The purpose of the paper is to find the heating rates of underlying surface and air temporal and spatial temperature shear which lead to the stable genesis of wall-free non-stationary vortices. These vortices were generated over underlying surface of aluminum sheet due to its controlled heating from below as a result of development of unstable stratification of air. It is strictly emphasized that in contrary of previous studies no mechanical rotation devices and/or underlying surface rotation were used for the vortices generation. (C) 2012 Elsevier Ltd. All rights reserved.