Using Mie-Notch and in situ DSD to Calibrate Radar and Retrieve Noise Power and Fine Vertical Air Velocity Structures in Small Cumulus Observed by an Airborne FMCW cloud Radar

The first Mie minimum or Mie notch in radar measured Doppler spectra has been used to retrieve vertical air velocity in precipitating cloud for more than a decade. Here, this technique is applied to observations from an airborne FMCW radar for the first time. The retrieved vertical air velocities are highly correlated with those observed directly from the aircraft. Retrievals in heavily precipitating cumulus clouds provide an unprecedented view of the detailed fine structure of drafts. Furthermore, vertical air velocity can be removed and power spectra directly related to the drop size distribution (DSD) can be recovered. Combined with the in-situ measured DSD, the recovered power spectra are used to calibrate the FMCW radar, which makes radar calibration possible even in the field provided in-situ measured DSD is available. However, the conventional Rayleigh scattering Power-Z (reflectivity-factor) relationship is not valid and Mie theory and backscattering cross sections must be used. In addition, the recovered power spectra can be used to determine the power level of the noise signal. The FMCW radar, which does not have the traditional dead-zone associated with pulsed radars, allows for a direct comparison of the in-situ measurements obtained at cloud base to the radar observations from the closet sampling volume.