The forecast G1 storm finally arrived, upsetting band conditions and sending DST values reeling. Solar wind velocities exceed 500 km/s and the Bz is pointing slightly to the South. Terrestrial noise did not help as intense storms in the Midwest and central US impacted stations across North America.
Larry, W7IUV / WH2XGP, received a single report from VK2XGJ:
Neil, W0YSE/7 / WG2XSV, laments the dog days of summer:
Steve, VE7SL, reported that he decoded five WSPR stations and was decoded by eight unique stations including fourteen reports from WH2XCR.
Merv, K9FD/KH6 / WH2XCR, reports that high winds have damaged multiple antennas at his station. Merv provided the following comments:
Regional and continental WSPR breakdowns follow:
There were no reports from the trans-Atlantic, trans-African, or trans-Equitorial paths. UA0SNV was present but no reports have been filed at this time.
In the Caribbean, Eden, ZF1EJ, reported my signal during the session:
Laurence, KL7L / WE2XPQ, decoded VE7SL and WH2XGP and shared two-way reports with WH2XCR:
Merv, K9FD/KH6 / WH2XCR, operated with a damaged antenna system but still did pretty well:
Jim, W5EST, presents “PART 3: HOW INTERPRET SNR PEAKS AND VALLEYS ON MF/LF?”:
“Remarkably, the fewer number of nighttime peaks and valleys at 2200m compared to 630m leads to an interesting deduction. The math I blogged yesterday suggested that rate of change r in ionospheric reflectivity/absorption is relatively slow and/or that the ionospheric dapple’s ground speed s is relatively high. That way their ratio r/s is small compared to the number of dapples per kilometer √ρ distributing dapples horizontally at ionospheric altitude.
I’m emphasizing dapples per kilometer √ρ now because the dapple density ρ per square km suggests that dapples are randomly distributed like spots on a jaguar. But SNR peaks and valleys could result from ionospheric waves as well as dapple-spots. Compare with a water analogy: http://www.abc.net.au/news/2010-12-17/childs-play-at-goma/2379720 (scroll 1/3 to pool photo).
One might wonder whether you can justifiably compare 630m and 2200m in terms of peaks and valleys of SNR. Perhaps 630m and 2200m behaviors are totally independent if their RF wavefronts are reflected at different altitudes and see different “surfaces” or contours of the ionosphere. However, if the contours aren’t too far apart in altitude, then because of the nighttime continuity of the ionosphere as a physical entity, the contours probably are relatively similar in shape–like pages of a magazine when you deform it.
Today, let’s consider how motion of ionospheric contours, relative to a place where your signal reflects, makes your MF/LF signal act like an RF scanning beam to possibly resolve features in the underside terrain of the ionosphere. Resolution means maximum number of resolvable dapples/km.
WSPR’s 2 minute slots and stations’ TxPct apparently establish the timewise resolution and spatial resolution instead of the 630 meter band’s wavelength-based resolution. See the Appendix. Ten two-minute WSPR2 transmissions at a high 50% TxPct (15/hr) take 40 minutes to complete. The Appendix calculations are subject to correction and refinement, but so far they suggest that 630m and 2200m waves theoretically can resolve finer peak/valley event structures that WSPR’s decoder would ignore–if such ionospheric structures exist that densely.
On 2200m, the actual observed number of events per hour may be relatively few, I believe. This suggests that the number of incident temporary ionospheric disturbances (TIDs) is relatively low crossing the midpath reflection. Or wavelengths of ionospheric waves there are relatively long. Or a relatively slow ionospheric drift or wind is primarily responsible for carrying a subsisting dappled ionospheric texture across the MF/LF midpath reflection location.
All this calculation and thinking don’t make it the last word. If you have questions, suggestions, better wisdom, you name it, we deeply appreciate anything you’d like to contribute!
It’s time I looked at some WSPR SNR sequences for the 630/2200m bands with these questions in mind. I hope to do so in another blog post. GL.
APPENDIX: ESTIMATED RESOLUTION OF IONOSPHERIC STRUCTURE BY MF/LF WAVELENGTH
I arbitrarily regard ionospheric features around 2 wavelengths (2λ) to be the smallest resolvable features as far as a given wavelength signal is concerned. The corresponding maximum practical spatial resolution MPR in number of dapples per kilometer is about 1/(10×2λ) or 0.05/λ.
MPR = ~1/(10×2λ) = 0.05/λ.
Why this MPR formula? I emphasize “practical” resolution because SNR samples are the measurement here. For a peak or valley of SNR to be observed, an SNR sequence resulting from ionospheric underside areas about 2λ in diameter needs to have a definite increase/decrease or decrease/increase that includes about 10 values more or less. The 2-minute slots of the WSPR decoder and your station’s transmit percentage TxPct may not let SNRs be reported that fast, as discussed above.
The actually-present dapples-per-km √ρ that can be observed won’t be more than the resolution MPR. Math can express it this way:
√ρ < MPR = ~0.05/λ(km).
At this point, the numbers need to get more intuitive. So let’s use a number N’ to talk about maximum resolvable dapples per 100km to supplement the actual dapples per km that I designated√ρ. Also, put in frequency instead of wavelength. Then:
N’ = ~ 100 x 0.05/λ(km) = ~5/λ (dapples/100km) = f (5/c) > 100√ρ
where f is frequency and c = 3×105km/sec is the speed of light. Doing some arithmetic gives:
N’(per 100km) < ~ 16.7 f(MHz), which is about 8 dapples/100km at 0.475MHz and 2 dapples/100km at 0.137MHz.
But what about maximum resolvable dapples per hour? That would more nearly correspond in some sense to what I’d designate a Maximum Time Resolution MTR. Find the MTR of a wave traveling at speed s in ionosphere by multiplying N’, the maximum resolvable dapples per 100km, times the speed s by which dapples pass across the midpath reflection:
MTR = N’ s
What speed value should be used? In the nighttime, I think the fastest that speed is likely to be is the speed of sound s 100-250m/sec in the ionosphere.* Ionospheric horizontal drift speeds are likely lower, on the order of 100m/sec.** Ground speed of a wave in a drifting ionosphere would presumably be the vector sum (velocity arrows head-to-tail) of drift velocity and wave velocity.
MTR = N’ s < ~ 16.7 f (dapples/100km)(250m/sec)(3600sec/hr)(100km)/105m
MTR = N’ s = 71 dapples/hr at 0.475MHz and 20 dapples/hr at 0.137MHz.
To get 10 SNR samples to resolve a dapple would call for a SNR sample rate of 12 samples per minute on 630m and 3-4 samples per minute on 2200m. [i.e., 10 samples/dapple x MTR (dapples/hr) x (1hr/60min)].
I conclude that the much slower 1 sample/4minutes SNR sample rate that WSPR supplies at 50% TxPct must therefore be establishing whatever resolution of ionospheric underside structure that WSPR SNR sampling is providing us.
*“MSTIDs typically have periods in the range of 10 to 60 min, with horizontal wavelengths of 100 to 300 km and horizontal speeds from 100 to 250 ms-1 .” (p.2) and 305m/s (p. 9) of: Harris, T. J., M. A. Cervera, and D. H. Meehan (2012), SpICE: A program to study small-scale disturbances in the ionosphere, J. Geophys. Res., 117, A06321. http://onlinelibrary.wiley.com/doi/10.1029/2011JA017438/full 60sec swept CW at 3-15 MHz for NVIS soundings Feb. 26-29, 2008, near Adelaide, Australia; 30 sec rate at low latitudes in Queensland; and 30 sec rate in Puerto Rico.
** Kouba, D., et al. (19 Feb 2008). Ionospheric drift measurements: Skymap points selection. Radio Science 43(1) : http://onlinelibrary.wiley.com/doi/10.1029/2007RS003633/pdf See p.9 Fig. 6 F and E region velocities; and compare p.6, Table 2 re F-region; and intro p.2, col. 1 bottom. E region daytime drift was measured by digisonde at frequencies down to 2.0 MHz at Pruhonice, Czech Republic. Nighttime E-region critical frequency fell below 2.0 MHz, so only daytime drift velocity components are shown in Fig. 6 for Feb. 3, 2006.”
Additions, corrections, clarifications, etc? Send me a message on the Contact page or directly to KB5NJD gmail dot (com)!