UNCLASSIFIED AD 273857 - DTICCorrimnda for RAort I ('Twilight Intensity at 200 Elevation', by F. Volz and R. M. Goody, 1960, AICRC-TN-60-284), p. 2, line 14. Should read ' ... the

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AD 273857

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3 , ,AFCRL-62-2E1 (a)c c Blue Hill Meteorological Observatory

00 _ _ __ __ _

I Division of Engineering & Applied Physics

C * Harvard University

TWILIGHT INTENSITY AT 200 ELEVATION

Results of Observations

By

F. E. Volz

December, 1961

AF19(604)- 4546 Scientific Report No.2

Prepared for

Geophysics Research Directorate A

Air Force Cambridge Research Center + IAir Research & Development Command

United States Air Force. Bedford, Massachuseth

U jA L

TISIA

P~equests for additional copies by Agencies of the Department ofDefense, their contractors, and other Government agencies should bedirected to the:

APMD SERVICES TECHNICAL INFORMATION AGENCYARLINGTON HALL STATIONARLINGTON 12, VIRGINIA

Department of Defense contractors nuat be established for AS"4IA ser-vices or have their 'need-to-know' certified by the cognizant militaryagency of their project or contract.

All other persona and organizations should apply to the:

U. S. DEPARTMENT OF COMMERCEOFFICE OF TECIRICAJ SERVICESWASHIfNGTCN 25, D.C.

'V,

~M

AFCiRL62-2 6J (a)

Division of Igiaeerng sad Applied hTys ic

laaulU of Oarzmtima

by

V. 3. Vo1:

Dember 1961

Alp 19-0(4546) Scientific Report No. 2

Prepared for

GKOElC ICI SSnM IIle --- --- 1

AIR I NcM AMD D DIU3I3T

IUU3 SID23 AIR Yamcllll3llD

TABI OF CONENTS

page

1. Introduction 1

2. Instrumentation and measurements 2

3. Calibrations 4

3.1 gain calibrations 4

3.2 Temperature dependence of photometer sensitivity 4

3.3 Absolute calibration of the photometer 6

3.3.1 General considerations 6

3.3.2 Sun calibration 8

3.3.3 Star calibrations 11

3.3.4 Noon measurements 12

4. Turbidity measurements 13

5. Evaluation of twilight records 14

6. Weather maps and cloud cross-sections 16

7. General coments on data presented on twilight graphsand data sheets 17

7.1 Logarithmic gradient 17

7.2 Color ratios 18

7.3 Relative green intensity 20

7.4 Weather map and cloud cross-section 20

7.5 Twilight data sheets 20

8. References 22

9. Results of observations 23 ff.Twilights 1 to 103 with omission of TV 23, 28, 29,55, 67, 81, 87, 92, 95, 96

Corrimnda for RAort I ('Twilight Intensity at 200 Elevation', by F. Volz

and R. M. Goody, 1960, AICRC-TN-60-284),

p. 2, line 14. Should read ' ... the diameter of the earth's shadow

varies ... Is

p. 19. Formulae in centre of page should read

- )

p. 21. Table 5. For 0 - 600 replace 25 by 80. For 0 - 250 replace

200 by 300.

Fig. 13. Replace d log IL/d 6 by d log IL/d log ID

p. 32. Table 6. The ozone distribution employed corresponds to that

in fig. 14c.

p. 39, line 3. Should read ' ... a weighted mean inverse scale

height

1. iamu i

A previous report (Volz and Goody, 1960; hereafter referred to as Rep.

I) gave a general outline of our twilight research, The aim of the measure-

ments is detection and quantitative analysis of dust scattering in the atmos-

phere as high as possible having regard to interference by the airglow and

unwanted scattering effects (in practice these give a useful upper limit of

80 km). The brightness of the twilight sky is recorded in 5 filter ranges

from 380 to 660 up, at an angle of elevation of 200, in the sunis vertical *

The instrumentation has been described in Rep. I, and a few results together

with some twilight computations were presented.

A total of about 100 twilights have been recorded, mainly between Sep-

tember, 1959, and September, 1960, with a few up to Wovember, 1961. In this

report, the results at 200 elevation will be presented in chronological

sequence in the form of logarithmic intensity gradients (d log I/d), color

ratios (CR) and absolute green intensities, all as functions of the sun

depression. Weather maps and cloud cross-sections along the path of the

setting (or rising) sun provide soe information on possible cloud interfer-

ence. Daytime turbidity data, visual purple light observations and astronomi-

cal data are also given. Details of the measurements, evaluation procedures

and data reduction will be discussed, together with procedures and results

of instrument calibrations. Discussion of the results and interpretation in

term of vertical dust distributions will however be treated in subsequent

Agart from a few special investigations where measurements were made at 7o

90 and 1600 elevation.

papers.

2. Instrumentation and measurement

A detailed description of the instrumentation has been given in Rep.

I, but the general features will be repeated here for better understanding

of the results.

A photometer of 41 cm effective focal length, with maximum aperture

f/3.3 at the focal plane and f/0.6 at the photowultiplier, was used. Sky-

light measurements from daytime to abeut 5 sun depression we'e made with a

circular field of view 0.67 0 in diameter (field stop D), and in the later

twilight with a rectangular field, 0.790 vertical by 4,450 horizontal. A

removable objective cover provided further means of changing the light flux

into the instrument in order to restrict the range of amplifier gain and

ranoe of illumination of the photomultiplier. Cover openings of 3 and 10

diameter were used at and shortly after sunset, and the full objective

opening was used for sun depressions greater than 60.

Four spectral bands were isolated by interference filters, having peak

response at 380 up (UV), 431 up (B - Blue), 516 map (G a Green) and 605 m

(0 - Orange) and half widths of 10 to 14 qi. The fifth spectral band was

formed by an RC2 absorption filter in conjunction with the 10 stage RCA

photomultiplier 6217 (spectral response S-10), g8virng an effective wavelength

of 659 mp (R - Red) with a half width of about 100 mp. These filters, together

with suitable neutral density filters to equalize mean deflections, are

mounted on a rotating disc and each filter is held in position for 6 seconds.

The multiplier output is fed to an amplifier with a phase-sensitive

-J-

detector. A chopper interrupts the light beam inside the photometer 150

times per second and also provides the reference signal for the sharply-

tuned amplifier. A gain switch at the amplifier input permits 7 gain

changes by a factor of 2. The amplifier output is recorded on a Leeds

and Northrup Speedomax Recorder with single trace, a time constant of 1

sec, and a chart speed of 2.5 cm per minute. The performance of the whole

equipment was generally excellent.

Several methods were used to monitor the sensitivity of the instrument.

The fundamental calibrations involved the measurement of sun and star inten-

sities (see §3.4) which were periodically compared with an internal sub-

standard (LI) consisting of a layer of Undark Luminescent Paint (U. S. Radium

Corp., Pale Green Paint, type 12 M) which could be placed in front of the

filters. This internal sub-standard could be frequently and directly com-

pared with the twilight sky and could reasonably be expected to hold its

intensity (subject to temperature corrections) between sun comparisons.

Unfortunately, a reading from the paint could only be taken with the green

filter, and it was necessary to assume constancy of color ratios. This

point was investigated by means of solar observations (§3.3.2 and fig. 2) and

with the aid of laboratory sub-standard lamps (LII and LIII) illuminating

ground-glass screens through filters simulating the color of twilight (BG 28

and Kodak Wratten CC 50 M).

The twilight measurements were always made with the same schedule of

electronic and optical gain settings. Electronic and optical gain changes

kept deflections greater than 1/4 full scale, except for UV which sometimes

gave a smaller deflection.

-4-

The azimuthal direction of the photometer was adjusted each 20 min*;

deflection changes during adjustment were less than 2% in all colors.

The twilight measurements were generally made by the author, but a few

were made by V. J. Walker and J. Gille (TW. 74, 75, 77, 79 and T. 85 to 92).

These twilights, and also the first 10 twilights, lack detailed visual obser-

vations of the purple light.

Measurements were always made with a cloud-free sky at the time of

twilight, and good to moderate visibility. No effort was made to avoid

distant clouds near or below the horizon.

3. Calibrations

3.1 Gain calibrations

As already described in Rep. I, an optical calibration of the amplifier

gain switch was in good agreement with electrical calibrations. Tests on

the amplifier failed to detect any deviation from linearity. Linearity of

the multiplier tube was also demonstrated indirectly. Further special tests

on gain and linearity have not been made &part from comparisons of solar and

star magnitudes as discussed below. Gain factors due to changes of aperture

and field of view were derived from recorded deflections during laboratory

tests and on twilight records. The factors depend slightly on wavelength.

3.2 Temoerature dependence of photometer sensitivity

The twilight measurements were made in the open air and the instrument

temperature varied over a wide range. The temperature dependence of the

sensitivity of the photometer in the different filter ranges was determined

three times on cold days using the standards LI (radium luminescent paint)

-5-

and LII (tungsten lamp) as light sources. Deflections were recorded with the

cold instrument, then at room temperature, after heating the instrument in a

large box, and then again at room temperature. LII and its controls were

always at room temperature, while the built-in LI was at instrument tempera-

ture.

Temperature (T) can influence both the emission of the luminescent paint,

IL(T), and the sensitivity of the photomultiplier, Since twiltght measurements

are compared directly with paint intensity in green light only the former

affects the absolute intensity measurements in green light. If we define

a temperature coefficient (at ) by

IL(T) - IL(T o ) (I + a(T - To))

its best value was found to be % " - 1.5 x 10- 3 o°-i,

Since standardization is only made in green light the differential

response to temperature of the photomultiplier for different wavelengths

bad to be found from the comparisons with LII. If CR(T) is a color ratio

measured with the instrument at temperature T, and if

CR(T) - CR(T ) (1 + ctca(T - To))

we found the best values given in Table 1.

All observations were corrected to standard conditions, although even

for changes as large as 300C the corrections are small.

TABLE I

Temperatule coefficients of measured color ratios

Color ratio RIG 0/G G/B B/U

ORx 10 340.3 +1.0 -3.0 +4.5

-6-

3.3 Absolute calibration of the ohotoeter

3.3.1 General considerations

The problem involved in making an absolute calibration can be stated

briefly as follows. Measurements at a normal twilight embrace a brightness

range of about 105 5 , a constant recorder deflection being maintained by

changing electronic gain settings and optical apertures. The latter are

calibrated against the former by means of accurate deflection measurements

with alternate aperture and gain changes, and are therefore as accurate as

the electrical calibration of the gain switch (see Rep, I for discussion).

A theoreticil discussion of the twilight data requires that they be expressed

in terms of the solar flux F QWI where , is the mean solar brightness,

about 5.5 orders of magnitude greater than the brightness of the daytime

sky, and u is the (variable) solid angle subtended by the sun.

To calibrate our instruments directly against the sun in its low-intensity

ranges requires measuring a brightness ratio of 10 , This problem is in the

same class as the measurement of the sun's stellar magnitude, an astrometric

problem of the greatest difficulty. To avoid direct involvement in such dif-

ficult problems the calibration can be performed in two parts:

(i) Comparison of solar intensity using lowest optical and electrical

gain settin-s with standard LI. This will vary from time to time as LI var-

ies and must be periodically repeated.

(ii) Comparison of lowest and highest optical and electrical gain set-

tings. This may be presumed not to vary with time and can be determined

once and for all.

-7-

In Rep. I we discussed two methods of performing (i). First we con-

structed a calibrated neutral density filter with a transmission of 8 x 10- 6

in green light. The difficulties in using such a filter are however legion,

and the attempt was soon abandoned. Secondly, we proposed to make direct

comparisons with the moon, which has a brightness about 10- 5 . 7 I.,and is

therefore suitable for spanning the gap between sun and early twilight.

However, the soon's albedo is variable, phase sensitive and poorly determined,

and further thought showed that it was better to use an artificial diffusing

surface of known optical characteristics. A Lambert's law diffusor has a

brightness I O cos i/x where i is the angle of incidence. Since U's=

6.75 x 10" radiang , the loss function is close to 10 5, and suitable for

direct comparison of sun and early twilight sky. This gives a comparison

of LI to F* - Isn, suitable for low gain settings. It is referred to as

the sun calibration and is discussed in §3.3.2.

(ii) can be accomplished by having faith in the linearity of the gain

switch. Let us consider two instrument conditions, suitable for early and

late twilight respectively:

Condition I a Gain setting 1; objective aperture 2 mm.

Condition II a Gain setting 7(-64x); full objective aperture.

If the instrument inspects a sourse of brightness I, with angular field of

view w , the deflection recorded will be

For sun, moon and stars, recorded with aperture greater than that of thosource, w is the angular size of the source. For diffuse sources w refersto the stop in the focal plane.

-8-

D mg (1)

where g is a gain factor, including both optical and electrical effects.

Our problem is to discover the ratio g1I/g.. Calibrating optical against

electrical settings and assuming the latter to be linear, we find

R - 8, w 5.4 x 10- 6 .

Two methods have been devised to verify this figure. Measurements

have been made on the total flux of fixed stars (§3.3.3, star calibrations).

Knowing the stellar magnitude of the sun this leads to a ratio Rs.

The second method involves direct measurements on the moon and on a

diffusor platemsimilar to that used for the sun measurements, when illum-

inated by moonlight. This gives a gain ratio close to R, and comparison

yields a third independent factor RM (§3.3.4).

3.3.2 Sun calibration

With the instrument in electrical and optical condition I, and field

stop D (see Rep. I, table 1), a magnesium oxide diffusor is placed st 450

to the optical axis of the photometer. The instrument is then pointed at

right angles to the sun so that the angle of incidence is also 450 (cos i -

1//2 ). Let f be the departure from Laibert's law (including absorption

effects), and let D0 be the recorded deflection. From equ. (1)

D 8L% f ?. *(2)

Since the amplifier gain varies we refer simultaneously to the paint

deflection (Db using condition I and field stop A. These conditions are

-9-

always reproduced and hence we may write

DL = K gII L , (3)

and include in the constant K corrections for the fact that the light stan-

dard is inside the instrument and not in the sky. We do not need to know

the magnitude of K. From (2) and (3)

- f (4)D L V, L 7r V

The diffusor consists of magnesium oxide smoke deposited on an alumi-

num plate. A diaphragm in front of the diffusor limits the amount of sky-

light reaching it to about 1% of noontime solar radiation. The smoke is

prepared shcrtly before each measurement as recommended by de Vaucouleurs

(1951). Five layers of smoke from magnesium ribbon strips about 10 cm long

should eliminate the optical properties of the substra*e. The values of f

(the deviations from the cosine law) were measured by de Vaucouleurs for

the conditions used here. They are 0.945 and 0.918 at 400 Wq and 600 Wi

respectively for freshly-prepared diffusors. After 5 mcnchs, f is 0.86

and 0.895 for the same wavelengths.

F varies with the air mass (sec z, z - zenith angle) and olar distance

(r) according to

F -T sec z r 2F F 0 e (), (5)

rwhere T is the optical depth of the atmosphere, and F the solar constant.

If we write

-10-

D De esec z (0 r (6)

equ. (4) becomesD aL f oO

- (7)

DL KIL x/i r

On some occasions T was determined with the aid of a small sun photometer

(Volz, 1959), while on others measurements were made over a range of zenith

angles and the intercept (sec z - o) of the curve of log D as a function of

sec z determined.

The only variable quantity on the R.R.S. of equ. (7) is I L , and the

ratio DL/D is therefore a direct measure of the variability of the phos-

phor. Fig. Ishows how the ratio has varied with time over two calendar

years.

From September, 1959, to November, 1960, the photometer w4 kept out-

side under a thin wooden shelter and was subjected to a wide range of tem-

peratures. A very slow, temperature-dependent diffusion of radon, trapped

in the binder glue of the paint could perhaps explain the seasonal varia-

tion of the brightness of the phosphor.

A few values of D for all filters are presented in Fig. 2, after

applying a correction for variable f of the diffueor plates, in the form of

solar color ratios. These data, taken together with a few laboratory meas-

urements of color ratios for LII, indicate no change with time of transmis-

sion of the filters or of spectral sensitivity of the photoiultiplier. In

the data presented in the body of the report, color ratios of skylight are

presented in units of these solar color ratios.

4P

ooP4 11- *i z I

I I0 021 0

"4 1 I00

Id I Io 'aON.

-11-

3.3.3 Star calibrations

With the instrument set in condition II, a star of zero magnitude at

516 qA is allowed to drift across the field of view and the deflection Do*

at zero air mass is deduced. This reading is obtained by making measure-

ments on a number of bright stars at different zenith angles. Johnson (1957)

gives visual and blue magnitudes (see Allen, 1955, for details of equivalent

vavolengths) for the fifty brightest stare referred to AOv stars as a base.

With these data, all star recordings can be reduced to zero magnitude AOv

at 516 mp, and the extrapolation to zero air mass is accomplished by plot-

ting the results as a function of this parameter.

From equs. (1) and (3), we have

D*

D3F (8)DL 81 KIL

and from equ. (7)*

D0F

D s F %f (9)o 0

From a number of different observations, we find an average value

D-9.. 0.19 ± 0.01.Da

0

The quantity

m(516) - - 2.5 lo10 Fo a/Fo (10)

-12-

is the stellar magnitude of the sun at 516 W. According to do Vaucouleurs

the sun is a G2v star, with visual magnitude -26.73, corresponding to a mag-

* 10nitude of -26.62 at 516 W or F 0/Fo 0 4.47 x 10 . There is some doubt as

to the visual magnitude of the sun, and the absolute scale of stellar photom-

etry. The figures given here differ, for instance, from those of Allen

(1955). There are also uncertainties attached to interpolating to X

516 q.

The value of ab to be inserted in equ. (9) was found to differ

from values given in Repo I, Table 1, which were obtained by geometric

reduction of measurements on the angular size of field stop A. New direct

measurements have been made on the field stop D using drift curves of the

planet Jupiter and the displacement of a distant light source. The effect-

i,. angular diameter was found to be 0.670 , Inserting these figures in

equ. (9), w find

R 5.3 x 10" 6

3.3.4 Noo= measurement

The procedure here was to measure the recorder deflection under condi-

tion I using a field stop larger then tho angular size of the moon:

DX - gz 1M

Almost simultaneously a measurement was made in condition I, with field

Private coomunication, This figure is supposed to be the best value to usein conjunction with Johnson's stellar magnitudes.

-13-

stop D, using a large diffusing plate employed in a manner analogous to that

of the sun calibrations. The surface brightness of the plate is

14 H-I f

and the deflection is

D M(diff) g2%

We have therefore

- ~ N fD _ fg11 DM (dtiff) /2

Measurements of DM/DM(diff) were complicated by the interference of

diffuse sky-light, which was eliminated by making additional measurements

with the moon artificially eclipsed. There resulted

DM

D (diff) . 0.241

and hence

M - 5.55 x 10 "6 .

4. Turbidity measurements

Primary scattering in the twilight occurs principally at high levels,

and is modified on the downward path to the instrument by the variable haze

extinction in the lower atmosphere. All observations given in this report

have been multiplied by a factor

-14-

S/sin e (11)

where T X is the optical depth of atmospheric haze separated from that of

the molecules, and C - 200 is the angle of elevation of the photometer axis.

The turbidity coefficient

X - 0.434 T, (12)

was usually measured before sunset or after sunrise at 440 and 640 UV with

a small auydliary photometer (Volz, 1959). Measurements close to the twi-

light were sometimes impossible;on these occasions the uncertainty in B may

be as high as 0.01. Its value at 500 W is given in the data sheets while

for other wavelengths it is sufficient to use the relation

B X -1.5 (13)

It is emphasized that all data have been multiplied by T 1 , but the

correction can be removed, if desired, with the aid of the turbidity coef-

ficients given in the data sheets.

5. Evaluation of twiliaht records

As in Rep. I, the results are presented in term of the derivative of

log intensity with respect to sun depression and color ratios. In addition,

the green intensity is compared with that of a representative twilight (TW 7),

whose absolute intensity is given in Table 3.

A preliminary evaluation disregarded the gain factor and worked on a

time scale rather than a scale of sun depression. Color ratios (CR) were

-15-

computed each minute, and also the 'slope' or ratio of deflections for each

filter at beginning and end of each minute (the logarithm of the 'slope' is

proportional to d log I/dt). These slopes are very sensitive to the care

with which the analysis is undertaken, and frequent checks had to be made*

All unusual or interesting features were checked personally by the author,

although short-lived deviations, which were clearly not associated with

large-scale atmospheric phenomena were sometimes not explored in detail.

The factor dt/d6 is required to convert from the 'slope' to the data

given here. The factor for 420131N is givcn in fig. 3. The abcissa was

then altered to be linear in 6.

Color ratios were corrected for instrument temperature (Table 1) and

for tropospheric turbidity. From equs. (11), (12) and (13), we have

T '(X 1) B(XI) - B(. 2 )log T.1(X2) sin C

T X

L500 - 500 J sinC

- k B (14)sin e

Table 2 shows the values of k used in the reduction. If the exponent

TABLE 2

Turbidity correction factor, k.

RIG O/o GIB B/U

40.285 40.20 40.30 40.25

0.0 42* 13' N

.0

WCL NAIN F SU ME

00

0'0

Thenser ilutrs ho dt alon the ctve24 ne'ln

ar.3.e rojctedont the mindear1 as &unin oresentnd thecdat

-16-

in equ. (13) were increased or decreased by 0.5, for typical turbidity con-

ditions, log CR would change by jO.03 - a relatively small uncertainty. No

attempt has been made to allow for changing values of the exponent.

The rapid decrease of the sky brightness during twilight makes it incon-

venient to give absolute intensities of all or even one color for a whole

twilight. More instructive, enabling quick comparison between different twi-

lights, is a graphical representation of deviations of the intensity of twi-

light from a standard twilight. These relative intensities were computed

for each twilight in green light only; the intensities for other colors can

be calculated from the color ratios, if required.

Deviations from the standard twilight were corrected for solar distance,

sensitivity of the amplifier and the tropospheric haze. As a standerd we

chose one of a series of closely similar twilights in Fall, 1959, apparently

undisturbed by cloud effects. Intensities for this twilight, based on the

reduction factor Re, are given in Table 3.

6. Wegther maps and cloud cross-sections

During twilight the troposphere is opaque to sunlight with wavelength

less than about 500 aq. For longer wavelengths however, the troposphere is

translucent and haze, clouds or mountains located at a distance from the

observer in the direction of the sun will intercept the solar rays and

increase the height of the earth's shadow. Isolated clouds cause the 'cre-

puscular rays' which are often observed during the twilight. In order to

obtain a rough impression of the cloud-cross section along the path of the

Intensities for the standard tvilight (TW 7)

- 516 muj, c - 200

60 (o911/f) + 8 60 (logIoI/F) + 8 60 (108101/F) + 8

2.5 5.502-4 6.619 3 5.329 10 1.953

3.5 5.120-3 6.531 4 4.882 11 1.511

4,5 4.63-2 6.423 5 4.383 12 1.134

5.5 4.144-1 6.288 6 3.907 13 0.809

0 6.117 7 3.434 14 0.543

1 5.918 8 2.956 15 0.324

2 5.654 9 2.451 16 0.248

Note: TV 7 in fact was only measured to 110 sun depression; the extension

to 160 is based on 3 and 4.

-17-

setting sun, appropriate sections of weather maps were prepared *

In fig. 4 are plotted positions of the setting sun and directions of

the sunlight for three deelinations (D). For convenience the location of

stations in the weather maps presented here has been given with respect to

a straight**" sunset line (see insert in fig. 4). Data for the maps were

taken mainly from working weather maps of the Department of Meteorology at

MIT for 0 and 12 h GMT (19 and 07 b EST), or if these were not available

from Weather Bureau Daily Weather Maps. From these data, tentative cloud

cross-sections along the sunset line were constructed. Because the angle

between the sunset line and the direction of sunlight is large for sun

depressions > 100, cloud cross-secticn should have been constructed along

the instantaneous path of sunlight. However, the spersity and the low

information content of veather reports did not allow for such details, or

for consideration of the movements of cloud systems between the time of the

map and the twilight observation.

The weather maps were prepared and analyzed by J. Wagner of MIT.

7. aynral comrts on data r.resented on twilipht %rthsan.dAta sheets

7.1 Logarithmic gradient

The sun depression scale has been calculated for sea level, without

considering atmospheric refraction.

The scale of d log I/d6 is given only for Red, but can be transposed

for use with other colors. This scale is slightly non-linear (it is linear

DDirect observation of low-elevation clouds are recorded on the data sheets.

-18-

in the 'slope', see §5), Crosses or heavy dots denote carefully checked

values. The line is drawn freehand.

The 6-scale on the graphs of every tenth twilight (TW 1, 11, 21, etc.,)

has been supplemented by values of median scattering height (H m) in Red and

Blue as derived from calculations of twilight models in Rep. I. Features

on the gradient curves for different colors of undistu-:bed twilights some-

times occur at equal H ,

7.2 ColrL-ati

Ordinates are decadic logarithms of color ratios in units of color

ratios for the extraterrestrial sun. The curves are usually not labeled and

confusion can occur sometimes with RIG and C/G. This can always be resolved

because for 8 2 5° , the R/G curve is invariably above the 0/3 curve. The

amount by which the observed values of log R/G were lowered to allow for

tropospheric haze attenuction is indicated by a mark (T) at the bottom

scale at 6 - 0.

Visual observations of purple light intensity and crepuscular rays are

noted near the top of the CR curve. Unaided eye observations of the purple

lieht are very difficult, and were made with brownish sun glasses, looking

into a convex spherical mirror in orler to increase both the saturation of

red colors and the field of view. The purple light scale (PL) is from 0 to

5. Peak intensities are usually from 3 to 50 sun depression. Reported

intensities refer to elevation 20 to 300; purple lights at lower elevation

usually have a longer duration.

The twilight arch is often interrupted by darker, bluish beams, diverg-

ing from the location of the sun (crepuscular rays). The brigheness and color

-19-

contrast to the (apparently) unshadowed twilight arch is usually very small.

Up to about 60 sun depression, shadow often extend to the anti-twilight,

but may be too weak to be seen near the zenith. Just before complete dis-

appearance, at about 80 sun depression, the shadows usually extend to no more

than 100 elevation. Only shadow beam passing through the field of view of

the photometer are of direct interest for the discussion of our measurements

and, in TW 72, alternate measurements were made in the dark and bright seg-

ments. The half circles above the color ratio curves denote the twilight

arch: crepuscular shadow are marked by black; an open half circle by itself

at 6 - 70 indicates that no trace of shadows could be seen throughout the

twi light.

Occasionally aurorae were noticed in the late twilight, and sometimes

rocket trails were observed. The occurrence of these phenomena is also

noted on the color ratio curves.

In addition to interference by the airglow and Boston city lights, many

of our measurements in the late twilight are affected by scattered soon

light. Letters under the number of the twilight on the color ratio curves

indicate tho state of the moon according to the sobema in Table 4

(appropriate to the evening twilight).

Because of a counterplay of Moon brightness s d scattering phase func-

tion of air and haze, the influence of the moon on late twilight intensity

can be of the same order for cases NQ to WF. For X4T the influence may be

neglected,

Moonlieht intensity code

Time sequence of evening twilight,

Code Position of Noon Noon phase

Moon rise 1 hr* after start of

astronomical twilight

MO No Moon to

2 days after New Noon

NQ In twilight arch to

6 days after Nev Noon

E In southern sky to

4 days before Full Noon

W Full Noon rising on eastern tohorizon 1 to 2 days after Full Noon

(Noon rise at start of astro-

nomical twilight)

Hr Shortly after Full Noon; ie., tolate twilight measureuent takenshortly before Noon rise

Noon risc 1 hr. after start of

astronomical twilight.

-20-

7.3 Relativ aereen intenuitv

Here the logarithm of Green intensity of the twilight, referred to a

standard twilight, are given. Standard values (TW 7) were presented in

Table 3.

7.4 Weathor may and cloud cross-section

The sunset (or sunrise) section of weather maps is shomn. The sunset

line, which is curved on ordinary maps, has been rectified. The North direc-

tion for Boston is marked by an arrow. Under the weather map is drawn the

cloud cross-section, showing the vertical distribution and amount of cloud

along the sunset line, as estimated from the weather map.

7.5 Twilight data sheets

Daytiue sky: Visual observations of color and brightness of circum-

solar sky light, characterizing the aerorol size distribution (Volz, 1961).

0 0Turbidity types refer to the sky from about 50 to 3 distance from the sun;

Aureole twe1L to scattering near the sun. Turbidity type 1 is characterized

by a steady increase of sky brightness and a decrease of bluLshness from

about 500 to about 20 from the sun. With types2 and 3, the sun is surrounded

by a bright disc of about 200 radius of nearly constant brightness. The

disc of type 2 is uniformly whitish, while the outer border of the disc of

type 3 is brownish and the inner part bluish.

The description of the Aureole types a, b and c is virtually the same as

for Turbidity types 1, 2 and 3 if angles are reduced by a factor 10 to 20.

The Aureole intensity scale is from 0 (no Aureole) to 3 (inner part of Aureole

somewhat glaring with 8% transmitting sun sheas). Mhs aala Gan be exta-

polated with the aid of sun glass transmitting 0.6%,

-21-

Relations between Turbidity type and twilight are only expected if a fin-

ite fraction of atmospheric aerosol i located above the tropopause.

Turbid:tv coefficient: Decadic attenuation coefficient of haze alone, at

500 mI, per unit air mass.

Vii ,iU.: Based on observations of distant mountains shortly before sunset.

Sunset or Sunris: Calculated in Eastern Standard Time, for longitude and

latitude of Blue Hill Observatory, for center of sun. No account is taken

of the altitude of the site or atmospheric refraction.

Horzgn: Haze and cloud observations. Observations of near-horizon haze

structure and of clouds during twilight in azimuth of measurements.

-22-

8. Rfeec.

Allen, C.W. 1955 'Astrophysical quantities'. Univ. of London Press.

Johnson, R.I. 1957 'The fifty brightest stars'. Sky and Telescope 1A, p. 470.

deVaucouleurs, 0. 1951 'Constantes do Is diffusion Rayleigh daub lea get

et lee liquid..'. Am. de Phys. 12. Ser. ft. pp. 213 - 324.

Volt, F., and Goody, R.N. 1960 'Twilight intensity at 20 0 elevation'.

AFCRC-Tlq-60-284.

Volt, F. 1959 'Photometer sit Selen Photoelement zur spektralen Hessung der

Sonnenstrahlung und zur Destimung der Wellenl" egnabh&lngigkeit der Dunst-

trubuns'. Arch. Meteor. Geophys. Bioklim.. S 3Q pp. 100 -131.

-1961 'Scattering function and polarization of skylight in the ultra-

violet to the near infrared region, with haze of scattering type 2'.

Journ., Meteor. 11, pp. 306 - 316.

a23a

9. Results of obegrations

Tvilights 1 to 103 with omission of TW 23, 28, 29, 55, 67, 81, 87, 92, 95,

96.

SUN DEPRESSION 8-30 .2 -0 Ol 1- 2- 3- 4- 5 6 7 8- 9* 100 V 12* 131 14* 15'

COORAT O TW I-og~C Pt: O S.M

006

0 0- .. .. . .

0002

0 to 0 oC0 10 KMRE

0I,

-01 1

0-. r .6'A I U

0% -04

TWILIGHT 1

September 12, 1959, Horning

Daytime sky: Turbidity type: 1.3Aureole type: al.

Turbidity coefficient: 0.02

Visibility: 100 km

Sunrise: 05 25 EST

Declination: 44,30

Instrument temperature: +100

Horizon: Distant, low Sc over sea.

Color ratio graph: Points of log CR at 6 - -80; for

B/G replace G/B, and add R/G to

the circle near log G/l 0.

SUN DEPRESSION 8-3 - 1 * 3 4 6* 7- 8- 9- 10- 11- 12- 131 14* 15

.4

.2

0-

Go0

SUN DEPRESSION a-3- -2 -1- 0' 1- 2- 3 4' 5 6- 7 8- 9- 10 11 12' 13' iv 15

COLOR RATIO P 2TW 2tog. CR M H

04.~.............................

02

02-

-01

lot~ ** TW I E

T I

0 0

TWILIGHT 2

September 12, 1959, Evening

Daytime sky: Turbidity type: 1,7Aureole type: ab2,


Visibility: 120 km,

Sunset: 17 57

Declination: 44.2

Instrument temperature: 200C

Horizon: In West below 10 elevation

hazy

SUN DEPRESSION 8-3. -2 * O' 2* 3' 4' 50 6* 7 8 90 10* 11' 12 13* 14 15

GRADIENT kT W 3

-dlog 1/0S/

.4O -, .

0 -

so-.

UvO

SUN DEPRESSION

-3* -21 -1* 0, 1* 2* 3 4* 5* V 7' 6 9* 10' It' 12- 13- 14- 15-

COLOR RATIO rw 3It", CR PIL 2 #40

0-

0-Q~ ....

.4

0-

02

01

02 It Tr I I I I I

toeg

00-

00.

-QINiIN

1)#

10 .0

-- I , ,- Kin

TWILIGHT 3

September 13, 1959, Morning

Daytiime sky: Turbidity type: 1.7Aureole type: ab2


Visibility: 65 kmu

Sunrise: 05 26.5

Declination: +3,85 0

Instrument temperature: +11 0

Horizon: Single faint haze strips up to

5 0 elevation before sunrise.

SUN DEPRESSION 9

-30 -2- -1- 0 . 2- 3- 4 5- 6 7- 8' 9 10 11- 12- 13' 14' 15-

COLO RATOg I T/d4

REDO

ORg CR

0-

0S

0/ tog. CR

4 *,~4

02-.5 goA~tIIRMtog KW

o 01- -- ,

TWILIGHT 4


Daytime sky: Turbidity type: 1.7

Aureole type: ab2

Turbidity coefficient: 0.02+

Visibility: 100 km

Sunrise: 05 27

Decliration: +3.6


Horizon: Hazy below 20 elevation.

Weather: D:ring twilight Ac in NU

appearing, covering oun soon

after sunrise.

SUN DEPRESSION 8-3- -2- -1- 0 1- 2- 3- 4- 5 6 7- 8 9- 10- 11' 12 13' 14' 15o

GRADIENT W

-diog 1/di.4

.2

REDO

0-

0-

U V0

SUN DEPRESSION 3-3* -2o -1* 0, 1* 2o W 4 5o 6* 7* * 9 10* no 12* 13o W 15*

COLOR RATIO TW 5tog. CR PL' <? MO

0-

0-

04

0-

2

04- KAP mg.air~

0.2

I.* lo- lo-wS

bOYM

0 - 0

TWILIGHT 5


Daytime sky: Turbidity type: 1.9 As foregoing

Aureole type: day and at

Turbidity coefficient: > 0.085 noon

Visibility: f 30 km

Sunrise: 06 42

Declination: -1,70

Instrument temperature: 100

Horizon: Before PL dense Ci fll. appear-

ing, record discontinued.

SUN DEPRESSION 8

-3- -2- -1- 0. 1. 2- 3 4 5' 6* 70 80 9- 100 He 12- 13- 4W 15T I

GRADIENT TW 6

-diog lIMS

0

OR 0

G0 -

80

uv

SUN DEPRESSION 8

-3- 2- -1- O* 1. 2 3- 4 5- 6 7- 0' 9- 10- 11- 12- 13' 14' I5

COLOR RATIO TW 6

tog. CR PL: M H~~ I

0-

4

2. .............. ........

0 j

02- RELATIVE BR*MTPiESSI

0.I-

-0.1

0. is-'6

F0 I

oil 11#61

lot@ NaoDATE OF MAP: 010'" ES

20006., 1151n 00 0

0 '0

TWILIGHT 6

October 12, 1959, Evening


Aureole type: ab4


Sunset: 17 04

Declination: -7,2o

Instrument temperature: 10 0

Horizon: Scattered Ac below 20

Haze lenses < 80

SUN DEPRESSION S-3 -2. -1. Do 1- 2 31 4 5- 6 7- 9- 10 0- 12 13# 14- 15

GOORATION TW 7

Ldog CR M

RE0

0

S1 -T -1 T I I I I-

COLO RATIONC TWIUG

00_

NI22

U00

00 10 50 20K

0. 1

14,11 Jo-"O W

NILIGHT 7

October 13, 1959, morning

Daytime sky: Turbidity type: 1.7Aureole type: aO

Turbidity coefficient: 0,02

Visibility: 100 km

Surise: 05 59

Declination: .7,4

Instrumngt temperature: 8 0

Horizon: ScC Joe 10 Shortly before SR

f."&. haze strip, below 60.

SUN DEPRESSION 8

- -2 -1. 0' 1 2" 3 4'6 7* 8°

90 10* 11* 2I 13" 14" 15'

GRADIENT TW8

-diog I/db.4

RE00

OR _

-0-

0-

Uv

SUN DEPRESSION I-3* -2' -1* 0' 1 2 3 4' 5* 6* 7* e* 91 I0* V 12. 13' 14- 15#

COLOR RATIO TW 8

O oqCR PL: I MF

0-

R,,t

04

.................

0. ..... .--. ... .

02

0 2 - 9"A' - " ' "

G-

":::Top:: ..-

• . o.

p2I .

I, - ,I

0 10

KM ,ee el KM i I|

0 - l , O "0

MrILIGUT 8

October 16, 1959, Morning

Daytime sky; Turbidity type: 1.6

Aureole type: al

Turbidity coefficient: - 0.05

Visibility: 30 lan

Sunrise: 06 03

Declination: -8.60


Horizon: 05 40 Ac below 100 . Horizon very

haze below 50

05 20 Azimuth shift because of Ci

traces.

SUN DEPRESSION 3

-31 -2 f 0- P 2- 3- 4 * 6- 7- 8- 9 10- 11- 12- 13- 14 15

.67 GRAIEN I TT W 9

.4

REDO

0-

0

SUN DEPRESSIPOW 3-3- -2 - 0' r 2 31 4 5* 6 7* S 91 100 11* 12, 13 14* 15'

If I I I I I I I

COLOR RATIO TW9tooCIR Pt.. 2- MF

0-

0*0

*4

0-

02 2

701

Qo-

cri

tm W6TE

~ ,,'- -Is

TWILIGHT 9



Aureole tyep: al


Visibility: 40 km

Sunset: 16 58

Declination: -8.6°

Ins tru ent temperature: 120

Horizon: Shortly after sunset, fine haze

veils up to 200.

SUN DEPRr.SSION 3-3 -2- -1- 1- 2- 3- 4 6* 7 8' 9 10' lie 12' 13* 140 15

.6

.4

REDO

OR 0

G0

SUN OEPRESSIOd 8-3- -2o -1- 0 11 2o 3 4P 5 6* 71 8 V 10* 11 12' 13* 14 15

COLOR RATIO TW 10tog6 CR PL: 2.. 0 Cl M T

0-

...................... *

0-

-02

0.I

0.1-i

0...

,b a 9f j

I 16 40 W OF m:W:"ima

00Am,-~ " - - n0 -

TWILIGHT 10



Aureole type: a6

Turbidity coefficient: 0.07 5

Visibility: 30 ka

Sunset: 16 52

Declination: -10 0


Horizon: Hate below 30

Distant St clouds from 11W to NE.

Remarks: Details of gradient In B and UiV

partly obscured by undulatory

zero drifts of recorder due to

chopper trouble.

SUN DEPRESSION a-30 -20 -1 of 1. 29 Y 40 6 71 8 r 10* 110 10 130 140 15'

0-

0

GO

20 40 so s0 100 ~ I30 s 40 60 s 100 .20 IN. BOLUE

SUN DEPRESSINOd--2 -1* 0" 1 2 Y 4* V 61 7* S 9 101 11 1" &3 W4

COLOR RATIO TW It

toU CR PL: 0,5 mm

0- 0

0- ........

.....................4

0-

02-2

I r,

00-

-01

am * 4 a P* iof m

/0 971 0

0. go050 000~

TWILIGHT 11

October 21, 1959, Morning

Daytiime sky: Turbidity type: 1.4

Aureole type: al


Visibility: 100 km

Sunrise: 06 08

Declination: -10,6 0

Ins trument temperature: +2 0

Hiorizon: At 8 - 6 0 Sc traces in field

of viev, at 2 0 thin Ci; azimuth

changed.

SUN DEPRESSION II-3* -2' -1' 0* 1 2* 3 4 * 6* 7' 8- 9- 10 11- 12o 13- 14o 15-

GRADIENT W1

4

.2

RED 0

OR0

60o

Uvj

-30 -2 -10 , 1' 2' W 4- 50 go ' 6 9- W Ito V2 &S W4 150

COLOR RATIO TW Itto@. CR PLO0.51 I zm

0-

.................

-02 ~~..... ..

02 E.TV

w/tv 1201I

00-

4u3 i W INS OM O MAP:

0[ 0

TWILIGHT 12


Daytim sky: Turbidity type: 1.5

Aureole type: a2


Visibility: < 80 km

Sunset: 16 51

Declination: -10.7


Hlorizon: Boston hate in West below 20

SUN DEPRESSION 8-3 -2. -1. 0' 1- 2 3- 4- 6 7* 8* 9* 0* 11' I?* 13* 4' 15

.4

0

Uv

SUN DEPRESSION 8-3* -2* -1* 0 1* 20 W 4* 5 6 7 a, 91 IO* W1 12* 13* 14* 15'

COLOR RATIO TW 13

tog. CR P1: 05 2 (I) MODcra

6 .*. 0HIGH ALTITUDE

-04~~ ... ...... . . . . . . . . . . . . .

................ ...........

0

Go -

-0.1-

rn5-

0 01

TWILIOHT 13

October 28, 1959, batsing


Aureole type: a2


Visibility: 115 km

Sunset: 16 40

Declination: -12*90


Horizon: Shortly after sunset; fine haze

up to 100; few Cu clouds below

10 in NW.

Before the end of twilight: Sc

banks below 20 in West$

Balloon: Large High Altitude Balloon

observed from 12 to 130 sun

depression; brightness rapidly

decreasing. Elevation about 70,

azimuth ca 2350.

SUN DEPRESSION a-3- -2 -1- 0* 1* 2 3' 4' 5 6' 7' 8 9- 10 11- 120 13* 14 15'

GRADIENT T 1

-d log I /db

Ov 0

SUN DEPRESSION a-W .20 _I* 0* 1* 2* Y0 4* 5* V 70 81 9* 10* 1 12' 13 140 15'

COLORn RATIO TW 14I t~cRPLI I M

0-

0o .. ....... ...

04.....................

0. . . . . 4

............

010

00-

-01

0.,

102 = K M m Soo 0 50 I0j 5

1 1/,/,/Km

TWLIGRT 14

November 9, 1959, Evening


Aureole type: a3


Visibility: 70 km

Sunset: 16 25

Declination: -16.8


Horizon: Rather hazy below 10, fine

haze below 150

Gradient graph: Maximum of gradient in Red is

0.83 at 5.00 sun depression.

SUN DEPRESSION 8-3* -21 -1 0' 1- 2- 3- 4- V 7* 8 90 10* I* 12* 131 14* 15*

.6 1 1 11 1 1

.4

.2.

0-

6 o

SUN DEPRESSION II-3* -21 -to Op i 2* Y 0 5' V 71 S* V 10* It* t2 13* 14* 15

COLOR RATIO TW 15tog, CR M~ MH

Pl. I0 lb Ci

O *

000

0 *

02. MIAT. . . .O.00N

-0

**0iq

20010 1500 m 5w

10 10

0 0

TWILIGHT 15

November 10, 1959, Evening


Aureole type: a3


Visibility: 70 ka

Sunset: 16 24

Declination: -17.1 0

Instrument, tewerature: +1W C

SUN DEPRESSION a3-1 2- 3 4° 6 7 8 9 10 11- 12 ° 13 " 14 " 150

GRADIENT W1-diog I/d

.2°-

RED

O

OOR RAIOTW

0-U01

80

SUN DEPRESSION 3-3 -2 - . O* 1 21 Y 4* 5* 6* 7* 8* 9 100 11* 12- 13. 14o 15o

COLOR RATIO TW 16

9b t"CR Pt.: I2 Aft_ MF

04O-..

2-. ............. ."2 "

0 I)

01- "1

,... .*%4... ..

m.0.

2TO

O- an~~~~ as rI I

gm 40~ Ko1

" /, 1

QO0

TWILIGHT 16

November 12, 1959, Evenine

Daytime sky: Turbidity type:-Aureole type: a0O.5

Turbidity coefficient: 009 2

Visibility: 17 km

Sunset: 16 22


Instrument temperature: +86a

Horizon: At sunset haze layer up to

8 0, later blask haze border

up to 2 0

Weather: After 50 sun depression thin

Ci fields froma West

SUN DEPRESSION 3-3- -2- -1- 0 1. 2- 3- 4 5-/6 7- 8 9- 10 11' IP? 13' 14- 15.

GRADIENTTW 17

4

REDO

ORO

G0 -

a0

Uv

SUN DEPRESSION 8--2 -I* 0' I 21 Y 41 5* G* 7* 9 10* 1I* 12o I3 14' 15o

COLOR RATIO PL: 1 15 d= TW 17

U(qCR .

0C

0

04 ...

02

fog o wo17

0I-

00-

W' TW 17 M

M"- 1/m. /1 /l

0 50000 200K10 iCo

Kml01 I'M

TWILIGHT 17

November 26, 1959, Morning


Aureole type% al


Visibility: 57 km

Sunrise: 06 54

Declination: -20.8

Instrument temperature: +20 C

Horizont Shortly after sunrise vertical

light pillar up to 100 eleva-

tion.

Weather: At 50 sun depression small

Cu fra. passing. Shortly

after sunrise Ac9 in waves

Evening: PL 1.5 - 2, slightly shadowed.

Shortly after sunset Ci appear-

ing.

SUN DEPRESSION &-3. -2 '1* 0' 1* 2 30 4* - 6 1 6* 9* 10* 110 I2* 13* 14* 15*

GRADIENT

-dlog 1id0

.2

RED0

ORO

G

0-

Uv

SUN DEPRESSION S-3. -2* -1* O* 1 2* 3* 4 5* 6i* 7* 8 9' 10' 11' 12* 13' 14* 15*ICOLOR RATIO mTW to

tog.~ CR PL! .5 1.5 2.24 2-.*". mo

.6

0-

-04 ~.... ........

.- ........

-Q2.. .. ......

0- o

Q-'

ZO~6.OF 1500 no0 15T

Km low/f lo o

TWILIGHT 18

Novcnber 30, 1959, Evening


Aureole type: aO.5


Visibility: 38 kmi

Suniset: 16 08,8


Ins trumlent temperature: 0 0C

Horizon: Haze up to 12 0 elevation.

In W..t St. layer from 1

to 2 0 elevation.

SUN DEPRESSION 3-3. -2. -1. 0- 1 2* Y 4 60 7- G 9* 111 12- 13- 14 IS"

COORATION TIN 19

OR 0 C 0L LL 2

0-

0

00/

0-

02-4

Go-G

O-3

-07*1

TW 11 Mh:

100

TWILIGHT 19

December 4, 1959, Morning


Aureole type: a3


Visibility: 16 km

Sunrise: 07 03

Declination: -22.40


Horieon: Sunrise in haze bands, which

contain Ac strips; haze up to

20 elevation. Haze top appar-

ently only : 200 m above obser-

ver.

Gradient graph: Maximum of gradient in Red is

0.93 at 4.50 sun depression.

SUN CEPRESSION 8-3- -2- -1- 0 IQ 2- 30 4 5- 6- 70 8' 90 3 11* 12 Y 130 40 15

T W 20

4 -d log I/d$ S

REDO ~~

ORA

0-

S UNDEPRESSION-3. -2. -i. 0 1- 2- 31 4' 5' 6* 10 8O It- 12' 13* 14 150

COLOR RATIO TW 20tog,,CR PL 1 5 0 MO

0-.... . ....

04

02

00

02. RELATIVE BRIOMTPES4

00-

-01I

01 * 10 1. 0

0m ,t tf0 0 l j 0 & 61 0 0 0 0 0 Km

10 1 ~0

TWILIGHT 20


Daytime sky: Turbidity type: 1.3+

Aureole type: aO


Visibility: 30 km

Sunrise: 07 08

Declination: -22.90

Instrument temperature: -5

Horizon: Sharp haze border at 20 elevation,

Observatory just below haze top.

SUN DEPRESSION a3*-2 -1* 0' 1* 2* 31 4* 5 6' 70 8 9 10' Il 12- 13* 141 150

GRADIENT TW2

-d log I/db

0-

H. 20 40 60 80 100 gW . REDUv ____________I__

SUN DEPRESSION 8-3* -2* _I* 0' 1 2* 3 4* 5* 6* 7' * 6 10* II* 12* 3* 14' I5*

COLOR RATIO P L 3 2. T TW 21

0-N

0-

0-

44

0-

NtJ.ATVE SOJK40NES1

22

I;' a In* T a I~ON 4~~t

TWILIGHT 21

December 9, 1959, Evening

Daytime sky: Turbidity type: 1.7 atnoAureole type: a2-3f atno

Turbidity coefficient: 0,03 7Visibility: 65 km

Sunset: 16 07.2

Declination: -2299 0


Horizon: Daes haze up to 2.5 0

SUN DEPRESSION S

-3* -2* -1 0' 1' 2* 3 " 4* 51 6' 7# 8* 9 " 10 O 1I1 12* 13* 14 " 15*

ORO

0

Uv o

SUN DEPRESSION a-3. .2

° -1. 0. 1* 2* 3 4 e 5 7 9 10' 11* 12' 13* 14 ° I5

COLOR RATIO TW22

PL: 0 2 1.5 = No

0 6

0 . - . . ... .....0-

-022

....... ° ... * ',

0

02" IIMLATrN DRW.ws

0-

-0I

fw 22

0100 9£5-AT OF i ° I0" It ~

10 ,1 0 "-" , o

TWILICIT 22


Daytime sky: Turbidity type: 1.SAureole type: a3


Visibility: 70 km

Sunrise: 07 05

Declination: -22.9 °


Horizon: At horizon (S to NE) St and Ac

clouds up to 50 elevation.

At 70 sun depression yellowish

haze up to 60 elevation, appar-

ently in higher tropospheric

levels.

At sunrise, faint haze strips

up to 50 elevation.

Remarks: Tilight 23 only from 6 to 110

sun depression measured; data

not presented.

TWILIGIr 23


Observations started at 4.50 sun depression after disappearance of

Ci traces out of field of view. Data and graphs not presented but

quite similar to the ones of Twilight 22.

SUN DEPRESSION 8.30 -2* -1' 00 1- 2 3 4 5A 6- 7 B' 90 10 111 120 130 140 150

GRADIENTTW 24

SUN log 1/d Ill

OLO R RAIW2

0-0

4v 0

*0* 02 I * 1 1 Y 4 * V 7 0 9 1 00 S

t*C L 0 m4

0%-

0.-

0-

W11. A24

*0002

Kow -.. ,

,

100

TWILIGUT 24

December 14, 1959, MorninS


Aureole type: al

Turbidity coefficient: 0.01 6

Visibility: 80 km

Sunrise: 07 12


Ins trument tenperature: -4 0

Horizon: At about 4 0 sun depression

faint haze wves from 12 to

180 elevation. Some city

haze very low over sea.

SUN DEPRESSi0N a73 2' A1 * 1 2 3 4 6' 7* 8* 90 10- 11- 12' 13' 14' I5-

GRADIENT T2

-dlog 1/dIl

00

0 0

go-

SUN DEPRESSIONd 9- -2 -. 0 . 2* 3 4' 5' 6' 7* 91 10* i1 12- 13 14 15-

COLOR RATIO rW 25tog, CR PL: 2 055,M

0-

RO

04

.........

..... .. ... .. . ..... . . . . .. . .

I0r

-01

-S0.

r.. 5r Tw as

I / Tw15

/ ~ ~ M 49ST

Km4 1,0.Km Km

0

TWILIGHT 25



Aureole type: a2


Visibility: 100 km

Sunset: 16 07.5

Declination: -23.20


Horizon: Thin Ci in wst up to 5 eleva-

tion.

Anti-twiliaht: Earth shadov at sunset in 20

elevation, northern part 20

hiSher.

SUN DEPRESSION 8-3* -20 -1. 0* 1- 2 3' 4' 6* 7* 0 9 10* 11* 12 13' 14* 1

GRADIENT TW 26

-d log I /db

00

0

go-

SUN DEPRESSION 8-39 -2* -1 'O 1- 2* 3 4* 5* 61 71 8* 9* 10* 1I* 12* 13* 14* 15*

COLOR RATIO TW 26It". CR PL:' 0.21.523 CiMMO0

0-

-4 77.

...............

0-

026

001

-0I1

0.. 15 5I.

on Tw as E

WTE OF MP12AI/

2OI= K50 tO 010 10

KMI~ , / / ""

0o - 10

TWILIGHT 26



Aureole type: a2

Turbidity coefficient: 0.02_

Visibility: 115 km

Sunset: 16 09.2


Instrument temperature: -50

Horizon: UP to 100 elevation distant Ac

and St clouds,

Anti-twilight: Irregular shape of earth shadow

before sunset

-30 -2 -i. 0' 1' 2* 3' 4 5 61 7 8 9 to* 111 12* 13* 14* 15'

.6 T I

GRADIENT W2

-dlog I/d$

.2

OR0

0

G0 -

Uv

SUN DEPRESSION S-3* -2* -1* Ol L 3* 4' 5* 6* 7 8* 9* 1* II* 12* 13' 14* 15*

COLOR RATIO 441C TW 27

tg RPL: 23-4 ma

0-

.04

0 02

000

-

0.

w. a 0'

s BOSTON

Kmr OFU MA5:0**.55

TWILIGHT 27

January 1, 1960, Evening


Aureole type: --

Turbidity coefficient: .013

Visibility: 130 ka

Sunset: 16 16.5

Declination: -23°


Horizon: Strong haze strips up to 30

elevation.

Anti-twilight: Upper border of earth shadow

sharp from S to ME, but not in

N direction (compare purple

light observations).

TWILIGHT 28


Local Sc clouds interfering from 4 to 60 sun depression; measurements

not continued. At 4 sun depression PL 2,

TWILIGHT 29


Very hazy. At 30 sun depression, measurements discontinued because

of local Ac clouds. At 3.50 sun depression PL 1 - 2.

SUN DEPRESSION 8-3- -2- 00 O 1, 2' 3Y 4' 50 60 7 80 9* 00 11 I 12D 130 140 150

.6-

GRADIENT T3

A-diog I/d8

2-

REDO

0-

*0-

Uv

SUN DEPRESSION 8-3* -21 -11 OP 1* 2 Y 41 5 6* 7 8 90 10' 11' 12* 13* 14* 15*

COLOR RATIO TW 30

t"flCR PL 2 2 331-4 L"14-hMH

0-6

*t-..*. ....

0-............*

04

................. *.....

-02

..........

02- 15LA4V RW 30TES

001

-. o. 10 8 o.o

2WT 15' wAP 0/*~

2000o (in 150 E0 0

00O

10 1-0

TWILIGHT 30



Aureole type: a3


Visibility: 115 km

Sunset: 16 23


Instrument temperature: -10 0

Anti-twilir~ht: Earth shadow at 40sun

depression very irregular.

Weather map: Before midnight front system

moving rapidly from SW Into sun-

set line.

SUN DEPRESSION 83 -2- -1- 0. 1. 2 30 40 6* 7* 8* 9* 100 11' 12- 13* 141 5*

RED0

OR0-

S

076O1 20 40 60 9 mR

Uv

SUN DEPRESSION II~3 -2- -1- 0' 1* 2 Y 4- 5* 6- T 9 10* 1 IL 13 14- 15.

COLOR RATIO TW 31too. CR PL I 2L jliMF

0-

4

0-

.2 .......

941.. .. .........

02- LT ""3

al'

00-

-0.1

2000 Km 500 500 0

0 0

TWILIGHT 31

January 11, 1960, Evenins

Daytime sky: Turbidity type: 1.7Aureole type: a2

Turbidity coefficient: Z,0,0 2

Visibility: 130 km

Sunset: 16 25.5

Declination: -22.0

Instrument temperature: -6 0

Horixon: Haze border at 20 elevation

SUN DEPRESSION &-3. -2" -1. 0. 1. 2- 3" 4" 5!,--.6" 7 8" 9- iO 11- 2 13" 14" 15"

GRADIENT TW 32

-dlog I/d8.4

.2eR

0_

0

Uv

SUN DEPRESSION S-3* -2o -. 0 t' 2 3* 4o 50 7G T 9 10* 11* 12" 130 14, 15*

COLOR RATIO TW 32S tog CR P: T2. 4 421

O- o

O

4 .. . .

*.4

O" .. •*.° ~" °."........° .

2

lk .oo.32

-

FI-o- so on anupof _______

"So. I E O &

10 Ii i 1 I- Km "S !.I eol r 'r ,

TWILIGHT 32

January 12, 1960, Morning

Daytime sky: Turbidity type: 1.4_Aureole type: aO


Visibility: 130 km

Sunrise: 07 18

Declination: -21.90

Instrument temperature: -12 0 C

Horizon: Low Sc clouds over sea.

Anti-twilight: At 30 sun depression in S direc-

tion partly shadowed by Ci clouds

which are visible in SR.

-3" -2" -1. 0. 1. 2 3- 4" 5 6- 70 o•

90 11* 12" 13- 14- 1S•

I8 I I I I I i1 r

GRADIENT T3

-dlog I/db.4

.2

RED0-

OR 0

G0-

Uv

GO'-- -- '-- --

SUN DEPRESSION a-31 -2* -l* 0* I. 2. 3' 40 5 6' 7* a' 9 10' 1I1 12* 13

° 14* 15*

COLOR RATIO TW 33£",CR PL: 5.4 M MT

0 *' %* ROCKE T TRAIL

0-

0 6 *. ..... ........

04 0

4O . . .

2 ............. . . ...

-0

02- LATIVt IY 331" 11,

0I-

00-

I- ,

0. ..

02

15 0*

I2- S. ' t TW 33

St-0 - -

Il iTO

Oft DATE OF MAP:1 0/LiT

2000Km 1500 K)00 500 0IC to

Km --- , oo ,oo01 10-

TWILIGHT 33

January 16,1960, Evening

Daytime sky: Turbidity type: 1,8.

Aureole type: &2


Visibility: 80 km

Sunset: 16 31

Declination: -21.20

Instrument temperature: -5°

Horizon: Raze strips up to 200 elevation,

clarly visible up to 70 un

depression. At about 70 sun

depression, reddish haze strips

up to 30 elevation.

Rocket trail: Bright, distorted rocket trail in

left edge of twilight segment first

observed at 11.50 sun depression

(17 40 EST). Trail extending from

about 5 to 100 elevation, azimuth

2120 (sun at 2500). Color photograph

at 6 - 12.70 . Brightness of trail

quickly diminishing at 6 - 13°; trail

no more visible after 6 - 13.50.

SUN DIEPRESS ON a-3- -2' -i* O 1- 2- 3 43 5- 6- 70 8- 9 o* it iv 13 141 15*

GRADIENT W3

.4 -dilog I /d3

EDO

OR 0

G 0

uv

SUN DEPRESSION a-31 -20 -1 0' 1* 2* W 4 5* 6 7* 8' 9* 10* Vi 12' 13' 14* 15'

COLOR RATIO TW 34togCR PL: I Q5 Q2

0-

0-

04

.................

........... .........

000

0- 5 10. 15

Ift Tw 1 111

016~ DATE Or' MAP0

0 fi1

2000 KMI IUO S0Uoo 0

0[ 0

TWILIGHT 34



Turbidity coefficient: 0101i

Visibility: 135 km

Sunset: 16 34

Declination: -21lO


Horizon: In early twilight strong haze

strips up to 15 0 elevation.

Moderately deLse Ci below 2 0

elevation.

Moon: MO

SUN DEPRESSION 8-3- -2- -1- 0. 1. 2- 3- 4 4 7* 8* 91 10* 110 12* 131 14' 15*

I. I .. /V

GRADIENT TW 35

-dlog l/dil

.2

RED0

ORO

'iv

SUN DEPRESSION 8-3* -2 -1- O* 1* 2 3 4 5* 61 7* 9- 10* 11- 12- 13- 14- 15

COLOR~ RATIO ROCKET TDAIL TW 35tog,0CR

PL: 3 4

0

0- r02 .~ . . .

......... .........

02- RLAT'VtE DR"GTWWS

00-

-01.________~

0. 0.

~~~5 0*,, ,IC

0W 5 E

TWILIGHT 35




Visibility: 75 km

Sunset: 16 43.2

Declination: -19.00

Instrument temperature: 0°C

Horizon: Below 30 elevation a few thin Ci

clouds and haze. Very distant, ver-

tical rocket trail, extending to

about 10 elevation, in center of

twilight segment. Trail gives raise

to a sharp crepuscular ray at sun

depression 4.4 to 5.50 At begin-

ning, trail bright and orange, at

5,50 sun depression dark red, and

illumination cea ing.

SUN DEPRESSION 8-3# -2 -1- 0. 0. 2 3' 4 * 70 8* 9* 100 1 I?* 2 130 14* 15

.6-GRADIENT W3

-dlog l/dS

2-

RED0-

ORO0

a 0

Uv

SUN DEPRESSION S-3* -2 -1* 01 1- 2' 3 4 5- 6 * a- 91 10* 11- 12- 13 14' 15'

COLOR RATIO TW 36

togCR PL: 1#23 .4 2 nma

0-6

0-

-02 .......

02- ftLATrA1 SRIGHTE

01-

-0.1

-3.

20* 15. V* V. 8

L- TON

to M IVDATE OF MAp14

U

KM 0

TWILIGHT 36

February 3, 1960, Evening


Aureole type: a2


Visibility: 130 km

Sunset: 16 54

Declination: -16o8 °


Anti-twilight: Very bright and colorful

Remarks: Details of gradient in Blue and UV

from 3 to 60 sun depression

partly obscured by undulatory

zero drifts of recorder due to

chopper trouble.

SUN DEPRESSION 8-30 -2' "1* 0* 1' 2* 3 4" I 6 ° 7° 81 9 10 111 12" 13- 14* 15'

.1

GRADIENT TW 37-d l 4/d I

A/ 2

MOO-

OLO RAI .3

0% t"C PL 421 = .

06

p t . .... . ... .. .O-"

-04

-3 %.. . ;;4 5 ;76:,"..1 12 1* 4 5

0- ...... ...... '

-02 S/u....... • .... . .... ... ... ... .

COLOR51 RTOW 37£oC PL32IM

0..

Do

-01-

-3 2 0 * 5. 10I

*3.... 4 "

./

.1Jaa4T37

0 TON

-0I0

00 1 ...... - * 8m

1.3 TW i 37 li//0

i'l mm m " " -

TWILIGHT 37



Aureole type: a2


Visibility: 115 im

Sunset: 16 55.2


Instrumnt temperature: +6 0

Horizon: Doee haze strips (of indVstrial

origin) below 50 elevation, Some

clouds visible below 0.5 0 eleva-

tion.

SUN DEPRESSION 8-3- -2- -lo 0. 1 2o 3 4o 5 61 7* 8 91 1O 1* 121 13 14' 15*

.6 GRADIENT TW38

-G:og I/d&

.2

REDO f

ORO I

SUN DEPRESSION 3-3* -2o -to Do 1- 2* 30 4o 5 61 7* 9 0. O .1 12o 13* w I5

COLOR RATIO TW 36

t", CR PL: L52 4 41 2 MCI

00

al.

0 0

00 1

0r 0

TWILIGHT 38


Daytime sky: Turbidity type: 1.6 an

Aureole type: al i at noonTurbidity coefficient: 0.065

Visibility: 65 km

Sunset: 17 11

Declination: .12.80


Horizon: Rather hazy up to 30, haze strips

up to 200 elevation.Remarks: Course of gradients near 40 sun

depression questionable because

of uncertainty of zero position

on chert.

SUN DEPRESSION 11

-3- -2- -1- 0. 1. 2 3- 4 6 7 So go 100 II. 12 13* 14 15'

GRAOIENTTW 39

.4

.ED

0

OR 0

6 0

60

Uvo____________

SUN DEPPRESSION 8-3. -2. -1. 0 1* 2* 3 41 5* 6' 70 o go 10" 11* 12* 13" 14- 15-

COLOR RATIO TW 39

t"%CR PL: 2 34 1 I k

0-

t0-

0-

02

............

0

U41 39

"~wj III1 f

500~ M=W10

10 toKm,,,,P.. Km,

0 - 0

TWILIGNT 39

February 23, 1960, Morning

Daytime sky: Turbidity type: 1.8.Aureole sky: al-2

Turbidity coefficient: 0.034 (before 07 00)

later on 0.025

Visibility: 50 ka

Sunrise: 06 37

Declination: -10.2

Instrumnt temperature: -30

Horizon: Toward E strong sea haze up to

20 elevation. Around 06 00 haze

strips up to 60 elevation.

Shortly after sunrise, up to

07 30, cloudy. banded haze on

eastern horizon below 80 eleva-

tion observed. Haze was appar-

ently located in upper tropospheric

levels.

SUN DEPRESSION S-3. -2. -1. O 1. 2- 3- 4- 5- 6 7- 8- 9- 0- 11 12- 13- 14- 15-6 1 1 i 1 1 1

GRADIENT TW 40

. -dlog I/dS.4 .

OR O

0

Uvo

SUN DEPRESSION 8-3 "2 -11 O . 2* 3°

41 5* 6* 7° 81 91 10' 111 12* 13* 14o 15*

COLOR RATIO TW 40(og.CR Mo

PL: 2 I

0-6

0-

04 , o

.02 "..

OD

02 0 .°o* . ..'" °,o,° ° .%

oA, 40

0.I

00.

-0

iI I I- IO* to Is-

I a'a-a-- i~n/6°

/A/I t

01/g0 ill [S00 00 80010

KU___________________________

TWILIGRT 40


Daytime sky: Turbidity type: 1,7

Aureole type: a2-3


Visibility: 100 km

Sunset: 17 19

Declination: -10.2

Instrument temperature: +0.50

Horizon: Partly dark grey bme bands up to

80 elevation,

Cu fra clouds very close to hori-

zon in W to N,

Documents

UNCLASSIFIED AD 273857 - DTICCorrimnda for RAort I ('Twilight Intensity at 200 Elevation', by F. Volz and R. M. Goody, 1960, AICRC-TN-60-284), p. 2, line 14. Should read ' ... the