土壤干旱化对短期气候影响的数值模拟

用加进了奥勒冈州立大学陆面模式(OSULSM)的美国PSU／NCAR第五代中尺度模式(MM5)进行了减少土壤含水量对短期气候影响的模拟试验,目的在于探讨我国北方干旱化对短期气候的影响。试验结果表明,对整个模拟区域月降水总量没有明显的影响,但对不同地区有明显的影响。对月降水量较大地区的影响表现为使月降水量有一定程度的减少,而对月降水量中等以下地区的影响则相反,使月降水量略有增加。分析结果表明,其原因是土壤含水量减少会造成地面潜热通量减少、感热通量增加和陆面温度增高,最后生成一个浅薄的偏差热低压。这个偏差热低压在对流层低层有偏差辐合上升气流与之相配合,在对流层中层以上则与偏差辐散下沉气流相伴。这对于浅薄的降水系统的发展是有利的,但对于强大而深厚的降水系统的发展则不利。

Numerical Simulation of the Effect of Soil Drought on Short-Term Climate in North China

Using the PSU NCAR fifth-generation mesoscale model (MM5) couple with an advanced land surface model(OSULSM), a numerical experiment of the effect of the decreased soil moisture on the short-term climate have been performed in order to better understand the influence of soil drought on the short-term climate in North China. The results from the experiment indicate: With the decrease of the soil moisture, the monthly mean rainfall (MMR) of the whole experimental domain is only slightly changed. But it results in the large MMR negative anomalies for the large MMR regions and the small MMR positive anomalies for the middle and small MMR regions. This is because the decreased soil moisture may produce a large, shallow anomaly depression due to the increase of surface sensible heat flux and surface skin temperature and the decrease of surface latent heat flux for the continent region. This anomaly depression with anomaly ascent flow in the lower troposphere and anomaly descent flow in the middle troposphere weakens the intense precipitation systems and intensifies the weak systems.