摘要:

The results from a simple beam‐swinging experiment are presented. Both the transmitting and receiving antennas are swung in azimuth as well as in elevation in such a way that the scattering angle remains constant. The permittivity field appears to be nonisotropic in most cases, whereas the fluctuating air velocity field generally is nearly Isotropi

ISSN:0148-0227    

DOI:10.1029/JZ069i004p00569

年代:1964

数据来源: WILEY

摘要:

A determination of the diameter of the lightning stroke is made by allowing lightning discharges to pass through fiberglas screen. Twelve holes were produced (melted) in fiberglas screen by lightning discharges: six holes with diameters between 2 cm and 3.5 cm, six holes with diameters between 2 mm and 5 mm.

ISSN:0148-0227    

DOI:10.1029/JZ069i004p00583

年代:1964

数据来源: WILEY

摘要:

In the preceding article,Uman[1964] describes an ingenious method of observing the diameter of the lightning flash to a grounded metal conductor mounted on an elevated structure. His method gives significant results, but he is disturbed because there are discrepancies between his observations and those ofHill[1963] on damage to metal conductors and those of his colleaguesEvans and Walker[1963], who used photography. These results are not necessarily contradictory, as they represent observations of different aspects of a most complex phenomenon.The lightning flash, which may consist of a sequence of several strokes to a well‐grounded metal conductor which projects some distance above the ground, consists of the following chain of events. Initially a stepped leader [Schonland, 1956] stroke originating from an internal predischarge within the cloud [Loeb, 1953, 1958;Clarence and Malan, 1957] forges earthward at some 107cm/sec. It may have a rather large diameter but its more conducting core is not too extensive in area of cross section. As the leader approaches the earthed conductor its high negative tip potential creates such a high field at the metal conductor that a positive streamer process moves upward toward the stepped leader from one to several meters. Under special conditions this streamer process may extend to kilometers [McEachron, 1939;Berger, 1961, 1962]. In doing so the positive streamer process may have several highly conducting branches [Nasser, 1959a, b, 1962;Nasser and Loeb, 1963;Kritzinger, 1962]. The intense field distortion at the junction of positive streamer branches and negative streamers then sends ionizing space waves of potential [Loeb, 1957 ;Westberg, 1959;Loeb and Cravath, 1935], called return strokes [Schonland, 1956], up the axis of the stepped leader channel and down the positive streamer channel at speeds of 5 × 108to 1010cm/sec. These render the channels conducting. Usually the main discharge will favor the most conducting of the branched streamer channels, but one or two others could be involved as we

ISSN:0148-0227    

DOI:10.1029/JZ069i004p00587

年代:1964

数据来源: WILEY

摘要:

A preliminary analysis of the response characteristics of spherical balloon wind sensors is presented. It is shown that smooth superpressure spheres do not provide accurate detailed wind profiles and that the response characteristics can be improved by the addition of roughness elements. Experimental data show that surface roughness elements on a spherical balloon stabilize the drag force vector and reduce the lift force. Spurious aerodynamically induced motions are significantly reduced, and the balloon more accurately senses the true wind.

ISSN:0148-0227    

DOI:10.1029/JZ069i004p00591

年代:1964

数据来源: WILEY

摘要:

A one‐year study was made of the salt concentrations of rainfall and the static water table across the lower Rio Grande Valley of Texas. A linear decrease in salt concentration was observed with logarithmic distance inland. The concentrations of individual ions determined, except calcium, follow the logarithmic relationship. The salt content of the shallow, saline groundwater also decreases with distance inland. The decline in groundwater salt concentration with distance inland was more rapid than the decline in annual salt deposition by rainfal

ISSN:0148-0227    

DOI:10.1029/JZ069i004p00599

年代:1964

数据来源: WILEY

摘要:

A study was made to determine whether low‐flow frequency distributions in Illinois could be reliably estimated from meteorological data and geologic factors. The development of such a method is desirable because of the general lack of long‐term streamflow records. In this study, use was made of 50‐year records of precipitation from 62 locations and data from 12 stream‐gage stations with 45‐year or longer records. When the state was divided into six different geomorphic regions it was found that the low‐flow frequencies for any basin in each region could be reliably estimated by the precipitation frequency distribution and a geomorphic index. The regional geomorphic indices were developed through use of data from the 12 basins with long streamflow records. The method developed is applicable for basins of any size, for recurrence intervals of five years or longer, and for drought durations of 12 months or longer. Although based upon Illinois data, the method should be applicable to other regions in the United States and other parts o

ISSN:0148-0227    

DOI:10.1029/JZ069i004p00605

年代:1964

数据来源: WILEY

摘要:

The quantity of summer soil moisture lost from logged forest openings was related to the length of time since the creation of the opening, in the subalpine forest zone of the Sierra Nevada west side, near the Central Sierra Snow Laboratory, California, at an elevation of 6000 to 7000 feet. Soil moisture depletion was measured in forest openings which were created in 1959, 1955, 1950, and 1948, and in the forest surrounding these openings. Soil moisture was found to be uniformly near field capacity in all plots in early June. Later soil moisture was lost most rapidly from the forested parts of the plots and at progressively slower rates toward the center of the openings. The rate of moisture loss was greatest in early summer and then decreased as the availability of moisture decreased. Maximum soil moisture depletion occurred in early September, nearly all the available moisture being depleted from the forest. The quantity of residual soil moisture increased toward the center of the openings. At the period of maximum soil moisture depletion, openings 1 year old were found to have 6.9 inches more soil moisture per 4 feet of soil than the surrounding forest had, which is an expression of the quantity of moisture saved as a result of the logging operation. In openings 5 years old, the saving has decreased to 2.9 inches, after 10 years to 1.2 inches, and after 12 years to 0.7 inch. A projection of the regression indicates that the moisture saving at maximum depletion will become negligible 16 years after cutting.

ISSN:0148-0227    

DOI:10.1029/JZ069i004p00615

年代:1964

数据来源: WILEY

摘要:

The Lewis‐Milne equation,describes the advance of water down a border check when constant flowqper unit width is introduced at its head,cis the mean water depth,xis the distance of advance at timet, and the cumulative infiltration function isy(t). The paper deals primarily with the solution of (0) and the interdependence ofx(t)andy(t). The results are of relevance to other methods of surface irrigation. (0) is valid only ifxis a monotonic increasing function oft. Sufficient conditions arey≥ 0,dy/dt≥ 0,d2y/dt2≤ 0. Normally, the physical restrictions onyare such that these conditions are realized and (0) is valid. The general solution of (0), ‘the infiltration‐advance problem’ is found by means of the Faltung theorem of the Laplace transformation. The solutions of (0) for the various common forms ofyfollow readily. The ‘Horton’ solutions had been found previously by other methods. The new particular solutions are for the Kostiakov‐Lewis equation and for the equationy=St1/2+At, which was developed from a detailed physical study of infiltration. The solutions for this form ofyare treated at some length. The power series and asymptotic expansion forms give insight into behavior at small and large times. The relative importance of the parameters is shown to bec, S, andAat small times andA, S, andcat large times. Appropriate dimensionless forms simplify the graphical presentation of the solutions. The forms ofxfor variousy(t)in the limitc→ 0 are presented. The inverse problem of deducingyfrom observedxandcis considered. The formal solution is given, and a simple method is developed in which known solutions of the infiltration‐advance problem are used. With additional assumptions it applies also to the case where n

ISSN:0148-0227    

DOI:10.1029/JZ069i004p00621

年代:1964

数据来源: WILEY

摘要:

This report presents the results of a program of numerical analysis of nonlinear partial differential equations which describe nonsteady soil moisture transfer. The results, when combined with experimental data, are intended for use in determining the soil moisture transfer characteristics of various types of soil. The results of this study indicate that linear theory is significantly inaccurate in representing unsaturated transient flow of water in soils for finite perturbations. On the other hand, for step‐function transient outflow experiments performed for determination of soil moisture transfer characteristics, the numerical solutions presented here allow all data obtained from the experiments to be used in characterizing the soil water diffusivity over the full range of the step. If there is a significant membrane impedance, the determination of the soil water diffusivity becomes much more complex. Because of the limited number of solutions presented, practical determinations of the diffusivity require that the membrane impedance effects be minimized. This can be done by increasing the soil slab thickness, by decreasing the pressure step size, and by working at high matric suctions. It is concluded that the effects of gravity on laboratory transient outflow experiments are negligibl

ISSN:0148-0227    

DOI:10.1029/JZ069i004p00633

年代:1964

数据来源: WILEY

摘要:

In this experimental study evidence was obtained on the relationship between the velocity of sound and the moisture content of the soil. The velocity of sound in unsaturated soils at shallow depths was shown to be proportional to the 1/6 power of the effective pressure. Thus the effective stress concept, used in conjunction with the Hertz theory, was proved valid.

ISSN:0148-0227    

DOI:10.1029/JZ069i004p00643

年代:1964

数据来源: WILEY