Magnetic reconnection vs. KHI: is the debate really over?

Transcription

1 Magnetic reconnection vs. KHI: is the debate really over? A. Masson et al. ESAC, 11-Mar-2016 ESA UNCLASSIFIED For Official Use

2 Outline 1. Big picture (just an attempt) 2. Selected Cluster/DS/Themis science highlights at the magnetopause a. Magnetic reconnection b. K-H instability c. Cluster operations at the magnetopause 3. Implications for a new mission?

3 1. The Big picture (just an attempt) Region and/or physical process Discovery Deep Understanding Forecast

4 1. The Big picture (just an attempt) Region and/or physical process Discovery Deep Understanding Forecast Proper Inst. Multi-Spacecraft

5 1. The Big picture (just an attempt) Region and/or physical process Discovery Deep Understanding Forecast Proper Inst. Radiation belts Explorer 1 Van Allen Probes Multi-Spacecraft

6 1. The Big picture (just an attempt) Region and/or physical process Discovery Deep Understanding Forecast Proper Inst. Radiation belts Explorer 1 Van Allen Probes Multi-Spacecraft Auroral zone/m-i Injun/Viking Fast Cluster but

7 1. The Big picture (just an attempt) Region and/or physical process Discovery Deep Understanding Forecast Proper Inst. Radiation belts Explorer 1 Van Allen Probes Multi-Spacecraft Auroral zone/m-i Injun/Viking Fast Cluster Magnetic Reconnection/KHI ISEE Polar/Geotail Cluster/MMS Substorm GB Themis Plasmasphere/RC GB and Luna2 IMAGE Twins Solar wind heating/turbulence Helios Thor Cluster Mercury Mariner 10 Messenger Bepi-Colombo Jupiter Voyager Galileo/Juno/Juice Saturn Voyager Cassini GB magnetometers Single Image, Canopus SuperMAG

8 2. Magnetopause processes 2a. Intermittent vs. quasi steady reconnection Nature of reconnection at the magnetopause Continuous? Intermittent? Quasi-steady? Can reconnection be intermittent even when the solar wind plasma and IMF orientation are stable? i.e. intrinsically intermittent? Before Cluster Many single satellites and a few two-spacecraft missions observations at the magnetopause or in the mid-altitude cusp But a crossing with one s/c lasts only a few minutes Existence of continuous reconnection during northward IMF i.e. tailward of the cusp where external magnetosheath flow is fast was unclear [Cowley and Owen, 1989]

9 2a. Intermittent vs. quasi steady reconnection [Phan et al., GRL, 2003] IMF Bz>0 for ~4 h Proton auroral spot ~ 4h Jets on linked field lines Spot brightness consistent with energy fluxes of prec. H+ =>Magnetic recon. tracer

10 2. Magnetopause processes 2a. Intermittent vs. quasi steady reconnection Reconnection at the magnetopause Cluster observations and Cluster/IMAGE studies led to the following conclusions 1. When SW conditions are stable: continuous reconnection for a few hours at the local magnetopause for both southward and northward IMF are observed 2. When IMF changes: reconnection site moves, FTEs can be formed and intermittent reconnection is observed 3. Key controlling factor: steadiness of solar wind conditions and IMF Intermittency is not a fundamental property of the reconnection process at the magnetopause

11 2. Magnetopause processes 2a. Component vs. anti-parallel reconnection? Reconnection at the dayside magnetopause: Pre-Cluster era controversy between Component reconnection (merging) model vs. Anti-parallel reconnection Many indirect observations before Cluster era could not discriminate Sampling the X-line directly at the magnetopause are rare. Cluster observations provided evidence of the existence of component merging model [Retino et al., 2004; Sonnerup et al., 2004; Dunlop et al., 2011]

12 2. Magnetopause processes 2a. Component AND anti-parallel reconnection Anti-parallel merging Component merging Both anti-parallel and component reconnection can occur at the dayside magnetopause under the same IMF conditions and that both phenomena might be the local signatures of a global reconnection picture [Dunlop et al., PRL, 2009] Credit: ESA

13 2. Magnetopause processes 2a. Diffusion regions Cluster MMS Ion diffusion region Importance of cold ions Electron diffusion region (MMS) Credit: ESA MMS/Cluster

14 2. Magnetopause processes 2b. K-H instability at the magnetopause Solar wind plasma entry process during Northward IMF, flanks, LL First direct estimate of the size of K-H plasma swirls/vortices thanks to multiple spacecraft Length scale: 40,000-55,000 km [Hasegawa et al., Nature, 2004] No indication yet on the microphysical process causing the possible plasma transport in the KH vortices Credit: ESA

15 2. Magnetopause processes 2b. K-H instability at the magnetopause Magnetic reconnection found to be the microphysical process causing the plasma transport in the KH vortices (2D simulations) [Nykyri et al., Ann Geo., 2006]

16 2. Magnetopause processes 2b. K-H instability at the magnetopause Solar wind plasma entry process Under ANY IMF conditions! [Hwang et al., JGR, 2011, 2012] K-H vs. Magnetic reconnetion Occurence 7 years Themis data statistics confirm its importance 19% under any IMF conditions [Kavosi and Raeder, Nature Comm, 2015] Themis ~ the equatorial plane 19% is most probably a lower limit Not a negligeable mechanism of plasma entry Credit: ESA

17 2. Magnetopause processes 2b. K-H instability at the magnetopause Haven t we underestimated the importance of K-H instability in terms of plasma entry in the magnetosphere? Don t you think a dedicated mission to study the K-H process in the equatorial and polar orbits would make sense? Key question Quantitative picture of plasma entry K-H vs. Magnetic reconnetion Credit: ESA

18 2c. Future operations at the magnetopause

19 3. What next? Big question: How plasma gets in under which solar wind conditions? At the moment, we try to predict tsunami in the pacific ocean with a couple bueys Possible scenario Many micro-sat with electric propulsion along the magnetopause (at the moment only GEO) Orbit of Equator-S type and Polar-S type Minimum instrumentation: B, ions Any idea?