A revisiting of the parametrization of downward longwave radiation in summer over the Tibetan Plateau based on high-temporal-resolution measurements
<p>The Tibetan Plateau (TP) is one of the research hot spots in the climate change research due to its unique geographical location and high altitude. Downward longwave radiation (DLR), as a key component in the surface energy budget, has practical implications for radiation budget and climate...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-04-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/20/4415/2020/acp-20-4415-2020.pdf |
| Summary: | <p>The Tibetan Plateau (TP) is one of the research hot spots in the climate change
research due to its unique geographical location and high altitude. Downward
longwave radiation (DLR), as a key component in the surface energy budget,
has practical implications for radiation budget and climate change. A
couple of attempts have been made to parametrize DLR over the TP based on
hourly or daily measurements and crude clear-sky discrimination methods.
This study uses 1 min shortwave and longwave radiation measurements at
three stations over the TP to parametrize DLR during summer months. Three
independent methods are used to discriminate clear sky from clouds based on
1 min radiation and lidar measurements. This guarantees the strict selection
of clear-sky samples that is fundamental for the parametrization of
clear-sky DLR. A total of 11 clear-sky and 4 cloudy DLR parametrizations are
examined and locally calibrated. Compared to previous studies, DLR
parametrizations here are shown to be characterized by smaller root-mean-square errors (RMSEs) and higher coefficients of determination (<span class="inline-formula"><i>R</i><sup>2</sup></span>).
Clear-sky DLR can be estimated from the best parametrization with a RMSE of
3.8 W m<span class="inline-formula"><sup>−2</sup></span> and <span class="inline-formula"><i>R</i><sup>2</sup>>0.98</span>. Systematic overestimation of
clear-sky DLR by the locally calibrated parametrization in one previous
study is found to be approximately 25 W m<span class="inline-formula"><sup>−2</sup></span> (10 %), which is very
likely due to potential residual cloud contamination on previous clear-sky
DLR parametrization. The cloud base height under overcast conditions is shown to
play an important role in cloudy DLR parametrization, which is considered
in the locally calibrated parametrization over the TP for the first time.
Further studies on DLR parametrization during nighttime and in seasons
except summer are required for our better understanding of the role of DLR
in climate change.</p> |
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| ISSN: | 1680-7316 1680-7324 |