Parker Solar Probe Theory Group presentations occur by telecon at 12 PM EST on the fourth Thursday of the month. 

To join or contribute a talk please email Marco Velli (mvelli@ucla.edu) or Aleida Higginson (aleida.higginson@jhuapl.edu). 

 

 

Date Presentation

November 1, 2018

 

Title: Solar-Wind Observations of Collisional Thermalization among Multiple Ion-Species

Presenter: Bennet Maruca (University of Delaware; e-mail: bmaruca@udel.edu)

Abstract:

The rate of Coulomb collisions among ions in the solar wind is low enough that significant departures from thermal equilibrium (e.g., different ion species having different temperatures) are frequently observed.  Nevertheless, collisions have been found to play an important role in the plasma's large-scale evolution as it expands from the corona and through the heliosphere.  Many statistical analyses have found that the temperature ratio of the two most abundant ions, protons (ionized hydrogen) and alpha-particles (fully ionized helium), is heavily influenced by collisional thermalization.  This ongoing study expands on this work by including oxygen +6, which, during select periods (of cold, slow, dense plasma), the Wind spacecraft's Faraday Cups can measure at high cadences.  Using well-established models of collisional relaxation, the in-situ measurements at 1 AU can be used to estimate ion conditions earlier in the plasma's expansion history.  Assessing the physicality of these predictions can indicate to what degree preferential heating and/or heating beyond the corona affected the plasma's evolution.

 

PDF File: 

Telecon Recording: 

 

September 22, 2016

Title: A Data-Driven Analytic Model for Proton Acceleration by Large-Scale Solar Coronal Shocks

Presenter: Kamen Kosarev (Smithsonian Astrophysical Observatory, USA; e-mail: kkozarev@cfa.harvard.edu)

Abstract:

We have recently studied the development of an eruptive filament-driven, large-scale off-limb coronal bright front (OCBF) in the low solar corona, using remote observations from the Solar Dynamics Observatory’s Advanced Imaging Assembly EUV telescopes. In that study, we obtained high-temporal resolution estimates of the OCBF parameters regulating the efficiency of charged particle acceleration within the theoretical framework of diffusive shock acceleration (DSA). These parameters include the time-dependent front size, speed, and strength, as well as the upstream coronal magnetic field orientations with respect to the front’s surface normal direction. Here we present an analytical particle acceleration model, specifically developed to incorporate the coronal shock/compressive front properties described above, derived from remote observations. We verify the model’s performance through a grid of idealized case runs using input parameters typical for large-scale coronal shocks, and demonstrate that the results approach the expected DSA steady-state behavior. We then apply the model to the event of 2011 May 11 using the OCBF time-dependent parameters derived by Kozarev et al. We find that the compressive front likely produced energetic particles as low as 1.3 solar radii in the corona. Comparing the modeled and observed fluences near Earth, we also find that the bulk of the acceleration during this event must have occurred above 1.5 solar radii. With this study we have taken a first step in using direct observations of shocks and compressions in the innermost corona to predict the onsets and intensities of solar energetic particle events.

 

Powerpoint File: SPP_TheoryGroup_KamenKozarev_09222016.pptx

August 18, 2016

Title: What is behind the maltese cross?

Presenter: Andrea Verdini (Observatoire de Paris, France; e-mail: andrea.verdini@obspm.fr)

Abstract:

The spectral anisotropy of turbulent structures has been measured in the solar wind since 1990, relying on a gyrotropy assumption around the mean magnetic field axis. However, early and recent works (Dong et al. 2014) indicate that this hypothesis might be partially wrong. In this seminar we discuss the questions  (i) Are the usual interpretation of the measurements at 1 AU (the so-called maltese cross) in term of a sum of slab and 2D turbulence correct? (ii) what information is really contained in the maltese cross?

To this end,  direct numerical simulations of the MHD equations including the transverse stretching exerted by the mean solar wind flow (EBM equations) are carried out and the genuine 3D anisotropy of turbulence as well as that one resulting from the assumption of axisymmetry around the mean field, B0 are studied and compared. The relevance to observations by SPP will also be discussed.

 

PDF File: maltese.pdf

Telecon Recording: SPP_TheoryGroup_AndreaVerdini_08182016.arf

 



Page Last Modified: November 21, 2018