PB 161618

92o. 117

VARIATIONS IN FREQUENCY OF

OCCURRENCE OF SPORADIC E,

1949-1959

BY

W. B. CHADWICK

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

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I
NATIONAL BUREAU OF STANDARDS

technical ^^ote

117

October 1961

VARIATIONS IN FREQUENCY OF

OCCURRENCE OF SPORADIC E,

1949 -1959

by

W. B. Chadwick

NBS Technical Notes are designed to supplement the Bureau's regular publications program. They provide a means for making available scientific data that are of transient or limited interest. Technical Notes may be

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VARIATIONS IN FREQUENCY OF OCCURRENCE OF SPORAUIC E. 1949-1959

By

W. B. CHADWICK

Central Radio Propagation Laboratory

National Bureau of Standards, Boulder, Colorado

ABSTRACT

The question of the dependence of sporadic E on the sunspot cycle has

largely been unresolved, with many investigators obtaining conflicting

answers. In this report results are given covering daily-hourly values

of fEs for eleven years at three ionosphere sounding stations. College,

Washington, and Huancayo, chosen as representative of the three main sporadic-£ zones. These stations experienced a minimum of equipment changes

and changes of location during this period. Scaling procedures were monitored over the eleven years by a data quality-control group at the

National Bureau of Standards. The period included the highest average sunspot number for over 200 years.

Correlation coefficients for yearly count of fEs > 5 Mc vs. yearly

average sunspot number were found to be: College, -0.68 (daytime only,

-0.63); Washington, -0.52 (night only, -0.52); Huancayo, -0.42 (night only,

-0.66). Various hourly and monthly correlations were obtained. Of the

153 correlation coefficients listed in the paper, 147 are negative.

Certain correlations of fEs with magnetic index Ap are presented.

The remarkably consistent results obtained by use of the Phillips formula

logioP = a + bf, are given. (P=probability of occurrence of fEs> T; f=frequency(Mc); a, b are adjustable constants).

An incidental outcome is the confirming of diurnal and seasonal

trends at stations in the auroral, north temperate,and equatorial zones,

making use of many more data than hitherto available.

Variations in Frequency of Occurrence of Sporadic E. 1 949-1959

1. Introduction

Many studies have been made (Wells, 1946; Phillips ^ 1947; McNicol

and Gipps, 1951; Smith, 1951; Matsushita, 1953; Peterson, 1954; Davidson,

1955; Besprozvannaya and Lovcova, 1956; Smith, 1957) in an attempt to

decide whether sporadic E is more prevalent at the low or high part of

the 11-year cycle of solar activity. In general the results have been

inconclusive. For instance, Phillips (1947) reported a negative correlation with sunspot number, at Washington, whereas Wells (1946) found no consistent relationship between sunspot number and sporadic E at Watheroo

from 1939 to 1944. Matsushita (1953) obtained at Huancayo a positive

correlation of 0.60 between monthly median daytime fEs and sunspot number

for the period Aug. 1944 - July 1952. Other reports (*, +) have noted

discrepancies in longtime trends of sporadic E between Washington and

Watheroo. However, the recent recordbreaking maximum has given an opportunity to compare frequency of occurrence of sporadic E at widely

different levels of sunspot number. Furthermore, it has been possible

to choose three representative ionosphere stations, in existence for an extended period of time, and presumably somewhat stable in manner of

operation over an eleven year period. It was desired also to choose

ionosphere sounding stations under the technical control of one organization. Change of equipment characteristics such as relative power

emission and sensitivity of reception throughout the frequency range, as well as changes in interpretation of ionograms, would thus presumably be

held to a minimum. (**) The three stations selected were Fairbanks

(College), representative of a location where the auroral type of sporadic

E is prevalent; Washington, a station in the temperate sporadic-E zone;

and Huancayo, where equatorial type Es is common in the day hours. Thus

all three main sporadic-E zones (Smith, 1957) are represented. Respective

geomagnetic latitudes are 64°N, 50°N, and 1°S.

The parameter chosen for study was the count of fEs >5 Mc. By so doing, it was hoped to avoid contamination of the sporadic-E count with

scaled values which were really fE rather than fEs, as well as to minimize any possible effect of D-region absorption. (Appleton and Piggott,

1954)

The correlation coefficients given in this report were obtained from

comparison of various series of eleven terms each. For example, the values

in Table 1 were calculated from the numbers represented graphically in

figure 1.

* Report IRPL-F12, O.T.S., U.S. Dept. of Commerce, Wash., 1945

+ Report IRPL-R35, O.T.S. , U.S. Dept. of Commerce, Wash., 1946

*

Report IRPL-R34, O.T.S., U.S. Dept. of Commerce, Wash., 1946
2

2. Uniformity of Data

The equipment was changed at all three stations during the period

covered by this report. Therefore, it was felt desirable to go back

prior to 1952 for as few years as possible, and still have an eleven*

year period somewhat representative of a particular solar cycle.

2.1 Equipment Changes. 1949-1959 (Gladden. 1959 )

Fairbanks: To March 1951, OTM automatic multifrequency

ionosonde

Since March 1951, CRPL Model C-3

Washington: To July 1950, CRPL Model C-2

Since June 1950, CRPL Model C-3

Both C-2 and C-3 used in June 1950

Huancayo: To December 1951, DTM automatic multifrequency

ionosonde

Since December 1951, CRPL Model C-3

2.2 Change of Location

Washington: To September 1949, Sterling, Virginia

(39.0ON, 77.50W)

Since September 1949, Ft. Belvoir, Virginia

(38.70N, 77. l^W)

There was no indication in the detailed data of any break in

the type of scaled results because of the above, except possibly for

Huancayo. Because of the necessity for normalization of certain Huancayo

data (see next paragraph) it is believed that the Huancayo data are not

so uniform in quality as for the other two stations.

2.3 Normalization of Data

Because of an unusual amount of outages attributable to equipment failure, the count for the following months at Huancayo was normalized by multiplying by a factor of proportionality, or, for certain

hours, changed to more nearly correspond to average conditions:

September 1949, May 1950, June 1950, August 1951, September

1951, November 1951, February 1959, April 1959

The count for the month of March 1959 was entirely supplied empirically,

making use of diurnal and seasonal trends in adjacent months and for other

years. The large correlation coefficient for March (Table 3) is thus suspect. However, omitting the month entirely and using only 10 years of

March data reduced the coefficient only by -.02 to -.79.
2.4 Change of Scaling Practice

Up until the year 1957, values of fEs*were recorded; in 1957,

1958, 1959, values of foE?*Were scaled, (At Huancayo, foEs was scaled

for the first 4 months of 1949 as well). It was considered better to

obtain values of correlation coefficients for unweighted and weighted

counts of fEs and foEs >5 Mc, rather than to attempt the formidable and

extremely time consuming task of deciding whether each individual value

displayed on the original records really was foEs or fEs for the period

during which foEs was scaled. In fact, a large number of values on the

tabulation sheets were qualified by Vi*.

3. Conventions Used in Obtaining Correlation Coefficients

In obtaining coefficients such as in Tables 1 and 2, the count for

the period when foEs was scaled, was obtained for foEs >4.2 Mc at Fairbanks and Washington, and for foEs >4.6 Mc at Huancayo. The count was also obtained for foEs >5 Mc at the respective locations. Three sets of

coefficients were obtained, (1) using the count for foEs >4.2 (or 4.6) Mc,

(2) assigning the count for foEs >4.2 the weight 3, the count for foEs

>5 Mc the weight 1, and (3) using an unweighted average. The coefficients

became larger in absolute value (in the negative direction) in proceeding

from (1) to (3). The coefficients shown in Tables 1 and 2 are those ob»

tained from process (2).

For Tables 3, 4 and 5, two sets of coefficients were obtained, using process (1) and process (3). The coefficients shown are those obtained from process (3).

* fEs: Highest frequency on which echoes of the sporadic type are observed from the lower part of the E layer. (CCIR, Sixth Hfeeting,

Geneva 1951)

** foEs: The ordinary wave top frequency corresponding to the highest

frequency at which mainly continuous trace is observed. (First Report

of the Special Committee on World-Wide Ionospheric Soundings (URSI/AGI),

Sept. 1956).

-•- Measurement questionable because the ordinary and extraordinary components are not distinguishable. (Second Report of the Special

Committee on World-Wide Ionospheric Soundings (URSI/AGI), May 1957).
In addition, for Tables 3 and 4, comparison was made using smoothed

12-month running average sunspot numbers as well as monthly numbers, for

both process (1) and process (3). There was little difference in results

from the values shown in Tables 3 and 4, and no conclusions of this paper

would be changed as a result of the use of average numbers.

4. Estimation of Sunspot Numbers for the Latter Half of 1959

At the time of writing this paper, Zurich provisional numbers were available for July and August 1959. The following estimated numbers were used for September thru December 1959:

145, 139, 135, 130.

The Zurich provisional numbers, when available, turned out to be

146, 140, 136 and 132 respectively.

5. Diurnal. Seasonal, and Yearly Variations of Count

Figure 1 shows the total count and percentage of fEs >5 for each

year for each station. Also plotted is the yearly Zurich sunspot number.

In figures 2 and 3, which show the diurnal variation in count and

percentage for the period for each of the three stations, the shaded

portions represent hours of minimum count. For Washington and Fairbanks,

they are the hours for which the count is less than half the maximum count

for any hour; for Huancayo, one-fifth is used. They do not necessarily

correspond to day or night hours.

Figures 4 and 5 show percentages by months, both for all hours and

for hours of minimum count. In figures 6-8 percentages by hours are

given. The hours chosen are representative ones for the individual stations. It is seen that the peaks in the graphs do not always correspond

to the years of minimum sunspot number. Thus it is clear that the overall variation shown for the entire eleven year period has considerable

variation within itself when smaller blocks of data are used.

6. Correlation Coefficients and Their Variations

In Tables 1 through 5 the relationship of sporadic E occurrence to

solar activity is described by presenting correlation coefficients of

count of fEs >5 Mc vs. sunspot number. Each coefficient was obtained

from 11 pairs of data by the use of autonratic machine computation.

In Tables 1 and 2 the fEs count refers to the number of hours throughout the entire year that Es occurred, and the yearly sunspot number used

is the mean number for the whole year. In Tables 3, 4, and 5 these totals are broken down into time intervals. Table 3 refers to Es occurrences and

sunspot numbers in each individual month of the year. Table 4 does the same except that only data for selected hours are included. Table 5 shows

how the correlation coefficient varies with hour of the day during the
ll»year period under consideration.

A word of caution concerning the coefficients given in Tables

3, 4, and 5. There is a question as to whether it is proper to obtain correlation coefficients by comparing a series of values (sporadic E) subject to seasonal and diurnal effects,, with a series of

values (sunspot numbers) not subject to such effects. However, the

coefficients listed in these tables were readily obtainable. Furthermore, the prevailisig types of sporadic E at Fairbanks at night

(auroral and retardation types) are not believed to be subject to

seasonal variations in frequency of occurrence. Nor is the prevalent daytinte type at Huancayo (equatorial sporadic E). The attempt to classify sporadic E into nine types according to the appearance of the trace on the ionogram, is of comparatively recent

origin.* l^erhaps when a large body of data on types of sporadic E

has been accumulated there will be more justification for obtaining

correlation coefficients between frequency of occurrence of certain

specific types and sunspot nMibers month by month or hour by hour.

Again^ it is possible that the abrupt change between 1800 and 19(X)

for Huancayo, Table 5, reflects a change from the equatorial type

sporadic E to the flat type, and perhaps also the well-known change

in the shape of the ionospheric layers at Huancayo from daytime to

evening (Wright, 1959),

* First Report of the Special Committee on World-Wide Ionospheric

Soundings (URSI/AGI), Sept. 1956. Second Report, May 1957.
7. Application of the Formula loqinP = a •«• bf

Figure 9 gives the results of applying the Phillips (1947) formula

to certain series of data. It is noted that the value of the slope, b,

which is negative, is higher in absolute value at the maximum part of the

solar cycle, thus confirming the main conclusion of this paper. This was also found to be true in every one of fourteen additional comparisons made

in the same manner: 1957 vs. 1954; 1957 day vs. 1954 day; 1957 night vs. 1954 night; high (count) month 1957 vs. high month 1954; low month 1957

vs. low month 1954. There was also the same relative consistency in the

position of the points of intersection. This consistency became less, as might be expected, as the periods of comparison became shorter. Of course,

fEs must be >fE before this formula can be applied, regardless of the

position of The point of intersection.

8. Correlation of Sporadic E Occurrence at Fairbanks with Yearly Average Ad

Correlation coefficients are given in Table 6 for yearly average Ap vs. total yearly count. Total yearly count of fEs >7 Mc at Fairbanks is included. An apparent improvement in negative correlation at Fairbanks for

count of fEs >7 Mc vs. sunspot number (-.79, -.70 day and -.02 night) is not

borne out for Ap. Two monthly correlations, for September (month of maximum

average Ap over the 11-year period) and Decendaer (month of minimum average

Ap) for Fairbanks, night, gave coefficients of -.23 and -.29. It is interesting to note that when Smith (1957) compared quiet periods with disturbed

periods, he found a positive correlation in the auroral zone with magnetic

activity and a negative correlation in the high north tenqperate zone at

Washington.

9. Discussion of Results: Conclusions

In obtaining correlation coefficients between eleven pairs of variables, if there is no autocorrelation, a coefficient of +.602 is significant at the 95 percent level, and one of +.735 at the 99 percent level.

While there may be some autocorrelation in these series, it is believed to

be slight, so that certain general statements may be made. Exact values

of coefficients undoubtedly have not been found, in view of the above discussion of the quality and uniformity of the data, and the necessity for

adopting certain conventions.

(a) From figure 1 and Table 1, it is clear that there is a negative

correlation between occurrence of fEs >5 Mc and sunspot number, for these

three stations, and for the period 1949 - 1959. The correlation coefficient for Fairbanks may possibly be significant at the 95 percent level.

(b) The diurnal variations, as was expected, followed the pattern

previously observed many times for the three main sporadic-E zones - auroral, temperate, and equatorial. (Smith, 1957)

(c) The unshaded portions of figures 4 and 5 represent a nearly
constant count in the cases of Huancayo and Fairbanks, (equatorial and auroral types of fEs) but the seasonal variation is clearly shown for Washington.

In this connection, it is of interest to compare the coefficients in Tables

1 and 2. The correlation coefficient for the hours of miniiBum occurrence of

fEs, as defined above, at Fairbanks remains possibly significant; at Washington there is no change, while at Huancayo it becomes significant, another indication of the well-known fact that equatorial- type sporadic E is a day-time

phenomenon. Tables 3 and 4 give the comparison month-by-month.

(d) It is of interest to apply the critical levels of .602 and .735 to

the tables of coefficients. However, there is great uncertainty involved as

to the accuracy of results. In Table 5 we find the largest coefficients in

absolute value arranged in a pattern for Fairbanks (1800-0200) and Huancayo

(1900-2200). For Washington, we have high coefficients at 1700 and 2000,

and the ones at 1800 and 1900 are also worth remarking. Finally, there is a minor pattern of high coefficients at 0800 (Fairbanks and Washington) and at

0500-0600 (Huancayo). It is interesting that the hours of 1900-2200 at

Huancayo represent the period when the equatorial hump in the ionosphere is

present as shown by true-height studies. (Wright, 1959) Note that there is an abrupt change between the coefficient for 1800 (+.07) and for 1900 (-.91).

Why there should be this definite pattern of coefficients for these stations

is hard to explain.

(e) In Table 3 (totals) the highest coefficients are for the month of

March at Fairbanks and at Huancayo (Section 2.3). If smoothed 12-month running averages instead of monthly numbers are used, the respective coefficients

are -.87 and -.80. At Washington the highest is for July, the corresponding

coefficient using running averages being -.83. No explanation is offered. In Table 4 (selected hours) there is no coefficient significant at the 99 percent level.

(f) There is a high positive correlation (+.77) between the total yearly amount of fEs >5 Mc at Fairbanks and at Huancayo. This is probably due to

the large number of occurrences of high values of the auroral type at the

former and of equatorial type at the latter station.

(g) The ratio of total occurrence of foEs >5 Mc to (foEs plus ^) >5

Mc is essentially constant for 1957, 1958, 1959, at each of these three

stations.

For Fairbanks, the average ratio is: 0.58 range 0.05

Washington " " ** '• 0.47 " 0.06

Huancayo ** " '* " 0.92 " 0.05

This means, for instance, that at Washington for these three years about

53 percent of the values of foEs >4.2 were between 4.3 and 5.0 Mc inclusive.

This result indicates that over this range of foEs the value of "b" remained

nearly constant in the expression

logjQ (Pj^) = b (f

J - f2) (Smith, 1957)
8

REFERENCES

Appleton, E. V., and W. R, Piggott, J. Atm. Terr. Phys. 5, 141 (1954)

Besprozvannaya, A. S., and V. A. Lovcova, Tr. Arctic Res. Inst.,

Leningrad, 15 (1956), Canadian Translation DRB, T250R

Davidson, David, Tech. Report No. 230, Cruft Laboratory, Harvard

University, Cambridge (1955)

Gladden, S. C. , NBS Tech. Note No. 28, pp. 91, 93, 105, Washington (1959)

Matsushita, S., J. Geomagn. Geoelect. , Kyoto 5, 118 (1953)

McNicol, R. W. E. , and G. de V. Gipps, J. Geophys. Res. 56, 17 (1951)

Peterson, A. M. , URSI-IRE Spring Meeting, Washington (1954)

Phillips, M. L. , Trans. AGU 28, 71 (1947)

Smith, E. K. , Tech. Report No. 7, Ionosphere Project, School of Elec. Eng.

,

Cornell University, Ithaca (1951)

Smith, E. K. , NBS Circular 582 (1957)

Wells, H. W. , Proc. IRE 34, 950 (1946)

Wright, J. W. , J. Geophys. Res. 64, 1631 (1959)
TABLE 1

YEARLY COmr or fRs >5 Mc vs. YEARLY SUNSPOT NUMBEU . 194Q - 1959

Station Correlation Coefficient

Fairbanks (Collecje), Alaska -.60

Washington (Sterling, Va. ; Ft. Belvoir, Va. ). . -.52

Huancayo, Peru , -.42

TABLE 2

YEARLY COUNT^ SELECTED HOUIiS ^ vs. YEARLY SUNSPOT NUMBER

Station Hours Correlation Coefficient

Fairbanks 0700-2000, 150°W -.63

Washington 1900-0600, 75°W -.52

Huancayo 1900-0500, 750iV -.66
10

TABLE 3 MONTHLY COUNT

vs. MONTHLY SUNS POT NmBER

Correlation Coefficients

TABLE 4 M0^^^1ILY COUNT. SELECTED

HOURS, vs. MOr^HLY SUNSPOT NUMBER

Fairbanks Washinqlon Huancayo

Jan -.56 + .37 Jul -.11

Feb -.60 -.35 Aug -.00

Mar -.86 -.19 Sept-. 47

Apr -.58 -.48 Oct -.06

May -.71 -.43 Nov -.17

June -.71 -.41 Dec -.44

Jul -.59 -.79 Jan -.25

Auq -.32 -.04 Feb -.65

Sept -.51 -.59 Mar -.81

Oct -.41 -.60 Apr -.55

Nov -.28 -.51 Mav -.42

Dec -,46 -.50 Jun -.19

Correlation Coefficients

Fairbanks Wash inq ton Huancayo

Jan -.60 + .41 Jul -.45

Feb -.52 -.44 Auq -.43

Mar -.67 -.39 Sept-. 62

Apr -.61 -.42 Oct -.08

May -.65 -.51 Nov -.50

June -.66 -.35 Dec -.70

Jul -.46 -.62 Jan -.29

Auq -.17 -.44 Feb -.69

Sept -.37 -.28 Mar -.49

Oct -.26 -.51 Apr -.32

Nov -.42 -.43 Mav -.68

Dec -,59 -.40 Jun -.53

Station Hours

Fairbanks

Washington

Huancayo

0700-2000, 150°W

1900-0600, 750W

1900-0500, 75°W
11

TABLE 5 YEARLY COUNT ^ BY HOUItS . vs. YEARLY SUNSPQT NIL^IBEH

Hour Fairbanks

Station

Washington Huancavo

Correlation Coefficients

00 -.78 -.36 -.30

01 -,75 -.50 -.29

02 -.74 -.43 -.27

' 03 -.73 -.35 -.39

04 -.72 -.44 -.42

05 -.59 -.50 -.70

06 -.57 -.44 -.63

07 -.46 -.57 -.51

08 -.61 -.78 -.51

09 -.60 -.52 -.50

10 -.54 -.24 -.48

11 -.56 -.60 -.48

12 -.57 -.40 -.44

13 -.55 -.38 -.23

14 -.56 -.41 -.13

15 -.48 -.41 + .11

16 -.65 -.46 +.22

17 -.67 -.88 +.39

18 -.76 -.72 + .07

19 -.04 -.69 -.91

20 -.38 -.78 -.90

21 -.77 -.53 -.92

22 -.79 -.07 -.83

23 -.83 -.51 -.44
12

TABLE 6 YEARLY AVG. MAGNETIC ACTIVITY INDEX, Ap. vs. TOTAL YEARLY COUNT

Correlation Coefficients

fEs >5 Mc fEs >7 Mc

Station All Hours Day Night All Hours Day Night

Fairbanks -.48 -.62 -.30 -.47 -.58 -.32

Washington +.31 + .34 + .23

Huancayo -.50 -.32 -.52
O

1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 I960

Figure 1 Yearly Count and l^ercentage of fEs>5 Mc vs Yearly

Sunspot Number, 1949-1959.
3800 —

3500

3000 —

2500

2000

3O

o

1500

1000

500

95

87

75

62

ui 50 ^

UJo

IT

37

25

12

2 4 6 8 10 12 14 16 18 20 22

Figure 2 Diurnal Variation, Count and Percentage of fEs>5 Mc,

Huancayo, 1949-1959.
17 OC

1500 -

1000 -

zo

o

500 -

- 42

37

- 25

o

4

O

(TUJ

Q. 12

2 4 6 8 10 12 14 16 18 20 22

o

u

800 -

500 -

200 -

20

12 <

zUJo

(TUJ

Q.

Figure 3 Diurnal Variation, Count and Percentage of fEs>5 Mc,

(a) Fairbanks and (b) IVashington, 1949-1959.
50

45 -

40

35 -

30 -

ui5 25

^ 20

15

10

AVERAGE PERCENTAGES: ALL HOURS: 45

: 19-05 = 5

bases: JANUARY 8184 FEBRUARY 7440

APRIL 7920

JULY AUG. SEPT. OCT. NOV. DEC. JAN. FEB. MAR. APR. MAY JUNE

Figure 4 Monthly Percentages of fEs>5 Mc, for All Hours, and for Hours

of Minimum Count (shaded) 1900-0500, Huancayo, 1949-1959.
AVERAGE PERCENTAGE : 10,

3

FOR BASES SEE R6.

4

JAN. FEB. MAR. APR

<9<U

K

til a.

AVERAGE PERCENTAGE: 19, 5 FOR BASES SEE FIG. 4

JAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPT OCT. NOV. DEC.

(b) Figure 5 Monthly Percentages of fEs>5 Mc, for All Hours, and for Hours

of Minimum Count (shaded) (a) 1900-0600, Washington,

(b) 0700-2000, Fairbanks,

1949-1959,
60

50

Hill °^^° ii

40 11^ 1

30 TTTTTT ninillbn

20

10 -

'49 III

'54 '59

2000

40 - 30

iim

20

10

L

jii h-

•54

Figure 6 Percentages for Certain Hours, 1949-1959, Fairbanks, fEs>5, 7 Mc.

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Luther H. Hodges, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director

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WASHINGTON, D.C.

Electricity. Resistance and Reactance. Electrochemistry. Electrical Instruments. Magnetic Measurements.

Dielectrics. 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.

Mechanics. Sound. Pressure and Vacuum. Fluid Mechanics. Engineering Mechanics. Rheology. Combustion

Controls. Organic and Fibrous Materials. Rubber. Textiles. Paper. Leather. Testing and Specifications. Polymer Structure. Plastics. Dental Research.

Metallurgy. Thermal Metallurgy. Chemical Metallurgy. Mechanical Metallurgy. Corrosion. Metal Physics. Electrolysis and Metal Deposition.

Mineral Products. Engineering Ceramics. Glass. Refractories. Enameled Metals. Crystal Growth. Physical

Properties. Constitution and Microstructure. Building Research. Structural Engineering. Fire Research. Mechanical Systems. Organic Building Materials. Codes and Safety Standards. Heat Transfer. Inorganic Building Materials. Applied Mathematics. Numerical Analysis. Computation. Statistical Engineering. Mathematical Physics, Operations Research. Data Processing Systems. Components and Techniques. Digital Circuitry. Digital Systems. Analog Systems.

Applications Engineering.

Atomic Physics. Spectroscopy. Infrared Spectroscopy. Solid State Physics. Electron Physics. Atomic Physics.

Instrumentation. Engineering Electronics. Electron Devices. Electronic Instrumentation. Mechanical Instru- ments. Basic Instrumentation. Physical Chemistry. Thermochemistry. Surface Chemistry. Organic Chemistry. Molecular Spectroscopy. Molecular Kinetics. Mass Spectrometry.

Office of Weights and Measures. BOULDER, COLO.

Cryogenic Engineering. Cryogenic Equipment. Cryogenic Processes, Properties of Materials. Cryogenic Technical Services. Ionosphere Research and Propagation. Low Frequency and Very Low Frequency Research. Ionosphere Research.

Prediction Services. Sun-Earth Relationships. Field Engineering. Radio Warning Services. Radio Propagation Engineering. Data Reduction Instrumentation. Radio Noise. Tropospheric Measurements.

Tropospheric Analysis. Propagation-Terrain Effects. Radio-Meteorology. Lower Atmosphere Physics.

Radio Standards. High Frequency Electrical Standards. Radio Broadcast Service. Radio and Microwave Materials. Atomic Frequency ana Time Interval Standards. Electronic Calibration Center. Millimeter-Wave Research. Microwave Circuit Standards. Radio Systems. High Frequency and Very High Frequency Research. Modulation Research. Antenna Research.

Navigation Systems.

I'pper Atmosphere and Space Physics, Upper Atmosphere and Plasma Physics. Ionosphere and Exosphere

Scatter. Airglow and Aurora. Ionospheric Raaio Astronomy.