Mean Westerly Jet Streams in the Southern Hemisphere

2013 ◽  
pp. 128-148 ◽  
Author(s):  
H. R. Phillpot
Keyword(s):  
Southern Hemisphere ◽  
Jet Streams ◽  
Westerly Jet

scholarly journals Cyclonic and anticyclonic contributions to atmospheric energetics

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Satoru Okajima ◽  
Hisashi Nakamura ◽  
Yohai Kaspi
Keyword(s):  
Storm Track ◽  
Mean Flow ◽  
Weather Variability ◽  
Jet Streams ◽  
Near Surface ◽  
Westerly Jet ◽  
Track Dynamics ◽  
New Findings ◽  
Atmospheric Energetics ◽  
Thermally Driven

AbstractMigratory cyclones and anticyclones account for most of the day-to-day weather variability in the extratropics. These transient eddies act to maintain the midlatitude jet streams by systematically transporting westerly momentum and heat. Yet, little is known about the separate contributions of cyclones and anticyclones to their interaction with the westerlies. Here, using a novel methodology for identifying cyclonic and anticyclonic vortices based on curvature, we quantify their separate contributions to atmospheric energetics and their feedback on the westerly jet streams as represented in Eulerian statistics. We show that climatological westerly acceleration by cyclonic vortices acts to dominantly reinforce the wintertime eddy-driven near-surface westerlies and associated cyclonic shear. Though less baroclinic and energetic, anticyclones still play an important role in transporting westerly momentum toward midlatitudes from the upper-tropospheric thermally driven jet core and carrying eddy energy downstream. These new findings have uncovered essential characteristics of atmospheric energetics, storm track dynamics and eddy-mean flow interaction.

scholarly journals The South Atlantic–South Indian Ocean Pattern: a Zonally Oriented Teleconnection along the Southern Hemisphere Westerly Jet in Austral Summer

Atmosphere ◽  
2019 ◽  
Vol 10 (5) ◽  
pp. 259 ◽  
Author(s):  
Zhongda Lin
Keyword(s):  
Indian Ocean ◽  
Interannual Variability ◽  
Southern Hemisphere ◽  
Austral Summer ◽  
South Atlantic ◽  
The South ◽  
South Indian Ocean ◽  
Westerly Jet ◽  
South Indian ◽  
Zonal Wavenumber

Extratropical teleconnections significantly affect the climate in subtropical and mid-latitude regions. Understanding the variability of atmospheric teleconnection in the Southern Hemisphere, however, is still limited in contrast with the well-documented counterpart in the Northern Hemisphere. This study investigates the interannual variability of mid-latitude circulation in the Southern Hemisphere in austral summer based on the ERA-Interim reanalysis dataset during 1980–2016. A stationary mid-latitude teleconnection is revealed along the strong Southern Hemisphere westerly jet over the South Atlantic and South Indian Ocean (SAIO). The zonally oriented SAIO pattern represents the first EOF mode of interannual variability of meridional winds at 200 hPa over the region, with a vertical barotropic structure and a zonal wavenumber of 4. It significantly modulates interannual climate variations in the subtropical Southern Hemisphere in austral summer, especially the opposite change in rainfall and surface air temperature between Northwest and Southeast Australia. The SAIO pattern can be efficiently triggered by divergences over mid-latitude South America and the southwest South Atlantic, near the entrance of the westerly jet, which is probably related to the zonal shift of the South Atlantic Convergence Zone. The triggered wave train is then trapped within the Southern Hemisphere westerly jet waveguide and propagates eastward until it diverts northeastward towards Australia at the jet exit, in addition to portion of which curving equatorward at approximately 50° E towards the southwest Indian Ocean.

scholarly journals Characterization of West African Jet Streams and Their Association to ENSO Events and Rainfall in ERA-Interim 1979–2011

2014 ◽  
Vol 2014 ◽  
pp. 1-12 ◽  
Author(s):  
Churchill Okonkwo ◽  
Belay Demoz ◽  
Sium Tesfai
Keyword(s):  
Decadal Variability ◽  
Southern Oscillation ◽  
Rainfall Variability ◽  
West African ◽  
Boreal Summer ◽  
Boreal Winter ◽  
Jet Streams ◽  
Enso Events ◽  
Westerly Jet ◽  
Sahel Region

The interannual variability of West African jet streams and their association with rainfall are reexamined using European Reanalysis ERA-Interim 1979–2011. The objective of the study is to characterize their climatology and role in rainfall variability in western Sahel. Wavelet analysis was used on wind speed data and implications to ENSO were discussed subsequently. Our results show that while the low-level African Westerly Jet (AWJ) correlates well with rainfall south of the equator in boreal winter months, the Tropical Easterly Jet (TEJ) and African Easterly Jet (AEJ) correlate better with rainfall north of the equator in the boreal summer months. Results of interannual-to-decadal variability in 200 mb, 600 mb, and 850 mb of zonal wind reveal that there is enhanced variability in the 2–8 year band. Also, the TEJ, AEJ, and AWJ fluctuations are coupled with variations in southern oscillation. Further analysis suggests a statistically significant association between TEJ and the El Niño events of the 1980s that led to intense drought in the Sahel region of West Africa. The 2007 moderate La Niña shows a statistically significant coherence with the 500 mb, 600 mb, and 850 mb jets. These associations are also phase locked, suggesting that the association may be more than by chance.

scholarly journals A Nonlinear Multiscale Theory of Atmospheric Blocking: Dynamical and Thermodynamic Effects of Meridional Potential Vorticity Gradient

2020 ◽  
Vol 77 (7) ◽  
pp. 2471-2500 ◽  
Author(s):  
Dehai Luo ◽  
Wenqi Zhang
Keyword(s):  
Potential Vorticity ◽  
Large Amplitude ◽  
Three Dimensional ◽  
Interaction Model ◽  
Nonlinear Behavior ◽  
Vertical Variation ◽  
Jet Streams ◽  
Westerly Jet ◽  
Slow Decay ◽  
Long Lifetime

AbstractIn this paper, an extended nonlinear multiscale interaction model is proposed to examine nonlinear behavior of eddy-driven blocking as a Rossby wave packet in a three-dimensional background flow by dividing the background meridional potential vorticity gradient (PVy) into dynamical PVy related to the horizontal (mainly meridional) shear of background westerly wind (BWW) and thermodynamic PVy associated with the meridional temperature gradient (MTG). It is found that eddy-driven baroclinic blocking with large amplitude in the midtroposphere tends to have a longer lifetime (~20 days) in a baroclinic atmosphere with stratification than eddy-driven barotropic blocking without vertical variation (less than 15 days). It is shown that barotropic blocking shows a northwest–southeast orientation and has long lifetime, large retrogression, and slow decay only for weaker barotropic BWW and in higher latitudes. In a baroclinic atmosphere with stratification, baroclinic blocking shows long lifetime, strong eastward movement, slow decay, weak strength, and less local persistence for large barotropic BWW and under , but becomes less slow decay, weak retrogression, and large local persistence for small barotropic BWW and . Such a blocking with a north–south antisymmetric dipole, large amplitude, and long local persistence, characterized by a persistent large meander of westerly jet streams, is easily seen when baroclinic BWW and are small in the lower to midtroposphere. Comparatively, the magnitude of plays a larger role in the blocking change than that of , whereas the vertical variation of MTG is more important for the blocking change than the MTG itself for some cases.

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