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Energy Conversion Regions in the Plasma Sheet: Cluster Observations

This presentation discusses the observations of energy conversion regions in the plasma sheet using Cluster satellite data. It explores the relationship between energy conversion and the energy input from the solar wind, as well as the transport of energy to the ionosphere. The results show a clear correlation between energy conversion regions and various factors such as magnetic field direction and high-speed flows. This research provides valuable insights into the energy dynamics in the Earth's magnetosphere.

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Energy Conversion Regions in the Plasma Sheet: Cluster Observations

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  1. Cluster observations of energy conversion regions in the plasma sheet Hamrin, M., Norqvist, P., Marghitu, O., et al. e-mail: hamrin@space.umu.se Department of Physics, Umeå University, Sweden Nordic Cluster Meeting, Uppsala, August 2011 Hamrin, Nordic Cluster Meeting, 2011

  2. - Background - Our previously published papers on plasma sheet (PS) energy conversion. Recently we have obtained experimental evidence of the relation between PS energy conversion and the energy input at the magnetopause the energy flow towards the ionosphere Work in progress… Now I’m looking for advice from you! Splinter? Hamrin, Nordic Cluster Meeting, 2011

  3. - Introduction: The Plasma sheet - ~20 years ago, the view on PS transport processes changed by the discovery of BBFs [Baumjohann et al., JGR, 1990; Angelopoulos et al., JGR, 1992]. PS plays a fundamental role for the energy conversion and transport processes in the Earth’s magnetosphere (Msp). Primary energy source: Solar wind kinetic energy, transferred into the Msp by means of reconnection [Paschmann et al., Nature, 1979]. Tail reconnection releases energy stored in the tail magnetic field.  Magnetic energy converted to kinetic energy (BBFs). Energy is transported away as Poynting flux and particle flux. Possibly recurring conversions in the PS between electromagnetic energy and kinetic energy (plasma bulk and thermal) forms [Hamrin et al., JGR, 2011]. Some energy dissipated in the auroral ionosphere [Hamrin et al., Ann Geophys, 2006, Hamrinet al., Ann Geo, JGR, 2011]. Appealing to explore the structure of the PS energy conversion and transport in relation to the SW energy input and auroral dissipation! Hamrin, Nordic Cluster Meeting, 2011

  4. E∙J<0 (generator) Mechanical energy Electromag. energy E∙J>0 (load) • - TOOLs - Power density Poynting’s theorem: Energy of bulk motion: Plasma acc./decel. by Lorenz force, JB Study E∙J in the PS with Cluster! (JB)v= (-vB)J=EJ Hamrin, Nordic Cluster Meeting, 2011

  5. - Cluster observations- E∙J ∑E∙J J=B from FGM <E>=Esc/n from CIS -vB Reference frame of irreversible energy dissipation: neutral wind system ≈ GSE (GSM) We study clearly identifiable regions of energy conversion: “ECR” = Energy Conversion Region: “CLR” = Concentrated Load Region“CGR” = Concentrated Generator Region ‘Automatic’ECR database: 2001, 2002, 2004, 15-20RE. 428/127 CLRs/CGRs from 220 Cluster PS passages (2730h) Hamrin, Nordic Cluster Meeting, 2011

  6. - (statistically) Observed ECR characteristics - 1. Concentrated regions (time, space) of energy conversion Consistent with high level of fine structure in PS 2. CLRs are stronger and more frequent than CGRs Consistent with PS on the average behaving as a load 3. CLRs/CGRs preferring locations towards CPS/PSBL (high/low ) Consistent with MHD simulation [Birn and Hesse, Ann Geo, 2005] 4. ECR life time and (cross-tail) scale size = 1-10 min and a few RE Consistent with BBF scale size [Nakamura et al., Adv Space Res, 2005; Walsh et al., Ann Geo, 2009], MHD simulation [Birn and Hesse, Ann Geo, 2005]and BBF duration [Juusola et al., JGR, 2009] 5. Energy conversion increases with the geomagnetic activity (AE, Kp) 6. Correlated with auroral activity (AE and event investigations) Consistent picture of the PS energy conversion! Hamrin, Nordic Cluster Meeting, 2011

  7. - New stuff - Now heading towards the new results linking the PS energy conversion to…1. …SW input into the Msp2. …transport of energy to the ionosphere (BBFs, Poynting flux) Hamrin, Nordic Cluster Meeting, 2011

  8. - (1.) ECR VS. SW input - #ECRs Bz(T-20min)<0 Bz(T-20min)>0 Dayside reconnection (SW energy input) is favorable towards southward IMF Bz ECRs are more common after periods of stable southward IMF Expected but now we have verification! More significant result for CLRs. Perhaps because of differences between the spatial distributions of CLRs and CGRs with respect to the Cluster orbit (?) #ECRs Bz(T-20min)<0 Bz(T-20min)>0 Hamrin, Nordic Cluster Meeting, 2011

  9. - (1.) ECR VS. SW input - Some extra material… Number of ECRs observed t hours after stable 1h-intervals of southward or northward IMF. The memory of the IMF direction remains up to ~5h. Why? ’Stablelevel’ of fluctuations Hamrin, Nordic Cluster Meeting, 2011

  10. - (2.1) ECR vs. BBF - Norm # ECRs Vtot [km/s] |Vtot| [km/s] ECRs are associated with high speed flows (cf. background data – gray) ECRs are more common during GSM Vx>0 than Vx<0 (not shown) Vx generally gives the most dominant contribution to Vtot, but there are many ECRs where the Vyz contribution cannot be neglected (not shown) Manuscript in preparation, Marghitu et al. Hamrin, Nordic Cluster Meeting, 2011

  11. - (2.1) ECR VS. BBF - Main conclusion 1: There is a strong correlation between high speed flows and ECRs. (Future research: Linking generators to the breaking of the plasma) Hamrin, Nordic Cluster Meeting, 2011

  12. - (2.2) ECR vs. Poynting flux - Sx within ECRs and RAND intervals (background reference data) Observation 1. Background data  Poynting flux is small and directed towards the Earth. Interpretation: Cluster is generally earthward of NENL Observation 2. CLRs and CGRs are correlated with a strong Poynting flux towards the Earth (consistent). Interpretation: During times of increased PS energy conversion (ECRs observed), we observe increased Poynting flux (superposition) towards the Earth/ionosphere, where some energy may be dissipated in auroral processes (e.g. correlation between ECRs and AE, Kp). Norm # ECRs Sx (GSM) Sx<0, away from Earth Sx~0 Sx>0, towards Earth Hamrin, Nordic Cluster Meeting, 2011

  13. - Summary and Conclusions - Observational evidence: Verifying the role of the PS as an important link in the chain of processes controlling energy conversion and transfer from the SW and to final auroral dissipation Dayside reconnection is expected to be efficient during southward IMF. PS energy conversion should therefore correlate with IMF direction. Now this is experimentally verified! Also verified that PS energy conversion correlates well with 2.1 earthward plasma flows and 2.2 earthward Poynting flux. Further discussions and suggestions? Splinter? Hamrin, Nordic Cluster Meeting, 2011

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