@article{29d9dc90bf8447098c18f39b3c9189a4,
title = "Solar east-west flow correlations that persist for months at low latitudes are dominated by active region inflows",
abstract = "Context. Giant-cell convection is believed to be an important component of solar dynamics. For example, it is expected to play a crucial role in maintaining the Sun's differential rotation. Aims. We reexamine early reports of giant convective cells detected using a correlation analysis of Dopplergrams. We extend this analysis using 19 years of space- and ground-based observations of near-surface horizontal flows. Methods. Flow maps are derived through the local correlation tracking of granules and helioseismic ring-diagram analysis. We compute temporal auto-correlation functions of the east-west flows at fixed latitude. Results. Correlations in the east-west velocity can be clearly seen up to five rotation periods. The signal consists of features with longitudinal wavenumbers up to m = 9 at low latitudes. Comparison with magnetic images indicates that these flow features are associated with magnetic activity. The signal is not seen above the noise level during solar minimum. Conclusions. Our results show that the long-term correlations in east-west flows at low latitudes are predominantly due to inflows into active regions and not to giant convective cells.",
keywords = "Sun: Activity, Sun: Helioseismology, Sun: Interior, Sun: Oscillations, convection, waves",
author = "Hanson, {Chris S.} and Duvall, {Thomas L.} and Birch, {Aaron C.} and Laurent Gizon and Sreenivasan, {Katepalli R.}",
note = "Funding Information: Acknowledgements. CSH thanks Jishnu Bhattacharya for insightful discussions. Funding: The Center for Space Science at NYU Abu Dhabi is funded by NYUAD Institute Grant G1502. This work was designed at a workshop supported by the TIFR-Max Planck partner group program. LG acknowledges partial support from ERC Synergy Grant WHOLE SUN 810218. Data: This work utilizes data obtained by the Global Oscillation Network Group (GONG) program, managed by the National Solar Observatory, which is operated by AURA, Inc. under a cooperative agreement with the NationalScience Foundation. The data were acquired by instruments operated by the Big Bear Solar Observatory, High Altitude Observatory, Learmonth Solar Observatory, Udaipur Solar Observatory, Instituto de Astrof{\`i}sica de Canarias, and Cerro Tololo Interameri-can Observatory. The HMI data is courtesy of NASA/SDO and the HMI Science Team. The HMI LCT maps are courtesy of Bj{\"o}rn L{\"o}ptien. The results presented here may be obtained from the authors upon request. Software: In this study we used python 3.6.7 (www.python.org/downloads/release/python-367/), with the packages numpy 1.17.2 (https://numpy.org/devdocs/release/ 1.17.2-notes.html), scipy 1.3.1 (https://docs.scipy.org/doc/scipy/ reference/release.1.3.1.html) and astropy 3.2.2 (www.astropy.org/). Processing of MDI and HMI data to produce data that is not available from the JSOC pipeline was performed using NetDRMS on the compute cluster at MPS and NYUAD. Publisher Copyright: {\textcopyright} ESO 2020.",
year = "2020",
month = dec,
day = "1",
doi = "10.1051/0004-6361/202039108",
language = "English (US)",
volume = "644",
journal = "Astronomy and Astrophysics",
issn = "0004-6361",
publisher = "EDP Sciences",
}