The physical cause of partial reflection from the mesosphere is of interest. Data are presented from an image-forming radar at Brighton, Colorado, that suggest that some of the radar scattering is caused by parallel elongated structures lying almost directly overhead. Possible physical sources for such structures include gravity waves and roll vortices

Adams, G. W.

Brosnahan, J. W.

Walden, D. C.

English

NASA Technical Reports Server

274 
4.4D EVIDENCE FOR PARALLEL ELONGATED STRUCTURES I N  WE MESOSPHERE 
G. W. Adams*, J. W. Brosnahan** and D. C. Walden** 
*Center for  Atmospheric and Space Sciences, Utah S t a t e  University, 
Logan, UT 84322 
**Tycho Technology, Inc., P. 0. Box 1716, Boulder, CO 80306 
***Space Environment Laboratory, NOAAIERL , Boulder , CO 80302 
ABSTRACT 
The physical cause of "pa r t i a l  ref lect ion" from the mesosphere has been 
sought for  some t i m e .  We present da t a  from an image-forming radar  a t  Brighton, 
Colorado, t h a t  suggest t h a t  some of the radar s ca t t e r ing  i s  caused by p a r a l l e l  
elongated s t ructures  lying almost d i r e c t l y  overhead. Possible physical sources 
f o r  such s t ructures  include g rav i ty  waves and r o l l  vort ices .  
INTRODUCTION 
Radar soundings of the mesosphere have indicated anisotropic  sca t t e r ing  
s ince  the i n i t i a l  work of GARDNER and PAWSEY (1953) and GREGORY (1961). Signals 
s ca t t e r ed  from t h i s  region are often characterized by well-defined amplitude 
fading, o r  pulsation, pat terns ,  with quasi-periods of one t o  some tens  of 
seconds, and by sca t t e r ing  t h a t  i s  s t a b l e  i n  a l t i t u d e  fo r  minutes t o  days. 
number of models have been proposed t o  explain the "pa r t i a l  reflection' '  r e s u l t s  : 
(GARDNER and PAWSEY, 1953; IIINES, 1960; GREGORY, 1961; BELROSE and BURKE, 1964; 
PIGGOTT and THRANE, 1966; FLOOD; 1968; AUSTIN e t  al.,  1969; AUSTIN and MANSON, 
1969; GREGORY and MANSON, 1969; MANSON et  al . ,  1969; VON BIEL, 1971; BEER, 1972; 
COHEN and FERRARO, 1973; MANSON e t  al . ,  1973; MAWEWS e t  a l . ,  1973; NEWMAN and 
FERRARO, 1973; TANENBAUM e t  al., 1973; HARPER and WOODMAN, 1977; SCRLEGEL e t  
a l . ,  1978; HOCKING, 1979; JONES and GRUBB, 1980; SCRLEGEL et  al.,  1980; and 
JONES e t  al . ,  1982). 
A 
We report  here on mesospheric measurements made with an imaging radar a t  
Brighton, Colorado, t h a t  indicate  occasional large differences i n  r e tu rns  on two 
orthogonal l i nea r  polarizations.  Echo locat ion indicates  t h a t  these r e tu rns  
come from within 2.5 degrees of zenith.  We present f i r s t  a descr ipt ion of the 
experiment and of the r e su l t i ng  data.  Our in t e rp re t a t ion  of the data  i n  terms 
of p a r a l l e l  elongated s t ructures  i s  then given, followed by speculation about 
the possible  physical cause of the inferred s t ructures .  
EXPERIMENTAL CONFIGURATION 
The data  reported here were obtained with the NOAAINSF HF Radar (GRUBB, 
1979) and the Middle-Atmosphere Image-Forming Radar (MAIFR) which are located 
near  Brighton, Colorado. The HF radar  i s  a f l e x i b l e  dual-Doppler radar, used i n  
the work described here to  dr ive the large 2.66-MtIz MAIFR antenna array,  and t o  
sample the ten antennas t h a t  comprise the array sequentially i n  pairs. Each of 
the ten antennas consis ts  of a coaxial-coll inear (BALSLEY and ECKLUND, 1972) 
s t r i n g  of e igh t  half-wave dipoles as shown i n  Figure 1, fed a t  the center. The 
pat tern of a s ingle  antenna i s  fan-shaped, being 16 degrees wide i n  the direc- 
t i o n  p a r a l l e l  t o  the antenna, and 100 degrees wide i n  the transverse d i r ec t ion  
(Figure 2). Five of the antennas a r e  p a r a l l e l  t o  each other  and t o  the north- 
south a x i s ;  the other  f i v e  a r e  p a r a l l e l  and east-west. Dipole-to-dipole spacing 
along an antenna i s  0.331; antennas a re  spaced 0.7071 apart .  Pulses of length 
4.5 km (30 vsec) were transmitted a t  50 pulses/sec, with 50 kW peak-pulse-power 
a t  the antenna terminals. For transmission, w e  used e i t h e r  the center antenna 
of each l i n e a r  array,  giving a crossed-fan-shaped beam, or a l l  ten antennas, 
giving an approxhuately c i r c u l a r  beam about 16 degrees wide. I n  both configura- 
t ions,  the two polar izat ions were f ed  together and i n  phase. For reception, a 
https://ntrs.nasa.gov/search.jsp?R=19840019054 2020-03-22T09:43:28+00:00Z
275 
Figure 1. Middle-atmosphere image-forming radar antenna. 
Location: Boot Lake (Brighton) Colorado, Area: 25.6 
acres = lo5 m2, height:  0.15 A ,  frequency: 2.66 MHz, 
A: 112 m. 
four-pulse average was used on each antenna, so t h a t  one complete data s e t  was 
obtained every 0.4 seconds. 
DATA 
Figure 3 shows log amplitude vs. a l t i t u d e  p l o t  fo r  one of the east-west 
antennas ( top) ,  one of the north-south antennas (center) ,  and a composite of the 
two p lo t s  (bottom). 
around 70 km, which i s  much more noticeable on the east-west antenna than on the 
north-south. 
on-line graphics display,  and relabeled. This display shows the  s i x  most recent 
soundings fo r  a s ing le  antenna, which corresponds t o  a time spread of 2.4 
seconds i n  t h i s  experiment. 1 
The f ea tu re  of i n t e r e s t  here i s  the well-defined layer 
(This f igu re  was taken with a camera d i r ec t ly  from the HF radar 's  
Figure 4 i s  a time h i s to ry  of the l i nea r  voltage amplitude a t  70 lun for the 
s a m e  p a i r  01 antennas as i n  Figure 3. Notice t h a t  the north-south antenna shows 
a smaller but q u i t e  d i s t i n c t  s ignal  which i 5  of ten correlated,  but sometimes 
ant icorrelated,  with the voltage on the east-west antenna. 
cha rac t e r i s t i c  fading pat tern and deep nu l l s .  
Notice a l so  the 
Figure 2. Single antenna (a) longi tudinal  view, (b) transverse view. 
276 
W 
(3 
5 P 
-4 
a 
z 
Q 
W 
f 
0 
TIME (SECONDS) 
Figure 4. 
410 
E 100 
o> so 
c_ 
5 
a 0  
X 
W 
0 20 40 Bo 80 
EAST-WEST ANTENNA 
0 20 40 60 80 
NORTH-SOUTH ANTENNA 
. 
0 20 40 Bo 80 
Q O  
COMPOSITE 
Figure 3. 
Figure 5 shows the corresponding phase h i s t o r i e s  of four of the east-west 
antennas. Untortunately, the northernmost antenna was not operative a t  t h i s  
t i m e ,  so w e  show da ta  from the #I (southernmost) through #4 (next-to-northern- 
most) antennas. 
p lo t s ,  the l a rges t  s ign i f i can t  differences across the array are less than 30 de- 
grees. The antenna spacing i s  0.1071,  so a maximum 30-degree phase difference 
between ill and il4 corresponds t o  a locat ion within 2.5 degrees of zenith i n  the 
north-south meridian. The north-south antennas have phase h i s t o r i e s  (not shown) 
t h a t  ais0 indicate  a locat ion within 2.5 degrees of zeni th  i n  the east-west 
meridian. The main transmit beam i s  16 degrees wide, so the indicated centroid 
While there  a re  some differences i n  d e t a i l  among the four 
I80 I80 
0 
J 0  
a 
a 
n 
5 c 
d 
G o  
v) 
Q 
I 
'L) 
v) 
I a 
- le0 -180 
0 410 0 410 
TIME,seconds TIME, seconds 
180 
N 
0 
t 
G O  
a 
In 
9 
-180 
0 410 
TIME, seconds 
Figure 5. 
277 
of the s c a t t e r e r  i s  w e l l  within the main beam. Notice t h a t  there  i s  less than 
90 degrees n e t  phase difference across the almost ?-minute phase his tory of the 
f i r s t  three antennas. However, there i s  a 180-degree phase discont inui ty ,  in- 
d i ca t ive  of interference among mul t ip l e  t a rge t s ,  a t  t = 200 seconds. The fou r th  
antenna recovers from t h i s  discont inui ty  oppositely from the other  three,  in- 
dicat ing t h a t  the "perfect" discont inui ty  lay between the t h i r d  and fourth an- 
tenna s. 
These measuranents were made using a narrow transmit beam ( a l l  ten 
antennas). Measurements a t  other times using a much wider beam gave r e s u l t s  not 
noticeably d i f f e ren t  from these. 
DISCUSSION 
The f i r s t  suspicion, of course, i s  t h a t  the observed differences between 
the two polar izat ions were caused by sidelobe ac t iv i ty .  
r e s u l t s  i n  Figure 5,  however, show t h a t  the radar re turns  come from very nearly 
overhead. 
The echo-location 
Since the individual antenna beams a r e  fan-shaped, it would be possible for  
a large elongated s t ruc tu re  (20 x 170 km, say) t o  f i l l  one antenna beam while 
only in t e r sec t ing  the orthogonal beam. Indeed, w e  have recent ly  found a high 
co r re l a t ion  between the occurrence o f  infrared s t ructures  of similar dimensions 
and increased radar scat ter ing,  pa r t i cu la r ly  around 85 km (PETERSON and ADAMS, 
1983; ADAM e t  al . ,  1983). 
explain the r e s u l t s  presented here fo r  two reasons. F i r s t ,  the  f i r s t  Fresnel 
zone i s  4 km i n  diameter a t  70 km, so a continuous sca t t e re r  much larger  than 
t h i s  would not r e tu rn  much more power. Second, our measurements made a t  other 
t i m e s  with a l t e rna t ing  wide and narrow transmit beams a l so  indicate  t h a t  there  
i s  no substant ia l  o f f -ve r t i ca l  scat ter ing.  
observed radar s ca t t e r ing  correspond i n  scale  to  the observed infrared 
s t ruc tu res ,  of course. 
overhead gradient maxima of some very large s t ructure . )  
However, such l a rge  s t ructures  seem unlikely t o  
(There i s  no requirement t ha t  the 
The radar s ca t t e r ing  may be specular, caused by the 
The voltages shown i n  Figure 4 indicate  power r a t i o s  of as  high as 20 to  1. 
I f  we suppose t h a t  the sca t t e r ing  r e s u l t s  from the presence of a simple 
elongated s t ruc tu re ,  and t h a t  the s t ruc tu re  l ies within the f i r s t  Fresnel zone, 
then maximum dimensions of 4 km x 200 meters a r e  indicated. 
t h a t  i f  the transverse dimension i s  less than the r ada r ' s  half-wavelength of 56 
meters, then the transverse cross  sect ion w i l l  be much smaller than dimensional 
scal ing would indicate .  A s ing le  elongated s t ruc tu re ,  however, would not 
explain the fading pa t t e rn  and deep n u l l s  seen i n  Figure 4. Multiple s t ruc tu res  
might. Such deep fading i s  frequently accompanied by 180-degree phase 
d i scon t inu i t i e s  such as the one a t  t = 200 seconds discussed above. Deep fading 
and phase d i scon t inu i t i e s  a r e  symptomatic of mult i target  interference patterns.  
KELLEHER (1966) reported frequent quasi-per iodici t ies  i n  the s p a t i a l  s t ruc tu re  
of the ground d i f f r ac t ion  pat tern of radar pulses. MARKER (1981) has d i r ec t ly  
observed groups of p a r a l l e l  r o l l s  i n  the troposphere. Optical  observations 
(PETERSON and ADAMS, 1983 , and references therein)  typical ly  show several  
p a r a l l e l  bands. 
observations . 
SUMMARY AND CONCLUSIONS 
Notice, however, 
Such a model seems t o  have po ten t i a l  fo r  explaining our 
We have shown data indicat ing t h a t  r e tu rns  on two orthogonal polar izat ions 
can d i f f e r  by a f ac to r  of 20, while simultaneous echo-location measurements 
locate  the sca t t e re r  t o  within 2.5 degrees of zenith.  Deep fading and 180- 
degree pnase d i scon t inu i t i e s  a r e  seen. 
elongated s t ructures .  
These data can be explained by p a r a l l e l  
278 
Either g rav i ty  waves o r  r o l l  v o r t i c e s  a r e  poss ib le  sources f o r  p a r a l l e l  
elongated s t ruc tu res .  
p resent ,  tend t o  be  s t a t iona ry  i n  a l t i t u d e  f o r  many minutes, so we would suggest 
t h a t  e i t h e r  ho r i zon ta l  waves or  long columnar r o l l s ,  probably generated by 
pass ing  g rav i ty  waves or  l o c a l  wind shears,  a r e  the most l i k e l y  cause. 
such waves o r  r o l l s  would manifest  themselves i n  the  manner presented he re  only 
when they were i n  alignment wi th  one of the  po la r i za t ions  (we see both eas t -wes t  
and north-south domination a t  d i f f e r e n t  t imes) ,  our casua l  observa t ion  t h a t  such 
phenomena are present  about 10% of the  time would i n d i c a t e  t h a t  such s c a t t e r e r s  
are ac tua l ly  present  most o t  the  t i m e .  
ACKNOWLEDGEMENTS 
The polarization-dependent r e tu rns ,  when they are 
Since 
W e  apprec ia te  t he  considerable e f f o r t  made by John W. Neuschaefer. This 
material i s  based upon work supported by the  National Science Foundation under 
Grant No. ATM-8117275. 
REFERENCES 
Adams, G. W., A. W. Peterson, J. W. Brosnahan, J. W. Neuschaefer and D. C. 
Walden (1983), Mesospheric s t r u c t u r e s  observed simultaneously with 2.6-MHz 
rada r  and in f r a red  photography, submitted t o  J. Atmos. Terr. Phvs. 
Austin,  G. L., R. G. T. Bennett and M. R. Thorpe (19691, The phase of waves 
p a r t i a l l y  r e f l e c t e d  from the  lower ionosphere (70-120-km1, 3.  Atmos. Terr. 
Phys.. 31, 1099-1106. 
Austin,  G. L. and A. H. Manson (1969), On t he  na ture  of t he  i r r e g u l a r i t i e s  t h a t  
produce p a r t i a l  r e f l e c t i o n s  of r ad io  waves from the  lower ionosphere (70-100 
km), Radio Sci.. 14, 35-40. 
Balsley,  B. B. and W. L. Ecklund (19721, A po r t ab le  coaxia l  c o l l i n e a r  antenna, 
IEEE Trans. Ant. Prop. AP-20, 513-516. 
Beer, T. (19721, D-region parameters from the  ex t raord inary  component of p a r t i a l  
r e f l e c t i o n s ,  Ann. Geovhvs. 28, 341-347. 
Belrose, J. S. and M. J. Burke (19641, Study of t he  lower ionosphere using 
p a r t i a l  r e f l e c t i o n ,  J. Geovhvs. Res. 69, 2799-2818. 
Cohen, D. J. and A. J. Fer raro  (19731, Modeling the  D-region p a r t i a l  r e f l e c t i o n  
experiment, Radio Sci.,  8 ,  459-465. 
Flood, W. A. (19681, Rwised  theory f o r  p a r t i a l  r e f l e c t i o n  D-region measure- 
ments, J. Geophvs. Res.. 73, 5585-5598. 
Gardner, F. F. and J. L. Pawsey (19531, Study of t he  ionospheric D-region us ing  
p a r t i a l  r e f l e c t i o n s ,  J. Atmos. Ter r .  Phvs., 3, 321-344. 
Gregory, J. B. (1961), Radio wave r e f l e c t i o n s  from the  mesosphere, J. Geophvs. 
Res., 66, 429-445. 
Grubb, R. N. (19791, The NOAA SEL HF r a d a r  system (ionospheric sounder), 
Tech. Memo. No. ERL SEL-55. 
Harper, R. M. and R. F. Woodman (19771, Preliminary mul t ihe ight  r ada r  observa- 
t i o n s  ot waves and winds i n  the  mesosphere over Jicamarca, J. Atmos. Terr. 
Phvs., 39, 959-963. 
Hines, C. 0. (1960), I n t e r n a l  atmospheric g rav i ty  waves a t  ionospheric he ights ,  
279 
Can. J. Phvs., 38, 1441-1481. 
Hocking, W. K. (1979), Angular and temporal cha rac t e r i s t i c s  of p a r t i a l  
r e f l ec t ions  from the D-region of the ionosphere, J. Geophvs. Res., 84, 
845-851. 
Jones, R. M., G. W. Adams and D. C. Walden (19821, Preliminary ionospheric 
p a r t i a l  r e f l e c t i o n  measurements a t  Brighton, Colorado, on 9 January 1981, 
NOAA Tech. Mem #ERL SEL-60. 
Jones, R. M. and R. N. Grubb (1980), D-region p a r t i a l  r e f l ec t ion  Doppler 
measurements with the NOAA/NpI d i g i t a l  HF radar,  Max-Planck I n s t i t u t  f u r  
Aeronomie, Report No. MPAE-W-02-80-20. 
Kelleher, R. F. (19661, Some s t a t i s t i c a l  propert ies  of the ground d i f f r a c t i o n  
pat terns  of v e r t i c a l l y  r e f l ec t ed  radio waves, J. Atmos. Terr. Phys., 28, 
213-223 
Manson, A. E., J. B. Gregory and D. G. Stephenson (19731, Winds and wave motions 
(70-100 km) as measured by a p a r t i a l  r e f l e c t i o n  radiowave system, J. Atrnos. 
Terr. Phvs.. 35, 2055-2067. 
Manson, A. H., M. W. J. Merry and R. A. Vincent (19691, Relationship between the 
p a r t i a l  r e f l e c t i o n  of radio waves from the lower ionosphere and i r r e g u l a r i t i e s  
as measured by rocket probes, Radio Sci.,  4, 955-958. 
Marker, W. S. (1981), Dual Doppler observations of d i f fus ion  and r o l l s ,  Pre- 
p r i n t  20th Conf. Radar Meteorol., AMS, 536-545. 
Mathews, J. D., J. H. Shapiro and B. S. Tanenbaum (19731, Evidence fo r  
d i s t r ibu ted  sca t t e r ing  i n  D region pa r t i a l - r e f l ec t ion  processes, J. Geophvs. 
8266-8275. 
Mewman, D. B., Jr. and A. J. Ferraro (19731, Sens i t i v i ty  study of the p a r t i a l  
r e f l e c t i o n  experiment, J. Geophys. Res.. 78, 774-777. 
Peters_on, A. W. and G. W. Adams_(1983), OH airglow phenomena during the  July 
5-6, 1982 t o t a l  lunar ecl ipse,  to appear i n  Applied Optics. 
Piggott ,  W. R. and E. V. Thrane (1966), The e f f ec t  of i r r e g u l a r i t i e s  i n  
co l l i s ion  frequency on the amplitude of weak p a r t i a l  r e f l ec t ions ,  J. Atmos. 
Terr. Phys., 28, 311-314. 
Schlegel, K., A. Brekke and A. Haug (19781, Some cha rac t e r i s t i c s  of the qu ie t  
polar D-region and mesosphere obtained with the p a r t i a l  r e f l ec t ion  method, 
J. Atmos. Terr. Phvs., 40, 205-213. 
Schlegel, K., E. V. Thrane and A. Brekke (1980), P a r t i a l  r e f l ec t ion  r e s u l t s  i n  
t h e  auroral  D-region explained i n  terms of acoust ic  waves, J. Atmos. Terr. 
Phvs.. 42, 809-814. 
Tanenbaum, B. S., J. H. Shapiro and J. E. Reed (1973), Phase-difference 
d i s t r ibu t ions  i n  a D-region par t ia l - ref lect ion experiment, Radio Sci., 8, 
43 7-448. 
von B i e l ,  H. A. (1971), Amplitude d i s t r ibu t ions  of D-region p a r t i a l  r e f l ec t ions ,  
J. Geophys. Res. ,  76, 8365-8367. 


Evidence for parallel elongated structures in the mesosphere

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server