Dr Fan Lei

Senior Research Fellow

Academic and research departments

Surrey Space Centre.


A. D. P. Hands, F. Lei, C. S. Davis, B. J. Clewer, C. S. Dyer, K. A. Ryden (2022)A New Model for Nowcasting the Aviation Radiation Environment With Comparisons to In Situ Measurements During GLEs, In: Space weather20(8)

Significant increases to the atmospheric radiation environment are recorded by a network of ground level neutron monitors as ground level enhancements (GLEs). These space weather phenomena pose a risk to aviation via single event effects in aircraft electronics and ionizing dose to passengers and crew. Under the UK Space Weather Instrumentation, Measurement, Modeling and Risk programme, we have developed a new model to provide nowcasts of the aviation radiation environment, including both the galactic cosmic ray (GCR) background and during GLE events. The Model for Atmospheric Ionising Radiation Effects (MAIRE+) uses multiple data sources to characterize primary GCR and GLE particle spectra and combines these with precalculated geomagnetic and atmospheric response matrices to predict particle fluxes from ground level to 20 km altitude across the entire globe. Two European neutron monitors (located at Oulu in Finland and Dourbes in Belgium) are used as the primary indicators of GLE intensity in order to maximize accuracy over UK airspace. Outputs from MAIRE+ for the historical GLEs in September and October 1989 are compared to recalibrated empirical data from a solid‐state detector that was carried on Concorde in that period. The model will be hosted in the UK and will provide additional capability to the Met Office Space Weather Operations Center (MOSWOC). Plain Language Summary Ionizing radiation in the atmosphere is primarily caused by galactic cosmic rays (GCR) interacting with the upper atmosphere, creating showers of secondary radiation. At aviation altitudes the radiation environment is hundreds of times more intense than that experienced at the ground level. This relatively stable background level of radiation is punctuated by space weather events called ground level enhancements (GLEs), when energetic solar protons arrive at Earth and lead to elevated atmospheric radiation levels that can be orders of magnitude greater than background levels. Under the UK Space Weather Instrumentation, Measurement, Modeling and Risk programme, we have developed a new model to provide nowcasts of the aviation radiation environment, including both the GCR background and during GLE events. Through our Model for Atmospheric Ionising Radiation Effects, we show how data from ground level neutron monitors can be used to characterize the atmospheric radiation environment from ground level to 20 km altitude across the entire globe. Key Points The new Model for Atmospheric Ionising Radiation Effects (MAIRE+) is presented MAIRE+ uses neutron monitor data, sunspot number, Kp, and geostationary proton flux to nowcast the aviation radiation environment Model outputs are compared to data from a solid‐state detector carried on board Concorde during ground level enhancements in 1989

C Dyer, Alexander Hands, Keith Ryden, F Lei (2017)Extreme Atmospheric Radiation Environments & Single Event Effects, In: IEEE Transactions on Nuclear Science65(1)pp. 432-438 IEEE

Data from ground-level radiation monitors and cosmogenic nuclides are combined to a give a probability distribution for severe radiation events related to the well quantified event of 23 February 1956. Particle fluxes, single event effects rates and dose rates are calculated for ground-level and aerospace systems. The event of February 1956 would provide a challenge to air safety while more extreme events seen in historical records would challenge safety-critical ground systems. A new space weather hazard scale based on this event could be used to give rapid assessment of the radiation hazard using high latitude neutron monitor data.

Alexander Hands, F Lei, Keith Ryden, C Dyer, Craig Underwood, C Mertens (2016)New Data and Modelling for Single Event Effects in the Stratospheric Radiation Environment, In: IEEE Transactions on Nuclear Science64(1)pp. 587-595 IEEE

The upper atmosphere is a transition region between the neutron-dominated aviation environment and satellite environment where primary protons and ions dominate. We report high altitude balloon measurements and model results characterising this radiation environment for single event effects (SEE) in avionics. Our data, from the RaySure solid-state radiation monitor, reveal markedly different altitude profiles for low linear energy transfer (LET) and high LET energy depositions. We use models to show that the difference is caused by the influence of primary cosmic ray particles, which induce counts in RaySure via both direct and indirect ionization. Using the new Model of Atmospheric Ionizing Radiation Effects (MAIRE), we use particle fluxes and LET spectra to calculate single event upset (SEU) rates as a function of altitude from ground level to the edge of space at 100 km altitude. The results have implications for a variety of applications including high altitude space tourism flights, UAVs and missions to the Martian surface.

A. D. P Hands, F Baird, K. A Ryden, C. S Dyer, F Lei, J. G Evans, J. R Wallbank, M Szczykulska, D Rylett, R Rosolem, S Fowler, D Power, E. M Henley (2021)Detecting Ground Level Enhancements Using Soil Moisture Sensor Networks, In: Space Weather19(8)e2021SW002800

Ground level enhancements (GLEs) are space weather events that pose a potential hazard to the aviation environment through single event effects in avionics and increased dose to passengers and crew. The existing ground level neutron monitoring network provides continuous and well-characterized measurements of the radiation environment. However, there are only a few dozen active stations worldwide, and there has not been a UK-based station for several decades. Much smaller neutron detectors are increasingly deployed throughout the world with the purpose of using secondary neutrons from cosmic rays to monitor local soil moisture conditions (COSMOS). Space weather signals from GLEs and Forbush decreases have been identified in COSMOS data. Monte Carlo simulations of atmospheric radiation propagation show that a single COSMOS detector is sufficient to detect the signal of a medium-strength (10%–100% increase above background) GLE at high statistical significance, including at fine temporal resolution. Use of fine temporal resolution would also provide a capability to detect Terrestrial Gamma Ray Flashes (via secondary neutrons) which are produced by certain lightning discharges and which can provide a hazard to aircraft, particularly in tropical regions. We also show how the COsmic-ray Soil Moisture Observing System-UK detector network could be used to provide warnings at the International Civil Aviation Organization “Moderate” and “Severe” dose rate thresholds at aviation altitudes, and how multiple-detector hubs situated at strategic UK locations could detect a small GLE at high statistical significance and infer crucial information on the nature of the primary spectrum.