Lightning-ignited wildfires and long-continuing-current lightning in the Mediterranean Basin: Preferential meteorological conditions

Abstract

Abstract. Lightning is the major cause of natural ignition of wildfires worldwide and produces the largest wildfires in some regions. Lightning strokes produce about 5 % of forest fires in the Mediterranean basin and are one of the most important precursors of the largest forest fires during the summer. Lightning-ignited wildfires produce significant emissions of aerosols, black carbon and trace gases, such as CO, SO2, CH4 and O3, affecting air quality. Characterization of the meteorological and cloud conditions of lightning-ignited wildfires in the Mediterranean basin can serve to improve fire forecasting models and to upgrade the implementation of fire emissions in atmospheric models. This study investigates the meteorological and cloud conditions of Lightning-Ignited Wildfires (LIW) and Long-Continuing-Current (LCC) lightning flashes in the Iberian Peninsula and Greece. LCC lightning and lightning in dry thunderstorms with low precipitation rate have been proposed to be the main precursors of the largest wildfires. We use lightning data provided by the World Wide Lightning Location Network (WWLLN), the Earth Network Total Lightning Network (ENTLN) and the Lightning Imaging Sensor (LIS) onboard the International Space Station (ISS) together with four databases of wildfires produced in Spain, Portugal, Southern France and Greece, respectively, in order to produce a climatology of LIW and LCC lightning over the Mediterranean basin. In addition, we use meteorological data provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5-reanalysis data set and by the Spanish State Meteorological Agency (AEMET) together with the Cloud Top Height (CTH) product derived from Meteosat Second Generation (MSG) satellites measurements to investigate the meteorological conditions of LIW and LCC lightning. According to our results, LIW and a significant amount of LCC lightning flashes tend to occur in dry thunderstorms with weak updrafts. Our results suggest that lightning-ignited wildfires tend to occur in high-based clouds with a vertical content of moisture lower than the climatological value, as well as with a higher temperature and a lower precipitation rate. Meteorological conditions of LIW from the Iberian Peninsula and Greece are in agreement, although some differences possibly caused by highly variable topography in Greece and a more humid environment are observed. These results show the possibility of using the typical meteorological and cloud conditions of LCC lightning flashes as proxy to parameterize the ignition of wildfires in atmospheric or forecasting models.

Comment on acp-2021-125

“…Our analysis suggests that LCC-lightning occurrence over Europe can be parameterized in atmospheric models using meteorological variables as proxy. Such a parameterization can be used in future studies to improve the modeling of fire occurrence and its atmospheric emissions in such models, where different atmospheric variables are used as proxies for the occurrence of lightning [e.g., (Tost et al, 2007;Murray et al, 2012;Gordillo-Vázquez et al, 2019)]. The launch of the Meteosat Third Generation (MTG) geostationary satellites of the EUropean organization for the exploitation of METeorological SATellites (EUMETSAT) in 2022 will provide for the first time a continuous monitoring of the occurrence of lightning flashes and fires in Europe and Africa through the instruments Lightning Imager (LI) and Flexible Combined Imager (FCI) from 2023, after the commissioning phase (Stuhlmann et al, 2005).…”

“…However, European studies are rare. Lightning is the major cause of ignition in the European boreal forests (Granström, 2001;Larjavaara et al, 2005b, a;Granström and Niklasson, 2008;Rolstad et al, 2017) and one of the main cause of ignition in the Alps (Conedera et al, 2006;Moris et al, 2020). In the Mediterranean basin, lightning causes about 5% of the total number of forest fires (Vázquez and Moreno, 1998;Camia et al, 2010;Koutsias et al, 2013), while the rest of fires are man-caused.…”

“…CG lightning discharges are initiated between two cloud regions with opposite sign electrical charges before escaping from clouds (Rakov and Uman, 2003). After the onset of the discharge, an advancing streamer corona guides the propagation of the leader, a high-temperature plasma channel.…”

“…In this work, we use optical observations reported from the space-based instrument Lightning Imaging Sensor (LIS) to investigate the continuing current phase of lightning discharges over Europe (Bitzer, 2017). For a more extensive description of the physical characteristics of lightning discharges and their electromagnetic emissions, we refer to Rakov and Uman (2003), Some evidence suggests that LCC lightning flashes are precursors of LIW. This was originally proposed by McEachron and Hagenguth (1942) working with laboratory sparks, who suggested that ignition by natural lightning is usually caused by a discharge having an unusual LCC phase.…”

A parameterization of Long-Continuing-Current (LCC) lightning in the lightning submodel LNOX (version 3.0) of the Modular Earth Submodel System (MESSy, version 2.54)

“…Lightning flashes containing a discharge in which a continuing electrical current flows during more than 40 ms are usually referred to as Long-Continuing-Current lightning (LCC-lightning) (Brook et al, 1962). LCC-lightning has been associated with lightning-ignited fires (e.g., Fuquay et al, 1967;Latham and Williams, 2001;Pineda et al, 2014;Pérez-Invernón et al, 2021b), as the long duration of the discharge can favor ignition. This assumption is supported by laboratory experiments (e.g., McEachron and Hagenguth, 1942;Feng et al, 2019;Zhang et al, 2021).…”