An objective global climatology of polar lows based on reanalysis data

Stoll, Patrick; Graversen, Rune; Noer, Gunnar; Hodges, Kevin I.

doi:10.1002/qj.3309

Cited by 52 publications

(148 citation statements)

References 36 publications

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“…Regardless, Stoll et al . () found that the 10 m wind speed was not very effective at identifying polar lows. As a measure of intensity we use the maximum relative vorticity (at 925 hPa) for each polar low track, but no threshold is applied to this quantity.…”

Section: Methodsmentioning

confidence: 96%

“…For this we use a box of 132 × 132 km (11 × 11 grid cells), similar to the 2° latitude radius used by Stoll et al . (). It should be noted that the wind speed threshold in the definition is based on observations, while modelled 10 m wind speed is a diagnostic field which is often subject to tuning.…”

Section: Methodsmentioning

confidence: 97%

“…The detection algorithm is based on three criteria: vorticity at 925 hPa, SST-500 difference, as well as a threshold on wind speed at 10 m above sea level. In their comparison of the effectiveness of different criteria for detecting polar lows, Stoll et al (2018) ranked the SST-500 difference third best among the 18 MCAO criteria, only marginally worse than the first two. In their study, the threshold including 90% of all polar lows was 41.4 K. Zahn and von Storch (2008) used 43 K, while MET Norway uses 40 K as threshold in operational polar low forecasting.…”

Section: Trackingmentioning

confidence: 99%

“…For the wind speed criterion we have used 15 m/s as threshold (as in Heinemann and Claud, 1997), while Zahn and von Storch (2008) used 13.9 m/s (near-gale, as in Rasmussen, 2011). For this we use a box of 132 × 132 km (11 × 11 grid cells), similar to the 2 • latitude radius used by Stoll et al (2018). It should be noted that the wind speed threshold in the definition is based on observations, while modelled 10 m wind speed is a diagnostic field which is often subject to tuning.…”

Section: Trackingmentioning

confidence: 99%

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Polar low variability and future projections for the Nordic and Barents Seas

Landgren

Batrak

Haugen

et al. 2019

Quart J Royal Meteoro Soc

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Polar lows are intense mesoscale cyclones occurring during winter over open sea areas in certain polar sub‐regions. Due to their small size, they are not explicitly represented in present global climate models or Earth system models. In this study 18 members of the CESM Large Ensemble were dynamically downscaled to ∼12 km horizontal mesh width using the quasi‐hydrostatic ALARO model within the HARMONIE script system in climate mode (HCLIM‐ALARO). The domain covers the Nordic and Barents Seas. One historical and two future time‐periods were selected. For validation, the ERA‐Interim reanalysis was also downscaled. A cyclone‐tracking algorithm was used to identify tracks of individual polar lows. Their frequency of occurrence, lifetime, and maximum relative vorticity were estimated. Relative to ERA‐Interim, the historical frequency of occurrence of polar lows was slightly overestimated in the Nordic Seas and underestimated in the Barents Sea, which is likely due to positive biases in sea‐surface temperature and sea‐ice concentration. For future climate projections, the regions of polar low genesis are diagnosed to move northwards in accordance with the sea‐ice retreat. In the Nordic Seas, the number of polar lows decreases at the beginning of the season, while there is an increase in March. In the Barents Sea, a February–April increase in the occurrence of polar lows is seen.

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Section: Methodsmentioning

confidence: 96%

Section: Methodsmentioning

confidence: 97%

Section: Trackingmentioning

confidence: 99%

Section: Trackingmentioning

confidence: 99%

See 2 more Smart Citations

Polar low variability and future projections for the Nordic and Barents Seas

Landgren

Batrak

Haugen

et al. 2019

Quart J Royal Meteoro Soc

View full text Add to dashboard Cite

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“…The preferred region for cyclogenesis is generally where both a strong temperature gradient and an upper-level trough are found (e.g., Davies, 1997;Shimada et al, 2014;Uccellini, 1990). Around Antarctica, the strongest temperature gradient is found along the fringes of the ice pack, making the sea ice edge a preferred region for cyclogenesis (e.g., Schlosser et al, 2011;Stoll et al, 2018;Yanase & Niino, 2007). High baroclinic instability associated with the horizontal temperature gradient is crucial for the formation and the intensification of the cyclones (Davies, 1997;Uccellini, 1990;Yanase & Niino, 2007), but cyclogenesis occurs only at the entrance and exit regions of upper-level troughs (e.g., Kolstad, 2011;Shimada et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

Polar Cyclones at the Origin of the Reoccurrence of the Maud Rise Polynya in Austral Winter 2017

et al. 2019

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This study examines the role of atmospheric forcings in the occurrence of open‐ocean polynyas by investigating the case of the austral winter 2017's polynya located in the Lazarev Sea sector to the east of the Weddell Sea, known as the Maud Rise polynya or the Weddell Polynya. The ice‐free zone appeared in mid‐September 2017 and grew to as large as 80,000 km2 by the end of October 2017 before merging with the open ocean after the sea ice started to retreat at the beginning of the austral summer. Using a combination of satellite observations and reanalysis data at high spatiotemporal resolution, we found that severe cyclones, occurring over the ice pack, have a deterministic role in creating strong divergence in the sea ice field through strong cyclonic surface winds leading to the opening of the polynya. The occurrence of intense and frequent cyclones over the ice pack during austral winter 2017 was unusual, and it occurred under an enhanced strong positive meridional transport of heat flux and moisture toward Antarctica associated with an amplification of the atmospheric zonal wave 3 and a strong positive Southern Annular Mode index. We found that the opening of the polynya was not primarily due to direct ice melt by thermodynamic effects but rather to strong dynamical forcing by the winds on the sea ice, as in the case of coastal polynyas. Indeed, the meridional transport of heat toward Antarctica occurred over the Weddell Sea sector (i.e., to the east of the Lazarev Sea sector where the polynya is located) whereas the Lazarev Sea sector was under the influence of equatorward transport of cold air masses at that time. Our results show that the supply of warm and moist air coming from the west side of the South Atlantic Ocean into the Weddell Sea significantly increased the potential for cyclone formation as measured by the Eady growth rate leading to intense and frequent cyclogenesis over the ice pack, far south from the ice edge. After cyclogenesis in the Weddell Sea, these cyclones intensified as they moved eastward spinning over the Lazarev Sea with intensity comparable to category 11—violent storms—in the Beaufort scale. The cyclonic winds generated sea ice divergence by pushing the ice away from the cyclone center: To the east, north of it and to the west, south of it, which led to the reoccurrence of the Maud Rise polynya in mid‐September 2017.

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Sensitivity of air-sea heat exchange in cold-air outbreaks to model resolution and sea-ice distribution

Spensberger

Spengler

2020

Preprint

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Marine cold air outbreaks (CAOs) constitute a large fraction of the air-sea heat exchange in the polar regions (e.g., Papritz & Spengler, 2017). These atmosphere-ocean interactions are most intense near the sea ice edge and within the Marginal Ice Zone (MIZ), which is also the location where our models and are often least accurate (e.g., Bourassa et al., 2013Bourassa et al., , 2021. In addition to challenges with parameterizations, the magnitude and distribution of these air-sea heat exchanges are also sensitive to the representation of mesoscale atmospheric phenomena (e.g.,

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An objective global climatology of polar lows based on reanalysis data

Abstract: Here we present an objective global climatology of polar lows. In order to obtain objective detection criteria, the efficacy of several parameters for separating polar lows

Cited by 52 publications

References 36 publications

Polar low variability and future projections for the Nordic and Barents Seas

Polar low variability and future projections for the Nordic and Barents Seas

Polar Cyclones at the Origin of the Reoccurrence of the Maud Rise Polynya in Austral Winter 2017

Sensitivity of air-sea heat exchange in cold-air outbreaks to model resolution and sea-ice distribution

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