Nowcasting SAF products
Cloud Top Height
The cloud top temperature and height (CTTH), developed within the SAF NWC context, aims to support nowcasting applications. This product contributes to the analysis and early warning of thunderstorm development. Other applications include the cloud top height assignment for aviation forecast activities. The product may also serve as input to mesoscale models or to other SAF NWC product generation elements.
The CTTH product contains information on the cloud top temperature and height for all pixels identified as cloudy in the satellite scene.
Precipitating clouds
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.
Rapid developing thunderstorm
The Rapidly Developing Thunderstorms product is a tool for monitoring convection from MSG data and is used for early detection of storm clouds.
The basic objectives of the Rapidly Developing Thunderstorms product are twofold: the automatic identification, monitoring and tracking of intense convective systems as well as the detection of rapidly developing convective cells. In other words, this product aims to assist in the automated detection of convection clouds.
The convective systems are presented like "objects" within the satellite images together with their most relevant properties (size, movement, minimum temperature, area and temperature trends, etc.) generated for the expected significant weather. The product highlights the most active convective cells. It may also serve as input for the automated convection detection used in aviation meteorology.
The Rapid developing thunderstorm product is used during the early stages of thunderstorm identification - from the time when convective clouds form to the stage at which the cloud shield has developed at the vertical level of the tropopause.
Stability analysis imagery
Total Precipitable Water (TPW) is the amount of liquid water, in mm, if all the atmospheric water vapour in the column were condensed. High values of TPW in clear air often become antecedent conditions prior to the development of heavy precipitation and flash floods. When high TPW values areas present a lifting mechanism and warm advection in low levels, heavy precipitation often occurs. These data can provide to forecasters an important tool for very short range forecasting. Within the SAF NWC context, the main goal is to provide TPW data in clear air pixel by pixel in image format for Nowcasting purposes.
Stability analysis imagery
The Stability Analysis Imagery (SAI) was developed by the NWC SAF. The central aim of the SAI is to provide estimations of the atmospheric instability in cloud-free areas. Among all potential indices the Lifted Index (LI) has been implemented and codified and presented in this case for central Europe on the 19th June 2006. The lifted index of SAI is only done for clear sky conditions, therefor for SAI the first step is to compute the Cloud Mask product (CMa). This CMa allows the identification of cloud free and cloud contaminated areas. The SAI product itself uses the corrected normalized IR SEVIRI radiance values of the following channels WV6.2, WV7.3, IR8.7, IR9.7, IR10.8, IR12.0 and IR13.4μm), and provides as output the normalized lifted index.
GII
Global instability index (GII) is an airmass parameter indicating the stability of the clear atmosphere. The GII product should serve as a nowcasting tool to identify the potential of convection and possibly of severe storms in still preconvective conditions. The applied retrieval method makes use of six MSG SEVIRI thermal bands, and together with the a priori information of forecast profiles, the scheme infers an updated atmospheric profile for each MSG pixel, from which instability indices can be computed. Several instability indices are used in this case and presented. The images are presented in 1 hour sequence.
K-Index - Flash material not existing
The K-index is a widespreaded method amongst meteorologists to make a stability analysis of the atmosphere. In the above link the K-index as computed by the GII algorithm is presented in 1 hourly interval.
Lifted Index - Flash material not existing
A second index that is computed from GII is the Lifted Index. In 1 hour interval the Lifted Index is presented for the 19th June 2006 over Central Europa.
Precipitable Water - Flash material not existing
One final product to be presented is the precipitable water. For a Meteorologist this product can be of extreme value when doing a nowcast. It represents the total atmospheric water vapor contained in a vertical column of unit cross-sectional area extending between any two specified levels, commonly expressed in terms of the height to which that water substance would stand if completely condensed and collected in a vessel of the same unit cross section.