Precipitating Clouds PGE04 SAFNWC    Table of contents 1.- Goal of PC product  2.- PC algorithm summary description  3.- List of inputs for PC  4.- Coverage and resolution 5.- Description of PC outputs 6.- Example of PC visualisation Access to "User Manual for the PGE04 of the SAFNWC/MSG Scientific Part" for a more detailed description.

 

1.- Goal of PC product

The objective of the PC product is to support detailed precipitation analysis for nowcasting purposes. The focus is on the delineation of non-precipitating and precipitating clouds for light and heavy precipitation, rather than quantifying the precipitation rate. Particular attention will be given to the identification of areas of light frontal precipitation.

The product provides probability results, i.e. probabilities of precipitation intensities in pre-defined intensity intervals. From the probabilities a categorical estimate of precipitation intensity may be derived. It is not intended to provide information on the type of precipitation.
 

2.- PC algorithm summary description

The precipitating clouds product gives the likelihood of precipitation in intensity classes. A linear combination of those spectral features, which have the highest correlation with precipitation, is used to construct a Precipitation index PI. For each value of the PI, the probability of precipitation in the respective classes is then determined from a comprehensive dataset of collocated satellite data, precipitation rates from surface radar and surface temperatures from NWP. Special attention has been given to spectral features in the visible, which implicitly contain information on cloud microphysical properties at the cloud top, such as effective radius and cloud phase. The algorithm to retrieve information on the presence (including rough intensity estimations) of precipitation is based on the Cloud Type output. The algorithm relies much on the microphysical information available in both the 1.6 micron and 3.9 micron channels.  For each algorithm a day and a night version exists. The threshold at which sun zenith angle to switch from day to night algorithm is configurable.

3.- List of inputs for PC
 

• Satellite imagery:

T0.6 m	T0.8 m	T1.6 m	T3.9 m	T8.7 m	T10.8 m	T12.0 m
Mandatory	Mandatory	Mandatory	Mandatory	TBD	Mandatory	Mandatory

 

• NWCSAF/MSG Products used as inputs:

  
  CT (Cloud Type)
   
   

• Auxiliary data:
   
  • NWP surface temperature
  • Sun zenith, satellite view zenith, and sun-satellite view relative azimuth difference angle

5.-Description of PC outputs

The PC product shall consist of a numerical value for the likelihood of precipitation within the following four precipitation intensity classes:
 

• no precipitation (R < 0.1 mm/hr)
• light to moderate precipitation: 0.1 mm/hr < R < 5.0 mm/hr
• intensive (convective) precipitation: 5.0 mm/hr < R


The following probability classes will be used:

      0% (= 0-5%)
     10% (= 5-15%)
     20% (= 15-25%)
     30% (= 25-35%)
     40% (= 35-45%)
     50% (= 45-55%)
     60% (= 55-65%)
     70% (= 65-75%)
     80% (= 75-85%)
     90% (= 85-95%)
     100% (= 95-100%)

A processing flag summerising processing conditions for each pixel is included in the PC product. It does not contain explicit quality information since the probability of precipitation in each of the intensity classes will give an indication of the uncertainty of the estimate.

6.- Example of PC visualisation

Total precipitation likelihood (sum of classes 2 and 3) from MSG night time algorithm,  for 25 January 2004, 12:00.
 
 

(Click on thumbnail for full-sized this image)
Total precipitation likelihood (sum of classes PC1 and PC2) from MSG day time algorithm (most northers part night algorithm), 25 January 2004, 12:00.