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A Comparison of the Diel Cycle of Modeled and Measured Latent Heat Flux During the Warm Season in a Colorado Subalpine Forest
Journal of Advances in Modeling Earth Systems ( IF 6.8 ) Pub Date : 2018-03-08 , DOI: 10.1002/2017ms001248
Sean P. Burns 1, 2 , Sean C. Swenson 2 , William R. Wieder 2, 3 , David M. Lawrence 2 , Gordon B. Bonan 2 , John F. Knowles 3, 4 , Peter D. Blanken 1
Affiliation  

Precipitation changes the physiological characteristics of an ecosystem. Because land‐surface models are often used to project changes in the hydrological cycle, modeling the effect of precipitation on the latent heat flux λE is an important aspect of land‐surface models. Here we contrast conditionally sampled diel composites of the eddy‐covariance fluxes from the Niwot Ridge Subalpine Forest AmeriFlux tower with the Community Land Model (CLM, version 4.5). With respect to measured λE during the warm season: for the day following above‐average precipitation, λE was enhanced at midday by ≈40 W m−2 (relative to dry conditions), and nocturnal λE increased from ≈10 W m−2 in dry conditions to over 20 W m−2 in wet conditions. With default settings, CLM4.5 did not successfully model these changes. By increasing the amount of time that rainwater was retained by the canopy/needles, CLM was able to match the observed midday increase in λE on a dry day following a wet day. Stable nighttime conditions were problematic for CLM4.5. Nocturnal CLM λE had only a small (≈3 W m−2) increase during wet conditions, CLM nocturnal friction velocity u was smaller than observed u, and CLM canopy air temperature was 2°C less than those measured at the site. Using observed u as input to CLM increased λE; however, this caused CLM λE to be increased during both wet and dry periods. We suggest that sloped topography and the ever‐present drainage flow enhanced nocturnal u and λE. Such phenomena would not be properly captured by topographically blind land‐surface models, such as CLM.

中文翻译:

科罗拉多亚高山森林暖季期间模型潜热通量和实测通量的Diel周期比较

降水改变了生态系统的生理特征。由于通常使用地表模型来预测水文循环的变化,因此对降水对潜热通量λE的影响进行建模是地表模型的重要方面。在这里,我们将来自Niwot Ridge亚高山森林AmeriFlux塔的涡流-协方差通量的有条件采样diel合成与社区土地模型(CLM,版本4.5)进行了对比。关于暖季期间测得的λE:在高于平均水平的降雨后的第二天,λE在中午增加≈40W m -2(相对于干旱条件),夜间λE从≈10W m -2增加干燥条件下,在潮湿条件下超过20 W m -2。使用默认设置,CLM4.5无法成功为这些更改建模。通过增加雨水被冠层/针保留的时间,CLM能够匹配在潮湿天后的干燥天所观察到的午间λE的增加。对于CLM4.5,稳定的夜间条件是有问题的。夜间CLM λE只有少量(≈3脉冲W M -2在潮湿条件下)的增加,CLM夜间摩擦速度ü *比观察到的更小的ù *,和CLM冠层空气温度为2℃小于那些在现场进行测量。使用观察到的u 作为CLM的输入增加了λE ; 但是,这导致CLMλE在潮湿和干燥时期都会增加。我们建议,倾斜的地形和不断出现的排水流量会增强夜间u λE。诸如CLM之类的地形盲目地表模型无法正确捕获此类现象。
更新日期:2018-03-08
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