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Snow Studies. Part I: A Study of Natural Variability of Snow Terminal Velocity

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  • 1 Department of Atmospheric and Oceanic Sciences, McGill University, Montreal, Quebec, Canada
  • | 2 Kyungpook National University, Daegu, South Korea
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Abstract

The variability and the uncertainties in snowfall velocity measurements are addressed in this study. The authors consider (i) the instrumental uncertainty in the fall velocity measurement, (ii) the effect of unstable falling motion on the accuracy of velocity measurement, and (iii) the natural variability of homogeneous snow terminal fall velocity. It is shown that, when periods of homogeneous characteristics of snow are selected to minimize the mixture of particles of different origin, the standard deviation of snowfall velocity within each period tends to stabilize at a value between 0.1 and 0.2 m s−1.

In addition, the variability of snow terminal fall velocity is examined with three control variables: surface temperature Ts, echo-top temperature Tt, and the depth of precipitation system H. The results show that the exponent b in the power-law relationship V = aDb has little effect on the variability of snowfall velocity: the coefficient a correlates much better with the control variables (Ts, Tt, H) than the exponent b. Hence, snowfall velocity can be modeled with a varying coefficient a and a fixed exponent b = 0.18 (V = aD0.18) with good accuracy.

* Current affiliation: University of Miami, Miami, Florida

+ Previous affiliation: McGill University, Montreal, Quebec, Canada

Corresponding author address: Isztar Zawadzki, Department of Atmospheric and Oceanic Studies, McGill University, 805 Sherbrooke St. West, Montreal, Quebec H3A 2K6, Canada. Email: isztar.zawadzki@mcgill.ca

Abstract

The variability and the uncertainties in snowfall velocity measurements are addressed in this study. The authors consider (i) the instrumental uncertainty in the fall velocity measurement, (ii) the effect of unstable falling motion on the accuracy of velocity measurement, and (iii) the natural variability of homogeneous snow terminal fall velocity. It is shown that, when periods of homogeneous characteristics of snow are selected to minimize the mixture of particles of different origin, the standard deviation of snowfall velocity within each period tends to stabilize at a value between 0.1 and 0.2 m s−1.

In addition, the variability of snow terminal fall velocity is examined with three control variables: surface temperature Ts, echo-top temperature Tt, and the depth of precipitation system H. The results show that the exponent b in the power-law relationship V = aDb has little effect on the variability of snowfall velocity: the coefficient a correlates much better with the control variables (Ts, Tt, H) than the exponent b. Hence, snowfall velocity can be modeled with a varying coefficient a and a fixed exponent b = 0.18 (V = aD0.18) with good accuracy.

* Current affiliation: University of Miami, Miami, Florida

+ Previous affiliation: McGill University, Montreal, Quebec, Canada

Corresponding author address: Isztar Zawadzki, Department of Atmospheric and Oceanic Studies, McGill University, 805 Sherbrooke St. West, Montreal, Quebec H3A 2K6, Canada. Email: isztar.zawadzki@mcgill.ca

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