Global Energetics of Solar Flares. VII. Aerodynamic Drag in Coronal Mass Ejections

Abstract

The free energy that is dissipated in a magnetic reconnection process of a solar flare, generally accompanied by a coronal mass ejection (CME), has been considered as the ultimate energy source of the global energy budget of solar flares in previous statistical studies. Here we explore the effects of the aerodynamic drag force on CMEs, which supplies additional energy from the slow solar wind to a CME event, besides the magnetic energy supply. For this purpose we fit the analytical aerodynamic drag model of Cargill (2004) and Vrsnak et al. (2013) to the height-time profiles r(t) of LASCO/SOHO data in 14,316 CME events observed during the first 8 years (2010-2017) of the SDO era (ensuring EUV coverage with AIA). Our main findings are: (i) a mean solar wind speed of w = 472 ± 414 km s −1 , (ii) a maximum drag-accelerated CME energy of E drag < ∼ 2×10 32 erg, (iii) a maximum flare-accelerated CME energy of E f lare < ∼ 1.5×10 33 erg; (iv) the ratio of the summed kinetic energies of all flare-accelerated CMEs to the drag-accelerated CMEs amounts to a factor of 4; (v) the inclusion of the drag force slightly lowers the overall energy budget of CME kinetic energies in flares from ≈ 7% to ≈ 4%; and (vi) the arrival times of CMEs at Earth can be predicted with an accuracy of ≈ 23%.Subject headings: Sun: corona -Sun: coronal mass ejections 1.

Global Energetics of Solar Flares. IX. Refined Magnetic Modeling

“…The Gold-Hoyle flux rope test: Highly twisted flux ropes with a large number of helical windings are thought to drive the expulsion of coronal mass ejections from a coronal flare site out to the heliosphere (Gold and Hoyle 1960). Such a highly twisted structure with 5 windings could be reproduced with the old VCA-NLFFF code (Aschwanden 2013a), while the new VCA3-NLFFF code could only produce magnetic field lines with less than a half winding turn (Aschwanden 2019), but this inability is consistent with the expected non-existence of nonlinear force-free field solutions at N twist > ∼ 1 due to the kink instability criterion. However, such Gold-Hoyle structures may exist as transients in interplanetary space, where force-freeness is not required.…”

“…3 right panels), no matter how large the non-potential force-free α parameter (or b) is chosen, which implies that helical geometries with more than one full turn cannot be reproduced with the new VCA3-NLFFF code. The most likely explanation for this limit is that helical magnetic field lines with a twist of more than one turn are not force-free, as it is theoretially expected from the kink instability criterion Hood and Priest 1979;Török et al 2003;Kliem and Török 2006;Kliem et al 2014), as well as from observational evidence (N twist < ∼ 0.5) of the helical twisting number (or the Gauss braiding linkage number) of coronal loops in solar active regions (Aschwanden 2019). Helical flux ropes as envisioned by Gold and Hoyle (1960) may still exist in interplanetary space, but are transient and require a time-dependent solution of the non-forcefree magnetic field.…”

“…Previously we developed the original vertical-current approximation nonlinear force-free field code (VCA-NLFFF) code that has been described and continuously improved over a decade (Aschwanden and Sandman 2010;Sandman and Aschwanden 2011;Aschwanden et al 2012Aschwanden et al , 2014aAschwanden et al , 2016aAschwanden 2013aAschwanden , 2013bAschwanden , 2013cAschwanden , 2015Aschwanden , 2016bAschwanden , 2019Aschwanden and Malanushenko 2013;Warren et al 2018). In the following we mention the most significant changes in the data analysis method of the new VCA3-NLFFF code only.…”

“…One of the most important tasks in our study is the energy partition and energy closure in flares. Quantitative information on different forms of energies and their partition in flares and CMEs became more available lately (Emslie et al 2012;Mann 2016a, 2016b;Aschwanden et al 2014aAschwanden et al , 2015aAschwanden et al , 2016a2017;Aschwanden 2016aAschwanden , 2017Aschwanden and Gopalswamy 2019). Virtually no statistical study on flare energies existed 5 years ago (Aschwanden 2004(Aschwanden , 2019a.…”

Global Energetics of Solar Flares and Coronal Mass Ejections

“…Future work may include STEREO data (Temmer et al 2010), which has a higher temporal cadence and spatial coverage in the lower corona (r < ∼ 3 R ⊙ ) that are occulted in coronagraphs like LASCO/SOHO. Coverage in this distance range is crucial to study acceleration and deceleration by the solar wind, by including aerodynamic drag effects (Cargill 2004;Vrsnak et al 2004Vrsnak et al , 2013Aschwanden and Gopalswamy 2019).…”