Seasonal Variation of LF/MF Sky-Wave Field Strengths

The most recent LF/MF sky-wave data bank has been revisited and reorganized by this author for the purpose of studying seasonal variation. Measured monthly median field strengths of about 100 propagation paths from different regions of the world have been tabulated and studied. Conventional wisdom suggests that field strengths are the strongest during spring and autumn and are the weakest during summer. The current study, which is based on a much larger data bank, suggests that the conventional wisdom is only true under certain conditions and only true in certain areas of the world. This paper attempts to discuss seasonal variation in more detail, both qualitatively and quantitatively. A number of representative examples will be given. Impact of other factors affecting seasonal variation will be pointed out and discussed also.