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Cooling and Moistening of the Planetary Boundary Layer in Interior Alaska Due to a Postfire Change in Surface Energy Exchange
Journal of Geophysical Research: Atmospheres ( IF 4.4 ) Pub Date : 2020-09-09 , DOI: 10.1029/2020jd032968
Masahito Ueyama 1 , Takahiro Yamamori 1 , Hiroki Iwata 2 , Yoshinobu Harazono 1
Affiliation  

Boreal forest fires can alter the surface energy exchange due to postfire land cover change, which influences the regional climate through changes in scalar budgets within the planetary boundary layer (PBL). In this study, we estimated the changes in potential temperature and moisture budgets within the convective boundary layer (CBL) associated with postfire changes in surface energy exchange in interior Alaska. We integrated 9 years of paired eddy covariance measurements at mature evergreen and postfire young forests, radiosonde observations, and a mixed‐layer slab model. The postfire increase in albedo and decreased Bowen ratio decreased the sensible heat flux and PBL height, resulting in cooling magnitudes in the CBL up to 3–5°C in spring months and smaller cooling magnitudes (0.4°C) in other months. The cooling in the CBL decreased at a rate 0.5°C yr−1 from 8 to 13 years after the fire via vegetation recovery but was still recognizable 13 years after the fire. The postfire change moistened the CBL in summer months due to the decreased PBL height and increased latent heat flux in the postfire young forest. Interactions between fire‐induced surface changes and PBL dynamics should be evaluated further for understanding long‐term climatic change and ecosystem responses to climate change.

中文翻译:

由于表面能交换的后火变化,阿拉斯加内部行星边界层的冷却和增湿

北方森林大火会由于火灾后的土地覆盖变化而改变表面能交换,这会通过行星边界层(PBL)内标量预算的变化影响区域气候。在这项研究中,我们估计了对流边界层(CBL)内潜在的温度和湿度预算的变化,该变化与阿拉斯加内部的表面能交换的后燃变化有关。我们在成熟的常绿和大火后的幼林中整合了9年的成对涡旋协方差测量,无线电探空仪观测和混合层平板模型。火灾后反照率的增加和Bowen比值的降低降低了显热通量和PBL高度,从而导致CBL在春季月份的冷却幅度高达3-5°C,而在其他月份则降低了冷却幅度(0.4°C)。-1在火灾后8至13年通过植被恢复恢复,但在火灾13年后仍可识别。夏季,由于火后幼林中PBL高度的降低和潜热通量的增加,篝火后的变化使CBL湿润。应进一步评估火灾引起的表面变化与PBL动力学之间的相互作用,以了解长期的气候变化和生态系统对气候变化的响应。
更新日期:2020-09-21
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