Atmospheric Jet Stream Research Articles

Rotation of the atmospheres of the Earth and planets

The most striking features of the general circulation of the Earth’s atmosphere are its average ‘super-rotation’ relative to the solid Earth at about 10 m s -1 , and the concentration of much of the motion in jet streams with speeds of about 30 m s -1 . Changes in the pattern of winds, and variations in the distribution of mass within the atmosphere produce fluctuations in the angular momentum associated with this ‘super-rotation’, namely, the axial component H 3 of the total angular momentum of the atmosphere H i ,i = 1,2,3, and also in the equatorial components H 1 and H 2 . Fluctuations in H 3 during the Special Observing Periods of the recent ‘First GARP Global Experiment’ (FGGE, where GARP is the Global Atmospheric Research Programme) later have been investigated. They are well correlated with short-term changes of up to about 10 -3 s in magnitude in the length of the day (allowing for lunar and solar tidal effects on the moment of inertia of the solid Earth), exhibiting pronounced contributions on timescales of about seven weeks and one year and they are consistent with the sum of H 3 and the axial component of the angular momentum of the Earth’s crust and mantle being conserved on short timescales, without requiring significant angular momentum transfer between the Earth’s liquid core and overlying solid mantle on such timescales. Fluctuations in H 1 and H 2 on timescales much less than the Chandlerian period (14 months) but rather more than a few days make a major contribution to the observed wobble of the instantaneous pole of the Earth’s rotation with respect to the Earth’s crust, which has a variable amplitude of several metres. A theoretical basis has now been established for future routine determinations of fluctuations in H i for the purposes of meteorological and geophysical research, including the assessment of the extent to which movements within the solid Earth associated with major earthquakes (magnitude much greater than 7.9) and motions in the liquid metallic core might occasionally contribute to the. excitation of the Chandlerian wobble. Venus’s atmosphere ‘super-rotates’ at an average speed of about ten times that of the underlying planet, which, owing to angular momentum exchange with the atmosphere, should (like the solid Earth) undergo detectable changes in rotation period. Each of the giant planets Jupiter and Saturn exhibits a sharply-bounded equatorial atmospheric jet stream moving at 100 m s -1 (Jupiter) or 400 m s -1 (Saturn) in a positive (i.e. eastward) direction relative to higher latitude parts of the atmosphere, the average rotation of which is close to that of the hydrogen-metallic fluid interior (as determined from radio-astronomical observations). The theoretical interpretation of these observations presents challenging problems in the dynamics of rotating fluids.

Real-Time Jetstream Tracking: National Benefit from an ST Radar Network for Measuring Atmospheric Motions

Attention is directed to a wind measurement system that could be of significant cost benefit to the airline industry and the nation. A network of Stratosphere-Troposphere (ST) radars can provide continuous wind measurements through the troposphere and lower stratosphere with resolutions of 0.5 to 1.0 km in altitude and a fraction of an hour in time. United States air carriers consume in excess of 37 billion liters of fuel per year. Existing estimates by other workers indicate 1–3% savings in fuel costs are possible, given accurate and timely knowledge of the location of the atmospheric jet stream, which would allow for optimal use of this variable tail wind (or avoidance of unnecessary head winds). Current and readily available technology can provide an ST radar network with fine spatial resolution capable of continuous real-time jetstream monitoring across the continental United States. The cost of such a network should be recovered in less than one year, if the potential savings indicated were realized....

Fronts and wave disturbances in Gulf Stream and atmospheric jet stream

Similarities in their basic features, including spatial variations of frontal structure along the current, suggest that Gulf Stream meanders are dynamically analogous to atmospheric jet stream waves, with descending motions upstream and ascending motions downstream from a wave trough. In a symmetrical wave with uniform speed along the current it is shown that confluence, together with the distribution of vertical motions, accounts for the greater baroclinity in the frontal zone at troughs than at crests, a necessary feature of such a wave. Gross features of the three‐dimensional motions are discussed for an eddy in the process of cutting off to form a Gulf Stream ring. Prior to its detachment from the slope water mass, deduced sinking motions exceed, by 2 orders of magnitude, the vertical motions in ring eddies that have become isolated. The large downward volume flux during the formative stage is associated with the asymmetrical structure (more water pouring into a cold tongue on its west side than leaves it on its east side) and with the vertical distribution of volume transport (greater inflow than can be accommodated by horizontal expansion in the upper layers). The inflation time for a Gulf Stream ring is about a month, much shorter than the decay time.

Linear and nonlinear contributions to the growth and decay of the large-scale atmospheric waves and jet stream

Linear and nonlinear contributions to the growth and decay of the large-scale atmospheric waves and jet stream

Linear and nonlinear contributions to the growth and decay of the large-scale atmospheric waves and jet stream

To study the growth and decay of the atmospheric wave motions in middle latitudes, we have analyzed the mechanism for the kinetic energy change in wavenumber domain, and computed the composite average of each term in the kinetic energy equation at various stages in the life cycle of the atmospheric waves. It is found that for the first 1 to 2 days the extra-long waves of wavenumbers 1 and 3 grow by receiving kinetic energy from other finite amplitude waves through nonlinear interactions; in the next 1 to 2 days, they grow by gaining energy through nonlinear interactions and converting available potential to kinetic energy. These waves then maintained their peak energy for 3 to 4 days through the balance between the energy supply from conversion of available potential energy to kinetic energy and nonlinear interactions, and the energy lost by dissipation. The contribution of nonlinear interactions then changes to negative; and in the next 3 to 4 days, the waves decay by losing energy through nonlinear interactions and dissipation. The average life cycle of these extra-long waves is about 10 to 11 days. Similar results have been found with regard to the synoptic-scale waves of wavenumbers 4 to 8. They also intensify by receiving energy and decay by losing energy through nonlinear interactions among finite amplitude waves. Nevertheless, the conversion of the available potential energy to kinetic energy plays a more important role in the growing stage of the synoptic-scale waves than for the extra-long waves. The average life cycle for the synoptic-scale waves is about 6 to 8 days. It is interesting to note that the characteristics of waves of wavenumber 2 are quite different from those of the other waves. In all stages of its life cycle, the contribution of nonlinear interactions is negative and the conversion term always has large positive values. We have also analyzed the intensification and decay of the subtropical jet stream, and found that it is greatly affected by the convergence and divergence of eddy momentum flux. The fluctuations of the net momentum flux are mainly contributed by the synoptic-scale waves of wavenumbers 4 to 8. DOI: 10.1111/j.2153-3490.1978.tb00814.x

Numerical investigation of internal waves in jet streams including nonlinear effects

Internal waves in an atmospheric jet stream are discussed, using both linear and non-linear theory. In the former case., the wave phase-speeds depend only on the total static stability in the jet stream layer. In the latter case, the temperature profile curvature plays the main role in the behaviour of gravity-type waves.

Stability of a two-layer fluid model to nongeostrophic disturbances

Sufficient conditions for stability of a linear inviscid two-layer model to nongeostrophic disturbances are derived. A bound on the growth rate of an unstable disturbance is also found. When the Rossby number R 0 <1, these conditions reduce to the results established by Pedlosky (1964) within the confines of quasi-geostrophic theory. The present analysis provides a theoretical framework for further investigations of fluid systems characterized by strong concentrations of horizontal momentum, such that R 0 ?0(1). Application to atmospheric jet streams and the Gulf Stream, for example, is suggested by observationally established characteristics of these flow regimes. DOI: 10.1111/j.2153-3490.1973.tb01590.x

Atmospheric waves and the ionosphere

A review of evidence supporting the existence of atmospheric waves is presented, and a simple, theoretical approach for describing them is shown. Suggestions for gravity wave sources include equatorial and auroral electrojet, auroral and polar substorm heating, atmospheric jet streams, and large oceanic tides. There are reviewed previous studies dealing with the interaction between ionization and atmospheric waves believed to exist at ionospheric heights. These waves include acoustic waves, evanescent waves, and internal atmospheric gravity waves. It is explained that mode analysis, often employed when an increased number of layers is used for a more complete profile, is inapplicable for waves very close to a source.

Semi-inertial velocity variations along the Gulf Stream axis

It is suggested that velocity variations along the Gulf Stream core may be characterized by a Lagrangian periodicity of a full pendulum day, on the average, as in the atmospheric jet stream. This is consistent with the condition that particle velocities vary at twice the rate of change of the geostrophic velocity.

A Boundary Layer Interpretation of the Low-level Jet

The inertial boundary layer theory developed by Charney and Morgan to explain the intensification of currents near the western boundary of an ocean is applied to the northward flowing atmospheric jet stream observed in the lowest two kilometers over the central United States; here the mountainous spine of Central America serves as a barrier to the westward flowing trade-wind current and deflects it to the north. Because of diurnal frictional changes caused by surface heating and cooling, the jet undergoes a marked diurnal variation with a noctural maximum so strong that the current becomes super-geostrophic. The dynamic consequences of the unbalanced current are examined in the light of theories by Tepper and Veronis. DOI: 10.1111/j.2153-3490.1961.tb00098.x

A Boundary Layer Interpretation of the Low-level Jet

The inertial boundary layer theory developed by Charney and Morgan to explain the intensification of currents near the western boundary of an ocean is applied to the northward flowing atmospheric jet stream observed in the lowest two kilometers over the central United States; here the mountainous spine of Central America serves as a barrier to the westward flowing trade-wind current and deflects it to the north. Because of diurnal frictional changes caused by surface heating and cooling, the jet undergoes a marked diurnal variation with a noctural maximum so strong that the current becomes super-geostrophic. The dynamic consequences of the unbalanced current are examined in the light of theories by Tepper and Veronis.

On the Vertical and Horizontal Concentration of Momentum in Air and Ocean Currents

In this and a following paper an investigation is made into the factors which are responsible for the characteristic “streakiness” of certain atmospheric and oceanic current systems. As a first step a search is made for the factors which might give rise to the striking vertical concentration of momentum observed in many well-defined atmospheric and oceanic jet streams. A straight, parallel, heteorogeneous and incompressible current with a free surface, hydrostatic pressure distribution and a continuous density field is analyzed theoretically to determine the particular distribution of velocity with depth which, for a prescribed volume transport within each isopycnic layer, leads to a minimum value for the transfer of momentum. This requirement leads to a certain “critical” relationship between the velocity and density distribution which in the case of a two-layer system reduces to the well-known critical relative speed at an internal fluid boundary. In the general case of a continuous density distribution it is found that currents which are subjected to momentum losses and hence tend to approach the “critical” velocity distribution in many cases must shrink vertically and develop a sharp velocity maximum at or below the free surface. The nature of the structural changes to be anticipated depends ultimately upon the numerical value of a certain “internal” Froude Number which is a function of the initial velocity distribution as well as of the total density range. DOI: 10.1111/j.2153-3490.1951.tb00772.x

On the Vertical and Horizontal Concentration of Momentum in Air and Ocean Currents: I. Introductory Comments and Basic Principles, with Particular Reference to the Vertical Concentration of Momentum in Ocean Currents

In this and a following paper an investigation is made into the factors which are responsible for the characteristic “streakiness” of certain atmospheric and oceanic current systems. As a first step a search is made for the factors which might give rise to the striking vertical concentration of momentum observed in many well-defined atmospheric and oceanic jet streams. A straight, parallel, heteorogeneous and incompressible current with a free surface, hydrostatic pressure distribution and a continuous density field is analyzed theoretically to determine the particular distribution of velocity with depth which, for a prescribed volume transport within each isopycnic layer, leads to a minimum value for the transfer of momentum. This requirement leads to a certain “critical” relationship between the velocity and density distribution which in the case of a two-layer system reduces to the well-known critical relative speed at an internal fluid boundary. In the general case of a continuous density distribution it is found that currents which are subjected to momentum losses and hence tend to approach the “critical” velocity distribution in many cases must shrink vertically and develop a sharp velocity maximum at or below the free surface. The nature of the structural changes to be anticipated depends ultimately upon the numerical value of a certain “internal” Froude Number which is a function of the initial velocity distribution as well as of the total density range.