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Final Report Summary - HIMWARC (High Impact Weather in the Arctic, fundamental understanding and future projections (HIMWARC))

HIMWARC helped to extend our fundamental knowledge and concomitantly aided our understanding of present levels of uncertainty with respect to future changes of high impact weather in the Arctic.
The weather in the Arctic features several severe types of extremes such as polar lows and strong low-level winds in the vicinity of topography. These extremes influence the socio-economic structure of the affected regions and communities by extensive material damages and loss of lives. Our current understanding of the formation and intensification of these weather phenomena is still at a rather low level compared to our understanding of similar phenomena in mid-latitudes. This limits our forecasting capabilities and hence restrains our abilities of mitigation measures. Furthermore, a detailed and comprehensive assessment of changes with respect to high impact weather in the Arctic in a future climate will also be limited to our understanding of the underlying processes giving rise to these phenomena.
HIMWARC´s approach to address these issues was twofold. Firstly, the project aimed to extend our fundamental understanding of high impact weather in the Arctic. Secondly, the findings were incorporated into improved diagnostics to assess future changes in spatial distribution, frequency, and intensity of Arctic severe events. The pursuit of these goals was aided by the affiliation of HIMWARC with the WMO WWRP Polar Prediction Project.
Overall, HIMWARC was able to make a significant contribution to enhancing our understanding of polar lows and thereby gave insights into how predictions of polar lows might be improved in the future. In particular, HIMWARC’s research pinpointed the relevance of diabatic process associated to latent heat release in polar lows during their development. The dominance of these processes led to the conclusion that most polar lows can be seen as developing as a phenomenon called diabatic Rossby vortex, which refers to a hybrid cyclone that draws its energy from both baroclinic and diabatic effects. This finding further substantiated that diabatic processes can be of leading order in the Arctic, despite the Arctic air not holding large amounts of moisture compared to the mid-latitudes. The main reason for this is that the horizontal and vertical scales of the system are reduced compared to mid-latitudes leading to a higher effectiveness of the energy conversion via diabatic processes.
Furthermore, the project assessed future climate scenarios for polar low occurrence in the Nordic seas highlighting that some previous conclusions about the association of polar lows to large-scale weather patterns and the sea ice edge might not hold and that the actual ingredients determining polar low occurrence might be more complicated. These results indicate that we can still not be sure if there will be fewer, more, weaker, or stronger polar lows in the future and further assessments are needed, best using high-resolution model data resolving polar lows, to address this issue further.

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Liv-Grethe Gudmundsen, (Adviser)
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Record Number: 191921 / Last updated on: 2016-11-15
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