GB/T 36744-2018 in English

《GB/T 36744-2018紫外线指数预报方法》由TC345（全国气象防灾减灾标准化技术委员会）归口，主管部门为中国气象局。

GB/T 36744-2018 Forecasting method for ultraviolet index

1 Scope

This standard specifies a UV index forecasting method for revising terrestrial UV irradiance based on cloud cover, weather phenomena and surface albedo.

This standard is applicable to UV index forecasting and related scientific research.

2 Terms and definitions

For the purposes of this document, the following terms and definitions apply.

2.1
solar ultraviolet (UV)
solar radiation in the wavelength range of 100 nm to 400 nm in the solar spectrum, referred to as ultraviolet
Note: Solar ultraviolet can be divided into three bands according to the biological effects of different wavelengths, see Annex A for details.

2.2
UV irradiance
solar ultraviolet radiation power received per unit area
Note: It is expressed in Watts per square meter (W/m2).
[QX/T 87-2008, definition 3.2]

2.3
UV index (UVI)
quantitative index of effective irradiance level of ground surface solar ultraviolet radiation.
[GB/T 21005-2007, definition 3.10]
Note 1: The UV index is used to measure the extent of possible damage to human skin, eyes and other tissues and organs caused by ultraviolet irradiance at the time of maximum sunlight in a certain area. The higher UV index, the more severe damage to human body.
Note 2: See Annex B for classification of UV index levels.

3 Index forecasting method

3.1 Calculation of UV index

The UV index can be calculated by using Equation (1):

(1)
Where,

IUV — UV index forecasting value, dimensionless value, non-zero integer, rounded;

Quv — ground UV irradiance forecasting value, in Watts per square meter (W/m2);

Cer — equivalent erythema correction factor, which is 0.01;

DI — UV irradiance equivalent to the unit UV index, which is 0.025 W/m2.

3.2 Forecasting of ground UV irradiance

The forecasting value of UV irradiance reaching the ground can be calculated by using Equation (2):

Quv = (QA·a)·η·R (2)

Where,

Quv — ground UV irradiance forecasting value, in Watts per square meter (W/m2);

QA — Astronomical irradiance, in watts per square meter (W/m2), the amount of solar irradiance reaching the upper boundary of the Earth's atmosphere as determined by the astronomical position of the sun towards the Earth, see Annex C;

a — atmospheric transparency coefficient, which comprehensively reflects the weakening effect of clear air on total solar irradiance, has no dimensional value and ranges from 0 to 1 (obtained by historical data statistics, see Annex D);

η — the proportion of ultraviolet irradiance to the total solar irradiance [changes with time (month/season) in a year, in percentage (%), obtained through historical data statistics, see Annex E];

R — ground UV irradiance correction factor, calculation method is shown in Equation (3).

3.3 Ground UV irradiance correction factor

3.3.1 Calculation equation of correction factor

When there are cloudy, haze, dust and other weather or ground snow, ice and other phenomena, the correction factor shall be determined according to the influence factors and the impact degree. The ground UV irradiance correction factor can be calculated by using Equation (3):

R = Rca·Rwp·Rsa (3)

Where,

R — Ground UV irradiance correction factor;

Rca — Cloud cover correction factor, the values are shown in Table 1;

Rwp — Weather phenomenon correction factor, the values are shown in Table 2;

Rsa — Ground albedo correction factor, the values are shown in Table 3.

3.3.2 Cloud cover correction factor

The cloud cover correction factor shall be determined by the total cloud cover. Total cloud cover refers to the total number of clouds covered by all the sky, generally divided into 0 to 10, 0 means the sky is cloudless, 10 means the sky is completely covered by clouds. The values of cloud cover correction factors are specified in Table 1.

Table 1 Cloud cover correction factors

Foreword II
Introduction III
1 Scope
2 Terms and definitions
3 Index forecasting method
Annex A (Informative) Solar ultraviolet
Annex B (Informative) Classification of UV index levels
Annex C (Informative) Calculation of astronomical irradiance
Annex D (Informative) Experimental results of atmospheric transparency coefficient
Annex E (Informative) Experimental results of proportion of UV radiation to total solar radiation
Bibliography