EMS Annual Meeting Abstracts
Vol. 20, EMS2023-136, 2023, updated on 06 Jul 2023
https://doi.org/10.5194/ems2023-136
EMS Annual Meeting 2023
© Author(s) 2023. This work is distributed under the Creative Commons Attribution 4.0 License.
The impact of changing sea ice on the mid-latitude circulationand extra-tropical cyclones
- University of Helsinki, Institute for Atmospheric and Earth system Research, Dynamic Meteorology, Finland (daniel.kohler@helsinki.fi)
The Arctic is warming close to 4 times faster than the global average, a phenomenon known as
Arctic amplification. This reduces the meridional temperature gradient, sea-ice concentration, and
baroclinicity in the lower atmosphere. How these changes to the large-scale environment impact the
number and intensity of mid-latitude cyclones remain unclear. We hypothesise that the extraction of
available potential energy by extra-tropical cyclones (ETCs) - known as eddy efficiency - is impacted
by Arctic amplification and contributes to changes in ETC count, intensity, and deepening rate.
ETCs obtain their kinetic energy via various sources, for example latent heating or eddy-mean-flow
interaction. One mechanism prevalent in ETCs is the conversion of available potential energy into
kinetic energy. The mechanism’s efficiency is governed by the alignment of the mean baroclinicity
and eddy heat flux. This is referred to as the eddy efficiency. We hypothesise that it is affected
by changes in the polar regions. To test this, three 40-year long OpenIFS simulations are run with
sea-ice concentrations and sea surface temperatures in the Arctic and Antarctic according to the
current climatology, the SSP126 scenario, and the SSP585 scenario. The mid-latitude circulation in
both hemispheres is examined in each experiment. We diagnose changes to the eddy heat flux, mean
baroclinicity, and atmospheric static stability individually. Moreover, we calculate the eddy efficiency
and decompose it into two terms: the tilt orientation and magnitude term. In addition, we associate
the ETC count, intensity, and deepening rate to the mid-latitude circulation characteristics.
Preliminary results indicate that the jet stream weakens in climates with reduced baroclinicity. We
will also present results showing how the number, intensity and deepening rate of ETCs, as well as the
eddy efficiency change, and how the vertical and horizontal circulation structure relates to the eddy
efficiency in the different simulations.
Arctic amplification. This reduces the meridional temperature gradient, sea-ice concentration, and
baroclinicity in the lower atmosphere. How these changes to the large-scale environment impact the
number and intensity of mid-latitude cyclones remain unclear. We hypothesise that the extraction of
available potential energy by extra-tropical cyclones (ETCs) - known as eddy efficiency - is impacted
by Arctic amplification and contributes to changes in ETC count, intensity, and deepening rate.
ETCs obtain their kinetic energy via various sources, for example latent heating or eddy-mean-flow
interaction. One mechanism prevalent in ETCs is the conversion of available potential energy into
kinetic energy. The mechanism’s efficiency is governed by the alignment of the mean baroclinicity
and eddy heat flux. This is referred to as the eddy efficiency. We hypothesise that it is affected
by changes in the polar regions. To test this, three 40-year long OpenIFS simulations are run with
sea-ice concentrations and sea surface temperatures in the Arctic and Antarctic according to the
current climatology, the SSP126 scenario, and the SSP585 scenario. The mid-latitude circulation in
both hemispheres is examined in each experiment. We diagnose changes to the eddy heat flux, mean
baroclinicity, and atmospheric static stability individually. Moreover, we calculate the eddy efficiency
and decompose it into two terms: the tilt orientation and magnitude term. In addition, we associate
the ETC count, intensity, and deepening rate to the mid-latitude circulation characteristics.
Preliminary results indicate that the jet stream weakens in climates with reduced baroclinicity. We
will also present results showing how the number, intensity and deepening rate of ETCs, as well as the
eddy efficiency change, and how the vertical and horizontal circulation structure relates to the eddy
efficiency in the different simulations.
How to cite: Köhler, D. and Sinclair, V.: The impact of changing sea ice on the mid-latitude circulationand extra-tropical cyclones, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-136, https://doi.org/10.5194/ems2023-136, 2023.
