EGU2020-19488
https://doi.org/10.5194/egusphere-egu2020-19488
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

The response of Northern Hemisphere polar lows to2climate change in a 25 km high-resolution global climate model

Len Shaffrey1, Helene Bresson2, Kevin Hodges1, and Giuseppe Zappa1
Len Shaffrey et al.
  • 1University of Reading, National Centre for Atmospheric Science, Department of Meteorology, Reading, United Kingdom of Great Britain and Northern Ireland (l.c.shaffrey@reading.ac.uk)
  • 2Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Potsdam, Germany

Polar lows are small, intense cyclones that form at high latitudes during winter. Their high wind speeds and heavy precipitation can have substantial impacts on shipping, coastal communities and infrastructure. However, climate models typically have low resolutions and therefore poorly simulate Polar Lows. This reduces the confidence that can be placed in future projections of extreme high latitude weather and associated risks.

In this study, Polar Lows are assessed for the first time in a high-resolution (25 km) global climate atmosphere-only model, N512 HadGEM3-GA3, for both present-day and future RCP 8.5 climate scenarios. Using an objective tracking algorithm, the representation of Polar Lows in the N512 HadGEM3-GA3 present-day simulation is found to agree reasonably well the NCEP-CFS reanalysis. RCP8.5 scenario conditions are generated by adding SST changes between 1990-2010 and 2090-2110 from the RCP8.5 experiments with the HadGEM2-ES model to observed SSTs from the present-day climate. In the RCP8.5 N512 HadGEM-GA3 simulations, the number of Northern Hemisphere Polar Lows are projected to substantially decrease (by over 60%) by the end of the 21st century, which is largely due to an increase in atmospheric static stability. However, new regions of Polar Low activity along the northern Russian coastlines are found where the Arctic sea ice is projected to retreat.

How to cite: Shaffrey, L., Bresson, H., Hodges, K., and Zappa, G.: The response of Northern Hemisphere polar lows to2climate change in a 25 km high-resolution global climate model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19488, https://doi.org/10.5194/egusphere-egu2020-19488, 2020

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  • CC1: Comment on EGU2020-19488, Oskar Landgren, 04 May 2020

    Hi Hélène and Len! Very nice work! I am glad to see there is a paper submitted and looking forward to reading it!

    I have two questions:

    1. Since the global model is atmosphere-only, how is the marginal ice zone handled? Could it have implications for formation of Cold-Air Outbreaks and thus Polar Lows?

    2. Are the results sensitive to the chosen tracking parameters?

    Best regards,
    Oskar Landgren
    oskar.landgren@met.no

    • AC1: Reply to CC1, Len Shaffrey, 04 May 2020

      Hi Oskar,

      Thanks for the comments!

      1. Since the global model is atmosphere-only, how is the marginal ice zone handled? Could it have implications for formation of Cold-Air Outbreaks and thus Polar Lows?

      The sea ice concentrations and thicknesses are prescribed. They're taken from HadGEM2-ES simulations used in AR5 for the historical and RCP8.5 experiments. I'd imagine in a fully coupled simulation there would be the possibility of a polar low (and the COA in which a PL might be embedded) changing the SST and sea ice distributions. We've had a look at a fully coupled version of this model for a present-day simulation and it also does a reasonable job of simulating PLs, but it would be interesting to look more at the co-variability of the sea ice and PLs.

      2. Are the results sensitive to the chosen tracking parameters?

      The relative climare change response is not very sensitive (although the absolute numbers are). I don't have the numbers to hand but we have some sensitivity tests in the paper.

      Kind regards

      Len