We present surface-layer measurements of temperature fluctuation variance from a site characterized by small-scale inhomogeneities. Periods of marked radiative forcing are selected. The data characterized by diabatic conditions and vertical heat flux larger than some threshold (here, chosen to be 0.01 K ms(-1)) agree quite well with the convective scaling (v'(2)) over bar /v(2)* alpha (-z/L)(-2/3) in unstable cases, and with the z-less parameterisation (v'(2)) over bar /v(2)* similar or equal to const (with a large scatter) in stable cases. For near-neutral cases, the similarity function diverges because of the loss of significance of the temperature scale. Departures from similarity are highlighted in cases with smaller thermal fluxes, because horizontal heterogeneity and unsteadiness become important as production terms.