Human-induced changes in wind, temperature and relative humidity during Santa Ana events
Human-induced changes in wind, temperature and relative humidity during Santa Ana events
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DOI：
10.1007/s10584-011-0300-9
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发表时间：
2011-12-01
期刊：
影响因子：
4.8
通讯作者：
Kim, Jinwon
中科院分区：
文献类型：
--
作者：
Hughes, Mimi;Hall, Alex;Kim, Jinwon
南加州的圣安娜风事件的频率和特征进行了研究，在12公里分辨率下尺度的20世纪末和世纪中期的国家大气研究中心社区气候系统模型全球气候变化情景运行的时间段。世纪中期每个冬季的圣安娜天数比20世纪后期少约20%。由于这两个时期之间唯一的系统性和持续性差异是人为强迫的水平，因此这种影响是人为的。在这两个时间段，圣安娜风部分是由冬季寒冷的空气在沙漠中聚集在沿海山脉和邻近的海洋上空的温暖空气之间的温差驱动的。然而，这种下降机制在世纪中期明显减弱。这是因为有充分证据表明，与短暂的气候变化有关的差异变暖，沙漠内陆的变暖程度高于海洋。因此，造成圣安娜频率下降的机制源于气候对温室气体增加的响应的一个众所周知的方面，但如果没有中尺度大气动力学，就无法理解或模拟。除了在圣安娜频率的变化，我们调查在圣安娜期间的变化，在其他两个气象变量已知是相关的火灾天气条件-相对湿度和温度。我们发现相对湿度降低，温度升高。这两种变化都有利于火。同时考虑风、温度和相对湿度变化的火灾行为模型对于得出与圣安娜事件相关的未来火灾风险和增长的可靠结论是必要的。虽然我们的研究结果受到样本量相对较小的限制，但它们说明了由于合理的中尺度过程而引起的可观察和可解释的区域气候变化。
The frequency and character of Southern California's Santa Ana wind events are investigated within a 12-km-resolution downscaling of late-20th and mid-21st century time periods of the National Center for Atmospheric Research Community Climate System Model global climate change scenario run. The number of Santa Ana days per winter season is approximately 20% fewer in the mid 21st century compared to the late 20th century. Since the only systematic and sustained difference between these two periods is the level of anthropogenic forcing, this effect is anthropogenic in origin. In both time periods, Santa Ana winds are partly katabatically-driven by a temperature difference between the cold wintertime air pooling in the desert against coastal mountains and the adjacent warm air over the ocean. However, this katabatic mechanism is significantly weaker during the mid 21st century time period. This occurs because of the well-documented differential warming associated with transient climate change, with more warming in the desert interior than over the ocean. Thus the mechanism responsible for the decrease in Santa Ana frequency originates from a well-known aspect of the climate response to increasing greenhouse gases, but cannot be understood or simulated without mesoscale atmospheric dynamics. In addition to the change in Santa Ana frequency, we investigate changes during Santa Anas in two other meteorological variables known to be relevant to fire weather conditions-relative humidity and temperature. We find a decrease in the relative humidity and an increase in temperature. Both these changes would favor fire. A fire behavior model accounting for changes in wind, temperature, and relative humidity simultaneously is necessary to draw firm conclusions about future fire risk and growth associated with Santa Ana events. While our results are somewhat limited by a relatively small sample size, they illustrate an observed and explainable regional change in climate due to plausible mesoscale processes.