Cloud cover

Cloudiness or cover is in meteorology, the term for a collection of condensed water in the atmosphere, which is visible to the naked eye as a whole and not touch the ground. Cloudiness should thus be both the fog, as well as the mist that is formed from suspended solid particles in the air, distinguished.

Individually recognizable elements of cloudiness are called cloud. The extent of coverage of the sky with clouds is usually estimated by the weather observer, nowadays also detected by special sensors or weather cameras. In contrast, the data from weather satellites are only available regionally. At most weather stations specified in the synoptic -eighth subdivision will be used. We also speak of the unit " Okta ".

• 2.1 Standard sky 2.1.1 standard lighting situations
• 2.1.2 standard

Classification

While the coverage was formerly often estimated in tenths, details are now given in eighth notes in the rule. The scale starts at 0/8 or 0/ 10 = cloudless, are continued cheerful at 1-2/8 = 3/8 = partly cloudy, cloudy 4-6/8 = 7 /8 = Mostly cloudy and finally 8 / 8 = covered ( see table at right ).

In everyday language, is " overcast" or covered often supplemented by turbid when the clouds not only cover the whole sky, but are also dark and high humidity.

Classification of meteorological

The meteorological service summarizes the eighth: The best weather condition is " clouds and visibility okay " ( CAVOK ), the almost cloudless sky was formerly with "sky clear" ( SKC ), today with "no significant clouds" ( NSC) for no clouds below 5000 ft or no significant clouds or " no clouds detected" ( NCD) called at automatic stations. It follows "few " (FEW ) cloudy for a little further with 3-4/8 "scattered " (SCT ) or scattered clouds, 5-7/8 "broken " ( BKN ) for broken cloud ceiling and 8/ 8 " overcast" (OVC ) for a dense, closed cloud cover. Furthermore, 9/8 obscured ( OBSC ) if the sky is not visible.

Classification of CIE

The International Commission on Illumination ( CIE) defines some sky conditions. Sunny sky (german sunny sky ) denotes the sky, where the sun shines, the degree of cloudiness is initially irrelevant. As a clear sky ( engl. clear sky ) a heaven in which less than 30 percent of the area of ​​sky covered by clouds. As teilbewölkten Heaven ( engl. partly cloudy sky ) one in which between 30 and 70 percent of the area of ​​sky is covered with clouds. As a cloudy sky (English cloudy sky ), is covered with more than 70 percent of the area of ​​sky with clouds a. As an overcast sky (English sky overcast ) a sky with a fully closed cloud cover, that is 100 percent of the area of ​​sky is covered with clouds. This sky conditions have implications for daylighting design, and photography for the determination of the color temperature which is depending on the sky between 5500 K and 7500 K.

State of sky

As the sky condition, the International Commission on Illumination defines a function that depends on the solar altitude.

These celestial states are partially used for the calculation of daylight factors; they also have implications for daylighting design, and photography for the determination of the color temperature, which varies depending on the sky.

Standard sky

The sky is a standard CIE standard that models the spatial luminance distribution of the sky under different weather conditions mathematically. He aims to be a universal basis for the classification of measured luminance distributions of the sky and provide a method for calculating the sky luminance for daylighting design.

Standard defines the relative luminance distributions, i.e., the luminance of the sky at any point of the hemisphere will be described as a function of the luminance in the peak. In order to obtain absolute luminance distributions for daylight calculations, the model can be used with specified values ​​of the luminance or the zenith of the horizontal illuminance.

Standard lighting situations

Due to the fixed values ​​occupancy of five luminance gradation parameters (a ... e) following standard lighting situations can be created:

Standard

Joint ISO / CIE Standard ISO 15469:2004 (E) / CIE S 011 / E: 2003 ': Spatial distribution of skylight - CIE standard general sky

( engl spatial distribution of daylight - CIE general sky standardized)

The CIE Standard General Sky includes as special cases the CIE Standard Clear Sky and the CIE standard overcast sky and thus replaces the standard CIE S003 - 1996: Spatial distribution of daylight - CIE standard overcast sky and clear sky.