Using Statistical Multivariable Models to Understand the Relationship Between Interplanetary Coronal Mass Ejecta and Magnetic Flux Ropes
- 301 Downloads
In-situ measurements of interplanetary coronal mass ejections (ICMEs) display a wide range of properties. A distinct subset, “magnetic clouds” (MCs), are readily identifiable by a smooth rotation in an enhanced magnetic field, together with an unusually low solar wind proton temperature. In this study, we analyze Ulysses spacecraft measurements to systematically investigate five possible explanations for why some ICMEs are observed to be MCs and others are not: i) An observational selection effect; that is, all ICMEs do in fact contain MCs, but the trajectory of the spacecraft through the ICME determines whether the MC is actually encountered; ii) interactions of an erupting flux rope (FR) with itself or between neighboring FRs, which produce complex structures in which the coherent magnetic structure has been destroyed; iii) an evolutionary process, such as relaxation to a low plasma-β state that leads to the formation of an MC; iv) the existence of two (or more) intrinsic initiation mechanisms, some of which produce MCs and some that do not; or v) MCs are just an easily identifiable limit in an otherwise continuous spectrum of structures. We apply quantitative statistical models to assess these ideas. In particular, we use the Akaike information criterion (AIC) to rank the candidate models and a Gaussian mixture model (GMM) to uncover any intrinsic clustering of the data. Using a logistic regression, we find that plasma-β, CME width, and the ratio O 7/O 6 are the most significant predictor variables for the presence of an MC. Moreover, the propensity for an event to be identified as an MC decreases with heliocentric distance. These results tend to refute ideas ii) and iii). GMM clustering analysis further identifies three distinct groups of ICMEs; two of which match (at the 86 % level) with events independently identified as MCs, and a third that matches with non-MCs (68 % overlap). Thus, idea v) is not supported. Choosing between ideas i) and iv) is more challenging, since they may effectively be indistinguishable from one another by a single in-situ spacecraft. We offer some suggestions on how future studies may address this.
KeywordsCoronal mass ejections Magnetic flux ropes Magnetic clouds
P.R. gratefully acknowledges the support of NSF’s FESD program as well as NASA SR&T and GI programs, the latter through a subcontract with NRL. We also acknowledge the use of Ulysses observations from NASA/GSFC’s Space Physics Data Facility’s COHOWeb service, and thank the Ulysses PIs who have made their observations available via this source.
- Afifi, A., Clark, V., May, S.: 2011, Practical Multivariate Analysis, 5th edn. Texts in Statistical Science, Taylor & Francis, London. ISBN9781439816806. Google Scholar
- Ebert, R.W., McComas, D.J., Elliott, H.A., Forsyth, R.J., Gosling, J.T.: 2009, Bulk properties of the slow and fast solar wind and interplanetary coronal mass ejections measured by Ulysses: Three polar orbits of observations. J. Geophys. Res. 114, 1109. doi: 10.1029/2008JA013631. CrossRefGoogle Scholar
- Gopalswamy, N.: 2010, Corona mass ejections: A summary of recent results. In: Dorotovic, I. (ed.) 20th National Solar Physics Meeting, 108 – 130. Google Scholar
- Hammond, C.M., Crawford, G.K., Gosling, J.T., Kojima, H., Phillips, J.L., Matsumoto, H., Balogh, A., Frank, L.A., Kokubun, S., Yamamoto, T.: 1995, Latitudinal structure of a coronal mass ejection inferred from Ulysses and Geotail observations. Geophys. Res. Lett. 22(10), 1169 – 1172. ADSCrossRefGoogle Scholar
- McLachlan, G., Peel, D.: 2000, Finite Mixture Models 44, Wiley-Interscience, New York, 82. http://pubs.amstat.org/doi/abs/10.1198/tech.2002.s651. MATHCrossRefGoogle Scholar
- Odstrcil, D.: 2009, Numerical simulation of interplanetary disturbances. In: Pogorelov, N.V., Audit, E., Colella, P., Zank, G.P. (eds.) Numerical Modeling of Space Plasma Flows CS-406, Astron. Soc. Pac., San Francisco, 141 – 148. Google Scholar
- Press, W.H., Teukolsky, S.A., Vetterling, W.T., Flannery, B.P.: 2007, Numerical Recipes: The Art of Scientific Computing 29, Cambridge University Press, Cambridge 501. http://www.jstor.org/stable/1269484?origin=crossref. MATHGoogle Scholar
- Richardson, I.G., Cane, H.V.: 2010, Near-Earth interplanetary coronal mass ejections during Solar Cycle 23 (1996 – 2009): Catalog and summary of properties. Solar Phys., 189 – 237. doi: 10.1007/s11207-010-9568-6.
- Richardson, I.G., Cane, H.V.: 2011, Identification of interplanetary coronal mass ejections at Ulysses using multiple solar wind signatures, and comparison with ICMEs observed at the Earth and in the inner heliosphere. AGU Fall Meeting Abstracts, SH31B – 1979. Google Scholar
- Rodriguez, L., Zhukov, A.N., Dasso, S., Mandrini, C.H., Cremades, H., Cid, C., Cerrato, Y., Saiz, E., Aran, A., Menvielle, M., Poedts, S., Schmieder, B.: 2008, Magnetic clouds seen at different locations in the heliosphere. Ann. Geophys. 26, 213 – 229. doi: 10.5194/angeo-26-213-2008. ADSCrossRefGoogle Scholar
- Schieb, P.A.: 2011, Geomagnetic storms. Technical report. http://www.oecd.org/dataoecd/57/25/46891645.pdf.