Boundary layer evolution and regional-scale diurnal circulations over the Mexico Basin and Mexican plateau
Boundary layer evolution and regional-scale diurnal circulations over the Mexico Basin and Mexican plateau
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墨西哥盆地和墨西哥高原的边界层演化和区域尺度日环流
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发表时间：
2007
期刊：
影响因子：
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通讯作者：
J. Doran
中科院分区：
文献类型：
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作者：
C. Whiteman;S. Zhong;X. Bian;J. Fast;J. Doran
在1997年2月和3月的测量活动中收集的数据表明，位于墨西哥高原顶部的墨西哥盆地（也称为墨西哥谷）没有发展出通常与盆地相关的强烈夜间逆温，也没有表现出昼夜逆转的谷风系统。数据分析，二维和三维数值模拟与区域大气模拟系统（RAMS），和拉格朗日粒子扩散模式被用来解释hese观测和研究地形和区域的昼夜环流对边界层演变的影响在墨西哥盆地及其周围地区在冬季干燥的好天气期间。我们发现，边界层的演变和以上的盆地主要是由区域的昼夜环流，墨西哥高原上方的空气和周围的沿海地区一般较冷之间的发展。对流边界层（CBL）的爆发性增长在高原上上午晚些时候达到海拔2250米（4500 rn rnsl）的中午，和一个强大的斜压区的边缘上形成的高原分离的温暖CBL空气从其较冷的环境。下午早些时候，由于冷空气泄漏到高原上，并通过通道和低洼高原边缘进入盆地，加热和CBL增长的速度减慢。然而，高原边缘平原-高原环流的强烈上升分支阻碍了流向高原的气流，特别是在有山脉或陡坡的地方。高原上空的空气在下午晚些时候和傍晚早些时候开始异常快速和深度冷却，此时地面能量收支逆转，CBL衰减，空气通过斜压区加速进入高原。在盆地底部附近的气流会聚和盆地和高原上的相关上升运动在3小时内产生冷却，相当于白天加热的一半。虽然汇聚到高原上的空气来自高原和高原以上的海拔高度，但这些空气在白天早些时候被平原高原环流带到高原斜坡上的凉爽，潮湿的沿海流入所改变。
Data collected in a measurement campaign in February and March 1997 showed that the Mexico Basin (also called the Valley of Mexico), located atop the Mexican plateau, fails to develop the strong nocturnal inversions usually associated with basins and does not exhibit diurnally reversing valley wind systems. Data analyses, twoand three-dimensional numerical simulations with the Regional Atmospheric Modeling System (RAMS), and a Lagrangian particle dispersion model are used to interpret hese observations and to examine the effects of topography and regional diurnal circulations on boundary layer evolution over the Mexico Basin and its surroundings during fair weather periods in the winter dry season. We show that the boundary layer evolution in and above the basin is driven primarily by regional diurnal circulations that develop between the air above the Mexican Plateau and the generally cooler surrounding coastal areas. A convective boundary layer (CBL) grows explosively over the plateau in the late morning to reach elevations of 2250 m agl (4500 rn rnsl) by noon, and a strong baroclinic zone forms on the edges of the plateau separating the warm CBL air from its cooler surroundings. In early afternoon the rates of heating and CBL growth are slowed as cool air leaks onto the plateau and into the basin through passes and over low-lying plateau edges. The flow onto the plateau is retarded, however, by the strongly rising branch of a plain-plateau circulation at the plateau edges, especially where mountains or steep slopes are present. An unusually rapid and deep cooling of the air above the plateau begins in late afternoon and early evening when the surface energy budget reverses, the CBL decays, and air accelerates onto the plateau through the baroclinic zone. Flow convergence near the basin floor and the associated rising motions over the basin and plateau produce cooling in 3 hours that is equivalent o half the daytime heating. While the air that converges onto the plateau comes from elevations at and above the plateau, it is air that was modified earlier in the day by a cool, moist coastal inflow carried up the plateau slopes by the plainplateau circulation.