Synoptic-Scale and Mesoscale Environments Conducive to Forest Fires during the October 2003 Extreme Fire Event in Southern California
Synoptic-Scale and Mesoscale Environments Conducive to Forest Fires during the October 2003 Extreme Fire Event in Southern California
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DOI：
10.1175/2008jamc1818.1
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发表时间：
2009-03-01
影响因子：
3
通讯作者：
Charney, J. J.
中科院分区：
文献类型：
--
作者：
Huang, Chenjie;Lin, Y. -L.;Charney, J. J.
本研究利用观测资料和数值模拟结果诊断的天气尺度和中尺度环境，有利于森林火灾在2003年10月的极端火灾事件在南加州。提出了一个三阶段过程来说明观测中明显的天气尺度强迫，特别是高压脊和高空急流条纹，导致其出口区域的中α尺度沉降，以及数值模式模拟的中尺度强迫，特别是波浪破碎和湍流以及波浪引起的临界水平，这导致严重的下坡（圣安娜）风。数值模拟显示，在加州南部，有两股干燥空气到达地面。第一次干空气高潮是由于地面冷锋后水汽辐散和等压面调整的结果。第二次干燥空气潮到达加州南部，因为中α到中β尺度的沉降和海岸山脉上波浪引起的临界水平分阶段将干燥空气从上层急流出口区域输送到地面，并将干燥空气混合到加州南部海岸山脉背风侧的行星边界层。背风面的破波区作为内边界将山波能量反射回地面，并通过与向上传播的山波的部分共振产生严重的下坡风。
This study has employed both observational data and numerical simulation results to diagnose the synoptic-scale and mesoscale environments conducive to forest fires during the October 2003 extreme fire event in southern California. A three-stage process is proposed to illustrate the coupling of the synoptic-scale forcing that is evident from the observations, specifically the high pressure ridge and the upper-level jet streak, which leads to meso-alpha-scale subsidence in its exit region, and the mesoscale forcing that is simulated by the numerical model, specifically the wave breaking and turbulence as well as the wave-induced critical level, which leads to severe downslope (Santa Ana) winds. Two surges of dry air were found to reach the surface in southern California as revealed in the numerical simulation. The first dry air surge arrived as a result of moisture divergence and isallobaric adjustments behind a surface cold front. The second dry air surge reached southern California as the meso-alpha-to meso-beta-scale subsidence and the wave-induced critical level over the coastal ranges phased to transport the dry air from the upper-level jet streak exit region toward the surface and mix the dry air down to the planetary boundary layer on the lee side of the coastal ranges in southern California. The wave-breaking region on the lee side acted as an internal boundary to reflect the mountain wave energy back to the ground and created severe downslope winds through partial resonance with the upward-propagating mountain waves.