SynRad v1.0: A radar forward operator to generate synthetic radar return signals from volcanic ash clouds

Abstract. In this work, SynRad, a new radar forward operator for the ATHAM volcanic plume model is introduced. The operator is designed to generate synthetic radar signals from ground-based radars for volcanic ash clouds simulated by ATHAM. A key novelty of SynRad is a ray tracing module which traces radar beams from the antenna to the ash cloud and calculates path attenuation due to hydrometeors and ash. The operator is designed to be compatible with the one-moment microphysics scheme in ATHAM, but can be easily extended to other one- or two-moment schemes in ATHAM or any weather prediction model. The operator can be used to test candidate locations at which to operationally deploy portable high frequency or multi-frequency (from long to short wavelength) radar(s). Optimal frequency or frequencies (for a multi-frequency radar) can be identified which balances the trade-off between a higher return signal and the higher path attenuation that comes at these higher frequencies. A case study of the eruption of the Raikoke volcano in 2019 is used to evaluate the performance of SynRad. The measurement process of a C-band radar is simulated using SynRad and the operator was able to generate realistic fields of the equivalent radar reflectivities, echotops and vertical maximum intensities. Ideally, higher frequency microwave radars will be designed and constructed specifically for monitoring volcanic eruptions. This is certainly possible in the coming years which makes feasibility studies on the capability of higher frequency radars timely.