A Dynamical Explanation of the Topographically Bound Easterly Low‐Level Jet Surrounding Antarctica

Fulton, Scott R.; Schubert, Wayne H.; Chen, Zhengqing; Ciesielski, Paul E.

doi:10.1002/2017jd027192

Cited by 9 publications

(21 citation statements)

References 23 publications

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“…At all times shown in the plots, the meridional gradient u is large at 688-758S, which is consistent with the climatologically strong radiative cooling at the Antarctic surface (e.g., Fulton et al 2017). The maximum of the anomaly of |$ H u| is observed at t = 0 h on the south flank of the westerly anomaly at the same level.…”

Section: B Composite Analyses Of Tropopause Fold Eventssupporting

confidence: 81%

“…It is well known that the Antarctic troposphere contains unique atmospheric flows, including katabatic winds (e.g., Parish and Bromwich 1987) and a persistent easterly low-level jet surrounding the Antarctic plateau (e.g., Fulton et al 2017). These characteristic flows come from the steep topography of the Antarctic continent and strong radiative cooling on the surface of the continent.…”

Section: Introductionmentioning

confidence: 99%

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Dynamical Analysis of Tropopause Folding Events in the Coastal Region of Antarctica

2022

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Tropopause folding events (TFs) are characterized by the rapid and deep descent of the tropopause and is considered to play a significant role in mass exchange between the stratosphere and troposphere. In the present study, TFs occurring in the Antarctic coastal region were examined using ERA-5 data set. First, the climatological distribution of TF frequency in the extratropics of the Southern Hemisphere was examined. Similar to results from previous studies, TFs were found to often occur along the coast of Antarctica, which is located more than 1000 km south of the maximum of the eddy kinetic energy of synoptic-scale disturbances. This result suggests that the climatological pattern of frequency of TFs in the southern high latitudes cannot be explained only by the geographical distribution of storm tracks. Next, a composite analysis of TFs at Syowa Station was performed. When the negative anomaly of the tropopause height was greatest, strong Q-vector divergence and downwelling were observed in the vicinity of the TF locations. The distribution of Q vectors is related to a local westerly jet and strengthening of the frontal structure associated with meridionally contracted synoptic-scale disturbances. The roles of the topography of the Antarctic Plateau and the radiative cooling on the surface of the continent during the contraction of the disturbances are also discussed based on ray-tracing theory.

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Section: B Composite Analyses Of Tropopause Fold Eventssupporting

confidence: 81%

Section: Introductionmentioning

confidence: 99%

Dynamical Analysis of Tropopause Folding Events in the Coastal Region of Antarctica

2022

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“…Firstly, surface r values against ASCAT and station measurements are on average highest for ERA5, indicating the most faithful representation of variability in the 10 m winds on short timescales. Secondly, higher resolution in ERA5 supports more realistic coastal orography which is critical in coastal regions; JRA-55 and MERRA-2 coastal orography is not as steep and theory suggests that the slope is likely to be important for both katabatic winds and for a deeper baroclinic layer in the coastal zone (Fulton et al, 2017). Lastly, the temperature profile appears to be most realistic in ERA5, with JRA-55 and MERRA-2 exhibiting substantial cold biases in the lowest 1000 m a.g.l.…”

Section: Implications For Use Of Reanalysis Datasetsmentioning

confidence: 96%

“…One important driver is katabatic forcing, which sustains shallow terrain-following drainage flow towards the coast (Ball, 1960;Parish and Bromwich, 1987) but its offshore extent is a source of uncertainty as the flow often stops abruptly at the coastal margin (e.g., Yu and Cai, 2006;Tomikawa et al, 2015;Vignon et al, 2020) and its behaviour in models is sensitive to the representation of the atmospheric boundary layer (King et al, 2001;Parish and Cassano, 2003;Orr et al, 2014). Representation of orography is important as long-wave cooling over the steep coastal slopes sets up both katabatic flows near the surface and a deeper layer of terrain-following isentropes above it which explains the easterly 'low-level jet' structure (Fulton et al, 2017). Orography is also critical for blocking and barrier winds induced by steep Antarctic coastal slopes Cassano, 2001, 2003;Orr et al, 2014;Weber et al, 2016;Yamada and Hirasawa, 2018).…”

mentioning

confidence: 99%

Reanalysis representation of low-level winds in the Antarctic near-coastal region

Harrison

Biri

Bracegirdle

et al. 2022

Preprint

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Abstract. Low-level easterly winds encircling Antarctica help drive coastal currents which modify transport of circumpolar deep water to ice shelves, as well as the formation and distribution of sea ice. Reanalysis datasets are especially important at high southern latitudes where observations are few. Here, we investigate the representation of the mean state and short-term variability of coastal easterlies in three recent reanalyses, ERA5, MERRA-2 and JRA-55. Reanalysed winds are compared with summertime marine surface wind observations from the ASCAT scatterometer and surface and upper air measurements from coastal stations. Reanalysis coastal easterlies correlate highly with ASCAT (r=0.91, 0.89 and 0.85 for ERA5, MERRA-2 and JRA-55 respectively) but notable wind speed biases are found close to the coastal margins, especially near complex orography and at high wind speeds. To characterise short-term variability, 12-hourly reanalysis and coastal station winds are composited using self-organising maps (SOMs), which cluster timesteps under similar synoptic and mesoscale influences. Reanalysis performance is sensitive to the flow configuration at stations near steep coastal slopes, where they fail to capture the magnitude of surface wind speed variability when synoptic forcing is weak and conditions favour katabatic forcing. ERA5 exhibits the best overall performance, has more realistic orography and a more realistic jet structure and temperature profile. These results demonstrate the regime behaviour of Antarctica’s coastal winds and indicate important features of the coastal winds which are not well characterised by reanalysis datasets.

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“…As discussed in section 7, this disadvantage is sometimes overcome through the use of a massless layer. Fulton et al (2017) have applied the concept of a massless layer in solving the PV invertibility principle for the topographically bound low-level jet surrounding Antarctica.…”

Section: The Meridional Circulation Equation In the Height Coordinatementioning

confidence: 99%

Elliptic Transverse Circulation Equations for Balanced Models in a Generalized Vertical Coordinate

Schubert,

Fulton,

Ciesielski

2017

Preprint

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When studying tropical cyclones using the f -plane, axisymmetric, gradient balanced model, there arises a second-order elliptic equation for the transverse circulation. Similarly, when studying zonally symmetric meridional circulations near the equator (the tropical Hadley cells) or the katabatically forced meridional circulation over Antarctica, there also arises a second order elliptic equation. These elliptic equations are usually derived in the pressure coordinate or the potential temperature coordinate, since the thermal wind equation has simple non-Jacobian forms in these two vertical coordinates. Because of the large variations in surface pressure that can occur in tropical cyclones and over the Antarctic ice sheet, there is interest in using other vertical coordinates, e.g., the height coordinate, the classical σ-coordinate, or some type of hybrid coordinate typically used in global numerical weather prediction or climate models. Because the thermal wind equation in these coordinates takes a Jacobian form, the derivation of the elliptic transverse circulation equation is not as simple. Here we present a method for deriving the elliptic transverse circulation equation in a generalized vertical coordinate, which allows for many particular vertical coordinates, such as height, pressure, log-pressure, potential temperature, classical σ, and most hybrid cases. Advantages and disadvantages of the various coordinates are discussed.

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A Dynamical Explanation of the Topographically Bound Easterly Low‐Level Jet Surrounding Antarctica

Cited by 9 publications

References 23 publications

Dynamical Analysis of Tropopause Folding Events in the Coastal Region of Antarctica

Dynamical Analysis of Tropopause Folding Events in the Coastal Region of Antarctica

Reanalysis representation of low-level winds in the Antarctic near-coastal region

Elliptic Transverse Circulation Equations for Balanced Models in a Generalized Vertical Coordinate

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