Climatological analysis of melting layer altitude in landfalling atmospheric rivers using weather radars

Abstract:

The melting layer altitude marks the atmospheric swath in which hydrometeors undergo a phase transition from solid to liquid. When storm systems interact with topography, the melting layer plays a critical role in determining the snowline elevation, and its accurate characterization is therefore essential to assess and predict snowfall, snowpack, and ultimately water resource availability. Over recent decades, an uphill migration of snowlines associated with winter precipitation along the Sierra Nevada has been observed. Similarly, studies using reanalysis data and vertically-pointing research radars have detected an increase in the melting layer altitude, and have attributed this change to anthropogenic warming. Here, we leverage an observational tool from operational meteorology – doppler weather radars – to assess climatological changes in landfalling atmospheric rivers along the central Californian coast. In this pilot study, we employ archived data from a single WSR-88D radar, KMUX, located in San Francisco, CA. Using phase-driven reflective signatures, we identify the altitude and depth of the melt level and layer within landfalling atmospheric rivers. We assess climatological change by analyzing the AR melt layer altitude mean, variance, and change over the observational period. In addition, recent advances in radar technology, to include dual-polarimetric characterization, provide information on hydrometeor shape, phase heterogeneity, and precipitation intensity – all of which, when assessed over time, can lend greater clarity to climatological and microphysical environmental change. Characterizing landfalling atmospheric rivers using weather radars can validate previous findings, as well as add to the understanding of how climate change affects the properties of precipitation.