The Science of the Polar Vortex and Jet Stream

At least since around 2001 we have study papers connecting […]

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Climate State

Date Posted:

January 7, 2014

At least since around 2001 we have study papers connecting the polar vortex / jet stream behavior to anomalies, such as cold weather outbreaks or precipitation changes. The polar vortex phenomenon was described as early as 1853. In recent years studies linked changes in the cryosphere to the polar vortex. Feel free to suggest further study papers in the comments.

Stratospheric sudden warmings (SSWs) are a ubiquitous feature of the wintertime flow in the northern hemisphere. Discovered more than sixty years ago (Sherhag, 1952) when radiosonde observations began to provide routine observations at altitudes higher than 20km above the surface of the earth, these events take their name from a rapid temperature increase of several tens of Kelvin over a few days in the high northern latitudes.  URL (NASA)

The video above is from the open access study “Influence of Arctic sea ice on European summer precipitation” URL.

 

2001

Stratospheric Polar Vortex Influences Winter Cold, Researchers Say

DOI: 10.1175/JCLI-D-12-00466.1 | URL

A mechanism to explain how the behavior of the stratosphere may affect tropospheric weather patterns has been proposed by scientists at the University of Illinois. If correct, the idea could be included in models to better understand the climate system and predict the weather.

“Recent observations have suggested that the strength of the stratospheric polar vortex influences circulation in the troposphere,” said Walter Robinson, a UI professor of atmospheric sciences. “We believe there is a weak forcing in the stratosphere, directed downward, that is pinging the lower atmosphere, stimulating modes of variability that are already there.”

The polar vortex is a wintertime feature of the stratosphere. Consisting of winds spinning counterclockwise above the pole, the vortex varies in strength on long time scales because of interactions with planetary waves  global-scale disturbances that rise from the troposphere. “The polar vortex acts like a big flywheel,” Robinson said. “When it weakens, it tends to stay weakened for a while.”

Other researchers have noted a statistical correlation between periods when the polar vortex is weak and outbreaks of severe cold in many Northern Hemisphere cities.

“When the vortex is strong, the westerlies descend all the way to Earth?s surface,” Robinson said. “This carries more air warmed by the ocean onto the land. When the vortex is weak, that?s when the really deep cold occurs.

Stratospheric Harbingers of Anomalous Weather Regimes

DOI: 10.1126/science.1063315 | URL

Observations show that large variations in the strength of the stratospheric circulation, appearing first above ∼50 kilometers, descend to the lowermost stratosphere and are followed by anomalous tropospheric weather regimes. During the 60 days after the onset of these events, average surface pressure maps resemble closely the Arctic Oscillation pattern. These stratospheric events also precede shifts in the probability distributions of extreme values of the Arctic and North Atlantic Oscillations, the location of storm tracks, and the local likelihood of mid-latitude storms.

Our observations suggest that these stratospheric harbingers may be used as a predictor of tropospheric weather regimes.

2004

Dynamical Mechanisms for Stratospheric Influences on the Troposphere

DOI: 10.1175/1520-0469(2004)061<1711:DMFSIO>2.0.CO;2 | URL

The dynamical mechanisms through which stratospheric forcing can influence tropospheric annular modes are explored. A torque is applied to the stratosphere of an idealized general circulation model, and, under some circumstances, a robust tropospheric response is observed. These tropospheric responses, while initiated by stratospheric forcing, are maintained locally by interactions with transient eddies, and they closely resemble the intrinsic annular modes of the model.

Manipulations of the model are consistent in showing that planetary waves, and not only the zonally symmetric secondary circulations induced by stratospheric forcing, are important for transmitting dynamical signals to the troposphere. Specifically, it is found that the tropospheric response is significantly reduced when planetary waves are suppressed in the stratosphere by additional damping or when the strength of the stratospheric jet is increased.

Wave diagnoses indicate that the confinement of these waves within the troposphere, when stratospheric winds are enhanced, leads to increased planetary wave deceleration of the zonal winds in the high-latitude upper troposphere.

2005

Stratosphere-troposphere evolution during polar vortex intensification

DOI: 10.1029/2005JD006302 | URL | PDF

The dynamical mechanisms through which stratospheric forcing can influence tropospheric annular modes are explored. A torque is applied to the stratosphere of an idealized general circulation model, and, under some circumstances, a robust tropospheric response is observed. These tropospheric responses, while initiated by stratospheric forcing, are maintained locally by interactions with transient eddies, and they closely resemble the intrinsic annular modes of the model.

Manipulations of the model are consistent in showing that planetary waves, and not only the zonally symmetric secondary circulations induced by stratospheric forcing, are important for transmitting dynamical signals to the troposphere. Specifically, it is found that the tropospheric response is significantly reduced when planetary waves are suppressed in the stratosphere by additional damping or when the strength of the stratospheric jet is increased.

Wave diagnoses indicate that the confinement of these waves within the troposphere, when stratospheric winds are enhanced, leads to increased planetary wave deceleration of the zonal winds in the high-latitude upper troposphere.

2010

A link between reduced Barents-Kara sea ice and cold winter extremes over northern continents

DOI: 10.1029/2009JD013568 | URL

The recent overall Northern Hemisphere warming was accompanied by several severe northern continental winters, as for example, extremely cold winter 2005–2006 in Europe and northern Asia. Here we show that anomalous decrease of wintertime sea ice concentration in the Barents-Kara (B-K) seas could bring about extreme cold events like winter 2005–2006. Our simulations with the ECHAM5 general circulation model demonstrate that lower-troposphere heating over the B-K seas in the Eastern Arctic caused by the sea ice reduction may result in strong anticyclonic anomaly over the Polar Ocean and anomalous easterly advection over northern continents.

This causes a continental-scale winter cooling reaching −1.5°C, with more than 3 times increased probability of cold winter extremes over large areas including Europe. Our results imply that several recent severe winters do not conflict the global warming picture but rather supplement it, being in qualitative agreement with the simulated large-scale atmospheric circulation realignment. Furthermore, our results suggest that high-latitude atmospheric circulation response to the B-K sea ice decrease is highly nonlinear and characterized by transition from anomalous cyclonic circulation to anticyclonic one and then back again to cyclonic type of circulation as the B-K sea ice concentration gradually reduces from 100% to ice free conditions.

We present a conceptual model that may explain the nonlinear local atmospheric response in the B-K seas region by counter play between convection over the surface heat source and baroclinic effect due to modified temperature gradients in the vicinity of the heating area.

2012

Evidence linking Arctic amplification to extreme weather in mid-latitudes

DOI: 10.1029/2012GL051000 | URL

Arctic amplification (AA) – the observed enhanced warming in high northern latitudes relative to the northern hemisphere – is evident in lower-tropospheric temperatures and in 1000-to-500 hPa thicknesses. Daily fields of 500 hPa heights from the National Centers for Environmental Prediction Reanalysis are analyzed over N. America and the N. Atlantic to assess changes in north-south (Rossby) wave characteristics associated with AA and the relaxation of poleward thickness gradients.

Two effects are identified that each contribute to a slower eastward progression of Rossby waves in the upper-level flow: 1) weakened zonal winds, and 2) increased wave amplitude. These effects are particularly evident in autumn and winter consistent with sea-ice loss, but are also apparent in summer, possibly related to earlier snow melt on high-latitude land.

Slower progression of upper-level waves would cause associated weather patterns in mid-latitudes to be more persistent, which may lead to an increased probability of extreme weather events that result from prolonged conditions, such as drought, flooding, cold spells, and heat waves.

2013

Extreme summer weather in northern mid-latitudes linked to a vanishing cryosphere

DOI: 10.1038/nclimate2065 | URL

The past decade has seen an exceptional number of unprecedented summer extreme weather events1234 in northern mid-latitudes, along with record declines in both summer Arctic sea ice56and snow cover on high-latitude land7. The underlying mechanisms that link the shrinking cryosphere with summer extreme weather, however, remain unclear89101112. Here, we combine satellite observations of early summer snow cover and summer sea-ice extent13 with atmospheric reanalysis data14 to demonstrate associations between summer weather patterns in mid-latitudes and losses of snow and sea ice.

Results suggest that the atmospheric circulation responds differently to changes in the ice and snow extents, with a stronger response to sea-ice loss, even though its reduction is half as large as that for the snow cover. Atmospheric changes associated with the combined snow/ice reductions reveal widespread upper-level height increases, weaker upper-level zonal winds at high latitudes, a more amplified upper-level pattern, and a general northward shift in the jet stream.

More frequent extreme summer heat events over mid-latitude continents are linked with reduced sea ice and snow through these circulation changes.

Influence of Arctic sea ice on European summer precipitation

DOI: 10.1088/1748-9326/8/4/044015 | URL

The six summers from 2007 to 2012 were all wetter than average over northern Europe. Although none of these individual events are unprecedented in historical records, the sequence of six consecutive wet summers is extraordinary. Composite analysis reveals that observed wet summer months in northern Europe tend to occur when the jet stream is displaced to the south of its climatological position, whereas dry summer months tend to occur when the jet stream is located further north.

Highly similar mechanisms are shown to drive simulated precipitation anomalies in an atmospheric model. The model is used to explore the influence of Arctic sea ice on European summer climate, by prescribing different sea ice conditions, but holding other forcings constant. In the simulations, Arctic sea ice loss induces a southward shift of the summer jet stream over Europe and increased northern European precipitation. The simulated precipitation response is relatively small compared to year-to-year variability, but is statistically significant and closely resembles the spatial pattern of precipitation anomalies in recent summers.

The results suggest a causal link between observed sea ice anomalies, large-scale atmospheric circulation and increased summer rainfall over northern Europe. Thus, diminished Arctic sea ice may have been a contributing driver of recent wet summers.

Winter and Summer Northern Hemisphere Blocking in CMIP5 Models

DOI: 10.1175/JCLI-D-12-00466.1URL

The frequencies of atmospheric blocking in both winter and summer and the changes in them from the twentieth to the twenty-first centuries as simulated in 12 models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) are analyzed. The representative concentration pathway 8.5 (RCP8.5) high emission scenario runs are used to represent the twenty-first century. The analysis is based on the wave-breaking methodology of Pelly and Hoskins. It differs from the Tibaldi and Molteni index in viewing equatorward cutoff lows and poleward blocking highs in equal manner as indicating a disruption to the westerlies. One-dimensional and two-dimensional diagnostics are applied to identify blocking of the midlatitude storm track and also at higher latitudes.

Winter blocking frequency is found to be generally underestimated. The models give a decrease in the European blocking maximum in the twenty-first century, consistent with the results in other studies. There is a mean twenty-first-century winter poleward shift of high-latitude blocking but little agreement between the models on the details. In summer, Eurasian blocking is also underestimated in the models, whereas it is now too large over the high-latitude ocean basins.

A decrease in European blocking frequency in the twenty-first-century model runs is again found. However, in summer there is a clear eastward shift of blocking over eastern Europe and western Russia, in a region close to the blocking that dominated the Russian summer of 2010. While summer blocking decreases in general, the poleward shift of the storm track into the region of frequent high-latitude blocking may mean that the incidence of storms being obstructed by blocks may actually increase.

Quasiresonant amplification of planetary waves and recent Northern Hemisphere weather extremes

DOI: 10.1073/pnas.1222000110| URL

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.

Linkages between Arctic Sea Ice Loss and Mid-Latitude Weather Patterns: A Workshop September 12-13, 2013 URL

See also  CNN: Why Are We Still Debating Climate Change?

Rising global average temperatures, and especially intense warming in the northern polar regions, are leading to a rapid loss of the sea ice cap that covers the Arctic ocean. Emerging research may indicate that large losses of Arctic sea ice cover can have dramatic impacts upon weather patterns across the heavily populated northern mid-latitudes, and that such impacts could increase as ice cover continues to retreat in the coming decades. The workshop will address the following questions:

  • What do we currently understand about the mechanisms that link declines in Arctic sea ice cover, loss of high-latitude snow cover, changes in arctic-region energy fluxes, atmospheric circulation patterns, and the occurrence of extreme weather events?
  • What may be the possible implications of more severe loss (and eventually, total loss) of summer Arctic sea ice upon weather patterns at lower latitudes?
  • What are the major gaps in our understanding, and what sort of observational and/or modeling efforts are needed to fill those gaps?
  • What are the current opportunities and limitations for using Arctic sea ice predictions to assess the risk of temperature/precipitation anomalies and extreme weather events over northern continents? How might these capabilities improve over time?
See also  Hurricane Douglas NASA/NOAA satellite view/report July 23, 2020

Warm Arctic, Cold Continents: A Common Pattern Related to Arctic Sea Ice Melt, Snow Advance, and Extreme Winter Weather

2013, Oceanography 26(4):150–160, http://dx.doi.org/10.5670/oceanog.2013.70&nbsp;URL

2014

Atmospheric science: Long-range linkage

DOI: 10.1038/nclimate2079 | URL

Evidence indicates that the continued loss of Arctic sea-ice and snow cover may influence weather at lower latitudes. Now correlations between high-latitude cryosphere changes, hemispheric wind patterns and mid-latitude extreme events are shown for the Northern Hemisphere.

Equatorial signatures of the Pacific Meridional Modes: Dependence on mean climate state

Abstract Extratropical atmospheric variability can impact tropical climate in the Pacific sector via the Pacific Meridional Modes (PMMs). The South PMM (SPMM) has a larger equatorial signature than the North PMM (NPMM) for the same amount of extratropical variability. Here we explain this interhemispheric asymmetry using an atmospheric general circulation model coupled to a slab ocean model. By imposing an anomalous interhemispheric heating gradient, we strengthen the northeasterly trades and weaken the southeasterly trades, shifting the Intertropical Convergence Zone south of the equator.
As a result, the SPMM no longer influences the equatorial region while the NPMM shows strengthened linkages to the central-western equatorial Pacific. By demonstrating that background winds determine the propagation of the wind-evaporation-sea surface temperature feedback fundamental for the PMMs, we conclude that the interhemispheric asymmetry between the PMMs is largely attributed to the asymmetric mean trades in the Pacific. The results have implications for both paleoclimate studies and model development. DOI: 10.1002/2013GL058842

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