A new 3D solar wind speed and density model based on interplanetary scintillation

TL;DR

This paper introduces a new 3D model of solar wind speed and density based on interplanetary scintillation data, improving understanding of solar wind evolution and its interaction with interstellar matter.

Contribution

The paper presents a novel statistical filtering method and an analytic formula for modeling the latitudinal profiles of solar wind speed and density using IPS tomography data from 1985 to 2020.

Findings

The model aligns well with previous results, confirming the robustness of IPS-based solar wind studies.

A flexible analytic formula effectively captures the latitudinal variations of solar wind speed.

Refined data filtering enhances the accuracy of solar wind profile modeling.

Abstract

The solar wind (SW) is an outflow of the solar coronal plasma, expanding supersonically throughout the heliosphere. SW particles interact by charge exchange with interstellar neutral atoms and on one hand, they modify the distribution of this gas in interplanetary space, and on the other hand they are seed population for heliospheric pickup ions and energetic neutral atoms (ENAs). The heliolatitudinal profiles of the SW speed and density evolve during the cycle of solar activity. A model of evolution of the SW speed and density is needed to interpret observations of ENAs, pickup ions, the heliospheric backscatter glow, etc. We derive the Warsaw Heliospheric Ionization Model 3DSW (WawHelIon 3DSW) based on interplanetary scintillation (IPS) tomography maps of the SW speed. We take the IPS tomography data from 1985 until 2020, compiled by \citet{tokumaru_etal:21a}. We derive a novel statistical method of filtering these data against outliers, we present a flexible analytic formula for the latitudinal profiles of the SW speed based on Legendre polynomials of varying order with additional restraining conditions at the poles, fit this formula to the yearly filtered data, and calculate the yearly SW density profiles using the latitudinally invariant SW energy flux, observed in the ecliptic plane. Despite application of refined IPS data set, a more sophisticated data filtering method, and a more flexible analytic model, the present results mostly agree with those obtained previously, which demonstrates the robustness of IPS studies of the SW structure.