Geoeffective interplanetary magnetic field (IMF) from in situ data: realistic versus idealized spiral IMF

Abstract

The geoeffective, southward IMF (B_text {s}) given in the GSM reference frame as nature presents is compared with that based on idealized, spiral IMF. We obtained B_text {s} and B_text {s} sorted by the IMF polarity (B_text {s} fields) from in situ data at a high 16-second resolution. Idealized IMF is derived by omitting the fluctuation of the IMF in the GSEQ Z-direction. Results are: the absolute value of realistic B_text {s} is larger than the one from idealized IMF; realistic B_text {s} polarity fields exist in all seasons, while those from idealized IMF exist only around spring/fall when the IMF points toward/away from the Sun; idealized B_text {s} fields match the predictions of the Russell–McPherron (RM) model almost ideally. The present study has resolved the issue related to the patterns and absolute values of the observed B_text {s} fields and those from the RM model that assumes an idealized IMF. It confirms that B_{z,text {GSEQ}} plays a crucial role for B_text {s}. Finally, it paves a way to properly link the variations seen in geomagnetic activity with the pattern of the measured B_text {s} fields.