On the average configuraton of the geomagnetic tail

Over 3000 hours of Imp 6 magnetic field data obtained between 20 and 33 R E in the geomagnetic tail have been used in a statistical study of the tail configuration. A distribution of 2.5‐min averages of B z as a function of position across the tail reveals that more flux crosses the equatorial plane near the dawn and dusk flanks than near midnight . The tail field projected in the solar magnetospheric equatorial plane deviates from the x axis due to flaring and solar wind aberration by an angle α = −0.9 Y SM −2.7, where Y SM is in earth radii and α is in degrees. After removing these effects, the B y component of the tail field is found to depend on interplanetary sector structure. During an ‘away’ sector the B y component of the tail field is on average 0.5γ greater than that during a ‘toward’ sector, a result that is true in both tail lobes and is independent of location across the tail. This effect means the average field reversal between northern and southern lobes of the tail is more often 178° rather than the 180° that is generally supposed.