Point-by-point comparisons of ISEE-1 spherical double probe dawn-to-dusk electric field measurements and ISEE-2 plasma flows, converted to electric fields, are presented during a three hour time interval in the magnetotail when the plasma density varied from less than 0.1 to about 1 cm−3. The zero lag cross-correlation coefficient between 768 second averages of the two data sets was 0.93. The cross-correlation coefficient decreased with shorter averaging intervals due to the increasing magnitude of statistical uncertainties, becoming 0.49 for 9 second averages. A statistical relative uncertainty between pairs of points in the two data sets, estimated by inclusion only of counting statistics in the plasma measurement and time variations of the observed electric field during the measurement interval, is able to account for at least 75% of the deviations between the two data sets. During this three hour interval, the spacecraft potential (measured by the double probe instrument) varied as the logarithm of the product of the plasma density and square root of electron temperature (measured by the fast plasma analyzer), in agreement with expectations from simple Langmuir probe theory.
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