@article{fdi:010079358,
  title = {{P}reliminary investigation of the relationship between differential phase shift and path-integrated attenuation at the {X} band frequency in an {A}lpine environment},
  author = {{D}elrieu, {G}. and {K}hanal, {A}. {K}. and {Y}u, {N}. and {C}azenave, {F}r{\'e}d{\'e}ric and {B}oudevillain, {B}. and {G}aussiat, {N}.},
  editor = {},
  language = {{ENG}},
  abstract = {{T}he {R}ad{A}lp experiment aims at developing advanced methods for rainfall and snowfall estimation using weather radar remote sensing techniques in high mountain regions for improved water resource assessment and hydrological risk mitigation. {A} unique observation system has been deployed since 2016 in the {G}renoble region of {F}rance. {I}t is composed of an {X}-band radar operated by {M}eteo-{F}rance on top of the {M}oucherotte mountain (1901m above sea level; hereinafter {MOUC} radar). {I}n the {G}renoble valley (220m above sea level; hereinafter a.s.l.), we operate a research {X}-band radar called {XPORT} and in situ sensors (weather station, rain gauge and disdrometer). {I}n this paper we present a methodology for studying the relationship between the differential phase shift due to propagation in precipitation ({P}hi(dp)) and path-integrated attenuation ({PIA}) at {X} band. {T}his relationship is critical for quantitative precipitation estimation ({QPE}) based on polarimetry due to severe attenuation effects in rain at the considered frequency. {F}urthermore, this relationship is still poorly documented in the melting layer ({ML}) due to the complexity of the hydrometeors' distributions in terms of size, shape and density. {T}he available observation system offers promising features to improve this understanding and to subsequently better process the radar observations in the {ML}. {W}e use the mountain reference technique ({MRT}) for direct {PIA} estimations associated with the decrease in returns from mountain targets during precipitation events. {T}he polarimetric {PIA} estimations are based on the regularization of the profiles of the total differential phase shift ({P}si(dp)) from which the profiles of the specific differential phase shift on propagation ({K}-dp) are derived. {T}his is followed by the application of relationships between the specific attenuation (k) and the specific differential phase shift. {S}uch k-{K}-dp relationships are estimated for rain by using drop size distribution ({DSD}) measurements available at ground level. {T}wo sets of precipitation events are considered in this preliminary study, namely (i) nine convective cases with high rain rates which allow us to study the phi(dp)-{PIA} relationship in rain, and (ii) a stratiform case with moderate rain rates, for which the melting layer ({ML}) rose up from about 1000 up to 2500ma.s.l., where we were able to perform a horizontal scanning of the {ML} with the {MOUC} radar and a detailed analysis of the phi(dp)-{PIA} relationship in the various layers of the {ML}. {A} common methodology was developed for the two configurations with some specific parameterizations. {T}he various sources of error affecting the two {PIA} estimators are discussed, namely the stability of the dry weather mountain reference targets, radome attenuation, noise of the total differential phase shift profiles, contamination due to the differential phase shift on backscatter and relevance of the k-{K}-dp relationship derived from {DSD} measurements, etc. {I}n the end, the rain case study indicates that the relationship between {MRT}-derived {PIA}s and polarimetry-derived {PIA}s presents an overall coherence but quite a considerable dispersion (explained variance of 0.77). {I}nterestingly, the nonlinear k-{K}-dp relationship derived from independent {DSD} measurements yields almost unbiased {PIA} estimates. {F}or the stratiform case, clear signatures of the {MRT}-derived {PIA}s, the corresponding phi(dp) value and their ratio are evidenced within the {ML}. {I}n particular, the averaged {PIA}/phi(dp) ratio, a proxy for the slope of a linear k-{K}-dp relationship in the {ML}, peaks at the level of the copolar correlation coefficient (rho(hv)) peak, just below the reflectivity peak, with a value of about 0.42 d{B} per degree. {I}ts value in rain below the {ML} is 0.33 d{B} per degree, which is in rather good agreement with the slope of the linear k-{K}-dp relationship derived from {DSD} measurements at ground level. {T}he {PIA}/phi(dp) ratio remains quite high in the upper part of the {ML}, between 0.32 and 0.38 d{B} per degree, before tending towards 0 above the {ML}.},
  keywords = {{FRANCE} ; {ALPES} ; {GRENOBLE} ; {CHAMROUSSE} ; {MOUCHEROTTE}},
  booktitle = {},
  journal = {{A}tmospheric {M}easurement {T}echniques},
  volume = {13},
  numero = {7},
  pages = {3731--3749},
  ISSN = {1867-1381},
  year = {2020},
  DOI = {10.5194/amt-13-3731-2020},
  URL = {https://www.documentation.ird.fr/hor/fdi:010079358},
}