una relación entre la radiación solar entrante y grados-hora de la temperatura

7/27/2019 Una relacin entre la radiacin solar entrante y grados-hora de la temperatura

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Agr. Meteorol., 6 (1969) 435-438

Agricultura( Meteorology Elsevier Publishing Company, Amsterdam Printed in The Netheriands

A RELATION BETWEEN INCOMING SOLAR RADIATION AND DEGREE-HOURS

OF TEMPERATURE

A. WALTER'

Formerly Director of the British East African Meteorological Service, Nairobi (Kenya)

(Received April 17, 1969)

SUMMARY

A curve is derived showing the relation between incoming solar radiation, asmeasured by a Linke Pyranometer, and the degree-hours of temperature between sunrise

and sunset at Nairobi (Kenya).

INTRODUCTION

In a paper published in this journal (WALTER, 1967) a method was outlined for

deriving an evaluation of the number of degree-hours from the records of third order

climatological stations.

In view of the increasing interest shown in the measurement of the biologicalheat balance in the field for agricultural purposes as evidenced at the symposium

held on April 28th, 1967, organised by the Royal Society and the Royal Meteorolo-

gical Society at the Meteorological Society's Rooms, London, it has been con-

sidered of some interest to publish the results of certain measurements made under

the direction of the author between 1938 and 1943, when Director of the East

African Meteorological Service and not hitherto published.

THE METHOD

The observed values of the number of degree-hours between sunrise and

sunset obtained by integrating the area below the diurnal temperature curve and

the corresponding values of incoming solar radiation on a horizontal surface are

shown on a scatter diagram in Fig.1 . This scatter diagram was graduated by

means of the orthogonal polynomials for n = 68, given by FISHER and YATES

(1948, p.78). The resulting polynomial is:

x = 260.97 + 21.945769 y 0.366705 y2 + 0.003110 y3

where v is the number of degree-hours of temperature between sunrise and sunset

1 Present address: "Bon Secours", London Road, Ramsgate, Kent (England).


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436 A. WALTER

Eguation to curveX=260.97 + 21.945769 y -0.366705 y2 + 0.003110 y3

> 4 0 0

3 0 0

2 0 0

1 0 0

200 300 400 500 600 700 800 900 1000 1100 Degree -hours of temperature between sunrise and sunset

Agr. Meteoro/., 6 (1969) 435-438

Fig.1. Scatter diagram with graduated curve showing relation between radiation and degree-hours of

temperature.

and y is counted from 1 to 66 corresponding to radiaton 115 g cal. cm2

to 765 cal. in

intervals of 10. The correlation between degree-hours and radiation, as read off this

curve, is r = 0.984.All the instruments for measuring total radiation from the sun depend for

their results on the heating effect on a prepared surface as recorded by a thermo-

couple protected, in some way or other, from environmental influences. In the

high-altitude tropics these influences are at a minimum, but in high latitudes the

effects may be considerable; whether in the tropics or high latitudes they will

average out by taking mean values for periods of 5, 10 or 15 days according to the

degree of weather variability and leave, in the mean, a significant measure of the

direct heating effect of the sun's rays. The high correlation which was found to

exist in Nairobi between the heat records as measured by the number of degree-hours and the radiation measurements can only be accounted for on the assumption

that the environmental influences do average out.

To be of use in agricultura! practce, radiation values are required over wide

areas. To obtain these values directly from the instruments in general use, of

which there are many varieties, demands a staff of technical officers for their

control and for the measurements of their results. Moreover, if used on a scale

commensurate with the needs of agriculture the cost is prohibitive. It is suggested

that, for agricultural purposes, where radiation influences are suspected, the heat

balance, as recorded by the number of degree-hours, should be tried as a substitute

and the corresponding radiation values read off the curve in Fig. 1.

To enable research workers to draw a large scale curve, the ordinates


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A SOLAR RADIATION/DEGREE-HOURS CURVE 437

Agr. Meteorol., 6 (1969) 435-438

of radiation, corresponding to every 40 degree-hours are given in Table 1.

In table IV of the notes published in this journal in 1967, it was shown that

considerable variation occurred in the heat balance as measured by degree-hours,

even when the changes in the mean temperature were very small. In Table II of thepresent paper the percentage variation in the mean monthly values of solar

radiation are shown. These confirm the variations in degree-hours given in table IV

of the previous notes.

TABLE I

ORDINATES OF THE GRADUATED CURVE SHOWN IN FIG.1 GIVING THE RELATION BETWEEN THE NUMBER OF

DEGREE-HOURS FROM SUNRISE TO SUNSET, AT KABETE, NAIROBI (KENYA) AND INCOMING SOLAR RADIATION

AS RECORDED BY A LINKE PYRANOMETER ON A HORIZONTAL SURFACE

Degree-hours

(celtigrade)

Radiation

(g-cal. cm2)

Degree-hours

(centigrade)

Radia tion (g-

cal . cm2)

160 90 680 388

200 91 720 433

240 94 760 492

280 105 800 544

320 123 840 593

360 143 880 639

400 164 920 678

440 188 960 713

480 212 1000 746

520 240 1040 774560 272 1080 791

600 306 1120 800

640 345 1160 800

TABLE II

HIGHEST AND LOWEST MEAN MONTHLY VALUES OF SOLAR RADIATION IN G-CAL. CM2 FOR FIVE YEARS

1938-1943

MONTHLY

AT KABETE, NAIROBI,

VALUE

(KENYA), WITH PERCENTAGE VARIATION ON THE LOWEST MEAN

Month Highest Year Lowest Year Percentagevariation

Jan. 694 1943 580 1941 20

Feb. 640 1942 602 1939 6

Mar. 662 1943 537 1942 23

Apr. 573 1939 485 1938 18

May 482 1940 414 1938 16

June 477 1940 321 1943 49July 383 1940 299 1943 28

Aug. 411 1940 344 1942 20

Sept. 584 1940 407 1938 43

Oct. 583 1939 485 1938 20Nov. 556 1939 476 1938 17

Dec. 628 1940 518 1938 21


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Agr. Meteoro!., 6 (1969) 435-438

438 A SOLAR RADIATION/DEGREE-HOURS CURVI:

REFERENCES

WALTER, A., 1967. Notes on the utilization of records from third order climatological station , for

agricultura) purposes.Agr. Meteoro!., 4(2): 137-143.

FISHER, R. A. and YATES, E., 1948. Statistical rabies for Biological, Agricultura! and Medical Research.(3rd Ed.) Hafner, New York, N.Y., 120 pp.

una relación entre la radiación solar entrante y grados-hora de la temperatura

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