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TRANSCRIPT
^ecUnic&l v^ote 40-10
MEAN ELECTRON DENSITY VARIATIONS
OF THE QUIET IONOSPHERE
NO. 10- DECEMBER 1959
J. W. WRIGHT, L R. WESCOTT,
AND D. J. BROWN
U. S. DEPARTMENT OF COMMERCENATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS
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NATIONAL BUREAU OF STANDARDS
CecAmcaJ 92ote 4Q-\0
ISSUED MARCH 24, 1963
MEAN ELECTRON DENSITY VARIATIONS
OF THE QUIET IONOSPHERE
NO. 10- DECEMBER 1959
J. W. Wright, L R. Wescott, and D. J. Brown
Central Radio Propagation Laboratory
NBS Boulder Laboratories
Boulder, Colorado
NBS Technical Notes are designed to supplement the Bu-reau's regular publications program. They provide a
means for making available scientific data that are of
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listed or referred to in the open literature.
For sale by the Superintendent of Documents, U.S. Government Printing Office
Washington 25, D.C. - Price 35 cents
CONTENTS
PAGE
I. Introduction «, 1
II. Description of Basic Data 3
III. Description of Graphical Representation 6
IV. Discussion and Applications of the Data 7
Acknowledgments , 9
References 10
Hourly Vertical Cross Sections Along75°W Geographic Meridian 12
Isoionic Maps (150, 200, 250, 300, 350, 400 km;Nmax, hmax, Scat, Shmax, Shinf) 36
Electron Density vs. Time Curves (N(t)),
(Newfoundland, Ft. Monmouth, WhiteSands, Grand Bahama, Puerto Rico) 47
in
ABSTRACT
The CRPL has initiated a program for large-scale
computation of electron density profiles from ionospheric
vertical soundings. Scaling is performed at field stations,
permitting computation of hourly profiles at the Central
Laboratory. These profiles are combined to form hourly
mean quiet profiles for each station and month. The results
of this program for the month of December are illustrated
graphically. This report is the tenth of a series illus-
trating the electron density variations in the mean quiet
ionospher<
meridian.
ionosphere between latitudes 15 N and 50 N along the 75 W
IV
MEAN ELECTRON DENSITY VARIATIONS
OF THE QUIET IONOSPHERE No. 10 - December 1959
J. W. Wright, L. R. Wescott and D. J. BrownCentral Radio Propagation Laboratory
I. Introduction
Part of the basic responsibility of the Central Radio Propagation
Laboratory is to gather ionospheric, solar, or other geophysical data
necessary in the pursuit of research leading to improvements in radio
communication and knowledge of the earth's upper atmosphere. The
existing network of ionospheric vertical sounding stations is an
important source of such data. Typically, the radio sounding data
directly provide observations of peak electron densities (correspond-
ing to "critical" frequencies foE, foFl, foF2), data on Sporadic E,
and certain derived propagation data such as maximum usable fre-
quencies or MUF factors (Smith, 1939).
In fact, the vertical sounding is potentially capable of providing
the complete electron density profile of the underside of the ionosphere
(i.e. , below hmaxF2) and of providing a basis for extrapolation to
much greater altitudes. However, because a lengthy and difficult
calculation is required, little of this work had been done until quite
recently when techniques and computers have become available and
the exigencies of the IGY and satellite programs have made it impera-
tive.
In the course of its development of facilities for electron density
profile calculations, the CRPL has succeeded in devising means by
which basic data for this purpose may be scaled by the individual field
stations, thereby decentralizing and simplifying the most onerous part
of the work. Through its own station network and those of the U. S.
2
Army Signal Radio Propagation Agency, and through cooperation with
closely associated stations in other countries, the CRPL has initiated
an extensive systematic data reduction program, from which hourly
electron density profiles are being computed for the following stations:
Puerto Rico (NBS, January 1959)Grand Bahama Island (U. S. Army Signal Corps, February 1959)Fort Monmouth, New Jersey (U.S. Army Signal Corps, Feb. 1959)White Sands, New Mexico (U.S. Army Signal Corps, March 1959)St. Johns , Newfoundland (Def. Res. Tel. Establ. Canada, June 1959)Adak, Alaska (U.S. Army Signal Corps, June 1959)Okinawa, Ryukus (U.S. Army Signal Corps, June 1959)Thule, Greenland (U.S. Army Signal Corps, July 1959)Huancayo, Peru (January I9 60)
Talara, Peru (January I960)Baguio, Philippines (February I960)
Affiliation and approximate date of initial participation in this program
are given in parentheses.
The hourly electron density profiles are extensively used in the
research programs of CRPL and are supplied directly to certain other
agencies as part of various research and practical activities. However,
in this comparatively early stage, broad dissemination of the computed
data is a somewhat difficult problem.
In an attempt to make at least a summary of the results of the
program widely and rapidly available, the CRPL has initiated the
present series of reports. These provide graphical representations of
the monthly mean quiet hourly electron densities from certain of the
stations in the preceding list, from which a fairly clear picture of the
local ionosphere morphology may be obtained.
These reports contain N(h) data for the stations at Newfoundland,
Fort Monmouth, Grand Bahama Island, White Sands, and Puerto Rico.
Pertinent facts concerning these stations are given in the following
table:
Table 1
Geomag. Coordinates Geog. Coordinates
fH Lat. Dip
St. Johns, Newf. 1.38Mc/s 58. 5°N 72°N 47°33'N 52°40'W
Ft. Monmouth, N. J. 1.46 51.7°N 71.5°N 40°15'N 74°01'W
White Sands, N. M. 1.30 41.2°N 60°N 32°24'N 106°52'W
Grand Bahama Island 1.30 37.9°N 59.5°N 26°40*N 78°22'W
Puerto Rico 1.15 30°N 51.5°N 18°30'N 67°12'W
II. Description of Basic Data
True heights of reflection of radio waves are calculated from the
observed or "virtual" heights by the method of Budden (1954); this
method need not be described here, but it should be pointed out that
full correction for geomagnetic field effects is made and that the
usual restrictions to monotonic profiles apply.
Tabulations of the mean electron density data at 10 km intervals
and certain related quantities are the bases for the graphs and charts.
A sample for the Puerto Rico Decqrrber data, is given on Page 11.
The table on the following page identifies the quantities appearing on
the tabulation.
Quantity Units Remarks
Average Elec-tron Density (N)
3 3xlO = electron/cm
_5(10 on maps)
Body of table; given at each10 km of height from thelowest hmin to 950 km.
NMAX xlO^ = electron/cm( 10 ~5 on maps)
The mean value of Nmax.
COUNT Count of the number of
profiles entering the mean.
HMIN Kilometers The average height of zeroor very low electron density,obtained by linear extrapo-lation of the electron densityof the individual profiles.
HMAX Kilometers The average height of maxi-mum electron density, determined by fitting a parabolato the upper portion of the
individual profiles.
SCAT Kilometers One half of the half -thick-ness of the parabola bestfitting the upper portion of
the F-region profile. Ap-proximates the scale heightnear the true HMAX.
SHMAX 10xlO = electrons/
cm column
on maps)(1012
Obtained by averaging theintegration of the individualprofiles between the limitsHMIN and HMAX.
SHINF xlO = electrons/
(1013
cm column
on maps)
The average total numberof electrons in a column to
infinity obtained by extrap-olation of observed profilesinto the region above HMAX.(See text. )
5
The following particular features of the tabulated data should be
noted:
A. Averaging process . Each hour of each day is identified with
its magnetic character figure , Kp. For each hour, those days for
which Kp is less than 4+ are included in the "quiet" average. The
other days are similarly combined to form a "disturbed" average;
however, this rarely has physical significance because the number of
disturbed periods is usually small and the behavior of the ionosphere
during disturbed hours is not consistent. Thus, graphs for these
latter averages are not presented here.
B. Determination of hmax. The nature of the "true height"
process is such that no direct measure of hmax F2 is obtained, the
virtual height at Nmax being immeasurable. A useful procedure is
to fit the portion near hmaxF2 with a suitable curve and to determine
hmax from this curve. A parabola is quite satisfactory for this pur-
pose; it is fitted to two of the highest true heights and the measured
value of Nmax(foF2).
C. Extrapolation of profiles above hmax . Before averaging, the
individual profiles are extrapolated above hmax by a Chapman distri-
bution of 100 km scale height. This assumed model seems to agree
well with the few published measurements dealing with the profile of
the F region above hmax (Wright, I960). Extrapolation is necessary
in order to calculate homogeneous averages near hmax, and the average
profiles are, in fact, given to 950 km.
D. Integrated electron densities . The total number of electrons
in a unit column of the ionosphere between the effective bottom (hmin)
and hmax is called Shmax; it is obtained by numerical integration of
the observed profiles between these limits. An estimate of the total
electron content to infinity, based upon the Chapman model, is called
Shinf. It is obtained by adding to Shmax the quantity N^ = 2. 82 HNmaxwhere H is an (assumed constant) scale height for the region above
hmax. Current evidence (Wright, I960) indicates H = 100 km, is an
acceptable choice.
III. Description of Graphical Representation
The relative smoothness of mean quiet ionosphere data lends
itself to various kinds of graphical presentation which offer con-
venient aids to the visualization of the height, geographic, and tem-
poral variability of the ionosphere. Included here are three such
graphical forms prepared from the tabulations described in Section II.
A. Vertical cross sections of the ionosphere along the 75 Wmeridian . Pages 12 through 35 give, for each hour, a vertical cross
section of the mean quiet ionosphere along a meridian section,
nominally the 75 W geographic meridian, for the month of December
1959. Contours are parametric in "plasma" frequency (f]\f) related to
electron density N by
2 ,312,400 fN (Mc/s) = N(electrons/cm ).
The height of maximum electron density is represented by a dashed
line. Note that the vertical scale is expanded about 5. 5 times.
With the exception of White Sands, each of these stations is
reasonably close to the 75 W meridian (see Table 1). There is the
possibility that some of the anomalies imposed by White Sands on
these contours are the result of the well-known longitudinal asymmetry
of the ionospher >.
B. Local time vs. Latitude Maps . Another form of presentation,
useful for indicating the two-dimensional geographic variations of the
ionosphere, is that illustrated by the maps of pages 36 through 45.
Here, for fixed levels in the ionosphere (150, 200, 250, 300, 350,
400 km), contours of electron density are drawn in the latitude vs.
local time plane. To the extent to which longitude anomalies are
negligible, these maps give also the longitude vs. latitude distribution
of electron densities at the indicated heights when it is noon over the
75 W meridian. Similar maps for the peak density, Nmax; its height,
hmax; its characteristic thickness, Scat; the total electron content to
Nmax, Shmax; and the estimated total electron content, Shinf, are also
shown.
C. Electron density vs. time curves (N(t) curves) . The mean
quiet diurnal variation of electron density between 150 and 400 km
heights above the sounding stations is illustrated by these curves.
Dashed lines are used wherever the electron density at any height
falls below the peak density (i. e. when the height hmaxF2 falls below
the height for the curve in question.) Such electron densities are the
result of the extrapolations by the Chapman model discussed in
Section II C.
IV. Discussion and Applications of the Data
Mean quiet electron density data over wide geographic areas are
essential for application to numerous problems of both practical and
scientific interest. For example, the assessment of the radio refrac-
tion errors and Faraday rotation effects in satellite tracking requires
a knowledge of the electron density profile in the direction of the satel-
lite or an estimate of the electron density at the satellite itself.
Alternatively these properties of the ionosphere, or estimates of the
total electron content in a column, may be measured by observations
from rockets and satellites, or from radar moon-echoes, and com-
pared with ground-based observations of the kind shown here.
Frequently it will be necessary to use instantaneous density data
because of the considerable variability of the ionosphere about the
quiet mean. In such cases, the mean data are of value as a "reference
level" in the design of the experiment; for example, in the choice of
radio frequencies, satellite heights, antennas, etc.
Since electron density data represent virtually our only source of
continuous, widespread data on the earth's upper atmosphere, such
data also are essential to geophysical problems involving the electrical,
neutral, and magnetic properties of the atmosphere.
8
For example, data on the vertical cross sections may be compared
with theoretical expectations for the meridional height dependence of
the quiet ionosphere. Several workers (Hirono, 1955; Martyn 1956)
have investigated the equilibrium height (of hmax) for an ionosphere
controlled by diffusion, height-varying electron loss rate, and uniform
(or zero) vertical electron drift. The results are qualitatively in agree-
ment with these observations in predicting a rise of hmax towards the
equator in daytime and a reversal of this tendency at night.
The N(t) curves are perhaps the most physically significant repre-
sentation of electron density data. The strong solar control at all levels
and the important perturbations of this solar control in the upper F
region may be easily seen.
Acknowledgm ents
We are indebted to Mr. A. H. Shapley for guidance in the
initiation of this work, and to Dr. H. H. Howe for the develop-
ment of the computer programs upon which the whole system
heavily depends. This series of reports results from the com
bined efforts of the NBS Electron Density Profile Group,
including at various times L.. R. Wescott, L.. Hayden, D. J.
Brown, F. J. Burmont, I. Ford, N. Moore, M. Durham,
G. Lira, under the direct supervision of G. H. Stone hocker.
The cooperation of the U. S. Army Signal Radio Propagation
Agency is gratefully acknowledged.
10
References
Budden, K. G. , "A method for determining the variation of
electron density with height (N(z) curves)
from curves of equivalent height against fre-
quency (h'(f) curves). Proc. Cambridge Conf.
on the Physics of the Ionosphere, pp 332-339,
September 1954, Pub. by the Physical Society
(1955).
Martyn, D. F. , "Processes controlling ionization distribution
in the ionosphere," Aust. J. Phys. 9_, pp 1 61 -
165, March 1956.
Hirono, M. ,
Smith, N. ,
Wright, J. W.
"Effect of gravity and pressure gradient on
vertical drift in the FZ region," Rpt. on Iono.
Res. in Japan , 9, No. 2, pp 95-104, (1955).
"The relation of Radio Skywave Transmission
to Ionosphere Measurements," Proc. IRE, 27,
No. 5, pp 332-347, (1939).
"A model of the F region above hmaxF2,"
Journal of Geophysical Research, 65_, pp185-191, January I960.
11
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51
* U. S. GOVERNMENT PRINTING OFFICE : 1963 O - 681816
U. S. DEPARTMENT OF COMMERCELuther H. Hodges, Secretary
NATIONAL BUREAU OF STANDARDSA. V. Astin, Director
THE NATIONAL BUREAU OF STANDARDS
The scope of activities of the National Bureau of Standards at its major laboratories in Washington, D.C., andBoulder, Colorado, is suggested in the following listing of the divisions and sections engaged in technical work.In general, each section carries out specialized research, development, and engineering! in the field indicated byits title. A brief description of the activities, and of the resultant publications, appears on the inside of thefront cover.
WASHINGTON, U. C.
Electricity. Resistance and Reactance. Electrochemistry. Electrical Instruments. Magnetic MeasurementsDielectrics. High Voltage.
Metrology. Photometry and Colorimetry. Refractometry. Photographic Research. Length. Engineering Metrology.Mass and Scale. Volumetry and Densimetry.
Heat. Temperature Physics. Heat Measurements. Cryogenic Physics. Equation of State. Statistical Physics.
Radiation Physics. X-ray. Radioactivity. Radiation Theory. High Energy Radiation. Radiological Equipment.Nucleonic Instrumentation. Neutron Physics.
Analytical and Inorganic Chemistry. Pure Substances. Spectrochemistry. Solution Chemistry. Standard Refer-ence Materials. Applied Analytical Research, Crystal Chemistry.
Mechanics. Sound. Pressure and Vacuum. Fluid Mechanics. Engineering Mechanics. Rheology. CombustionControls.
Polymers. Macromolecules: Synthesis and Structure. Polymer Chemistry. Polymer Physics. Polymer Charac-terization. Polymer Evaluation and Testing. Applied Polymer Standards and Research. Dental Research.
Metallurgy. Engineering Metallurgy. Microscopy and Diffraction. Metal Reactions. Metal Physics. Electrolysisand Metal Deposition.
Inorganic Solids. Engineering Ceramics. Glass. Solid State Chemistry. Crystal Growth. Physical Properties.
Crystallography.
Building Research. Structural Engineering. Fire Research. Mechanical Systems. Organic Building Materials.
Codes and Safety Standards. Heat Transfer. Inorganic Building Materials. Metallic Building Materials.
Applied Mathematics. Numerical Analysis. Computation. Statistical Engineering. Mathematical Physics. Op-erations Research.
Data Processing Systems. Components and Techniques. Computer Technology. Measurements Automation.Engineering Applications. Systems Analysis.
Atomic Physics. Spectroscopy. Infrared Spectroscopy. Far Ultraviolet Physics. Solid State Physics. ElectronPhysics. Atomic Physics. Plasma Spectroscopy.
Instrumentation. Engineering Electronics. Electron Devices. Electronic -Instrumentation. Mechanical Instru-
ments. Basic Instrumentation.
Physical Chemistry. Thermochemistry. Surface Chemistry. Organic Chemistry. Molecular Spectroscopy. Ele-mentary Processes. Mass Spectrometry. Photochemistry and Radiation Chemistry.
Office of Weights and Measures.
BOULDER, COLO.
Cryogenic Engineering Laboratory. Cryogenic Equipment. Cryogenic Processes. Properties of Materials. Cryo-genic Technical Services.
CENTRAL RADIO PROPAGATION LABORATORY
Ionosphere Research and Propagation. Low Frequency and Very Low Frequency Research. Ionosphere Re-search. Prediction Services. Sun-Earth Relationships. Field Engineering. Radio Warning Services. Vertical
Soundings Research.
Radio Propagation Engineering. Data Reduction Instrumentation. Radio Noise. Tropospheric Measurements.Tropospheric Analysis. Propagation-Terrain Effects. Radio-Meteorology. Lower Atmosphere Physics.
Radio Systems. Applied Electromagnetic Theory. High Frequency and Very High Frequency Research. Fre-
quency Utilization. Modulation Research. Antenna Research. Radiodetermination.
Upper Atmosphere and Space Physics. Upper Atmosphere and Plasma Physics. High Latitude Ionosphere
Physics. Ionosphere and Exosphere Scatter. Airglow and Aurora. Ionospheric Radio Astronomy.HRADIO STANDARDS LABORATORY
IRadio Physics. Radio Broadcast Service. Radio and Microwave Materials. Atomic Frequency and Time-Interval
Standards. Radio Plasma. Millimeter-Wave Research.
Circuit Standards. High Frequency Electrical Standards. High Frequency Calibration Services. High Frequency
Impedance Standards. Microwave Calibration Services. Microwave Circuit Standards. Low Frequency Calibration
Services.
NBS