The main seasonal features of the middle atmosphere are arising from the different dynamical basic states in winter and summer. The development of the two controversial circulation systems and the also different peculiarities of transition between them in spring and autumn create the completely dominant seasonal variations in strato- and mesosphere. Even in the plasma structures of the mesospheric D-region the seasonal variation is towering above the amplitudes of extraterrestrial influences. From standard ionospheric sounding, significant seasonal D- and E-region effects, adhering to equally significant structure changes in the neutral gas in the height region from 20 to 100 km were discovered. Results about such typical seasonal features are summarized

Lauter, E. A.

English

NASA Technical Reports Server

SEASONAL CIIARACTERISTICS OF A_SOSPHERIC PLASMAAND _{EIR TRANSITIONS
E. A, Lauter
' Academy of Sciences of the GDR
Central Institute of Solar-Terrestrial Physics
Observatory of Ionospheric Research
DDR-2565 Kuhlungsborn, GDR
The main seasonal features of the middle atmosphere are arising from the
different dynamical basic states in winter and summer. The development of the
,: two controversial circulation syst,_s and the also different peculiarities of
transition between tht_a in spring and autumn create the completely dominant
seasonal variations in strato- and mesosphere. Even in the plasma structures of
the mesospheric D-region the seasonal variation is towering above the amplitudes
of extraterrestrial influences. Therefore, the conventional monitoring of the
D-reglon by radio wave propagation methods is still important for the explora- /
lion of atmospheric processes in mesosphere and lower thermosphere and the modes ,,
of action in the stratosphere. Due to the activities of the IGY and IQSY there ,'
are now available long series of such data for fliddleEurope (50"-60"N) in Iono-
spheric Bulletins of the ItPILindau (FRG), ZISTP-OIF Kuhlungsborn (GDR), de Bill
(Netherlands) and Uppsala (Sweden). From standard ionospheric soundin_, from AI
and A3 absorption measurements and from winds in the meteor region we known the
existence of significant seasonal D- and E-region effects, adhering to equally
significant structure changes in the neutral gas'in the height region from 20 to
IO0 ha.
/ _,_e have stz_arized results about such typical seasonal features in Figures
I and 2. Following at first the sectors of representation in Figure I we may
give.the following statements:
.;
1
/ (I) In raid-latitudes a pronounced increase of the occurrence probability of the ..
sporadic E-layer .exists in summer, lasting from the beginning of }layup to the
end of August (SPR_GER, 1981) (typical duration time (TDT) of the phenomenon .'"
130 days). . ..
(2) In the meteor-wind region there exists a regime, which can be described by
four seasonal periods (_PR_IGER et al..,1974; GREGORY etal., 1982): _wo wdst _
'wind periddscorrespond to the main development of the stratospheric circulation
systems. Representing the upper boundary of the _miform circulation from tropo- _ . .
sphere to mesosphere in.winter, rather stable we_t winds e_ist in the 90
.. ... region from late October towards March, culminating in intensity around winter .........
solstice (TDT 140 days). A second west wind period from flayto September
belongs to a fluctuating thermospheric circulation, existing Within and above
the cold summer mesopause, Two rather significant transition periods a_e
separating these two wind regimes. The moat pronounced oneis the wind reversal ....
in spring, i.e. east winds from flarch15 till Hay I0, with a maximum around
April IO. The second transition period occurs in autumn between early September
and late October with disappearing westerlies and calms in the zonal circula-
tion. Both transition periods are reacting, with significant phase changes in
the tidal wind components, on the d,.cresseor reversal of the zonal circulation
in the mesospheric wind system below.
(3) The most remarkable seasonal feature of the D-region is the ionization
enhancement in the height region from 80-100 kmj the winter anomaly, lasting in
our latitude from very late October up to the first days of }_rch (TDT 130
"" days). It is beat observed on frequencies around 1.8 _Iz (Figure Ic and Figure
2)_ which penetrate the whole D-region, when they are reflected at the bottom of
the E-layer. An incre=sed electron density gradient at the bottom of the D-
: f
G
,)
!
/ .'i ' !
https://ntrs.nasa.gov/search.jsp?R=19850012154 2020-03-22T18:37:46+00:00Z
\ _ I - . /
/
!
!
I
I
76 J
I,
$ ,O,H=D,J.F H A ,H J J fA S
b)_..:r[_R_a.'_ -0 _
• .q.°°, t- . . . ..
_ ..,. "_,_
_z 02 "
•" _ O0-
"q -OZ
Jo 3of_
,._ 20.
0-
$0
30 . _!!
_ Figure 1. a) Lower thermosphere: probability of E
occurrence; b) _eteor winds; c) Upper mesosphere
(86 k_), high frequency absorption (full line),
variation of EO content in respect to Autumn (dots);
d) Pressure at 80 km from rockets (full line) and
from VLF phase height (dots); e) Circt_npolar zonal
circulation at 30 mb; f) Planetary wave _mplitude
at 30 mb.
region accompanies this phenomenon, which is thought to be produced by an "'
enhanced content of nitric oxide in and above the winter-time cyclonic polar
, ...... • vortex. From low. frequency •phase beight..analysis we can find an.estimation for" ....
the seasonal trend of gO increase in 86 I_, relative to normal autt=n conditions
(LAUTER et al., 1983). .The dotted trend tn Figure le informs us that a NO . ...... ._
increase by a factor of 2.5 in this height-may describe-the anomalous ionization i.
around winter solstice. This extr_e ionization enhancement in winter is .... _i
" """ followed by an ionization deficit in spring, when on all frequencies (Figure 2) """ "'.""
an absorption minimum occurs. " .:f
• . . (4) In mid-latitudes the pressure at 80 k= undergoes n rather continuous varia-
tion as to be seen from rhe'Volgograd rocket results (Figure Id)." The winter
minim'_ of pressure corresponds to the maximu_ of the mesospheric circulation.
There is a rather fast transltion.towards a pressure maxi.r_u_-inspring(April),. ." =- • -. -.- - • •
shifLing to late }_arch with greater heights. Analyzed for the same height from \
VLF reflection height observations, the relative pressure variation (dotted \
trend in Figure Id) is in renarkable coincidence with the rocket results,
demonstrating also the spring maximum and the small but rather steady pressure
decrease over the whole summer up to October, when the drop towards winter level :_
becomes sharper, t
(5) The change of the basic states of the middle atmosphere is, of course, seen _-
\
best in the circumpolar zonal circulation, expressed in Figure le in terms of
the gradient of the 30 mb level between 50°N and the pole (geopotential meters
per degree of latitude). It is easily seen that the westerlies in winter are
rather steeply decreasing towards spring, defining a mean reversal date to
easterlies of April 2 for the last 25 years. Contrarily, the autumn reversal is
much smoother and more precisely at the very end of August. That means that the
winter status of the stratosphere has a typical duration time of 215 days in
comparison with the stnnmerstatus of 150 days. The latter is caused mainly by
the radiation transfer of the atmospheric ozone layer and defines the decoupling
of meso- and stratospheric energetics from the lower atmosphere. The wind
reversal dates in spring are widely fluctuating from year to year obviously in
- .connectionwith the quasi-biennia ! wave and preceding major stratospheric . . .= .
warmings, which generally retard the spring reversal (_ITZlt_ and LAUTER, 1982).
(6) As a further important parameter of the middle atmospheric dynamics we show
in Figure If for the 30 mb-level the mean annual trend of the planetary wave
amplitude (wave number I and 2) relative to its spring and autumn values. It
can be seen that the duration of strongly enhanced pl_netary wave ==nplitudes
(amounting to three times the equinox amplitude) is from the beginning of
November to the end of February (TDT : 120), comparable with the duration of
the winter anomaly. This par_neter normally increases rather steadily up to
mid-winter, but often fluctuates rather heavily afterwards, especially in
connection with stratospheric wannings.
._ Summarizing the results from Figure I we may say, that the annual trends of
'_ middle atmosphere parameters do inform us about significant seasonal variations
i '_ from the stratosphere upwards to the lower thermosphere, but the coupling
_': between the presented paraneters is not yet wel| explored. For example, we
expect indeed that the occurrence of sporadic E-layer is connected with wind
shears, but we have not yet detected a connection between E -layer and the
meteor winds. In the same way we have no clear connection _etween the tidal
structure of the meteor winds and the thermal regime of the mesosphere. On the
/ f:- other hand we know that a significant coupling exists from middle stratosphere
to the mesopause region in winter and spring. The development and intensity of
the ionospheric winter anomaly is dependent on the development and intensity of
the stratospheric-'mesospheric circumpolar cyclonic vortex. The winter anomaly,
i.e. the enhanced NO-content, disappears rather suddenly when the reversal of
the stratospheric wind syst_n occurs, during a major stratospheric warming event
as well as in spring. The coupling of the zonal winds in winter is also well
detectable up to the meteor region in winter.
Beside the dominating winter features in the middle otmosphere par_eters, ""
the significant transitions from winter to s,_mer state in this height region
have to be considered. We call these remarkable features the "spring
singularity" of the middle atmosphere, which includes:
- The final break-down of the cyclonic stratospheric vortex, i.e. the wind
reversal to strato- and mesospheric east winds.
- The disappearance of the upward propagation of plJnetary waves in the middle
stratosphere.
- The pressure maxim_n in lower and mlddle mesosphere.
- The total disappearance of the winter NO accumuli_tion in the D-region, a
significant minimum of ionospheric absorption.
- The well developed temporal reversal of zonal win_s in the meteor zone.
.\ _hese features of the spring singularity are repeated every year between
f
I'
f
711
aiddle of t~r~h anj ~~d of Apr.;. announcln~ Ih. deeouplinl of Ihe lay.ra froa
Ih. Cliddl. alnoll,t:HI'. It il .. ell .nollu II.al Ihl! Iu::~r Hat .. or Ihl! Cli~dl ..
aIClolpl.. r .. t:al 0100 1"..0" "I'll d ..vrlol"'d FIOrrUlr. (~.r.. oppout. "iedl in at-.o-
'1'1'11"1' .nd lo" .. r thrBo.rt' .. r .... [.-hyrr ('ecurrrne .. ). It II Bueh Ie •••nown
Ihat AI,,, Ihf' f)-rrf.lon ha' a u~iHflCjH.t '\Co<."t"C ItIlU •• In fll"r .. Z " .. t.av ..
I~~rr[oc. rrpc ....."ted Ihr annual Ir ...d~ o{ lonnlthrrlC IblOCrllOU on diffrct-nt
lr"qurncie •• AI 1111:h fcC'!U""Clrl (r,~"rr 2a) the "Inl .. r I'o4XU.lC c!oou... t .... Al
an.1 Al ~... a ...rra"nt. hav. n.1I u",e I\on,i a"d co"',ar41>1 .. _phllld". Tovardl lov.r
fr-'1"rnclf'" Ih~ A) (210~ liLt> 1,·t.ll~tlIl·... 1 varUtH'" I. prurnl ""h ur.i.·. in
"inlrr ~~ ••r~rr L~d Dinl~ in .pr,r.~ and aulunn. On lOll flr~urnelr. (f • 200
,l,:&) a ·, .. 11 <! .. v.. I,,~rd .=M'r l"~t.I"'= of ablot P! Ion r~III" 1•• 1Inr. Iron K4y 10
:;q:I...,Lu (fDr • 1)0 d.ya). Thll rnhanc ..d .lr':~r Ibaorrtion 11 Clon ro""arkllbly
d ...... It'ped on 10\1 lind v("ry lov Irt''lu..nc I.... 'thi I d ( ..et of • vrry lov dectton
donuly I(r • .ltrnt at Ihe Wltl(>;\ (II tl;e {)-rr;:ioc il .Ire-arly dr-Ie-ctabl .. lit lunri ••
~ondjclo~. and i, I •• tl~t ov .. r IhC' full day. Srp.cAtrd by Ihe- l~rlnK
Oln,uhrlly. n... Hvcrul o( t". frrq"o:ney depC'nolC'c.ce of lono.phuic lIblorption
ia a Ii .. ry 'iF-nlf IClnl ir.tite'lor lor Iht> tCMtltir.iI [r01> "int .. r to .,.,.,...r I.,acon
in I .... D-re-t.ICln.
t[
t
.
I
I
L
I
~-
" flluht'r IIl\nil ionl .e'lIcf... l diHerrnc .. in th.. 1""::1 It.tt> of the "'!ao-
II,h.. r., II Ihe hct. that the' Inllvrnet' 01 lol.r activity ul'0n D-rt>pon i. nuch
corco rroncunced in '~'".... r thar. In vict .. r. Fro.. 30 ye-.ra of D-re~lon oblrrv4tioD
"t' flnd correlat".nl 00'.11. Ihr .ol.r aClivity of r ~ (1.9 in ,'.r-:>er and r ~ 0.6 in
winlrr ~onlhl. tti. £tv~a evidt'nct' Ih.1 Ihr wintt'r O-rr&iOD ctructure i. cueh
..ore drp"ndrnt on u,,~ int.-rnal .1l::olphC'ric prOCrlar. Ihan Ihe au:.::>r.r onr •
A S C N , #I A 14 J J A J a
r.J cf
- AJ (l77SH:r)
.it '5 " A1 (ltXJOAfg){I'} TOI 5
0
dl
"(.leJ 5
t 0
,~
If{dS} 5
I 0
Fi&UH 2. TI:~ allnu.1 tnnd of iouo.phedc
.blorption on differrnt Crt'q~e-ncirl.
REFl:Rrncrs
[nt&i.n. C. and E. A. LA~t~r (19E2). Z. Metrorol •• 32. 20?
Cregory. J. fl., C. F.. Y.eelt and A. II. "..tnlon (962). J. AbO', Trrr. Phy •• , 44,
649.
Lautrr. E. A•• J. Tliubenheic ~~d C. v~n Co.~,rt (1983). J. AreOG. Trrr. Phy •• ,
(in prn.).
Svrrntrr. K. (1981). Crrlanda eritr. Crophy •• Leip&i&. 2Q. 30~.
Sprn"tf!r, K., R. Sctu:ir.dcr t. H. CI"f'iligflr. D. ~ur&chn~r end 8. Schllniog
(1974). HIII-SrP-Rrport roo 2. Crntral lnltitutc 01 Sol.r-Terrestrial
Phy.ic •• S.,rlin. COR.
,"
,..'
. -- d--'
-- -~ -.- - ._------
® . (
. .. .... ~ ...". r:' p"... "':'
tt=~=.~:r~'Z\~!":"'?"·~::=::.%1.7;;;~"~r;:~r~-:;'i~~.i~~.. ~~-·~~er·'Il;;r.cs.~·*,"'?m~~~~~


Seasonal Characteristics of Mesospheric Plasma and Their Transitions

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server