  We study the influence of stratification on stellar turbulent convection near
the stellar surface and in depth by carrying out 3D high resolution
hydrodynamic simulations with the ASH code. Four simulations with different
radial density contrast corresponding to different aspect ratio for the same
underlying 4 Myr $0.7 M_\odot$ pre-main sequence star model are thus performed.
We highlight the existence of giant cells which are embedded in the complex
surface convective patterns using a wavelet and time correlation analysis.
Next, we study their properties such as their lifetime, aspect ratio and
spatial extension in the different models both in latitude and depth according
to the density contrast. We find that these giants cells have a lifetime larger
than the stellar period with a typical longitudinal width of 490 Mm and a
latitudinal extension increasing with the radial density contrast overpassing
50\degree of latitude for the thickest convective zone. Their rotation rate is
much larger than the local differential rotation rate increasing also with the
radial density contrast. However, their spatial coherence as a function of
depth decrease with the density contrast due to the stronger shear present in
these more stratified cases.
