In the adjoining letter, Dessler [1961] argues that the interface between the solar wind and the geomagnetic field is stable and cannot, therefore, generate hydromagnetic waves. According to our interpretation, his argument may be paraphrased as follows: He observes that, for many sudden commencement geomagnetic storms, surface magnetograms show no marked change in the level of disturbances from the period before the sudden commencement until well into the initial phase of the storm. He applies the attenuation factors calculated by Francis and Karplus [1960] to the measurements of the 1 cps component of the magnetic disturbances obtained at the surface. From this calculation, he concludes that, during the initial phase of these geomagnetic storms, the amplitudes of hydromagnetic disturbances above the ionosphere are less than 1. Assuming that the sudden commencement indicates the presence of a solar wind, he further concludes that hydromagnetie disturbances are not generated in the region between the geomagnetic field and the solar wind and that this interface is, therefore, inherently stable. He subsequently accounts for the hydromagnetie disturbances which are frequently observed at the earth as having been produced by fluctuations in the energy density of the impinging solar wind.

Coleman, P. J., Jr.↗

NASA NTRS1960

STL MAGNETOMETER EXPERIMENT - PIONEER V

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Sonett, C. P.↗

NASA NTRS1959

Evidence Concerning Instabilities of the Distant Geomagnetic Field: Pioneer I

The search-coil magnetometer carried on Pioneer I has yielded evidence of complex geomagnetic behavior at great distances from the earth. This paper is intended to report only some preliminary observations; in particular, what appears to be directional instability in the field. A comprehensive statistical analysis, to be reported later, is still in progress.

Sonett, C. P.↗