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\section{Introduction} \section{Introduction}Massive stars, in a general sense, have convective cores and radiative  envelopes \cite{Kw90}. The introduction   of the so called ``iron peak" in stellar opacities \cite{Irw92} led, however,   to the prediction of a small convection  zone in the envelope of sufficiently luminous massive main sequence models  which originates from an opacity peak associated with   partial helium ionization. These two convection zones comprise   almost negligible amount of mass.   The reality of the iron opacity bump, as predicted by various groups \cite{Irw92,2005MNRAS.360..458B},  is unambiguous. It is most obvious in the field of  stellar pulsations. Only the inclusion of this feature allows an agreement of  observed and predicted instability regimes in the HR diagram, from the white  dwarf regime \cite{1993MNRAS.260..465S,1997ApJ...483L.123C}, for main sequence stars \cite{2001MNRAS.327..881D}, and up to hot supergiants \cite{2006ApJ...650.1111S}.  While the envelope convection zones may, at first glance, be negligible for the internal   evolution of hot massive stars, they may cause observable  phenomena at the stellar surface. The reason is that  the zones are located very close to the photosphere for some mass   interval (see below).  Here, we will discuss which observed features in hot stars might be  produced by these near surface convection zones. In particular, we examine   whether a link exists between these convective regions and   observable small scale velocity fields at the stellar surface   and in the stellar wind,"microturbulence".   A similar idea has been used to explain microturbulence   in low mass stars \cite{Edm78}, in which deeper   envelope convection zones reach the photosphere.   While \cite{Edm78} concludes that the   same mechanism {\em cannot} explain microturbulent velocities in O and B stars,   the iron-peak induced sub-photospheric convection zones in these stars had not yet been   discovered. We demonstrate in this paper that these convection zones may not only  cause motions which are observable, but possibly even directly affect the evolution:  First, we discuss how photospheric velocity fields may affect the   structure of massive star winds by inducing clumping at the base of the wind and thereby affecting the   stellar mass-loss. And second, we argue that the near surface convection zones  may generate magnetic fields which -- if they migrate to the surface -- further affect  the stellar wind mass-loss and, more significantly, the associated stellar angular momentum  loss.  We construct grids of massive main sequence star models, for various metallicities,   that allow us to predict the occurrence and properties of sub-surface convection zones as function  of the stellar parameters (Sect.~\ref{results}). We then compare the model predictions with  observed stellar properties, e.g., empirically derived microturbulent velocities   and observations of wind clumping in hot massive stars (Sect.~\ref{comparison}).