CR2025_04 Understanding the mechanisms linking the solar wind and terrestrial lightning

Lead Supervisor: Chris Scott, Department of Meteorology, University of Reading

Email: chris.scott@reading.ac.uk

Co-supervisors: Keri Nicoll, Department of Meteorology, University of Reading; Graeme Marlton, Met Office; Brian Hare, ASTRON (NL radio astronomy) and University of Groningen

Evidence is mounting that variations in the space weather environment (controlled by the sun) can affect processes in Earth’s lower atmosphere.  It has been demonstrated that lightning rates over Europe are modulated by the arrival of high speed solar wind streams that arrive at Earth from the sun^[1,2] and that there is a direct link between lightning and the Earth’s ionosphere³ (the electrified portion of the Earth’s upper atmosphere). However, the mechanisms linking these processes are still poorly understood. This project aims to improve our understanding on this topic.

The project will have two stages. The first will be to expand on previous studies which found a link between lightning discharge rates and high speed solar wind from the sun^[1,2] .  This was previously undertaken using lightning data from the Met Office’s Arrival Time Difference (ATD) lightning detection system which used data from pre 2007 and only sampled part of an 11 year solar activity cycle. The proposed study would take lightning positioning data from the Met Office’s ATD network and its new lightning detection system, LEELA, which, when combined, would give almost 35 years of lightning data to analyse, allowing composite analysis to be run on multiple high speed solar winds across more than one solar cycle. In addition to this, the data can be reprocessed to provide previously unavailable amplitude data, allowing us to see if the lightning strike intensity and flash multiplicity is also modulated along with the frequency of lightning.

The second part of this project will seek to fully understand the mechanisms between solar wind streams and the increased lightning activity. There are two potential options.

• Conduct an observation campaign using balloon-borne high energetic particle sensors, (developed at the University of Reading) to observe changes in solar energetic particles during the passage of high speed solar wind streams at Earth. Identifying changes in the atmospheric profile induced by the solar wind will provide insight into the mechanism behind solar wind modulation of lightning.
• Through a collaborative relationship with ASTRON, who operate the LOw Frequency ARray (LOFAR) radio telescope, we will exploit the telescope’s high time and spatial resolution to map out lightning strikes in three dimensions, while detecting any simultaneous signature in the Earth’s ionosphere (the electrically charged part of the Earth’s upper atmosphere). Through this collaborative agreement we have co-authored a proposal for 100 hours of observation time in 2025 after the LOFAR upgrade, which should allow several lightning strikes and the associated ionospheric conditions to be observed across a solar wind event. LOFAR2.0 comes online in 2026, and operates for 5 years. the observation time is spread over the 5 years.

The results from both parts of this project are of significance to the Met Office. Firstly high speed solar wind streams are predictable well in advance. By fully understanding the effect on lightning we will be able to provide improved warnings to the public and stakeholders about potential increases in number and intensity of lightning strikes. Furthermore the Met Office’s LEELA lightning location system is sensitive to the condition of the ionosphere. This project will enable us to understand how changes in the solar wind may affect the lightning detection capabilities and in turn see how changes in lightning intensity and frequency feedback into the ionosphere. Finally, lightning has become a World Meteorological Organisation climate monitoring variable and this project will enable us to identify which increases in lightning are due to a changing climate and which can be attributed to solar wind streams.

Training opportunities:

This project comes with CASE funding from the UK Met Office, which comes with the opportunity of a placement of at least 3 months duration at the Met Office headquarters in Exeter.

In addition, there will be a fieldwork element requiring the preparation and launch of balloon-borne sensors on a campaign basis when high-speed solar wind streams are forecast at Earth.

There may also be an opportunity to visit The Netherlands to work with the LoFAR radio telescope team.

Student profile:

This project would be suitable for students with a degree in physics, meteorology or closely related environmental or physical science. 

Co-Sponsorship details:

The project will receive a CASE award from the Met Office.

References:

1. Scott, C. J. , Harrison, R.G. , Owens, M.J. , Lockwood, M. and Barnard, L.  (2014) Evidence for solar wind modulation of lightning. Environmental Research Letters, 9 (5). 055004. ISSN 1748-9326 doi: https://doi.org/10.1088/1748-9326/9/5/055004
2. Owens, M. J. , Scott, C. J. , Lockwood, M. , Barnard, L. , Harrison, R. G. , Nicoll, K. , Watt, C. and Bennett, A. J. (2014) Modulation of UK lightning by heliospheric magnetic field polarity. Environmental Research Letters, 9 (11). 115009. ISSN 1748-9326 doi: https://doi.org/10.1088/1748-9326/9/11/115009
3. Davis, C. J. and Johnson, C. G. (2005) Lightning-induced intensification of the ionospheric sporadic E layer. Nature, 435. pp. 799-801. ISSN 0028-0836 doi: https://doi.org/10.1038/nature03638