Abstract
Abstract. Lightning flashes can produce a discharge in which a continuing electrical current flows for more than 40 ms. Such flashes are proposed to be the main precursors of lightning-ignited wildfires and also to trigger sprite discharges in the mesosphere. However, lightning parameterizations implemented in global atmospheric models do not include information about the continuing electrical current of flashes. The continuing current of lightning flashes cannot be detected by conventional lightning location systems. Instead, these so-called long-continuing-current (LCC) flashes are commonly observed by extremely low-frequency (ELF) sensors and by optical instruments located in space. Reports of LCC lightning flashes tend to occur in winter and oceanic thunderstorms, which suggests a connection between weak convection and the occurrence of this type of discharge. In this study, we develop a parameterization of LCC lightning flashes based on a climatology derived from optical lightning measurements reported by the Lightning Imaging Sensor (LIS) on board the International Space Station (ISS) between March 2017 and March 2020. We use meteorological data from reanalyses to develop a global parameterization that uses vertical velocity at the 450 hPa pressure level as a proxy for the ratio of LCC to total lightning in thunderstorms. We implement this parameterization into the LNOX submodel of the Modular Earth Submodel System (MESSy) for usage within the European Center HAMburg general circulation model (ECHAM)/MESSy Atmospheric Chemistry (EMAC) model and compare the observed and simulated climatologies of LCC lightning flashes using six different lightning parameterizations. We find that the best agreement between the simulated and observed spatial distribution is obtained when using a novel combined lightning parameterization based on the cloud-top height over land and on the convective precipitation over ocean.
Highlights
Lightning flashes are formed by electrical discharges with duration ranging between a few hundred of microseconds and hundreds milliseconds (Rakov and Uman, 2003)
We find that the best agreement between the simulated and observed spatial distribution is obtained when using a novel combined lightning parameterization based on the cloud-top height over land and on the convective precipitation over ocean
We have developed for the first time two parameterizations that use the updraft strength at the 450 hPa pressure level as a proxy for the ratio of LCC(> 9 ms) and LCC(> 18 ms) lightning to total lightning
Summary
Lightning flashes are formed by electrical discharges with duration ranging between a few hundred of microseconds and hundreds milliseconds (Rakov and Uman, 2003). 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. We present a simple LCC lightning parameterization which relates the ratio of LCC lightning to total lightning in thunderstorms with the updraft strength at a specific altitude We implement this novel parameterization as an upgrade of the LNOX submodel (Tost et al, 2007) of the Modular Earth Submodel System (MESSy) and test it with the European Center HAMburg general circulation model (ECHAM)/MESSy Atmospheric Chemistry (EMAC) model (v2.54). We test the parameterization by comparing the simulated seasonal spatial distribution of LCC lightning during 2018 with lightning data reported by LIS on board the International Space Station (ISS LIS)
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