玛曲高寒草甸夏季近地层微气象和CO_2通量特征分析

Analysis of the near-surface micrometeorology and CO_2 flux over the Maqu alpine meadow in summer

利用2015年夏季玛曲高寒草甸观测资料,从中选取7月10个连续完整的观测日,分析了近地层气象要素、地表辐射和能量传输以及CO_2通量日变化特征。结果表明:夏季玛曲地区气温和比湿昼夜差异较大,最大温差为19.2℃,平均风速为2.7 m·s^(-1),风向以东风为主。晴天条件下向下短波辐射可达1 200 W·m^(-2)左右,平均地表反照率为0.22,均大于藏北那曲地区。净辐射峰值可达850 W·m^(-2)左右,陆-气间能量传输以潜热输送为主。10 d能量闭合度平均值为0.61,能量不平衡程度较大。夏季玛曲高寒草甸表现为"碳汇", CO_2通量平均值为-0.20 mg·m^(-2)·s^(-1),晴天碳吸收最大速率为-14.05 mg·m^(-2)·s^(-1),显著大于阴天,最大碳吸收时长为13 h, CO_2密度平均值为530.7 mg·m^(-3)。

For a better comprehension of the characteristics of the micrometeorology and CO2 flux in M aqu alpine meadow in the Yellow River source regions during summer,in-situ measured data in Zoige Plateau Wetlands Ecosystem Research Station w ere collected. The continuous and integrated surface and near-surface meteorological elements,such as ground surface radiation and albedo,energy balance and closure ratio,CO2 flux and density from July 4 to 13 in 2015 w ere collected,and their daily variations w ere analyzed. The analyses show that:The variation tendency of specific humidity is almost converse w ith that of air temperature,and both have significant difference betw een daytime and nighttime. Wind speed in daytime is larger than that in nighttime,and east w ind is the dominated w ind direction. Soil moisture show s a sustainable decrease during fine days. The peak value of dow nw ard shortw ave radiation reaches up to about 1 200 W·m-2,close to that in Lake Ngoring lakeside and larger than that in Nagqu. The daily averaged albedo is 0. 22,close to those in Lake Ngoring lakeside alpine meadow and northern Tibetan Plateau,and larger than those in Litang and Haibei alpine meadow. The peak value of the net radiation is about 850 W·m-2. There are negative ground heat flux,latent heat flux and sensible heat flux during nighttime. The energy transfer betw een land surface and atmosphere is dominated by latent heat.Otherw ise,the averaged energy closure ratio is 0. 61. The averaged CO2 flux and density over the M aqu alpine meadow are-0. 20 mg·m-2·s-1 and 530. 7 mg·m-3,respectively.