Long‐distance Correlations of Interplanetary Parameters: A Case Study with HELIOS Available to Purchase

In recent work, promising agreement has been obtained between measured indices of geomagnetic activity (Dst, and cross‐polar cap potential) and their predicted values using interplanetary input from probes in the inner heliosphere (∼0.7 AU) when the probe was close to, (5), and even substantially displaced from, (4), the Earth‐Sun line. Implicit in this agreement is a good correlation of, at least, the basic temporal profiles of the major interplanetary parameters at the two observing sites. In this work we discuss a case study using Helios 1 and 2 data when the spacecraft are lined ‐ up and separated by an almost constant radial distance of 0.2 AU. In the period studied, the interplanetary medium consists of a fast stream being trailed by a magnetic cloud in a slower flow. Good correlation is found between the plasma and field observations at the two sites. Two lag times, reflecting the two types of major structures in the interval chosen, are determined. Evidence of evolutionary processes are briefly discussed. Spectral analysis confirms the results obtained from time series analysis.