New features in the occurrence of Ps6 geomagnetic pulsations associated with the interplanetary space and the magnetopause

New features of Ps6 geomagnetic pulsations characterizing their durations, local time of occurence, ratio to western and eastern electrojets, WTS and FTS events and interplanetary space. It is shown that minimum of Alfven velocity square in the interplanetary space along the Sun-Earth line VAX2 and Bz<0 are, as a rule, accompanied by origination of substorms with Ps6. Taking into account that min VAX2 under other equal conditions corresponds to increment maximum of Kelvin-Helmholz instability on geomagnetopause, the hypothesis related to this instability as a source of Ps6 is proved