大孔径闪烁仪的通量印痕分析与应用

Flux Footprint Analysis and Application for the Large Aperture Scintillometer

针对北京密云站的长期通量观测进行大孔径闪烁仪的平均印痕区域分析。首先从2008年全年8 152组湍流观测资料,以整体湍流特征量σw/u*以及其他数据合理性判据进行质量控制,获得6 806组有效数据;然后用一个解析解模型逐时次计算大孔径闪烁仪的二维印痕,并进行统计平均,获得各季平均印痕分布;将当地气象条件根据风向、风速和稳定度分为12类,分别统计各类条件的平均印痕分布。最后,以实测感热通量为例,计算当地实际湍流通量的气候平均印痕区域。结果表明,当地大孔径闪烁仪的平均通量印痕季节变化不大;各类气象条件中,稳定度和风向是影响印痕区域大小和方向的重要因素,风速影响相对较小;以实际湍流通量为权重的气候平均印痕可更准确反映观测结果的空间代表性,其分布与简单平均的印痕分布有所不同。

Mean flux footprints were analyzed for long-term measurements of a large aperture scintillometer（LAS） in Miyun county,Beijing.A set of half-hourly mean,full-year turbulence data in 2008 was used for the analysis.As a quality control,one of the integral turbulent characteristics,σw/u＊,was used to exclude that part of data which may violate the Monin-Obukhov similarity,in combining with other reasonability assessments.We yielded a sub-set data of 6 806 available from the total of 8 152 in the year.A footprint model based on an analytical solution was applied to calculate the 2-dimenasional footprints for the LAS measurements.Accordingly,seasonal mean footprints,as well as the mean footprints for 12 types of meteorological conditions at this site,were calculated.Wind direction,wind speed and atmospheric stability were used to determine the meteorological type.Finally,as an example,footprint climatology for sensible heat flux was derived,by averaging the footprints with the real flux measurements as the weight function.Results showed that： the mean footprint at this site varied little seasonally,stability and wind direction influenced the footprint size and location significantly while the wind speed played a relatively weak role in it.Long-term mean turbulent fluxes and their spatial representativeness can be expressed better by the flux-weighted mean footprint,which differed from the simple mean footprint slightly at this site,for the case of sensible heat flux.