Abstract
Abstract. Collection efficiency transfer functions that compensate
for wind-induced collection loss are presented and evaluated for unshielded
precipitation gauges. Three novel transfer functions with wind speed and
precipitation fall velocity dependence are developed, including a function
from computational fluid dynamics modelling (CFD), an experimental fall
velocity threshold function (HE1), and an experimental linear fall velocity
dependence function (HE2). These functions are evaluated alongside universal
(KUniversal) and climate-specific (KCARE) transfer functions with
wind speed and temperature dependence. Transfer function performance is
assessed using 30 min precipitation event accumulations reported by
unshielded and shielded Geonor T-200B3 precipitation gauges over two winter
seasons. The latter gauge was installed in a Double Fence Automated
Reference (DFAR) configuration. Estimates of fall velocity were provided by
the Precipitation Occurrence Sensor System (POSS). The CFD function reduced
the RMSE (0.08 mm) relative to KUniversal (0.20 mm), KCARE (0.13 mm), and the unadjusted measurements (0.24 mm), with a bias error of
0.011 mm. The HE1 function provided a RMSE of 0.09 mm and bias error of
0.006 mm, capturing the collection efficiency trends for rain and snow well.
The HE2 function better captured the overall collection efficiency,
including mixed precipitation, resulting in a RMSE of 0.07 mm and bias error
of 0.006 mm. These functions are assessed across solid and liquid
hydrometeor types and for temperatures between −22 and 19 ∘C. The results demonstrate that transfer functions incorporating
hydrometeor fall velocity can dramatically reduce the uncertainty of
adjusted precipitation measurements relative to functions based on
temperature.
Subject
General Earth and Planetary Sciences,General Engineering,General Environmental Science
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