Solar activity influences the ionospheric D region. That influence manifests itself both in the form of various solar induced disturbances and in the form of the D region dependence on solar activity parameters (UV-flux, interplanetary magnetic field, solar wind etc.) in quiet conditions. Relationship between solar activity and meteorological control of the D region behavior is considered in detail and examples of strong variations of aeronomical parameters due to solar or meteorological events are given

Danilov, A. D.

English

NASA Technical Reports Server

N90-28198
183
Ghh_E_AL OVERVIE_ OF £HE SOLAR ACTIVITI EFFECTS
ON £11E LOWER IONOSPHERE
A.D. Danilov
Institute of Applied Geophysics,
Glebovs_aya, 20-b, _oscow, I07_5_, USSR
Abstract
Solar activity influences the ionospheric D - region. _hat
influence manifests 0oth in the form of various solar induced
disturbances and in the form of the D - region dependence on
solar activity parameters (UV-flux, interplanetary magnetic
field, solar wind ets) in quiet conditions. Relation between
solar activity and meteorological control of the D region beha-
viour is considered in detail and examples of strong variations
of aeronomical parameters due to solar or meteorological events
are given.
_he question of solar activity (SA) influence on the iono-
spheric D-region is not as simple as it might look at the first
approach. The matter is, that D-region as well as the whole
ionosphere occurs as a result of the ionization process in the
terrestrial neutral atmosphere which in its Sum is completely
controlled by the sun. Thus, considering solar activity influ-
ence on the D-region one has to distinguish direct effects,
when this influence comes through variations of ionizing agents
(electromagnetic, or corpuscular), and indirect ones, when solar
activity alters the state of neutral medium, which leads to
corresponding changes in the sta_e of the ionized component.
The direct effects are more obvious and easy _o understand.
2hey come from the fact that the electron concentration _g_
which we consider as the most important characteristic of the
D-region is defined (in quazi-equilibrium conditions) by
q = /e#otef f (z)
q oeing _he ionization rate and_ef f - effective recombination
coefficient. All the direct effects of SA on the D-region are
contained in q even though O(ef f may vary and be dependent on
SA through indirect effects.
_hus, it is worth briefly considering the ionization sour-
ces in the D-region and discussing _heir variations with SA.
It is well _nown that most part of the D-region ionization is
due to solar Layman-_ emission interacting with nitric oxide mo-
lecules. Layman is considered as a stable enough emission. Its
variations during the whole solar cycle lie between 3.1OII and
6.10 II photons cm -2 _ -I (SI_ION, i982). According to review
(_USI_0V, I_87) various authors accept for Lg - variations from
minimum to maximum SA values of 30-I0_. _hese variations are
much smaller, than uncertainities (and probably - variations)of
_0-concentraCions at the D-region heights. Lhus, one should not
expect well pronounced variations of _he D-region behaviour
with SA due to Ly-_ variations. _Ae o_her sources of the D-region
https://ntrs.nasa.gov/search.jsp?R=19900018882 2020-03-19T21:12:50+00:00Z
184
ionization are _-raFs (_$3.0 nm), galactic cosmic rays and
solar emission with _ = I02.7-III.8 nm (the lat_er ionizing
only excited 02 (4A_) molecules). Variations of IO2.7-Iii.8
nm emission do not essentially exceed _hat of Ly-_ (see 2able
I) so we hardly have here a source of strong D-region varia-
tions durin_ SA-sycle. Variations of the galactic cosmic rajs
with solar activity are well Known. Ionization rate q due to
cosmic rays in t_e D-region during solar minimum is nearly
twice that during solar maximum.
fable I
_mplitude of maximum _o minimum SA (i_i/m) variations of
various ionization sources
Source Ly-_ I02.7-Iii. 8nm X-rays Cosmic rays
m/m i._-2 2-_.5 5-10 0.6
kefo (NUSINOV,I987) (HLN2ER_GGER, (B_KS and (BRASSEUR
198I) KOCKARTS, and SOLO-
1974 ) _ON, 1984 )
2he most changeable ionizing agent in the D-region is
X-rays. _ariations of ibs intensity during solar cycle depends
on wavelength and generally are strong enough. 2he values of
X-ray flux for _ = 4.I - 3.I nm and levels of SA (ver$ quiet,
quiet, moderate, hish) accorging to BANK_ and_K0_KARTS (I973)
are 7_ IOn, 1.5 IO7, _.0 IOW and 4.5 IOt cm-_s -_.
_zg. ± snows q - values in _he D-region due to various
ionization sources and their possible variations from minumum
SA(m) to maximum SA(_). It is seen that even during high SA
bhe imput of X-rays in the ionizatiQn rate q is small in the
most part of the D-region. _hat means that we should hardly
expect regular changes of the D-region ionization rate during
SA cycle stronger Chart variatiQns of Ly-_ intensity.
Looking at formula (I) we see that the latter me_Is that
we should expec_ _ variations with the amplitude of I.I5-I.4
if there is a quadratic recombination law (_ _#_ is constant
a_ fixed height) an_ of 1.3-2 if there is a l_$ar law (_eff
vary nearly as _-±).
In fact that is what we see in due experimental data -
regular variations of the D-region electron concentration in
the solar cycle are ra_her weak and much less, _han that due
to various disturbances. _o illustrate _ha_, we use the figure
snowing _e_ variation with solar zenith angle_ for summer
conditions (DANILOV etal., I982) and mark at each point the
value of FIO.7 - flux for the day of _he experiment (see Fig._).
As one can see from _hat Figure there seems to be no pronounced
aependence on FI0.7 - all Che experimental points lie on the
same curve representing _ - dependence on_ .
_uite differenb picture we have for various events, mani-
festing _A. There we have very s_rong variations of ionization
ra_e q wi_h consequenb changes of all _he D-region parameters.
Table 2 shows variations of q due Do x-rays ionization during
solar flares of various intensity (prominent, strong, moderate)
according to _I_RA (I974).
185
Table 2.
Ionization rates in the D-region due to solar flares
according to _II_RA (I974)
h, km q cm-_ s-i
Prominent Strong _oderate
60 2.I01 1.5 1.2 £0 -I
b5 b. IO I 4 4. IO- I
70 1.5 IO 2 1.2 IO I I
75 5 IO 2 _ IO I 3.5
80 1.5 IO 3 IO 2 IOI
85 3 I03 2.5 IO 2 2.5 IO I
Fig._ presents variations of q-values during SPE eventm (S_;IDER,
I979). Comparing both sets of q with Fig.I one can see, that
the ionization rates due to X-rays and energetic particles in
disturbed conditions are several magnitude higher than in quiet
conditions. It is worth emphasizing that during very strong SPE
or aEP (relative electron precipitation) events strong ioniza-
tion may take place even at altitudes much lower than normal
D-region down to 30-_0 km (see BRASSEUR and SOLOMON, I98_). An
example of that also give curves 5-7 in Fig.3.
Strong variations of q in the D-region should inevitably
lead to essential changes not only of _e_ but of the whole re-
combination cycle as well, including O(ef f, ra_e of clustered
ions formation B, ion composition parameter ft, negative ions
parameter _ and so on. For SPE events we have data on the
effective recombination coefficieat which show that there in
fact is a variation (decrease of m(^_) during _he events. Fig._
(D_ILOV and SIMONOV, i98I) show v_IQes ofO(ef f for summer
(I97_) and winter (I969) SPE-events. _$ is well seen that O(__
in disturbed conditions (/'sT@ IO _ cm-_) is much lower =_
(esyecially for winter S_)" than for quiet conditions (_ IO _
cm'_"). 9beery of the ionization cycle in the upper D-region
(DAi_ILOV, I986) gives a clear explanation to that fact - the
decrease Offer f is due to decrease of the ion composition
parameter f+ (f+ = [clus_qO +, 0._. That effect has been measu-
red for I969 SPE- event'(NARCIST, I972).
Table 3
Values of the ion composition parameter f+ for quiet winter
conditions and for Sovember, I969 SPE
Day Night
80 km 85 _m 80 km 85 km
,,inter
(average) 2.0 5" IO -I 2 I01 > IO -I
SPE-I9G9 9.I0 -3 1.9"IO -4 I.b'iO -2 5.9'I0 -_
lh
The f*- parameter_ts own turn decreases because of the
reducing of the effectiveness of clus_erea ion formation B. In
186
the S2E conditions _he primary ions produced by the process of
ionization became 02 instead of _0 _ in quite conditions and
+
that leads to substatutioa of B (no ÷) by B(02) , the latter at
fixed height being lower, than the former.
in the lower part of the D-re_ion where there _s a satura-
tion of clustered ions (f+,> 10) an_ variations of f - parameter
does not influence _eff, the latter during disturbances of SrE-
type still changes, but due to decrease of t_e negative ion
parameter _ , because
where _ and c_ - averaged cons_amts of dissotiative recom-
bination and mutual recombination process correspondingly.
_rincipally the same picture should oake place during
sudden ionospheric disturbances SiD, following solar flares.
During SID we observe strong enchancement of _ and reducing
of _ef f (_ITRA I974) but there is no ion composition measure-
ments to check the effects of f÷ decrease.
_veaker, but nevertheless much pronounced changes of the
D-region parameters de _aKe place during other events, produ-
ced by the energetic particle fluxes (Auroral Absorption AA,
REP). In all those cases we have increase in the electron
concentration due to enhanced q-values and decreased_eff.
One more commen_ should be made concerning Fig.4.There is
a well pronounced difference between _eff - values for summer
and wi_te_ SFE. 2his difference reflects _he fact that there is
a s_rong seasonal variation of _(eff (see D_ILOV and SIMONOV,
198I) due to seasonal variations of the ion composition, produced
by meteorological processes (D_ILOV, i98o). _hat means that
effect of solar event (for example SFE) is modulated by the meteo-
rological influence. In our particular case that means _hat the
same SPA-pro_on fluxes (the same q) produce much s_ronger
disturbances of the electron concentration in winter _an i_
summer,
Summarising _he above said one may s_ate _ha5 there are
two t_pes of influence on the ionospheric D-region - direc_
solar and meueorological. If we compare t_le ma6_e_ude of 5he
effects due to SA and meteorological control we wll find (see
fable 4) _hat regular variasions of 5he meteorological origin
are much stronger than Shat due to SA. For spontaneous distur-
0ances the picture i_ quite opposite - the amplitudes of varia-
tions for the principal parameters are higher for SA-produced
e ven_ s.
Above we have already mentioned the effect of _ef f
decrease dux'ing S_S-even_s. fnat decrease strongly depends
on _he season, and taa_ is a good example of _ae u_eteorolo-
gical control filtering the effects of SA. In fact it happens
rather often, because _he _eaction of the D-region to _he ex-
ternal dis_urbancb tin the form of X-rays or cor_uscules)
depends upon the internal state of the D-region _ion composi-
_ion,_ - ratio, effective recombination coefficient), deuer-
mined mainly by _ne neutral a_mosphere and so co,_rolled b_
the meueorological p_ocesses.
187
Table 4
Amplitudes of SA _nd meteorological effects
in the upper D-region
f+[ei °_ef f
Regular
SA < 5o% _ 50% _ 5o%
Seasonal 2 2-3 5-I 0
Spontaneous
SPE _ I0_2 _ 10 102-103
WA _ I0 _ 3-4 _ 30
A good exam@le of that state-
ment provides Fig.5 (D_ILOV e_ al., I985), demonstrating
seasonal variation of the sudden phase anomaly (_PA) effects
in VLF. Fig._ shows that the reaction of the D-region on solar
flares is different for summer and winter, which manifests the
meteorological control of the pure effect of SA.
2here is the other side of the medal. Having some ways to
influence the middle atmosphere dynamics and/or _ermodynamics
by SA without direct effect on the D-region we have indirect
SA influence on the latter through the alteration of the meteo-
rological situation. 2he most obvious example is variation of
solar UV-emission in 120-200 nm interval. £his emission is not
able to change q-values in the D-region, but influences the
Og dissotiation and so 6_ _he £ormation of the ozone should
al_er dynamical picture in _he whole middle atmosphere. _he
latter, as we understand now, is strictly connected with many
aspects of structure and photochemistry (including conditions
for propagation of internal gravity ways) and so will influence
the D-region _hrough minor constituents, temperature dependence
of reaction rates, turbulence ets. £hat is what we call indirect
influence of SA on the lower ionosphere.
2hat kind of influence is prooably _he one which provides
observed connection of the D-re_ion behaviour with such mani-
festations of SA as solar wind (see LASYOVICKA I988) and geo-
magnetic activity. If we put aside events with strong enough
electron precepitation we will find Ohat there is no correla-
tion _itn geomagnetic activity and no or ra_her weak correla-
tion with solar activity (LA_TOVICKA and SKOBODA, 1987). fhe
latter means that ( since we cannot imagine negative influen-
ce of SA on the D-region) _he direct positive effect of SA is
compensated by the i_direc_ one _hrough SA infl_,ence on _he
middle atmosphere as a whole.
Reference
_anKs P. and Koc_arts G., I_7P, Aeronomy, Academic Press, _ew
_ork.
Brasseur G. a_d S.Solomon, I_84, Aeronomy of _ae _iddle _tmo-
sphere, D.Reidel Publ. Gomp., Dordrec_t.
Danilov _.D., I986, in.: ionospheric issledovania (in Russian)
Danilov A.D., A.B.Orlov, L.P._orosova, V.P._ishuk, I98_, Geo-
magnetism i aeronomia (in Russian), V.2#, #.3Ii.
188
Danilov A.D. and A.G.Simonov, I98I, in.: ionospheric issledo-
vania (in Russian) _, P.54.
Danilov A.D., A.G.Simonov, _.V.Smirnova, S.U.Le domskaya,
I982, in: Pros_ranstveano vremennaya structure niznei
ionospheri (in Russian), ioscow, IZ_IR_, P.43.
Lastovicaa J., I988, Annales geophysical, V.6, P.40I.
Lastovicka J. and K._voboda, I987, physicia Sci'ipta, V.35,
_.9o6.
Mitra A.P., I974, ionospheric effects of solar flares, D.
Reidel Publ. Comp., Dordrecht.
Harcisi R.S., I972, Aeronomy Report, University of illinois,
_._8, P.I82.
_usinov A.A., I987, In: Itogi nauki i techniki (in Russian)
_oscow, V.26, P.80.
Simon P., I982, Solar i_nys., V.74, P.273.
Swider W., i979, In: Solar-£errestrial Prediction Proceedings,
Boulder, US Dept.Commerce, V.4, P.599.
h, Km
90
82
7/+
/I
/
I
3 2 o
Fig.i. ionization rates in She D-_±on for maximum_ (_)
and minimum (m) SA due to various sources: L,_
plus i_0 - qI; _ =III.8 - I02.7 nm plus 02 4A_ ) -
q2; x rays - qs; cosmic rays - q_.
f_[e],cm-s
153o _ ? 153 80 Km
lZ6'V • °°B1 1_9 •7o_-"%_.,
98 6B i17_o130
.k
_r\ 153
I I I I f I I I I
_o 30 _o 70 9o%0
189
Fig.2. Electron concentration measured on rockets in summer
at various solar zenith angles _ . _umbers at the
points show solar I0.7 - cm flux at tAe day of the
flight-
190
h, Km
IO0
8O
60
40
/
i 2/,
+ 5/6
I I I
Fig.3. Ionization ra_es in the D-region duming SPE-events
according to Swider (I979) (I-3 _ov.Igb9 event,
4-7 Aug. I97_ event)
_n se_,crn .
I I I
-6
X
\\
\
0 -- ,'iI'TT±R, ....
)_ -- _U,,E<'.R, eclipse
80Kin
@
0
\ 0
0"_- -.. ___
0
i I I
Fig._. Vaz'ia_ions of ;he el fec;ive recombination coefficient
_ef± in suJ_mer (solid line) and winber (broken line)
conditions (Danilov and _imonov, 198I). r_V.,,'_,_,,.:.i_]c_r_L<
06 >00_ Q[_ALITY
191
--.1
"" _O_ --_ O 2 _'""
° \°-.._o__0__o..'/_
"_e...... _ o
i i I [ I i I i I I
Fig.5. Seasonal variation of P (fraction of illuminated time
when S_A effects were oOserved) in 1979 according to
Danilov e_ al. (1983). (I - Leningrad, _ - Atlhlungs-
born).
L.,_'_:.NAL PAGE IS
OF r_
, :o_,R QUALITY


General overview of the solar activity effects on the lower ionosphere

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server