CR2025_42 The Cause-mic Universe: Tracing Links between Solar Flare Variability (Quasi-Periodic Pulsations) and Earth’s Ionosphere with Causality

Lead Supervisor: Nachiketa Chakraborty, Department of Computer Science, University of Reading

Email: n.chakraborty@reading.ac.uk

Co-supervisors: Laura Hayes, Dublin Institute of Advanced Studies (DIAS); Malcolm Dunlop, Science and Technology Facilities Council; Mathew Owens, Department of Meteorology, University of Reading

Solar flares are outbursts of radiation across the electromagnetic waveband produced by the Sun impacting us here on Earth. While the basic physics underlying the mechanisms (like reconnection and instabilities) are well understood, the exact sequence of processes/events leading to specific flaring episodes are harder to trace. Specifically, X-ray and extreme ultraviolet flares show signs of (quasi)-periodic pulsations/oscillations (QPP) on timescales of minutes [1]. These appear to be synchronous with ionospheric pulsations – changes in electron density tracked by (very low frequency or VLF) radio emission as shown in figure below. These are very recent observations, and the origins of these purported pulsations are not understood. What triggers these events and drives them on is still ambiguous [1]. To probe this requires a fundamental revision of methodology – combining innovations in causal inference and signal processing and applying them to time-series observations of solar flares. Moreover, this rapid variability in the ionosphere can have significant impact on the Earth’s atmosphere and the environment in general [5]. It can trigger other processes in the Earth’s atmosphere like atmospheric gravity waves and alter forecasts of atmospheric dynamics. And it can also disrupt communication and navigation technology. Hence, it is critical to study origins of (rapid) ionospheric variability.
To this end, we pose the following questions-

1. What are the causes driving these QPPs, and their relation to the transient component of the flares [1,2,3]? What are physical mechanisms underlying this aspect of X-ray flares?
   Are these observed pulsation truly (quasi)-periodic? And if so, what is their significance [4]?
2. Can we demonstrate QPP / variability leads to ionospheric pulsations? For this we will need to perform lead/lag studies using non-linear, causal estimators [2,3] rather than use linear correlation methods.
   What is the impact on the dynamics of the Earth’s atmosphere? Can these change composition strongly on short timescales or impact acoustic gravity waves [1]?

These questions are not only interesting scientifically but are vital for forecasting space weather and its impact on us here on Earth. Space weather through solar eruptions has a dynamical influence on the Earth’s atmosphere. For example, the rapid (quasi-periodic) variability of the X-ray and EUV emission and the associated variability of Earth’s ionosphere, can trigger processes in Earth’s atmosphere like gravity waves (acoustic disturbances). These in turn impact small scale weather events like decelerating jet streams and circulation of polar vertices as also long-term climate perturbations [1,5]. Ionospheric variability can also cause disruptions for communication and pose hazard for astronauts and satellites. With our increasing dependence on satellite technology and presence in space for scientific, strategic but also commercial / industrial and environmental purposes, our understanding of these impacts is vital and preparation critical. This project aims to contribute to this big picture goal.

Training opportunities: 

During the PhD, the student will have opportunities to undergo training in both aspects of mathematical methods and the application domain. This is in addition to participation in conferences, which will also contribute to the academic/professional development (notably networking). The training plan will be regularly discussed and updated through discussions with the supervisors.

1. Summer schools run by London Mathematical Society.
2. The Data Assimilation Research Centre (DARC) offers a 4-day training in the fundamentals of Data Assimilation, the set of statistical/mathematical methods used for forecasting and parameter estimation.
3. NCAS runs several training sessions.

Student profile:

This project would be ideally suited to a student with suitable undergraduate training in the natural sciences especially physics, astronomy, geophysics and meteorology, mathematics, etc. It would be desirable if the student possesses some basic programming skills. 

Co-Sponsorship details:

The project will receive co-sponsorship from DIAS. This will be in the form of a placement and collaborative visits.

 References:

1. Laura A. Hayes et al., 2017, JGR Space Physics, “Pulsations in the Earth’s Lower Ionosphere Synchronized With Solar Flare Emission”
   https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017JA024647
2. N. Chakraborty, H. Turner, M. Owens, M. Lang, “Causal Analysis of Influence of Latitudinal Solar-Wind Structure on Corotation Forecasts” Solar Physics, 298 ISSN: 1573-093X, https://dx.doi.org/10.1007/s11207-023-02232-4
   N. Chakraborty and Peter Jan van Leeuwen, “Using mutual information to measure time lags from nonlinear processes in astronomy” Phys. Rev. Research 4, 013036, 18 January 2022
3. https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.4.013036
   F. Ait Benkhali, W. Hofmann, F.M. Rieger, & N. Chakraborty, A&A 634, A120 (2020) “Evaluating quasi-periodic variations in the γ-ray light curves of Fermi-LAT blazars” https://www.aanda.org/articles/aa/abs/2020/02/aa35117-19/aa35117-19.html
4. Adam Mann, PNAS, Sep, 2019, 116 (39) 19218-19221 “To improve weather and climate models, researchers are chasing atmospheric gravity waves”  https://doi.org/10.1073/pnas.1912426116