ITU-R P840-6 Cloud and Fog Model

An ITU cloud and fog model based on the most recent revision of ITU recommendation ITU-R P840. This model supersedes all previous versions of the cloud and fog model.

Parameter	Description
Cloud Ceiling	Height of the cloud layer above the ground.
Cloud Layer Thickness	Thickness of the clouds and fog layer.
Cloud Temperature	Temperature of the clouds and fog layer.
Liquid Water Content Density Value	Amount of water content within the clouds and fog layer.
Liquid Water Percent Annual Exceeded	The user-specified, time value percentage that the annual values of total columnar content of cloud liquid water exceeded for an average year. See Note.
Liquid Water Percent Monthly Exceeded	The user-specified, time value percentage that the monthly values of total columnar content of cloud liquid water exceeded for the average month specified below. See Note.
Liquid Water Average Data Month	The month (1 for January through 12 for December) of the year used to get the average cloud liquid water content data.

The recommendation also includes the global averages for cloud water content. These averages are computed over a year and also over each month of the year, based on the data gathered over several years.

You can choose the cloud liquid water content value to exceed for a specified percentage above the average (from 0.1% to 99%) of the average time.

For example, a lower percentage value will point to higher cloud liquid water content. The cloud water content value can spike far above the annual or monthly average one percent of the time in a year or a month. Compare this to the 90% value. This 90 % value will be very close to the annual monthly average.

Annual data exists for 0.1, 0.2, 0.3, 0.5, 1, 2, 3, 5, 10, 20, 30, 50, 60, 70, 80, 90, 95 and 99% of the time. Monthly data exists for 1, 2, 3, 5, 10, 20, 30, 50, 60, 70, 80, 90, 95, and 99 percent of the time. Values for other percentages are computed by interpolation.

The ITU-R dataset is from 0° to 360° in longitude and from +90° to –90° in latitude, with a resolution of 1.125º in both latitude and longitude. The total columnar content of reduced cloud liquid water at any desired location on the surface of the Earth are derived by interpolating the data.