A Lightning Parameterization for the ECMWF Integrated Forecasting System

Abstract

A new parameterization able to diagnose lightning flash densities is proposed for the ECMWF Integrated Forecasting System, including its tangent-linear and adjoint versions. Total lightning densities are expressed as a function of hydrometeors contents, convective available potential energy, and cloud-base height output by the convective parameterization. Potential future applications range from the computation of NOx emissions by lightning in atmospheric chemistry models, severe convection forecasting, and data assimilation. In this study, a decade-long experiment is used to calibrate the simulated global annual mean flash density against the LIS/Optical Transient Detector (OTD) climatological value. On the seasonal and continental scales, the new parameterization is shown to agree well with the LIS/OTD observations. In forecast mode, output lightning densities are found to be almost independent of the horizontal resolution used in the model. Decade-long experiments also show that the new parameterization gives better results overall than the main existing lightning parameterizations designed for global models. Sensitivity experiments using its adjoint version are also performed to assess its potential for the future assimilation of lightning observations in the ECMWF 4D-Var system.