A climatology of low‐level jets in the mid‐latitudes and polar regions of the Northern Hemisphere

Tuononen, Minttu; Sinclair, Victoria A.; Vihma, Timo

doi:10.1002/asl.587

Cited by 31 publications

(64 citation statements)

References 24 publications

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“…All scales of atmospheric motion are coupled to surface turbulent fluxes by virtue of their effect on the lower tropospheric winds, temperature, humidity, and stability. For example, low-level jets in the Arctic enhance turbulent fluxes through increased wind speeds and are commonly associated with synoptic-scale baroclinicity over ice-free seas, strong gradients in topography, and the sea ice edge [172]. Synoptic-scale cyclone activity dominates the Arctic atmospheric circulation on short spatial and temporal scales [173][174][175] driving strong SH and LH fluxes [176][177][178].…”

Section: Atmospheric Circulationmentioning

confidence: 99%

On the Increasing Importance of Air-Sea Exchanges in a Thawing Arctic: A Review

et al. 2018

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Forty years ago, climate scientists predicted the Arctic to be one of Earth's most sensitive climate regions and thus extremely vulnerable to increased CO 2 . The rapid and unprecedented changes observed in the Arctic confirm this prediction. Especially significant, observed sea ice loss is altering the exchange of mass, energy, and momentum between the Arctic Ocean and atmosphere.As an important component of air-sea exchange, surface turbulent fluxes are controlled by vertical gradients of temperature and humidity between the surface and atmosphere, wind speed, and surface roughness, indicating that they respond to other forcing mechanisms such as atmospheric advection, ocean mixing, and radiative flux changes. The exchange of energy between the atmosphere and surface via surface turbulent fluxes in turn feeds back on the Arctic surface energy budget, sea ice, clouds, boundary layer temperature and humidity, and atmospheric and oceanic circulations. Understanding and attributing variability and trends in surface turbulent fluxes is important because they influence the magnitude of Arctic climate change, sea ice cover variability, and the atmospheric circulation response to increased CO 2 . This paper reviews current knowledge of Arctic Ocean surface turbulent fluxes and their effects on climate. We conclude that Arctic Ocean surface turbulent fluxes are having an increasingly consequential influence on Arctic climate variability in response to strong regional trends in the air-surface temperature contrast related to the changing character of the Arctic sea ice cover. Arctic Ocean surface turbulent energy exchanges are not smooth and steady but rather irregular and episodic, and consideration of the episodic nature of surface turbulent fluxes is essential for improving Arctic climate projections.

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Section: Atmospheric Circulationmentioning

confidence: 99%

On the Increasing Importance of Air-Sea Exchanges in a Thawing Arctic: A Review

et al. 2018

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“…The interactions between Arctic anticyclone and approaching cyclones are likely responsible for the strong winds observed in both LLJ cases. The primary reason for the proximity of LLJs near the sea ice edge, reported in some studies (Tuononen et al, ; J. Zhang et al, ), is more likely due to the influence of the sea ice‐water contrast on these interactions on a larger spatial scale and over a longer time than due to the local effect of the thermal contrast. For example, the cold sea ice surface in cold seasons aids the expansion of anticyclones into the Arctic Ocean over sea ice from nearby continents.…”

Section: Discussionmentioning

confidence: 95%

“…The thermal wind is one of the main mechanisms that create and maintain LLJs in the presence of baroclinicity (Andreas et al, ; Guest et al, ; Jakobson et al, ; Vihma et al, ). In the Arctic, LLJs and strong surface winds are found frequently close to the sea ice edge (Z. Liu et al, ; Tuononen et al, ; Vihma & Brümmer, ; J. Zhang et al, ). Given the large thermal contrast between sea ice and open water, the wind shear generated by the baroclinicity may contribute significantly to elevated LLJs near the ice edge, as well as surface ice edge jets.…”

Section: Discussionmentioning

confidence: 99%

“…In polar regions, LLJs are frequently observed near the sea ice edge, the narrow boundary region between sea ice and open water (Andreas et al, ; Vihma & Brümmer, ; Z. Liu et al, ). Using reanalysis data, a recent study showed the LLJs occur more frequently near the sea ice edge than in the central Arctic Ocean (Tuononen et al, ). Surface winds are also found to be stronger in regions near the sea ice edge, especially during cold seasons (Shaw et al, ; Kolstad & Bracegirdle, ; J. Zhang et al, ).…”

Section: Introductionmentioning

confidence: 99%

“…Liu et al, 2015). Using reanalysis data, a recent study showed the LLJs occur more frequently near the sea ice edge than in the central Arctic Ocean (Tuononen et al, 2015). Surface winds are also found to be stronger in regions near the sea ice edge, especially during cold seasons (Shaw et al, 1991;Kolstad & Bracegirdle, 2008;J.…”

Section: Introductionmentioning

confidence: 99%

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Low‐Level and Surface Wind Jets Near Sea Ice Edge in the Beaufort Sea in Late Autumn

Liu

Schweiger

2019

JGR Atmospheres

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Low‐level wind jets (LLJs) and strong surface winds are frequently observed near the sea ice edge in the presence of strong thermal contrast between open water and sea ice. Two LLJ cases near the sea ice edge in the Beaufort Sea are examined using dropsonde observations made from Seasonal Ice Zone Reconnaissance Survey flights. Ensembles of Polar Weather Research and Forecast simulations with and without sea ice demonstrate the contribution of the surface thermal contrast to the boundary layer structure, the LLJ, and surface ice edge jets. Because the surface temperature contrast only influences the lower most hundreds of meters in the atmospheric boundary layer, its contribution to the temperature gradient and wind speed at the level of the LLJ is limited. The sea ice does strengthen the LLJ by extending the LLJ northward over sea ice and increasing the maximum LLJ wind speeds by up to 13% and as much as 29% further north at a lower altitude. However, the primary reason for the observed strong winds in these two cases are the synoptic interactions between anticyclones and approaching cyclones. The effect of the surface thermal contrast on surface winds is controlled by a separate mechanism. The cold and stable boundary layer over sea ice prevents the momentum transport from the LLJ to the surface. This leads to weaker surface winds over sea ice and confines the strong surface winds close to the sea ice edge. This mechanism contributes to the frequent occurrence of the surface “ice edge jets.”

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Low‐Level Baroclinic Jets Over the New Arctic Ocean

et al. 2018

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During the Sea State cruise in the fall of 2015, in the Chukchi/Beaufort Sea region, there were five strong (>10 m s−1) surface wind events associated with low‐level atmospheric jets. These jets were analyzed using rawinsonde observations, ship measurements, and a numerical forecast model. The jets occurred when easterly winds aligned with the ice edge, generating low‐level baroclinicity in a direction favorable for increasing the geostrophic wind speed toward the surface. The maximum wind speed usually occurred at the top of the atmospheric boundary layer with wind speeds greater than 8 m s−1 extending through the capping inversion to 2,000–3,000 m elevation, with winds decreasing toward the surface in the boundary layer due to friction. The width (crosswind) dimensions of the jets were 250–400 km and they existed downwind for as long as the winds remained generally parallel to the ice edges, typically several hundred kilometers. Thermal winds calculated from crosswind‐oriented rawinsonde temperature profiles matched the observed vertical wind speed gradients in the inversion regions, indicating that the jets were in quasi‐geostrophic (inversion layer) or quasi‐frictional (boundary layer) balance, with low Rossby numbers. We define these as “baroclinic” type jets, which are distinct from “ice/sea breeze” type jets which flow more down the pressure and density gradients, and have high Rossby numbers. The operational model analyses matched the observations quite well, giving confidence that these types of jets can be simulated and predicted as long as the models have sufficient resolution and accurately parameterize vertical heat fluxes.

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A climatology of low‐level jets in the mid‐latitudes and polar regions of the Northern Hemisphere

Cited by 31 publications

References 24 publications

On the Increasing Importance of Air-Sea Exchanges in a Thawing Arctic: A Review

On the Increasing Importance of Air-Sea Exchanges in a Thawing Arctic: A Review

Low‐Level and Surface Wind Jets Near Sea Ice Edge in the Beaufort Sea in Late Autumn

Low‐Level Baroclinic Jets Over the New Arctic Ocean

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