This paper presents an investigation of a lake-land breeze atmospheric circulation responsible for strong horizontal and vertical inhomogeneities of moisture distribution which affected the refractivity in the neighborhood of a microwave line-of-sight link, as observed during a multi-instrument radiometeorological experiment carried out in S¿o Paulo, Brazil. A boundary layer and mesoscale atmospheric model was used to simulate the local circulation within the link region and to compute the time evolution of the vertical structure of the atmospheric refractive index. A ray-tracing model was also used to calculate the intensity of the received signals from the measured refractive index vertical profiles. The integrated simulation results were then compared with the measurements. The good agreement obtained between the measured and the simulated characteristics of the temperature and moisture advection, as well as between the measured and the calculated received signal levels, indicates that the lake-land breeze circulation mechanism is a likely source of the propagation phenomena observed in the microwave link. ¿ American Geophysical Union 1995