摘要:

A transmission line model which incorporates general discharge velocities is presented, and formulas for the current and charge densities are derived. The resultant formulas for the electromagnetic fields are given in a form applicable to intercloud and intracloud discharges. A spectral study of a vertical discharge results in a velocity equation. This equation relates the velocity of ionization of the discharge to the current at the base of the discharge and the radiation field of the sferic. Analysis of a dimensionless parameter for a Bruce‐Golde type discharge and an example suggest that vertical discharges may become horizontal after entering the clou

ISSN:0148-0227    

DOI:10.1029/JC082i003p00391

年代:1977

数据来源: WILEY

摘要:

A strong enough longshore impulse leaving the coast to the left (looking downwind) generates ‘Full’ upwelling in which the thermocline comes to intersect the free surface. This problem is beyond the scope of linearized (small displacement) theory, but it may be treated as a simple geostrophic adjustment problem in which the wind stress is supposed to be exerted impulsively on a two‐layer fluid. A minimum impulse is found to be necessary for a full upwelling to develop from hydrostatic equilibrium, the magnitude of which is close to the product of top layer depth and propagation velocity of long waves on the thermocline. When the upwelling‐favoring wind impulse is greater than the minimum, the upwelled front moves offshore by a distance proportional directly to the extra impulse (above the minimum) and inversely to top layer depth times Coriolis parameter. Upwelling episodes observed in Lake Ontario during the International Field Year for the Great Lakes (IFYGL) and feasibility studies before IFYGL show a frontal behavior in good quantitative agreement with the simple theoretical model. The offshore component of the impulsively exerted wind leaves the position of the front unaffected. However, a sustained offshore wind increases somewhat the offshore displacement due to a prior longshore impulse. The effect is relatively weak, and an offshore wind alone rarely produces full upwelling. A sustained longshore wind acting on an already upwelled thermocline generates considerable negative potential vorticity. Adjustment following such a ‘second’ longshore impulse produces a more complex thermocline shape and under certain conditions a frontal countercurrent. In a closed basin, full upwelling following a wind stress impulse occurs over only a portion of the shoreline. Given quiescent conditions, the upwelled front may be expected to propagate alongshore, somewhat as an internal Kelvin wave. Observations in October 1972 in Lake Ontario show frontal motions resembling internal Kelvin waves. However, only one half of the wave propagates, that half in which particle velocities have the same direction as the wave propagation velocity. Furthermore, the propagating warm zone is much narrower than the cold upwelled zone which developed under a succession of previous wi

ISSN:0148-0227    

DOI:10.1029/JC082i003p00397

年代:1977

数据来源: WILEY

摘要:

The nonlinear problem of steady flow of an incompressible stratified fluid of finite depth over an obstacle is investigated by using a numerical algorithm which solves both obstacle height and flow fields simultaneously instead of solving the flow fields, given the obstacle height. We also find, for a given upstream condition, a maximum obstacle height over which steady flows are possible, not allowing discontinuities or closed streamlines. This maximum height is a functional of the upstream density stratification and the velocity shear. We calculate this functional dependence for a number of specific upstream conditions. It is also shown that the number of layers required in the model to represent a flow field increases as the Froude number decreases or as the vertical wave number increases. The hydrostatic and finite depth assumptions are essential in our method.

ISSN:0148-0227    

DOI:10.1029/JC082i003p00420

年代:1977

数据来源: WILEY

摘要:

Characteristics of southern hemisphere (SH) 200‐mbar flow are examined by using geopotential height fields constructed with the aid of a satellite‐based thermal structure. Similar northern hemisphere (NH) satellite‐based fields are developed in order to make interhemispheric comparisons. Results indicate that both zonal and meridional components of the SH eddy kinetic energy are as large as their NH counter‐parts. The SH flow is in general more dependent on transient eddies, especially with regard to the meridional flow. In winter the difference in standing eddy magnitude is apparent only in the north‐south component. In summer both zonal and meridional components have smaller standing eddy contributions in the SH. The meridional spectra show a preference for intermediate size (k= 4, 5) transient waves. Ratios of zonal to meridional energies indicate that, especially at intermediate wavelengths, the SH waves are ‘more meridional’ than th

ISSN:0148-0227    

DOI:10.1029/JC082i003p00427

年代:1977

数据来源: WILEY

摘要:

Results from the joint National Center for Atmospheric Research/Department of Transportation wintertime 1973 airborne lidar experiment are presented. At the time of the experiment, which was between major volcanic events affecting the stratosphere, the aerosol loading was at or near a 10‐year low. These data therefore represent good ‘baseline’ measurements for future compa

ISSN:0148-0227    

DOI:10.1029/JC082i003p00433

年代:1977

数据来源: WILEY

摘要:

An improved instrument for measuring maximum electric field intensity over a surface is described. Data obtained with the instrument during the summer of 1975, primarily in New York State, indicate that field intensities of as high as 130 kV m−1occur over lakes during thunderstorms. Possible implications of these data are discusse

ISSN:0148-0227    

DOI:10.1029/JC082i003p00438

年代:1977

数据来源: WILEY

摘要:

Observations of the motion field associated with the plume formed by the outflow of the Connecticut River into the coastal seawater of Long Island Sound are presented. Approximately 35 drogues and drifters were tracked for each of three experiments using an airborne camera. The trajectories and the Eulerian velocity field deduced from them are presented. The offshore boundary of the plume was formed by a front where there was a strong discontinuity at the surface in both the velocity and density fields. In addition to a vigorous outflow of plume surface water away from the river mouth and parallel to the plume axis, the observations showed a pronounced surface flow toward the front and normal to the axis which was consistent with frontal convergence. The speed of plume water was found to be highly supercritical. The motion of nearby ambient seawater appeared to be little affected by the plume.

ISSN:0148-0227    

DOI:10.1029/JC082i003p00441

年代:1977

数据来源: WILEY