Meteonorm Definitions

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

Day of the yeardy-
Hour of the yearhy-
Local Timetclock time: does not include daylight saving, thus for UK all times are GMT.
Hourhhour 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 monthdm-
Global Radiation HorizontalGGhTotal 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 horizontalGBhSolar radiation arriving on a horizontal surface directly from the sun.
Diffuse Radiation horizontalGDhSolar radiation which has been scattered by the atmosphere arriving on a horizontal surface directly from the sun.
Height of Sunhsalso know as solar altitude, the vertical angle of the sun in the sky (zero at sunrise/sun-set)
Solar AzimuthγThe horizontal angle representing the position of the sun in the sky. Various conventions are used with different software. In Meteonorm an azimuth angle of 0o represents the Sun (or rather, direction from which direct radiation arrives) as South. East is -90o and West +90o. When no radiation is available the angle is set to zero!
BeamGBnDirect Radiation intensity in the direction of the beam: represents the maximum collectable direct radiation on any surface.
Hemispherical Radiation tilted planeGGkMeteonorm 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: 0o represents a horizontal surface e.g a flat roof and 90o a vertical surface e.g a wall. Hemispherical can be considered to mean the same as global.
Diffuse radiation tilted planeGDksee Hemispherical Radiation tilted plane and Diffuse Radiation horizontal
Hemispherical Radiation trackedGGnTotal radiation (direct and diffuse) on a moving plane oriented towards the sun.
Global IlluminanceLGtotal 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 IlluminanceLDintensity 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 radiationG0radiation 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 incomingLinThermal (longwave) radiation received from the sky. Useful in assessment of radiative cooling potential. Misleading nomenclature as L also used for Illuminance.
Radiation balanceRThe 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 planeεhLongwave 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 planeεvLongwave emissivity of sky at horizon.
Air TemperatureTaTemperature of air away from building surface (i.e excluding radiation absorbed by building surface and then transferred to air by convection).
Mixing RatioMxassumed to be mass ratio of water vapour to dry air in grammes moisture/kg air). Usually referred to as Specific Humidity
Dew Point TemperatureTdTemperature at which saturation (100% relative humidity) occurs with air at given Mixing Ratio.
Wet Bulb TemperatureTpTemperature of saturated air with same heat content (enthalpy) as given air.
Relative HumidityRHCommon 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 FractionNProportion 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 TemperatureTsAssume 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 SpeedFF-
Wind DirectionDDDirection from which wind comes (0o (North) clockwise through to 359o)
Air PressurepAtmospheric Pressure in hPa. Unusual units which appear to be hundreds of Pascals (N/m2. More common to express as kPa (thousands of Pascals).