High-Resolution Vertical Profiles of X-Band Polarimetric Radar Observables during Snowfall in the Swiss Alps

Abstract

An X-band polarimetric radar was deployed in the eastern Swiss Alps at an altitude of 2133 m. Radar measurements were complemented with several weather stations deployed in an altitude range from 1500 to 3100 m as well as with a fixed GPS ground station that was used to infer integrated water vapor estimates. Around 8000 vertical profiles of polarimetric radar observables above the melting layer collected during two months are analyzed. First, the behavior of the mean profiles of reflectivity at horizontal polarization Zh, differential reflectivity Zdr, copolar cross correlation ρhv, and specific differential phase shift Kdp are interpreted from a microphysical point of view. It is shown that the whole evolution of snowflakes, from pristine crystals at temperatures around −30°C to dendritic crystals around −15°C, to large aggregates around 0°C, is well captured by the polarimetric radar variables. In a second step, the profiles are analyzed as functions of high and low water vapor and snow accumulation conditions. It is found that the vertical profiles of polarimetric radar variables have distinct features in low versus high water vapor conditions. High water vapor conditions appear to favor the occurrence of crystal aggregates at high altitudes/low temperatures. It is shown with a hydrometeor identification scheme that graupel-like particles are found to be dominant right above the melting layer for snow events with high accumulation intensities. The present analyses show that measurements from X-band dual-polarization radar can be useful to characterize the dominant microphysical processes during precipitation in mountainous regions.

Polarimetric radar and in situ observations of riming and snowfall microphysics during CLACE 2014

“…Similar trends were observed when a different hydrometeor classification method was employed (i.e., the method of Dolan and Rutledge, 2009, not shown here). The relation between riming and snowfall intensity was also qualitatively observed by Schneebeli et al (2013) in a different location in the Swiss Alps. It must be noted that these results rely on radar-based hydrometeor classification (i.e., indirect measurements), and also that riming does not exclude the occurrence of other microphysical processes, notably aggregation.…”

“…The peak of K dp , below altitudes of higher Z DR and above altitudes of higher Z H , is a well-known but still not completely understood signature observed during snowfall (Kennedy and Rutledge, 2011;Bechini et al, 2013;Schneebeli et al, 2013;Andric et al, 2013;Hubbert et al, 2014). The proximity of this signature with respect to the −15 • C level (blue line in Fig.…”

“…The system, named MXPol, is an X-band (3.2 cm wavelength) radar with angular resolution of about 1.5 • and range resolution of 75 m (complete specifications are given in Schneebeli et al, 2013;Scipion et al, 2013). MXPol provides as main products the reflectivity factor at horizontal polarization Z H (dBZ), differential reflectivity Z DR (dB), copolar cross-correlation coefficient ρ hv , specific differential phase shift upon propagation K dp ( • km −1 ), mean Doppler velocity v (m s −1 ) and Doppler spectrum width σ v (Doviak and Zrnić, 2006).…”

Measurements of precipitation in Dumont d'Urville, Adélie Land, East Antarctica

“…This system, described in Schneebeli et al (2013) and in Scipion et al (2013), is a scanning dual-polarization Doppler radar. During its operation period at DDU, it was mainly collecting data at 75 m radial resolution and a maximum radial distance of 30 km, mostly conducting different types of scans within a repeating scanning sequence of 5 min: (i) plan position indicator (PPI) scans, i.e., quasi-horizontal slices of the atmosphere, (ii) range height indicator (RHI) scans, i.e., vertical slices of the atmosphere, and (iii) static vertical profiles, such as the ones performed by the MRR.…”

Retrieval of the raindrop size distribution from polarimetric radar data using double-moment normalisation

“…Also used were data from a METEK GmbH micro rain radar (MRR Peters et al, 2002Tridon et al, 2011) within the network, which provided vertical profiles of estimated DSDs recorded with 100 m vertical resolution and 10 s integration time. MXPol, a transportable Doppler dual-polarisation weather radar (for instrument details see Schneebeli et al, 2013), was located to the north-east of the disdrometer network. In 2013, MXPol recorded "stacked" plan position indicator (PPI) scans above the Parsivel network at elevations of 4, 5, 6, 8, 10, 12, 14, 16, and 20 • above horizontal, with a return time of about 6 min.…”