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meteoblue calculates radiation for the land and sea surface and for atmospheric layers, both as incoming direct and indirect sunlight, as well as reflected radiation from clouds or surface.

Radiation is expressed as Watt/m² for each forecasting time. Other units (aggregated radiation energy) or scales (joules/cm²/h) can be supplied.

SW means Short Wave, LW means Long Wave radiation. Radiation "down" is radiation from the sky to the ground. Radiation "up" is the radiation from the ground to the sky.

Latent heat is the amount of energy in the form of heat released or absorbed by a chemical substance during a change of state (i.e. solid, liquid, or gas), or a phase transition. In the atmosphere, when a molecule of water evaporates from the surface of any body of water, energy is transported by the water molecule into a lower temperature air parcel that contains more water vapour than its surroundings. Because energy is needed to overcome the molecular forces of attraction between water particles, the process of transition from a parcel of water to a parcel of vapour requires the input of energy causing a drop in temperature in its surroundings.
If the water vapour condenses back to a liquid or solid phase onto a surface, the latent energy absorbed during evaporation is released as sensible heat onto the surface. The large value of the enthalpy of condensation of water vapour is the reason that steam is a far more effective heating medium than boiling water, and is more hazardous.

# Difference between "instant" and "backwards" values

For PV production, GTI, GHI and others, we have hourly values, so, for example we have 2 different values for 17:00 at 30.03.2016.
What time interval represents the "instant value" for 17:00 and what time interval represents the "backwards value" for 17:00?
The "backwards value" for 17:00 represents the time interval between 16:00 and 17:00.
The time interval for the "instant value” is the value which the model is calculating for 17:00.

Let’s take 3 examples (fake values, only for illustration):

1. The weather is sunny: the radiation is 800 W at 16:00 and 700 at 17:00
The "backwards value" for 17:00 will be the average,    750 W
The "instant value” is the value at 17:00, so                 700 W

2. The weather is sunny, then a cloud arrives at 16:30: the radiation is 800 W at 16:00, 750 at 16:30 and 300 at 17:00
The "backwards value" for 17:00 is the average, say     600 W
The "instant value” is the value at 17:00, so                 300 W

3. The weather is changeable, with clouds at 16:00 and sun at 17:00: the radiation is 800 W at 16:00, 600 W at 16:30 and 700 at 17:00
The "backwards" value for 17:00 will be the average,    700 W
The "instant value” is the value at 17:00, so                 700 W
So, for production, the backwards value is definitely more useful.