Diagnosing the Impacts of Northern Hemisphere Surface Albedo Biases on Simulated Climate
Diagnosing the Impacts of Northern Hemisphere Surface Albedo Biases on Simulated Climate
复制标题
诊断北半球表面反照率偏差对模拟气候的影响
作者：
C. Thackeray;C. Fletcher;C. Derksen
许多地球系统模型在积雪覆盖的表面的反照率的大小和季节周期方面存在重大偏差。各种结构和参数缺陷已被确定为这些反照率偏差的潜在原因，与植被分布和丰度、雪反照率以及森林冠层对雪的截留有关。然而，由于很难将反照率偏差与其他复杂的过程和反馈分开，人们对反照率偏差如何直接影响模拟气候知之甚少。在这项研究中，我们使用国家大气研究中心社区地球系统模型(CESM)进行了一些新的模拟，用来自观测或其他模型模拟的指定值取代了该模型的内表面反照率计算。结果表明，虽然地表反照率的偏差在冬季最大，但春季的偏差对地表气候的影响最大，因为入射的太阳辐射要强得多。在CESM中校正反照率季节周期的偏差可以减少春季北部地区的气候温度偏差，并部分校正北极海平面气压偏差，但由于补偿误差，总体气候偏差并不总是减少。此外，我们施加了从其他具有较大正负反照率偏差的气候模型中提取的反照率模式，以说明可能导致的气候响应。规定的地表反照率对地表辐射、近地表陆地温度以及更罕见的大气环流产生重大影响。这一点很重要，因为春季平均气候的微小变化可能会对积雪和地表辐射制度产生重大影响。
Many Earth system models contain substantial biases in the magnitude and seasonal cycle of the albedo of snow-covered surfaces. Various structural and parametric deficiencies have been identified as potential causes of these albedo biases, related to vegetation distribution and abundance, snow albedo, and the representation of snow interception by forest canopies. There is, however, little understanding of how the albedo biases directly influence simulated climate because of difficulties in isolating them from other complex processes and feedbacks. In this study, we conduct a number of novel simulations using the National Center for Atmospheric Research Community Earth System Model (CESM), replacing the model’s internal surface albedo calculation with values prescribed from observations or from other model simulations. Results show that while biases in surface albedo are largest in winter, those during spring have the greatest impact on surface climate because incoming solar radiation is much stronger. Correcting biases in the seasonal cycle of albedo in CESM reduces climatological temperature biases across the boreal region in spring and partially corrects Arctic sea level pressure biases, but due to compensating errors, overall climate biases are not always reduced. Additionally, we impose albedo patterns extracted from other climate models with large positive and negative albedo biases to illustrate the climate responses that can result. Prescribed surface albedo produces significant impacts on surface radiation, near-surface land temperatures, and, more rarely, atmospheric circulation. This is important because small changes to mean climate during spring can have major implications for the snow and surface radiation regimes.