Role of latitude of source region in Solar Energetic Particle events

Abstract

Solar Energetic Particle (SEP) measurements from the Ulysses spacecraft have shown that the latitudinal separation between the parent solar flare and the nominal footpoint of the detecting spacecraft is an important parameter in ordering characteristics of the observed time-intensity profiles during SEP events. In this study, we consider data from the GOES and Wind spacecraft over one solar cycle, to address the question of whether the same trend can be observed from in-ecliptic SEP measurements at 1 AU. Because of the inclination of the ecliptic plane with respect to the heliographic equatorial plane, the latitudinal separation between the location of the parent flare associated to an SEP event and the footpoint of a near-Earth detecting spacecraft can vary in latitude between 0 and about 40 degrees. By analyzing a sample of 477 well connected solar events (with source region in W20-W80) and characterized by a magnitude of the associated flare >C8.0, we derive a probability P of observing an SEP event as a function of the latitudinal separation. We find that the P is largest for latitudinal separations between 4° and 12°. Outside this range, including separations smaller than 4° and in the interval [12°, 28°], P remains approximately constant.