Simulating lightning into the RAMS model: implementation and preliminary results

Abstract

Abstract. This paper shows the results of a tailored version of a previously published methodology, designed to simulate lightning activity, implemented into the Regional Atmospheric Modeling System (RAMS).The method gives the flash density at the resolution of the RAMS grid scale allowing for a detailed analysis of the evolution of simulated lightning activity.The system is applied in detail to two case studies occurred over the Lazio Region, in Central Italy. Simulations are compared with the lightning activity detected by the LINET network. The cases refer to two thunderstorms of different intensity which occurred, respectively, on 20 October 2011 and on 15 October 2012.The number of flashes simulated (observed) over Lazio is 19 435 (16 231) for the first case and 7012 (4820) for the second case, and the model correctly reproduces the larger number of flashes that characterized the 20 October 2011 event compared to the 15 October 2012 event.There are, however, errors in timing and positioning of the convection, whose magnitude depends on the case study, which mirrors in timing and positioning errors of the lightning distribution. For the 20 October 2011 case study, spatial errors are of the order of a few tens of kilometres and the timing of the event is correctly simulated. For the 15 October 2012 case study, the spatial error in the positioning of the convection is of the order of 100 km and the event has a longer duration in the simulation than in the reality.To assess objectively the performance of the methodology, standard scores are presented for four additional case studies. Scores show the ability of the methodology to simulate the daily lightning activity for different spatial scales and for two different minimum thresholds of flash number density. The performance decreases at finer spatial scales and for higher thresholds.The comparison of simulated and observed lighting activity is an immediate and powerful tool to assess the model ability to reproduce the intensity and the evolution of the convection. This shows the importance of using computationally efficient lightning schemes, such as the one described in this paper, in forecast models.

Multi-sensor analysis of convective activity in central Italy during the HyMeX SOP 1.1

“…Some general considerations can be obtained from the results shown: (i) the linear correlation between TAG and the number of strokes (total and −CG) supports the theory for which the amount of graupel aloft, often associated with the negative charge in the clouds (Saunders, 1993), is directly related to the mechanism of lightning production, and (ii) the linear relation between the columnar IWC g and flash number density found using radar observations for the 15 October 2012 is in agreement with results obtained by PE05 for TRMM measurements and with the model results obtained by FO13. This important finding could be exploited for applications involving lightning data simulation and/or assimilation in NWP models in order to improve the forecast of the convection (Lynn et al, 2012;Federico et al, 2014).…”

“…The precipitation event was associated with a trough that deepened significantly over the northern Tyrrhenian Sea, pushed a frontal system eastward, and advected moist air from the Tyrrhenian Sea inland to fuel deep convection on the Tyrrhenian coast, west of Rome. The synoptic-scale system moved rapidly to the east and triggered a line of convection that crossed the western half of central Italy from north to south within a few hours (see also Federico et al, 2014). Most of the precipitation produced by this system occurred in the late afternoon of 15 October across the western part of CI and on the western slopes of the Apennines.…”

“…Lightning information is useful to monitor the evolution of convective events (e.g., Gatlin and Goodman, 2010) as well as to assess the NWP model ability to reproduce their intensity and predict their evolution in time (e.g., Federico et al, 2014). Robust relationships of lightning activity to cloud microphysics and dynamical properties (such as updraft strength) could be exploited by assimilating lightning data into NWP models to improve the initiation and forecast in both time and space of convective activity (Lynn et al, 2012;Lagouvardos et al, 2013).…”

Improvement of RAMS precipitation forecast at the short-range through lightning data assimilation

“…The LINET "strokes" are grouped into "flashes" before assimilation in the model. In particular, all events recorded by LINET that occur within 1 s and in an area with a radius of 10 km are binned into a single flash (Federico et al, 2014).…”

“…In a recent study, Federico et al (2014) introduced a scheme to simulate lightning in RAMS (Regional Atmospheric Modeling System). Because the lightning distribution is well correlated to areas of deep convection, they concluded that lightning simulation can be a useful tool to evaluate the reliability of the NWP forecast in real time.…”