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干旱区近地表水汽特征及其对凝结水发生的响应

Near-surface water vapor dynamics and its response to condensation events in arid regions

  • 摘要: 为探明干旱地区近地表水汽特征及凝结水发生过程水汽动态,选取沙漠边缘(TD)、干旱区(CANX)和半干旱区(SANX)3种地理条件作为研究对象,采用流体静力学积分法计算了近地表水汽通量和水汽含量,用叶片湿度传感器测算了地上5 cm处凝结水量:分析了水汽时空特征、凝结水发生过程和无凝结水昼夜水汽动态。结果表明:观测时段TD、CANX和SANX年均凝结水量分别为13.35、22.68和32.80 mm,差异显著(P<0.05)。3个测站水汽通量、水汽含量差异显著(P <0.05),SANX水汽通量、水汽含量峰值在7月,TD和CANX在8月,TD、CANX和SANX最大月平均水汽通量分别为21.2、19.4 和13.9 kg/(m·s),最大月平均水汽含量分别为11.23、11.35和13.69 mm。水汽传输具有特定的风向,TD为0°~60°和150°~210°、CANX为180°~240°、SANX为0°~30°、120°~240°和300°~359°。凝结水发生时,水汽通量、水汽含量呈下降趋势,凝结水量与水汽含量呈负相关(P <0.05);凝结水消散阶段,水汽通量、水汽含量呈增加趋势。无凝结水发生昼夜,水汽通量先降低后增加,水汽含量呈增加趋势。研究结果对于揭示不同地理条件近地表水汽特征和用近地表水汽动态推断凝结水发生过程具有参考价值。

     

    Abstract: Near-surface water vapor condensation is one of the most crucial steps to fully utilize atmospheric water sources in ecological agriculture. It is often required to clarify the dynamic relationship between near-surface water vapor and condensation. This study aims to investigate near-surface water vapor dynamics and their response to condensation events in arid regions. Three geographical conditions of northwest China were selected to capture the meteorological parameters, including the southeast margin of the Tengger Desert (TD), the arid belt of the center in Ningxia Hui Autonomous Region (CANX), and the semi-arid region in Ningxia Hui Autonomous Region (SANX). The hydrostatic integration was employed to calculate water vapor flux and content within a 100 m range above ground at each observation point, based on the evolution patterns of meteorological factors with hight at the Yinchuan radiosonde station. The leaf wetness sensor of PHYTOS31 was used to calculate the condensation water amount at 5 cm above ground. A correlation analysis was performed on the water vapor, condensation water, and meteorological parameters. The results indicate that there were significant differences in annual total condensation water at TD, CANX, and SANX sites (P<0.05), with annual averages of 13.35, 22.68, and 32.80 mm, respectively, during the observation period. Spatiotemporal variations in water vapor flux and content were significant (P <0.05) at all three stations, thus peaking in summer and declining in winter. Minimum monthly water vapor flux at TD, CANX, and SANX were 1.9, 2.3, and 1.8 kg/(m·s), respectively, while minimum monthly water vapor content was 1.3, 1.45, and 1.60 mm, respectively. Peak water vapor flux and content occurred in July at SANX, and in August at TD and CANX. Water vapor flux was markedly higher at the southeast margin of the Tengger Desert and arid region than that in the semi-arid regions, with 21.2, 19.4, and 13.9 kg/(m·s) for the maximum TD, CANX, and SANX, respectively. The monthly average water vapor content was highest at the SANX site (13.69 mm), while those were 11.35 and 11.23 mm, respectively, at the TD and CANX sites. The primary wind direction ranges influencing water vapor flux and content at the three stations were: TD with 0°–60° and 150°–210°, CANX with 180°–240°, and SANX with 0°–30°, 120°–240°, and 300°–359°. In terms of a single condensation event, both water vapor flux and content decreased during the condensation accumulation phase, whereas there was an increase when the condensation dissipated. Condensation content showed a significant negative correlation with water vapor content (P<0.05). The correlation coefficients for TD, CANX, and SANX were −0.652, −0.751, and −0.722, respectively. Water vapor flux first decreased and then increased during the diurnal cycle without condensation, due to the absence of water vapor phase change. While water vapor content shared an increasing trend. Water vapor flux and content exhibited a significant negative correlation (P<0.05) during the process. These findings can also provide valuable insights to characterize near-surface water vapor dynamics under diverse geographical conditions.

     

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