List of forthcoming and past seminars:
Schedule 
Speaker  Title and Abstract 
December 16, 2019
10:0012:00 Sala Pléyades 
Prof Jeff Khun IfA, Hawaii  Title: The cold Helium Corona and new ideas for sensitive coronal IR magnetometry 
October 16, 2019 11:0012:00 Sala Pléyades 
Supriya Hebbur Dayananda Instituto de Astrofísica de Canarias 
Title: A new method to probe the solar corona

September 23, 2019
12:0013:00 Sala GTC 
Alejandro Alvarez Laguna Laboratoire de physique des plasmas/Centre de Mathématiques Appliquées, Ecole Polytechnique, Paris (France) 
Title: Mathematical and numerical modeling of solar and laboratory plasmas in chemical and thermal nonequilibrium based on multifluid and multicomponent models
Abstract: In the recent years, simulation tools solving the multifluid plasma equations have been proposed for studying different phenomena in astrophysical and laboratory plasmas. The multifluid equations consider mass, momentum, and energy conservation laws for each species within plasma, that interact among each other by means of elastic and inelastic collisions.They are able to represent nonequilibrium dynamics beyond standard singlefluid magnetohydrodynamics (MHD) models. The transport fluxes of the multifluid equations depend on collisional data and are derived from the kinetic theory by means of multiscale expansion such as the ChapmanEnskog perturbative solution. In this talk, we will present the derivation of the multicomponent/multifluid equations from kinetic theory and the consistent computation of transport properties by means of a spectral Galerkin method using the LaguerreSonine polynomial approximation. The numerical discretization of the nonequilibrium plasma equations is difficult to solve as it contains very dispare time scales. We discuss advanced numerical techniques for stiff systems of equations such as fully implicit, wellbalanced, operator splitting or asymptoticpreserving schemes. These techniques allow for more efficient numerical algorithms, while preserving the stability and accuracy of the solution. The proposed numerical methods are implemented in massively parallel codes for GPU/CPU architectures and adaptive mesh refinement. We present results of multifluid models for the study of chromospheric magnetic reconnection, the propagation of magnetosonic waves in the low sun atmosphere, and laboratory plasmas. 
September 19, 2019 11:0012:00 Sala Pléyades 
Vyacheslav (Slava) Lukin
Program Director, Plasma Physics
Division of Physics, National Science Foundation

Title: Magnetic Reconnection in the Lower Solar Atmosphere
Abstract: I will describe recent efforts to selfconsistently model magnetic reconnection processes in weakly ionized plasmas, with a focus on the solar chromosphere. The solar chromosphere is a complex and dynamic boundary layer of the solar atmosphere where interdependence of the magnetic field evolution, radiation transport, plasma reactivity, and dissipation mechanisms make it a particularly difficult system to model and understand. Past studies have focused on the microphysics of multifluid magnetic reconnection at magnetic nulls[1]. Here, the previous work is extended by considering a range of spatial scales and plasma β values in a configuration with component magnetic reconnection[2]. We show that in all cases the nonequilibrium reactivity of a weakly ionized plasma is important for determining the properties of a reconnection region and explore current sheet stability to secondary instabilities. [1] Leake, et al, ApJ 760 (2012); Leake, et al, PoP 20 (2013); Murphy & Lukin, ApJ 805 (2015).
[2] L. Ni, et al, ApJ 852 (2018); L. Ni, et al, PoP 25 (2018).

May 20th, 2019 11:0012:00 Aula 
Momchil E. Molnar
George Ellery Hale Graduate Fellow CU Boulder/National Solar Observatory 
Title: PROBING THE TURBULENT QUIET CHROMOSPHERE WITH ALMA AND IBIS Abstract: We present observations of the solar chromosphere observed simultaneously with the Atacama Large Millimeter Array (ALMA) and the Interferometric BIdimensional Spectropolarimeter (IBIS) at the Dunn Solar Telescope (DST). This dataset combines spectrally resolved observations in the optical and near infrared with the high cadence (∼2 seconds) images in the millimeter continuum. We compare the different diagnostics available in multiple lines. A key result from our study is the demonstration that certain NLTE chromospheric diagnostics are well correlated to the LTE temperature measurements from ALMA. Spectral synthesis with RH and 1D model atmospheres provides insight into the source of these correlations, but also highlights the need for caution when interpreting the ALMA observations. 
March 20th, 2019 11:0012:00 Sala Pléyades 
Dr Pere L. Palle Dra Marian Martínez González IAC 
Title: SolarSONG, present and future
Abstract: SolarSONG is a solar infrastructure that allow Sunasastar observations using the spectroscopic capabilities of the HertzsprungSONG telescope. It was conceived for helioseismology with the aim to increase our knowledge on the solar interior. Nowadays, this initiative is fully operational and is providing interesting scientific results. In this talk, we will summarise the concept of SolarSONG, we will present the latest results on global helioseismology, and we will present new future ideas to upgrade this instrument. 
March 6th, 2019 11:0012:00 Sala Pléyades 
Dr Valentín MartinezPillet
NSO 
DKIST status and SPRINGGBSON network 
November 7th, 2018 11:0012:00 Sala Pléyades 
Dr Hendrik C. Spruit
MaxPlanck Institut für Astrophysik,
Garching, Germany 
Title: Dynamo surprises Abstract: Numerical simulations of dynamos over the past 2 decades, as well as lab experiments, have turned up several most curious and unexpected phenomena. They are sufficiently severe to put our common intuition of astrophysical dynamos in disarray. The field is still in the process of making sense of these problems. I'll try to summarize them from a broader perspective, with examples from accretion disks, the solar " 
October 23, 2018 11:0012:00 Sala Pléyades 
Piyush Agrawal
Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder 
Title: Transport of Internetwork Magnetic Flux Elements in the Solar Photosphere Abstract: The motions of smallscale magnetic flux elements in the solar photosphere can provide some measure of the Lagrangian properties of the convective flow. Measurements of these motions have been critical in estimating the turbulent diffusion coefficient in fluxtransport dynamo models and in determining the Alfvén wave excitation spectrum for coronal heating models. We examine the motions of internetwork flux elements in Hinode/ Narrowband Filter Imager magnetograms and study the scaling of their mean squared displacement and the shape of their displacement probability distribution as a function of time. We find that the mean squared displacement scales superdiffusively with a slope of about 1.48. Superdiffusive scaling has been observed in other studies for temporal increments as small as 5 s, increments over which ballistic scaling would be expected. Using high cadence MURaM simulations, we show that the observed superdiffusive scaling at short increments is a consequence of random changes in barycenter positions due to flux evolution. We also find that for long temporal increments, beyond granular lifetimes, the observed displacement distribution deviates from that expected for a diffusive process, evolving from Rayleigh to Gaussian. This change in distribution can be modeled analytically by accounting for supergranular advection along with granular motions. These results complicate the interpretation of magnetic element motions as strictly advective or diffusive on short and long timescales and suggest that measurements of magnetic element motions must be used with caution in turbulent diffusion or wave excitation models. We propose that passive tracer motions in measured photospheric flows may yield more robust transport statistics. NASA ADS link 
October 19, 2018
11:0012:00 
Travis Metcalfe

Title: The Limitations of Gyrochronology for Old Field Stars

October 17, 2018
11:0012:00
Sala Pléyades

Piyush Agrawal
Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder 
Title: A preliminary report on inverting for gas pressure using SIR inversion code Abstract: Here i will talk about our preliminary results on inverting for gas pressure in the solar photosphere using SIR inversion code and the problems we have faced so far in trying to do so. We are trying to synthesize and invert the temperature (T) and electronic pressure (Pe) of a smooth Muram simulation, as SIR computes gas pressure (Pg) from these thermodynamic parameters. To idealize the problem, all other atmospheric parameters (B, Vmic, Vz etc) are set to zero (not inverted) for now. Here, we try to answer the following questions :

October 10, 2018
11:3012:00 Sala Ómega 
Dr. Sarah A. Jaeggli Daniel K. Inouye Solar Telescope Scientist, Assistant Astronomer 
Title: Status update on DLNIRSP Abstract: The Diffraction Limited NearInfrared Spectropolarimeter is an innovative new integral field spectrograph that is part of the first generation of instruments for the National Solar Observatory’s Daniel K. Inouye Solar Telescope on Haleakala, Maui. DLNIRSP is currently being integrated and tested at the University of Hawaii’s Institute for Astronomy and will be delivered to the telescope in 2019. I will give an overview of the instrument and discuss some the the challenges we’re facing. 
October 10, 2018 11:0011:30 Sala Ómega 
Lucas Tarr George Mason University & U.Hawaii IfA, USA 
Title: MHD simulations of stratified atmospheres containing magnetic null points
Abstract: In this talk I will discuss my recent simulations using the resistive MHD code LARE (Arber et al 2001), in which I inject compressive MHD wavepackets into a stratified atmosphere that contains a magnetic null point. The 2.5D simulation represents a slice through a small ephemeral region or area of strong plage. The strong gradients in field strength and connectivity related to the presence of the null produce substantially different dynamics compared to the more slowly varying fields typically used in simple sunspot models. The wavenull interaction collapses the null into a current sheet and generates a set of outward propagating (from the null) slow mode shocks confined to field lines near each separatrix. A combination of oscillatory reconnection and shock dissipation ultimately raise the plasma's internal energy at the null and along each separatrix by 2550% above the background. The resulting pressure gradients must be balanced by Lorentz forces, so that the final state has contact discontinuities along each separatrix and a persistent current at the null. 

