APPENDIX

Radiation Parameters

G, global solar radiation, is the total quantity of shortwave solar radiant energy emitted by the sun's disc as well as that scattered diffusively by the atmosphere and clouds passing through a unit area in the horizontal in units of time. It is also referred to as incoming total shortwave radiation.

D, diffuse solar radiation, is that part of shortwave radiation scattered by the atmosphere reflected diffusely and transmitted by clouds and passing through a unit horizontal area in units of time. This radiation comes from a solid angle of 2P with the exception of the solid angle subtended by the sun's disc.

I_H, direct solar radiation on a horizontal surface, is the quantity of solar radiant energy emitted from the solid angle subtended by the visible disc of the sun and passing through a unit area in the horizontal in units of time. This is also called the vertical component of the direct solar radiation.

I_H = G - D.

I_N, direct solar radiation at normal incidence, is the quantity of shortwave radiation energy emitted by the solid angle subtended by the visible disc of the sun and passing through a unit area held normal to the solar beam at the earth's surface in units of time.

I_N = (G - D)/sin (h)

where h is the angle of elevation of the sun.

Mean Daily Radiation and Sunshine Parameters

ETR -extraterrestrial radiation on a horizontal surface for a whole day, (kWh/km² )
n -actual sunshine duration during a day (hours)
N -maximum possible duration of sunshine
N' -maximum possible sunshine during a day with solar elevation >=5° (hours)
G -daily sum of global solar radiation (kWh/m² )
D -daily sum of diffuse solar radiation (kWh/m²)
I_H -daily sum of direct solar radiation on a horizontal surface (kWh/m²)
G(c) -daily sum of global solar radiation in a clear sky under average conditions (kWh/m²)
CI -clearness index (= G/ETR) (dimensionless).
WS -sunset hour angle, degrees; when divided by 7.5 gives the duration of the day (hours)

Clear-Sky Noon RadiaJion Parameters

I - direct solar radiation for clear-sky noon under average conditions (kW/m²)
I_H -direct solar radiation on a horizontal surface under average conditions (kW/m²)
D -diffuse solar radiation on a horizontal surface under average conditions (kW/m²)
G -global solar radiation on a horizontal surface under average conditions (kW/m²)
W -total precipitable water vapor in the atmosphere (g/cm²)
P -barometric pressure at station level (mbar)

Mean Hourly Meteorological Parameters

T_M -mean hourly temperature, °C
RH -mean hourly relative humidity, percent
W -mean wind speed for certain specified synoptic hours ranging from 1 to 6 in a day, km/h
R -mean total rainfall for a day from 0830 IST to 0830 IST next day, mm
SH -specific humidity
-ratio of minimum and maximum temperature