Daytime incoherent scatter measurements of electron temperature and density fluctuations in F layer of ionospher

Doupnik, J.

Nisbet, J. S.

English

NASA Technical Reports Server

. I  6 
- .  
'Electron Temperature and Density Fluctuations * 
in the Daytime Ionosphere" 
BY 
GPO PRICE f 
J. Doupn 
and 
J. S. Nisbet 
I--.._. 
/ I  /50 
Ionosphere Research Laboratory 1 Hard copy (HC) 
The Pennsylvania State University 
University Park,  Pennsylvania 
I I n  Microfiche (MF) 
Abstract 
Large electron temperature fluctuations have been observed in the 
F region during the day using incoherent scat ter  measurements a t  Arecibo. 
The behavior is quite variable f rom day to  day. 
When the fluctuaticns occur large changes in the equilibrium density 
distribution result  and the electron densities in the layer change rapidly. 
The relationship between the electron densities, thermal  energies 
and heat transport  ra tes  during these events is discussed. 
I !6 29347 
UCCESSION NUMBER) i / 7  
: M573&V (CODE1 (PAGES) t /3 
I d T E O O R Y I  (NASA CR O R  TMX O R  AD N 6 M B E R )  
*The work described in this paper was supported under NASA Grant No. NsG-134-61, 
and is based on measurements made in cooperation with the Arecibo Ionospheric 
Observatory.  
University with the support of the Advanced Research Projects Agency under 
a r e sea rch  contract with the A i r  Force Office of Scientific Research. 
The Arecibo Ionospheric Observatory is  operated by Cornel1 
https://ntrs.nasa.gov/search.jsp?R=19660020057 2020-03-16T19:24:30+00:00Z
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j -.. b 
1. Observations 
In a s e r i e s  of incoherent backscatter measurements  a t  Arecibo, 
Puerto Rico by Nisbet and Carlson (1965) in the summer  and winter of 
1964 large fluctuations were noticed in the electron density and temperature.  
A considerable amount of data w s obtained in the winter when the magnetic 
activity was very  low and solar  conditions were quiet. 
L J L b  
I a 
One day, December 18, will be considered in detail. Peak electron 
densities for  this day a r e  shown in Figure 1. The major  daytime features 
a r e  a smal l  maximum a t  08:15 Hrs.  and a large maximum of about twice the 
normal  density centered on 11:OO h r s .  In the next two hours ,  the densities 
dropped to  their  normal  daytime values. The densities for this figure were 
computed f rom Arecibo ionograms. 
To examine the consistency of this effect f rom day to day, Figure 2 
shows the maximum electron densities as a function of t ime for  severa l  days 
within a two week period. It is apparent that though large fluctuations occur 
on almost  all days the t imes  of occurrence a r e  not the same,  and that the 
charac te r  changes f rom one day t o  another. 
The peak electron density alone does not give a good indication of the 
physical processes  occurring in the layer when large movements a r e  present.  
Figure 3 shows the integrated electron densities up to 460 k m  obtained f rom 
backscatter profiles compared with the peak electron densities shown in the 
first figure. It is apparent that the electron content of the layer a s  well a s  the 
peak electron density increases  by a factor of two around 11:OO when compared 
to  the contents and densities two hours before o r  after.  The i r regular i t ies  
thus do not represent  mere ly  a redistribtuion of ionization. 
shows the K 
This figure also 
indices and the decimetric solar  flux, both of which indicate no 
P 
abnormai  events. 
' -  
. a  
I 
L 
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Figure 4 shows electron density height profiles f rom backscatter 
measurements throughout this event. 
portion where the electron densities were increasing is shown, and on the 
right the period when they were decreasing. 
increasing phase of the event the electron densities increase uniformly through- 
out the layer above 200 km, while below 200 km there is little variation. F r o m  
On the left hand side of the figure the 
It is apparent that in  the 
11:OO until noon, the electron density decrease occurs in the region of the 
maximum and above, the height of the maximum drops,  and the densities 
below the peak increase.  
decrease is quite uniform in the region of the peak. 
F r o m  noon until 13 hours the electron density 
To investigate the behavior below the peak in somewhat greater  detai 
Figure 5 shows the electron densities during the same periods reduced from 
ionograms using the technique developed by Doupnik and Schmerling (1 965). 
Again, the same general  trends a re  apparent. 
density increases  uniformly throughout the period. 
occurring in the F 2  layer.  
decreasing portion of the event the electron densities a r e  la rger  in the region 
of 180 km. 
In the F1 regioii the electron 
The major variations a r e  
However, it should be noticed that during the 
Figure 6 shows the observed ion temperatures a t  several  altitudes. 
Also shown a r e  the neutral  temperatures f rom the Har r i s  and P r i e s t e r  (1962) 
model for  S It is apparent that in the morning and in the late 
afternoon the neutral  temperatures predicted by the models show much 
slower changes with time than the measured ion temperatures.  
would be expected that ion and neutral temperatures should follow one another 
very  closely. 
provide useful data on the diurnal variation of the neutral  temperatures .  
= 70. 
10.7 
A t  225 km it 
It would therefore appear that the backscatter spectra can 
- 3 -  
2. Production and Loss in the Laver 
To examine the electron density behavior it is first necessary to 
consider to what extent the observed phenomena agree with what is known 
about production and loss  mechanisms in the layer.  
To avoid, to  the maximum extent possible, the necessity for  con- 
sidering t ransport  within the layer,  the continuity equation was integrated 
over the height region 140 km to 460 km. 
continuity equation and the expressions used for the production and loss 
t e rms .  
Figure 7 shows the integrated 
Variations of neutral  density a r e  important for  the examination of 
For  the present analysis, models due to  Harr is  loss  and production rates .  
and P r i e s t e r  (1962) were employed with a first order  modification to  make 
the ion and neutral  temperatures  agree at 225 km. 
The loss  was assumed to follow ion-atom interchange with molecular 
nitrogen followed by dissociative recombination. 
to  follow a Chapman distribution. 
independent of the neutral  atomic oxygen distribution and dependent on the 
so la r  zenith angle. The production was normalized to be equal to the loss 
at 11:OO a.m. when the rate of change of electron content was zero. 
particle f l u x  into o r  out of the region was assumed. 
Production was assumed 
The integrated production was thus 
N o  
Figure 8 shows the integrated production and loss  during the period 
f r o m  08:OO to  15:OO hours.  
e lectron density was increasing rapidly the calculated production was greater  
than the calculated loss ,  and that when the content was decreasing the loss  
was grea te r  than production. 
approximately equal. 
It is apparent that during the periods when the 
During the afternoon, production and loss were 
- 4 -  
In Figure 9 a r e  shown the observed rate  of change of electron content 
and that calculated f r o m  the difference between integrated production and 
loss. F r o m  09:OO to 13:OO hours the agreement is quite satisfactory. Out- 
side this period the assumptions made about the neutral atmosphere and the 
variation of the production function deteriorate. 
The observed electron density fluctuations can thus be explained 
without invoking any sudden increase in production, loss ,  o r  electron f l u x  
into the observed region. 
3 .  Mechanisms for the Fluctuation 
~ 
While the preceding analysis has shown that production and loss alone 
can account for  the fluctuations, a mechanism for  producing the instability 
is required. 
Figure 10 shows the electron temperatures derived f rom incoherent 
In the period around 11:OO hours when backscatter spectra during the day. 
the electron densities a r e  large, the electron temperatures have a minimum 
which is very pronounced a t  300 km and above. 
electron densities a r e  decreasing the electron temperatures increase until 
13:OO hours when the layer shape stabilizes. 
After 11:OO hours when the 
Figure 11 shows the heat fluxes f rom electrons to  ions during this 
period calculated using an expression due to Hanson (1 963) 
T.  * 
It. lb puatd&cd i;ldt &e iGStEi%Ii t -y  r z a u ? t z  f rcrr ,  tCe fslls=..iz* 6 n--T*pc r -----. 
A small increase in electron density in the region of the peak will increase 
the r a t e  of heat t ransfer  f rom electrons to ions, reducing the electron 
- 5 -  
temperature,  and hence the plasma scale height. Downward diffusion will 
follow to equalize the distribution, thus further increasing the heat t rans  - 
port  and reducing the scale heights. 
The mechanism f o r  the initiation of the events can only be hypothesized 
at present,  but there  does s e e m  t o  be a correlation between the time a t  which 
the electron densities start to increase and the ion temperatures  on the 
preceding night. 
Reference s 
~~ ~ 
Carlson, H. C . ,  and J. S. Nisbet, (1965) "Electron Densities and Temperatures  
in the F-Region f rom Backscatter Measurements a t  Arecibo", 
Presented to the NATO Advance Study Institute on "Electron Density 
Profiles i n  the Ionosphere and Exosphere", Finse,  Norway, April 1965. 
Doupnik, J. R . ,  and E. R. Schmerling, (1965) "The Reduction of Ionograms 
f rom the Bottomside and Topside", Pennsylvania State University, 
Ionosphere Research Laboratory Scientific Report 230. 
Hanson, W. B . ,  (1963) "Electron Temperatures  in the Upper Atmosphere", 
Space Research 111, John Wiley. 
H a r r i s ,  I. and W. P r i e s t e r ,  (1962) "Theoretical Models for the Solar Cycle 
Variation of the Upper Atmosphere", NASA Tech. Note 1444. 
Quinn, T .  P. and J. S. Nisbet, (1965) "Recombination and Transport  in the 
Nighttime F- Layer of the Ionosphe re 'I, J. Geophys. Res. 30, 1 13 - 130. -
Swider, W . ,  (1963) "The Ionic Structure of the Ionosphere", Pennsylvania 
State Unive r si ty , Ionosphere Re search  Laboratory Scientific 
Report 201. 
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Electron Temperature and Density Fluctuations in the Daytime Ionosphere

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