The low-frequency conductivity of snow near the melting temperature

Abstract

Dielectric measurements of snow were carried out in the temperature range - 15° to 0°C and in the frequency range 50 Hz to 5 MHz. The snow samples (about 400 kg m-3 density) used were stored snow (average particle size: 2 mm) and hoar-frost (particle size: <1 to 5 mm). The frequency characteristics of dielectric parameters showed a dielectric dispersion (Davidson-Cole type) around 30 kHz and a low-frequency dielectric dispersion (Cole-Cole circular law type). The a.c. conductivity showed a dielectric dispersion around 30 kHz and two characteristic constant values in the frequency ranges above 1 MHz and below 100 Hz (the high-frequency conductivity σ∞ and the low-frequency conductivity σLOW). The low-frequency conductivity σLOW showed a peak at about -2°C. This behavior has never been noted by previous researchers. The σLOW showed an activation energy of about 1 eV below -5°C. This means that the σLOW is mainly caused by a surface conduction. The activation energy increased with increasing temperature above -5°C. This means that the σLOW in this temperature range is affected by the quasi-liquid layer on ice surfaces. The σLOW above -2°C decreased with increasing temperature. The apparently curious behavior near the melting temperature is attributed to the numerous free ice surfaces within the porous snow. This conclusion was reached because our measurements without the free ice surfaces showed no such conductivity peaks for solid polycrystalline ice samples and for snow samples soaked with kerosene in the cooling process.