Nelson Institute Center for Climatic Research, University of Wisconsin-Madison, Madison, WI, 53706, USA.
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, 91109, USA.
Nat Commun. 2017 Nov 30;8(1):1873. doi: 10.1038/s41467-017-02021-1.
Classic, model-based theory of land-atmosphere interactions across the Sahel promote positive vegetation-rainfall feedbacks dominated by surface albedo mechanism. However, neither the proposed positive vegetation-rainfall feedback nor its underlying albedo mechanism has been convincingly demonstrated using observational data. Here, we present observational evidence for the region's proposed positive vegetation-rainfall feedback on the seasonal to interannual time scale, and find that it is associated with a moisture recycling mechanism, rather than the classic albedo-based mechanism. Positive anomalies of remotely sensed vegetation greenness across the Sahel during the late and post-monsoon periods favor enhanced evapotranspiration, precipitable water, convective activity and rainfall, indicative of amplified moisture recycling. The identified modest low-level cooling and anomalous atmospheric subsidence in response to positive vegetation greenness anomalies are counter to the responses expected through the classic vegetation-albedo feedback mechanism. The observational analysis further reveals enhanced dust emissions in response to diminished Sahel vegetation growth, potentially contributing to the positive vegetation-rainfall feedback.
传统的基于模型的萨赫勒土地-大气相互作用理论促进了以地表反照率机制为主导的正植被-降水反馈。然而，无论是提出的正植被-降水反馈还是其潜在的反照率机制，都没有使用观测数据令人信服地证明。在这里，我们提出了关于该地区提议的正植被-降水反馈在季节到年际时间尺度上的观测证据，并发现它与水分循环机制有关，而不是经典的基于反照率的机制。萨赫勒地区遥感植被绿色度在后期和后季风期的正异常有利于增强蒸散、可降水量、对流活动和降水，表明水分循环增强。与经典植被-反照率反馈机制所预期的相反，识别到的适度低空冷却和异常大气下沉是对正植被绿色度异常的响应。观测分析还进一步揭示了对萨赫勒植被生长减少的增强的尘埃排放，这可能有助于正植被-降水反馈。
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