## Abstract

A comparative study of the use of X- and S-band polarimetric radars for rainfall parameter retrievals is presented. The main advantage of X-band polarimetric measurements is the availability of reliable specific differential phase shift estimates, K_{DP}, for lighter rainfalls when phase measurements at the S band are too noisy to produce usable K_{DP}. Theoretical modeling with experimental raindrop size distributions indicates that due to some non-Rayleigh resonant effects, K_{DP} values at a 3.2-cm wavelength (X band) are on average a factor of 3.7 greater than at 11 cm (S band), which is a somewhat larger difference than simple frequency scaling predicts. The non-Rayleigh effects also cause X-band horizontal polarization reflectivity, Z_{eh}, and differential reflectivity, Z_{DR}, to be larger than those at the S band. The differences between X- and S-band reflectivities can exceed measurement uncertainties for Z_{eh} starting approximately at Z_{eh} > 40 dBZ, and for Z_{DR} when the mass-weighted drop diameter, D_{m}, exceeds about 2 mm. Simultaneous X- and S-band radar measurements of rainfall showed that consistent K_{DP} estimates exceeding about 0.1° km^{-1} began to be possible at reflectivities greater than ∼26-30 dBZ while at the S band such estimates can generally be made if Z_{eh} > ∼35-39 dBZ. Experimental radar data taken in light-to-moderate stratiform rainfalls with rain rates R in an interval from 2.5 to 15 mm h^{-1} showed availability of the K_{DP}-based estimates of R for most of the data points at the X band while at the S band such estimates were available only for R greater than about 8-10 mm h^{-1}. After correcting X-band differential reflectivity measurements for differential attenuation, Z_{DR} measurements at both radar frequency bands were in good agreement with each other for D_{m} < 2 mm, which approximately corresponds to Z_{DR} ≈ 1.6 dB. The Z_{DR}-based retrievals of characteristic raindrop sizes also agreed well with in situ disdrometer measurements.

Original language | English (US) |
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Pages (from-to) | 952-963 |

Number of pages | 12 |

Journal | Journal of Atmospheric and Oceanic Technology |

Volume | 23 |

Issue number | 7 |

DOIs | |

State | Published - Jul 2006 |

Externally published | Yes |

## ASJC Scopus subject areas

- Ocean Engineering
- Atmospheric Science