Impact of land surface processes on mesoscale convective initiation over Africa in ensemble model simulations: 3 Case studies using UKMO Unified Model

Impact of land surface processes on mesoscale convective initiation over Africa in ensemble model simulations: 3 Case studies using UKMO Unified Model
V S Semeena¹, C Taylor¹ and A Hartley²
1. UK Centre for Ecology and Hydrology, Wallingford, Oxfordshire, OX10 8BB, UK
2. Met Office, FitzRoy Road, Exeter, Devon, EX1 3PB, UK

The populations of the developing world have a greater need for accurate weather predictions because national economies and personal livelihoods depend very heavily on weather-sensitive factors including agriculture, water resources and public health.   Climate related risk is an obstacle in improving food security and rural livelihood in Africa.   An effective system to provide reasonable forecast can have a great positive impact on the life quality in African continent.    Thus predicting an event with accuracy is essential to provide early warning of heavy rainfall and floods that may lead to loss of life and property. Past studies have shown the importance of the land surface on the development of African convective storms. Here we are using 72 hour ensemble model simulations to evaluate the representation of land and its influence on convection in forecast models.   
Three episodes of heavy rainfall events are identified over western and eastern African region over late springtime of 2019 for this study.   A heavy rainfall event is recorded over SW Mali on 25th April 2019 followed by the development of a convective system over northern Benin on 29th April 2019.   The latter one develops into a mesoscale system on 30th April extending up to western Nigeria and this convective initiation in the afternoon and development into a larger system by late evening continues until 3rd May.    Our eastern African case examines the daytime development of convective cells which develop over southern Sudan, and grow into a mesoscale system which crosses over to Congo by midnight.  17 ensemble members simulation of the UK Met Office Unified Model (UKMO-UM) that were run for a forecasting testbed within the African SWIFT (Science for Weather Information and Forecasting Techniques) is used to understand the role of land surface temperature (LST) and soil moisture (SM) in formation of mesoscale systems.  Single-model ensemble simulations of the UM in global domain at 0.2813 X 0.1875 degree longitude, latitude resolution and the regional convection permitting (CP) model in 2 different horizontal resolutions – 8.8km and 4.4km – are performed.   Results are compared with LST from Meteosat Second Generation (MSG) satellite data and precipitation data from Global Precipitation Measurements (GPM).   Both global and regional models capture the main features though the convective initiation takes place much earlier in the models than in reality.   We notice that the representation of rivers and wetlands in the global model affects the spatial patterns of surface fluxes, in turn introducing biases into the forecast.    Further comparison of surface fluxes in the ensemble simulations of these case studies with observed LST and SM illustrate the importance of land initialisation for short term forecasts.