INFLUENCES OF SOLAR-WIND PARAMETERS AND GEOMAGNETIC-ACTIVITY ON THE TAIL LOBE MAGNETIC-FIELD - A STATISTICAL STUDY

The size and magnetic field strength of the tail lobe at the downstream distance of 10 to 22.6 R(E) are examined statistically by utilizing data from the magnetometer on board the ISEE 1 satellite. The probability that the satellite encounters the lobe region is mapped on the tail cross section, the Y-Z plane. It is found that the magnetotail lobe expands in association with increasing auroral electrojet activity. This expansion is particularly evident at the dawn and dusk flanks of the magnetotail, while the lobe region seems not to expand appreciably near the aberrated X axis. The lobe field strength, B(L), is found to be represented as B(L) (nT) = 1.03 x 10(3) R-1.20, where R denotes the geocentric distance in Earth radii. Multiple regression analyses reveal that the lobe field strength principally depends on the dynamic pressure (P(D)) and static pressure (P(S)) of the solar wind as well as on the IMF B(z). It is also shown that the flaring angle of the tail lobe, theta, is represented as sin2-theta = 1.97 x 10(-5) P(D)-0.47 \AL\0.11, where AL denotes the auroral electrojet AL index.