A Comparison of the Diel Cycle of Modeled and Measured Latent Heat Flux During the Warm Season in a Colorado Subalpine Forest
A Comparison of the Diel Cycle of Modeled and Measured Latent Heat Flux During the Warm Season in a Colorado Subalpine Forest
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DOI：
10.1002/2017ms001248
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发表时间：
2018-03-01
影响因子：
6.8
通讯作者：
Blanken, Peter D.
中科院分区：
文献类型：
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作者：
Burns, Sean P.;Swenson, Sean C.;Blanken, Peter D.
降水改变了生态系统的生理特性。由于陆面模式经常用于预测水文循环的变化，模拟降水对潜热通量λ E的影响是陆面模式的一个重要方面。在这里，我们对比有条件采样昼夜复合材料的涡协方差通量从尼沃特岭亚高山森林AmeriFlux塔与社区土地模型（CLM，版本4.5）。关于暖季期间测量的λ E：在高于平均降水量的第二天，中午λ E增加了约40 W m（-2）（相对于干燥条件），夜间λ E从干燥条件下的约10 W m（-2）增加到潮湿条件下的20 W m（-2）以上。使用默认设置，CLM4.5无法成功地对这些更改进行建模。通过增加雨水被树冠/针叶保留的时间，CLM能够匹配在潮湿的一天后的干燥的一天中午观察到的λ E的增加。稳定的夜间条件对CLM4.5来说是个问题。夜间CLM λ E只有一个小的（约3 W m（-2））增加，在潮湿的条件下，CLM夜间摩擦速度u（*）小于观察到的u（*），CLM冠层空气温度是2摄氏度低于在现场测量。使用观测到的u（*）作为CLM的输入增加了λ E;然而，这导致CLM λ E在潮湿和干燥时期都增加。我们认为，倾斜的地形和始终存在的排水流增强夜间u（*）和λ E。这种现象不能被地形盲陆面模式（如CLM）正确捕捉。
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 lambda E 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 lambda E during the warm season: for the day following above-average precipitation, lambda E was enhanced at midday by approximate to 40 W m(-2) (relative to dry conditions), and nocturnal lambda E increased from approximate to 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 lambda E on a dry day following a wet day. Stable nighttime conditions were problematic for CLM4.5. Nocturnal CLM lambda E had only a small (approximate to 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 degrees C less than those measured at the site. Using observed u(*) as input to CLM increased lambda E; however, this caused CLM lambda E to be increased during both wet and dry periods. We suggest that sloped topography and the ever-present drainage flow enhanced nocturnal u(*) and lambda E. Such phenomena would not be properly captured by topographically blind land-surface models, such as CLM.