A measurement of sea ice albedo over the southwestern Okhotsk Sea

In order to estimate sea ice albedo around the marginal sea ice zone of the southwestern Okhotsk Sea, we conducted the measurement of albedo aboard th e ice breaker Soya in early February of 1996 and 1997. Using upward and dow nward looking pyranometers mounted at the bow of the ship, we obtained albe do data. We also measured ice concentration and thickness quantitatively by a video analysis. The observations show a good correlation between albedo and ice concentration. From a linear regression, sea ice albedo (ice concen tration = 100 %) is estimated to be 0.64 +/- 0.03 at the 95 % confidence le vel. The developed snow grains on sea ice due to sea water and/or solar rad iation may be responsible for this somewhat lower value, compared with that over the snow-covered land fast ice in the polar region. Deviations of the observed values from this regression have a statistically significant corr elation with solar zenith cosine at the 99 % level, and with ice thickness at the 95 % level. The linear regression formula which predicts albedo is a lso derived as the variables of ice concentration and solar zenith cosine. Although the regression coefficients are both statistically significant, th e coefficient of ice concentration is much more significant in this formula than that of solar zenith cosine. The deviation of the observed albedo fro m this regression seems to be mainly caused by ice surface conditions rathe r than by ice thickness or cloud amount. All these results suggest that sno w cover on sea ice plays an important role in determining the surface albed o. We also did albedo observations of dark nilas with snow-free surface, they were estimated as 0.10 and 0.12 for ice thickness of 1 to 1.5 cm and 2 to 3 cm, respectively.