Jet Stream‐surface tracer relationships: Mechanism and sensitivity to source region

Air may seem hot and humid, hot and dry, damp and cold, or freezing cold. Vigorous weather systems may create abrupt changes when one air mass replaces another with distinct properties. ‘Global weather systems’ explains that air masses can be classified into categories based on the humidity and temperature of their source region: arctic or antarctic continental, polar continental, tropical continental, arctic maritime, polar maritime, tropical maritime, and equatorial maritime. The boundary between two air masses with differing temperatures and humidities is known as a front and there are three forms: cold, warm, and occluded. Jet streams, including Polar jets, Subtropical jets, and the Equatorial Jet Stream, are also discussed.

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On the Dynamics of the General Atmospheric Circulation

Australian Journal of Chemistry ◽

10.1071/ch9500001 ◽

1950 ◽

Vol 3 (1) ◽

pp. 1

Author(s):

CHB Priestley

Keyword(s):

Angular Momentum ◽

Source Region ◽

Surface Wind ◽

Vertical Wind Shear ◽

Geostrophic Wind ◽

Jet Stream ◽

Total Strength ◽

Near Surface ◽

Anticyclonic Eddies ◽

The Tropics

The annual flow of angular momentum across latitudes 30-35� effected by north and south currents lying side by side (cyclonic and anticyclonic " eddies ") appears insufficient to balance the angular momentum generated at the surface in lower latitudes. The discrepancy suggests that there must be also a mean poleward drift of air at upper tropospheric and lower stratospheric levels across the latitudes of the mean surface high pressure belt, with a counterdrift which occurs at least in part in near-surface levels. A variety of auxiliary evidence supports the existence of these flows, which are indicated as intermittent or fluctuating components with mean speed over a long period of the order of a few miles per hour and so, at upper levels, only on the margin of direct observation. The origin of the poleward component is associated with the strong anticyclonic shear to equatorward of the jet stream axis. Since these drifts are found in latitudes where the vertical wind shear is greatest, - they constitute an important agency in the transport of angular momentum from its source region in the tropics to the sink region of higher latitudes. This significant contribution is masked in studies of interchange which invoke the assumption of geostrophic wind. The " index " representing the total strength of the tropical easterly surface winds, which fluctuates considerably, relates closely to the rate of generation of angular momentum in the tropics. On the basis of the drifts referred to above, a descriptive theory of the index cycle is developed, which links the fluctuations of index with the fluctuations in strength and in latitude of the jet stream. Quantitative checks are applied to this theory wherever possible and no discrepancy appears, while the normal sequence of synoptic events agrees broadly with that ascribed to the mutual interactions of surface wind strength, jet-stream, and drift.

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Observations, Simulations, and Dynamics of Jet Stream Variability and Annular Modes

Journal of Climate ◽

10.1175/2010jcli3235.1 ◽

2010 ◽

Vol 23 (23) ◽

pp. 6186-6199 ◽

Cited By ~ 34

Author(s):

Joseph Kidston ◽

D. M. W. Frierson ◽

J. A. Renwick ◽

G. K. Vallis

Keyword(s):

Wind Speed ◽

Zonal Wind ◽

Source Region ◽

Baroclinic Instability ◽

Jet Stream ◽

Mean Flow ◽

Annular Mode ◽

Annular Modes ◽

Real Atmosphere ◽

The Mean

Abstract The characteristics of the dominant pattern of extratropical variability (the so-called annular modes) are examined in the context of the theory that eddy-driven jets are self-maintaining. It is shown that there is genuine hemispheric symmetry in the variation of the zonal wind in the Southern Hemisphere but not the Northern Hemisphere. The annular mode is shown to be baroclinic in nature; it is associated with changes in the baroclinic eddy source latitude, and the latitude of the eddy source region is organized by the mean flow. This behavior is expected if there is a baroclinic feedback that encourages the maximum baroclinic instability to be coincident with the maximum zonal wind speed, and discourages the meridional vacillation of the eddy-driven jet stream. It is shown that the strength of the thermally indirect circulation that gives rise to the baroclinic feedback appears to influence the time scale of the annular mode. When the thermally indirect circulation is stronger the annular mode has a longer e-folding time in a simplified GCM. Preliminary results indicate that the same dynamics are important in the real atmosphere.

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