Thesis Defense: Effects Of The Solar Cycles And Longer-Term Solar Variations

Monday, July 22, 2019
10:00 AM - 11:00 AM
301 Morse Hall
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 Speaker:  Fatemeh Rahmanifard, Ph.D. Candidate

Advisor:  Nathan Schwadron
Title:  Effects Of The Solar Cycles And Longer-Term Solar Variations: Modulation Of Galactic Cosmic Radiation And Filtration Of Neutral Atoms From The Local Interstellar Medium

Recent solar conditions include a prolonged solar minimum (2005-2009) and a weak solar maximum in cycle 24. The Heliospheric Magnetic Field (HMF) strength was consistently weaker in solar cycle 24 compared to the previous maxima during the space age. These anomalies may indicate that we are entering an era of persistent decline in solar activity. I investigated past secular (grand) minima, especially the Maunder period (1645-1715) to gain further insight into the evolution of HMF during periods of extremely low activity. As a result of the unprecedentedly low solar activity, the fluxes of galactic cosmic rays (GCRs) have increased to levels never reported previously in the space age, which might limit safe human space exploration over long-term missions (e.g., to Mars). I used CRaTER data to examine the correlation between HMF, solar wind speed, and the modulation potential of the GCRs through solar cycle24. I used these results to estimate the deep space radiation environment; assuming that the present unusually low solar activity will persist and worsen in the coming years. 
Variations in the level of solar activity affect our heliosphere’s interaction with the Very Local Interstellar Medium (VLISM), as well. As the sun moves through the LISM, neutral atoms travel through the heliosphere and can be detected by IBEX. Interstellar neutral (ISN) hydrogen atoms travel on almost hyperbolic trajectories to the inner heliosphere. They are subject to solar gravity and radiation pressure as well as ionization processes. For ISN H, the radiation pressure decelerates individual atoms and shifts the longitude of their observed peak relative to that of ISN He. I used IBEX data to investigate how radiation pressure shifts the ISN H signal over almost an entire solar cycle (2009 to 2018) and created a new methodology to determine the Lyα effective radiation pressure. My study of IBEX H response functions prepares for future IMAP data, which will enable a significant reduction of uncertainties and improvements in our understanding of the effects of radiation pressure on interstellar neutral atoms.

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