Sensitivity of an apparently hurricane-like polar low to sea surface temperature

Polar lows are intense, small-scale cyclones in the high latitudes. Typically, polar lows are initiated through baroclinic processes, but they sometimes evolve into a post-baroclinic mature stage where air-sea interaction becomes more important. In this stage some polar lows have developed hurricane-like cloud structures, and idealised axisymmetric hurricane models have indicated that air-sea interaction-fuelled pressure drops of up to 50 hPa are theoretically possible in polar environments. Here we study a polar low that formed in an extreme marine cold air outbreak over the Barents Sea and which had cloud structures with similarities to hurricanes. Using a high-resolution weather model, we artificially modified the sea surface temperatures (SSTs) to assess if the polar low was close to developing into a true hurricane-like system, with air-sea interaction processes leading to intensification in the post-baroclinic, mature phase of its life cycle. The polar low simulations with SSTs augmented by 2–6 K produced more intense mature phases than the control experiment (with unmodified SSTs). The intensity of the polar low in the latter of these, which it must be pointed out was unrealistic with an SST increase of 6 K, surpassed the intensity in the earlier baroclinic phase. The experiment where the SSTs were reduced by 2 K did not produce a much weaker polar low than the control run. Broadly speaking, our experiments suggest that in this case large and unrealistic SST increases would be needed for apparently hurricane-like polar lows to exhibit true hurricane-like behaviour, but nevertheless air-sea interaction did drive a more intense and prolonged mature phase.

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