Data from: Characteristics and mechanisms of non-stationary turbulence in a megacity area

The observational data were collected from the 325-m meteorological tower in Beijing, China (39.58°N, 116.22°E) from January 1 to December 31, 2017. The site is surrounded by a typical urban landscape, including dense buildings and roads. The sonic anemometer (Model Windmaster Pro, Gill, UK) was equipped at 140 m to measure wind components and air temperature at a frequency of 10 Hz. According to the vertical structure of the urban boundary layer, the observation at 140 m can reflect the turbulence in the surface layer. After quality control and screening of the observation data, 7167 groups of 30-minute segments were retained.

## Description of the data and file structure

1. Turbulence_statistics includes the proportion of each atmospheric stability, and turbulence statistics as a function of non-stationary level. Columns represent non-stationary levels 1-9, and rows represent atmospheric stability (strongly unstable, weakly unstable, near-neutral, weakly stable, strongly stable conditions) and turbulence statistics (turbulent transport efficiency, momentum flux, TKE) respectively in order.

2. Absolute_flux_contribution includes the absolute-flux contribution of four quadrants. Columns 1-4 represent absolute-flux contribution (Q1-Q4, respectively), and the fifth column represents non-stationary levels.

3. fft_mean_overlap and f include energy spectra and natural frequency. The first layer of cells represents u and w variables, the second layer represents stability (unstable, near-neutral, stable conditions, respectively), and the third layer of cells represents the normalized energy spectrum under non-stationary levels.

4. case.zip includes the original turbulence time series for three cases.

本观测数据采集自中国北京325米气象塔（39.58°N，116.22°E），观测时段为2017年1月1日至2017年12月31日。该观测场周边为典型城市景观，包含密集建筑群与道路交通网络。研究于140米高度安装了超声风速仪（型号Windmaster Pro，英国Gill公司），以10赫兹的频率采集风速分量与气温数据。根据城市边界层垂直结构特征，140米高度的观测可反映近地面层的湍流运动。经质量控制与数据筛选后，最终保留7167组30分钟时长的观测片段。

数据与文件结构说明
1. 湍流统计（Turbulence_statistics）：包含各大气稳定度占比，以及以非平稳等级为自变量的湍流统计量。表格列对应非平稳等级1至9，行依次代表大气稳定度（强不稳定、弱不稳定、近中性、弱稳定、强稳定）与湍流统计量（湍流输送效率、动量通量、湍流动能(Turbulent Kinetic Energy, TKE)）。
2. 绝对通量贡献（Absolute_flux_contribution）：包含四个象限的绝对通量贡献值。第1至4列分别对应四个象限（Q1至Q4）的绝对通量贡献，第5列代表非平稳等级。
3. 快速傅里叶变换平均重叠度（fft_mean_overlap）与特征频率（f）：包含能谱与固有频率。数据数组分为三层：第一层对应u、w两个风速分量变量，第二层对应大气稳定度（依次为不稳定、近中性、稳定条件），第三层对应非平稳等级下的归一化能谱。
4. case.zip：包含三个典型案例的原始湍流时间序列数据。