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These show simulations of the upward flux of visible radiation (as would be detected by a weather satellite).   This is derived from the model representation of reflectances reflected visible radiation (brightness) derived from underlying model forecast cloud tops and surfaces.  The brightness reflectances can brightness can then be used to produce pictures equivalent to the visible images available from geostationary satellites.

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• The area of coverage includes high latitudes but every pixel is assumed to be an overhead (nadir) view.
• The solar illumination is always assumed to be directly overhead.  This means that cloud structures can still be seen at times and locations even when in reality it is dark.
• Unlike on real visible images, shadowing from clouds is never represented.
• The displayed cloud reflectance is because reflectance depends on optical depth.  This can cause uncertainty as:
  • sometimes low cloud does not show up well. The reflectance can be close to the reflectance from the surface and then clouds can’t be distinguished from terrain.
  • the amount of cloud condensate along the optical path is incorrect in the model, and/or because the optical path in the simulated image is not the same as the optical path in reality.

Users should check model cloud fields to get a complete picture.

Simulated infra-red imagery

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