Publications by authors named "Stefan Petri"

8 Publications

  • Page 1 of 1

Investigating Mesozoic Climate Trends and Sensitivities With a Large Ensemble of Climate Model Simulations.

Paleoceanogr Paleoclimatol 2021 Jun 5;36(6):e2020PA004134. Epub 2021 Jun 5.

Department of Geology University of Vienna Vienna Austria.

The Mesozoic era (∼252 to 66 million years ago) was a key interval in Earth's evolution toward its modern state, witnessing the breakup of the supercontinent Pangaea and significant biotic innovations like the early evolution of mammals. Plate tectonic dynamics drove a fundamental climatic transition from the early Mesozoic supercontinent toward the Late Cretaceous fragmented continental configuration. Here, key aspects of Mesozoic long-term environmental changes are assessed in a climate model ensemble framework. We analyze so far the most extended ensemble of equilibrium climate states simulated for evolving Mesozoic boundary conditions covering the period from 255 to 60 Ma in 5 Myr timesteps. Global mean temperatures are generally found to be elevated above the present and exhibit a baseline warming trend driven by rising sea levels and increasing solar luminosity. Warm (Triassic and mid-Cretaceous) and cool (Jurassic and end-Cretaceous) anomalies result from pCO changes indicated by different reconstructions. Seasonal and zonal temperature contrasts as well as continental aridity show an overall decrease from the Late Triassic-Early Jurassic to the Late Cretaceous. Meridional temperature gradients are reduced at higher global temperatures and less land area in the high latitudes. With systematic sensitivity experiments, the influence of paleogeography, sea level, vegetation patterns, pCO, solar luminosity, and orbital configuration on these trends is investigated. For example, long-term seasonality trends are driven by paleogeography, but orbital cycles could have had similar-scale effects on shorter timescales. Global mean temperatures, continental humidity, and meridional temperature gradients are, however, also strongly affected by pCO.
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http://dx.doi.org/10.1029/2020PA004134DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8251552PMC
June 2021

Projected changes in persistent extreme summer weather events: The role of quasi-resonant amplification.

Sci Adv 2018 10 31;4(10):eaat3272. Epub 2018 Oct 31.

Earth System Analysis, Potsdam Institute for Climate Impact Research, Potsdam, Germany.

Persistent episodes of extreme weather in the Northern Hemisphere summer have been associated with high-amplitude quasi-stationary atmospheric Rossby waves, with zonal wave numbers 6 to 8 resulting from the phenomenon of quasi-resonant amplification (QRA). A fingerprint for the occurrence of QRA can be defined in terms of the zonally averaged surface temperature field. Examining state-of-the-art [Coupled Model Intercomparison Project Phase 5 (CMIP5)] climate model projections, we find that QRA events are likely to increase by ~50% this century under business-as-usual carbon emissions, but there is considerable variation among climate models. Some predict a near tripling of QRA events by the end of the century, while others predict a potential decrease. Models with amplified Arctic warming yield the most pronounced increase in QRA events. The projections are strongly dependent on assumptions regarding the nature of changes in radiative forcing associated with anthropogenic aerosols over the next century. One implication of our findings is that a reduction in midlatitude aerosol loading could actually lead to Arctic de-amplification this century, ameliorating potential increases in persistent extreme weather events.
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http://dx.doi.org/10.1126/sciadv.aat3272DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6209391PMC
October 2018

Alberta wildfire 2016: Apt contribution from anomalous planetary wave dynamics.

Sci Rep 2018 Aug 17;8(1):12375. Epub 2018 Aug 17.

Potsdam Institute for Climate Impact Research (PIK), Member of the Leibniz Association, P.O. Box 60 12 03, D-14412, Potsdam, Germany.

In May-June 2016 the Canadian Province of Alberta suffered one of the most devastating wildfires in its history. Here we show that in mid-April to early May 2016 the large-scale circulation in the mid- and high troposphere of the middle and sub-polar latitudes of the northern hemisphere featured a persistent high-amplitude planetary wave structure dominated by the non-dimensional zonal wave number 4. The strongest anticyclonic wing of this structure was located over western Canada. In combination with a very strong El Niño event in winter 2015/2016 this favored highly anomalous, tinder-dry and high-temperature conditions at the surface in that area, entailing an increased fire hazard there. This critically contributed to the ignition of the Alberta Wildfire in May 2016, appearing to be the costliest disaster in Canadian history thus far.
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http://dx.doi.org/10.1038/s41598-018-30812-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6098075PMC
August 2018

Role of quasiresonant planetary wave dynamics in recent boreal spring-to-autumn extreme events.

Proc Natl Acad Sci U S A 2016 06 6;113(25):6862-7. Epub 2016 Jun 6.

Potsdam Institute for Climate Impact Research, D-14412 Potsdam, Germany; Santa Fe Institute, Santa Fe, NM 87501

In boreal spring-to-autumn (May-to-September) 2012 and 2013, the Northern Hemisphere (NH) has experienced a large number of severe midlatitude regional weather extremes. Here we show that a considerable part of these extremes were accompanied by highly magnified quasistationary midlatitude planetary waves with zonal wave numbers m = 6, 7, and 8. We further show that resonance conditions for these planetary waves were, in many cases, present before the onset of high-amplitude wave events, with a lead time up to 2 wk, suggesting that quasiresonant amplification (QRA) of these waves had occurred. Our results support earlier findings of an important role of the QRA mechanism in amplifying planetary waves, favoring recent NH weather extremes.
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http://dx.doi.org/10.1073/pnas.1606300113DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4922183PMC
June 2016

Record Balkan floods of 2014 linked to planetary wave resonance.

Sci Adv 2016 Apr 15;2(4):e1501428. Epub 2016 Apr 15.

Potsdam Institute for Climate Impact Research, Earth System Analysis, 14473 Potsdam, Germany.; University of Potsdam, 14469 Potsdam, Germany.

In May 2014, the Balkans were hit by a Vb-type cyclone that brought disastrous flooding and severe damage to Bosnia and Herzegovina, Serbia, and Croatia. Vb cyclones migrate from the Mediterranean, where they absorb warm and moist air, to the north, often causing flooding in central/eastern Europe. Extreme rainfall events are increasing on a global scale, and both thermodynamic and dynamical mechanisms play a role. Where thermodynamic aspects are generally well understood, there is large uncertainty associated with current and future changes in dynamics. We study the climatic and meteorological factors that influenced the catastrophic flooding in the Balkans, where we focus on large-scale circulation. We show that the Vb cyclone was unusually stationary, bringing extreme rainfall for several consecutive days, and that this situation was likely linked to a quasi-stationary circumglobal Rossby wave train. We provide evidence that this quasi-stationary wave was amplified by wave resonance. Statistical analysis of daily spring rainfall over the Balkan region reveals significant upward trends over 1950-2014, especially in the high quantiles relevant for flooding events. These changes cannot be explained by simple thermodynamic arguments, and we thus argue that dynamical processes likely played a role in increasing flood risks over the Balkans.
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http://dx.doi.org/10.1126/sciadv.1501428DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4846427PMC
April 2016

Quasi-resonant circulation regimes and hemispheric synchronization of extreme weather in boreal summer.

Proc Natl Acad Sci U S A 2014 Aug 11;111(34):12331-6. Epub 2014 Aug 11.

Potsdam Institute for Climate Impact Research, 14412 Potsdam, Germany; and Santa Fe Institute, Santa Fe, NM 87501

The recent decade has seen an exceptional number of high-impact summer extremes in the Northern Hemisphere midlatitudes. Many of these events were associated with anomalous jet stream circulation patterns characterized by persistent high-amplitude quasi-stationary Rossby waves. Two mechanisms have recently been proposed that could provoke such patterns: (i) a weakening of the zonal mean jets and (ii) an amplification of quasi-stationary waves by resonance between free and forced waves in midlatitude waveguides. Based upon spectral analysis of the midtroposphere wind field, we show that the persistent jet stream patterns were, in the first place, due to an amplification of quasi-stationary waves with zonal wave numbers 6-8. However, we also detect a weakening of the zonal mean jet during these events; thus both mechanisms appear to be important. Furthermore, we demonstrate that the anomalous circulation regimes lead to persistent surface weather conditions and therefore to midlatitude synchronization of extreme heat and rainfall events on monthly timescales. The recent cluster of resonance events has resulted in a statistically significant increase in the frequency of high-amplitude quasi-stationary waves of wave numbers 7 and 8 in July and August. We show that this is a robust finding that holds for different pressure levels and reanalysis products. We argue that recent rapid warming in the Arctic and associated changes in the zonal mean zonal wind have created favorable conditions for double jet formation in the extratropics, which promotes the development of resonant flow regimes.
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http://dx.doi.org/10.1073/pnas.1412797111DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4151761PMC
August 2014

Quasiresonant amplification of planetary waves and recent Northern Hemisphere weather extremes.

Proc Natl Acad Sci U S A 2013 Apr 1;110(14):5336-41. Epub 2013 Mar 1.

Potsdam Institute for Climate Impact Research, D-14412 Potsdam, Germany.

In recent years, the Northern Hemisphere has suffered several devastating regional summer weather extremes, such as the European heat wave in 2003, the Russian heat wave and the Indus river flood in Pakistan in 2010, and the heat wave in the United States in 2011. Here, we propose a common mechanism for the generation of persistent longitudinal planetary-scale high-amplitude patterns of the atmospheric circulation in the Northern Hemisphere midlatitudes. Those patterns--with zonal wave numbers m = 6, 7, or 8--are characteristic of the above extremes. We show that these patterns might result from trapping within midlatitude waveguides of free synoptic waves with zonal wave numbers k ≈ m. Usually, the quasistationary dynamical response with the above wave numbers m to climatological mean thermal and orographic forcing is weak. Such midlatitude waveguides, however, may favor a strong magnification of that response through quasiresonance.
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http://dx.doi.org/10.1073/pnas.1222000110DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3619331PMC
April 2013
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