How to identify and forecast severe space weather events

Abstract

This paper reviews some of the work performed by the authors over the past decade regarding the identification and forecasting of severe space weather. Severe space weather (SvSW) is defined as those causing damage of ground installations such as transformers resulting in power outage and/or tele-communication networks resulting in communication failure; normal space weather (NSW) does not cause such severe effects. Severe space weather (ScSW) events are caused by very energetic coronal mass ejections (CMEs) from the Sun, in particular by the sharp changes at their leading edge or front. It is shown that (1) it is the ICME (interplanetary CME) front of large velocity jump ΔV by over 275 km s−1 and sufficiently large southward interplanetary magnetic field (IMF Bz) at and beyond the velocity jump that causes SvSW. (2) A derived parameter of the geomagnetic storms called impulsive strength (IpsDst) giving the average value of Dst during the storm main phase (MP) can distinguish between SvSW and NSW. (3) The product of the observed velocity jump and associated IMF Bz southward (ΔVBz) ≤ −15000 km s−1 nT or −15 mV/m) can be used for forecasting SvSW. (4) If one can estimate ΔVBz at the Sun-Earth L1 point based on observations such as from the Advanced Composition Explorer (ACE) satellite, it is possible to forecast an SvSW event with an advance warning time of about half an hour.