06/27/2023
By Kalpa Henadhira Arachchige

The Kennedy College of Science, Department of Physics & Applied Physics invites you to attend a Ph.D. Dissertation defense by Kalpa Harindra Henadhira Arachchige “Optimization of Numerical Simulations of the Solar Wind from the Sun to 1 AU.”

Degree: Doctoral
Date: Wednesday, July 5, 2023
Time: 1 p.m.
Location: WAN 405 (Hybrid); please email Kalpa Henadhira Arachchige for the Zoom meeting link.

Committee Chair: Prof. Ofer Cohen, Department of Physics & Applied Physics, University of Massachusetts Lowell

Committee Members:

  • Prof. Paul Song, Department of Physics & Applied Physics, University of Massachusetts Lowell
  • Prof. Noah Van Dam, Department of Mechanical and Industrial Engineering, University of Massachusetts Lowell

Abstract
The accuracy of solar wind predictions relies heavily on the input and the free parameters in solar wind models. To achieve precise predictions, utilizing an optimized space weather simulation tool is crucial. In the first part of this thesis, we introduce a synthetic magnetogram derived from a dynamo simulation as input for solar wind magnetohydrodynamics (MHD) simulations. We perform a quantitative study that compares the Alfvén wave solar atmosphere model (AWSoM-R) results within the Space Weather Modeling Framework (SWMF) for the observed (real) and the synthetic solar magnetogram input. We compare the results by analyzing the observed Extreme Ultra-Violet (EUV) images and comparing them with the reproduced results from the model. We also extract the simulation data along the earth’s trajectory to compare the solar wind result with in-situ observations. Initially, we conducted model optimization using the real magnetogram input, ensuring that the model parameters were adjusted to achieve better agreement with the observed data. Subsequently, we tested the model’s performance by applying the optimized parameters to the synthetic magnetogram input for a selection of Carrington Rotations (CRs) spanning solar cycles 23 and 24. Our results help quantify the ability of dynamo simulations to produce input to solar wind models and, thus, provide predictions for the solar wind at 1 au. In this study, we further investigate the relationship between solar wind predictions and the free parameters of the AWSoM-R model across different phases of Solar Cycle 24. Our results demonstrate that two critical free parameters of AWSoM-R, namely the Poynting flux to magnetic field ratio (SA/B⊙) and the transverse correlation length of the Alfvén waves perpendicular to the magnetic field (L⊥√B) at the lower boundary significantly influence the heating, acceleration, and predictions of the solar wind at 1 au. To establish a quantitative link, we fit these parameters to a six-order polynomial function based on the observed sunspot numbers during Solar Cycle 24, presenting an empirical relation with the sunspot number. The study encompasses steady-state simulations of the solar wind throughout various phases of Solar Cycle 24. The findings not only enhance our understanding of the role played by Alfvén waves in the solar atmosphere but also provide insights into how they impact solar wind observations at 1 au. Furthermore, these findings hold the potential for improving solar wind predictions throughout the different phases of Solar Cycle 24.