雷

Top rain radical - the indexing component. Pictures clouds with falling raindrops. Marks 雷 as a weather phenomenon: thunder rolls during storms, so the rain radical anchors it in the same family as 雪 (snow), 雾 (fog), 霜 (frost), 露 (dew), 电 (lightning, when fuller).

Bottom 田 - historically a single circle (eventually replicated in oracle bone forms) showing the rolling sound of thunder echoing across the land. Standardized later to the field-square shape. Carries the rumbling-roar meaning, not "rice paddy" - the resemblance to 田 is graphic only.