Diurnal variation in electron densities and temperatures in F region from backscatter measurements over Puerto Ric

Carlson, H. C.

Nisbet, J. S.

English

NASA Technical Reports Server

d 
Elsctron Densities and Tenperatures in the F-Region 
from Backscatter Measurements at Arecibo 
by 
H. C. Carlson 
J. S. Nisbet 
INARY DATA 
;2%b - ABSTRACT 
The diurnal variation in electron densities and temperatures 
in the F-region above Arecibo, Puerto Rico is discussed. The 
morning build-up and nighttime decay of temperatures on several 
summer and winter days is presented as a function of height, 
and possible explanations are given f o r  the seasonal differences, 
Up to 375 km the ion temperatures appeared to be in good 
agreement with estimates of the neutral-particle temperatures 
except f o r  a period of several hours after sumise when signifi- 
cant departures were observed in the region of 300 km. Electron 
temperatures were generally observed to be about three times 
the ion temperatures during the day and t o  have a rather irregular 
behavior from day to day. 
During the night, ratios of electron-to-ion tempepatures, 
in excess of 1.2 were observed at all times in the region of ”.” . ...-- I - .  - 
the Fmax. 
N65-23662  
https://ntrs.nasa.gov/search.jsp?R=19650014061 2020-03-17T00:07:40+00:00Z
.. 
. L  
- 1 -  
The s i t e  of the  Arecibo Ionospheric Observatory i n  Puerto 
Rico has important advantages as a loca t ion  t o  study F region 
phenomena. 
well t o  t he  south of the  auroral region. Because i t s  geographic 
l a t i t u d e  i s  about 18 
magnetic and so la r  e f f ec t s  can be separated t o  some extent;. 
The s t a t i o n  i s  s i tua ted  close t o  the termination of the magnetic 
she l l  w i t h  L = 1.5; thus both  the length of the f i e l d  l i n e  and 
t h e  proton content contained i n  a tube subtending a un i t  area 
i n  the  F region a r e  much smaller than for higher l a t i t u d e  s t a -  
t i o n s  such a s  the  Millstone H i l l  Radar Observatory of M.I.T. 
The conjugate region l i e s  close enough t o  the  South Atlant ic  
anomaly t h a t  points throughout t h e  F region have conjugate 
points below sea leve l ;  therefore e f f e c t s  r e su l t i ng  f rom trapped 
p a r t i c l e s  can be neglected. 
It i s  t o  t he  north of the  equatorial  anomaly and 
0 0 
and its geomagnetic l a t i t u d e  i s  29 
Figure 1 shows the  behavior of t he  ion and electron tempera- 
t u re s  a t  75 kxi i n t e rva l s  throughout an in t e rva l  of twenty-eight 
hours on December 17 t o  18th,  1964. 
temperatures i n  the  F region were about th ree  times the  ion 
temperatures, w i t h  a marked d i p  occurring a t  about 1O:OO. 
During the  night the  temperatures decreased slowly a f t e r  sunset, 
and i n  the  225 k m  t o  400 km a l t i t u d e  range the  r a t i o  of e lectron-  
to-ion temperatures exceeded 1.5 throughout t he  night .  A t  about 
2 :3O t h e  electron temperature a t  375 k m  and 450 k m  s t a r t ed  to 
increase very rapidly even though loca l  sunrise  a t  these a l t i t u d e s  
was not u n t i l  5:2O 
During the  day the  electron 
- 2 -  
The daytime behavior i s  i l l u s t r a t e d  i n  more d e t a i l  i n  
f igu re  2, which shows the behavior of t he  electron temperatures 
a t  300 k m  f o r  four winter days. 
t he  days were very similar a s  f a r  a s  so l a r  conditions were 
concerned the  behavior of the electron temperature was very 
d i f f e ren t .  Of pa r t i cu la r  i n t e r e s t  a r e  t h e  sudden changes i n  
e lectron temperature t h a t  occur during the day. Such changes 
i n  the electron temperature a r e  of -obvious importance i n  the 
skudy of the  F layer ,  f o r  it i s  apparent t h a t  they w i l l  be 
accompanied by la rge  changes i n  t h e  equilibrium p ro f i l e .  When 
the electron temperature i s  decreasing, t he  plasma sca le  height 
i s  decreasing, and the  electron content above the  maximum w i l l  
consequently decrease, causing ions t o  d i f fuse  downwards. Th i s  
w i l l  result i n  an increase i n  the peak electron density. The 
increase i n  e lectron density w i l l  change the  r a t e  of  heat t rans-  
p o r t  f rom the  electrons,  resul t ing i n  a fu r the r  change i n  tempera- 
tu re .  Equilibrium w i l l  be established when the  recombination 
causes a su f f i c i en t  reduction i n  e lectron density. A corres- 
ponding inverse e f f ec t  can be produced by an increase i n  
temperature associated w i t h  a decrease i n  density. 
shows the  peak electron density and the  electron temperature a t  
300 k m  on Dec. 18, 1964 t o  i l l u s t r a t e  these changes. 
It i s  apparent t h a t  although 
Figure 3 
Figure 4 shows a s e r i e s  of temperature and d e m i t y  p ro f i l e s  
throughout t h i s  disturbance on December 18, 1964. It i s  apparent 
t h a t  there  i s  a very l a rge  increase i n  the  electron densi ty  
-. - 3 -  
and e lec t ron  content between 8:oo and 10: 00 hours accompanied 
by a decrease i n  e lectron temperature. From 1O:OO t o  l3:OO 
hours the  density and content are decreasing very rapidly and 
the  electron temperature i s  increasing. The equations f o r  the  
d e n s i t i e s  ar,d temperatures i n  the l aye r  a r e  thus t i g h t l y  coupled 
and, a s  i s  apparent from Figure 3 ,  can depart considerably from 
an equilibrium p ro f i l e  duri-ng the period around noon. 
e r ro r s  may be made therefore ,  i f  under such conditions the  
l a y e r  i s  considered t o  be i n  equillbrium. Although the  behavior 
appears very var iab le  from day t o  day, it i s  l i k e l y  that averaged 
over a prolonged period, such as a month, a minimum i n  e lec t ron  
dens i t i e s  a t  around noon could r e s u l t  i n  the  "noon b i t e  out" 
observed i n  some averaged measurements of peak electron density. 
The behavior during such dfsturbances i s  of considerable Interest 
because of the  mechanisms involved and because the  nonequilibriwn 
d i s t r ibu t lons  a l low an independent estimate o f  recombination 
and d i f fus ion  coef f ic ien ts .  Doupnik and Nisbet (1965) i n  another 
paper, t o  be presented a t  t h i s  meeting, discuss the  de ta i led  
behavior dur ing  such events. 
Serious 
Figure 5 shows t h e  build-up i n  e lec t ron  and ion temperatures 
a s  a function of time f o r  winter and summer days, During t h e  
Summer the  electron temperatures maifitain t h e i r  nighttime value 
u n t i l  l oca l  sunrise  and then increase rap id ly  at a l l  a l t i t u d e s .  
I n  winter, however, t he  electron temperatures start  increasing 
well before l o c a l  sunrise a t  a l t i t u d e s  of 300 k m  and above. 
- 4 -  
The conjugate p o i c t  f o r  krecibo l i e s  a t  50's 67OW and the  
l o c a l  s m r i s e  f o r  t h i s  point is also included. It i s  apparent 
tha t  because it i s  i n  the  southern hemisphere at a raelat ively 
high l a t i t u d e ,  s?m.rise i n  the conjugate ionosphere takes place 
much e a r l i e r  than a t  Arecibo, The e a r t h ' s  shadow reached a 
maximm altit-ade of 500 ban a t  the conjugate point on Dee, 17 
t o  18th.  
T h i s  suggests t h a t  the r i s e  -En electron temperature before 
dam i s  produced by photoelectrdons from the conjugate ionosphere. 
These e l e c t r o m  wou16 t raverse  khe f i e l d  l i n e  i n  less than one 
minute, so %ha.& the  displacement of the  minimm of the  electron 
temperature from l o c a l  midgfght can be ascribed mainly t o  -the 
time constant for electron cooling when the  heat source i s  
rex07.7 ed . 
Figupe 6 shows the  behavior  at sunset of t ne  electron 
temperatures for s-imr;ner and winter days. It i s  apparent that 
i n  suiner,  when the  sxn s e t s  a t  the conjugate point before i t  
s e t s  at Arecibo, the  electron temperature drops i n  about one 
and one-half hours t o  a nighttime value. T h i s  i s  f n  reasonable 
agreement w i t h  the  delay i n  t h e  Eighttime minimu? of e lectron 
temperatures 3-2 winter. Ir? winter the  electron temperature 
decreases Slowly a t  375 k x  and. 450 km while t he  conjugate point 
i s  illuminated. It I s  apparefit that  the conjugate ionospheres 
a r e  cov-pled by 'she photoelectrons a.nd t h a t  e lectron temperatures 
and hence the  electron densitzes a r e  relafved. I n  p a r t i c u l a r  
- 5 -  
a. 4 
when one o r  the  other  hemisphere i s  i n  darknesss photoelectrons 
w i l l  traaverase t3e magnetic f i e l d  l i n e s  from the  sunlit ionosphere 
t o  produce heating i n  the  conjugate ionosphere. A s  already 
discussed an increase i n  e lectron temperature above the Fmx 
w i l l  produce a decrease i n  the peak electron densi ty  i f  the 
e lec t ron  content i s  unchanged. It i s  suggested that  the predawn 
reductLon i n  e lectron dens i t ies  of ten obsen7ed i s  due t o  heating 
of t he  upper ionosphere by photoelectrons from the  conjugate 
loca+Jions. 
Figure 7 shows the  total heat input required t o  maintain 
t h e  electron and ion temperatures observed Quring the night 
when the e n t i r e  fielci  l i n e  was i n  darkrless, during the  predawn 
period when t h e  ionosphere above the  conjugate point had been 
i l luminated f o r  3 hows, and after loca l  sunrise.  Based on an 
average energy of 13 ev, f luxes of a t  l e a s t  2 x 10- p a r t i c l e s  
per  square meter second would be reqxired to maintain the tempera- 
tulles observed p r io r  to dawn i f  a l l  t he  energy of the photo- 
12 
electrons were assumed t o  be u t i l i z e d  i n  heating the  ambient 
e lectrons.  T h i s  f igure  has t o  be d iv ided  by the  f r ac t ion  of 
t he  energy u t i l i z e d  i n  heating the electrons t o  give the  t o t a l  
photoelectron f l u x  from t he  conjugate poir,t. Carlson (1965) 
i n  another paper t o  be presented a t  t h i s  meeting considers the 
qxestLon of a f lux  of photoelectrons f rom the conjugate point 
and the  consequent implications i n  d e t a i l  . 
- 6 -  
The behavior of t h e  ion and e lectron temperatures and 
dens i t i e s  as a function of height and t i m e  i n  the dawn and sun- 
set  periods i s  being investigated t o  provide information on 
the  production and thermalization processes i n  the F region, 
Conclusions 
Ion dens i t i e s  afid electron temperatures were observed t o  
be ve ry  c losely re la ted ,  and la rge  f luc tua t ions  i n  both occurred 
on separate days, 
able from day t o  day. Observations of t h e  behavior of t he  
layer under such nonequilibrium cofiditions are expected t o  
provide useful information on the  production, Combination, and 
t ransport  processes i n  the dayt ime ionosphere. 
These changes were observed t o  be  very v a r i -  
When the  ionosphere above Arecibo was i n  darkness, and the  
conjugate ionosphere w a s  illuminated, heating of the  upper iono- 
sphere by photoelectrons was observed a t  Arecibo. 
r i s e  i n  electron temperature and predawn decreases i n  peak 
e lec t ron  dens i t i e s  can be explained by t h i s  heating. 
The predawn 
A s  shown by Doupnik and Nisbet  (1965) i n  another paper 
presented a t  t h i s  meeting, during t h e  daytime a decreasing elec- 
t r o n  temperature i n  the  upper F region and the  associated drop 
i n  sca l e  heights  leads t o  a peak e lec t ron  densi ty  which continues 
t o  increase .unt i l  recombination e f f e c t s  become dominant, T h i s  
increase implies  an increase i n  ne t  e lec t ron  content. I n  another 
paper presented a t  t h i s  meeting Carlson (1965), shows tha t  during 
1 
t he  winter nighttime a 
w i t h  zi conjugate point 
- 7 -  
decreasing electron temperature associated 
s w s e t  again tends t o  increase the peak 
e lec t ron  density (recombination e f f e c t s  would have t o  proceed 
s lowly  enough f o r  t h i s  process t o  dominate i f  an actual  increase 
i s  t o  be seen). 
t i o n  leading t o  l oca l  i o n  and photoelectron production, however, 
the  e f f ec t  of t he  upward heat conduction and t h e  onset of recom- 
binat ion dominance i s  not present a s  i n  the  daytime case, Thus 
the  content remains e s sen t i a l ly  constant and the  electron density 
merely undergoes red is t r ibu t ion  i n  accordance w i t h  the  changing 
temperatures and scale  heights. Both of these e f f e c t s  a r e  re -  
ve r s ib l e  i n  that  the  processes proceed i n  the  opposite sense 
when the  electron temperature increases. 
In  the absence of the  solar u l t r a v i o l e t  radia- 
I n  both  cases an increase i n  e lectron temperature leads t o  
a decrease i n  c r i t i c a l  frequency, but the  nighttime processes 
a r e  very di f fe ren t  from the daytime processes. The d i s t inc t ion  
outlined here must be real ized i n  in te rpre t ing  ionosonde data. 
Comparison of winter and summer electron temperatures j u s t  
before and a f t e r  s m i s e  and sunset should provide in t e re s t ing  
information on heat t ransport  processes i n  the  upper F region. 
- 8 -  
Acknowledgments 
The authors would l i k e  t o  express appreciation t o  Dro 
David C. Kleinecki f o r  making the conjugate-point calculations.  
Par t ia l  support of t h i s  work was provided by NASA Grant NsG 
134-61 
Observatory which i s  operated by Cornell University w i t h  the 
support of the  Advanced Research Projects  Agency under a research 
contract  w i t h  the  A i r  Force Off ice  of S c i e n t i f i c  Research. 
Observations were made a t  the Arecibo Ionospheric 
a .  b 
0 
.. \. 
0 
0 
0 
6J 
0 
0 
0 - 
E 
0 
0 
rr) 
Y 
!z 
t 
F 
W 
3 
a 
a 
W e z 
z 
E u
W 
,I 
W 
E 
0 
0 Io 
k 
s 
0 
/" 
0 
0 
0 
6 J  
w 
0 
W 
d 
c. 
0 
0 n - 
0 
0 
0 
In - 0 8 0 0 0 0 Y) 0 nl In CJ g 5  g 8 rr) # 
0 0 
4 E  IC) 0 z y  4 t H 0 0 m 0 0 nJ 0 v) - 
r. V 
2 
Y 
0 
M * 
0 "f 
8 
WX 001 us - x  d 3  WXOOZ us I 
8 
0 
CU 
Y 
0 0 
1 I 
0 
O 5  nJ 
co 
0 
0 
0 
(D 
L 0 
8 -
L. ,r x L u  
8 
8 
0 
0 
8 
a0 -
I 
b -
n 
a0 
b 
I 
0 
0 
0 cu 
0 
0 
0 
-L 
00s ss 
002 ss 
001 ss 
0 ’i. c 
n 
4 
0 
0 
0 
0 
0 
0 
u) 
. 
-. c 


Electron densities and temperatures in the f-region from backscatter measurements at arecibo

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server