Present–day and future lightning frequency as simulated by four CMIP6 models

Abstract

The lightning flash frequency (LFF, also referred to as lightning flash rate) in four models from the Coupled Models Intercomparison Project, phase 6 is examined. For the present day (PD, 1995–2014), the models exhibit very divergent simulation of LFF in terms of multi–annual averages, interannual variability, and temperature sensitivity. The global mean multi–annual average flash frequency differs by a factor of two between the models, and only two of four models are within the reasonable distance from the LIS/OTD (Lightning Imaging Sensor/Optical Transient Detector) satellite retrievals. The model–data and inter–model differences are even more pronounced at a regional scale and during northern summer. CMIP6 simulations show a general increase in lightning flash frequency from the present day to the late 21st century, especially for the simulations with higher anthropogenic \(\textrm{CO}_2\) emissions into the atmosphere. LFF sensitivity coefficient \(\beta\), which is based on differences between PD and the late 21st century are positive over most continental areas with typical values from 10 to \(20 {\% \, \textrm{K}^{-1}}\) for annual mean LFF and from 20 to \(60 {\% \, \textrm{K}^{-1}}\) for JJA averages over the northern extra–tropical continents (and even up to \(100 {\% \, \textrm{K}^{-1}}\) in some regions for individual models). At the global scale and for annual averages, this sensitivity is from 5 to \(17 {\% \, \textrm{K}^{-1}}\). In addition, this sensitivity is markedly different from its counterpart derived from the regression of LFF on surface air temperature for PD period. The latter counterpart is negative at the global scale and changes sign between different regions (i.e, it is positive over the North America south–east and is negative over the south–western part of North America and over the India Peninsula). These regional peculiarities are reasonably simulated by the models.