Some particular observations on diurnal phase variations ... · RADIO SCIENCE Journal of Research...
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RADIO SCIENCE Journal of Research NBS /USNC-URSI Vol. 680, No. I, Ja nuary 1964 Some Particular Observations on Diurnal Phase Variations of VLF Transmissions Received in Paris B. Decaux and A. Gabry Contri bution From Centre National d'Etudes de s Tele communications, Pari s-Bagneux, Fr ance Observations made in Paris, Franc e, of the phase of var ious fr equenc y s tabili zed VLF transmitters are report ed. Descriptions are giv en of the seasonal dependence of the diurnal phase s hift on an arctic path, effects following so lar flares, e ff ects of two solar ecli pses, and observation following the high-al titude nucl ear explosion of Jul y 9, 1962. For some years the ONET Fr equeney Department has continuously r ecorded the phase of the stabilized VLF transmissions. The initial aim. of this record- in g was to compare the ONET's Atomiclu-on stand- ard to atomic standards of other laboratories in the world. Afterwards, intercst in g researching research on perturbation s cfl,used to the transit-time of the transmissions by the propa gat ion phenomena , led to an exten ion of the equipment. The recordin gs were made at first on GBR 16 kc /s, and successively on other transmissions when they were stabilized. At the present time, six transmissions are recorded: GBR 16 l\O/s (4}f yem·s), NAA :1 4, 7 kc/s (2 years), NBA 18 kc/s (3 years), NPG/ NLK fir t 18, 6 now 24 kc/s (2 years ), NPM 19 , 8 kc/s (2 years), and NSS 22, 3 kc/s (2 years). The re cording or NPM is almost unusable in summer , because of the very poor siglml-to-noise ratio. The recording equipment uses a servo phfl,se-foll ower and synchronous detection. In addition to the phase recordin g, the ampli tude of the signals is also recorded. The var ious well-known forms of the phase curves rel ated to the hours and the seasons were clearly observed on all the transmissions. This pfl,per will, however, deal only with departures observed during particular geographic situfl,tions fl,nd ionospheric phenomena. Fil'st, 3 years of recording of NBA transmissions give a good knowledge of the seasonal evolu tion of the variations at the time of sunrise and sunset [Decfl,ux et al., 1961 a and 1963b]. It is well known that the received phase changes quicldy when the sun rises in each reflection point in the D-region, and remains nearly constant during the transition of the shfl,dow line from one reflection point to the other [Ricker, 1963]. The var i ation at the S Wl set is more pro gressive. We have compared the observed and calcul ated valu es of the time interval between the successive points. The observed valu es are deduced from ex- perimental curves by averaging on several conseeu- tive days. The calcul ated values take in to account the progressive shifting of the gro und refl ection points, and also the influence of the ozone lnyer . The differences between observed and caleuh),t ed 21 values, for various typical epochs of lhe seasons, do not generally exceed 5 min. It is interesting to note that the amp litude of phase variation between night and dfLY chfl, nges sli ghtly from sea on to sraso n: 70 p.sec at win tel' s olstices, 80 ,usec at summer solstices, 75 p'sec at equi- noxes. The wnves path at ni ght would be about 200 km greater than the len gth of the great circle Ba.lboa-BfI,gn eux. The NPM and NPG/ NLK paths cross a pm"L of arctic polar regions. The in terpre tation of N PM phase curves is uncertain because of the low siglH), strength, but the NPG/ NLK records are excellent [Decaux et al., 196 3c]. The Jim Creek-Paris path cross the pol ar region on about 2,000 km (X of" the total length). Therefore one observes the well known "double humped " curves, ince the part 0 p at h crossing the polar region are, according Lo the season, continually in light, or continu fl, lly in clark. }.iforeovel' this path hns an interestin g peculiarity: both extremities have nem-Iy equal latitudes ( Jim Oreek: 48° 12' , Bagneux: 48°46'). Then the part of the great circle beyon d the polfLr circle is in the middle of the total path, and the 60 ° W is an axis of sym. metr y (fig. 1). Near 0400 UT, the path is thus en tirely in dark at every time or yefl,l" , except from the end of" April to the midd le of August . Between those two limits, the wfI,ve path pass progressively, on all its length, from night to day fl,nd vice-versa. Then the phase curves have the characteristic forms, successively indicated in figure 2, expb in ed below. At spring equinox ( fi g. 2fL) the form is the classic trapezium. At tbe beginning of 1hy ( fi g. 2b) the night effect (pefLk) l asts for very sbort tim.e near 0400 UT. In the middle of May ( fi g. 2e) a d ayli ght eff ect (dip) fL pp ears near 0400 U T . From the beginning of June t ill nearly the 10th of Jul y (fig. 2d), the dfLy light effect is eomplete at 0400. Near the 1 st of A ugu st the day and ni ght eff ects are prnctically eq ual (fi g. 2e); then one obsen 'es, during a Yery few days, a inversion, from the 0400 (dip) to a peale The fig u ee 2f and . 2g shows the C Ul'\Tes are practically inverted around the 20th of August and the 20th of December. In August, the curve
Transcript of Some particular observations on diurnal phase variations ... · RADIO SCIENCE Journal of Research...
RADIO SCIENCE Journal of Research NBS/USNC-URSI Vol. 680, No. I , January 1964
Some Particular Observations on Diurnal Phase Variations of VLF Transmissions Received in Paris
B. Decaux and A. Gabry
Contribution From Centre National d'Etudes des Telecommunications, Pari s-Bagneux, France
Observations made in Paris, France, of the phase of various fr equency s tabili zed VLF transmitters are reported. Descriptions are given of the seasonal dependence of the diurnal phase shift on an arctic path, effects following solar flares, effects of two solar ecli pses , and observation following the high-altitude nuclear explosion of July 9, 1962.
For some years the ONET Frequeney Department has continuously recorded the phase of the stabilized VLF transmissions. The initial aim. of this recordin g was to compare the ONET's Atomiclu-on standard to atomic standards of other laboratories in the world. Afterwards, intercstin g researchin g research on perturbations cfl,used to the transit-time of the transmissions by the propagation phenomena, led to an exten ion of the equipment. The recordin gs were made at first on GBR 16 kc/s, and successively on other transmissions when they were stabilized. At the present time, six transmissions are recorded: GBR 16 l\O/s (4}f yem·s), NAA :1 4, 7 kc/s (2 years), NBA 18 kc/s (3 years), NPG/NLK fir t 18, 6 now 24 kc/s (2 years), NPM 19, 8 kc/s (2 years), and NSS 22, 3 kc/s (2 years). The recording or NPM is almost unusable in summer, because of the very poor siglml-to-noise ratio. The recording equipment uses a servo phfl,se-follower and synchronous detection. In addition to the phase recordin g, the amplitude of the signals is also recorded.
The various well-known forms of the phase curves related to the hours and the seasons were clearly observed on all the transmissions. This pfl,per will, however, deal only with departures observed during particular geographic situfl,tions fl,nd ionospheric phenomena.
Fil'st, 3 years of recording of NBA transmissions give a good knowledge of the seasonal evolution of the variations at the time of sunrise and sunset [Decfl,ux et al., 1961a and 1963b]. It is well known that the received phase changes quicldy when the sun rises in each reflection point in the D-region, and remains nearly constant during the transition of the shfl,dow line from one reflection point to the other [Ricker, 1963]. The variation at the SWlset is more progressive.
We have compared the observed and calculated values of the time interval between the successive points. The observed values are deduced from experimental curves by averaging on several conseeutive days. The calculated values take in to accoun t the progressive shifting of the ground reflection points, and also the influence of the ozone lnyer. The differences between observed and caleuh),ted
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values, for various typical epochs of lhe seasons, do not generally exceed 5 min.
It is interesting to note that the amplitude of phase variation between night and dfLY chfl,nges slightly from sea on to sraso n: 70 p.sec at win tel' solstices, 80 ,usec at summer solstices, 75 p'sec at equinoxes. The wnves path at night would be about 200 km greater than the length of the great circle Ba.lboa-BfI,gneux.
The NPM and NPG/NLK paths cross a pm"L of arctic polar regions. The in terpre tation of N PM phase curves is un certain because of the lo w siglH), strength, but the NPG/NLK records are excellent [Decaux et al., 1963c]. The Jim Creek-Paris path cross the polar region on about 2,000 km (X of" the total length). Therefore one observes the well known "double humped" curves, ince the part 0
path crossing the polar region are , according Lo the season, continually in light, or continu fl,lly in clark. }.iforeovel' this path hns an interestin g peculiarity: both extremities have nem-Iy equal latitudes (Jim Oreek: 48°12' , Bagneux: 48°46'). Then the part of the great circle beyon d the polfLr circle is in the middle of the total path, and the 60° W meridi~Ln is an axis of sym.metry (fig. 1).
Near 0400 UT, the path is thus en tirely in dark at every time or yefl,l" , except from the end of" April to the middle of August . Between those two limits, the wfI,ve path pass progressively, on all its length, from night to day fl,nd vice-versa. Then the phase curves have the characteristic forms , successively indicated in figure 2, ~LI1d expbined below.
At spring equinox (fi g . 2fL) the form is the classic trapezium. At t be beginning of 1hy (fig . 2b) the night effect (pefLk) lasts for very sbor t tim.e near 0400 UT. In the middle of May (fig. 2e) a daylight effect (dip) fLppears near 0400 UT . From the beginning of June t ill nearly the 10th of July (fig. 2d), the dfLylight effect is eomplete at 0400. Near the 1st of A ugust the day and night effects are prnctically equal (fig. 2e); then one obsen 'es, during a Yery few days, a f~),st inversion, from the 0400 (dip) to a peale The figu ee 2f and . 2g shows the CUl'\Tes are practically inver ted around the 20th of August and the 20th of D ecember. In August, the curve
FIGURE 1. The NPGj NLK to Paris path .
shows a peak of 0400 (a short instant in total dark), in December shows a dip at 1600 UT (a short instant in total light) . The dissymmetry of characteristic dates referring to the solstices can be explained by the displacement of the shadow-line in the D layer, in comparison with the shadow-line on the ground, of about 500 km towards the night side.
Some sudden ionospheric disturbances have been observed [Decaux and Gabry, 1961b]. A fast phase advance appears generally at the beginning of disturbance. Moreover we have observed at different times, a day and a half or 2 days afterwards, phase undulations with about 2-hr periods. One observed such undulations, during night, for GBR on the 13th of November 1960 and for NBA on the 28th of March 1961. The multiple disturbances of the 23d and 25th of May 1963 have produced phase advances of 5 to 25 j.l.sec depending on the transmission being observed. Moreover, NBA has shown on the 25th of May similar undulations, but during daylight . .
The solar eclipses effects, on the 15th of February 1961 [Decaux et al., 1961c] and on the 20th of July 1963, were carefully studied. On the 15th of February 1961 we carried the recording equipment for GBR and NBA to southern France, in the totality zone. The GBR waye path was practically in daylight, but % of the NBA path was still dark. At the time of the eclipse, the phase recovered, for the two transmissions to a value nearly equal to the night value (fig. 3). We must remark that the maxi-
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mum of the effect on NBA took place a few minutes before the maximum of the eclipse on the ground, and on GER a few minutes after this maximum; the difference between the two maxima was about 10 Inll1.
On the 20th of July 1963, the eclipse crossed the wave paths of the five American transmissions. The NPM reception was too weak for use. The NEA transmissions was unfortunately broken off from 2040 to 2200 UT, just during the eclipse, preventing any observation. The NPG/NLK (24 kc/s) phase variation, normally existing near 2100 UT, was six times greater during the eclipse (delay: about 10 j.l.sec); moreover, the reception strength was about twice its normal value (fig. 4) . The NAA phase was about 8 j.l.sec late during the maximum of the eclipse. On NSS the influence of the eclipse was not noticeable.
The high altitude thermonuclear explosion on the 9th of July 1962 produced a very large variation of amplitude and phase on all VLF waves. The phase advance was 10 j.l.sec for NAA and NPG/NLK, and 35 j.l.sec for N EA, about a third of the normal daily variation in this season (fig. 5) . The NBA amplitude increased suddenly simultaneously with the phase change. GBR waves received in Paris are always a combination between the groundwave and the ionospheric wave; then the phenomena are somewhat complicated. On the 9th of July 1962, the GBR phase was delayed by 18 j.l.sec. It is to note that the nearest point of the path was at 12,200 km from the explosion [Decaux et al., 1963a].
ci)
.-~ UeJ
Jt l*-14t
~ ..: r r Q -t
FIGURE 2. The seasonal evolution of the diurnal phase shift of NPG/ NL[{ obseTved i n Pm·is.
AJI those phenomena, appeared abou t 2 to 3 min after the explosion. They lasted 3 hI' for NPG/ NLK, 6 hI' for NAA and NBA, 10 hr for GBR; those last periods are roughly in proportion to the distance between explosion and each transmitter.
On the 20th and 26th of October and on the 1st of November 1962, explosions (below D layer) produced phase fl,dvances, on NPM waves only, reaching up to 20 !.!sec and quickly recovering.
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Preliminary simultaneous recording experiments. with common local phase reference, was developed between Bagneux and the Meudon Observatory (distance 6 km) on the NBA transmission. Some of phase difference discrepancies were observed.
Several phase recording equipments for VLF transmissions are planned by CNET in other areas of the world, principally in central Africa, Kerguelen Islands, and Terre Adelie (Antarctic) in relation with the LQ.S.Y.
I
] M F
r _J, NBA '.
Phase 1~
I I J.
GbR
FIGU RE 3. Observations during the ecli pse of 16 February 1961. ('l' he dotted lines show t he normal behavior.)
N LK
Op.;h;....-._.....;9:p.;h~ ___ .....;2~+" .
1"?~ NBA
GBR
fO/'-'l NAA
{Ol4s
111'/ NU(
14h. T.U. FIG U RE 4. Observations during the ecli pse of 20 J uly 1963.
(The dotted lines show the normal behavior.)
NAA h
FIGU RE 5. Observations on J1ily 9, 1962. (The dotted lines show n ormal behavior.)
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References
D ecaux, B ., A. Fran ces, and A. Gabry (D ec. 1961a) , Influen ce des cond[t ions g60graphiques et saisonnieres sur la vari at ion d iurn e de la d uree de t ra jet des ondes m yriam 6triques, Comp t. Rend . Acad. Sci. 253, 2877- 2879.
D ecaux, B., and A. Gabry (Apr. 1961b) , Var ia t ion diurne de la du rce de trajet des ondes myriametriques, Compt. Hend . Acad. Sc i. 252, 2187- 2189.
Decaux, B., A. Ga bry, J . Lachatre, and J. Lucas (Apr. 1961c), Influ ence de l 'eclipse tota le de soleil du 15 fevrier p . 961 sur la dur ee d e trajet des on des myriam etriques, Compt. R end . Aca d. Sci. 252, 2387- 2389.
D eca ux, B ., A. Frances, A. Gabry , and M . Reyssat (J an. 1963a), P erturbations p rodui tes par les explosions t hermonu cleaires en hau te alt it ude (plus particulierement celle du 9 juillet 1962) da ns la d uree de t ra jet et I'ampli-
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t ud e des ondes m yria metri qucs, Co mpt . R ene!. Acad . Sci. 256, 481- 4 4.
D ccaux, B. , A. F rances, A. Gab ry (J an. 1963b), Evolut ion saison niere de la variat ion diurne de la ph ase des ondes m yria m6triques sur Ie trajet P anama-Bag neux, Compt. R end . Acad. Sci. 256, 742- 744.
Decaux, B., A. F rances, and A. Ga bry (J uly 1963e), Changem ents rapides dans Ie r egime saisonnier de la var iation diu rne de la cluree d ' un trajet d 'ondes m Yl"i am 6triq ues passant au-dela d u cercle polaire, Compt. Hend. Aead. Sci. 257.
Hieker, J. (Mar .- Apr. 1963) , Sun set and sunrise in t he ionosphere: eff ects on p ropagation of long waves, J . Hes. NBS 67D (Hacl lO P rop .), No.2, 119- 138.
(P aper 68Dl-312)
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