Elementary Conversations About Solar-terrestrial and Space Physics

The idea behind having "elementary conversations" came from Eugene Parker's monograph "Conversations on electric and magnetic fields in the cosmos" published in 2007 by Princeton University Press.

In the present conversations we will discuss the complex systems we study from a simple point of view- a physical one. Almost all of us are narrowly focused on our small research field, or even on specific Space– or Ground– based missions and datasets. This series of conversations is intended to broaden our familiarity, understanding and comfort in the broad context of solar-terrestrial physics.

Hopefully in these conversations we can all benefit from the wider context of our collective research effort.

Fridays from 1:30–2:45 pm, at CG1-Captain Mary Room (2nd floor).

Upcoming Conversations:

Date/Time/Room	Title and Conversation Point
Upcoming Conversations
? July 2012 1:30–2:45 pm Captain Mary	TBA
Past Conversations
BC Low--"How to reconcile Maxwell and Newton to end up with the MHD Equations"
27 June 2012 1:30–2:45 pm Captain Mary	As the Sun Turns: Solar Differential Rotation and Meridional Circulation BC Low will present an informal derivation of MHD by amending the neutral fluid equations, ie, figuring out why being electrically conducting, the fluid sees the Lorentz force but not electric force, and, of course the induction equation.
Mark Miesch--"A Closer Look at the Mysteries of the Solar Dynamo"
11 May 2012 1:30–2:45 pm Captain Mary	As the Sun Turns: Solar Differential Rotation and Meridional Circulation (PowerPoint Link) Switching gears somewhat from the dynamo focus of many of these discussions, we will consider recent progress, puzzles and prospects on understanding the origin of differential rotation and meridional circulation in the solar interior. These of course are some of the essential physical ingredients of the solar dynamo models covered in Conversation 7 but nearly all dynamo models take them for granted. Here we face them head on, with the help of new insights based on a flurry of recent theoretical, numerical, and observational work. These include mean-field MHD models by Rempel, theoretical arguements by Balbus and collaborators, convection simulations by the ASH mob, and new measurements of the meridional flow by Ulrich and Hathaway. Particularly compelling current mysteries include the origin of global thermal gradients (warm poles) and the sub-surface structure of the meridional flow. Finally, we will address what all this means for the dynamo and solar magnetism.
27 April 2012 1:30–2:45 pm Captain Mary	Negotiating the Solar Dynamo Zoo (PowerPoint Link) Armed with the background of Conversation 6, we will consider how these and other physical ingredients (including turbulent diffusion) are actually put together to construct state-of-the-art dynamo models of the solar cycle. Unlike other discussions in this series, we'll focus less on fundamental physical puzzles and more on a practical survey of the current modeling landscape. It is intended as a primer for the uninitiated, giving those studying other aspects of solar, space, and atmospheric physics a feel for the triumphs and tribulations of current modeling efforts, including what different classes of models are capable of addressing and what they are not. Our survey will include several current mean-field modeling efforts as well as the 3D convective dynamo simulations by Charbonneau, Smolarkeiwicz, and collaborators. Finally, we will address how Spruit's criticisms covered in Conversation 2 may or may not apply to each of these classes of models.
16 March 2012 1:30–2:45 pm Captain Mary	A Tale of Two Alphas (PowerPoint Link) In this discussion we will compare and contrast two means of generating mean poloidal field in solar dynamo theory, namely the turbulent alpha-effect and the Babcock-Leighton alpha-effect. We will delve deep into their physical and mathematical origins and we will describe and critique their implemenation in mean-field solar dynamo models. We will also describe how they relate to their philosophical cousins, including the inverse cascade of magnetic helicity in MHD turbulence, turbulent and laminar magnetic induction, Spruit's spaghetti dynamo, and the nonlinear flux-tube dynamo of Cline et al. Along the way we will explore the profound role of magnetic helicity in modern solar dynamo theory, and its implications for photospheric and coronal observations. This will be part of a broader discussion on the crucial issue of how dynamos saturate, or in other words, what prevents the amplitude of the field from growing forever? It may sound technical but don't fret - we will make all effort to avoid the jargon of dynamo theory and focus instead on a conceptual physical description grounded in the basic MHD equations.
9 March 2012 1:30–2:45 pm Captain Mary	On Spaghetti, Stars, and the Three Pillars of Science (PowerPoint Link) This is largely a response to the Phil's thought-provoking second discussion, considering some of the same issues from a different perspective. In particular, we will take another look at Spruit's conceptual picture of how the solar dynamo works (this is where the spaghetti comes in) and we'll consider again how it fits in with theoretical, numerical, and observational results. Phil (for good reason) emphasized the more compelling aspects of Spruit's theory, including its profound simplicity and empirical footing. Here we will approach it from a more critical perspective, highlighting the equally profound potential complications with Spruit's vision. We will also talk in more general terms about the role of numerical simulations in solar and space research.
Phil G. Judge--"Surprises in solar physics"
2 March 2012 1:30–2:45 pm Captain Mary	Magnetic topology Decades ago Parker recognized that ideal MHD permits a host of solutions under force free conditions that are expected to be discontinuous. We will explore the arguments and implications for such "tangential discontinuities" and debate the issue- is the solar corona full of these things? What are the implications for understanding the free energy stored in coronal plasma, heating mechanisms, and interpreting remotely-sensed data?
24 February 2012 1:30–2:45 pm Captain Mary	Dirty laundry and solar magnetic evolution (PowerPoint Link) What is the role of small scale physical processes in determining the order observed in say, the existence of coronal holes? By looking at the physics behind "magnetic diffusivities" we will explore the relationship between small and large scale magnetic fields. Why is the Sun obliged to form a coronal hole, while at the same time store energy for release as a flare?
17 February 2012 1:30–2:45 pm Captain Mary	Ingredients in the "solar dynamo" (PowerPoint Link) For me, several surprises relate to the relatively high level of order exhibited by the varying solar magnetic field. We will discuss what these mean for the evolution of the Sun's magnetism.
10 February 2012 1:30–2:45 pm Captain Mary	An MHD perspective (PowerPoint Link) Solar and stellar data will be used to confront our understanding of solar magnetism, by asking, in the context of MHD, "why would the Sun choose to do that?