Potential of scanning Doppler polarimetric mm-radars for observing winds in extreme weather event cloud systems

The capability of microwaves to penetrate cloud and rain has placed radar in an unchallenged position for remotely surveying the atmosphere and quantifying the associated parameters. Although visible and infrared instruments on satellites can detect and track storms, only microwave observations can reveal the internal structure of a storm. In particular, radars with Doppler capability can provide quantitative information on highly dynamic atmospheric processes. With the advancements in space-borne atmospheric radar, initiated with TRMM, CloudSat, and the follow-on missions such as GPM and EarthCARE now in advanced state, the atmospheric science community is again challenged to explore new observation capabilities. This study focuses on assessing the potential of off-nadir scanning Doppler 35/94 GHz radar to measure the along line-of sight winds. Because of the potentially high winds involved in extreme weather phenomena and of the large Doppler fading introduced by the platform movement, polarization diversity capabilities are used to eliminate aliasing and drastically reduce noise errors. An end-to-end radar simulator suited for polarimetric Doppler space-borne radars has been exploited to simulate the performances of such a system when overpassing a hurricane, simulated with a cloud resolving 3D model. The simulation framework allows an overall assessment of the error budget for Doppler velocity measurements. Results show that: 1) multiple scattering related errors are confined to strong convective cores; 2) noise errors can be typically reduced down to the ~1m/s magnitude for integration lengths of the order of 10 km when SNR-thresholds and V-H pulse pair distances are properly selected; 3) non uniform beam filling errors do represent the major contributor to the overall error budget especially in the forward/backward sector of the scan. The performances of the radar will be discussed in relation to typical science requirements and recommendations for future directions in scanning Ka/W-band space-borne Doppler radar research will be given.