This was another very nice session and its amazing that it is August 1. The new season starts in one month so let hope that this consistency is representative of more good things to come.
Terrestrial weather was frightening yesterday afternoon based on the lightning map for stations in the East and Southeastern US. Amazingly the noise level here overnight and this morning was not bad in spite of a new storm system in the central US. It did not impact my morning CW sked in spite of using the transmit-vertical for receive as I tested a new approach (new for this station) to making a signal.
Geomagnetic activity was very quiet. The Bz was at unity or pointing slightly to the North. Solar wind velocity was calm near 330 km/s. DST values appear to be nominal. A geomagnetic storm is forecast for the coming days as a geoeffective coronal hole moves into position:
Steve, VE7SL, reports the completion of what is believed to be the first crossband SSB QSO with a 630-meter Maritime station. Steve explains:
“Just had a crossband QSO with VA7MM/ marine mobile . I was on 630m SSB and he was on 20m SSB. Certainly the 1st 630m SSB in VE land…as well as 1st maritime mobile work involving 630m. They are cruising further north of here in Georgia Strait and will down here (Mark and Toby VE7CNF) for an eyeball on the…weekend along with their XYL’s as they were last summer. About 40% of all 630m Canadians in one place!”
Steve also reports “that things definitely getting better to the west.” He decoded seven WSPR stations and was decoded by ten unique stations. WH2XCR decoded Steve 32 times and Laurence decoded Steve thirty times, many of which were at CW levels and a session best report of -8 dB S/N. Steve goes on to report “Nil from the east. My hat is off to the dedicated group of western spotters at this time of the year! I’m really amazed at how well this 68W TPO can do.” Steve also notes that he expects that its possible that the Pacific path will open up due to auroral activity in the coming days while suppressing the East / West path.
Neil, W0YSE/7 / WG2XSV, notes great activity and propagation in this report:
In the East, Phil, VE3CIQ, reported less activity with a late start to band openings there. This may be related to the number of large storms on the eastern half of the continent. Phil indicates that he decoded VE3EFF and WH2XGP on the transcontinental path and he was decoded by SWL/K9, WA3TTS and WI2XFI.
Larry, W7IUV / WH2XGP, wonder if the band is better, decoding seven WSPR stations and being decoded by twelve unique stations.
Rick, W7RNB / WI2XJQ, provided over 240 reception reports for stations during this session for seven stations:
Joe, NU6O / WI2XBQ, reports numerous single-digit S/N reports from stations to the North of his location in northern California. He indicates that these reports may be signalling the upcoming change in geomagnetic conditions.
Roger, VK4YB, has been using the travels of EJTSWL to perform some antenna testing and offers these details:
“EJTSWL has been roaming the Northern Territories and Queensland recently.He has provided valuable reports from a new direction from my QTH.I have always thought that my original top fed vertical was very directional.According to theory it should be end-fire, which is to the North-East and to the South-West.However, all the stations that I regularly communicate with are on this line. So I have neverbeen able to prove it. Until Now!I put up a second, near identical antenna, looking to the North-West and to the South-East.Whenever I used this antenna it was always about 10dB down on the original one.Was it just a fizzer or was it sending a good signal and nobody there to hear it?So tonight, with EJTSWL located right on its beaming heading, I switched to that antenna.My signal dropped about 10dB with everybody, as expected, except EJTSWL, who got me 8dB stronger! You beauty! I would be happy with that kind of directivity on 20m never mind 630m!I repeated the test numerous times and the improvement averaged out at 4.5dB. Still a very good result I think. This antenna may come in handy for JA or EU.73Roger, VK4YB”
Regional and continental WSPR breakdowns follow:
There were no reports from the trans-Atlantic, trans-African, or trans-Equatorial paths. UA0SNV was present but no reports have been filed at this time.
In the Caribbean, Eden, ZF1EJ, returned and reported signals from my station. His reports started very early in the evening, before dark here in Texas:
Laurence, KL7L / WE2XPQ, continues to see consistent sessions with a growing number of stations reporting him and being reported:
Merv, K9FD/KH6 / WH2XCR, had another very strong night on the VK path. Numerous post-sunrise reports were also registered. Merv’s reports are growing significantly as this season progresses and I am excited about the prospect of being able to receive him here again.
Jim, W5EST, presents, “PART 5: THEORY JUNGLE SAFARI IN E LAYER DURING 630M NIGHT”:
“Today’s illustration (left) depicts a relationship of E-region plasma frequency to altitude. Plasma frequency rises with E-region electron concentration, as its square root. Thanks to these electrons, the E-region presents your 630m signal a near-lossless GMF-permeated ionized region.
This magnetized ionized nighttime E-region confronts an ascending 630m RF signal ray with not one but two values of refractive index-squared (n2). Follow the brown arrows up from Altitude (km) to Plasma Frequency and then rightward to see these n2 values diverge as the RF gains altitude and plasma frequency rises. (Illustration at right follows the July 28 edition of this blog.)
The brown arrows point to whichever pair of n2 values on same-colored curves that correspond to the angle the 630m signal ray bears to the GMF. The two sepia 30° angle curves to which the brown arrows point suggest a path such as from South Carolina to the greater Chicago area, for instance.
Operating frequency at all times stays 630m near 475.5KHz, far below a GMF-determined gyrofrequency 1426KHz and deep down below HF. The explanations in Notes A & B below justify the E-region plasma frequency curve vs. altitude. The theory assumes that electrons and ions can recombine and that there are no vertical winds in the ionized region, and no thermal disequilibrium such as near sunset and sunrise. It’s just a starting point.
Theory could go on to explain how peak electron concentration and plasma frequency can vary from night to night. Acoustic ripples (gravity waves), solar flares and particle storms may further affect the E-region: so many things that make 630m rich with opportunities for us experimenters!
Tomorrow, let’s consider what today’s discussion implies for sunrise SR and sunset SS times. Then a future post can discuss O/X reflection paths along which a 630m signal travels in the nighttime E-region as its rays execute 630m hop reflections in the sky.
NOTE A: NIGHTTIME E-LAYER HAS A PLASMA FREQUENCY NEAR 630M
Recall that plasma frequency is proportional to the square root of the electron concentration.
The vertical structure of the E layer is primarily determined by the competing effects of ionization and recombination. At night the E layer weakens because the primary source of ionization is no longer present. After sunset an increase in the height of the E layer maximum increases the range to which radio waves can travel by reflection from the layer.
Zolesi and Cander (2013)* state that:
‘On average the electron density in the E layer corresponds to plasma frequency of ~3 MHz during the daytime. The night-time E layer remains weakly ionized with corresponding plasma frequencies between 0.4 and 0.6 MHz, which makes classical ionosonde measurements impossible. [JH emphasis.]’
Jenn p. 4 shows daytime E-region electrons peaking at 2×105/cm3.
Mitra (1957)** reported that negligible positive ion concentration at 87km increases to about 7×103/cm3 at 110 km. This statement bounds the graphical illustration example today.
E-region noon critical frequency was 3.62MHz in central US 7/29/16. http://www.spacew.com/www/foe.html Accordingly, I estimate nighttime critical frequency 677KHz = 3.62MHz x sqrt(7×103/cm3 / 200×103/cm3) using Mitra’s electron concentration for nighttime and Jenn’s daytime peak value. I identify E-layer critical frequency with peak plasma frequency. In VK, daytime E-layer critical frequency ranges 3.2-3.4MHz, so corresponding VK nighttime critical frequency would be 599KHz to 636KHz.
Throughout this discussion, recognize that GMF storms and geographic variations may significantly alter the peak plasma frequency from above to below 475 KHz. Scale the plasma frequency vs. altitude curve of today’s graphical illustration to suit.
*Zolesi,B., & Cander, L.R. (2013) Ionospheric Prediction and Forecasting. Springer Science & Business Media. p.88. https://books.google.com/books?id=bj65BAAAQBAJ&pg=PA88&lpg=PA88&dq=E-layer+plasma+frequency+night&source=bl&ots=qod825IG5C&sig=n44GrnCuXqyKd1ii8pEg3idifeo&hl=en&sa=X&ved=0ahUKEwjSwLuQw5nOAhXTdSYKHR-nCisQ6AEITTAH#v=onepage&q=E-layer%20plasma%20frequency%20night&f=false
**Mitra, A.P. (1957) Night-time Ionization in the Lower Ionosphere, J. Atmos. Terr. Phys. 10(3): Part I: Recombination Processes, 140-152; Part II: Distribution of Electrons and Positive and Negative Ions, 153-162. http://adsabs.harvard.edu/abs/1957JATP…10..153M
NOTE B: NIGHTTIME E-LAYER PRESUMABLY FOLLOWS CHAPMAN THEORY
For a presentation of Sydney Chapman’s classic theory (1931) of ionospheric electron density in the E and F1 regions, see Jenn.*** Regions following Chapman theory have a buoyancy and temperature in the high atmosphere.
As presented by Jenn, daytime E/F1 conditions are the primary focus. The sun shines at a zenith angle C into the layer, like 34° from zenith at equinox noon in Little Rock, AR and 90° at sunrise and sunset. The theory predicts that the topside of the ionized region will remain ionized about the same as the sun angle goes down. But the point of maximum ionization will balloon downward in altitude in the morning and ascend in altitude in the afternoon. Indeed, the ionized region overall will get thicker in its altitude range near solar noon.
Why should Chapman theory model the E-region at night? Galactic and interstellar radiation sources continue to bathe and ionize the E-region to some extent at night.**** Space weather in the vicinity of the high magnetosphere may also source some E-region ionization. Temperature and buoyancy remain involved in the nighttime E-region.
So Chapman theory still seems applicable except that I see no reason to assume a concentrated solar radiation source positioned at an elevation angle of the sun, as one would do to analyze the daytime E-region. Accordingly, I assume that nighttime radiation effectively acts as if it comes down from the zenith all night. In the theory, I neglect a daytime factor cos C by setting it to unity.
Define height h0 to be the altitude where maximum electron density N0 and corresponding maximum plasma frequency occur in the region. In the theory H=kT/mg involves physical and molecular constants and temperature T in °K. I use curve-fit H=9km to make the electron density negligible at 87km altitude. Further following Mitra** I use 110km for altitude of nighttime peak electron concentration.
The E-region plasma frequency as graphed is generally sufficient to reflect 137KHz (2200m) waves from altitudes 10-20km lower than the 100-110km altitudes from which the model would predict reflection of 475KHz (630m) RF.
The electron density according to Chapman theory at altitude h will be:
Ne(z)/N0 = exp[½(1 – z – e-z )] and z = (h – h0)/H.
Plasma frequency is proportional to square root of electron concentration Ne , and frequency is generally graphed log. This result follows, per the illustration.
ln[ωp /ωp,max]= ¼ (1 – z – e-z ) where z = (h – 110) / 9km.
****“X-ray stars 2-16Å may contribute significantly to the ionization at 80 to 90 km altitude during night when the star is around midnight culmination.” P. Waldteufel (1972). Incoherent Scatter and Vertical Incidence Observations. In McCormac, B.M. Ed. (1972) Physics and Chemistry of Upper Atmosphere: Proceedings of a Symposium. Boston: D. Reildel Publ. Co. p. 301-303. https://books.google.com/books?id=V__nCAAAQBAJ&pg=PA303&dq=plasma+frequency+night+mitra&hl=en&sa=X&ved=0ahUKEwjb4Oun0ZnOAhXJ2SYKHbG3AcQQ6AEILDAD#v=onepage&q=plasma%20frequency%20night%20mitra&f=false “
Additions, corrections, clarifications, etc? Send me a message on the Contact page or directly to KB5NJD gmail dot (com)!