绿洲内城镇气候效应的数值模拟

Numerical Simulation of the Climate Effect on Town in Oasis

利用数值模式MM5探讨了绿洲内的城镇以及城镇进一步扩大后对绿洲小气候的影响,模拟结果显示:在边长约50km的三角形绿洲内实际存在的远离绿洲中心的5km×4km的城镇,对绿洲小气候的影响较小;当城镇位于绿洲中心后,对绿洲小气候的影响将增强;城镇远离绿洲中心有利于绿洲的良性发展。当城镇范围扩大后,其对绿洲小气候的影响将变得明显,白天城镇上的辐合中心将减弱低层辐散的绿洲风强度,有利于绿洲周边荒漠暖干空气侵扰绿洲;向城镇辐合产生的上升运动,将使绿洲上的低层水汽向高空输送,加大水汽的损耗;绿洲内城镇的存在也升高了绿洲总体边界层高度,不利于水汽在低层的滞留;城镇的增大将不利于绿洲的良性发展。绿洲内的城镇增加相同的面积,横风向扩展城镇试验中城镇对绿洲冷岛效应的破坏强于城镇沿顺风向扩展。

Using the mesoscale numerical model MM5, the influence of the town and its increase to the oasis microclimate were studied. The simulated results showed that for the triangular oasis whose side length was about 50 km, the impact of the real town about 5 km×4 km which is far from the center of the oasis to the oasis microclimate was insignificant. When the town located at the center of the oasis, its influence to the oasis mieroclimate would be a little great. The town far from the center of oasis benefited the good development of the oasis. When the town was bigger, its influence became obvious, the convergence on the town would weaken the intensity of the divergent oasis breeze, which would benefit the invasion of the warm and dry air on desert on low levels into oasis. The updraft on the town would bring the vapor on low levels to high levels, and the loss of vapor would increase. The existence of the town made the boundary layer of oasis become deeper, which was unfavorable for the persistence of vapor at lower levels. All these prevented the sound development of the oasis. For the increase of the same area of the town,the breakage of the aggrandizement of the town along the cross wind was larger than that along the tail wind.