Reconstruction of Helio-Latitudinal Structure of the Solar Wind Proton Speed and Density

Justyna M Sokół,Maciej Bzowski,Munetoshi Tokumaru,Paweł Swaczyna

doi:10.1007/s11207-015-0800-2

Justyna M Sokół, Maciej Bzowski + Show 2 more

Open Access

https://doi.org/10.1007/s11207-015-0800-2

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Abstract

The modeling of the heliosphere requires continuous three-dimensional solar wind data. The in-situ out-of-ecliptic measurements are very rare, so that other methods of solar wind detection are needed. We use the remote-sensing data of the solar wind speed from observations of interplanetary scintillation (IPS) to reconstruct spatial and temporal structures of the solar wind proton speed from 1985 to 2013. We developed a method of filling the data gaps in the IPS observations to obtain continuous and homogeneous solar wind speed records. We also present a method to retrieve the solar wind density from the solar wind speed, utilizing the invariance of the solar wind dynamic pressure and energy flux with latitude. To construct the synoptic maps of the solar wind speed we use the decomposition into spherical harmonics of each of the Carrington rotation map. To fill the gaps in time we apply the singular spectrum analysis to the time series of the coefficients of spherical harmonics. We obtained helio-latitudinal profiles of the solar wind proton speed and density over almost three recent solar cycles. The accuracy in the reconstruction is, due to computational limitations, about 20%. The proposed methods allow us to improve the spatial and temporal resolution of the model of the solar wind parameters presented in our previous paper (Sok\'o{\l} et al. 2013) and give a better insight into the time variations of the solar wind structure. Additionally, the solar wind density is reconstructed more accurately and it fits better to the in-situ measurements from Ulysses.

Highlights

The heliosphere is a cavity in the local interstellar medium created by the solar wind (SW thereafter), the plasma that originates from the Sun
The SW is one of the main factors that create the heliospheric environment from distances within a few solar radii of the Sun to beyond the edge of the solar system, where it interacts with the surrounding interstellar medium
The distribution of the SW speed has a significant imprint on the production of energetic neutral atoms (ENA) of various energies (McComas et al, 2012, 2014)

Summary

Introduction

The heliosphere is a cavity in the local interstellar medium created by the solar wind (SW thereafter), the plasma that originates from the Sun. The required dimensions are: time, latitude, and distance to the Sun. In-situ measurements of the SW are available from the mid-1960s, but mostly in the ecliptic plane and at 1 AU (for recent review, see Bzowski et al, 2013). Bame et al, 1992; McComas, Gosling, and Skoug, 2000; McComas et al, 2000). In-situ measurements of the SW out of the ecliptic plane were only carried out by Ulysses from 1990 to 2009 They were point measurements, and a time series of these observations is in reality a convolution of variabilities in time, distance, and helio-latitude. The SW is observed by remote-sensing methods, by interplanetary scintillation (IPS thereafter; e.g. Hewish, Scott, and Wills, 1964; Houminer, 1971; Coles et al, 1980; Kojima et al, 2004) and by Lyman-α helioglow (e.g. Lallement, Bertaux, and Kurt, 1985; Bzowski et al, 2003) observed by the Solar Wind ANisotropy (SWAN) instrument onboard the SOlar and Heliospheric Observatory (SOHO)

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