CME rate : 1/3 (4) day -1 at solar min (max) [LASCO CME catalogue. Yahsiro et al., 2005]

1. Center for Space PhysicsBoston University Heliospheric flux buildup from coronal mass ejections:Suprathermal electron signaturesM.J. Owens1, N.U. Crooker1 and A.C. Pagel2. 1Center for Space Physics, Boston University. 2Department of Mathematics, University College London Abstract 2. Total heliospheric flux Suprathermal electrons streaming away from the Sun along magnetic field lines exhibit counterstreaming when the field lines form closed loops that are connected to the Sun at both ends, as commonly found in ICMEs. As the loops expand to the outer heliosphere, however, eventually the counterstreaming signature at the observing point in the inner heliosphere will cease because the sunward beam will disappear owing to scattering along its increasingly lengthening path. If the loop then interchange reconnects with an open field line back at the Sun, the antisunward electron beam will also disappear at the observing point, creating what is known as a “heat flux dropout (HFD),” since the electrons carry heat flux away from the Sun. Thus an HFD may be a signature of interchange reconnection as well as a necessary (but not sufficient) signature of disconnection, with which it is usually associated, where two open field lines reconnect at the Sun. We construct a model to estimate the percentage of flux involved in HFD generation by interchange reconnection in ICMEs over the course of a solar cycle and find that remarkably little is required to balance the flux budget. For example, if counterstreaming at 1 AU ceases when loop apices reach 10 AU, then the percentage of flux at 1 AU with an HFD signature from interchange reconnection would be only 2-3% at solar maximum and 0.25-0.5% at solar minimum. This is even less than the percentage of newly-identified HFDs with disconnection/interchange reconnection characteristics found in high-time resolution data. • Total flux at r (Φr) consists of 3 components: • Assuming Φr = 4πr2BR, variation in CME frequency (f) and BR from solar min to max is best matched by T½ = 40 days • Assume time between consecutive CME eruptions is simply 1/f, and that a flux equilibrium is reached at solar min and max conditions • Figure on left shows resulting occurrence of CSE and HFD signatures at • 1 AU for solar min and • max CME rates, for a • range of electron • scattering distances (R) • To match Gosling et al., • [1992] estimate of CSEs • at solar max, R ~ 8 AU • Electron scattering length • ~ 40 AU Static equilibrium 1. A single CME Flux evolution • Relax CME timing and equilibrium assumptions by driving simulation with LASCO CME timings. • Overall |B| variation very well matched • Using R=10: • Variation in CSEs: 3% at solar minimum to ~25% at solar maximum • Variation in HFDs: <1% at solar min to ~5% at solar maximum • Model electron signatures are more variable than model |B| LASCO CME rates • CME erupts at time t0carrying closed flux of φ0 = (1-D) φA • Where D is the fraction of the total CME flux that opens at launch (~50%), and φA is the total axial (I)CME flux (as provided by magnetic cloud estimates) • This CME flux can contribute to the flux observed at heliocentric distance r (Φr) only after time t0 + r/V • CME contribution to Φr at time t (> t0 + r/V) is the sum of ICME closed flux (φC) and inverted flux (φINV) • NOTE: CME eruption changes background open field topology, but contribution to Φr remains constant with time • Assuming rate of flux opening is proportional to amount of closed flux: • Where λis the decay constant of the CME closed flux, i.e., the interchange reconnection rate Electron signatures 3. Summary 4. Observations used • Developed a model of heliospheric flux variation in which: • Background open flux remains constant • All variation is provided by a buildup of CME flux • Despite long timescales (T½ = 40 days) for CME flux opening, there is no flux catastrophe • Using best observational estimates for free parameters: • Solar cycle variation in |B| at 1 AU is very well matched (as shown previously) • Suprathermal electron signatures from model match well with available observations • For CSEs occurrence ~ 15% at solar max -> R ~ 8AU • This suggests electrons scatter over a path length ~ 20 AU • Slight overestimate of HFD at solar min – no latitudinal dependence of CME signatures? • Detailed survey of suprathermal electron signatures at 1 AU required for comparison to model • Need observational estimate of R, the distance at which the strahl scatters • CME rate: 1/3 (4) day-1 at solar min (max) [LASCO CME catalogue. Yahsiro et al., 2005] • |B| at 1 AU: 5 (8) nT at solar min (max) [OMNI data] • D (fraction of CME flux that opens at launch): 50% [electron observations of Shodhan et al., 2000; Crooker et al., 2004; Riley et al., 2004] • φA (axial flux in ICME): 3e12 Wb [magnetic cloud survey of Lynch et al., 2005] • → T½ = 40 days and Φ0 = 1e15 Wb • CSEs percentages: ~15% at solar max, from ISEE 3 data[Gosling et al., 1992]. ~1% at solar min, but only 20% data coverage. • Higher estimate at solar max from ACE data [Skoug et al., 2005] • HFDs from disconnection/interchange reconnection at solar min: ~2%, from Wind observations[Pagel and Crooker, 2006] • “Fast” ICME flux opening: Closed flux = counterstreaming electrons (CSE) and inverted flux = single strahl (i.e., same as background open flux). No heat flux dropouts (HFDs) occur. • “Slow” ICME flux opening: necessary to consider a heliocentric distance (R) at which suprathermal electrons scatter. • Before ICME reaches R: closed flux = CSE, inverted flux = strahl (i.e., the same as in the fast ICME scenario) • After ICME reaches R: closed flux = strahl, inverted flux = HFD