Abstract:

In order to reveal the dynamic characteristics of water and heat flux, the response to meteorological factors and the characteristics of energy balance process of farmland ecosystem in northern China, based on the observation data of water and heat fluxes in 2015 and 2018-2019 of Yushu maize farmland ecosystem observation station, the characteristics of hourly, daily, monthly and interannual variation of water and heat fluxes in Yushu maize fields were analyzed, and the F_l (latent heat flux) and F_s (sensible heat flux) affected by temperature, precipitation, sunshine and other meteorological factors were analyzed. The seasonal changes of soil moisture content, water and heat flux and precipitation were compared, and the distribution of F_l, F_s and precipitation in each year was compared and analyzed in detail. In order to get the seasonal distribution of each variable and the variation characteristics of precipitation process, in addition, the diurnal and seasonal changes of net radiation and soil heat flux were analyzed, and the seasonal changes of soil heat flux and soil water content were compared. Finally, the seasonal and diurnal variations of the energy balance variables and the energy closure are analyzed. The results show that the diurnal variation of water and heat flux is a single peak quadratic curve, and the peak appears at noon (F_l: 229.2 W∙m^-2, F_s: 148.0 W∙m^-2). The annual variation of latent heat shows a single peak type, and the annual variation of sensible heat shows a double peak type, of which the highest values are, 114.3 W∙m^-2 (F_l), 51.7 W∙m^-2 (F_s). The diurnal and annual changes of net radiation and soil heat flux are similar to that of water and heat flux, but the peak of net radiation appears earlier and the peak of soil heat flux lags behind. The annual variation of F_l is positively correlated with temperature and precipitation, and negatively correlated with atmospheric pressure. Both F_l and F_s has significant responses to precipitation, and F_l is more sensitive to precipitation, but continuous precipitation has a hindrance to F_s. The equilibrium analysis of various energy terms shows energy unclosed phenomenon. At the same time, there are obvious diurnal and annual changes in the situation of energy unclosed. Summer is better than winter, and day is better than night. The average energy closure ratio reaches 83% in July and more than 89% in the daytime in September.

Key words: maize farmland, latent heat flux, sensible heat flux, meteorological factors, energy change, Yushu City

摘要：

为揭示中国北方农田生态系统的水热通量动态特征及其对气象因子的变化响应和能量平衡过程特征,利用榆树市玉米农田生态系统观测站2015年、2018—2019年水热通量观测数据,分别对榆树市玉米农田水热通量的小时、日、月份、年际变化特征,潜热通量（F_l）、感热通量（F_s）受气温、降水、日照等气象因子的相关影响,土壤含水量、水热通量的季节变化和降水,各年份F_l、F_s和降水的分布情况进行了详细的分析,以得出各变量的季节分布和降水过程中的变化特征;还对净辐射、土壤热通量的日变化和季节变化,土壤热通量和土壤含水量的季节变化进行对比分析;最后对能量平衡中各项能量的季节变化、日变化,以及能量闭合情况进行分析。结果表明,水热通量的日变化呈单峰型二次曲线,峰值出现在正午,其中F_l为229.2 W∙m^-2,F_s为148.0 W∙m^-2。潜热年变化呈单峰型,显热年变化呈双峰型,F_l、F_s最高值分别为114.3、51.7 W∙m^-2。净辐射和土壤热通量的日变化和年变化都和水热通量相似,但是净辐射峰值出现的时间提前,土壤热通量峰值出现的时间滞后。F_l的年变化与气温、降水呈正相关,与气压呈负相关。F_l和F_s对降水过程都有显著的响应,F_l对降水的反应更加敏感,而连续的降水对F_s有阻碍作用。各种能量项的平衡分析呈现能量不闭合现象,同时能量不闭合情况表现有明显的日变化和年变化,夏季好于冬季,白天好于夜间。7月平均能量闭合比率达到83%,9月白天的能量闭合度达到89%以上。

关键词: 玉米农田, 潜热通量, 感热通量, 能量变化, 气象因子, 榆树市