Assessment of the Efficacy of Lightning Forecast Over India: A Diagnostic Study

Abstract

Lightning has emerged as one of the major weather hazards in India. Lightning forecasts are introduced into the operational National Centre for Medium Range Weather Forecasting regional unified model (NCUM-R) to predict the events in advance. A new blended electric scheme following McCaul et al. (2009) is employed to predict the lightning flash count as a useful tool for day-to-day prediction of thunderstorm activity and intensity. A total of four numerical experiments, namely CNTL, EXP1, EXP2, and EXP3, were conducted by using the NCUM-R based on the graupel water path (GWP) amount and the process allowing the snow-rain collisions to form a graupel. The numerical simulation forecasts are compared with the Indian Air Force and Indian Institute of Tropical Meteorology earth network lightning sensor data. A case study of a convective system associated with a severe lightning event that occurred on 7 February 2019 over the northern region of India is diagnosed. The observations indicate stronger lightning cells present over the Haryana–Punjab region, with a leaf-like extension through south-eastwards and continuing up to the Himalaya foothills. Such south-eastward progression of the lightning system is well captured in all the experiments. However, when the GWP threshold is set to 200 g m−3, and allowing for the snow-rain collision process, the counts are improved by approximately 50% compared to the control run, and is closely agree with the observation count. Temporal evolution characteristics of the vertical distribution of the hydrometeors and vertical velocity support the formulation of the revised lightning parameterization scheme. Statistical metrics were computed for the pre-monsoon month indicating the robustness of the model with the revised scheme. Hence, the revised scheme is chosen for the operational implementation of the lightning flash prediction system of the NCUM-R. Further modifications of the electric scheme are warranted based on the cloud microphysics response over different weather regimes.