It is a well-known fact that in winter the midlatitude lower ionosphere differs considerably from that in summer. Attempts to explain the possible causes of the winter anomaly in the lower ionosphere were made. Integrated ground-based and rocket experiments were performed in the USSR. The rockets M-100B launched in Volgograd (psi = 48.7 deg N; lambda = 44.3 deg E; psi = 43.1 deg) provided weight profiles of electron density, wind and temperature. Radio wave absorption data obtained by a I method in Volgograd and F sub min parameters values obtained at a number of Soviet ionosone stations were used to determine the situation in the lower ionosphere. It was found that a correct interpretation of the midlatitude winter radio wave absorption changes is possible only if the whole spatial-time pattern of the event is taken into account

Rapoport, Z. T.

English

NASA Technical Reports Server

i  85-20459
_INTER ANOmaLYOF _[E LONER IONOSPNERE AND ITS POSSIBLE CAUSES
Z. Ta. Rapoport
Institute of Terrestrial Magnetism
Ionosphere and Radio Wave Propagation (IZMIRAN)
142092 Troitsk, Moscow Region, USSR
INTRODUCTION
It is a well-known fact that in winter the midlatitude lower ionosphere
differs considerably from that in summer. This was first discovered as a result
of the analysis of _round-based measurements of radio wave absorption in England
(APPLETON, 1937). The phenomenon was named the radio wave ionospheric absorp-
tion winter anomaly. Later on, we began to speak about winter anomaly of the
lower ionosphere, having in mind that a number of parameters of ionized-and
neutral components of the medium behaves anomalously in winter.
The winter anomaly at midlatitudes shows itself distinctly in }_ and HF
radio wave ranges. On a long-time averagej the maximum value of absorption for
a constant solar zenith angle is observed during the winter solstice; it
decreases almost to summer values symmetrically towards the equinoctial periods,
Another distinctive feature of the winter anomaly is the enhanced day-to-day
variability of the absorption in winter compared with other seasons of the year,
Beside the general increase of absorption level, called normal winter anomaly
(SOIWENTEK, 1971), there are days and groups of days with excessively high
absorption. The zone where the anomaly is observed has a low-latitude boundary
below which the anomaly vanishes (see, e.g. LAUTER and SOL_.NING,1970; ELLI_b
etal., 1974). It should be also noticed that the magnitude of the effect and
o_ the duration of its occurrence decrease with latitude (e.g. RAPOPORT, 1974),
that the anomalous region has a cloudy or spotted structure (e.g. SHRESTIiA,
1971). The winter anomaly occurs also at high latitudes in the auroral zone in
any case but here the effects caused by sporadic energetic particle fluxes are
superimposed on those of the winter anomaly (RAPOPORT, 1979).
There have been many attempts to explain the winter anomaly. Ne should not
like to dwell upon all hypotheses suggested. We only want to Point out that
some scientists regard direct precipitation of energetic particles as the unique
cause of the anomaly at all latitudes where it is observed (e.g. SATO, 1981). _.
Other authors ass,_,e that the winter anomaly may have also the causes completely .
independent of particle precipitation, i.e., changes of t_nperature and gas
composition, mainly an increase of nitric oxide density ionized by Ly_an-
radiation (e.g. OFFERHANN et el., 1982). It se_ms to us that these opposite
stand points do not exclude each other, that they rmy operate simultaneously,
and their relative contribution is different in different cases, as it depends
considerably on the latitude of observation (e.g. THO_S, 1971; BRE}_R and
LAUTER, 1982). We think, next, that the intensity of energetic particle fluxes
in the auroral zone and the dynamical structure of the whole middle atmosphere
on the levels of the lower thermosphere and mesosphere are definitive for the
midlatitude mesosphere conditions. We also think that a correct interpretation
of the midlatitude winter radio wave absorption changes is possible only if the
whole spatial-time pattern of the event is taken into account. Our analysis is
based on data obtained during an integrated experimental program carried out in
the USSR in January 1981 and partially in January 1982.
INTEGRATED EXPERIMENTAL PROGRAM RESULTS
Integrated ground-based and rocket experiments were performed in the USSR
in January 1981 and 1982 as a part of the International Middle Atmosphere
Progrmn. The rockets H-100B launched in Volgograd (_ = 48.7"N; _ = 44.3°E;
https://ntrs.nasa.gov/search.jsp?R=19850012149 2020-03-22T18:38:29+00:00Z
5_
€ = 43.1") provided height profiles of electron density, wind and t_nperature.
Radio wave absorption data obtained by AI method in Volgograd and f . pars-
. , . mlnmeter values obtained at a number of oovzet lonosonde statzons were used to
determine the situation in the lower ionosphere. The results of these
integrated experiments have been presented at the COSPAR Sympositm in Ottawa
(PA_IOHOV et al., 1982) and in A_a-Ata (PAKIIOIIOVet al., 1983). The ground-
based data showed that absorption in Januarj 1981 was typical for winter
' conditions. The geomagnetic field during the whole month was rather quiet.
Excessive absorption was observed on January 12-16.
Figure I shows electron density altitude profiles (Ne(h)) obtained by using
the coherent frequency technique on rockets H-100B on the anu_alous day of
January 14 and on normal days of January 21 and 28 in the morning (Figurp Is)
and in the afternoon (Figure Ib), the solar zenith angle being X = 78°. These
profiles may be compared with that obtained on January 29, 1980, a day con-
sidered as free from the influence of winter _omaly. One may see that Ne
values on quiet winter days (Figure In) exceed Neva. es for the day free fro_
anomaly in a considerable altitude r_ge (= 75 te 90 km), whereas t[evalues are
higher on the day of the enhanced absorption than on a day with regular absorp-
tion (h = 70 to 95 km).
!
• b I
90
o_3 4_ -
21.01.Sl
?0 I _-Ts"
I_ _ 10_ _0€ 1_ 107 10) _04 10_
_t.€8-3 "-"
Figure I. Electron density altitude profiles cotained
by coherent frequency technique in Volgograd; solar
zenith angle × _ 78°. (a) forenoon profiles. (b)
afternoon profiles. 14 January is the day of exces-
give absorption; 21 and 28 January are days of normal
winter absorption. The profile obtained on 29 Febru-
ary 1980 at X = 80" is shown for comparison.
Figure 2a shows temperature profiles obtained on January 14, 21 and 28 as
well as the ClRA-72 standard profile. The lower part of the figure (b), shows
the measured tenperature deviations from the corresponding standard profile.
The characteristic shape of these AT (h) curves shows explicitly the influence
of atmospheric wave processes on rc_nperaturedistribution, not only during the
excessive absorption but on norms, days, too. It should be also noted that the
temperature was lower than the standard one on the day of excessive absorption
as well as on days of no_aal winter absorption in the region of enhanced
electron density (above "70 km). The temperature height distribLtion on the day
f- t
0|
...... t _
54
x I f\ "._C2U-R
lc _"...,_-__1 "'-_
G_ " ; " "'_ _°_"_
_c
h._ ," U_f [
...._ _\ ' l
1
[ ¢.... '1 .i
Figure 2. (a) Temperature altitude profiles above
Volgograd obtained on 14, 21 and 28 J_uary 1981.
The dashed llne shows the standard profile ¢IRA
1972. (b) Altitude profiles of temperature dif-
ferences _T = T meas.- TClRA.
with excessive absorption does not show any peculiarities. We should like to
call attention to this result, since a rise of the temperature is often con-
sidered as one of the most important causes of the winter anomaly because it
must reduce the ion clustering rate which, in its turn, must cause a decrease of
loss ratL and, hence, an increase of electron concentration (see, e.g. SECtiRIST, ..
1967).. • • .
The density of hydrated cluster ions which decisively affects the effective
recombination effective coefficient in D-region is to a considerable extent
dependent on the water vapour content of the medium (_ee, e.g. $E_iRIST, 1970).
Figure 3 (FEDYNSKI and YUSIIKOV,1979) displays water vapour density profiles
obtained above Volgograd on January I0 and on February 2, 1978. The day of
January I0 may be considered as an anomalous one (according to data from Hoscow,
mean of five near-noon values f • _ 2.5 M_Iz)while the day of February 2 is a
m_n
normal one (f • _ 1.3 F01z). One may see that the water vapour density on an
anom=lous day _s Considerably lower than on a normal one: at 60 km altitude it
is 6 times lower while it is 3.5 times lower at the altitude of 80 km. In this
way, it se_s that this result confiz_s the idea that the water vapour is one of
the _ost important factors determining the elect.on density increase and
excessive absorption in D-region. Uater vapour density was also measured in
January 1982 (Figure 4) -- the profiles ;_avebeen obtained on 13 and 19 January
1982 at nigi_tat × " 145_ and 144°, respectively. _ithin the measurement
accuracy these profiles coincide with that obtained in quiet winter conditions
on 2nd February 1978 also shown in Figure 4. Yet, the absorption was rather
high on the_e days in Volgograd (at 2.2 _Iz about 50 and 40 dB). _his suggests
that it was not water but other factors that determined the lowcr ionosphere
conditions during thi_ period.
f-
55
?fl \
-i50 e J
_ .fO4
o 2 [_Ol,y. ,nJ
Figure 3. Nater vapor density altitude profiles above
Volgograd on anomalous (10 January 1978) and auroral
(2 February 1978_ days.
h,k_
05
;.... I
i
°.
70 ?,
" " " " " ' ° ,1),1.8_
--19oi
60 ___2 _zz. 7s% .°
\
%
5o I I I
Figure 4. Nater vapor density (11,0) ,_ltitt_de _ro-
files above Volgograd on 28 and_19 January 1.q82
(X _145 ° and 1440j respectively). The profile o[
2 February 1978 £s sho_a_for the sako of ¢omr._rison.
\
'\x
\
L
56 OF F'O¢','_:,.,.._,..... ,,
Thus the experiments in Volgograd in January 1981 and January 1932 show
that both the temperature of the mesosphere and the water vapour density _my
serve only as additional factors and not as decisive factors which determine
excessive anomalous winter absorption occurrence at midlatitudes.
DISCUSSION .....
First of all it should be borne in mind that whatever hypothesis we accept,
it should explain all above mentioned peculiarities of the phenomenon. In
agreement with other authors (OFFERMANN etal., 1982; BREMER AND LAUTER, 1982)
we think that the enhancement of nitric oxide density is the main cause of
electron density enhancement in the midlatitude lower ionosphere. We believe
that nitric oxide is produced mainly at the ionospheric E region level, with
highest rates at high latitudes and particularly in the auroral zone _u_derthe
influence of precipitating particle (electro:_)fluxes.
Nore or less intense particle precipitation occurs pe:manently in the
auroral zone, so that the density of NO caused by this precipitation has all
features of the fluxes themselves, namely a very high time variability and
spatial inhomogeneity (these features are to a certain extent smoothed out
during the air transport). The auroral zone air being rich in NO is trat_sported
towards midlatitudes due to a stable winter cyclonic citer=polar vortex, As it
moves the nitric oxide produced at high latitudes at an altitude of 90-I00 km
may be transported by turbulence and vertical motions towards lower altitudes
(70-80 km) and it may produce there the above mentioned effects.
As there any experimental facts which might prove this asstm_ption?
First of all let us consider the data on air circulation, ..
/_ Constant pressure maps for the North lh_isphere plotted with a one week
time resolution for every 5 km in the altitude range 35 km to 60 km are
regularly issued by the Central Aerological Observatory (ATLAS, 1982). Figure 5
displays the maps of 60 km altitude for three weeks of January 1981, using geo-
magnetic coordinates. The dashed circle at a latitude of _ = 67 ° gi_os a
visualization of the auroral zone Position. Points at this figure show
positions of the observational stations. The wind at these altitudes may be
considered as cyclo-geostrophic, so that air is transported along the isobars.
One may presume that the circulation picture in general outlines the same at
greater altitudes, "'"
%
/ / it-IT' ,_. 1981 " 18-24 _, 1_81
Figure 5. Constant pressure maps (the Northern Ilemisphere) for the
level of 60 km on 4-10 January and on 18-24 January 1981 (in geo-
magnetic coordinates). The dashed circte drawn at s_= 67 Q indi-
cates the auroral zone. Each isobar is labelled by its pressure
(in millibars).
) ®
!: i_
_7
There is some basis for this assumption. Figure 6 sho,'s velocity and
direction of the zonal wind _easured by meteor radar in _uhLungsborn (GDR) (see
also t:OS_RT et el., 1982), at an altitude of about 95 tan, One clay see that the
wind rer, ait_ed westward throughout the vhole January which is natural if it
follows the cyclonic vortex. Figure 5 sho_,s that the isobars of the week
preceding the disturbed days (4-10 January 1981) follow r._inly the latitudea
._ below tilt, auroral zone. During the week of 11-17 January including the
' excessive absorption period they cross the auroral zo,e almost at halfway. The
next _eek (18-24 January) they pass tile auroral zone northward at a considerable
portion of their path. It should be especially t_nphasized that the ionospl,eric
disturbance on 12-16 January was preceded by a solar flare of it_portance 2,'i on 9
January with a subsequent weak magnetic storm with a gradual €omut.ncement
(CO5HI¢ I_\TA, 1981) followed by an increase of energetic particle precipitation
into the lower ionosphere and by an equatorward shift of the aurora! zone low
latitude boundary. If our hypothesis is valid this should _how i_self through
the time of the disturbance onsets at different stations as well as through the
magnitude of the effects itself.
Figure 7a shows f . (cos X" 0.2) values for a number of Soviet iono-
._%n
spheric stations (gahnxngrad, Moscowt Roster-on-Don, Arkhangelsk, Gorky,
Sverdlovsk, Salekhard, Alma-AtOp Novosibirsk, Yakutsk) during the event of the
winter anomalous absorption in January 1981. The character of fmln.
variability is different at different stations, nevertheless there xs an obvious
tendency: the increase of absorption begins earlier at western stations th_n at
eastern one_. This must he so if the disturbance source gores together with the
air in the cyclonic vortex, i.e. from west to east.
The quantity :'fmin which is the maximt_ difference of fmin values
observed on two successive disturbed days has been taken as a _casure of the
effect'v magnitude. This difference versus the longitude of the stations is
_hown in gigureTb.One may see that effect decreasesas the longitudeincreases
from west to east, following the air moving in the cyclonic vortex. If one
takes into consideration a certain space inhemogeneity of the winter _nomalous
absorption zone, the plot looks rather significant. The stations Hoscow and
Roatov-on-Don do not fit the general distribution of _f_in" This may be
/'- i
i
, ®
m
58
part_:lly explained by a more sensitive equipment o£ the t:oscowstation, while
Roster-on-Day is the lowest latitude station el all European stations of the
Soviet Union. Besides, the growth of f :_ values at these two stations is
slower than at other ones, taking more '_'_nor_eday. ""
/ ;;J__j
ol tO fJ'1 A-_ ._
/I_ ¢.O-
!i!i+iol+,+,0._" s,.b) 06" "*0._" ii i i i i i i ito zo ._ to _ !o Ro leof_i l_ _°
Figure 7. (a) fmln (cos X " 0.2) values at a number of Soviet stations .+
• • • . on _I-17 January 1981. The thick hori=ontal lines show the position
of the month by medians. K - Kaliningrad, H - /_oscow.R - Rector-on-
Don, A - Arkhangetsk, G - Gorkyo Sv - Sverdlovsk, Sa - Salekhard,
A-A Alma-Ata. N - Novosibirsk, Y - Yakutsko
(b) Afmin, the maximum difference of fmin values for two seccessive
days during the period II through 17 january 1981 for the stations
shown in Figure 7a.
Midlatltude absorption changes (of f . values) compared with constant
pressure _nps for January 1982 during a n_al winter period free of excessive
absorption occurrence also reveals a close relation between the two phenomena:
f • values are greater when the path along the isobars fro_ the auroral zone
t_X_he observation station is short than ia a case when this path is long
(PA_IOHOV et al., 1983).
So, our hypothesis explains all the peculiarities of the phenomenon -- both
the normal winter anomaly and the excessive one. In order to verify and to con-
firm the suggested hypothesis it is necessary to specify the character of
circulation on levels of the mesosphere and of the lover thermosphere. Nitric \
) . ® ....
59
oxide, _ater vapour and ozone densities in different geo-heliophysical
conditions for dif[erent latitudes should be known _ore precisely, too.
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Winter Anomaly of the Lower Ionosphere and Its Possible Causes

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