http://59.160.210.74:8080/jspui/bitstream/123456789/454/1/VLF%20signals%20in%20summer.pdf (Bose National Centre for Basic Sciences)

http://www.ursi.org/proceedings/procGA11/ursi/GP2-15.pdf

Paul,

I’m sending this link because the data seems unusual. I thought it might come in handy if something of this sort appears in efforts within this group; but I am not inclined to have confidence in the results of the attached unless I happen to run across similar independent results (and I did not, in my search last week). So, I’m planning to just file the attached but thought you might want to see it because it’s interesting if not well-supported by other studies.

Plots* in the link below show an interesting distribution of VLF broad daytime amplitude maxima that are (a) greater than, or (b) less than nighttime maxima.

The study used a single transmitter (18.2 kHz), and receivers at distances from 500 km to ~ 3,000 km, with two-week collections in summer and winter.

I tried to correlate (a) or (b) (daytime maxima greater than or less than nighttime maxima) with distance or bearing and did not find a reasonable correlation.

In winter 3 of 9 RX stations had daytime amplitude (broad) maxima greater than nighttime maxima.

In summer 3 of 12 RX stations had daytime amplitude (broad) maxima greater than nighttime maxima.

Winter “day maximum minus night maximum” (averaged over 2 weeks) ranged (by RX station) from +20 dB to -11 dB, with 6 of 9 RX stations on the - side; the winter average of all RX stations seemed to be around -0.5 dB

Summer “day maximum minus night maximum” (averaged over 2 weeks) ranged (by RX station) from +8 dB to -10 dB, with 9 of 12 RX stations on the - side; the summer average of all RX stations seemed to be around -2 dB

The wide range of “day maximum minus night maximum” results (by RX station), together with the absence of any apparent correlation with distance or bearing, makes this data seem unusual. Well, maybe not for LF/VLF.

* Figure 3 and Figure 7

73,  Jim AA5BW