Interface Region Imaging Spectrograph (IRIS) Observations of the Fractal Dimension in the Solar Atmosphere 

Markus J. Aschwanden Submitted: 20220721 10:31
While previous work explored the fractality and selforganized criticality
(SOC) of flares and nanoflares in wavelengths emitted in the solar corona (such
as in hard Xrays, soft Xrays, and EUV wavelenghts), we focus here on
impulsive phenomena in the photosphere and transition region, as observed with the
Interface Region Imaging Spectrograph (IRIS) in the temperature range of
T_{e} ≈ 10^{4}10^{6} K. We find the following fractal dimensions (in increasing
order): D_A=1.21 ± 0.07 for photospheric granulation,
D_A=1.29 ± 0.15 for plages in the transition region,
D_A=1.54 ± 0.16 for sunspots in the transition region,
D_A=1.59 ± 0.08 for magnetograms in active regions,
D_A=1.56 ± 0.08 for EUV nanoflares,
D_A=1.76 ± 0.14 for large solar flares, and up to
D_A=1.89 ± 0.05 for the largest Xclass flares.
We interpret low values of the fractal dimension
(1.0 ≈ D_A ≈ 1.5)
in terms of sparse curvilinear flow patterns, while high values
of the fractal dimension (1.5 ≈ D_A ≈ 2.0)
indicate near spacefilling transport processes, such as
chromospheric evaporation. Phenomena in the solar transition
region appear to be consistent with SOC models, based on
their size distributions of fractal areas A and (radiative) energies E,
which show power law slopes of α _A^{obs}=2.51 ± 0.21
(with α _A^{theo}=2.33 predicted), and α _E^{obs}=2.03 ± 0.18
(with α _E^{theo}=1.80 predicted).
Authors: Markus J. Aschwanden and Nived Vilangot Nhalil
Projects: None

Publication Status: Frontiers in Astronomy and Space Sciences (subm. 2022 Jul 21)
Last Modified: 20220727 10:13



Reconciling Power Law Slopes in Solar Flare and Nanoflare Size Distributions 

Markus J. Aschwanden Submitted: 20220425 11:40
We unify the power laws of size distributions of solar flare
and nanoflare energies. We present three models that predict the
power law slopes α _E of flare energies
defined in terms of the 2D and 3D
fractal dimensions (D_A, D_V): (i) The spatiotemporal
standard SOC model, defined by the power law slope
α _{E1}=1+2/(D_V+2)=(13/9)≈ 1.44;
(ii) the 2D thermal energy model,
α _{E2}=1+2/D_A=(7/3)≈ 2.33, and
(iii) the 3D thermal energy model,
α _{E3}=1+2/D_V=(9/5)≈ 1.80.
The theoretical predictions of energies
are consistent with the observational values
of these three groups, i.e.,
α _{E1}=1.47 ± 0.07;
α _{E2}=2.38 ± 0.09, and
α _{E3}=1.80 ± 0.18.
These results corroborate that the energy of nanoflares
does not diverge at small energies, since ( α _{E1}<2)
and ( α _{E3}<2), except for the unphyiscal 2D model
( α _{E2}>2). This conclusion adds an additional
argument against the scenario of coronal heating by nanoflares.
Authors: Markus J. Aschwanden
Projects: SDOAIA

Publication Status: ApJL (submitted 2022 April 25)
Last Modified: 20220426 16:10



Global Energetics in Solar Flares. XIII. The Neupert Effect and Acceleration of Coronal Mass Ejections 

Markus J. Aschwanden Submitted: 20211208 13:28
Our major aim is a heighttime model r(t) of the propagation of
Coronal Mass Ejections (CMEs), where the lower corona
is selfconsistently connected to the heliospheric path.
We accomplish this task by using the Neupert effect to derive
the peak time, duration,
and rate of the CME acceleration phase, as obtained
from the time derivative of the soft Xray (SXR)
light curve. This novel approach offers the advantage
to obtain the kinematics of the CME heighttime profile r(t),
the CME velocity profile v(t)=dr(t)/dt, and the CME
acceleration profile a(t)=dv(t)/dot from Geostationary Orbiting
Earth Satellite (GOES) and whitelight data, without the need
ofl hard Xray (HXR)} data. We apply this technique
to a data set of 576 (GOES X and Mclass) flare events observed
with GOES and the Large Angle Solar Coronagraph (LASCO).
Our analysis yields acceleration rates in the range of
a_A = 0.113 km s^{2}, acceleration durations of
tau_A = 1.245 min, and acceleration distances in the
range of d_A = 31063 Mm, with a median of d_A=39 Mm,
which corresponds to the hydrostatic scale height of
a corona with a temperature of T_{e} ~ 0.8 MK. The results are
consistent with standard flare/CME models that predict
magnetic reconnection and synchronized (primary) acceleration
of CMEs in the low corona (at a height of ~0.1 R_{☉},
while secondary (weaker) acceleration may occur further out at
heliospheric distances.
Authors: Markus J. Aschwanden
Projects: SoHOLASCO

Publication Status: submitted 2021 Dec 8
Last Modified: 20211210 15:08



The Solar Memory From Hours to Decades 

Markus J. Aschwanden Submitted: 20210729 11:43
Waiting time distributions allow us to distinguish at least
three different types of dynamical systems, such as (i) linear
random processes (with no memory); (ii) nonlinear, avalanchetype,
nonstationary Poisson processes (with memory during the exponential
growth of the avalanche rise time); and (iii) chaotic systems in the state of
a nonlinear limit cycle (with memory during the oscillatory phase).
We describe the temporal evolution of the flare rate \lambda(t) ∝ t^p
with a polynomial function, which allows us to distinguish linear
(p ≈ 1) from nonlinear (p ≳ 2) events.
The power law slopes α of observed waiting times (with full solar
cycle coverage) cover a range of α =2.12.4, which agrees
well with our prediction of α = 2.0+1/p = 2.32.5.
The memory time can also be defined with the time evolution of the
logistic equation, for which we find a relationship between the
nonlinear growth time τ_G = τ_{rise}/(4p) and
the nonlinearity index p. We find a nonlinear evolution for most
events, in particular for
the clustering of solar flares (p=2.2±0.1),
partially occulted flare events (p=1.8±0.2), and
the solar dynamo (p=2.8±0.5).
The Sun exhibits memory on time scales of
≈2 hours to 3 days (for solar flare clustering),
6 to 23 days (for partially occulted flare events), and
1.5 month to 1 year (for the rise time of the solar dynamo).
Authors: Aschwanden, M.J. and Johnson, J.R.
Projects: None

Publication Status: submitted
Last Modified: 20210801 20:58



Correlation of the sunspot number and the waiting time distribution of solar flares, coronal mass ejections, and solar wind switchback events observed with the Parker Solar Probe 

Markus J. Aschwanden Submitted: 20210611 12:47
Waitingtime distributions of solar flares and coronal mass ejections (CMEs) exhibit powerlawlike distribution
functions with slopes in the range of ατ ≈ 1.4–3.2, as observed in annual data sets during four solar cycles
(1974–2012). We find a close correlation between the waitingtime powerlaw slope ατ and the sunspot number
(SN), i.e., ατ = 1.38 + 0.01 × SN. The waitingtime distribution can be fitted with a Paretotype function of the at
form N(τ) = N0 (t0 + t) , where the offset τ0 depends on the instrumental sensitivity, the detection threshold of events, and pulse pileup effects. The timedependent powerlaw slope ατ(t) of waitingtime distributions depends only on the global solar magnetic flux (quantified by the sunspot number) or flaring rate, which is not predicted by selforganized criticality or magnetohydrodynamic turbulence models. Powerlaw slopes of ατ ≈ 1.2–1.6 were also found in solar wind switchback events, as observed with the Parker Solar Probe during the solar minimum, while steeper slopes are predicted during the solar maximum. We find that the annual variability of switchback events in the heliospheric solar wind and solar flare and CME rates (originating in the photosphere and lower corona) are highly correlated.
Authors: Aschwanden, M.J. and Dudok de Wit, T.
Projects: PSPWISPR

Publication Status: Aschwanden,M.J. and Dudok de Wit,T. 2021, ApJ 912:94
Last Modified: 20210612 00:56



Finite systemsize effectrs in selforganizing criticality systems 

Markus J. Aschwanden Submitted: 20210611 12:37
We explore upper limits for the largest avalanches or catastrophes in nonlinear energy dissipation systems governed by selforganized criticality. We generalize the idealized “straight” powerlaw size distribution and Pareto distribution functions in order to accommodate incomplete sampling, limited instrumental sensitivity, finite systemsize effects, and “Black Swan” and “Dragon King” extreme events. Our findings are as follows. (i) Solar flares show no finite systemsize limits up to L~200 Mm, but solar flare durations reveal an upper flare duration limit of hr. (ii) Stellar flares observed with Kepler exhibit inertial ranges of E ≈ 10^{3}4–10^{37} erg, finite system size ranges of E ≈ 10^{3}7–10^{38} erg, and extreme events at E ≈ (1–5) × 10^{38} erg. (iii) The maximum flare energies of different spectral type stars (M, K, G, F, A, giants) reveal a positive correlation with the stellar radius, which indicates a finite systemsize limit imposed by the stellar surface area. Fitting our finite systemsize models to terrestrial data sets (earthquakes, wildfires, city sizes, blackouts, terrorism, words, surnames, web links) yields evidence (in half of the cases) for finite systemsize limits and extreme events, which can be modeled with dual powerlaw size distributions.
Authors: Aschwanden, M.J.
Projects: SDOAIA

Publication Status: Aschwanden,M.J. 2021, ApJ 909:69
Last Modified: 20210612 00:56



Global energetics of solar flares. XII. Energy scaling laws 

Markus J. Aschwanden Submitted: 20210611 12:31
In this study we test 18 versions of 5 fundamental energy scaling laws that operate in large solar flares. We express scaling laws in terms of the magnetic potential field energy Ep, the mean potential field strength Bp, the free energy Efree, the dissipated magnetic flare energy Ediss, the magnetic length scale L, the thermal length scale Lth, the mean helically twisted flux tube radius R, the sunspot radius r, the emission measureweighted flare temperature Te, the electron density ne, and the total emission measure EM, measured from a data set of 173 GOES M and Xclass flare events. The 5 categories of physical scaling laws include (i) a scaling law of the potentialfield energy, (ii) a scaling law for helical twisting, (iii) a scaling law for Petschektype magnetic reconnection, (iv) the Rosner TuckerVaiana scaling law, and (v) the ShibataYokoyama scaling law. We test the selfconsistency of these theoretical scaling laws with observed parameters by requiring two criteria: a crosscorrleation coefficient of CCC>0.5 between the theoretically predicted scaling laws and observed values, and a linear regression fit with a slope of α ≈ 1 within one standard deviation σ. These two criteria enable us (i) to corroborate some existing (or modified) scaling laws, (ii) to reject other scaling laws that are not consistent with the observations, (iii) to probe the dimensionality of flare geometries, and (iv) to predict various energy parameters based on tested scaling laws.
Authors: Aschwanden, M.J.
Projects: GOES Xrays

Publication Status: Aschwanden,M.J. 2020, ApJ 903:23
Last Modified: 20210612 00:57



Global energetics of solar flares. XI. Flare magnitude predictions of the GOES class 

Markus J. Aschwanden Submitted: 20210611 12:25
In this study we determine scaling relationships of observed solar flares that can be used to predict
upper limits of the GOESclass magnitude of solar flares. The flare prediction scheme is based on the
scaling of the slowlyvarying potential energy Ep(t), which is extrapolated in time over an interval
of ∆t ≤ 24 hrs. The observed scaling of the dissipated energy Ediss scales with the potential field
energy as E ∝ E1.32. In addition, the observed scaling relationship of the flare volume, V ∝ E1.17, diss p diss
the multithermal energy, Eth ∝ V 0.76, the flare emission measure EM ∝ E0.79, the EMweighted th
temperature Tw, and the GOES flux, F8(t) ∝ Ep(t)0.92, allows us then to predict an upper limit of the GOESclass flare magnitude in the extrapolated time window. We find a good correlation (CCC≈ 0.7) between the observed and predicted GOESclass flare magnitudes (in 172 X and Mclass events). This is the first algorithm that employs observed scaling laws of physical flare parameters to predict GOES flux upper limits, an important capability that complements previous flare prediction methods based on machinelearning algorithms used in space weather forecasting.
Authors: Aschwanden, M.J.
Projects: GOES Xrays

Publication Status: Aschwanden,M.J. 2020, ApJ 897:16
Last Modified: 20210612 00:57



Global Energetics of Solar Flares, X. Petschek Reconnection Rate and Alfvén Mach Number of Magnetic Reconnection Outflows 

Markus J. Aschwanden Submitted: 20200507 13:48
We investigate physical scaling laws for magnetic energy dissipation
in solar flares, in the framework of the SweetParker model
and the Petschek model. We find that the total dissipated magnetic energy
E_{diss} in a flare depends on the mean magnetic field component
B_{f} associated with the free energy E_{f}, the length scale L of the
magnetic area, the hydrostatic density scale height lambda of
the solar corona, the Alfvén Mach number M_A=v_1/v_{A} (the ratio
of the inflow speed v_{1} to the Alfvénic outflow speed v_{A}), and the
flare duration au_f, i.e., E_{diss} = (1/4π) B_f^2 L lambda
v_{A} M_A au_f, where the Alfvén speed depends on the nonpotential
field strength B_{np} and the mean electron density n_{e} in the
reconnection outflow. Using MDI/SDO and AIA/SDO observations and
3D magnetic field solutions obtained with the verticalcurrent
approximation nonlinear forcefree field code (VCANLFFF) we measure
all physical parameters necessary to test scaling laws, which
represents a new method to measure Alfvén Mach numbers M_{A},
the reconnection rate, and the total free energy dissipated
in solar flares.
Authors: Markus J. Aschwanden
Projects: SDOHMI

Publication Status: ApJ (in press)
Last Modified: 20200511 15:28



Global Energetics of Solar Flares. IX. Refined Magnetic Modeling 

Markus J. Aschwanden Submitted: 20190918 13:37
A more accurate analytical
solution of the verticalcurrent approximation nonlinear forcefree
field (VCA3NLFFF) model is presented that includes besides the
radial (B_{r}) and the azimuthal
(B_{ϕ} ) magnetic field components, a
poloidal component (B_{θ} ≠ 0) also. This new
analytical solution is of secondorder accuracy in the
divergencefreeness condition, and of thirdorder accuracy in the
forcefreeness condition. We reanalyze the sample of 173 GOES M and
Xclass flares observed with the Atmospheric Imaging Assembly
(AIA) and Helioseismic and Magnetic Imager (HMI) onboard
the Solar Dynamics Observatory (SDO). The new code reproduces
helically twisted loops with a low winding number below the kink
instability consistently, avoiding unstable, highlytwisted structures
of the GoldHoyle flux rope type. The magnetic energies agree within
E_{VCA3} / E_{W} = 0.99±0.21 with the Wiegelmann
(WNLFFF) code. The time evolution of the magnetic field reveals
multiple, intermittent energy buildup and releases in most flares,
contradicting both the RosnerVaiana model (with gradual energy
storage in the corona) and the principle of time scale separation
(τ_{flare} ≪ τ_{storage}) postulated in
selforganized criticality models. The mean dissipated flare energy is
found to amount to 7%±3% of the potential energy, or 60%±26% of
the free energy, a result that can be used for predicting flare
magnitudes based on the potential field of active regions.
Authors: Markus J. Aschwanden
Projects: None

Publication Status: Aschwanden, M.J. 2019, ApJ 885:49
Last Modified: 20210612 00:57



Helical Twisting Number and Braiding Linkage Number of Solar Coronal Loops 

Markus J. Aschwanden Submitted: 20190227 08:49
Coronal loops in active regions are often characterized by
quasicircular and helically twisted (sigmoidal) geometries,
which are consistent with dipolar potential field models in
the former case, and with nonlinear forcefree field models
with vertical currents in the latter case. Alternatively,
Parkertype nanoflare models of the solar corona hypothesize
that a braiding mechanism operates between unresolved loop
strands, which is a more complex topological model. In this
study we use the verticalcurrent approximation of a nonpotential
magnetic field solution (that fulfills the divergencefree and
forcefree conditions) to characterize the number of helical
turns N_{twist} in twisted coronal loops. We measure the
helical twist in 15 active regions observed with AIA and HMI/SDO
and find a mean nonpotentiality angle (between the potential and
nonpotential field directions) of μ_{NP} = 15° ±
3°. The resulting mean rotational twist angle is
ϕ = 49° ± 11°, which corresponds to
N_{twist}=ϕ/360° = 0.14±0.03 turns with
respect to the untwisted potential field, with an absolute
upper limit of N_{twist} ≈ 0.5, which is far below the kink
instability limit of N_{twist} ≳ 1. The number of
twist turns N_{twist} corresponds to the Gauss linkage
number N_{link} in braiding topologies. We conclude that
any braided topology (with N_{link} ≥ 1) cannot explain
the observed stability of loops in a forcefree corona, nor
the observed low twist number. Parkertype nanoflaring can
thus occur in nonforcefree environments only, such as in the
chromosphere and transition region.
Authors: Markus J. Aschwanden
Projects: SDOHMI

Publication Status: ApJ (in press, February 27, 2019)
Last Modified: 20190227 12:12



Global Energetics of Solar Flares: VI. Refined Energetics of Coronal Mass Ejections 

Markus J. Aschwanden Submitted: 20170406 13:14
In this study we refine a CME model presented in an earlier study
on the global energetics of solar flares and associated CMEs, and
apply it to all (860) GOES M and Xclass flare events observed
during the first 7 years (20102016) of the Solar Dynamics Observatory
(SDO) mission, which doubles the statistics of the earlier study.
The model refinements include: (1) the CME geometry in terms of a
3D sphere undergoing selfsimilar adiabatic expansion; (2) the
inclusion of solar gravitational deceleration during the acceleration
and propagation of the CME, which discriminates eruptive and confined
CMEs; (4) a selfconsistent relationship between the CME centerofmass
motion detected during EUV dimming and the leadingedge motion observed
in whitelight coronagraphs; (5) the equipartition of the CME kinetic and
thermal energy; and (6) the RosnerTuckerVaiana (RTV) scaling law. The
refined CME model is entirely based on EUV dimming observations (using
AIA/SDO data) and complements the traditional whitelight scattering model
(using LASCO/SOHO data), and both models are independently capable to
determine fundamental CME parameters such as the CME mass, speed,
and energy. Comparing the two methods we find that: (1) LASCO is
less sensitive than AIA in detecting CMEs (in 24% of the cases);
(2) CME masses below m_cme ~ 10^{14} g are underestimated
by LASCO; (3) AIA and LASCO masses, speeds, and energy agree closely in the
statistical mean after elimination of outliers; (4) the CMEs parameters
of the speed v, emission measureweighted flare peak temperature T_{e},
and length scale L are consistent with the following scaling laws
(derived from first principles): v ~ T_{e}^1/2, v~ (m_cme)^1/4, and m_cme ~ L^{2}.
Authors: Markus J. Aschwanden
Projects:

Publication Status: 2017, ApJ 847:27 (19pp)
Last Modified: 20170925 09:09



SelfOrganizing Systems in Planetary Physics: Harmonic Resonances of Planet and Moon orbits 

Markus J. Aschwanden Submitted: 20170127 12:58
The geometric arrangement of planet and moon orbits into a
regularly spaced pattern of distances is the result of a
selforganizing system. The positive feedback mechanism
that operates a selforganizing system is accomplished by
harmonic orbit resonances, leading to longterm stable
planet and moon orbits in solar or stellar systems.
The distance pattern of planets was originally
described by the empirical TitiusBode law, and by a generalized
version with a constant geometric progression factor (corresponding
to logarithmic spacing).
We find that the orbital periods T_{i} and planet distances R_{i} from
the Sun are not consistent with
logarithmic spacing, but rather follow the quantized scaling
(R_{i+1}/R_{i}) = (T_{i+1}/T_{i})^{2/3} = (H_{i+1}/H_{i})^{2/3}, where
the harmonic ratios are given by five dominant resonances, namely
(H_{i+1} : H_{i}) = (3:2), (5:3), (2:1), (5:2), (3:1).
We find that the orbital period ratios tend to follow the quantized harmonic
ratios in increasing order. We apply this harmonic orbit resonance model
to the planets and moons in our solar system, and to the exoplanets
of 55 Cnc and HD 10180 planetary systems.
The model allows us a prediction of missing planets
in each planetary system, based on the quasiregular selforganizing
pattern of harmonic orbit resonance zones. We predict 7 (and 4) missing
exoplanets around the star 55 Cnc (and HD 10180).
The accuracy of the predicted planet and moon distances amounts
to a few percents. All analyzed systems are found to have
approx 10 resonant zones that can be occupied with planets
(or moons) in longterm stable orbits.
Authors: Markus J. Aschwanden
Projects:

Publication Status: 2018, New Astronomy 58C, 107123
Last Modified: 20170925 09:16



The Width Distribution of Loops and Strands in the Solar Corona  Are we Hitting Rock Bottom ? 

Markus J. Aschwanden Submitted: 20170104 16:32
In this study we analyze Atmospheric Imaging Assembly (AIA) and HiC
images in order to investigate absolute limits for the finest loop strands.
We develop a model of the occurrencesize distribution function of coronal
loop widths, characterized by a lower limit of widths w_{min}, a peak
width w_{p}, a peak occurrence number n_{p}, and a power law slope a.
Our data analysis includes automated tracing of curvilinear features with
the OCCULT2 code, automated sampling of the crosssectional widths of
coronal loops, and fitting of the theoretical size distribution to the
observed distribution. With MonteCarlo simulations and variable pixel
sizes Δ x we derive a first diagnostic criterion to discriminate
whether the loop widths are unresolved (w_{p}/Δ x ≈ 2.5±0.2),
or fully resolved (if w_{p}/Δ x ≳ 2.7). For images with
resolved loop widths we can apply a second diagnostic criterion that
predicts the lower limit of loop widths, w_{min} ≈ 3
(Δ x_{crit}0.37") Mm) as a function of the critical resolution
Δ x_{crit}. We find that the loop widths are marginally resolved
in AIA images, but are fully resolved in HiC images, where our model
predicts a lower limit of loop widths at w_{min} ≈ 100 km and
a most frequent (peak) value at w_{p} ≈ 300 km, in agreement with
recent results of Brooks et al. This result agrees with the statistics
of photospheric granulation sizes and thus supports coronal heating
mechanisms operating on the macroscopic scale of photospheric
magnetoconvection, rather than nanoflare heating models with unresolved
microscopic scales.
Authors: Markus J. Aschwanden and Hardi Peter
Projects: HiC

Publication Status: The Astrophysical Journal (2017 Jan 4, subm.)
Last Modified: 20170111 12:08



Global Energetics of Solar Flares and CMEs: V. Energy Closure 

Markus J. Aschwanden Submitted: 20170104 16:28
In this study we synthesize the results of four previous studies
on the global energetics of solar flares and associated coronal
mass ejections (CMEs), which include magnetic, thermal, nonthermal,
and CME energies in 399 solar M and Xclass flare events observed
during the first 3.5 years of the Solar Dynamics Observatory (SDO)
mission. Our findings are: (1) The sum of the mean nonthermal energy
of flareaccelerated particles (E_{nt}), the energy of direct heating
(E_{dir}), and the energy in coronal mass ejections (E_{CME}),
which are the primary energy dissipation processes in a flare, is found
to have a ratio of (E_{nt}+E_{dir}+
E_{CME})/E_{mag} = 0.87 ± 0.18,
compared with the dissipated magnetic free energy E_{mag}, which confirms
energy closure within the measurement uncertainties and corroborates the
magnetic origin of flares and CMEs;
(2) The energy partition of the dissipated magnetic free energy is:
0.51±0.17 in nonthermal energy of ≥ 6 keV electrons,
0.17±0.17 in nonthermal ≥ 1 MeV ions, 0.07±0.14 in
CMEs, and 0.07±0.17 in direct heating;
(3) The thermal energy is almost always less
than the nonthermal energy, which is consistent with the thicktarget model;
(4) The bolometric luminosity in whitelight flares is comparable with
the thermal energy in soft Xrays (SXR); (5) Solar Energetic Particle (SEP)
events carry a fraction ≈ 0.03 of the CME energy, which is consistent
with CMEdriven shock acceleration;
and (6) The warmtarget model predicts a lower limit of the
lowenergy cutoff at e_{c} ≈ 6 keV, based on the mean differential
emission measure (DEM) peak temperature of T_{e}=8.6 MK during flares.
This work represents the first statistical study that establishes energy
closure in solar flare/CME events.
Authors: Markus J. Aschwanden, Amir Caspi, Christina M.S. Cohen, Gordon Holman, Ju Jing, Matthieu, Kretzschmar, Eduard P. Kontar, James M. McTiernan, Richard A. Mewaldt, Aidan O'Flannagain, Ian G. Richardson, Daniel Ryan, Harry P. Warren, Yan Xu
Projects: SDOAIA

Publication Status: The Astrophysical Journal (accepted 2017 Jan 4, in press)
Last Modified: 20170111 12:08



Global Energetics of Solar Flares: IV. Coronal Mass Ejection Energetics 

Markus J. Aschwanden Submitted: 20160516 14:50
This study entails the fourth part of a global flare energetics project, in which the mass m_{cme}, kinetic energy E_{kin}, and the gravitational potential energy E_{grav} of coronal mass ejections (CMEs) is measured in 399 M and Xclass flare events observed during the first 3.5 yrs of the Solar Dynamics Observatory (SDO) mission, using a new method based on the EUV dimming effect. The EUV dimming is modeled in terms of a radial adiabatic expansion process, which is fitted to the observed evolution of the total emission measure of the CME source region. The model derives the evolution of the mean electron density, the emission measure, the bulk plasma expansion velocity, the mass, and the energy in the CME source region. The EUV dimming method is truly complementary to the Thomson scattering method in white light, which probes the CME evolution in the heliosphere at ≳2 R_{⊙}, while the EUV dimming method tracks the CME launch in the corona. We compare the CME parameters obtained in white light with the LASCO/C2 coronagraph with those obtained from EUV dimming with the Atmospheric Imaging Assembly (AIA) onboard SDO for all identical events in both data sets. We investigate correlations between CME parameters, the relative timing with flare parameters, frequency occurrence distributions, and the energy partition between magnetic, thermal, nonthermal, and CME energies. CME energies are found to be systematically lower than the dissipated magnetic energies, which is consistent with a magnetic origin of CMEs.
Authors: Aschwanden, M.J.
Projects: SDOAIA

Publication Status: ApJ, subm. 2016 May 16
Last Modified: 20160516 20:09



Tracing the Chromospheric and Coronal Magnetic Field with AIA, IRIS, IBIS, and ROSA Data 

Markus J. Aschwanden Submitted: 20160205 11:42
The aim of this study is to explore the suitability of chromospheric images for magnetic modeling of active regions. We use highresolution images (0.1") from the Interferometric Bidimensional Spectrometer (IBIS) in the Ca II 8542 Å line, the Rapid Oscillations in the Solar Atmosphere (ROSA) instrument in the Hα 6563 Å line, the Interface Region Imaging Spectrograph (IRIS) in the 2796 Å line, and compare nonpotential magnetic field models obtained from those chromospheric images with those obtained from images of the Atmospheric Imaging Assembly (AIA) in coronal (171 Å, etc.) and in chromospheric (304 Å) wavelengths. Curvilinear structures are automatically traced in those images with the OCCULT2 code, to which we forwardfitted magnetic field lines computed with the VerticalCurrent Approximation NonLinear Force Free Field (VCANLFFF) code. We find that the chromospheric images: (1) reveal crisp curvilinear structures (fibrils, loop segments, spicules) that are extremely wellsuited for constraining magnetic modeling; (2) that these curvilinear structures are fieldaligned with the bestfit solution by a median misalignment angle of ~47 deg; (3) the free energy computed from coronal data may underestimate that obtained from cromospheric data by a factor of ~ 24, (4) the height range of chromospheric features is confined to h ~ 4000 km, while coronal features are detected up to h ~ 35,000 km; and (5) the plasmabeta parameter is beta ~ 10^{5}10^{1} for all traced features. We conclude that chromospheric images reveal important magnetic structures that are complementary to coronal images and need to be included in comprehensive magnetic field models, a quest that is not accomodated in standard NLFFF codes.
Authors: Aschwanden, M.J., Reardon, K., and Jess, D.
Projects: SDOAIA

Publication Status: ApJ, subm. 2016 Feb 5
Last Modified: 20160209 14:59



The Vertical Current Approximation Nonlinear ForceFree Field Code  Description, Performance Tests, and Measurements of Magnetic Energies Dissipated in Solar Flares 

Markus J. Aschwanden Submitted: 20160201 11:19
In this work we provide an updated description of the Vertical
Current Approximation Nonlinear ForceFree Field (VCANLFFF)
code, which is designed to measure the evolution of the potential,
nonpotential, free energies, and the dissipated magnetic energies
during solar flares. This code provides a complementary and
alternative method to existing traditional NLFFF codes.
The chief advantages of the VCANLFFF code over traditional NLFFF
codes are the circumvention of the unrealistic assumption of a
forcefree photosphere in the magnetic field extrapolation method,
the capability to minimize the misalignment angles between observed
coronal loops (or chromospheric fibril structures) and theoretical
model field lines, as well as computational speed.
In performance tests of the VCANLFFF code, by comparing with the
NLFFF code of Wiegelmann (2004), we find agreement in the potential,
nonpotential, and free energy within a factor of about 1.3,
but the Wiegelmann code yields in the average a factor of 2 lower
flare energies. The VCANLFFF code is found to detect decreases
in flare energies in most X, M, and Cclass flares.
The successful detection of energy decreases during a variety
of flares with the VCANLFFF code indicates that currentdriven
twisting and untwisting of the magnetic field is an adequate
model to quantify the storage of magnetic energies in active
regions and their dissipation during flares.  The VCANLFFF
code is also publicly available in the Solar SoftWare (SSW).
Authors: Markus J. Aschwanden
Projects: SDOAIA

Publication Status: ApJ Suppl.Ser., subm. 2016 Feb 1
Last Modified: 20160203 09:17



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