边界层高度的不同诊断方法在京津冀及周边地区的适用性分析

Applicability Analysis of Different Diagnostic Methods for Boundary Layer Height in Beijing–Tianjin–Hebei Region and Its Surrounding Areas

利用2016~2021年京津冀及周边地区7个站的探空数据,分析了传统的位温梯度法、改进的位温梯度法、相对湿度梯度法、比湿梯度法和理查森数法5种大气边界层高度的诊断方法在京津冀及周边地区大气边界层高度计算的适用性。结果表明:5种方法计算的边界层高度差距在40~1000 m,传统的位温梯度法、相对湿度梯度法、比湿梯度法诊断的边界层高度普遍偏高,且存在较大的结构不确定性,理查森数法和改进的位温梯度法诊断的边界层高度偏低,前者的不确定性最小;5种方法在乐亭、北京、太原3个代表站得到的边界层高度具有明显的季节性和季节内差异,两种湿度法在乐亭呈现夏秋高、春冬低的特点,在北京和太原呈现春夏高、秋冬低的特点,其他3种方法在3个站均是春夏高、秋冬低的特点;相对湿度梯度法和比湿梯度法参数不确定性较大,传统的位温梯度法和改进的位温梯度法次之,理查森数法最小;在边界层高度计算结果月均值的时间一致性上,晚上各方法间的相关性明显高于白天,两种湿度法之间的相关系数始终最高,但与另外3种方法间的相关性均较差,理查森数法和改进的位温梯度法相关性较高,传统的位温梯度法因站点不同,与其他方法间的相关性波动较大。

Radiosonde data collected from seven stations in the Beijing–Tianjin–Hebei region and its surrounding areas from 2016 to 2021 were analyzed to assess the suitability of five different diagnostic methods for calculating the atmospheric boundary layer height.These include the traditional potential temperature gradient,improved potential temperature gradient,relative humidity gradient,specific humidity gradient,and Richardson number methods.The results show that the difference in the boundary layer height calculated by these five methods is between 40 and 1000 m.The boundary layer height determined using the traditional potential temperature gradient,relative humidity gradient,and specific humidity gradient methods is generally higher with large structural uncertainty.Meanwhile,the Richardson number method and improved potential temperature gradient method yield lower boundary layer heights,with the former presenting the least uncertainty.The boundary layer heights obtained with the five methods at the three representative stations of Laoting,Beijing,and Taiyuan exhibit obvious seasonal and intraseasonal differences.Among them,the two humidity-based methods present the characteristics of high boundary layer height in summer and autumn and low boundary layer height in spring and winter in Laoting.Meanwhile,they show high boundary layer height in spring and summer and low boundary layer height in autumn and winter in Beijing and Taiyuan.The other three methods display high values in spring and summer and low values in autumn and winter for all three stations.The relative humidity gradient method and specific humidity gradient method exhibit greater parameter uncertainty,followed by the traditional potential temperature gradient method and improved potential temperature gradient method.When examining the time consistency of the monthly mean of the boundary layer height calculation results,correlations between the methods are markedly higher at night than those during the day,and the correlation coefficient between the two humidity-based methods is consistently the highest.However,the correlation among the other three methods is poor.The Richardson number method and the improved potential temperature gradient method are highly correlated,and the traditional potential temperature gradient method fluctuates more greatly than the other methods due to differences in stations.