  The mechanisms governing the transition to turbulence in natural convection
boundary layers along strongly heated vertical walls remain neither very clear
nor well understood, because of the lack of experiments and the difficulties of
physical modelling. Our measurements bring experimental data focusing on this
transition in quiescent air along radiating and conducting plates in the whole
range of 2000 to 8000 W/m\^2 heating rate. The analysis of the time series
obtained by sliding window cross-correlation thermoanemometry leads us to point
out coherent turbulent structures on short heights throughout the thin boundary
layer, which seem to be governed by heat transfer and time-microscales of
turbulence through the inner sublayer. Physical interpretations are given to
relate to the observed heat transfer correlation and these turbulence
transition structures along with radiation and conduction.
