Diurnal asymmetry of surface albedo in a semi-arid grassland over the China's Loess Plateau

IF 2 4区 地球科学 Q3 METEOROLOGY & ATMOSPHERIC SCIENCES
Di Zhu, Jianrong Bi, Xiting Wang, Zhaozhao Meng, Jinsen Shi, Oufan Li
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Abstract

In current land surface models or satellite remote sensing retrievals, clear-sky surface albedo (α) is usually assumed to be symmetrical and relies only on the solar elevation angle (SEA). Based on 1-min high-resolution measurements of surface radiation fluxes, this study demonstrated that the diurnal variations of clear-sky surface albedo exhibited a significant asymmetrical pattern in both summer and winter seasons over a semi-arid grassland of the China's Loess Plateau. The results indicated that α values in the morning were generally larger than those in the afternoon at the same SEA, and diurnal asymmetry of surface albedo was distinctly prominent with SEA <40° in summer (before 9:30 a.m.) or SEA <20° in winter (before 10:00 am), and tended to diminish at midday. The averaged morning/afternoon albedo differences under sunny days were 0.05 (30.4%) and 0.09 (37.8%) in summer and winter seasons, respectively. Air relative humidity was positively correlated with the diurnal asymmetry of surface albedo, ascribed to probable formation of dew in the morning. Depression of the dew point was negatively linked to the morning/afternoon albedo differences, which was attributed to the strong scattering of incident sunlight by dewdrops could enhance the morning surface albedo. Such diurnal asymmetry of surface albedo should be included in the parameterization scheme of mesoscale and region-scale climate models in the semi-arid areas of China's Loess Plateau.

Abstract Image

中国黄土高原半干旱草原地表反照率的日非对称性
在目前的地表模型或卫星遥感检索中,晴空表面反照率(α)通常被假定为对称的,并且仅依赖于太阳仰角(SEA)。本研究基于 1 分钟高分辨率地表辐射通量测量结果,证明在中国黄土高原半干旱草原上,晴空地表反照率的昼夜变化在夏季和冬季均表现出明显的非对称模式。结果表明,在相同的海拔高度下,上午的α值一般大于下午的α值;夏季海拔高度为40°(上午9:30之前)或冬季海拔高度为20°(上午10:00之前)时,地表反照率的昼夜不对称现象明显突出,而到了中午则趋于减弱。夏季和冬季晴天上午/下午的平均反照率差异分别为 0.05 (30.4%) 和 0.09 (37.8%)。空气相对湿度与地表反照率的昼夜不对称呈正相关,这是因为露水可能在早晨形成。露点的降低与上午和下午的反照率差异呈负相关,这是因为露珠对入射阳光的强烈散射会提高上午的地表反照率。这种地表反照率的昼夜不对称应纳入中国黄土高原半干旱地区中尺度和区域尺度气候模式的参数化方案中。
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来源期刊
Atmospheric Science Letters
Atmospheric Science Letters METEOROLOGY & ATMOSPHERIC SCIENCES-
CiteScore
4.90
自引率
3.30%
发文量
73
审稿时长
>12 weeks
期刊介绍: Atmospheric Science Letters (ASL) is a wholly Open Access electronic journal. Its aim is to provide a fully peer reviewed publication route for new shorter contributions in the field of atmospheric and closely related sciences. Through its ability to publish shorter contributions more rapidly than conventional journals, ASL offers a framework that promotes new understanding and creates scientific debate - providing a platform for discussing scientific issues and techniques. We encourage the presentation of multi-disciplinary work and contributions that utilise ideas and techniques from parallel areas. We particularly welcome contributions that maximise the visualisation capabilities offered by a purely on-line journal. ASL welcomes papers in the fields of: Dynamical meteorology; Ocean-atmosphere systems; Climate change, variability and impacts; New or improved observations from instrumentation; Hydrometeorology; Numerical weather prediction; Data assimilation and ensemble forecasting; Physical processes of the atmosphere; Land surface-atmosphere systems.
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