Implementation of refractivity retrieval from ground clutter using the s-band KOUN radar

Phase variations of ground clutter radar returns are related to changes in the index of refraction of the atmosphere between the radar and the target. The index of refraction varies with pressure, temperature and relative humidity, so any phase change in returns from ground targets acts as an atmospheric record of these variables. Refractivity extraction can provide low-level moisture information useful for thunderstorm initiation forecasts, boundary-layer research and data assimilation in models. Therefore, this relatively new technique will become increasingly important over the coming years. Using the KOUN dual-polarization radar, we will show that the time-varying phase of ground clutter returns can be used to generate a field of near-surface index of refraction, usually limited to a 30-40 km range from the radar. With the ultimate goal of implementation of this technique on shorter wavelength radars, such as 3-cm gap-filling radars, we will present results from the S-band KOUN radar in Norman, Oklahoma, operated by the National Severe Storms Laboratory. Possible advantages related to the use of dual-polarization, such as multipath mitigation, will be studied. Case studies will be investigated including frontal passages and thunderstorm initiation along drylines.