TY - JOUR
T1 - An Atlas of Coronal Electron Density at 5R⊙, II
T2 - A Spherical Harmonic Method for Density Reconstruction
AU - Morgan, Huw
N1 - Funding Information:
I am grateful for the comments of an anonymous referee that greatly improved this article. The SOHO/LASCO data used here are produced by a consortium of the Naval Research Laboratory (USA), Max-Planck-Institut fuer Aeronomie (Germany), Labor-atoire d’Astronomie (France), and the University of Birmingham (UK). SOHO is a project of international cooperation between ESA and NASA. The STEREO/SECCHI project is an international consortium of the Naval Research Laboratory (USA), Lockheed Martin Solar and Astrophysics Lab (USA), NASA Goddard Space Flight Center (USA), Rutherford Appleton Laboratory (UK), University of Birmingham (UK), Max-Planck-Institut fur Sonnen-systemforschung (Germany), Centre Spatial de Liege (Belgium), Institut dOptique Theórique et Appliquée (France), and Institut d’Astrophysique Spatiale (France).
Publisher Copyright:
© 2019. The American Astronomical Society.
PY - 2019/5/1
Y1 - 2019/5/1
N2 - This is the second of a series of three papers that present a methodology with the aim of creating a set of maps of the coronal density over a period of many years. This paper describes a method for reconstructing the coronal electron density based on spherical harmonics. By assuming a radial structure to the corona at the height of interest, line-of-sight integrations can be made individually on each harmonic basis prior to determining coefficients, i.e., the computationally expensive integrations are calculated only once during initialization. This approach reduces the problem to finding the set of coefficients that best match the observed brightness using a regularized least-squares approach and is very efficient. The method is demonstrated on synthetic data created from both a simple and an intricate coronal density model. The quality of reconstruction is found to be reasonable in the presence of noise and large gaps in the data. The method is applied to both Large Angle and Spectrometric Coronagraph Experiment C2 and Solar Terrestrial Relations Observatory Cor2 coronagraph observations from 2009 March 20, and the results from both spacecraft compared. Future work will apply the method to large data sets
AB - This is the second of a series of three papers that present a methodology with the aim of creating a set of maps of the coronal density over a period of many years. This paper describes a method for reconstructing the coronal electron density based on spherical harmonics. By assuming a radial structure to the corona at the height of interest, line-of-sight integrations can be made individually on each harmonic basis prior to determining coefficients, i.e., the computationally expensive integrations are calculated only once during initialization. This approach reduces the problem to finding the set of coefficients that best match the observed brightness using a regularized least-squares approach and is very efficient. The method is demonstrated on synthetic data created from both a simple and an intricate coronal density model. The quality of reconstruction is found to be reasonable in the presence of noise and large gaps in the data. The method is applied to both Large Angle and Spectrometric Coronagraph Experiment C2 and Solar Terrestrial Relations Observatory Cor2 coronagraph observations from 2009 March 20, and the results from both spacecraft compared. Future work will apply the method to large data sets
KW - solar wind
KW - Sun: corona
KW - Sun: coronal mass ejections (CMEs)
KW - Solar wind
UR - http://www.scopus.com/inward/record.url?scp=85069950632&partnerID=8YFLogxK
U2 - 10.3847/1538-4365/ab125d
DO - 10.3847/1538-4365/ab125d
M3 - Article
SN - 0004-637X
VL - 242
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 1
M1 - 242
ER -