Characteristics of geoeffective CMEs - guidelines for space weather forecasting

Richardson, G.S. ORCID: 2019 Characteristics of geoeffective CMEs - guidelines for space weather forecasting. Nottingham, UK, British Geological Survey, 28pp. (IR/18/021) (Unpublished)

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Forecasts of geomagnetic activity are important for decision makers tasked with protecting vulnerable technological infrastructure from space weather. However, in the current operational forecast situation there may be relatively little near real-time data with which to make an immediate decision about the level of expected activity. Whilst advances in physical modelling techniques (for example, the WSA-ENLIL model) and increases in the number of different data sources and their availability are improving the situation, there remains a knowledge gap and forecasts still depend heavily on the judgement of the forecaster. The aim of this work is therefore to help space weather forecasters put coronal mass ejection (CME) reports into context, based on an analysis of past events. I have analysed 12 years of CMEs from Jan 1998 to Dec 2009, with a focus on the data available at the time of CME observation for forecasting. CMEs which, at the time of their observation, were identified as having a potential to impact the Earth have been assessed and correlated with resulting geomagnetic activity, based on the Kp index and NOAA G-scales. 45% of Earth-directed CMEs resulted in geomagnetic storms where Kp reached at least 6- (G2). Earth-directed CMEs that originated in the western heliohemisphere were more likely to become geoeffective, with 71% of those between heliolongitudes of 15º and 25º resulting in geomagnetic storms; however, CMEs near the limbs were also capable of becoming geoeffective. The percentage of Earth-directed CMEs which became geoeffective increased with increasing velocity, although there is a marked difference between the near real-time velocity estimates (from the real-time CACTus catalog) and the post event “definitive” LASCO catalog velocities. The results presented here will help in determining the likely geoeffectiveness of CMEs in an operational forecast environment.

Item Type: Publication - Report
Programmes: BGS Programmes > Seismology and Geomagnetism
Funders/Sponsors: British Geological Survey
Additional Information. Not used in RCUK Gateway to Research.: This item has been internally reviewed, but not externally peer-reviewed. Item made open by author in March 2021.
NORA Subject Terms: Earth Sciences
Date made live: 03 Mar 2021 09:38 +0 (UTC)

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