NEAR-EARTH MAGNETOTAIL SHAPE AND SIZE AS DETERMINED FROM THE MAGNETOPAUSE FLARING ANGLE

Knowledge of the average size and shape of the near-Earth magnetotail is an essential element for our understanding of the magnetospheric re sponse to the influence of the solar wind. An empirical model of the n ear-Earth magnetotail has been developed, which depends upon distance downtail (X(GSM)), the solar wind momentum flux (rho v(sw)(2)), and th e z(GSM) component of the interplanetary magnetic field (IMF B-z). Thi s model has been created by using the pressure balance relation to cal culate a set of flare angles for the nightside magnetopause in the reg ion -22 R(E) less than or equal to X(GSM) less than or equal to-10 R(E ). Observations of the magnetic field in the lobe by ISEE 2 and simult aneous observations of the magnetic field and plasma properties of the solar wind by IMP 8 were used to determine the internal and external pressure components, respectively. Examination of calculated flare ang le values reveal a dependence upon downtail distance and rho v(sw)(2). Normalized to the median downtail distance and dynamic pressure, the angle of flare of the magnetopause is found to increase linearly with decreasing B-z when the IMF is southward, but there is little variatio n when the IMF is northward. The empirical function derived for the fl aring angle of the magnetotail is used to determine a relation for the radius of the tail. Comparisons with previous empirical models and re sults are also performed. In addition, values of magnetic flux within the magnetotail are calculated for times of sudden impulse events.