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 response to the influence of the solar wind. An empirical model of the near‐Earth magnetotail has been developed, which depends upon distance downtail (x GSM ), the solar wind momentum flux (ρv 2 sw ), and the z GSM component of the interplanetary magnetic field (IMF B z ). This model has been created by using the pressure balance relation to calculate a set of flare angles for the nightside magnetopause in the region −22 R E ≤ x GSM ≤ −10 R E . Observations of the magnetic field in the lobe by ISEE 2 and simultaneous 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 angle values reveal a dependence upon downtail distance and ρv 2 sw . 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 variation when the IMF is northward. The empirical function derived for the flaring angle of the magnetotail is used to determine a relation for the radius of the tail. Comparisons with previous empirical models and results are also performed. In addition, values of magnetic flux within the magnetotail are calculated for times of sudden impulse events.