Abstract/Summary

A miniaturized scintillator (“microscintillator”), was flown on a meteorological radiosonde to observe energetic particles in the lower atmosphere. A PiN diode was used to measure the light from the microscintillator to count rates and energies of ionizing radiation from the ground up to the stratosphere (32 km). The flight, over the southern UK on August 27, 2018, occurred during a geomagnetic storm. Low-energy (50–150 keV) particles in the stratosphere were detected in addition to the usual signal from higher-energy cosmic rays. Unusually for these miniaturized radiosonde systems, which are designed to be disposable, the payload was retrieved. This allowed for re-calibration of the microscintillator, which confirmed the low-energy particle detection. Laboratory tests excluded thermal effects on the microscintillator instrument as the origin of the signal. Data from the NOAA POES spacecraft offer the explanation that the microscintillator detected bremstrahhlung X-rays from energetic electron precipitation (EEP). EEP events may affect weather and climate through a range of physical mechanisms, and this midlatitude observation, well away from the auroral oval, extends the region over which meteorological effects of EEPs need to be assessed. Our findings underline the value of balloon measurements in providing rapid response to space weather events. The energy-discriminating and altitude-sensitive capability of the microscintillator augments spacecraft observations from below.