufort Seas during the storm. Upper ocean mixing due to the storm results in sea surface cooling of up to 2C in coastal waters along the southern Beaufort Sea coast, with maximum storm-induced surface currents reaching 0.7 m/s. No significant ocean surface responses were found in the model domain covered with sea ice, as sea ice prevents the surface momentum exchange between the atmosphere and the underlying water. The significantly warmer SSTs simulated in the coupled run compared to the uncoupled run (up to 6C) are due to the high albedo of sea ice; the warmer SSTs further increase the downward kinetic energy transport through enhanced boundary turbulence. Moreover, the effect of increased open water results in enhanced storm-generated surface winds, by as much as ~ 4 m/s.

References: Holt, B. and M. Seelye (2001): The effect of a storm on the 1992 summer sea ice cover of the Beaufort, Chuckchi, and East Siberian Seas. J. Geophys. Res., 106, 1017-1032. Hudak, D. R. and J. M. C. Young (2002): Storm climatology of the southern Beaufort Sea. Atmosphere-Ocean, 40, 145-158. Serreze, M. C. and R. G. Barry (1988): Synoptic activity in the Arctic Basin, 1979-1985. J. Clim, 1, 1276-1295. Solomon S. M. et al. (1994): Coastal impacts of climate change: Beaufort Sea erosion study. Geological Survey of Canada. Open File 2890, p85. Yang, J., et al. (2004): Strom-driven mixing and potential impact on the Arctic Ocean. J. Geophys. Res., 109, C04008, doi:10.1029/2001JC001248.