The substructure of extremely hot summers in the Northern Hemisphere
In the last decades, extremely hot summers (here- after extreme summers) have challenged societies worldwide through their adverse ecological, economic and public-health effects. In this study, extreme summers are identified at all grid points in the Northern Hemisphere in the upper tail of the June...
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ftdatacite:10.3929/ethz-b-000421993 2023-05-15T15:19:32+02:00 The substructure of extremely hot summers in the Northern Hemisphere Röthlisberger, Matthias Sprenger, Michael Flaounas, Emmanouil Beyerle, Urs Wernli, Heini 2020 application/pdf https://dx.doi.org/10.3929/ethz-b-000421993 http://hdl.handle.net/20.500.11850/421993 en eng ETH Zurich info:eu-repo/semantics/openAccess Creative Commons Attribution 4.0 International https://creativecommons.org/licenses/by/4.0/legalcode cc-by-4.0 CC-BY Meteorology Climatology Text article-journal Journal Article ScholarlyArticle 2020 ftdatacite https://doi.org/10.3929/ethz-b-000421993 2021-11-05T12:55:41Z In the last decades, extremely hot summers (here- after extreme summers) have challenged societies worldwide through their adverse ecological, economic and public-health effects. In this study, extreme summers are identified at all grid points in the Northern Hemisphere in the upper tail of the June–July–August (JJA) seasonal mean 2 m temperature (T2m) distribution, separately in ERA-Interim (ERAI) re- analyses and in 700 simulated years with the Community Earth System Model (CESM) large ensemble for present-day climate conditions. A novel approach is introduced to characterise the substructure of extreme summers, i.e. to elucidate whether an extreme summer is mainly the result of the warmest days being anomalously hot, of the coldest days being anomalously mild or of a general shift towards warmer temperatures on all days of the season. Such a statistical characterisation can be obtained from considering so-called rank day anomalies for each extreme summer – that is, by sorting the 92 daily mean T2m values of an extreme summer and by calculating, for every rank, the deviation from the climatological mean rank value of T2m. Applying this method in the entire Northern Hemisphere reveals spatially strongly varying extreme-summer substructures, which agree remarkably well in the re-analysis and climate model data sets. For example, in eastern India the hottest 30 d of an extreme summer contribute more than 65 % to the total extreme-summer T2m anomaly, while the colder days are close to climatology. In the high Arctic, however, extreme summers occur when the coldest 30 d are substantially warmer than they are climatologically. Furthermore, in roughly half of the Northern Hemisphere land area, the coldest third of summer days contributes more to extreme summers than the hottest third, which highlights that milder-than-normal coldest summer days are a key ingredient of many extreme summers. In certain regions, e.g. over western Europe and western Russia, the substructure of different extreme summers shows large variability and no common characteristic substructure emerges. Furthermore, we show that the typical extreme-summer substructure in a certain region is directly related to the region’s overall T2m rank day variability pattern. This indicates that in regions where the warmest summer days vary particularly strongly from one year to the other, these warmest days are also particularly anomalous in extreme summers (and analogously for regions where variability is largest for the coldest days). Finally, for three selected regions, thermodynamic and dynamical causes of extreme-summer substructures are briefly discussed, indicating that, for instance, the onset of monsoons, physical boundaries like the sea ice edge or the frequency of occurrence of Rossby wave breaking strongly determines the substructure of extreme summers in certain regions. : Weather and Climate Dynamics, 1 (1) Text Arctic Sea ice DataCite Metadata Store (German National Library of Science and Technology) Arctic |
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op_collection_id |
ftdatacite |
language |
English |
topic |
Meteorology Climatology |
spellingShingle |
Meteorology Climatology Röthlisberger, Matthias Sprenger, Michael Flaounas, Emmanouil Beyerle, Urs Wernli, Heini The substructure of extremely hot summers in the Northern Hemisphere |
topic_facet |
Meteorology Climatology |
description |
In the last decades, extremely hot summers (here- after extreme summers) have challenged societies worldwide through their adverse ecological, economic and public-health effects. In this study, extreme summers are identified at all grid points in the Northern Hemisphere in the upper tail of the June–July–August (JJA) seasonal mean 2 m temperature (T2m) distribution, separately in ERA-Interim (ERAI) re- analyses and in 700 simulated years with the Community Earth System Model (CESM) large ensemble for present-day climate conditions. A novel approach is introduced to characterise the substructure of extreme summers, i.e. to elucidate whether an extreme summer is mainly the result of the warmest days being anomalously hot, of the coldest days being anomalously mild or of a general shift towards warmer temperatures on all days of the season. Such a statistical characterisation can be obtained from considering so-called rank day anomalies for each extreme summer – that is, by sorting the 92 daily mean T2m values of an extreme summer and by calculating, for every rank, the deviation from the climatological mean rank value of T2m. Applying this method in the entire Northern Hemisphere reveals spatially strongly varying extreme-summer substructures, which agree remarkably well in the re-analysis and climate model data sets. For example, in eastern India the hottest 30 d of an extreme summer contribute more than 65 % to the total extreme-summer T2m anomaly, while the colder days are close to climatology. In the high Arctic, however, extreme summers occur when the coldest 30 d are substantially warmer than they are climatologically. Furthermore, in roughly half of the Northern Hemisphere land area, the coldest third of summer days contributes more to extreme summers than the hottest third, which highlights that milder-than-normal coldest summer days are a key ingredient of many extreme summers. In certain regions, e.g. over western Europe and western Russia, the substructure of different extreme summers shows large variability and no common characteristic substructure emerges. Furthermore, we show that the typical extreme-summer substructure in a certain region is directly related to the region’s overall T2m rank day variability pattern. This indicates that in regions where the warmest summer days vary particularly strongly from one year to the other, these warmest days are also particularly anomalous in extreme summers (and analogously for regions where variability is largest for the coldest days). Finally, for three selected regions, thermodynamic and dynamical causes of extreme-summer substructures are briefly discussed, indicating that, for instance, the onset of monsoons, physical boundaries like the sea ice edge or the frequency of occurrence of Rossby wave breaking strongly determines the substructure of extreme summers in certain regions. : Weather and Climate Dynamics, 1 (1) |
format |
Text |
author |
Röthlisberger, Matthias Sprenger, Michael Flaounas, Emmanouil Beyerle, Urs Wernli, Heini |
author_facet |
Röthlisberger, Matthias Sprenger, Michael Flaounas, Emmanouil Beyerle, Urs Wernli, Heini |
author_sort |
Röthlisberger, Matthias |
title |
The substructure of extremely hot summers in the Northern Hemisphere |
title_short |
The substructure of extremely hot summers in the Northern Hemisphere |
title_full |
The substructure of extremely hot summers in the Northern Hemisphere |
title_fullStr |
The substructure of extremely hot summers in the Northern Hemisphere |
title_full_unstemmed |
The substructure of extremely hot summers in the Northern Hemisphere |
title_sort |
substructure of extremely hot summers in the northern hemisphere |
publisher |
ETH Zurich |
publishDate |
2020 |
url |
https://dx.doi.org/10.3929/ethz-b-000421993 http://hdl.handle.net/20.500.11850/421993 |
geographic |
Arctic |
geographic_facet |
Arctic |
genre |
Arctic Sea ice |
genre_facet |
Arctic Sea ice |
op_rights |
info:eu-repo/semantics/openAccess Creative Commons Attribution 4.0 International https://creativecommons.org/licenses/by/4.0/legalcode cc-by-4.0 |
op_rightsnorm |
CC-BY |
op_doi |
https://doi.org/10.3929/ethz-b-000421993 |
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1766349725578035200 |