The Loess Plateau, located in northern China, has a significant impact on the climate and ecosystem evolvement over the East Asian continent. In this paper, the preliminary autumn daily characteristics of land surface...The Loess Plateau, located in northern China, has a significant impact on the climate and ecosystem evolvement over the East Asian continent. In this paper, the preliminary autumn daily characteristics of land surface energy and water exchange over the Chinese Loess Plateau mesa region are evaluated by using data collected during the Loess Plateau land-atmosphere interaction pilot experiment （LOPEX04）, which was conducted from 25 August to 12 September 2004 near Pingliang city, Gansu Province of China. The experiment was carried out in a region with a typical landscape of the Chinese Loess Plateau, known as ＂loess mesa＂. The experiment＇s field land utilizations were cornfield and fallow farmland, with the fallow field later used for rotating winter wheat. The autumn daily characteristics of heat and water exchange evidently differed between the mesa cornfield and fallow, and the imbalance term of the surface energy was large. This is discussed in terms of sampling errors in the flux observations-footprint; energy storage terms of soil and vegetation layers; contribution from air advections; and low and high frequency loss of turbulent fluxes and instruments bias. Comparison of energy components between the mesa cornfield and the lowland cornfield did not reveal any obvious difference. Inadequacies of the field observation equipment and experimental design emerged during the study, and some new research topics have emerged from this pilot experiment for future investigation.展开更多
陆地表层水分的盈缺直接关系到局地气候变化。本文利用黄土高原塬区初夏至盛夏期两次陆面过程野外试验(LOess Plateau land surface process field EXperi ment 2005,LOPEX05和LOPEX06)的野外试验观测资料,分析了试验期间黄土高原白庙...陆地表层水分的盈缺直接关系到局地气候变化。本文利用黄土高原塬区初夏至盛夏期两次陆面过程野外试验(LOess Plateau land surface process field EXperi ment 2005,LOPEX05和LOPEX06)的野外试验观测资料,分析了试验期间黄土高原白庙塬区不同下垫面的水分蒸散和表层土壤水分盈缺状况。结果表明:在土壤水分比较充足的条件下,植被蒸腾增加量在正午时的峰值为0.05 mm.h-1,而较大降水发生后的首个晴日,冬小麦地和裸地的蒸散分别可达4.60 mm.d-1和3.70 mm.d-1。局地降水是影响陆面蒸散量变化的主要因素,而植被冠层的存在增加了陆面蒸散发量中的植物蒸腾量值。2006年4月下旬到7月中旬,裸地的水分缺失为16.3 mm.m-2,冬小麦地的水分缺失为39.9mm.m-2。其中缺失最严重的时间段为5月下旬到6月上旬,最大旬缺失量达16.5 mm.m-2,7月上旬和中旬,由于降水季节来临,土壤水分有少量盈余。在2005年7月中旬至8月下旬,玉米地和裸地的水分盈余分别为17.9 mm.m-2和25.3 mm.m-2。不同时间尺度的统计均表明,降水不仅是影响陆面蒸散量的主要因素,而且也是表层土壤水分盈缺的决定性因子。展开更多
文摘The Loess Plateau, located in northern China, has a significant impact on the climate and ecosystem evolvement over the East Asian continent. In this paper, the preliminary autumn daily characteristics of land surface energy and water exchange over the Chinese Loess Plateau mesa region are evaluated by using data collected during the Loess Plateau land-atmosphere interaction pilot experiment （LOPEX04）, which was conducted from 25 August to 12 September 2004 near Pingliang city, Gansu Province of China. The experiment was carried out in a region with a typical landscape of the Chinese Loess Plateau, known as ＂loess mesa＂. The experiment＇s field land utilizations were cornfield and fallow farmland, with the fallow field later used for rotating winter wheat. The autumn daily characteristics of heat and water exchange evidently differed between the mesa cornfield and fallow, and the imbalance term of the surface energy was large. This is discussed in terms of sampling errors in the flux observations-footprint; energy storage terms of soil and vegetation layers; contribution from air advections; and low and high frequency loss of turbulent fluxes and instruments bias. Comparison of energy components between the mesa cornfield and the lowland cornfield did not reveal any obvious difference. Inadequacies of the field observation equipment and experimental design emerged during the study, and some new research topics have emerged from this pilot experiment for future investigation.
文摘陆地表层水分的盈缺直接关系到局地气候变化。本文利用黄土高原塬区初夏至盛夏期两次陆面过程野外试验(LOess Plateau land surface process field EXperi ment 2005,LOPEX05和LOPEX06)的野外试验观测资料,分析了试验期间黄土高原白庙塬区不同下垫面的水分蒸散和表层土壤水分盈缺状况。结果表明:在土壤水分比较充足的条件下,植被蒸腾增加量在正午时的峰值为0.05 mm.h-1,而较大降水发生后的首个晴日,冬小麦地和裸地的蒸散分别可达4.60 mm.d-1和3.70 mm.d-1。局地降水是影响陆面蒸散量变化的主要因素,而植被冠层的存在增加了陆面蒸散发量中的植物蒸腾量值。2006年4月下旬到7月中旬,裸地的水分缺失为16.3 mm.m-2,冬小麦地的水分缺失为39.9mm.m-2。其中缺失最严重的时间段为5月下旬到6月上旬,最大旬缺失量达16.5 mm.m-2,7月上旬和中旬,由于降水季节来临,土壤水分有少量盈余。在2005年7月中旬至8月下旬,玉米地和裸地的水分盈余分别为17.9 mm.m-2和25.3 mm.m-2。不同时间尺度的统计均表明,降水不仅是影响陆面蒸散量的主要因素,而且也是表层土壤水分盈缺的决定性因子。
文摘基于陆面能量平衡原理,通过对搭载在欧洲空间局环境卫星(Environmental Satellite,ENVI-SAT)上中分辨率影像光谱仪(Medium Resolution Imaging Spectrometer,MERIS)2005年6月7,11和27日的遥感观测资料进行大气纠正等预处理后,得到估算瞬时蒸散发量所需要的地表反照率和植被覆盖度等值,并利用分裂窗法和ENVISAT上搭载的先进的沿轨迹扫描辐射计(Advanced Along-TrackScanning Radiometer,AATSR)的观测资料进行了地表温度的反演,进一步估算出黄土高原塬区午间瞬时净辐射、感热通量和土壤热通量。结合与卫星遥感观测资料同期研究区域气象站的太阳辐射、气温、日照时数和风速等气象要素资料,充分考虑到植被冠层和陆地表面对蒸散发量的不同影响,发展了一个可以估算陆面潜热的简化模型,并将瞬时蒸散发量转化为日蒸散发量。对卫星遥感估算的潜热通量,利用黄土高原塬区陆面过程野外观测试验(Loess Plateau land surface process field Experiments,LOPEXs)的地面通量观测资料进行验证,结果表明:二者最大相对差异为10.9%,最小相对差异为4.8%,并对差异误差产生的原因进行了分析和探讨。
