Estimations of the uncertainty in timing the relationship between magnetospheric and solar wind processes

We present here a statistical study quantifying the errors associated with the most commonly used methods for propagating discontinuities in the inter planetary magnetic field (IMF) from an upstream monitor to the magnetospher e by the magnetospheric and ionospheric communities. The purpose of this pa per is to show the quantified errors in the different techniques. Step chan ges in the IMF orientation were first identified at the WIND satellite. A t otal of 363 events were identified. Ninety percent of the events measured a t WIND (330) were clearly observed in the IMP 8 data. Of those events, the time delay between the satellites could be determined to within 2 min in 28 8 events. Four propagation methods were used to estimate the time delay bet ween WIND and IMP 8: (1) using only the X distance between the satellites; (2) assuming that the propagation front plane is in the plane of the Parker spiral; (3) using the IMF in the X-Y plane to estimate the propagation fro nt plane; and (4) using the total IMF to determine the Z component of the p ropagation front plane. The average ((E) over bar) and maximum (E-max) prop agation error tin minutes) as a function of Y-Z distance (in R-e) were dete rmined for each method. It is concluded that the average uncertainty in pro pagation is 7.5-8.5 min for off-axis distances of 30 R-e (which is the aver age WIND off-axis distance, and approximately the largest off-axis distance of IMP 8). For off-axis distances of 100 R-e (the largest off-axis distanc e of WIND), the uncertainties are 17.5-25 min, depending on the propagation method. (C) 2000 Elsevier Science Ltd. All rights reserved.