This study examined synoptic impacts on the occurrence of boundaries and their associated convection during summers from 2012 to 2016 over Hetao Irrigation District in North China, where there is a sharp vegetation contrast. Objective synoptic-pattern classification showed that boundary days, especially convective boundary days, were more frequent under a mid-troposphere high-pressure ridge or pre-trough pattern. Such patterns featured a warmer near-surface environment, stronger southerly winds, larger convective available potential energy (CAPE), and low-level moisture convergence. Relative to unfavorable patterns, boundaries under favorable patterns showed more apparent arid-area dependence, more dominant orientation along the line of vegetation contrast, more moved northward, formed and matured earlier, and triggered convection more dispersedly. Under each pattern, compared with nonboundary days, boundary days possessed higher near-surface temperatures and stronger ambient flows against the vegetation-contrast-induced circulations near the surface; plus, compared with nonconvective boundary days, convective boundary days possessed stronger updrafts, larger CAPE, and higher moisture and K index.

中文翻译：

---

对强烈植被对比区域中尺度边界及其相关对流发生的天气影响

本研究考察了 2012 年至 2016 年夏季植被对比鲜明的华北河套灌区边界及其相关对流发生的天气影响。客观天气型分类表明，边界日，尤其是对流边界日，在对流层中部高压脊或槽前模式下更为频繁。这种模式的特点是近地表环境较暖、南风较强、对流可用势能 (CAPE) 较大以及低层水汽辐合。相对于不利模式，有利模式下的边界对干旱地区的依赖更明显，沿植被对比线的主导方向更明显，向北移动更多，形成和成熟更早，引发对流更分散。在每种模式下，与非边界日相比，边界日具有更高的近地表温度和更强的环境流量，以对抗近地表植被对比引起的环流；另外，与非对流边界日相比，对流边界日上升气流更强，CAPE更大，水分和K指数也更高。