The following four lightning density parameters have been introduced with IFS cycle 45r1:

• Instantaneous total lightning flash density (litoti)
• Averaged total lightning flash density in the last hour (litota1)
• Averaged total lightning flash density in the last 3 hours (litota3)
• Averaged total lightning flash density in the last 6 hours (litota6)

They all account for cloud-to-ground flashes (between the the cloud and the Earth’s surface ) and intra-cloud flashes (between two cloud regions of opposite electric charge) and this is denoted by the word "total" in their names. Parametrization of lightning in the IFS estimates total lightning flash densities using information about convective hydrometeor amounts, convective available potential energy (CAPE) and convective cloud base height, which are diagnosed by ECMWF’s convection scheme. More about lightning parametrization in the IFS could be found here.

Instantaneous total lightning flash density represents the flash density during one time step of the model and users have to be aware that it is prone to larger errors, e.g. due to any spatial and temporal discrepancies between model convection and observed convection. 

Please note that all these parameters are archived in units [flashes.km^-2.day^-1] and therefore some unit conversion is needed if one wants to display lightning density for different time periods for example depending on the parameter used. Lightning density on the ecCharts is displayed in units [flashes.100km^-2.h^-1] which is chosen to facilitate the forecast interpretation by providing sensible values (see Fig.1). 

a)b)

Fig.1. Flash density forecast a) "litota6" as archived in units [flashes.km^-2.day^-1]; b) "litota6" in units [flashes.100km^-2.h^-1].