Keynote Talk: Peeping through the keyhole at the mesoscale variability of humidity: Some IHOP_2002 observations and future challenges of radar refractivity mapping

A technique has been developed to measure the refractive index of air by radar. Since refractivity is a function of temperature, pressure, and especially moisture, observations of the field of near-surface refractivity by radar gives us a unique albeit range-limited glimpse at the structure of the field of moisture at the mesoscale. In addition to making possible the observation of fronts, storm outflows, and boundary layer processes, refractivity can be used qualitatively, to identify convergence lines between air masses of different temperatures and/or moisture, as well as quantitatively to obtain fields of surface moisture. After a brief introduction of the principles behind this measurement, the presentation will focus on examples of data collected during IHOP_2002 as an excuse to illustrate some of the possibilities offered by refractivity measurements.