Radar Refractivity Retrieval: Challenges and Solutions

Radar refractivity retrievals have the potential to provide valuable insights into the variability in near-surface humidity. Radar signals propagate fractionally slower through more humid air masses and phase changes from ground clutter returns can be used to infer spatial patterns of humidity changes. Near-surface humidity can influence convective development and is still poorly represented in forecast models while other humidity observation methods generally have poor spatial representativity. It is anticipated that these retrievals will benefit Numerical Weather Prediction (NWP) models, especially for the forecasting of convective storms. Over the past five years, this technique has been developed for use on the UK's operational weather radars. The short wavelength (C band) and drifting frequency of the magnetron transmitters used by these radars have presented many challenges. Overcoming these challenges has also identified issues affecting the quality of retrievals even at longer wavelengths using klystron transmitters. We outline solutions to many of the challenges that have been encountered.