Wednesday, October 9, 2013

First snow accumulation since May

Telemetry from the Northern Ice Field shows a snowfall event last month, likely associated with the seasonal increase in humidity, the transition from dry season to the short rains. This was the first noteworthy, accumulating snow since early May.

Snow sensors indicate that the event began on 19 September and continued through the 27th. Averaging two series of measurements suggests 9-10 cm of accumulation. This snow isn't likely to persist, due to densification (settling) and ablation. The climate at this time of year remains quite dry and sunny, and several centimeters of surface lowering occurred on a single day, 5 October. Nonetheless, a 10 cm snowfall is sufficient to dramatically increase albedo and thus reduce the amount of solar radiation absorbed. The net effect is a reduction in the rate of ablation - for a period of perhaps weeks.

At the Northern Ice Field site where our measurements are concentrated, there has been effectively no net change in glacier thickness (mass balance) for 2 years; accumulation has balanced ablation. This will change if the 2013 short rains are delayed, as ablation can be rapid during October - November. We will visit the glaciers later this month, and are looking forward to seeing surface conditions and assessing the spatial variability of mass balance over the past year.

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