The substructure of extremely hot summers in the Northern Hemisphere
<p>In the last decades, extremely hot summers (hereafter 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 t...
| Main Authors: | , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-02-01
|
| Series: | Weather and Climate Dynamics |
| Online Access: | https://wcd.copernicus.org/articles/1/45/2020/wcd-1-45-2020.pdf |
| _version_ | 1818858875237957632 |
|---|---|
| author | M. Röthlisberger M. Sprenger E. Flaounas U. Beyerle H. Wernli |
| author_facet | M. Röthlisberger M. Sprenger E. Flaounas U. Beyerle H. Wernli |
| author_sort | M. Röthlisberger |
| collection | DOAJ |
| description | <p>In the last decades, extremely hot summers (hereafter 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.</p>
<p>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.</p> |
| first_indexed | 2024-12-19T09:03:14Z |
| format | Article |
| id | doaj.art-6d59bf2ba454447e9c278b99ff438245 |
| institution | Directory Open Access Journal |
| issn | 2698-4016 |
| language | English |
| last_indexed | 2024-12-19T09:03:14Z |
| publishDate | 2020-02-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Weather and Climate Dynamics |
| spelling | doaj.art-6d59bf2ba454447e9c278b99ff4382452022-12-21T20:28:26ZengCopernicus PublicationsWeather and Climate Dynamics2698-40162020-02-011456210.5194/wcd-1-45-2020The substructure of extremely hot summers in the Northern HemisphereM. RöthlisbergerM. SprengerE. FlaounasU. BeyerleH. Wernli<p>In the last decades, extremely hot summers (hereafter 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.</p> <p>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.</p>https://wcd.copernicus.org/articles/1/45/2020/wcd-1-45-2020.pdf |
| spellingShingle | M. Röthlisberger M. Sprenger E. Flaounas U. Beyerle H. Wernli The substructure of extremely hot summers in the Northern Hemisphere Weather and Climate Dynamics |
| title | 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_short | The substructure of extremely hot summers in the Northern Hemisphere |
| title_sort | substructure of extremely hot summers in the northern hemisphere |
| url | https://wcd.copernicus.org/articles/1/45/2020/wcd-1-45-2020.pdf |
| work_keys_str_mv | AT mrothlisberger thesubstructureofextremelyhotsummersinthenorthernhemisphere AT msprenger thesubstructureofextremelyhotsummersinthenorthernhemisphere AT eflaounas thesubstructureofextremelyhotsummersinthenorthernhemisphere AT ubeyerle thesubstructureofextremelyhotsummersinthenorthernhemisphere AT hwernli thesubstructureofextremelyhotsummersinthenorthernhemisphere AT mrothlisberger substructureofextremelyhotsummersinthenorthernhemisphere AT msprenger substructureofextremelyhotsummersinthenorthernhemisphere AT eflaounas substructureofextremelyhotsummersinthenorthernhemisphere AT ubeyerle substructureofextremelyhotsummersinthenorthernhemisphere AT hwernli substructureofextremelyhotsummersinthenorthernhemisphere |