Records of magnetic field as a function of altitude have been obtained from total‐field magnetometers mounted in two Aerobee sounding rockets which were fired from the seaplane tender USS Norton Sound in March 1949. The flights were made 60 miles apart at approximately 89° west longitude, 11° south latitude, or geomagnetic longitude 341°, geomagnetic latitude −1°. The first rocket, Aerobee Round A‐10, was fired on March 17 at 17h 20m 90th meridian time; Round A‐11 was fired on March 22 at 11h 20m 90th meridian time. In Aerobee A‐10 the field decreased between 20 and 105 km in accordance with the simple dipole field, while in Aerobee A‐11 a discontinuity of 4±0.5 milligauss was observed in the altitude range of 93 to 105 km. These results (1) establish experimentally the existence of a current system in the E‐region of the ionosphere which is responsible for the diurnal variation of the earth's magnetic field at sea level; and (2) lend strong support to the dynamo theory of the daily magnetic variation which was originally proposed by Balfour Stewart and Schuster.
Oscillations are defined as comprising only the more regular of the short‐period geomagnetic fluctuations (periods from 1 to 200 seconds) and may be recognized as representing electromagnetic energy in narrow frequency bandwidths and identified by objective criteria. The characteristics of these oscillations, as indicated by the available observational data, are examined with a view toward the eventual identification of their resonant sources. Three distinct frequency ‘bands’ are observed. Two of them, a 20‐sec band (that is, oscillations having similar characteristics and having periods centered at about 20 sec) and a 70‐sec band, are predominantly daytime phenomena, whereas the third, an 8‐sec band, occurs at night. The 8‐sec oscillations show a strong positive correlation, both in amplitude and duration, with the K index; this correlation is less pronounced for the 20‐sec band and is absent (or perhaps negative) for the 70‐sec band. An additional nighttime band containing periods longer than about 95 sec is not yet definitely established.
A correlation between geomagnetic fluctuations and meteoric activity was reported by Kalashnikov [1949], who used sensitive fluxmeters and a photographic recording technique. In his work, he noted an increase in the number of pulses in the vertical component over the dates of meteor showers. Hawkins [1958], using more sensitive equipment also sensitive to the vertical component, attempted to correlate pulses with visual meteors. His results were negative, indicating only such correlation as might be expected statistically.
Audio‐frequency geomagnetic fluctuation spectra are reported for three North American stations covering a latitude range of 41°. Recording stations were located at Panama City, Florida; White Oak, Maryland; and Point Barrow, Alaska. Fluctuation intensities throughout the frequency range 70 to 16,000 cps were observed to decrease with increasing latitude. Between 100 and 1000 cps, fluctuation amplitudes were inversely proportional to about the 3/2 power of frequency, the spectral slopes becoming somewhat steeper with increasing latitude. Between 1500 and 8000 cps, amplitudes decreased more rapidly with latitude than did those at other frequencies, and a spectral minimum was evident in this frequency range at Point Barrow. The vertical fluctuation component was smaller and decreased more rapidly with latitude than did the horizontal components. It is concluded that thunderstorm activity is the major source of the fluctuations throughout the audio‐frequency range, with the magnetic atmospherics being generated chiefly in the lower latitudes and propagated poleward. The relationship of the observed fluctuations to thunderstorm distributions is discussed. There is considerable agreement with the results of others, although a few discrepancies are apparent.
An Aerobee rocket containing a total‐field magnetometer was fired, and telemetered data gave a record of the earth's magnetic field during the flight. The recorded decrease in field was 28 milligauss (mG) at 368,000 feet, which agreed with dipole calculations to within 2 mG. This was the first step in an attempt to obtain direct experimental evidence of postulated current‐sheets in the upper atmosphere. The flight was intended chiefly as a test of the method and instrumentation, and was made at White Sands because of existing facilities there. The location was unfavorable to the ultimate purpose of the experiment, and no evidence of magnetic fields caused by current‐sheets was obtained. The results show, however, that the method is adequate for detection of the predicted effects at more favorable geomagnetic latitudes.
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