半干旱区不同下垫面地气相互作用研究

【作者】 涂钢；

【导师】 董文杰； 刘辉志；

【作者基本信息】 中国科学院研究生院（大气物理研究所） ， 气象学， 2007， 博士

【摘要】 干旱、半干旱区占世界陆地面积的40%左右,半干旱区对气候变化和土地利用改变非常敏感,同时土地利用/覆盖、水资源利用方式的改变都将会影响半干旱区面积的扩大或者减少,因此研究半干旱区陆面过程对于研究全球变化、半干旱区可持续发展有重要意义。而目前对半干旱区陆面过程的认识远不如湿润、半湿润地区,同时目前陆面过程模式在半干旱区模拟效果不甚理想。通过分析2003～2005年连续3年在半干旱区退化草地和农田下垫面(CEOP地面基准站,通榆)采用涡动相关法(Eddy Covariance,简称EC)测得的地气间湍流通量以及太阳辐射和地表常规气象观测资料,研究半干旱区不同下垫面地气相互作用日、季、年际变化特征,给出了地表反照率、空气动力学参数、整体输送系数等陆面过程参数的变化规律,并且讨论了土壤湿度对地表反照率的影响;研究不同年份的气候背景主要是降水过程对不同下垫面地气交换过程的影响,试图探讨气候变化和不同土地利用对地气间能量和物质交换过程的影响。得到的主要结果有:(1)半干旱区的降水年际变化较大,一年中干、湿季分明,生长季(5～9月)降水占到全年降水量的89.0%,生长季降水年际变化以及生长季内月降水的分布差异都会影响地气间物质和能量交换。(2)地表粗糙度全年平均:草地0.0022;农田生长季0.046,非生长季0.0015。退化草地和农田下垫面的地表反照率具有相似的日变化和季节变化,冬季较大、夏季较小;地表反照率的日变化随天气条件的不同而不同;3年平均地表反照率,退化草地在春、夏、秋、冬季分别为0.25、0.22、0.24、0.32,农田在春、夏、秋、冬季则分别为0.25、0.21、0.22、0.33。地表反照率随着太阳高度角增加而减小;地表反照率也与土壤湿度有关,夏季地表反照率与表层土壤湿度为负指数关系。接近中性时的整体输送系数CDN在农田、退化草地分别为(4.9±2.1)×10—3、(2.6±1.4)×10—3;CHN在农田、退化草地分别为(3.59±1.9)×10—3、(2.62±1.6)×10—3。(3)退化草地和农田下垫面近地层辐射、能量平衡各分量具有很强的日变化、季节变化,但辐射平衡各分量年际变化(不同年份)不大,能量平衡各分量年变化形态年际间相似,其差异受当年的气候背景影响较大,主要是降水的影响。净辐射日均值的年变化有明显的方向转换期,潜热通量全年几乎没有方向的改变,感热通量在冬季会出现负值,地热在冬季基本为负值。潜热通量夏季最大,感热通量春季最大;地热流通量夏季最大。潜热和感热通量的分配比率都呈反位相的变化,且农田和退化草地的变化趋势相似,潜热通量所占比例(55%)只在夏季超过感热通量(20%);两种下垫面的波文比月均值变化趋势十分相似,量级接近,夏季低,春、秋季高;夏季退化草原和农田下垫面波文比均小于或等于1。(4)不同下垫面对水分循环的影响不同,生长季农田的蒸散量总是大于退化草地,水分亏缺趋势明显,而退化草地生长季水分略有盈余(2004年干旱,除外)。(5)降水量和降水年内月分布形态差异,直接影响土壤湿度、植被生长等,从而影响地气间的水分交换。前一年的土壤湿度对第二年的地气交换有一定的影响。春季蒸散对降水的响应非常显著,而在夏季蒸散对降水的响应叠加了植被的作用,而与土壤湿度的变化一致。CO2通量交换主要受地表植被生育期的影响比较大,对降水的直接响应不明显。更多还原

【Abstract】 Based on three years(2003～2005) of the eddy covariance (EC) observation over the semi-arid area (44°25′N, 122°52′E, 184m a.s.l) in Tongyu, Northeast China over the degraded grassland and the cropland surface, the seasonal and diurnal variations of the exchange of the water,energy and CO2 flux have been investigated. Tongyu observational station is also one of the reference sites of the CEOP(Coordinated Enhanced Observing Period ).The main results are in the following:1. The rainfall was strongly influenced by the land cover in the semiarid area and had strong heterogeneity in growing season (from May to September), especially during the convective weather system in summer.2. The latent heat flux is larger over the cropland surface than that over degraded land surface in the growing season, while in the non-growing season, their difference is very few. The sensible heat flux is the main part of the available energy except that in the growing season in the semiarid area. In the growing season the latent heat flux has the same order with the sensible heat flux. The net radiation flux has seasonal variation, while in winter is less than the half of that in summer. The soil heat flux at the ground surface over the cropland surface is smaller than that over the degraded grassland surface in the growing season. The available energy over the cropland surface is larger than that over the degraded grassland surface in the growing season. The available energy over the cropland surface is larger than that over the degraded grassland surface in the growing season, while in the non-growing season there is very little difference.3. The soil volumetric water content is less than 15% in the surface layer 0-20cm ) in the non-growing season. In the growing season the soil volumetric water content has a good correlation with the rainfall. The soil volumetric water content has a rapid increase during the snowmelt period. The soil water content in the thin soil layer(at 0.05m,0.10m and 0.20m) clearly indicated the pronounced annual wet-dry cycle. 4. The CO2 flux is less than 0.2 mg m-2s-1 over two ecosystems except the growing season . during the growing season, the carbon dioxide flux over the cropland ecosystem is a little larger than that over the degraded grassland ecosystem.5. The land surface parameters, such as surface roughness , surface albedo and bulk transfer coefficient, are determined for the cropland and the degraded grassland. And their seasonal variations and differences between the two land surface are also given.6. The results of water balance over the two land surface show that the water deficit over the cropland is obvious.更多还原