Interplanetary sector structure: 1970--1972

IMP-3 i n t h e l a t t e r half of 1965 are discussed with r e l a t i o n t o previQus s a t e l l i t e observations of t h e interplanetary f i e l d . The seetor property remains a prominent feature of the observations, with t h e average f i e l d d i r e c t i o n a t t h e Archimedes spiral angle. The sector p a t t e r n has a 27-day recurrence period from 1962 t o 1964, and during the year 1964 the p a t t e r n appears t o be quasi-stable. I n 1965 the recurrence period is about 28 days, and the evolution of t h e p a t t e r n is more rapid, with new sectors appearing and expanding.