Refractivity measurements by radar offer us our first glimpse at the 2-D structure of near-surface moisture at the mesoscale. While most moisture measurements until now had been limited to point measurements and vertical profiles, refractivity measurements allow us to observe the time evolution of moisture field in the same way that radar reflectivity made possible the study of the mesoscale structure of precipitation.

During IHOP, 7 weeks of data were collected where we observed a great variety of events: fronts, dry lines, wave phenomena, conditioning of the boundary layer by surface conditions, convection initiation... In this talk, we will present many such events to expose the community to what can be observed using refractivity. We will focus in particular on the nature and origin of the many moisture gradients observed that do not seem to have any identifiable origin.