Polar Night (PN)

The Canadian High Arctic experiences nearly four months of darkness, which uniquely shapes the atmospheric environment in ways that are still not fully understood. The intense longwave radiative cooling creates nearly isolated dynamical regimes both near the surface with an extremely stable boundary layer capping the High Arctic surface and in the stratosphere with the polar vortex isolating the Arctic vertical column. The winter cooling in the Arctic is a vital sink for much of the radiative heating that occurs in the tropics and subtropics. Overall the Arctic has been warming twice as fast as the rest of the globe but measurements at Eureka over the past 30 years have revealed an amplification of 5x with similarly large amplifications at other locations in the Canadian High Arctic (Lesins et al., 2010). The warming is causing the polar sea-ice, ice sheets and permafrost to deteriorate, adversely affecting wildlife and human activities. Degradation of permafrost is already apparent at Eureka and the summer of 2012 has experienced the lowest Arctic sea-ice areal extent since satellite records began in the 1970s. These troubling trends are aided by the inability of the winter season to fully reform the melted ice from the previous summer. Understanding how the atmosphere functions during the Arctic night has suffered from a lack of field measurements, deemed too costly or too dangerous to undertake. With the pressing impacts of environmental change, this situation is unacceptable. This theme has two projects to address this gap: the Wintertime Environment (PN-WE); and the Polar Vortex (PN-PV).