15 research outputs found
Implications of Different Solar Photospheric Flux-Transport Models for Global Coronal and Heliospheric Modeling
The concept of surface-flux transport (SFT) is commonly used in evolving
models of the large-scale solar surface magnetic field. These photospheric
models are used to determine the large-scale structure of the overlying coronal
magnetic field, as well as to make predictions about the fields and flows that
structure the solar wind. We compare predictions from two SFT models for the
solar wind, open magnetic field footpoints, and the presence of coronal
magnetic null points throughout various phases of a solar activity cycle,
focusing on the months of April in even-numbered years between 2012 and 2020,
inclusive. We find that there is a solar cycle dependence to each of the
metrics considered, but there is not a single phase of the cycle in which all
the metrics indicate good agreement between the models. The metrics also reveal
large, transient differences between the models when a new active region is
rotating into the assimilation window. The evolution of the surface flux is
governed by a combination of large scale flows and comparatively small scale
motions associated with convection. Because the latter flows evolve rapidly,
there are intervals during which their impact on the surface flux can only be
characterized in a statistical sense, thus their impact is modeled by
introducing a random evolution that reproduces the typical surface flux
evolution. We find that the differences between the predicted properties are
dominated by differences in the model assumptions and implementation, rather
than selection of a particular realization of the random evolution.Comment: Accepted for publication in The Astrophysical Journa
On the Origin of the sudden Heliospheric Open Magnetic Flux Enhancement during the 2014 Pole Reversal
Coronal holes are recognized as the primary sources of heliospheric open
magnetic flux (OMF). However, a noticeable gap exists between in-situ measured
OMF and that derived from remote sensing observations of the Sun. In this
study, we investigate the OMF evolution and its connection to solar structures
throughout 2014, with special emphasis on the period from September to October,
where a sudden and significant OMF increase was reported. By deriving the OMF
evolution at 1au, modeling it at the source surface, and analyzing solar
photospheric data, we provide a comprehensive analysis of the observed
phenomenon. First, we establish a strong correlation between the OMF increase
and the solar magnetic field derived from a Potential Field Source Surface
(PFSS) model (). Moreover, we find a good
correlation between the OMF and the open flux derived from solar coronal holes
(), although the coronal holes only contain
of the Sun's total open flux. However, we note that while the OMF
evolution correlates with coronal hole open flux, there is no correlation with
the coronal hole area evolution (). The temporal
increase in OMF correlates with the vanishing remnant magnetic field at the
southern pole, caused by poleward flux circulations from the decay of numerous
active regions months earlier. Additionally, our analysis suggests a potential
link between the OMF enhancement and the concurrent emergence of the largest
active region in solar cycle 24. In conclusion, our study provides insights
into the strong increase in OMF observed during September to October 2014.Comment: accepted in Ap
Simulating Solar Maximum Conditions Using the Alfvén Wave Solar Atmosphere Model (AWSoM)
To simulate solar coronal mass ejections (CMEs) and predict their time of arrival and geomagnetic impact, it is important to accurately model the background solar wind conditions in which CMEs propagate. We use the Alfvén Wave Solar atmosphere Model (AWSoM) within the the Space Weather Modeling Framework to simulate solar maximum conditions during two Carrington rotations and produce solar wind background conditions comparable to the observations. We describe the inner boundary conditions for AWSoM using the ADAPT global magnetic maps and validate the simulated results with EUV observations in the low corona and measured plasma parameters at L1 as well as at the position of the Solar Terrestrial Relations Observatory spacecraft. This work complements our prior AWSoM validation study for solar minimum conditions and shows that during periods of higher magnetic activity, AWSoM can reproduce the solar plasma conditions (using properly adjusted photospheric Poynting flux) suitable for providing proper initial conditions for launching CMEs.Fil: Sachdeva, Nishtha. University of Michigan; Estados UnidosFil: Tóth, Gábor. University of Michigan; Estados UnidosFil: Manchester, Ward B.. University of Michigan; Estados UnidosFil: van der Holst, Bart. University of Michigan; Estados UnidosFil: Huang, Zhenguang. University of Michigan; Estados UnidosFil: Sokolov, Igor V.. University of Michigan; Estados UnidosFil: Zhao, Lulu. University of Michigan; Estados UnidosFil: Al Shidi, Qusai. University of Michigan; Estados UnidosFil: Chen, Yuxi. University of Michigan; Estados UnidosFil: Gombosi, Tamas I.. University of Michigan; Estados UnidosFil: Henney, Carl J.. University of Michigan; Estados UnidosFil: Lloveras, Diego Gustavo. Consejo Nacional de Investigaciónes CientÃficas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de AstronomÃa y FÃsica del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de AstronomÃa y FÃsica del Espacio; ArgentinaFil: Vasquez, Alberto Marcos. Consejo Nacional de Investigaciónes CientÃficas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de AstronomÃa y FÃsica del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de AstronomÃa y FÃsica del Espacio; Argentin
Approach to Integrate Global-Sun Models of Magnetic Flux Emergence and Transport for Space Weather Studies
The Sun lies at the center of space weather and is the source of its variability. The primary input to coronal and solar wind models is the activity of the magnetic field in the solar photosphere. Recent advancements in solar observations and numerical simulations provide a basis for developing physics-based models for the dynamics of the magnetic field from the deep convection zone of the Sun to the corona with the goal of providing robust near real-time boundary conditions at the base of space weather forecast models. The goal is to develop new strategic capabilities that enable characterization and prediction of the magnetic field structure and flow dynamics of the Sun by assimilating data from helioseismology and magnetic field observations into physics-based realistic magnetohydrodynamics (MHD) simulations. The integration of first-principle modeling of solar magnetism and flow dynamics with real-time observational data via advanced data assimilation methods is a new, transformative step in space weather research and prediction. This approach will substantially enhance an existing model of magnetic flux distribution and transport developed by the Air Force Research Lab. The development plan is to use the Space Weather Modeling Framework (SWMF) to develop Coupled Models for Emerging flux Simulations (CMES) that couples three existing models: (1) an MHD formulation with the anelastic approximation to simulate the deep convection zone (FSAM code), (2) an MHD formulation with full compressible Navier-Stokes equations and a detailed description of radiative transfer and thermodynamics to simulate near-surface convection and the photosphere (Stagger code), and (3) an MHD formulation with full, compressible Navier-Stokes equations and an approximate description of radiative transfer and heating to simulate the corona (Module in BATS-R-US). CMES will enable simulations of the emergence of magnetic structures from the deep convection zone to the corona. Finally, a plan will be summarized on the development of a Flux Emergence Prediction Tool (FEPT) in which helioseismology-derived data and vector magnetic maps are assimilated into CMES that couples the dynamics of magnetic flux from the deep interior to the corona
New insights into the first two PSP solar encounters enabled by modeling analysis with ADAPT-WSA
Parker Solar Probes's (PSP)'s unique orbital path allows us to observe the
solar wind closer to the Sun than ever before. Essential to advancing our
knowledge of solar wind and energetic particle formation is identifying the
sources of PSP observations. We report on results for the first two PSP solar
encounters derived using the Wang-Sheeley-Arge (WSA) model driven by Air Force
Data Assimilative Photospheric Flux Transport (ADAPT) model maps. We derive the
coronal magnetic field and the 1 Rs source regions of the PSP-observed solar
wind. We validate our results with the solar wind speed and magnetic polarity
observed at PSP. When modeling results are very reliable, we derive time series
of model-derived spacecraft separation from the heliospheric current sheet,
magnetic expansion factor, coronal hole boundary distance, and photospheric
field strength along the field lines estimated to be connected to the
spacecraft. We present new results for Encounter 1, which show time evolution
of the far-side mid-latitude coronal hole that PSP co-rotates with. We discuss
how this evolution coincides with solar wind speed, density, and temperature
observed at the spacecraft. During Encounter 2, a new active region emerges on
the far-side, making it difficult to model. We show that ADAPT-WSA output
agrees well with PSP observations once this active region rotates onto the
near-side, allowing us to reliably estimate the solar wind sources
retrospectively for most of the encounter. We close with ways in which coronal
modeling enables scientific interpretation of these encounters that would
otherwise not have been possible.Comment: 25 pages, 13 figures, accepted by Ap
A New Method Linking the Solar Wind Speed to the Coronal Magnetic Field
The release and acceleration of the solar wind is still an outstanding question. There are several aspects related to this phenomenon that still need to be investigated, and one of these is the identification of the region within the inner corona where the larger fraction of acceleration occurs. To address this matter, it is necessary to have reliable measurements of the solar wind speed between 1 and 10 solar radii ( R _⊙ ). Moreover, in order to describe the coronal plasma behavior, it is important to consider its interaction with the magnetic field. Within this context, our intent is to investigate a method to combine measurements of the solar wind with the extrapolated magnetic field in the corona to derive how the solar wind velocity evolves along the magnetic field lines, aiming at better understanding the sources, origins, and acceleration of the solar wind. To this purpose, we used outflow speed measurements of the coronal plasma derived by applying the Doppler dimming technique, as well as the global magnetic field configuration derived from the measured photospheric magnetic field by using the Wang–Sheeley–Arge model. These two sets of data are then combined for heliocentric distances between 2.6 and 5 R _⊙ . This paper presents the proposed method and the results obtained over two different Carrington rotations (CR 1923 and CR 1924), demonstrating the applicability of the method and the capability to link measured solar wind velocity to the extrapolated coronal magnetic field in order to derive the velocity profile
A New Technique for the Photospheric Driving of Non-Potential Solar Coronal Magnetic Field Simulations
In this paper, we develop a new technique for driving global non-potential simulations of the Sun's coronal magnetic field solely from sequences of radial magnetic maps of the solar photosphere. A primary challenge to driving such global simulations is that the required horizontal electric field cannot be uniquely determined from such maps. We show that an "inductive" electric field solution similar to that used by previous authors successfully reproduces specific features of the coronal field evolution in both single and multiple bipole simulations. For these cases, the true solution is known because the electric field was generated from a surface flux-transport model. The match for these cases is further improved by including the non-inductive electric field contribution from surface differential rotation. Then, using this reconstruction method for the electric field, we show that a coronal non-potential simulation can be successfully driven from a sequence of ADAPT maps of the photospheric radial field, without including additional physical observations which are not routinely available