Turbulence and Dissipation in the Solar Wind Plasma Current Challenges and New Diagnostics SHINE 2015 Workshop, Stowe, VT, July 6-10, 2015 Session Summary for Session 13: Chadi Salem (1) & Tulasi Parashar (2) (1)Space Sciences Laboratory, University of California, Berkeley, CA (2)University of Delaware, Newark, DE

Where does the challenge stand? SHINE 2013: The Challenge was formulated (White Paper by Parashar & Salem, 2013) and discussed for the first time in detail. SHINE 2014: The first step, a thorough code comparison, was discussed in detail (White Paper by Parashar & Salem, 2014) and we decided on the diagnostics to be used. A formal paper combining these white papers was accepted by Journal of Plasma Physics [Parashar, Salem, Wicks, Karimabadi, Gary & Matthaeus, JPP, 2015]: it outlines the challenge in detail and the simulations to be done, as well as diagnostics to be performed. We are in the process of performing the simulations. – Many groups are involved: Delaware, Calabria, San Diego, APL, Queen Mary Univ. of London, Imperial College London, Czech Republic, etc.

This year’s plan: 1 The first half of the session will discuss the preliminary results related to the problems described in the JPP paper. It will serve as a discussion platform for the preliminary results of the Challenge Simulations, as well as any other independent results that fit within the theme of turbulent dissipation. This discussion will hopefully serve as an important steering point for the first stage of the Challenge. Peter Gary will lead this discussion on Thursday afternoon. – We invite all the people interested in this discussion, whether you have an abstract submitted or not. – Please bring any slides that you deem relevant to the session/discussion.

Thursday Afternoon Session Focus: – Discuss the existing results from the challenge simulations & any other relevant simulations – Based on the discussion, decide if we want to steer the challenge in a slightly different direction Many contributed slides: – Jim Juno, Tulasi Parashar, Mike Shay, Joel Dahlin, Vladimir Zhdankin, Peter Gary, Luca Franci, Paul Bellan – Many people involved in discussion

Summary of Results Jim Juno – KAW problem in the challenge is essentially linear in reduced models like GK – Pending comparison results from other models Tulasi – Small kinetic boxes do not capture self consistent cascade and hence appropriate heating diagnostics. Shay, Dahlin – Reconnection heating shows some desirable features and the processes discussed in 2D persist nicely in 3D Vlad – Almost 50% dissipation occurs in 3% volume. Current sheets collaps to ~di thickness in pair plasma. Tak-Chu – Gyrokinetic OTV simulations. 2D and 3D have qualitative similarities BUT “Quantitative” differences. Luca Franci – Need very high PPC for convergent heating. Paul Bellan – Discussed an analytic framework for relativistic particle energization by circularly polarized waves.

Discussion/Conclusions The KH setup described in the Challenge Paper might be difficult to set up for reduced models. Two suggestions: – Modify the KH setup: change the tilted B field to sheared B – Perform Orszag Tang Vortex (OTV) OTV’s already performed by a few groups and might make the cross code comparison easier. Wait for other simulation models to perform the KAW problem. Hopefully comparative plots by AGU.

Curiously there was way more consensus in the room than expected!!!! Suggested big picture idea for the second stage of Challenge did not change with this discussion. “We will need very large 3D simulations for the second stage of the Challenge.” The results are slowly converging and we will start putting numbers on paper for the second stage soon!!

THIS MORNING SESSION

This year’s plan: 2 BATTLE OF METHODOLOGIES: Simulations. We are comparing some aspects of different simulation models as the first step. This part will serve as a platform to discuss additional limitations and advantages of various simulation methodologies (including model equations, numerical schemes as well as model geometries) An important question remains: – Where and how do the lines blur between different models? – Are the initial TurboChallenge tests enough or do we need to go beyond? Bill Matthaeus will lead the discussion on this (Friday Morning).

This year’s plan: 3 BATTLE OF METHODOLOGIES: Observations. How do we compare various observational analysis techniques used to interpret spacecraft data? We need ways to benchmark them against one another AND against simulation models. Jiansen He will lead the discussion on this Friday second half of the session This year’s discussion promises to be productive, stimulating and lively.