Abstract:
Based on observations of C-band frequency modulated continuous wave radar (BLH
Z), L-band radiosonde data (BLH
SD), gradient tower data and reanalysis data set (BLH
ERA5) 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 BLH
Z/L) conditions are analyzed. The main results are as follows: (1) There are significant correlation among BLH
Z , BLH
SD and BLH
ERA5, and the root mean square deviations among them are about 0.6 km. The BLH
Z have significant daytime variation at Naqu, and the daily range of the median of BLH
Z is approximately 0.7—0.8 km. At around 16:00 BT, BLH
Z reaches its maximum value with a median value of approximately 1.2 km. (2) All of
\sigma _\mathrmw,\sigma _\mathrmT and
RwT in surface layer gradually increase with increased SH. The
\sigma _\mathrmT generally increases linearly, and the increase rates of
\sigma _\mathrmw and
RwT gradually decrease when SH exceeds a certain threshold. When −
z/L<0.3, both
\sigma _\mathrmT 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
\sigma _\mathrmw^2 in mixing layer occurs at a height of approximately (0.25—0.3)×BLH
Z, with an average value of approximately 1.2—1.3 m
2/s
2. The
\sigma _\mathrmw^2 in mixing layer under strongly unstable stratification is slightly less than that under weakly unstable stratification; the average value of
\sigma _\mathrmw^2 in mixing layer increases with the increasing of SH. With the increase of
z/BLH
Z,
\sigma _\mathrmw^2 /
w_*^2 presents a first rapid increase and then gradually decreases, with the maximum value occurring at around 0.35×BLH
Z. (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.