By direct measurements of the gas temperature, the Atacama Large Millimeter/submillimeter Array (ALMA) has yielded a new diagnostic tool to study the solar chromosphere. Here, we present an overview of the brightness-temperature fluctuations from several high-quality and high-temporal-resolution (i.e. 1 and 2 s cadence) time series of images obtained during the first 2 years of solar observations with ALMA, in Band 3 and Band 6, centred at around 3 mm (100 GHz) and 1.25 mm (239 GHz), respectively. The various datasets represent solar regions with different levels of magnetic flux. We perform fast Fourier and Lomb-Scargle transforms to measure both the spatial structuring of dominant frequencies and the average global frequency distributions of the oscillations (i.e. averaged over the entire field of view). We find that the observed frequencies significantly vary from one dataset to another, which is discussed in terms of the solar regions captured by the observations (i.e. linked to their underlying magnetic topology). While the presence of enhanced power within the frequency range 3-5 mHz is found for the most magnetically quiescent datasets, lower frequencies dominate when there is significant influence from strong underlying magnetic field concentrations (present inside and/or in the immediate vicinity of the observed field of view). We discuss here a number of reasons which could possibly contribute to the power suppression at around 5.5 mHz in the ALMA observations. However, it remains unclear how other chromospheric diagnostics (with an exception of Hα line-core intensity) are unaffected by similar effects, i.e. they show very pronounced 3-min oscillations dominating the dynamics of the chromosphere, whereas only a very small fraction of all the pixels in the 10 ALMA datasets analysed here show peak power near 5.5 mHz. This article is part of the Theo Murphy meeting issue 'High-resolution wave dynamics in the lower solar atmosphere'.
|Number of pages||28|
|Journal||Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences|
|Early online date||21 Dec 2020|
|Publication status||Published - 08 Feb 2021|
Bibliographical noteFunding Information:
Data accessibility. The observational data are all publicly available at data archives of ALMA and NASA’s Solar Dynamics Observatory. Authors’ contributions. M.Sz., V.M.J.H. and S.J. performed the data reduction and post processing. X.Z. and T.W. did the magnetic-field extrapolations. S.J. performed the scientific analysis and drafted the manuscript, with assistance from S.W., B.F., M.St., D.B.J., R.J.M., X.Z., T.W., J.C.G.G., S.D.T.G., B.C., K.R. and S.M.W. All authors read and approved the manuscript. Competing interests. We declare we have no competing interests. Funding. This work is supported by the SolarALMA project, which has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 682462) and by the Research Council of Norway through its Centres of Excellence scheme, project no. 262622 (Rosseland Centre for Solar Physics). D.B.J. and S.D.T.G. are supported by an Invest NI and Randox Laboratories Ltd. Research and Development grant no. (059RDEN-1). Acknowledgements. D.B.J. and S.D.T.G. are grateful to Invest NI and Randox Laboratories Ltd. for the award of a Research and Development grant no. (059RDEN-1). X.Z. and T.W. acknowledge support by DFG-grant WI no. 3211/4-1. B.C. acknowledges support by NSF grant no. AGS-1654382 to NJIT. We wish to acknowledge scientific discussions with the Waves in the Lower Solar Atmosphere (WaLSA; www.WaLSA.team) team, which is supported by the Research Council of Norway (project no. 262622) and the Royal Society (award no. Hooke18b/SCTM). This paper makes use of several ALMA datasets with the following project numbers: ADS/JAO.ALMA#2016.1.00423.S, ADS/JAO.ALMA#2016.1.00050.S, ADS/JAO.ALMA#2016.1.01129.S, ADS/JAO.ALMA#2016.1.01532.S, ADS/JAO.ALMA#2016.1.00202.S, ADS/ JAO.ALMA#2017.1.00653.S and ADS/JAO.ALMA#2017.1.01672.S. We are grateful to Bart de Pontieu and Alexander Nindos, PIs of ALMA datasets linked to project nos. 2016.1.00050.S and 2017.1.00653.S, respectively, and for their useful comments. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), NSC and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. We are grateful to the many colleagues who contributed to developing the solar observing modes for ALMA and for support from the ALMA Regional Centres. The AIA and HMI data are courtesy of the NASA/SDO, as well as AIA and HMI science teams.
© 2020 The Author(s).
Copyright 2021 Elsevier B.V., All rights reserved.
- Sun: Chromosphere
- Sun: Oscillations
- Sun: Radio radiation
ASJC Scopus subject areas
- Physics and Astronomy(all)