TY - JOUR
T1 - Simulating Solar Near-surface Rossby Waves by Inverse Cascade from Supergranule Energy
AU - Dikpati, Mausumi
AU - Gilman, Peter A.
AU - Guerrero, Gustavo A.
AU - Kosovichev, Alexander G.
AU - McIntosh, Scott W.
AU - Sreenivasan, Katepalli R.
AU - Warnecke, Jörn
AU - Zaqarashvili, Teimuraz V.
N1 - Funding Information:
We thank A. Malanushenko for reviewing the entire manuscript and for providing helpful comments. We extend our thanks to an anonymous reviewer for a thorough review of an earlier version of the manuscript, and for the constructive comments, which have helped significantly improve our paper. This work is supported by the National Center for Atmospheric Research, which is a major facility sponsored by the National Science Foundation under cooperative agreement 1852977. We acknowledge support from several NASA grants, namely, M.D. acknowledges NASA-LWS award 80NSSC20K0355, NASA-HSR award 80NSSC21K1676, subaward from NASA-DRIVE Center award 80NSSC20K0602 (awarded to Stanford), and a subaward from NASA-HSR award 80NSSC18K1206 (awarded to NSO). We acknowledge COFFIES DRIVE Center team activity, which has enabled us to pursue this solar Rossby waves research as a team. T.V.Z. was supported by the Austrian Fonds zur Förderung der Wissenschaftlichen Forschung (FWF) project P30695-N27 and by Shota Rustaveli National Science Foundation of Georgia (project FR-21-467). J.W. acknowledges funding by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program with grant agreement No. 818665 “UniSDyn”. M.D. acknowledges 1 million core hours used in this study, from high-performance computing in Cheyenne through NCAR’s Strategic Capability computing grant of 12 million core hours with award number NHAO0020, and also divisional computing grant P22104000 provided to HAO by NCAR’s Computational and Information Systems Laboratory.
Publisher Copyright:
© 2022. The Author(s). Published by the American Astronomical Society.
PY - 2022/6/1
Y1 - 2022/6/1
N2 - 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 mainly gone 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 have previously been shown to play crucial roles in causing seasons of space weather through their nonlinear interactions with global flows and magnetic fields. We briefly discuss how various Rossby waves in the tachocline, convection zone, supergranule layer, and corona can be reconciled in a unified framework.
AB - 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 mainly gone 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 have previously been shown to play crucial roles in causing seasons of space weather through their nonlinear interactions with global flows and magnetic fields. We briefly discuss how various Rossby waves in the tachocline, convection zone, supergranule layer, and corona can be reconciled in a unified framework.
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U2 - 10.3847/1538-4357/ac674b
DO - 10.3847/1538-4357/ac674b
M3 - Article
AN - SCOPUS:85131684447
SN - 0004-637X
VL - 931
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 117
ER -