基于地基C波段垂直雷达的青藏高原大气边界层湍流特征研究OA北大核心CSTPCD

Based on observations of C-band frequency modulated continuous wave radar(BLHCR),L-band radiosonde data(BLHSD),gradient tower data and reanalysis data set(BLHERA5)at Naqu station in July and August 2014,the boundary layer height(BLH),turbulent statistical characteristics and turbulent spectrum in surface layer and mixing layer under different sensible heat fluxes(SH)and stability(z/L or BLHCR/L)conditions are analyzed.The main results are as follows:(1)There are significant correlation among BLHCR,BLHSD and BLHERA5,and the root mean square deviations among them are about 0.6 km.The BLHCR have significant daytime variation at Naqu,and the daily range of the median of BLHCR is approximately 0.7-0.8 km.At around 16:00 BT,BLHCR reaches its maximum value with a median value of approximately 1.2 km.(2)All of σw,σT and RwT in surface layer gradually increase with increased SH.The σT generally increases linearly,and the increase rates of σw and RwT gradually decrease when SH exceeds a certain threshold.When-z/L＜0.3,both σT and RwT rapidly increase with the increase of-z/L;when-z/L ≥0.3,the increase rate significantly decline.(3)The maximum value of σ2w in mixing layer occurs at a height of approximately(0.25-0.3)×BLHCR,with an average value of approximately 1.2-1.3 m2/s2.The σ2w in mixing layer under strongly unstable stratification is slightly less than that under weakly unstable stratification;the average value of σ2 in mixing layer increases with the increasing of SH.With the increase of z/BLHCR,σ2/w2 presents a first rapid increase and then gradually decreases,with the maximum value occurring at around 0.35×BLHCR.(4)With the increase of unstable stratification,the peak frequency of the normalized vertical velocity spectrum both in surface layer and mixing layer moves towards low frequency and its corresponding value(normalized power spectral density)increase.Both the scale of the turbulent vortex and turbulent intensity increase for strongly unstable stratification.