Information content of MPEF DIVergence product in diagnosing the environment of deep convection

The use of divergence fields retrieved by tracking cloud and humidity features in satellite water vapour imagery to characterise preconvective environments in cases of strong upper-level dynamics is explored. An hourly upper-troposphere DIVergence (DIV) product is inferred from Atmospheric Motion Vectors (AMVs) tracked in the 6.2μm channel of the Spinning Enhanced Visible and InfraRed Imager (SEVIRI) onboard Meteosat Second Generation (MSG). This is an advanced satellite product operationally available since 2008. A specific colour palette is introduced to highlight the information content of the DIV product in mid latitudes. To make this product suitable for using in support to deep convection forecasting, an interpretation scheme of DIV product overlaid by the cloud top brightness temperature lower than −40°C as derived from the corresponding 10.8μm infrared (IR) image is proposed. The potential for operational applications is considered, taking into account that the divergent/convergent upper-level flow at the onset of deep moist convection is a sign of the presence of positive/negative factors, respectively, for the further development of the storm. In this study, the deep convective cells considered are limited to those, reaching the middle troposphere or above. For that purpose, 1166 convective cells with cloud top temperature lower than −50°C that developed over Europe and the Mediterranean coast of Africa from 16 June to 22 July 2010 were investigated. The results show that 76% of all studied deep convective cells developed in areas of divergence (as seen by MPEF DIV product). In 92% of the cases of deep convection appearance (at either divergent or convergent upper-level flow) the convective cells further developed in areas of divergence (as derived by the MPEF DIV product). This relation can be useful for the purposes of convection nowcasting by considering three types of observational information derived by MSG satellite data: composite images of the divergence fields, IR channel 10.8μm images and instability indices, as well as NWP parameters of tropospheric instability and upper-level dynamics.