Polar lows in a globally coupled storm- and eddy-resolving (2.5 km) climate model (ICON-Sapphire)

Polar lows are intense subsynoptic cyclones on the meso-α to meso-β scale that develop over polar maritime environments. So far, only regional atmospheric models have been able to resolve polar lows due to their small spatiotemporal scales. Investigations with coupled regional atmosphere-ocean models are limited to a single study. We demonstrate the simulation of polar lows and their effects on the ocean and sea ice with the recently developed storm- and eddy-resolving configuration of the ICOsahedral Nonhydrostatic (ICON) model, called ICON-Sapphire. ICON-Sapphire globally couples the atmosphere, land, sea ice and ocean with a horizontal resolution of 2.5 km.
Although we focus on the Nordic Seas, ICON-Sapphire simulates polar lows in the northern and southern hemispheres covering the entire mesoscale. They form in different environments, for instance during marine cold air outbreaks or in low-level baroclinic areas at the marginal sea ice zone. Albeit short-lived phenomena, polar lows considerably affect the underlying ocean in ICON-Sapphire, leading to large heat losses, in particular close to the marginal sea ice zone, where they themselves induce cold air outbreaks. This ICON-Sapphire simulation is the first to show how polar lows interact with sea ice to create leads and polynyas due to strong wind stress. Leads and polynyas induce additional heat loss from the ocean that initiates the formation of new ice. Representing polar lows in global climate models increases the heat loss and ice formation from polar oceans, which are otherwise underestimated.