Statistical investigation of hourly OMNI solar wind data

Abstract

Hourly OMNI solar wind data are sorted into categories reflecting membership of each data point to either slow or fast solar wind streams, or to either coronal mass ejection or corotating interaction region environments. The categorization is inspired by Yermolaev et al. (2009) and modified from there. Durations and coverage fractions of each category are investigated, together with their dependence on the solar activity cycle. The results are in line with physical expectations for the solar wind at 1 AU. A further analysis, treating hourly solar wind fluctuations as a constrained random walk process, is carried out independently for each solar wind category and discussed. The resulting step size distributions are found to be largely symmetric across zero, resembling a random walk deviation from a long-term average. This constrained random walk can in principle be used to fill gaps in the OMNI data and perform other OMNI data extrapolations. Copyright 2011 by the American Geophysical Union.