North Pacific Sea Ice and its Associated Atmospheric Variability

The second EOF of north Pacific sea ice concentration variability in a fully coupled NCAR climate model simulation is characterized by a dipole, with anomalies of one sign in the Sea of Okhotsk and of opposite sign in the Bering Sea. This pattern of variability has been identified in the observations by previous researchers, thus, making it a particularly interesting area of investigation in a fully coupled model. In the model, positive (negative) sea ice concentration anomalies in the Sea of Okhotsk (Bering Sea) are associated with a strengthened Aleutian low consistent with warm air advection over the Bering region and cold air advection in the Sea of Okhotsk. Additionally, there are large scale atmospheric anomalies associated with these sea ice anomalies in air temperature, specific humidity, and turbulent heat fluxes. There are also large scale anomalies in the North Atlantic suggesting possible teleconnections between the north Pacific and north Atlantic.

In a fully coupled model as in the observations it is not possible to fully understand the nature of how the atmosphere and the sea ice interact. To the first order it is generally agreed that atmospheric sea level pressure anomalies force the sea ice anomalies. The associated anomalies in 500 mb geopotential height resembles an atmospheric wavetrain, suggesting a response to surface forcing, consistent with the modeling results of Honda et al. (1999). To understand the relationships we have examined in the coupled simulation, we are conducting sensitivity experiments by forcing the NCAR atmospheric model with fixed sea ice anomalies constructed from the coupled simulation. In this research we hope to better understand the role of North Pacific sea ice concentration anomalies on the large scale atmospheric circulation.