Additionally to the synoptic weather patterns, the meteorology of the PBL is strongly influenced
by the surface characteristics and turbulence structure. Therefore, we will in this introductory
section shortly summarise qualitative aspects the different processes influencing the PBL
conditions additionally to a more detailed discussion of the statistical methods used in general
and which we shall use throughout the text to describe the characteristics of the PBL. Both with
respect to mean characteristics, variability and fluxes the PBL is dominated by turbulent motion.
Therefore it is appropriate firstly to consider what we should understand with turbulence, a
subject that has filled many pages in the scientific literature.