Role of Interaction between Magnetic Rossby Waves and Tachocline Differential Rotation in Producing Solar Seasons

Dikpati, Mausumi; McIntosh, Scott W.; Bothun, G. D.; Cally, Paul Stuart; Ghosh, Siddhartha Sankar; Gilman, Peter A.; Umurhan, O. M.

doi:10.3847/1538-4357/aaa70d

Cited by 74 publications

(72 citation statements)

References 67 publications

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“…The periodicity of the bursts is a function of differential rotation amplitude as well as the effective gravity. Figure of Dikpati, McIntosh, et al () shows a more complex case of TNO, for which the period evolves with time, making the TNO more quasi‐periodic.…”

Section: Models For Hd and Mhd Rossby Waves In The Sunmentioning

confidence: 99%

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Space Weather Challenge and Forecasting Implications of Rossby Waves

Dikpati

McIntosh

2020

Space Weather

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Rossby waves arise in thin layers within fluid regions of stars and planets. These global wave‐like patterns occur due to the variation in Coriolis forces with latitude. In the past several years observational evidence has indicated that there are also Rossby waves in the Sun. Although Rossby waves have been detected in the Sun's photosphere and corona, they most likely originate in the solar tachocline, the sharp shear layer at the base of the solar convection zone, where the differential rotation driven by convection transitions to the solidly rotating radiative interior. These waves differ from their Earth's counterparts by being strongly modified by toroidal magnetic fields in the solar tachocline. Recent simulations of magnetohydrodynamics of tachocline Rossby waves and magnetic fields are demonstrated to produce strong “tachocline nonlinear oscillations,” which have periods similar to those observed in the solar atmosphere—enhanced periods of solar activity, or “seasons”—occurring at intervals between six months and two years. These seasonal/subseasonal bursts produce the strongest eruptive space weather events. Thus, a key to forecasting the timing, amplitude, and location of future activity bursts, and hence space weather events, could lie in our ability to forecast the phase and amplitude of Rossby waves and associated tachocline nonlinear oscillations. Accurately forecasting the properties of solar Rossby waves and their impact on space weather will require linking surface activity observations to the magnetohydrodynamics of tachocline Rossby waves, using modern data assimilation techniques. Both short‐term (hours to days) and long‐term (decadal to millennial) forecasts of space weather and climate are now being made. We highlight in this article the potential of solar Rossby waves for forecasting space weather on intermediate time scales, of several weeks to months up to a few years ahead.

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Section: Models For Hd and Mhd Rossby Waves In The Sunmentioning

confidence: 99%

“…The result is a westward moving wave pattern as shown by the relative positions of the heavy black wave. The whole figure is modified from Figure in Dikpati, McIntosh, et al ().…”

Section: Concept Of Rossby Wavesmentioning

confidence: 99%

Space Weather Challenge and Forecasting Implications of Rossby Waves

Dikpati

McIntosh

2020

Space Weather

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“…There are several physical mechanisms proposed that could cause the observed QBOs; flip-flop cycles, which is defined as the 180 • shift of the active longitudes with largest active regions (Berdyugina & Usoskin 2003), spatiotemporal fragmentation from differences in temporal variations in the radial profile Article number, page 1 of 13 arXiv:1904.03724v1 [astro-ph.SR] 7 Apr 2019 A&A proofs: manuscript no. Printer of the rotation rates (Simoniello et al 2013), instability of magnetic Rossby waves in the tachocline (Zaqarashvili et al 2010), and tachocline nonlinear oscillations, where periodically varying energy exchange takes place between the Rossby waves and differential rotation and the present toroidal field (Dikpati et al 2018). Additionally, a secondary dynamo working in the subsurface layers as the mechanism behind the QBOs is also proposed (Benevolenskaya 1998;Fletcher et al 2010), as the helioseismic observations revealed a subsurface rotational shear layer extending to a depth of 5% of the solar surface (Schou et al 1998).…”

Section: Introductionmentioning

confidence: 99%

Constraining non-linear dynamo models using quasi-biennial oscillations from sunspot area data

Inceoglu

Simoniello

Arlt

et al. 2019

A&A

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Context. Solar magnetic activity exhibits variations with periods between 1.5-4 years, the so-called quasi-biennial oscillations (QBOs), in addition to the well-known 11-year Schwabe cycles. Solar dynamo is thought to be the responsible mechanism for generation of the QBOs. Aims. In this work, we analyse sunspot areas to investigate the spatial and temporal behaviour of the QBO signal and study the responsible physical mechanisms using simulations from fully nonlinear mean-field flux-transport dynamos. Methods. We investigated the behaviour of the QBOs in the sunspot area data in full disk, and northern and southern hemispheres, using wavelet and Fourier analyses. We also ran solar dynamos with two different approaches to generating a poloidal field from an existing toroidal field, Babcock-Leighton and turbulent α mechanisms. We then studied the simulated magnetic field strengths as well as meridional circulation and differential rotation rates using the same methods. Results. The results from the sunspot areas show that the QBOs are present in the full disk and hemispheric sunspot areas and they show slightly different spatial and temporal behaviours, indicating a slightly decoupled solar hemispheres. The QBO signal is generally intermittent and in-phase with the sunspot area data, surfacing when the solar activity is in maximum. The results from the BL-dynamos showed that they are neither capable of generating the slightly decoupled behaviour of solar hemispheres nor can they generate QBO-like signals. The turbulent α-dynamos, on the other hand, generated decoupled hemispheres and some QBO-like shorter cycles. Conclusions. In conclusion, our simulations show that the turbulent α-dynamos with the Lorentz force seems more efficient in generating the observed temporal and spatial behaviour of the QBO signal compared with those from the BL-dynamos.

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“…Theoretical models of Rossby waves can take several forms, from purely linear eigenvalue models for finding frequencies of propagation (Rieger et al 1984;Wolff 1992;Oliver et al 1998;Schecter et al 2001;Ballester et al 2002Ballester et al , 2004Zaqarashvili et al 2007Zaqarashvili et al , 2009Zaqarashvili et al , 2010aZaqarashvili et al , 2010bZaqarashvili et al , 2015Dimitropoulou et al 2008;Balk 2014;Raphaldini & Raupp 2015;Gurgenashvili et al 2017;Klimachkov & Petrosyan 2017a, 2017bLondon 2017;Zaqarashvili 2018) and growth rates of unstable modes (Gilman & Fox 1997;Dikpati & Gilman 1999, 2001bGilman 2000;Gilman & Dikpati 2000Cally 2003;Cally et al 2003Cally et al , 2008Dikpati et al 2003;Arlt et al 2005;Gilman 2015Gilman , 2017 to fully nonlinear models that generate both phase propagation and amplitude oscillations (Dikpati 2012;Balk 2014;Raphaldini & Raupp 2015;Dikpati et al 2018). Global models for convection, differential rotation, and magnetic fields can also show some Rossby wave propagation characteristics even for the convection zone, even though such systems generally do not produce Rossby waves per se.…”

Section: Introductionmentioning

confidence: 99%

Phase Speed of Magnetized Rossby Waves that Cause Solar Seasons

Dikpati

Belucz

Gilman

et al. 2018

ApJ

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Motivated by recent analysis of solar observations that show evidence of propagating Rossby waves in coronal holes and bright points, we compute the longitudinal phase velocities of unstable MHD Rossby waves found in an MHD shallow-water model of the solar tachocline (both overshoot and radiative parts). We demonstrate that phase propagation is a typical characteristic of tachocline nonlinear oscillations that are created by unstable MHD Rossby waves, responsible for producing solar seasons. For toroidal field bands placed at latitudes between 5°and 75°, we find that phase velocities occur in a range similar to the observations, with more retrograde speeds (relative to the solar core rotation rate) for bands placed at higher latitudes, just as coronal holes have at high latitudes compared to low ones. The phase speeds of these waves are relatively insensitive to the toroidal field peak amplitude. Rossby waves for single bands at 25°are slightly prograde. However, at latitudes lower than 25°they are very retrograde, but much less so if a second band is included at a much higher latitude. This double-band configuration is suggested by evidence of an extended solar cycle, containing a high-latitude band in its early stages that does not yet produce spots, while the spot-producing low-latitude band is active. Collectively, our results indicate a strong connection between longitudinally propagating MHD Rossby waves in the tachocline and surface manifestations in the form of similarly propagating coronal holes and patterns of bright points.

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Role of Interaction between Magnetic Rossby Waves and Tachocline Differential Rotation in Producing Solar Seasons

Cited by 74 publications

References 67 publications

Space Weather Challenge and Forecasting Implications of Rossby Waves

Space Weather Challenge and Forecasting Implications of Rossby Waves

Constraining non-linear dynamo models using quasi-biennial oscillations from sunspot area data

Phase Speed of Magnetized Rossby Waves that Cause Solar Seasons

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