Peter Gilman

Mother's Day Superstorms: Pre- and Post-storm Evolutionary Patterns of AR 13664/8

whawkins — Tue, 24 Jun 2025 18:13:37 +0000

Mother's Day Superstorms: Pre- and Post-storm Evolutionary Patterns of AR 13664/8 whawkins Tue, 06/24/2025 - 12:13

Author:

whawkins

Jun 24, 2025

Top: Global-scale toroid patterns indicate ARs 13664 and 13668 were located in the south-toroid in such a way as to be sufficiently away from ARs in the north-toroid, indicating probability of their eruption; close proximity of ARs 13664 and 13668 indicates the possibility of complex interactions between them. Bottom: Small-scale evolution of AR13664/8 is shown with three snapshots from HMI continuum (left) and radial magnetic field(right). The active region at the right side of the first frame was denoted as AR13664 first, and AR 13668 emerged to the east of it. Multiple pairs of bipoles emerged with the positive and negative polarities seen in white and black, respectively.

The Astrophysical Journal: In the week including Mother's day 2024, active region (AR) 13664 became superactive when AR\,13668 emerged nearby, causing multiple X-class flares and CMEs, and activity level increased similar to that inferred from geomagnetic storms associated with the historic 1859 events. By analyzing bot global warped toroids on which the active regions are strung, and active-region-scale magnetic flux and helicity, we find: (i) North and South toroids have nearly identical warped patterns, with mostly longitudinal wave numbers $m=1-3$; (ii) in three longitude intervals North and South toroids were tipped away from each other in latitude, with a longitude phase-shift between them, creating locations most prone for AR eruptions; (iii) on active-region-scale, vector magnetic fields deviate far from potential fields, and therefore contain large amounts of magnetic 'free energy' available for conversion into kinetic energy and high temperature radiation; (iv) the positive and negative polarities converge toward each other, facilitating reconnection and magnetic energy release; (v) rapid changes in magnetic helicity caused by helicity injection from below that creates helicity imbalances. We conclude that the Mother's day superstorms were caused by enhanced magnetic complexity occurring due to intricate interactions among multiple active regions emerging at nearly the same locations. This suggests, predicting locations of magnetically complex ARs, and studying and tracking their eruptive states using different proxy parameters, can greatly improve our ability to forecast intense storms, not only hours but potentially weeks in advance.

Evolution Of Amplitude And Longitude Phase Of Tachocline Rossby Waves Diffusing To The Photosphere

whawkins — Tue, 29 Oct 2024 19:38:58 +0000

Evolution Of Amplitude And Longitude Phase Of Tachocline Rossby Waves Diffusing To The Photosphere whawkins Tue, 10/29/2024 - 13:38

Author:

whawkins

Oct 29, 2024

MNRAS— (Published: 05 November 2024) Physics of MHD Rossby waves in the tachocline-layer were studied by Dikpati, Gilman, Chatterjee et al. (2020) using a fluid-particle-trajectory approach along with solving vorticity and induction equations. By extending the 2020 MHD Rossby wave model to include a hydrodynamic turbulent convection zone (CZ), they were able to examine how MHD Rossby waves generated in the tachocline might diffuse upward through the CZ to the solar surface. Major findings from this current study include (i) pure hydrodynamic Rossby wave amplitudes decline with height due to viscous diffusion at a rate that is independent of viscosity and increases with longitude wavenumber, (ii) fast MHD Rossby waves amplitude declines faster with height for increasing toroidal field, due to their longitude-phase shifting with height, which increases dissipation of kinetic energy in the wave velocities, (iii) slow MHD Rossby waves decline even faster with height because their longitude-phase shifts more rapidly with height, due to their slow phase speed. Furthermore, it was also found that low wavenumber HD and fast MHD Rossby waves, originating in the tachocline, might be detected at the photosphere, but slow MHD Rossby waves should be virtually impossible to detect. An inference from fluid particle trajectories that wave amplitudes declining with height and longitude phase shifting with height associated with decline, implies a powerful mechanism for tangling of magnetic fields, distinct from convective turbulence effects.

Amplitude decline with height of fast and slow MHD Rossby waves at the top of the channel, centered at 45 degrees latitude, compared to the bottom as a function of toroidal field strength, in kiloGauss, for longitudinal wave numbers m = 1 − 10. Left frame: fast waves; right frame: slow waves. Waves for which amplitude at top is smaller than 10−5 compared to the bottom are not plotted. Amplitude decline with height of the zero kG slow wave is included as a limiting case, even though it does not actually exist in that limit. In the limit of zero toroidal field, the fast wave becomes the hydrodynamic Rossby wave.

Simulating Solar Near-surface Rossby Waves By Inverse-cascade From Supergranule Energy

whawkins — Wed, 26 Oct 2022 18:19:17 +0000

Simulating Solar Near-surface Rossby Waves By Inverse-cascade From Supergranule Energy whawkins Wed, 10/26/2022 - 12:19

Author:

whawkins

Oct 26, 2022

Astrophysical Journal—M. Dikpati, P. A. Gilman, G. A. Guerrero, A. G. Kosovichev, S. W. McIntosh, K. R. Sreenivasan, J. Warnecke, T. V. Zaqarashvili

Three snapshots during evolution of kinetic energy spectra in spectral space, for initial solid rotation, in a T42 model.

Rossby waves are found at several levels in the Sun, most recently in its supergranule layer. We show that Rossby waves in the supergranule layer can be excited by an inverse cascade of kinetic energy from the nearly horizontal motions in supergranules. We illustrate how this excitation occurs using a hydrodynamic shallow-water model for a 3D thin rotating spherical shell. We find that initial kinetic energy at small spatial scales inverse-cascades quickly to global scales, exciting Rossby waves whose phase velocities are similar to linear Rossby waves on the sphere originally derived by Haurwitz. Modest departures from the Haurwitz formula originate from nonlinear finite amplitude effects and/or the presence of differential rotation. Like supergranules, the initial small scale motions in our model contain very
little vorticity compared to their horizontal divergence, but the resulting Rossby waves are almost all vortical motions. Supergranule kinetic energy could have gone mainly into gravity waves, but we find that most energy inverse-cascades to global Rossby waves. Since kinetic energy in supergranules is three or four orders of magnitude larger than that of the observed Rossby waves in the supergranule layer, there is plenty of energy available to drive the inverse-cascade mechanism. Tachocline Rossby waves were previously shown to play crucial roles in causing "seasons" of space weather through their nonlinear interactions with global flows and magnetic fields. We discuss briefly how various Rossby waves in tachocline, convection zone, supergranule layer and corona can be reconciled in a unified framework.

Congratulations to Peter Gilman, elected AAS Legacy fellow!

kolinski — Mon, 22 Nov 2021 18:19:50 +0000

Congratulations to Peter Gilman, elected AAS Legacy fellow! kolinski Mon, 11/22/2021 - 11:19

Deciphering Deep-Origin of Active Regions From Analysis Of Magnetograms

kolinski — Tue, 16 Nov 2021 21:02:40 +0000

Deciphering Deep-Origin of Active Regions From Analysis Of Magnetograms kolinski Tue, 11/16/2021 - 14:02

Publication Name: ApJ; First HAO Author: Mausumi Dikpati; Authors: Mausumi Dikpati, Scott W. McIntosh, Subhamoy Chatterjee, P. Ambroz, A. A. Norton, P. A. Gilman, K. Jain, A. Munoz-Jaramillo

Author:

kolinski

Nov 16, 2021

Dikpati, et. al., derive magnetic toroids from surface magnetograms by employing a novel optimization method based on Trust Region Reflective algorithm. Toroids obtained are combinations of Fourier modes (amplitudes and phases) with low longitudinal wavenumbers. The optimization also estimates the latitudinal width of the toroids. We validate the method using synthetic data generated as random numbers along a specified toroid.

Three panels display the active-regions' toroid patterns (North blue and South red), derived from SoHO/MDI synoptic magnetograms for Carrington Rotations 2007, 2008 and 2009, i.e., just before and during the Halloween storms of 2003, which produced hazardous impact of space weather from 11 X-class and 46 M-class flares, and also beautiful aurorae as far south as Florida, Texas and Mediterranean Europe.

We compute shapes and latitudinal-widths of toroids from magnetograms, usually requiring several m’s to minimize residuals. A threshold field- strength is chosen to include all active regions in magnetograms for toroid derivation, while avoiding non-contributing weaker fields. Higher thresholds yield narrower toroids, with m = 1 dominant pattern. We determine the spatio- temporal evolution of toroids by optimally weighting amplitudes and phases of each Fourier mode for a sequence of 5 Carrington Rotations (CRs) to get the best amplitude and phases for the middle CR in the sequence. Taking more than 5 causes ‘smearing’ or degradation of toroid structure. While this method applies no matter at what depth the toroids actually reside inside the Sun, by comparing their global-shape and width with analogous patterns derived from MHD tachocline shallow-water model-simulations, we infer that their origin is at/near the convection-zone base. By analyzing the ‘Halloween’ storms as an example, we describe features of toroids that might have caused the series of space weather events in October-November of 2003. Calculations of toroids for several sunspot cycles will enable us to find similarities/differences in toroids for different major space weather events.

Dynamical Splitting Of A Spot-producing Magnetic Ring In A Nonlinear Shallow-water Model

kolinski — Mon, 15 Nov 2021 21:32:36 +0000

Dynamical Splitting Of A Spot-producing Magnetic Ring In A Nonlinear Shallow-water Model kolinski Mon, 11/15/2021 - 14:32

Publication: Astrophysical Journal; First HAO Author: Mausumi Dikpati; Authors as listed in article: Mausumi Dikpati, Aimee A. Norton, Scott W. McIntosh, Peter A. Gilman

Author:

kolinski

Nov 15, 2021

We explore the fundamental physics of narrow toroidal rings during their nonlinear magnetohydrodynamic evolution at tachocline depths. Using a shallow-water model, we simulate the nonlinear evolution of spot-producing toroidal rings of 6-degree latitudinal width and peak field of 15 kG. We find that the rings split; the split-time depends on the latitude of each ring. Ring-splitting occurs fastest, within a few weeks, at latitudes 20–25°. Rossby waves work as perturbations to drive instability of spot-producing toroidal rings; the ring-split is caused by the 'mixed stress' or cross correlations of perturbation velocities and magnetic fields, which carries magnetic energy and flux from the ring-peak to its shoulders, leading to the ring-split. The two split-rings migrate away from each other, the high latitude counterpart slipping poleward faster, due to migrating mixed stress and magnetic curvature stress. Broader toroidal bands do not split.

Snapshots during splitting of a 6-degree toroidal ring into two, overlaid in white arrow-vectors on the colormap, which represents deformation of thin fluid-layer's top-surface (red/orange denotes bulges and blue/dark-blue depressions). Panel (a) shows the ring is not split yet at t=3.064 (i.e. 11.2 days), (b) ring is just split into two at t=6.7023 (24.5 days), (c) split part of the ring is seen to move poleward at t=7.6556 (30 days). Poleward part of split ring splits again at t=12.311 (44.9 days). The snapshots are presented in dimensionless time (dimensional time can be obtained by multiplying by 3.65 in the unit of days).

Much stronger rings, despite being narrow, don't split, due to rigidity from stronger magnetic fields within the ring. Magnetogram analysis indicates emergence of active regions sometimes at the same longitudes but separated in latitude by 20-degrees or more, which could be evidence of active regions emerging from split-rings, which consistently contribute to observed high latitude excursions of butterfly wings during ascending, peak and descending phases of a solar cycle. Observational studies in the future can determine how often new spots are found at higher latitudes than their lower latitude counterparts, and how the combinations influence solar eruptions and space weather events.

Animation of figure

Peter Gilman

Mother's Day Superstorms: Pre- and Post-storm Evolutionary Patterns of AR 13664/8

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Evolution Of Amplitude And Longitude Phase Of Tachocline Rossby Waves Diffusing To The Photosphere

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Simulating Solar Near-surface Rossby Waves By Inverse-cascade From Supergranule Energy

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Congratulations to Peter Gilman, elected AAS Legacy fellow!

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Deciphering Deep-Origin of Active Regions From Analysis Of Magnetograms

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Dynamical Splitting Of A Spot-producing Magnetic Ring In A Nonlinear Shallow-water Model

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