Monitoring precipitation and lightning via changes in atmospheric gamma radiation

Atmospheric γ‐radiation has been measured since 1999 and recently at three elevations 220m from the first site to ascertain position dependency and optimal elevation for observing γ‐rays from radon and radon‐progeny found in precipitation. Radiation from time‐independent and diurnal components was minimized in order to ascertain the reliability, accuracy and practicality of determining precipitation rates from correlated γ‐rates. Data taken with 4–12.9cm3 NaI detectors at elevations above ground of 9.91, 14.2, 15.7, and 21.4 m were fit with a model assuming a surface and/or volume deposition of radon progeny on/in water droplets during precipitation which predicts γ ‐ray rates proportional to the 2/5 and/or 3/5 power of rain rates, respectively. With mostly surface deposition and age corrections for radon progeny, the correlation coefficients improved with elevation and reached a maximum at 0.95 around 20m. Atmospheric γ radiation enables monitoring precipitation rates to 0.3 mm/h with time resolution limited only by counting statistics. High γ‐ray rates, decreasing with 40‐minute half‐life following lightning may be indirectly due to ions accelerated in electric field.