Abstract/Summary

Fog is a high-impact weather phenomenon which is challenging to forecast accurately. Measuring changes in atmospheric electricity has been proposed as a complement to other fog prediction methods, since fog is known to produce changes in the potential gradient (PG). Many aspects of the relationship between PG and fog remain unexplored, to which modern instrumentation for continuous monitoring of PG and visibility brings a new perspective. We describe several automatic methods of detecting fog events and apply them to a large dataset to understand the evolution of the PG during fog development. The median PG increase in fog is found to be 58 V/m, which is statistically significant compared with the 17 V/m standard deviation of PG in the pre-fog hours. However, the median lead time of this increase before the fog onset was found to be 0.4 hours, compared to 0.6 hours using solely visibility data. While fewer fog events were able to be predicted using PG (55% of cases) than visibility (64% of cases), the PG was much more likely to give a longer lead time (of over 2 hours) than visibility (30% versus 13% respectively). This indicates that PG measurements would be a useful additional tool in fog prediction.