ALL meanings of d layer
d lay·er
D d - noun d layer the lowest area of the ionosphere, having increased ion density and existing only in the daytime: it begins at an altitude of about 70 km (c. 43 mi) and merges with the E layer 3
- noun d layer the lowest region of the ionosphere, characterized by mounting electron and ion density: exists, during the day only, from about 43 to 50 miles (70 to 80 km) altitude. 1