Precipitating Clouds (PC)


  1. Goal of the Precipitating Cloud product
  2. Precipitating Clouds algorithm summary
  3. Precipitating Cloud outputs

Goal of the Precipitating Cloud product

The online-processing for the Precipitating Clouds product derives the precipitation likelihood from avhrr and passive microwave data (amsu-a and mhs).

The objective of the pc product is to support detailed precipitation analysis for nowcasting purposes, especially in areas for which no radar data is available. The focus is on the delineation of non-precipitating and precipitating clouds and on giving a rough indication on intensity to be expected. The output is the likelihood of precipitation in three intensity intervals of light precipitation (0.1-0.5mm/h), moderate precipitation (0.5-5.0mm/h) and heavy precipitation (>5mm/h).

Precipitating Clouds algorithm summary

The algorithm to retrieve information on the presence (including rough intensity estimations) of precipitation is based on the Cloud Type output, and it uses the spectral information in the vis/ir of the avhrr and the mw information of the amsu-A and the mhs. With the passive mw data the scattering signal of precipitation size ice particles in the cloud. In addition to this signal also the 11 and 12 micron channels from avhrr are used in the retrieval.

The Precipitating Clouds product is aimed for Nowcasting applications. It shall give the forecaster a quick overview over the probability of precipitation in a few coarse intensity intervals. Important features are that the scheme shall work seamlessly over land and sea, and shall work for both day and night, and for both stratiform and convective cases. The product can be used by the forecaster as a complement to radar data, especially in areas without radar coverage.

Precipitating Clouds output

The pc product consists of a numerical value for the likelihood of precipitation within the following four precipitation intensity classes:

The likelihood for no precipitation (R < 0.1 mm/hr) can be derived from the three probabilities above as all should sum to 100%.

For each intensity the following probability classes are used:

Provision of the probability of precipitation in each of the intensity classes gives an indication of the uncertainty of the estimate.

The pc output also includes three quality/status/conditions flags, giving information about how processing was performed etc.