sunspots

New AI Based Methods for 3D Reconstruction of the Solar Photosphere

whawkins — Thu, 11 Dec 2025 22:16:55 +0000

New AI Based Methods for 3D Reconstruction of the Solar Photosphere whawkins Thu, 12/11/2025 - 15:16

Author:

whawkins

Dec 11, 2025

In a collaborative effort researchers at the University of Hawaiʻi Institute for Astronomy (IfA), the NSF funded National Solar Observatory and NSF NCAR’s High Altitude Observatory developed a new artificial intelligence based method to reconstruct the magnetic field in the solar atmosphere. The method uses a physics informed neural network to combine observations with physical constraints on the connectivity of magnetic fields to reconstruct a 3D volume of the solar atmosphere. The performance of the method was assessed with the help of synthetic data provided by the MURaM radiative MHD code, which is a joint development by NSF NCAR and the Max Planck Institute for Solar System Research in Germany.

UH press release

HAO research featured on AAS Nova

whawkins — Tue, 29 Jul 2025 21:03:34 +0000

HAO research featured on AAS Nova whawkins Tue, 07/29/2025 - 15:03

First Observation of Chromospheric Waves in a Sunspot by DKIST/ViSP

whawkins — Tue, 04 Apr 2023 16:33:16 +0000

First Observation of Chromospheric Waves in a Sunspot by DKIST/ViSP whawkins Tue, 04/04/2023 - 10:33

The Anatomy of an Umbral Flash

Author:

whawkins

Apr 4, 2023

Astrophysical Journal Letters: The Visible Spectro-Polarimeter of the NSF Daniel K. Inouye Solar Telescope collected its Science Verification data on 2021 May 7-8. The instrument observed multiple layers of a sunspot atmosphere simultaneously, in passbands of Ca II 397 nm (H line), Fe I 630 nm, and Ca II 854 nm, scanning the region with a spatial sampling of 0.04 arcsec1 and an average temporal cadence of 7.76 s, for a duration of 38.8 minutes. The slit moved southward across the plane of sky at 3.83 km s-1. The spectropolarimetric scans exhibit prominent oscillatory "ridge" structures that lie nearly perpendicular to the direction of slit motion (north to south). These ridges are visible in the maps of line intensity, central wavelength, line width, and both linear and circular polarization. Contemporaneous Atmospheric Imaging Assembly observations indicate that these ridges are purely temporal in character and are likely attributed to the familiar chromospheric 3 minute umbral oscillations. We observe in detail a steady umbral flash near the center of the sunspot umbra. Although bad seeing limited the spatial resolution, the unique high signal-to-noise ratio data enable us to estimate the shock Mach numbers (~2), propagation speeds (~9 km/s), and their impacts on the longitudinal magnetic field (dB ~ 50 G), gas pressure, and temperature (dT/T ~ 0.1) of subshocks over 30 s. We also find evidence for rarefaction waves situated between neighboring wave train shocks. The Ca II 854 nm line width is fairly steady throughout the umbral flash, except for a sharp 1.5 km/s dip immediately before, and a comparable spike immediately after, the passage of the shock front. This zigzag in line width is centered on the subshock and extends over 0.4 arcsec.

Detrended intensity, line width, azimuth, P, and B LOS cross sections, and raw Doppler cross sections, along the dashed cyan and magenta lines. The vertical dashed lines show the approximate locations of the Ca II 854 nm intensity peaks.

On the (In)stability of Sunspots

kolinski — Thu, 03 Mar 2022 21:55:08 +0000

On the (In)stability of Sunspots kolinski Thu, 03/03/2022 - 14:55

Publication: Astronomy & Astrophysics; Authors: H. Strecker, W. Schmidt, R. Schlichenmaier, M. Rempel

Author:

kolinski

Mar 3, 2022

The stability of sunspots is one of the long-standing unsolved puzzles in the field of solar magnetism and the solar cycle. The thermal and magnetic structure of the sunspot beneath the solar surface is not accessible through observations, thus processes in these regions that contribute to the decay of sunspots can only be studied through theoretical and numerical studies.

Aims: We study the effects that destabilise and stabilise the flux tube of a simulated sunspot in the upper convection zone. The depth-varying effects of fluting instability, buoyancy forces, and timescales on the flux tube are analysed.

Maps of the magnetic field strength at depth of z = −7.5 Mm beneath the solar photosphere at different times (indicated in red in each panel). The boundary of the sunspot (red line) is defined by the contour value Bc = 4781 G. At the beginning of the analysis, at t = 0 h, panel (a), the inner part of the flux tube is mainly undisturbed. Within 6 hours, regions of weaker field appear in the innermost part of the flux tube while the outer structure becomes more ragged, as is shown in panel (b). The increasing raggedness causes a degradation of the flux tube. This degradation process continues in time, as panels (c–e) show. At 29.75 h, the roundish structure of the flux tube has completely vanished. The degradation process takes place in all regions deeper than 1 Mm below the surface.

Methods: We analysed a numerical simulation of a sunspot calculated with the MURaM code. The simulation domain has a lateral extension of more than 98 Mm × 98 Mm and extends almost 18 Mm below the solar surface. The analysed data set of 30 hours shows a stable sunspot at the solar surface. We studied the evolution of the flux tube at defined horizontal layers (1) by means of the relative change in perimeter and area, that is, its compactness; and (2) with a linear stability analysis.

Results: The simulation shows a corrugation along the perimeter of the flux tube (sunspot) that proceeds fastest at a depth of about 8 Mm below the solar surface. Towards the surface and towards deeper layers, the decrease in compactness is damped. From the stability analysis, we find that above a depth of 2 Mm, the sunspot is stabilised by buoyancy forces. The spot is least stable at a depth of about 3 Mm because of the fluting instability. In deeper layers, the flux tube is marginally unstable. The stability of the sunspot at the surface affects the behaviour of the field lines in deeper layers by magnetic tension. Therefore the fluting instability is damped at depths of about 3 Mm, and the decrease in compactness is strongest at a depth of about 8 Mm. The more vertical orientation of the magnetic field and the longer convective timescale lead to slower evolution of the corrugation process in layers deeper than 10 Mm.

Conclusions: The formation of large intrusions of field-free plasma below the surface destabilises the flux tube of the sunspot. This process is not visible at the surface, where the sunspot is stabilised by buoyancy forces. The onset of sunspot decay occurs in deeper layers, while the sunspot still appears stable in the photosphere. The intrusions eventually lead to the disruption and decay of the sunspot.

Annie Maunder, A Pioneer of Solar Astronomy

kolinski — Thu, 18 Nov 2021 22:11:08 +0000

Annie Maunder, A Pioneer of Solar Astronomy kolinski Thu, 11/18/2021 - 15:11

Author:

kolinski

Nov 18, 2021

If you have visited the High Altitude Observatory (HAO) at NCAR in Boulder, CO, you may recall seeing the Maunder’s original butterfly diagram. The chart resembles three butterflies traveling west. Drawn by Annie S.D. Maunder and E. Walter Maunder, it demonstrated for the first time the movement of sunspot emergence from the poles toward the equator over the sun's 11-year cycle. In October of 2016, the Royal Observatory at Greenwich remembered Annie Maunder as one of the first women elected as a RAS Fellows: the A & G Forum (News, Views, and Events from the RAS Fellows) stated that "Annie Maunder was finally elected to RAS Fellowship in 1916."

A pioneer of solar astronomy

Annie Maunder

Annie was an outstanding observer and interpreter of sun activity. She was born Annie Scott Dill Russell in 1868 in Strabane, in what is now Northern Ireland. Although she was unusually well-educated for a women for her time and she had passed the Cambridge University degree examinations with honors in mathematics (1889), she was not allowed to receive a degree. Annie had the foresight to mail her butterfly diagram from London to the US, for protection, during the English Blitz. In 1946 it was gifted to Walter Orr Roberts where it remains on permanent display at HAO.

An excerpt from the a 2000 interview with Tom Bogden shares that Annie Maunder explained: "We made this diagram in a week of evenings, one dictating and the other ruling these little lines. We had to do it in a hurry because we wanted to get it before the [Royal Astronomical] Society at the same meeting as the other sunspot observers, whose views we knew to be heretical. As it turned out the diagram wiped [the other observers'] papers clean off the slate."

Maunder Diagram from 1940 by Annie Maunder and her husband Walt.

Annie worked with Walter Maunder at the solar department of the Greenwich Royal Observatory in England as a "lady computer" from 1891 until they married in 1895. Although Annie was required to resign when she married her boss, the two continued to collaborate on their own. Annie accompanied her husband on eclipse expeditions and developed a camera for photographing the corona.

Great Grandson of Walter & Annie Maunder Thanks HAO

kolinski — Thu, 18 Nov 2021 21:13:24 +0000

Great Grandson of Walter & Annie Maunder Thanks HAO kolinski Thu, 11/18/2021 - 14:13

Author:

kolinski

Nov 18, 2021

Andrew L Maunder wrote HAO: I just wanted to drop you an email to thank you for the recent bio pages for Walter and Annie S D Maunder presented on the UCAR NCAR website. In particular, I’m pleased to see the Elliot and Fry studio portrait being used for Annie. For so long there were no good images of her in the public domain, and so I have been very pleased to get this one out there for all to see.

I am a great grandson of Walter Maunder, and live over here in the USA in North Carolina. From the snapshots below you will see that I’m lucky enough to still have a few of their possessions (Walter’s New testament, and Annie’s birthday book).

Perhaps if my wife and I are ever able to make it out to Boulder, we may be able to visit and see the famous butterfly diagram?

Regards,
Andrew L Maunder

Annie Maunder's birthday book and her formal portrait.

Walter Maunder’s New testament with his formal portrait.

Opposite Polarity Magnetic Fields and Convective Downflows in a Simulated Sunspot Penumbra

kolinski — Thu, 18 Nov 2021 17:16:42 +0000

Opposite Polarity Magnetic Fields and Convective Downflows in a Simulated Sunspot Penumbra kolinski Thu, 11/18/2021 - 10:16

Publication Name: ApJ; First HAO Author's Name: M. Rempel

Author:

kolinski

Nov 18, 2021

Recent numerical simulations and observations of sunspots show a significant amount of opposite polarity magnetic fields within the sunspot penumbra. Most of the opposite polarity fields are associated with convective downflows.

Left panels: normalized continuum intensity at 630 nm. Middle panels: Stokes V far wing magnetogram. Right panels: bisector velocity at 80% for Fe i 6301.5 Å. First row: at simulation resolution. Second, third, and fourth rows: at Hinode (0.5 m), 1 m, and 1.5 m resolutions.

We present an analysis of 3D MHD simulations through forward modeling of synthetic Stokes profiles of the Fe I 6301.5 Å and Fe I 6302.5 Å lines. The synthetic Stokes profiles are spatially and spectrally degraded considering typical instrument properties. Line bisector shifts of the Fe I 6301.5 Å line are used to determine line-of-sight velocities. Far wing magnetograms are constructed from the Stokes V profiles of the Fe I 6302.5 Å line. While we find an overall good agreement between observations and simulations, the fraction of opposite polarity magnetic fields, the downflow filling factor, and the opposite polarity-downflow association are strongly affected by spatial smearing and presence of strong gradients in the line-of-sight magnetic fields and velocity. A significant fraction of opposite polarity magnetic fields and downflows is hidden in the observations due to typical instrumental noise. Comparing simulations that differ by more than a factor of two in grid spacing, we find that these quantities are robust within the simulations.

A distinct magnetic property of the inner penumbral boundary III. Analysis of simulated sunspots

kolinski — Thu, 18 Nov 2021 17:03:20 +0000

A distinct magnetic property of the inner penumbral boundary III. Analysis of simulated sunspots kolinski Thu, 11/18/2021 - 10:03

Publication Name: A&A; First HAO Author's Name: M. Rempel

Author:

kolinski

Nov 18, 2021

The analyses of sunspot observations revealed a fundamental magnetic property of the umbral boundary, the invariance of the vertical component of the magnetic field. We aim to analyse the magnetic properties of the umbra-penumbra boundary in simulated sunspots and thus assess their similarity to observed sunspots. Also, we aim to investigate the role of plasma $\beta$ and the ratio of kinetic to magnetic energy in simulated sunspots on the convective motions as these quantities cannot be reliably determined from observations. We use a set of non-grey simulation runs of sunspots with the MURaM code. The setups differ in terms of subsurface magnetic field structure as well as the magnetic field boundary imposed at the top of the simulation domain. These data are used to synthesise the Stokes profiles that are then degraded to the Hinode spectropolarimeter-like observations. Then, the data are treated like real Hinode observations of a sunspot and magnetic properties at the umbral boundaries are determined. Simulations with potential field extrapolation produce a realistic magnetic field configuration on their umbral boundaries.

Radial profiles of continuum intensity (b), magnetic field inclination (c), total magnetic field strength (d), vertical magnetic field strength (e), and horizontal magnetic field strength (f). The continuum intensity map of the observed sunspot with contours marking relative radial positions from 0.1 to 1 is shown in panel (a). The solid vertical lines mark the umbra-penumbra boundaries, the dashed vertical lines mark the penumbra-quiet Sun boundary. The horizontal lines in (b) and (e) mark the 50% quiet Sun intensity and 1876 G contour, respectively. Only sunspot simulations with a potential field top boundary condition (type 1 and alpha=1) have a vertical magnetic field strength values at the umbra-penumbra boundary that are similar to those observed.

Two simulations with potential field upper boundary, but different subsurface magnetic field structures, differ significantly in the extent of their penumbrae. Increasing the penumbra width by forcing more horizontal magnetic fields at the upper boundary results in magnetic properties that are not consistent with observations. This implies that the size of the penumbra is given by the subsurface structure of the magnetic field. Namely, the depth and inclination of the magnetopause shaped by the sunspot flux rope expansion with height. None of the sunspot simulations is consistent with observed properties of the magnetic field and direction of the Evershed flow at the same time. Strong outward directed Evershed flows are only found in setups with artificially enhanced horizontal component of the magnetic field at the top boundary that are not consistent with the observed magnetic field properties at the UP boundary. We want to stress out that the `photospheric' boundary of simulated sunspots is defined by a magnetic field strength of equipartition field value.

Superstrong photospheric magnetic fields in sunspot penumbrae

kolinski — Tue, 16 Nov 2021 22:29:50 +0000

Superstrong photospheric magnetic fields in sunspot penumbrae kolinski Tue, 11/16/2021 - 15:29

Publication Name: Astronomy & Astrophysics; First HAO Author: Matthias Rempel

Author:

kolinski

Nov 16, 2021

Recently, there have been some reports of unusually strong photospheric magnetic fields (which can reach values of over 7 kG) inferred from Hinode SOT/SP sunspot observations within penumbral regions. These superstrong penumbral fields are even larger than the strongest umbral fields in record and appear associated with supersonic downflows. The finding of such fields has been controversial since they seem to show up only when spatially coupled inversions are performed.

A portion of the inner penumbra in the MURaM sunspot simulation by Rempel (2015) with some filaments hosting a counter-Evershed flow (see also Siu-Tapia et al. 2018). The maps show: (a) the magnetic field strength B [G]; (b) the field inclination with respect to the vertical [deg], i.e. =0 represents a vertical field of umbral polarity, =90 a horizontal field, and =180 a vertical field of opposite polarity to the umbra; (c) radial flow velocity vr [km/s]; and (d) the vertical flow velocity vz [km/s]. Negative vr and vz values (red-to-yellow colors) indicate inflows and downflows, respectively. This sign convention differs from the one used in observational studies, where negative values denote flows moving towards the observer along the line-of-sight. The black contour lines where placed where the continuum intensity reaches 45% of the quiet sun level to indicate the umbra(left)-penumbra(right) boundary. All maps show the corresponding physical parameters at an optical depth of unity.

Here, we investigate and discuss the reliability of those findings by studying in detail observed spectra associated with particularly strong magnetic fields at the inner edge of the penumbra. We apply classical diagnostic methods and various inversions with different model atmospheres to the observed Stokes profiles, and compare the results with a magnetohydrodynamic simulation of a sunspot whose penumbra contains strong fields associated with supersonic downflows. The large splittings of the Fe I lines, their strong redshifts, and the multiple lobes observed in the Stokes V profiles are indeed unusual and are likely caused by unusually strong magnetic fields and supersonic downflows in the inner penumbra, which are associated to the rare phenomenon of counter-Evershed flows. We find evidence for such strong fields associated to counter-Evershed flows also in the MHD sunspot simulation.

sunspots

New AI Based Methods for 3D Reconstruction of the Solar Photosphere

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HAO research featured on AAS Nova

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First Observation of Chromospheric Waves in a Sunspot by DKIST/ViSP

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On the (In)stability of Sunspots

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Annie Maunder, A Pioneer of Solar Astronomy

Recent News

Great Grandson of Walter & Annie Maunder Thanks HAO

Recent News

Opposite Polarity Magnetic Fields and Convective Downflows in a Simulated Sunspot Penumbra

Recent News

A distinct magnetic property of the inner penumbral boundary III. Analysis of simulated sunspots

Recent News

Superstrong photospheric magnetic fields in sunspot penumbrae

Recent News