Meteonorm Definitions

Meteonorm Definitions

Please note: some symbols in this table may not be readable with Netscape!

Day of the year	d_y	-
Hour of the year	h_y	-
Local Time	t	clock time: does not include daylight saving, thus for UK all times are GMT.
Hour	h	hour of the day, refers to the hour interval i.e hour 1 refers to the the time between midnight and 1am, it may be interpreted as 00.30 Solar Time.
Day of the month	d_m	-
Month	m	-
Global Radiation Horizontal	G_Gh	Total Solar (i.e short-wave) radiation arriving on a horizontal surface. (Direct + Diffuse. Radiation for a given hour represents the mean radiation during that hour. Not entirely clear how this hour is defined (local or solar time).
Direct Radiation horizontal	G_Bh	Solar radiation arriving on a horizontal surface directly from the sun.
Diffuse Radiation horizontal	G_Dh	Solar radiation which has been scattered by the atmosphere arriving on a horizontal surface directly from the sun.
Height of Sun	h_s	also know as solar altitude, the vertical angle of the sun in the sky (zero at sunrise/sun-set)
Solar Azimuth	γ	The horizontal angle representing the position of the sun in the sky. Various conventions are used with different software. In Meteonorm an azimuth angle of 0^o represents the Sun (or rather, direction from which direct radiation arrives) as South. East is -90^o and West +90^o. When no radiation is available the angle is set to zero!
Beam	G_Bn	Direct Radiation intensity in the direction of the beam: represents the maximum collectable direct radiation on any surface.
Hemispherical Radiation tilted plane	G_Gk	Meteonorm allows you to specify the orientation of a fixed plane and derives how much radiation will strike that plane. The tilted plane is specified using inclination and azimuth. Solar Azimuth and Plane azimuth will be the same when the direct radiation is normal to the plane. Inclination is the pitch angle of the plane: 0^o represents a horizontal surface e.g a flat roof and 90^o a vertical surface e.g a wall. Hemispherical can be considered to mean the same as global.
Diffuse radiation tilted plane	G_Dk	see Hemispherical Radiation tilted plane and Diffuse Radiation horizontal
Hemispherical Radiation tracked	G_Gn	Total radiation (direct and diffuse) on a moving plane oriented towards the sun.
Global Illuminance	L_G	total daylight intensity received from the sky on a horizontal surface in lux (lumens/m²), comprises Skylight and Sunlight. Misleadingly referred to as Global Luminance in Meteonorm program. Does not appear to produce any data.
Diffuse Illuminance	L_D	intensity of daylight received from the sky on a horizontal surface in lux (lumens/m²), also called skylight or diffuse light. Referred to as Diffuse Lumninance in Meteonorm program.
Extraterrestrial radiation	G₀	radiation received outside the atmosphere: is a function of latitude and declination as well as time of day. For a given solar time and date should be the same for any location on the planet with same latitude
Longwave Radiation incoming	L_in	Thermal (longwave) radiation received from the sky. Useful in assessment of radiative cooling potential. Misleading nomenclature as L also used for Illuminance.
Radiation balance	R	The overall value of incoming radiation = (Solar Radiation + Thermal Radiation from the sky) - (Reflected Solar Radiation + Outgoing Thermal Radiation). Negative values represent more radiation leaving earth than entering. Longterm average over planet should be zero? (Global Warming).
Emissivity, horizontal plane	ε_h	Longwave emissivity of sky at zenith (ie directly above). There are various ways of modelling the thermal radiation emitted by the sky. The Stefan-Boltzmann Law states that it is dependent upon emissivity and Surface Temperature. Thus to apply this you would also need the Sky Temperature.
Emissivity, vertical plane	ε_v	Longwave emissivity of sky at horizon.
Air Temperature	T_a	Temperature of air away from building surface (i.e excluding radiation absorbed by building surface and then transferred to air by convection).
Mixing Ratio	M_x	assumed to be mass ratio of water vapour to dry air in grammes moisture/kg air). Usually referred to as Specific Humidity
Dew Point Temperature	T_d	Temperature at which saturation (100% relative humidity) occurs with air at given Mixing Ratio.
Wet Bulb Temperature	T_p	Temperature of saturated air with same heat content (enthalpy) as given air.
Relative Humidity	RH	Common definition is the mass of water vapour in air relative to the mass for saturated air at the same temperature. expressed as a percentage.
Cloud Cover Fraction	N	Proportion of cloud in sky, expressed in Octals where 0 is clear sky and 8 is totally overcast sky. 'Measured' by eye. At night the values are interpolated from final visible sky condition of first day and first visible sky condition of next day.
Surface Temperature	T_s	Assume this is temperature of local earth surface: taking into account that this will generally be greater than air temperature during day due to absorption of solar radiation and less than air temperature at night due to longwave emission of radiation to sky.
Wind Speed	FF	-
Wind Direction	DD	Direction from which wind comes (0^o (North) clockwise through to 359^o)
Air Pressure	p	Atmospheric Pressure in hPa. Unusual units which appear to be hundreds of Pascals (N/m². More common to express as kPa (thousands of Pascals).