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

TL;DR

This paper presents a method to reconstruct continuous three-dimensional solar wind proton speed and density over nearly three solar cycles using remote sensing data, spherical harmonics, and gap-filling techniques.

Contribution

It introduces a novel approach combining spherical harmonics and spectral analysis to fill data gaps and reconstruct solar wind parameters from IPS observations.

Findings

Reconstructed solar wind profiles with ~20% accuracy.

Improved spatial and temporal resolution of solar wind models.

Density estimates align well with Ulysses measurements.

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.