Recombination coefficients in F layer measured by ion density profiles derived from reduced ionogram

Mc Crory, D. R.

Nisbet, J. S.

English

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ombination in the Xigh 
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Inc oh e x. en t 
Scatter Measurements” 
by 
J. S. Nisbet 
D. McCrory 
/ The Ionosphere Research Laboratory 
The Pennsylvania State University 
University Park ,  Pennsylvania 
- - - t1v;  pp yv 9 fly DATA ABS TRAC T PiLLi.9 j g  
Previous measurements of recombination coefficier,ts in the F -reglor, 
by Quinn and Nisbet (1965) were  made using ion density profiles derived 
f r o m  reduced ionograms. Uncertainties resulted due to the lack of 
information on the profile of the top of the layer ,  on the temperatures  of 
electrons,  ions and neutral particles and about the profiles in the lower 
F-region at night. 
Prof i les  obtained at  the Arecibo Ionospheric Observatory have been 
used  to study the nighttime recombination. It is shown that a t  Arecibo 
l a rge  changes in the electron ion temperature ra t io  do occur a t  night in 
winter under low sunspot conditions up to about 0200 hours.  Such changes 
w e r e  one mechanism previously postulated to explain low values of 
recombination coefficient obtained using the ionogram data for winter low 
sunspot conditions. 
A considerable imFrovement in the consistency of the resul ts  is 
obtained by the use of the incoherent scatter measu remmts  and it is now 
1 possible to derive recombination coefficients with reasonable agr.eernsnt \ 
f r o m  hour to hour f r o m  twecty minutes of data. % 
Electron ion temperature ra t ios  of greater  than unity f 
throughout the night raising the question of nighttime pz  oduction and the 2 
effect of this on the resul ts  is discussed. L
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https://ntrs.nasa.gov/search.jsp?R=19660017923 2020-03-16T19:12:09+00:00Z
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1. Introduction 
In a previous paper Quinn and Nisbet (1965) have examined the 
recombination and diffusion processes  at night using electron density profiles 
reduced f rom ionograms. 
For these analyses it was found necessary to study the layer  as a 
whole because of the importance of downward t ransport  of ionization through 
the maximum. 
shape of the top of the layer ,  or a t  l eas t  about the changes in  the content 
above the peak as a function of time. 
extend beyond the maximum. 
This required that cer ta in  assumptions be made about the 
The reduced ionograms did not of course 
At night ionograms are subject to e r r o r s  a t  lower heights due to 
dispersion in the lower regions of the ionosphere. 
the dissociative recombination coefficient becomes important and it is h e r e  
that the lower boundary conditions for  the t ransport  velocity are established. 
It was  thus necessary to cor rec t  the profiles to the extent possible and this 
was  done using a s e r i e s  of correction factors  developed by Long (1962). 
These measurements  were  con3pared with neutral atmospheric temperatures  
estimated using the mean monthly 10. 7 c m  solar f l u x  and a relation derived 
It is in this region that 
by Jacchia  (1952) f r o m  satell i te retardation studiek 
Incoherent scat ter  measurements of the ionosphere provide 
measurements  of the electron density above and below the maximum. 
Measurements  of the electron and ion temperatures ,  indicate the ionic mass 
and a r e  not subject to dispersive e r r o r s  in  the lower ionosphere a t  night. A 
series of measurements  has  been made in cooperation with Cornel1 University 
at the Arecibo Ionosphere Observatory to investigate the effects of several  
of these  factors .  Recombination and diffusion coefficient calculations have 
been made and the initial resu l t s  w i l l  be discr ibed.  
l a r g e  differences between the summer  and winter behavior of the nighttime 
. 
Previous work had shown 
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ionosphere and this difference was substantiated by the summer  and winter 
measurements  at Arecibo. 
2. The Shape of the F region above the maximum 
The shape of the electron density profile above the maximum in the 
region where diffusion effects dominate and atomic oxygen is the major ion 
is dependent on the sum of the electron and ion temperatures .  
shows electron ard ion temperatures for one summer  and one winter night. 
In winter the electron temperatures in the upper ionosphere decrease steadily 
throughout the night until 2:30 a t  which time they start to increase again. 
effect is discussed by Carlson and Nisbet (1965) and is attributed to photo- 
electrons f r o m  the conjugate a rea  traversing the field l ines and producing 
heating of the electrons in the upper ionosphere. In summer  the electron 
temperature  drops rapidly in the first two hours after sunset and then remains 
stable at a value higher than the ion temperature,  throughout the remainder 
of the night. 
Figure 1 
This 
Figure 2 shows comparative values of the plasma scale  height 
calculated f o r  a summer and a winter night. 
electron and ion temperatures  measured using the incoherent backscatter 
spec t ra  assuming 0' as the major ion and f rom the relation given by 
Jacchia  (1962) assuming that Ti and Tn a r e  equal. It is apparent that on 
both the summer  and winter nights the effect of the electron temperature 
being much l a rge r  than the ion temperature r a i se s  the plasma scale height 
considerably alone that corresponding assuming T Ti and T equal. 
More  important perhaps is the change in scale height as a function of time, 
f o r  this controls the downward flux of electrons through the maximum. 
such an effect is not taken into account for recombination coefficients 
calculated f rom profiles below the maximum the resulting recombination 
Values a r e  given calculated f rom 
e '  n 
If 
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coefficients will be underestimated. 
winter when the conjugate location is illuminated for a good pa r t  of the 
night and thus the underestimation would be expected to be m o r e  ser ious  
in winter. An electron temperature that decreased throughout the night 
was one mechanism suggested by Quinn and Nisbet (1965) to explain the 
very  low values of recombination coefficient calculated in winter under low 
sunspot conditions 
The effect appears  to be l a rge r  in 
3.  Effects re la ted to the lower F region 
In the previous analysis mean monthly ionograms were  used which 
had been calculated by a modified Budden method. 
shown to resul t  in  an underestimation of the electron densit ies at low heights 
and a correct ion based on the work of Long (1962) was applied. 
Such profiles have been 
In the present  analysis incoherent scat ter  profiles have been used 
which do not suffer  f rom these disadvantages. Figure 3 shows electron 
density profiles measured a t  night using the incoherent scat ter  profiles. 
this graph a l s o  a profile is included reduced f rom an  ionogram measured at 
the same t ime using a recent reduction method developed by Doupnik and 
Schmerling (1965). 
are current ly  being studied. 
On 
Such differences between the two types of measurements  
In the previo’us work diffusioh coefficients were calculated. The decay 
in the electron densit ies at night was related to the recombination coefficient 
using neutral  atmosphere models. 
continuity equation to be integrated up to given heights to determine ion 
fluxes o r  ion velocities 
diffusion velocities calculated from the shape of the profile, diffusion 
coefficients were  calculated. 
These coefficients allowed the 
By comparing these ion velocities with normalized 
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This type of calculation is extremely sensitive to the assumptions 
made about the lower boundary condition and there  was thus considerable 
uncertainty about the effect of the correction applied. 
considered of considerable importance to repeat  the analysis with more  
accurate data. 
It was therefore 
Figure 4 shows the vertical velocity in me te r s  per  second calculated 
for a twenty minute period a t  around 21: 15 h r s .  on July 12, 1964. Also 
shown on this graph is a normalized diffusion velocity. 
the character is t ics  of the velocity profiles a r e  quite s imilar  t o  those 
obtained previously. 
profiles i s ,  
It i s  apparent that 
The diffusion coefficient calculated f rom these velocity 
1 
2. 16 x 1019 T2 sin’ I 
n - 2  - 1  D =  111 sec n(M) 
F r o m  the limited number of examples calculated to date the 
indications a r e  that the diffusion coefficients a r e  la rger  than those estimated 
based on the ionograms as previously corrected.  
incoherent scat ter  measurements to date a r e  only for two nights in summer  
under low sunspot conditions and much work remains  to be done before 
conclusive statements can be made. 
The resul ts  of the 
4. Recombination during a summer night 
Figure 5 shows the total electron content as a function of t ime 
during one summer  and one winter night. 
night in particular the electron content is not decreasing and in fact  does 
increase  during a major  portion of the night. 
It i s  apparent that on the winter 
During the summer  night the electron content decrease was la rge  
during the period f r o m  20 hours to midnight and the recombination coefficient 
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calculated for  individual periods w a s  determined. These were  found to be 
(Y assumed 
21:07 to 2 1 2 2  
23:15 to 23:55 
No l a rg  
(Y = 3 x 1 0 - l ~  m3 sec  
trend is apparent in these m 
p = ,368  x l o - '  sec  - 1  
30 0 
30 0 = .355 x io-* sec- '  
asurements  that would make i t  
appear that the production r a t e  is comparable with the loss  r a t e  during this 
period. 
After this period howerer,  the r a t e  of change of electron content 
becomes very small and the difficulties apparent in  the winter data are 
encountered. 
5. Recombination during a winter night 
In winter i t  is apparent that the integrated electron content did not in 
fact  decrease during the night. 
the conjugate location is in  darkness 
This effect is apparent at all  times even when 
It is thus of in te res t  to make an 
est imate  of the nighttime production. 
It was therefore decided to study the ionosphere throughout the day 
to determine production and loss  coefficients for  that day in another manner.  
Shortly after sunrise  the production and r a t e  of change of electron density 
terms predominate in the F 
possible to determine the production profile a t  that t ime in the region of the 
production maximum even if the diffusion and recombination coefficients a r e  
not assumed to be known within an order  of magnitude. 
profiles of the t e rms  of the continuity equation at 6:45 calculated using data 
f r o m  the incoherent scat ter  sounder. The recombination coefficient values 
chosen for these calculations were taken f rom Quinn and Nisbet (1965). 
region continuity equation. It is therefore 
I 
Figure 6 shows 
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The diffusion coefficient was chosen to be 
a purposly high estimate. 
a r e  small in the region of 180 km and a value for the production function 
was adopted. 
It is apparent that the lo s s  and diffusion t e r m s  
Z Z 
q = 2 x  10' exp [ 1 - - exp ( -  FT) ] 
The time period around 13 hours was next examined. It had been 
determined that a t  this t ime the region was stable at all heights and that it 
could therefore assumed that the production and loss  t e r m s  would be 
approximately in  balance. 
was modified to take account of changes in the solar  zenith angle and in  the 
atomic oxygen distribution. 
time and it is shown in Figure 6. The value of the recombination coefficient 
at 300 k m  was then calculated that would make the integrated production and 
The production fi.~nctir?n determined after s u n r i s e  
A production profile was calculated for this 
l o s s  in  the layer  equal. 
This value was found to  be 
p = 0.71  x sec-' 
30 0 
and agrees  well with mear nighttime values given by Quinn and Nisbet (1965) 
f o r  the neutral temperature  a t  that time. 
Based on the recombination r a t e  estimated a t  13:OO hours the 
recombination r a t e  was calculated as a function of height at midnight using 
neutral  atmospheric models due to Nicolet (1 962). 
' .  
- 7 -  
Figure 7A shows the thermal fluxes for  midnight and 13:OO hours.  
Figure 7B shows the estimated production a t  13:OO hours and the estimated 
loss  a t  midnight calculated in the manner described. 
total production required to maintain the nighttime ionosphere in winter is 
very  much smaller  than is present during the day. 
it is estimated that on the night investigated a total production of the order  of 
I t  is apparent that the 
F r o m  these calculations 
Q = 10" electrons m'2 sec-'  
would have been sufficient to maintain the observed electron densities. 
Production in this context should be interpreted as including any net ion f l u x  
downward at the 600 k m  altitude level. 
A c h o w  1 e dg m ent s 
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. The Arecibo Ionospheric Observatory is 
operated by the Cornel1 University with the support of the Advanced Research  
Pro jec ts  Agency under a research  contract  with the Air Fo rce  Office of 
Scientific Res  e a r  ch. 
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References 
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  No. 230. 
Dungey, J. W., "The Effect of Ambipolar Diffusion in the Nighttime F Layer", 
J. Atmospheric Ter res t .  Phys . ,  - 9, 90-102, 1956, 
Hanson, W. B . ,  Electron Temperatures in the Upper Atmosphere, Space 
Research III(Ed. W. Pr ies te r )  282-302, North Holland, Amsterdam, 1963. 
Hinteregger, H. E . ,  L. A. Hall and G. Schmidtke "Solar XUV Radiation and 
Neutral Par t ic le  Distribution in July 1963 Thermosphere". 
at Open Session of Working Group IV, Cospar, May 15, 1964. 
Florence,  Italy. 
Presented 
Jacchia,  L. G . ,  Variations in the Ear th ' s  Upper Atmosphere as revealed 
by Satellite Drag, Smithsonian Astrophys. Obs. Rept. , Cambridge, 
Mass . ,  December, 1962. 
Long, A. R. ,  The Distribution of Electrons in the Nighttime Ionosphere, 
J. Geophys. Res . ,  - 67, 989-997, 1962. 
Nicalet, M. , Density of the Heterosphere Related to Temperature ,  
Smithsonian Astrophys. Observatory, Spec. Rept. 75, Sept. 19, 1961. 
Quinn, T. P. and J. S. Nisbet, Recombination and Transport  in the 
Nighttime F Layer  of the Ionosphere, J. Geophys. Res.  - 70, 113-130, 
1965. 
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Recombination in the Nighttime F-region from Incoherent Scatter Measurements

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