Precipitating Clouds from Cloud Physical Properties (NWC/GEO PC-Ph) Table of contents 1.- Goal of PC-Ph product  2.- PC-Ph algorithm description  3.- List of inputs for PC-Ph 4.- Description of PC-Ph outputs 5.- Example of PC-Ph visualisation Access to "Algorithm Theoretical Basis Document for the Precipitation Product Processors of the NWC/GEO" for a more detailed description of the algorithm.

1.- Goal of PC-Ph product

PC-Ph product, developed within the NWC SAF context, is a Nowcasting tool that provides estimation on the probability of precipitation (PoP) occurrence.
PoP is defined as the instantaneous probability that a rain rate greater than or equal to 0.2 mm/h occurs at the pixel level.

2.- PC-Ph algorithm description

The PoP estimation is done using information on the cloud top microphysical properties, Effective Radius (Reff) and Cloud Optical Thickness (COT).
The microphysical properties are computed within the NWC/GEO CMIC product for daytime, so it is necessary to run CMIC product previous to run PC-Ph. The main limitation of this product is that only provides results during daytime.
Using Reff and COT the Cloud Water Path (CWP) is computed. CWP means Liquid Water Path for water clouds and Ice Water Path of ice clouds. This parameter is computed using the following equation:

For the retrieval of the probability of precipitation, the Cloud Water Path (CWP) is used. The following relation between CWP and PoP has been obtained in order to assign a PoP to each satellite pixel:

Where PoP is the Probability of Precipitation occurrence (%) and CWP is the Cloud Water Path (gm^-2).
Since the parameters used by this algorithm have a high dependence on illumination conditions, a study has been carried out in this sense. This study concluded that illumination conditions don't affect the quality of PC-Ph product.
For a better PoP area location a parallax correction can be applied to this product. This option is chosen by the user through the product model configuration file and it is applied by default. When the Parallax Correction is working, a spatial shift is applied to every pixel with PoP greater than 0%.

3.- List of inputs for PC-Ph

-NWC/GEO CMIC microphysical parameters:

Phase, COT and Reff parameters are mandatory inputs to PC-Ph.

- Satellite imagery:

IR10.8 SEVIRI brightness temperature at full IR spatial resolution is a mandatory input to compute Parallax Correction.

- Numerical model:

Temperature at 1000, 925, 850, 700, 500, 400, 300, 250 and 200 hPa
Geopotential at 1000, 925, 850, 700, 500, 400, 300, 250 and 200 hPa

This information is used by default for parallax correction. In case of lack of NWP parameters parallax correction will be run using a climatological profile.

- Ancillary data sets:

Climatological profile is necessary as a back up for Parallax correction in case NWP is not available. This information is included in the software package and is located in the $SAFNWC/import/Aux_data directory

- Model configuration file for PPh:

PPh model configuration file contains configurable system parameters in the generation process of both PC-Ph and CRR-Ph products. The PC-Ph product related parameters refers to ancillary datasets, numerical model data and parallax correction. The complete list of these parameters and the explanation of the most useful ones are available in the "User Manual for the Precipitation Product Processors of the NWC/GEO".

4.-Description of the main PC-Ph output

PC-Ph product is coded in NetCDF format and its content is the following:

- pcph output provides an estimation of the probability of precipitation from 0% to 100% of probability.

- pcph_status_flag provides information on the data availability, whether parallax correction has been applied and holes due to parallax correction for each pixel:

Data Availability:

Bit 0:            Reff or COT not computed (out of cloud, night time or undefined phase)

Bit 1:            Phase not computed or undefined

Bit 2:            IR band missing (used in parallax correction)

Applied Correction:

Bit 3:            Parallax correction applied

Other information

Bit 4:             pc_intensity was a hole because of the parallax correction, and then was filled by the median filter

5.- Example of PC-Ph visualisation

Below is shown an image corresponding to PC-Ph probability of precipitation output. It has been obtained at full resolution and parallax correction have been applied.

Figure 1: PC-Ph probability of precipitation for 9^th June 2015 at 15:00 UTC over Europe

References:

- Pilewskie, P. and Twomey, S., 1987. Discrimination of ice from water in clouds by optical remote sensing. Atmos. Res., 21:113-122

- Rosenfeld, D., and G. Gutman, 1994. Retrieving microphysical properties near the tops of potential rain clouds by multispectral analysis of AVHRR data, Atmos. Res., 34, 259-283, doi:10.1016/0169-8095(94)90096-5.

- Roebeling, R.A., A.J. Feijt and P. Stammes, Cloud property retrievals for climate monitoring: implications of differences between SEVIRI on METEOSAT-8 and AVHRR on NOAA-17 J. Geophys. Res., 2006, 111, 20210, doi:10.1029/2005JD006990.

- Roebeling, R.A. and I. Holleman, 2009. SEVIRI rainfall retrieval and validation using weather radar observations. J. Geophys. Res., D2120, 114.

- Daniel Rosenfeld, William L. Woodley, Amit Lerner, Guy Kelman, Daniel T. Lindsey, 2008. Satellite detection of severe convective storms by their retrieved vertical profiles of cloud particle effective radius and thermodynamic phase. J. Geophys. Res. D4, 113.- Gutierrez, J. M. and Aguado, F.: Quality image for the Spanish Radar National Composite, Proceedings of ERAD 2006, 318-320.

- Algorithm Theoretical Basis Document for "Precipitation products from Cloud Physical Properties" (PPh-PGE14: PCPh v1.0 & CRPh v1.0), 2013

- Product User Manual for "Precipitation products from Cloud Physical Properties" (PPh-PGE14: PCPh v1.0 & CRPh v1.0), 2013

- Validation Report for "Precipitation products from Cloud Physical Properties" (PPh-PGE14: PCPh v1.0 & CRPh v1.0), 2013