PROPAGATION EFFECTS ON THE LIGHTNING-GENERATED ELECTROMAGNETIC-FIELDSFOR HOMOGENEOUS AND MIXED SEA-LAND PATHS

The influences of the path of propagation on the shape and amplitude o f the electric fields and electric field derivatives generated by ligh tning return strokes were investigated. Results are presented for the cases where (1) both the lightning return stroke and the point of obse rvation are located over finitely conducting, homogeneous ground and ( 2) the lightning return stroke is located over sea and the point of ob servation is located over land at some distance from the sealand bound ary. For propagation paths over finitely conducting ground the electri c field derivative can decrease significantly in propagation distances as small as 1000 m. When the path of propagation is partly over sea a nd partly over land, the propagation effects on the electric radiation field derivative are significant unless the width of the land portion of the propagation path is less than a few tens of meters.