高寒草甸生态系统水热通量观测—垭口站涡动相关仪（2015-2017)

该数据集包含了2015年1月1日至2017年12月31日的黑河水文气象观测网上游垭口站涡动相关仪观测数据。站点位于青海省祁连县，下垫面是高寒草甸。观测点的经纬度是100.2421, 38.0142N，海拔4148 m。涡动相关仪的架高3.2m，采样频率是10Hz，超声朝向是正北向，超声风速温度仪（CSAT3）与CO2/H2O分析仪（Li7500A）之间的距离是15cm。
涡动相关仪的原始观测数据为10Hz，发布的数据是采用Eddypro软件处理的30分钟数据，其处理的主要步骤包括：野点值剔除，延迟时间校正，坐标旋转（二次坐标旋转），频率响应修正，超声虚温修正和密度（WPL）修正等。同时对各通量值进行质量评价，主要是大气平稳性（Δst）和湍流相似性特征（ITC）的检验。对Eddypro软件输出的30min通量值也进行了筛选：（1）剔除仪器出错时的数据；（2）剔除降水前后1h的数据；（3）剔除10Hz原始数据中每30min内缺失率大于10%的数据；（4）剔除夜间弱湍流的观测数据（u*小于0.1m/s）。观测数据的平均周期为30分钟，一天48个数据，缺失数据标记为-6999。因仪器漂移等原因引起的可疑数据用红色字体标识。涡动相关仪在冬季夜间会出现缺电的现象导致数据缺失；当存储卡存储数据出现问题导致10Hz数据缺失时(1.12-3.14,10.7-12.31)，数据由采集器输出的30min通量数据替代。
发布的观测数据包括：日期/时间Date/Time，风向Wdir（°），水平风速Wnd（m/s），侧向风速标准差Std_Uy（m/s），超声虚温Tv（℃），水汽密度H2O（g/m3），二氧化碳浓度CO2（mg/m3），摩擦速度Ustar（m/s），奥布霍夫长度L（m），感热通量Hs（W/m2），潜热通量LE（W/m2），二氧化碳通量Fc（mg/(m2s)），感热通量的质量标识QA_Hs，潜热通量的质量标识QA_LE，二氧化碳通量的质量标识QA_Fc。感热、潜热、二氧化碳通量的质量标识分为三级（质量标识0:（Δst <30, ITC<30）; 1: （Δst <100, ITC<100）; 其余为2）。数据时间的含义，如0:30代表0:00-0:30的平均；数据以*.xls格式存储。
水文气象网或站点信息请参考Li et al. (2013)，观测数据处理请参考Liu et al. (2011)。

This dataset contains eddy covariance system observational data collected at the Yakou Station, upstream of the Heihe River Hydrometeorological Observation Network, from January 1, 2015 to December 31, 2017. The station is located in Qilian County, Qinghai Province, with an underlying surface of alpine meadow. The geographic coordinates of the observation site are 100.2421, 38.0142°N, and the elevation is 4148 m. The eddy covariance system was installed at a height of 3.2 m, with a sampling frequency of 10 Hz. The ultrasonic transducer was oriented towards true north, and the distance between the ultrasonic anemometer-thermometer (model CSAT3) and the CO2/H2O analyzer (model Li7500A) was 15 cm.

The raw observational data from the eddy covariance system is at 10 Hz, while the released data are 30-minute averaged data processed using EddyPro software. The main processing steps include: outlier removal, delay time correction, coordinate rotation (double coordinate rotation), frequency response correction, ultrasonic virtual temperature correction, and WPL density correction. Meanwhile, quality assessments were conducted for each flux value, mainly including tests of atmospheric stability (Δst) and turbulence similarity characteristics (ITC). The 30-minute flux values output by EddyPro software were further screened according to the following criteria: (1) Remove data collected during instrument malfunctions; (2) Remove data within 1 hour before and after precipitation events; (3) Remove data with a missing rate greater than 10% in the 10 Hz raw data within each 30-minute period; (4) Remove nighttime weak turbulence observational data (u* < 0.1 m/s). The average period of the observational data is 30 minutes, with 48 data points per day. Missing data are marked as -6999. Suspicious data caused by instrument drift and other reasons are marked in red font. Data missing due to power outages at night in winter from the eddy covariance system, or missing 10 Hz data caused by memory card storage issues (January 12 – March 14, October 7 – December 31) are replaced by 30-minute flux data output by the data logger.

The released observational data include: Date/Time, wind direction Wdir (°), horizontal wind speed Wnd (m/s), lateral wind speed standard deviation Std_Uy (m/s), ultrasonic virtual temperature Tv (℃), water vapor density H2O (g/m³), carbon dioxide concentration CO2 (mg/m³), friction velocity Ustar (m/s), Obukhov length L (m), sensible heat flux Hs (W/m²), latent heat flux LE (W/m²), carbon dioxide flux Fc (mg/(m²s)), quality flag of sensible heat flux QA_Hs, quality flag of latent heat flux QA_LE, and quality flag of carbon dioxide flux QA_Fc. The quality flags for sensible heat, latent heat, and carbon dioxide fluxes are divided into three levels: Flag 0: (Δst < 30, ITC < 30); Flag 1: (Δst < 100, ITC < 100); all others are Flag 2. The meaning of the data timestamp: for example, 0:30 represents the average over the period 0:00–0:30. The data are stored in *.xls format.

Please refer to Li et al. (2013) for information on the hydrometeorological network and the station, and Liu et al. (2011) for the observational data processing procedures.