Secular Decrease in Ionospheric Potential
In analyzing the 120 ionospheric potential estimates obtained in my program the numbers seemed quite small compared to other estimates given in the literature. I was particularly aware of the work at NRL (Naval Research Laboratory, Washington, D.C.) by Clark (1958) since his potential gradient soundings were obtained in the same region as mine, off the eastern seaboard of the United States. My data indicated about 240 kV, and Clark estimated about 300 kV, which he corrected using the Carnegie curve to 280 kV (see Fig. 1). The vertical arrow pointing down shows these corrections for the unitary diurnal variation. Clark’s data were obtained in 1956. The bracket in the upper left corner of the figure represents the estimates of Chalmers (1954) based on the data published up to that time.
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