Bimodal Nature of Arctic Surface-Atmosphere Interaction

A study of atmospheric soundings, surface energy budget components, cloud data, and synoptic context during the winter at the SHEBA and ARM North Slope of Alaska (NSA) sites reveals that the Arctic snow layer, ice or land surface, and entire atmospheric column respond in concert to the advection of moisture and temperature from lower latitudes.

At SHEBA, the episodic nature of these influxes, and their daily to weekly persistence arise as consequence of atmospheric circulation systems in the Arctic basin being constrained to quasi-stationary patterns.

These influx periods may be diagnosed as occurring when the value of the surface net longwave radiation is near 0 W/m**2. When not subject to such atmospheric influxes, the snow-ice/land-atmosphere system relaxes to the other, quiescent, winter state, diagnosed by surface net longwave radiation values near -40 W/m**2 at SHEBA, and near -30 W/m**2 at NSA. The SHEBA snow-sea ice-atmosphere system spends 21% of the winter in the influx state, 66% in the quiescent state, and only 13% of the winter in transition between the two states, whereas the NSA snow-land-atmosphere system spends 44% in the winter influx state, 42% quiescent, and 14% in transition between the two states.

That the SHEBA winter surface-atmosphere system has only two stable states of behavior available to it occurs as result of the current Arctic climate system configuration, in which the Arctic surface temperatures are anchored near 235K by the ocean heat flux's constant addition of approximately 40 W/m**2 during quiescent periods, and in which the snow and atmosphere equilibrate with the ice surface during influx events. A similar analysis of the budget components for the NSA site is being conducted to ascertain why the magnitude and persistence of climate states at SHEBA and NSA differ.