雷暴等时线

Isobront \I"so*bront\ ([imac]"s[-o]*br[o^]nt), n. [Iso- + Gr.
bronth` thunder.] (Meteor.)
An imaginary line, or a line on a chart, marking the
simultaneous development of a thunderstorm, as noted by
observing the time when the thunder is heard at different
places.
[Webster 1913 Suppl.]