Several ingredients are necessary for convection to occur. Four of them are studied here: convective available potential energy of the most unstable level in a vertical profile (MUCAPE), deep-layer shear of the horizontal wind between 0 and 6 km (DLS), the lapse rate between 700 and 500 hPa (LR7050), and the mixing ratio of the lowest kilometer above ground (MR). Data are from ERA5, the latest global reanalysis produced by the ECMWF at unprecedented spatial and temporal resolutions of 31 km in the horizontal, 137 vertical levels and hourly time resolution spanning the years 1950-2019 (available at the time of the thesis: 2000 - 2018).
Seasonal distribution of convective parameters shows the Mediterranean basin as the dominant source of MUCAPE with peaks in summer that migrate towards the African coast in autumn, as does the mixing ratio. Deep layer shear is stronger in winter than in summer, associated with the position of the polar frontal zone. Lapse rate is generally high in winter and low in summer, except for North Africa, where it is at the highest values in summer. Monthly diurnal averages (monthly averages over all hours of the day) of MUCAPE exceed 200 J kg-1 in the Mediterranean basin in summer and early autumn, but do not reach this threshold in other regions. Monthly diurnal averages of DLS, on the other hand, exceed 10m s-1 (the lower limit for multicells) just for locations outside the basin in summer and early autumn. The monthly-averaged daily cycle of MUCAPE varies most in summer. It peaks over continents in the morning and over the sea at nighttime. In summer, in the Adriatic Sea and in the plains of central Europe, two peaks in the monthly-averaged diurnal cycles are observed and the analysis of mean vertical profiles highlights that the peak that generates convection depends on the environmental situation (for example the sounding with less convective inhibition). LR7050 shows small diurnal variability, except when thunderstorms form and make that part of the troposphere moist-adiabatically neutral. Diurnal variations of mixing ratio over the lowest kilometer are about 0.5 g kg-1 (equivalent to a warming of 1.2 K when condensed) with higher values during the afternoon over continents, which lowers the lifting and cumulus condensation levels and increases CAPE. The diurnal variation of DLS is only about 1-2 m s-1.