A network-based detection scheme of the jet stream core

Totz, Sonja; Mamdouh, Tarek; Petri, Stefan; Nocke, Thomas; Weinkauf, Tino; Coumou, Dim

doi:10.5194/esd-2016-37

Cited by 7 publications

(11 citation statements)

References 23 publications

(43 reference statements)

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“…In terms of the mean flow, there is a significant weakening of the westerlies in most parts of the study region and a poleward shift and narrowing of the PJ axis over eastern North America and the North Atlantic. This agrees with the outcome from other work (Wilcox et al, 2012;Molnos et al, 2017). The same is true for the meridional position of the subtropical jet stream over North Africa, indicating that the Tropics are extending poleward, as suggested by Wang (2001), Kossin (2014) and Lucas et al (2014).…”

Section: Discussionsupporting

confidence: 92%

“…This is indicative of a general poleward shift of tropical and extratropical circulation zones and has also been reported for the Southern Hemisphere (e.g. Wilcox et al ., ; Molnos et al ., ). It means that over the last 40 years the typical winter situation is getting closer to the former summer situation with the PJ trapped in a more poleward and spatially confined position (see subsection 3.1).…”

Section: Resultsmentioning

confidence: 97%

“…This phenomenon mainly arises from decreasing sea ice and snow cover extent, including the ice-albedo feedback, and is referred to as the Arctic amplification . Consequently, the meridional temperature gradient is weakening (Mann et al, 2017) and, according to the thermal wind balance, the westerly jet stream reduces in strength and shifts equatorward (Dethloff, 2006;Perlwitz et al, 2015;Molnos et al, 2017). This in turn affects the activity of planetary waves and extratropical cyclones, involving a negative phase of the North Atlantic Oscillation (NAO) and Northern Annular Mode (NAM) and stimulating a feedback of the stratospheric polar vortex that tends to elongate the circulation anomaly in time (Kim et al, 2014;Vihma, 2014;Jaiser et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

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Changes in mean flow and atmospheric wave activity in the North Atlantic sector

Paeth

Pollinger

2019

Quart J Royal Meteoro Soc

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In recent years, the midlatitudes are characterized by more intense heatwaves in summer and sometimes severe cold spells in winter that might emanate from changes in atmospheric circulation, including synoptic‐scale and planetary wave activity in the midlatitudes. In this study, we investigate the heat and momentum exchange between the mean flow and atmospheric waves in the North Atlantic sector and adjacent continents by means of the physically consistent Eliassen–Palm flux diagnostics applied to reanalysis and forced climate model data. In the long‐term mean, momentum is transferred from the mean flow to atmospheric waves in the northwest Atlantic region, where cyclogenesis prevails. Further downstream over Europe, eddy fluxes return momentum to the mean flow, sustaining the jet stream against friction. A global climate model is able to reproduce this pattern with high accuracy. Atmospheric variability related to atmospheric wave activity is much more expressed at the intraseasonal rather than the interannual time‐scale. Over the last 40 years, reanalyses reveal a northward shift of the jet stream and a weakening of intraseasonal weather variability related to synoptic‐scale and planetary wave activity. This pertains to the winter and summer seasons, especially over central Europe, and correlates with changes in the North Atlantic Oscillation as well as regional temperature and precipitation. A very similar phenomenon is found in a climate model simulation with business‐as‐usual scenario, suggesting an anthropogenic trigger in the weakening of intraseasonal weather variability in the midlatitudes.

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Section: Discussionsupporting

confidence: 92%

Section: Resultsmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

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Changes in mean flow and atmospheric wave activity in the North Atlantic sector

Paeth

Pollinger

2019

Quart J Royal Meteoro Soc

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“…Büntgen et al (2018) reported elevated 14 C values for some trees growing above 60ºN at the peak of the AD 774/5 Miyake event (Miyake et al 2012). The position of the present-day polar jet stream, which delineates the polar front, is presented as a latitudinal probability distribution by Molnos et al (2017), but a simple boundary is not easily established. We therefore used 60ºN for comparison of northerly trees with the other data.…”

Section: Intcal20 14 C Calibration Curve 729mentioning

confidence: 99%

The IntCal20 Northern Hemisphere Radiocarbon Age Calibration Curve (0–55 cal kBP)

et al. 2020

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Radiocarbon (14C) ages cannot provide absolutely dated chronologies for archaeological or paleoenvironmental studies directly but must be converted to calendar age equivalents using a calibration curve compensating for fluctuations in atmospheric 14C concentration. Although calibration curves are constructed from independently dated archives, they invariably require revision as new data become available and our understanding of the Earth system improves. In this volume the international 14C calibration curves for both the Northern and Southern Hemispheres, as well as for the ocean surface layer, have been updated to include a wealth of new data and extended to 55,000 cal BP. Based on tree rings, IntCal20 now extends as a fully atmospheric record to ca. 13,900 cal BP. For the older part of the timescale, IntCal20 comprises statistically integrated evidence from floating tree-ring chronologies, lacustrine and marine sediments, speleothems, and corals. We utilized improved evaluation of the timescales and location variable 14C offsets from the atmosphere (reservoir age, dead carbon fraction) for each dataset. New statistical methods have refined the structure of the calibration curves while maintaining a robust treatment of uncertainties in the 14C ages, the calendar ages and other corrections. The inclusion of modeled marine reservoir ages derived from a three-dimensional ocean circulation model has allowed us to apply more appropriate reservoir corrections to the marine 14C data rather than the previous use of constant regional offsets from the atmosphere. Here we provide an overview of the new and revised datasets and the associated methods used for the construction of the IntCal20 curve and explore potential regional offsets for tree-ring data. We discuss the main differences with respect to the previous calibration curve, IntCal13, and some of the implications for archaeology and geosciences ranging from the recent past to the time of the extinction of the Neanderthals.

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“…Jet streams are upper-level fast currents of westerly winds that circulate around the hemisphere. Under climate change a 20 weakening of the northern subtropical jet stream in winter is observed by most studies (Molnos et al, 2017;Rikus, 2015) though a few studies observe also a positive trend (Pena-Ortiz et al, 2013). The underlying drivers for those changes are still debated.…”

mentioning

confidence: 99%

The sensitivity of the large-scale atmosphere circulation to changes in surface temperature gradients in the Northern Hemisphere

Totz

Petri

Lehmann

et al. 2017

Preprint

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Abstract. 10Climate and weather conditions in the mid-latitudes are strongly driven by the large-scale atmosphere circulation.Observational data indicates that important components of the large-scale circulation have changed in recent decades including the strength of the Hadley cell, jet streams, storm tracks and planetary waves. Associated impacts cover a broad range, including changes in the frequency and nature of weather extremes and shifts of fertile habitats with implications for biodiversity and agriculture. Dynamical theories have been proposed that link the shift of the poleward edge of the Northern 15Hadley cell to changes in the meridional temperature gradient. Moreover, model simulations have been carried out to analyse the cause of observed and projected changes in the large-scale atmosphere circulation. However, the question of the underlying drivers and particularly the possible role of global warming is still debated. Here, we use a statistical-dynamical atmosphere model (SDAM) to analyse the sensitivity of the Northern Hemisphere Hadley cell, storm tracks, jet streams and planetary waves to changes in temperature fields by systematically altering the zonal and meridional temperature gradient as 20 well as the global mean surface temperature.SDAMs are computationally fast compared to more complex general circulation models (GCM) which enables us to scan a large and high-dimensional parameter space for sensitivity analyses using more than thousand individual model runs.Our results show that the strength of the Hadley cell, storm tracks and jet streams depends almost linearly on both the global mean temperature and the meridional temperature gradient whereas the zonal temperature gradient has little or no influence. 25The magnitude of planetary waves is clearly affected by all three temperature components. Finally, the width of the Hadley cell behaves nonlinearly with respect to all three temperature components.Under global warming the meridional temperature gradient is expected to change: Enhanced warming is expected in the Arctic, largely near the surface, and at the equator at high altitudes. Also there is a pronounced seasonality to these warming patterns. Using SDAMs to disentangle and separately analyse the effect of individual temperature changes might thus help to 30 understand observed and projected changes in large-scale atmosphere dynamics.Earth Syst. Dynam. Discuss., https://doi

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A network-based detection scheme of the jet stream core

Abstract: The comment was uploaded in the form of a supplement: http://www.earth-syst-dynam-discuss.net/esd-2016-37/esd-2016-37-AC4-supplement.pdf Interactive comment on Earth Syst. Dynam. Discuss.,

Cited by 7 publications

References 23 publications

Changes in mean flow and atmospheric wave activity in the North Atlantic sector

Changes in mean flow and atmospheric wave activity in the North Atlantic sector

The IntCal20 Northern Hemisphere Radiocarbon Age Calibration Curve (0–55 cal kBP)

The sensitivity of the large-scale atmosphere circulation to changes in surface temperature gradients in the Northern Hemisphere

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