摘要:

Surface observations of artificial Earth satellites permit the inference of upper atmosphere densities from changes in the orbital elements caused by drag. The atmospheric density between some 180 km to 400 km altitude appears to be appreciably higher, on the average, than was usually thought before satellite data became available. In order to be consistent with the observed phenomena, the atmospheric temperature at or below these altitudes must also be higher than that given by a number of model atmospheres.

ISSN:0148-0227    

DOI:10.1029/JZ064i001p00001

年代:1959

数据来源: WILEY

摘要:

Critical frequency data, ƒoF2, are analyzed in the polar regions for the period 1954 to summer 1957. The diurnal variation is largest in winter and smallest in summer. In winter little or no diurnal variation occurs north of 75°. The amplitude increases southward up to 11 Mc/s at 60°N with a minimum around 07h and a maximum between 12h to 14h. The daily variation is fairly symmetrical around the maximum. The pronounced daily variation lasts from fall through winter till spring. The annual variation shows a regular behavior, with steep gradients occurring around sunrise and sunset throughout the year. The latitudinal differences are small in summer, of the order of 1 Mc/s or less between 60° and 80°N, but large in winter. The lines of equal ƒoF2 seem to fall between the geographic and geomagnetic latitude circles. The diurnal variation in the Antarctic is different from that in the Arctic during the southern summer (November to February) because a dip occurs around

ISSN:0148-0227    

DOI:10.1029/JZ064i001p00005

年代:1959

数据来源: WILEY

摘要:

The angular distribution of enduring meteor bursts in forward scattering is studied and compared with the angular distributions observed for the short duration meteor bursts and the turbulent background component. It is concluded that the enduring, fading bursts are due to meteor trails which reflect in a specular manner throughout the time during which they can be observed.

ISSN:0148-0227    

DOI:10.1029/JZ064i001p00019

年代:1959

数据来源: WILEY

摘要:

A study is made of the run of areas of solar prominences around days of recurrent geomagnetic storms during the period 1917–1944. ”Character figures for darkH‐alpha flocculi,” taken from IAU Quarterly Bulletins of Solar Activity, are used as the measure of prominence areas. The earlier suggestions that the solarM‐regions may be identified as quiescent prominences have not been

ISSN:0148-0227    

DOI:10.1029/JZ064i001p00023

年代:1959

数据来源: WILEY

摘要:

If the signal pattern in the vicinity of three spaced receivers is assumed to be represented by a linear variation in distance and time for a short time interval τ, the apparent motion of the pattern must be normal to the lines of constant signal intensity. The instantaneous velocity of the ground pattern may be represented as the sum of the component of the average drift velocity in the direction of the gradient and a random velocity in the direction of the gradient. After the drift velocity has been determined by correlation analysis, the random velocity for each time interval may be obtained, and a spectral analysis of the random speed may be performed. This information may be used as an aid in describing the detailed motion of the signal pattern which is necessary in relating the observations to ionospheric motions

ISSN:0148-0227    

DOI:10.1029/JZ064i001p00027

年代:1959

数据来源: WILEY

摘要:

Daily sea‐water temperature measurements made at tide stations by the U. S. Coast and Geodetic Survey reveal anomalously low water temperatures during most summers at stations along the northern half of the east coast of Florida. The periods of colder water are accompanied by a lowering of sea level and by winds from directions most conducive to producing upwelling. Examination of daily variations in these factors at Daytona Beach during a year when the summer drop in mean water temperature exceeded 10°F shows the dependence of upwelling on the prevailing winds and suggests that the upwelling mechanism has no momentum but ceases at the coast as soon as the driving force is terminat

ISSN:0148-0227    

DOI:10.1029/JZ064i001p00033

年代:1959

数据来源: WILEY

摘要:

The mechanics of transportation of sand under the influence of wave action was studied using artificially induced radioactivity. A sample of naturally occurring quartz sand is taken from the area of study, subjected to slow neutron irradiation, and then reintroduced into the area. The movement of the quartz is traced by sampling the sediment on the bottom and assaying for phosphorus‐32, which is the principal radio isotope formed from the slow neutron irradiation of natural quartz sands.In a field experiment, 860 g of irradiated quartz sand was reintroduced as a point source on the sea floor off Scripps Beach. The experiment showed that the dispersal of sand by wave action was more rapid than expected, and that the movement of this small amount of sand could be followed for about 7 to 24 hr. The irradiated sand was released on the bottom by divers and samples were obtained on a grid at the time intervals of ¼, 1, 3½, 7½, and 24 hr, and several days later. At the point of introduction the water was 10 ft deep and the surface waves were about 1¼ ft high. The waves caused the sand to spread in an elliptical pattern with an elongate onshore‐offshore axis. The sampling indicated that the 860 g of irradiated fine sand had been dispersed over an area of approximately three‐quarters of a square mile in 24 hr. The sensitivity of detection for this experiment was approximately 1 grain of sand i

ISSN:0148-0227    

DOI:10.1029/JZ064i001p00041

年代:1959

数据来源: WILEY

摘要:

Expressions are derived for the vertical and horizontal components of the gravitational attraction due to a two‐dimensional body of arbitrary shape by approximating it to ann‐sided polygon. These expressions are put in forms suitable for solution by a high‐speed digital computer. As an example of the application of this method, the crustal section across the Mendocino fracture zone is deduced from the gravity anomalies. Assuming the crust to consist of a single homogeneous layer, overlain by water and sediment, it is found to be about three km thicker to the north of the fracture zone than to the south

ISSN:0148-0227    

DOI:10.1029/JZ064i001p00049

年代:1959

数据来源: WILEY

摘要:

The combined application of astronomic, geodetic, and gravimetric data to computations of the geoid is discussed. The general principle observed is that any adjustment should weight all observations inversely as their variances. Two conditions are imposed: (1) Geoid heights and deflections computed by Stokes' theorem from gravity data must equal those derived by astrogeodetic means. (2) The five harmonicsP1,P11sin λ,P11cos λ,P21sin λ, andP21cos λ must be absent from the adjusted gravity field. The ideal case is discussed, including provision for separate determinations of parameters by independent astronomic methods. Practical modifications are then introduced in turn: treating gravity anomalies as representative of areas; holding geodetic or astronomic observations constant; using a reduced number of astronomic stations; and comparing interpolated points of the astro‐geodetic and gravimetic geoids. The most significant discrepancy from the ideal case of most practical solutions made heretofore appears to be in the weighting of the gravimetric

ISSN:0148-0227    

DOI:10.1029/JZ064i001p00061

年代:1959

数据来源: WILEY

摘要:

From all astro‐geodetic material available at present, geoidal heights were computed on the 1927 North American Datum for the western hemisphere from Canada to Chile, and on the European Datum for the eastern hemisphere from Great Britain to Japan and from Scandinavia to South Africa. Improved reference ellipsoids were determined under various conditions for each hemisphere by the least squares method. Triaxiality is refuted. The Columbus Geoid, gravimetrically derived by W. A. Heiskanen, was used to connect the astro‐geodetic systems of the two hemispheres. By minimizing the differences between the astro‐geodetic and gravimetric geoid elevations at 75 points in the western hemisphere and 127 points in the eastern hemisphere, a theoretically absolute orientation based on the Hough ellipsoid was determined, leading to a tentative World

ISSN:0148-0227    

DOI:10.1029/JZ064i001p00073

年代:1959

数据来源: WILEY