Relationship between the atmospheric electric field and developed cumulonimbus clouds at the Kakioka Magnetic Observatory: Four hailstorms (6 May 2012, 4 April 2014, 16 June 2017, and 24 May 2018)
Mariko KUMAMOTO
Abstract
Four cases of hailstorms (on 6 May 2012, 4 April 4 2014, 16 June 2017, and 24 May 2018) have been observed by the Kakioka Magnetic Observatory in Ishioka City, Ibaraki Prefecture. Because we had been continuously monitoring the ground-level atmospheric electric field, it was possible to investigate the relationship between the atmospheric electric field and the structure of hailstorms. By comparing precipitation with data from the 3D radar of the Japan Meteorological Agency and Doppler radars installed at the Narita and Haneda International Airports, we determined the following characteristics of the variation of the atmospheric electric field.1) When a portion of the mid-level clouds with radar reflectivity of more than 53 dBZ (assumed to be the hail core region) approached 5 or 10 min before the occurrence of hail, the atmospheric electric field suddenly increased to the maximum positive potential.2) When the hail core region began to descend immediately before the occurrence of hail, the atmospheric electric field decreased sharply to the minimum negative potential.3) At the occurrence of hail, the atmospheric electric field fluctuations were observed in the positive and negative potentials. 4) When precipitation stopped, the atmospheric electric field changed sharply to the minimum negative potential. After the radar echo passed by, if cold advection was strong, the atmospheric electric field changed to the maximum positive potential. By monitoring changes in the atmospheric electric field and radar echoes, it may be possible to detect the arrival of a hail core region above an observation area from the changes noted in points 1), 2), and 3) and to recognize the danger immediately before hail begins to fall. In addition, in cases from April to October 2020 when the atmospheric electricity field varied widely, when cumulonimbus clouds developed and sudden heavy rain was at its maximum, the atmospheric electricity field was at the negative potential minimum or fluctuated around 0. It is considered that the former was associated with warm rain; the latter, with hail or with a hail core area overhead in the mid-level cloud. Besides it was the only case of precipitation at its maximum with a positive potential. These similar trends in prominent atmospheric electric field changes and precipitation at its maximum were observed in data of warm season (from April to October) from 2017 to 2020.
