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[1] Recent reductions in both the aerial extent and thickness of sea ice have focused attention on the effect climate change is having on the polar marine system. Concomitant with a reduction in sea ice has been an increased frequency of low-pressure depressions at high latitudes. Recent studies have shown that we can expect both increased in situ cyclogenesis and advection into the arctic region. Since theses cyclones are associated with warm air advection, increased wind speed, relative humidity, and cloud cover, their impact on snow surface energy balance may be significant. The thermophysical response of snow-covered first-year sea ice to a low-pressure disturbance is investigated along with its impact on surface-based radiometer brightness temperature measurements. The data were collected during the Canadian Arctic Shelf Exchange Study (CASES) between year days 33 and 34 of 2004. Snow grain size increased throughout the sampling period with growth rates of 1.28 and 2.3 mm 2 d À1 for thin and thick snow covers, respectively. This rate was much faster than expected on the basis of other similar experiments documented in the literature. Furthermore, brine volume migrated upward in both snowpacks owing to the action of wind pumping affecting the dielectric constant of the snow middle layers. This increase in permittivity caused a decrease in brightness temperatures at 85 GHz of approximately 5 K and 10 K in the vertical and horizontal polarizations, respectively. This signal is sufficiently large to impact interpretation of passive microwave signatures from space.Citation: Langlois, A., T. Fisico, D. G. Barber, and T. N. Papakyriakou (2008), Response of snow thermophysical processes to the passage of a polar low-pressure system and its impact on in situ passive microwave radiometry: A case study,