Horizontal and Vertical Turbulent Fluxes Forced by a Gravity Wave Event in the Nocturnal Atmospheric Surface Layer Over the Amazon Forest
Horizontal and Vertical Turbulent Fluxes Forced by a Gravity Wave Event in the Nocturnal Atmospheric Surface Layer Over the Amazon Forest
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亚马逊森林夜间大气表层重力波事件造成的水平和垂直湍流通量
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发表时间：
2011
期刊：
影响因子：
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通讯作者：
L. Sá
中科院分区：
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作者：
Marcelo Zeri;L. Sá
2002 年 10 月干湿季活动期间，在亚马逊地区进行大规模生物圈-大气实验 (LBA) 期间，在亚马逊西南森林上空检测到夜间重力波。根据摩擦速度值，大气表面层分层稳定，湍流活动较低。然而，波的通过（周期约为 180-300 秒）引起了二氧化碳 (CO2) 的负湍流通量和正感热通量，如通过 60 m（树顶上方约 30 m）处的涡协方差系统测量的。波浪运动过程中气温、比湿度和风速垂直剖面的演变表明，寒冷和干燥的空气占据了亚冠层空间，而植被上方测量到了高风速。使用小波技术对风速和标量高频数据进行分析，该技术能够在数据采样条件允许的几个频率下分解信号。结果表明，在波的传播过程中，垂直速度和空气温度的时间序列存在-90°的异相，这意味着没有直接的垂直热量传输。同样，垂直速度和 CO2 浓度的时间序列也存在 90° 的异相。该波与该变量的垂直通量没有直接关系，但其通过引起的混合导致了涡协方差系统测量的较小尺度的显着交换。水平速度与气温和CO2浓度之间的相位差分别为零和180°，这意味着相位和反相位关系。结果，波浪导致了正水平热通量和负水平二氧化碳通量。为了建模目的，必须在夜间边界层表面大气交换方案中考虑此类结果。
A nocturnal gravity wave was detected over a south-western Amazon forest during the Large-Scale Biosphere–Atmosphere experiment in Amazonia (LBA) in the course of the dry-to-wet season campaign on October 2002. The atmospheric surface layer was stably stratified and had low turbulence activity, based on friction velocity values. However, the passage of the wave, an event with a period of about 180–300 s, caused negative turbulent fluxes of carbon dioxide (CO2) and positive sensible heat fluxes, as measured by the eddy-covariance system at 60 m (≈30 m above the tree tops). The evolution of vertical profiles of air temperature, specific humidity and wind speed during the wave movement revealed that cold and drier air occupied the sub-canopy space while high wind speeds were measured above the vegetation. The analysis of wind speed and scalars high frequency data was performed using the wavelet technique, which enables the decomposition of signals in several frequencies allowed by the data sampling conditions. The results showed that the time series of vertical velocity and air temperature were −90° out of phase during the passage of the wave, implying no direct vertical transport of heat. Similarly, the time series of vertical velocity and CO2 concentration were 90° out of phase. The wave was not directly associated with vertical fluxes of this variable but the mixing induced by its passage resulted in significant exchanges in smaller scales as measured by the eddy-covariance system. The phase differences between horizontal velocity and both air temperature and CO2 concentration were, respectively, zero and 180°, implying phase and anti-phase relationships. As a result, the wave contributed to positive horizontal fluxes of heat and negative horizontal fluxes of carbon dioxide. Such results have to be considered in nocturnal boundary-layer surface-atmosphere exchange schemes for modelling purposes.