Black carbon in snow in the upper Himalayan Khumbu Valley, Nepal: observations and modeling of the impact on snow albedo, melting, and radiative forcing
International audience Black carbon (BC) in snow in the Himalayas has recently attracted considerable interest due to its impact on snow albedo, snow and glacier melting, regional climate and water resources. A single particle soot photometer (SP2) instrument was used to measure refractory BC (rBC)...
Published in: | The Cryosphere |
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Main Authors: | , , , , , , , , |
Other Authors: | , , , , , , , , , |
Format: | Article in Journal/Newspaper |
Language: | English |
Published: |
HAL CCSD
2015
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Subjects: | |
Online Access: | https://insu.hal.science/insu-01235700 https://insu.hal.science/insu-01235700/document https://insu.hal.science/insu-01235700/file/CRYOSPHERE%20Black%20carbon%20in%20snow%20in%20the%20upper%20Himalayan%20Khumbu%20Valley%20Nepal%20observations%20and%20modeling%20of%20the%20impact%20on%20snow%20albedo.pdf https://doi.org/10.5194/tc-9-1685-2015 |
Summary: | International audience Black carbon (BC) in snow in the Himalayas has recently attracted considerable interest due to its impact on snow albedo, snow and glacier melting, regional climate and water resources. A single particle soot photometer (SP2) instrument was used to measure refractory BC (rBC) in a series of surface snow samples collected in the upper Khumbu Valley, Nepal between November 2009 and February 2012. The obtained time series indicates annual cycles with maximum rBC concentrations before the onset of the monsoon season and fast decreases during the monsoon period. Detected concentrations ranged from a few up to 70 ppb with rather large uncertainties due to the handling of the samples. Detailed modeling of the snowpack, including the detected range and an estimated upper limit of BC concentrations, was performed to study the role of BC in the seasonal snowpack. Simulations were performed for three winter seasons with the snowpack model Crocus, including a detailed description of the radiative transfer inside the snowpack. While the standard Crocus model strongly overestimates the height and the duration of the seasonal snowpack, a better calculation of the snow albedo with the new radiative transfer scheme enhanced the representation of the snow. However, the period with snow on the ground without BC in the snow was still overestimated between 37 and 66 days, which was further diminished by 8 to 15 % and more than 40 % in the presence of 100 or 300 ppb of BC. Compared to snow without BC, the albedo is reduced on average by 0.027 and 0.060 in the presence of 100 and 300 ppb BC. While the impact of increasing BC in the snow on the albedo was largest for clean snow, the impact on the local radiative forcing is the opposite. Here, increasing BC caused an even larger impact at higher BC concentrations. This effect is related to an accelerated melting of the snowpack caused by a more efficient meta-morphism of the snow due to an increasing size of the snow grains with increasing BC concentrations. The ... |
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