Radio wave absorption data covering almost two years from Europe to Central Asia are presented. They are normalized by relating them to a reference absorption. Every day these normalized data are fitted to a mathematical function of geographical location in order to obtain a daily synopsis of radio wave absorption. A film of these absorption charts was made which is intended to reveal movements of absorption or absorption anomaly. In addition, radiance (temperature) data from the lower D-region are also plotted onto these charts

Friedrich, M.

Torkar, K. M.

English

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 {85 -20454
SYNOPSIS OF HID-LATITUDE RADIO WAVEABSORPTION IN EUROPE
K. H. Torkar
, Space Research Institute of the Austrian Academy of Scierces
c/o Technical University of Graz
Inffeldgasse 12, A-8010 Graz
Austria
H. Friedrich .-"
Department of Co_n_licatloas and Wave Propagation
Technical University of Gra_
Inffeldgasse 12, A-8010 Craz
Austria
,o
ABSTRACT
Radio wave absorption data covering almost two years from Europe to Central
Asia are presented. They are normalised by relating them to a reference
absorp:ion. Every day these normalised data are fitted to a mathematical
function of geographical location in order to obtain a daily synopsis of radio
wave absorption. A film of these absorption charts was made which is intended
to reveal movements of absorption or absorption anomaly. In addition, radiance
(temperature) data from the lower D-region are also plotted onto these charts.
No conclusions are drawn; the new procedure to evaluate absorption data is -- at
.-_- the present stage of processing -- merely intended to stimulate discussion and
" interest.
INTRODUCTION
Radio wave absorption in the IIF range occurs predominantly in the iono-
sphere's D-reg£on, i.e. at heights s,here absorption L is proportional to both
electron _ensity and collision frequency v. Since v is very well predictable
via atmospheric pressure (cf. e.g. FRIEDRIG! and TORILkR.1983) it is the
electron density }Itwhich determines the day-to-day variations of L. At hig_
latitudes all changes of Nc are attributable to variations of the ionising _
fluxes i.e. of char£ed particles; at low or _iddle latitudes, howwer, theo . . . ....
fluxes responsible for the for_ation of the daytime D-region (solar Lymsn-a,
X-rays, etc.) do not vary drastically, not even in the course of a sunspot
cycle. The observed day-to-day variations in (mid-latitude) radio wave
absorption by factors of 2 Zo 3, notably in winter (winter anomaly), are there-
fore generally attributed to changes in the concentration of nitric oxide (NO),
the only component of the middle atmosphere (_esosphere) which can be ionised by
the relatively strong solar I1Lyr_n-_line. The following analysis is plausible
if one assumes that changes in the NO-concentratlon are the principal cause for
changes of absorption.
DATABASEANDNORKALISATION
There have been numerous attempts to study the morphology of winter
anomalous absorption (e.g. BEY_OH and WILLIA_S, 1976), in recent times notably
by SATO (1981) _ho used fmln date from atatione in Europe. the USSR and North
America. The aim was to find a connection to geOmagnetic activity, but the
analysis is severely hampered by the relatively coarse classification of fmln"
In the present treatment we use absorption, i.e. loss of signal strength
• relative to absorption-free reflection. Both the methods AI (vertical
• incidence) and A3 (oblique incidence, i.e. reception of a distant transmitter)
i are used. Table I gives the acronyms of the various data sets, path lengths,
https://ntrs.nasa.gov/search.jsp?R=19850012144 2020-03-22T18:38:46+00:00Z
,/
• i
25
and AB vhlch use t_e same traneuitter but different _eceivers (distance of
the path mld-points ca, 120 km). Hence the observed rs_id variations must be
considered to be of ionospheric origin and no_ -- as one might be _empted to
believe -- poorly r_intained equipment or local interference.
Due to different path lengths, frequencies and the type of measurement
(daily integrated abnocption L_, noon-absorption Lr,oon etc.) the various data
sets shay necessarily d£ffcren_ seasorml trends _nd variab£1£tiea, llencethe
observed absorptions at various locations r.nybe covered up by the above
; mentioned, expected systematic effects. Therefore a procedure vas sought by !
vhich in a first approxirmtion these differeaces can be eliminated, I
i COnsequently a reference absorption for each data _et end each _onth vas ca[-
; culated. For this purpose electron densities vere computed for the
i i
"I
/ . .
26
Table I.
I u _u r_...m ak_arptlnn heisht
welqht
41
_ _ _2 °
)IX )) llOrby-K'_hlunqlboz_ 1.178 225 cos) =O.2 55.1_, 12.7£ 92.?2 90;1)
JR JulLusruh 2.000 - noon 1.61 0.65 cJ4.6N, I._.4U 91.24 104.C8
KN Klel-N_ust[elltz 2.775 220 cos% -0.2 0.42 O.75 53.9N, 11.6E 98.$O 99.4]
NN f_orddelCh-Neu$trelJtz 2.614 395 cos x =0.2 1.O5 53.5N, Io.I£ 91.25 89.83
NL Norddeich-Ll ndau 2.614 ;96 _ ") O.93 0.77 52.6N, 6.7F. 90.26 98.5?
DB De [lilt 1.850 noon 1.5) 0.90 52. IN, 5.2E 90.89 q6.47
[_Z ) Luxerr4_ourq°pz'4quo 6.090 f. IO r_oon 50.1N, 10. 1[ 89,O2 96. ]5
CG Cr_urq-Graz 2.6JO 502 !0 1.10 0.96 48.7N, 11.2E 87.69 95.29
+(2 (_ostoy-on- Don 2.000 - 'D 0.87 I.O7 47.2N, 39.7£ 92.7) 93.96
X4 Post ov-on-Don 4,000 - !p 0,48 0.74 47.2N, 39.7£ 83.35 83.1)
AI Al_a Ata 1.700 - noon O.97 I.o9 43.3N, 78.9E 68.$7 89.55
A2 Alma Ata 2,200 - noon 1,52 1.36 43.3N, 78.9E 90.?0 93.04
P5 Prl_tlna-S0fl_ 1.412 170 cos_ -O.2 O.71 1.26 42.7N, 22.2£ 93.37 92.29
71 Tbi list 1.7OO - L D 1.o_ 1.10 41.4N, 44.5£ 90.38 92.97
AA Aran)uez-El Arenosi l 1o 2.830 424 r,oo.I _| 0.90 1.O? 38.GN, 5.2N 87.14 09.51
•_'_ Aa Aran) ue z-Sale zl_a 2.630 )74 :D 1.13 1.17 38,4N, 3.254 88.0) 90.45
PA Pat ras )) tl ;D 0.87 1.O5 38.O:(. 23.8E 86.34 _} 88.96 s}
AS Ashkh _bad 1.8OO - noon 1.O4 1.12 37.9N, 58. OF. 68.98 89.94
_) not used In the further analysis, possibly qround wave propaqat/on
z) not used In the further analysis
,)
monitors the 31 and 49 m broadtail band! appr. linearly related to Rome-Athens on 6.080 _Izl
|ILIAS and GUPTAw 19797
*}
except March 22 to June 30, 19761 ¢os_ - 0.2 _"
_| exCept December 1975 to February "1976! L D ' '
i| a_p|lel to Rorr_-Athenm
frequencies and (path mid-'point) coordinates. Subject to the availability of
the raw data. daily integrated absorprlon (L[|, cf. ROSE and WIDDEL_ 1977)_ was
used_ otherwise values at noon or some constant solar zenith angle were
employed. Figure I shows the daily values of all stations from October 1974 to
June 1976.
The lowest curve is the stmapot n_mber, whereas _he uppermost curve
represents the average daily rlometer absorption at Enrsr_rsstmq (Greenland).
The latter is included as a measure of particle influx into the auroral zone,
since a connection of charged particle fluxes and mid-latitude absorption has
often been sought (e.g.Y._[LUH, 1967; TORKAR et al., 19_0). floweret,only the
northernmost data (JR) of February and October 1975 possibly show some direct
influence of particles. On the other hand, _ven the relatively large sunspot
numbers in August 1975 do nor show up as enhanced abserption in nny of the data.
In most darn one cno clearly observe the larger absorption in winter, however,
all show a larger variability in winter. Of special interest are the data sets
_'-.
c4
27
corresponding conditions of each station (noon, coax - 0.2 or at four typical
solar zenith angles X with equal time-spacing for LD) using the ion-chemical
model for low solar activity described elsewhere in detail (TORKAR and FRIEDRI_
1983). In this steady-state couputation the neutral atmosphere, including the
minor species, is taken frontother published models, in particular [_O] from
RUSG! etal. (1981). Absorption was then computed by a WKB ray-tracing calcul-
ation over a spherical Earth. The full SEN and NYLLER (1960) magnetoionic
formulae were employed, the magnetic field taken from CAIN ot al. (1967) and the
¢olliaion frequency set proportional to pressure from the AFGL seasonal
atmospheric model (COL£ and KA_TOR, 1978). The proportionality factor of
6.7xi05 m2 s-I N-I is the one recor_nended by FRIEDRICH and TORKAR (1983) based
on a number of rocket mensursments of u. The reference absorption thus
obtaiz_ed is indicated in Figure I as rmooth lines. Outside winter one can see
reasor_bly good agre_ent for the data KN, NL, OG, Tl. AA and AB. There is
notably an excess of the simulated absorption of HK. This _ay be due to ground
wave propagation at the fairly low frequency (I.178 _z) of the path which is
mainly over sea water. Another feature of the simulated absorption is, that at
higher latitudes in s_nmer the observed absorption ([_O]) is consistently higher
than in the model (JR, KN, _, DB, LP and also PS).
' For further evaluation the daily absorption values were divided by the
corresponding reference absorption. This new quantity (absorption enhancrment
"" AE) removes the differen_ sensitivity of the various measurements provided the
• geometry of the ray (penetration into the ionosphere) is the same.
A£ should, therefore, be proportional to an electron density ratio or the
square of the ratio of ion production rates; if one assumes that NO and Lyman-a
is the dominant production process of the absorbing D-region, AE is equal to
([NO]/[NO]ref)2*
Before combining all absorption measurements, normalized via AE in the
above manner, it was tested to what extent the various data sets measure the
same physical phcnomenon. Figure 2 shows relative contributions of the various
layers of height h to the total absorption of some of the stations using the
reference ionosphere (summer), where Ir(h) is defined as:
= .I h)lh!_ ](h). dB/_. km-1
Ir it(h)dh" ---L---'_ f--'
One can see that the height regions contributing to absorption differ greatly
.... from station to station. For want of more uniform data, all absorption measure-
ments were nevertheless treated as if they represented the same height regions.
l!encean absorption "drift" from e.g. JR to AS could just as well mean a down-
ward motion of enhanced electron (or NO) density at both stations.
CONSTRUCTIONOF ABSORPTION PATTERNS
The normalized data (absorption enhancement AE) still include variations
due to very local effects. Instead of constructing AE-patterns by interpolation j
between the individual measurcraenrs, all AE-values were fitted by analytical
functions. The number of locations, or -- more importantly -- the number of /
simultaneously available measurem.ents, restricts the order of the analytical
e;_presslonwhich can be fitted to the data. The simplest form is a plane in
general position requiring only three, preferably evenly spaced, points. A
somewhat higher _evel of complexity -- a circular paraboloid -- was chosen which
is determined by four parameters, namely location and value of the maximum, and
the curvature. This form is employed at the present stage of the an_.lysis;
higher orders have been tested, but found to lead to unrealistic excursions. In
28
J, &
.,. Figure 2. Relative absorption contributions of
different heights of s_e stations together with
the average absorption profile of all data setsb (summer).
an att_pt to account for the different height coverages (cf. Figure 2) weights
,__. w were giv_ to the different data sets according to:
w = lr_dh/T2dh
: Bert _ is the average specific absorption of all _easur_ents divided by the
average integral absorption. Its height variation is also sho_ in Figure 2.
Table I contains these weights for January and July, b_t for the further
computation these weights were also established for all other months.
Furthe_ore contained in this table is the mean height of the absorption
derived fro_ the same model computations. Those data which are based on
LD [= L_(l . n)] were given additio_l daily weights according to the quality
of the fit L- Lo(cOsx)n'_hlch led to the establishment of Lo and n. For every
/ day four par_eters _,ere dete_ined by fitting a psrabolold to all log(AE)-t
/ data by a least-mean-square procedure. In the film contours of absorption
enhanc_ent of 0.8, 1.0, 1.3, 1.6 etc. are sho_. In order to avoid too rapid
/ fluctuations of the absorption (AE-)patterns, running means of the four para-
meters are used, i.e. 50Z of the day in question and 25% each of the previous
and following days.
The cu_es are fitted to the data in geographic Cartesian coordinates and
the contours of constant absorption enhanc_ent then transformed to the
projection in which the satellite t_rature data are available. In the film
only those stations which provided data on the day in question are indicated by
small circles. Figure 3 shows two ex_ples where however, all possible stations
are indicated with their acron_s. From October 1975 on radiance (temperature)
data ot the PMR (= Pressure Hodulator Radiometer) of the University of Oxford
aboard the satellite NI_US-6 are available. The weighting function of the
highest channel 3000 peaks somewhere just bel_ 80 _. The t_peratures at that
height are surely not decisive for enhanced electron densities (electron loss
rates), but may be an indication of an _stable atmosphere, turbt'lencz and -- in
_. consequence -- of trans_rt of NO into the D-region.
F-
29
.
14511976 24 HAY
r,.2 ._,3 n=lO
o)
_.,o \_;,_o_,__ I \ ,_Y......._o/
.." ..... AA ,."" _ 16
"_._ . g. _
, .
008/1976 8 JAN
r.,2 - .35 n-ll
._- b)
i
°_.
Figure 3. Examples of absorption patterns obtained . . .--
by fitting an analytical function to the AE values
and mesospheric temperatures. (a) typical sunnmer,
Hay 24, 1976, (b) winter anomalous day January 8,
1976. r_-k2is the quality of the fit and n the
number of available data for the day.
CONCLUSIONS _|D IHPROVD_NTS
The quality of the presently available raw data does not permit to draw
flnnl conclusions concerning the magnitude or the motions of absorption. More
careful screening of the absorption data is envisaged_ but also the reference
absorption model, which mainly hinges on the adapted [NO]-model, may have to be
revised. For the derivation of velocities of absorption patterns it may perhaps
suffice to use the running mean as a reference, thereby avoiding errors intro-
du:ed by an unrepresentative reference absorption.
30
ACKNOWlEDGEmeNTS
_tostof the data used herein were made accessible by the cooperation of
other institutions, notably the Iteinrich-IIertz-lnstitut(Berlin), the Max-
Planck-lnstitut for Aeronomie (Katlenberg-Lindau), the World Data Centres in
Slough and _los:ow,the Astronomical Institute (Prague), the Geophysical
, Institute Sofia, the Technical University of Denmark (Lyngby) and the University
of Athens. The radiance data were generously provided by Dr. C. D. Fodgers of
the University of Oxford.
- _EFER_CE5
Beynon, W. J. G. and E. R. Williams (1976), J. Atmos. Terr. Phys., 38_,89.
Cain, S. H., S. J. Hendricks, R. A. Langel and W. V. Hudson (1967), J. Geomagn.
Geoelect., 19, 335.
Cole, Ao E. and A. J. Kantcr (1978), Air Force Reference Atmosphere, AF-GL-TR-
78-0051.
Friedrich, M. and K. M. Torkar (1983), J. Atmos. Terr. Phys., 4_55,267.
llias, D. J. and G. P. Gupta (1979), J. Atmos. Terr. Phys., 41, 601.
Maehlum, B. N. (1967), J. Geophys. Res., 72, 2287.
Rose, G. and H. U. Widdel (1977), J. Atmos. Terr. Phys., 39, 51.
' Rusch, D. W., R. G. Roble, J.-C. Gerard and A. I. Stewart (1981), in IIandbook
: forMAP, Vol. 2 (ed. by S. K. Avery), pp. 442-449.
Sato,T. (1981),J. Geophys.Res.,86, 9137.
: Sen, II.K. and A. A. Wyller (1960), J. Geophys. Res., 6__55,3931.
Torkar,K. H. and M. Friedrich(1983),J. Atmos. Terr. Phys.,455,369.
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Synopsis of Mid-latitude Radio Wave Absorption in Europe

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