| As an important indicator of planetary boundary layer,planetary boundary layer height?PBLH?presents obvious temporal and spatial changes.In this paper,the applicability and limitation of gradient method?GRD?,standard deviation method?STD?,ideal curve fitting method?ICF?and wavelet covariance transform method?WCT?for inversion of PBLH are compared and analyzed by using the ceilometer data at Chaoyang Station and Daxing station,which are in the urban and suburb of Beijing respectively,the conventional meteorological data of the two stations and the sounding data at the southern suburb observatory.Based on ICF,a two-step curve fitting method?2-S ICF?is established to realize the purpose of real time observation of PBLH.Based on WRF?Weather Research and Forecasting?numerical simulation,the simulation results of the structure of planetary boundary layer in Beijing with SLUCM?Single-Layer Urban Canopy Model?coupling and different boundary layer parameterization schemes are evaluated,and the understanding of urban uneven underlying surface is deepened through sensitivity test.The analysises show as follows:1.In the process of inversion of PBLH based on ceilometer,four different methods show significant differences due to the influence of their own algorithms:GRD pays attention to the attenuation degree of single-layer signal,which is related to the number of selected sliding average points,and is more sensitive to the signal-to-noise ratio of observation data.STD considers the dispersion degree of local signal,which is related to the range of deviation calculated,and the results show good continuity.ICF covers the whole layer of signals in the calculation process,which is related to the iterative method and the results show good stability.At night,ICF would be affected by the residual layer,confusing the judgment of PBLH.WCT calculates the signal gradient of two adjacent intervals,and the interval range is related to the scale parameter a,which has a certain noise reduction effect.In general,the maximum and minimum average PBLH is 1149m in GRD and 1065m in ICF,and WCT is slightly higher than STD by 9m.2.The new two-step curve fitting method?2-S ICF?improves the determination of PBLH by checking the existence of residual layer and replacing erf function with arctan function.The root mean square error?RMSE?of the fitting curve and the detection profile of the new algorithm is 2.51×10-7m-1sr-1,which is more in line with the actual profile characteristics than ICF(RMSE is 6.52×10-7m-1sr-1),and clearly distinguishes the unstable boundary layer in the daytime,the stable boundary layer at night and the residual layer above it.Comparing the new algorithm with the potential temperature gradient method based on sounding,the results show that:when PBLH is high,the PBLH obtained based on sounding is higher than that based on ceilometer in most cases,and overall the correlation coefficient of the two methods is 0.91,which verifies the feasibility of calculating PBLH based on 2-S ICF.3.The observation and analysis of 41 non-precipitation days from May to June 2017 show that PBLH of Chaoyang Station and Daxing station is different during the growth and attenuation period:Chaoyang Station shows a growth trend around 06:00,and Daxing station is about 1 hour later than it;after 16:00,Chaoyang Station declines slowly,and Daxing station declines faster.The mean PBLH of Chaoyang Station and Daxing station is 1035m and 943m in the daytime and 362m and 250m at night respectively.The increase of the intensity of the heat island at night leads to the more significant difference in PBLH between the two stations at night.4.A case study of sunny days from May 17 to 19,2017 shows that five test schemes?ACM2-no SLUCM?ACM2-SLUCM?YSU-SLUCM?MYJ-SLUCM?Bou Lac-SLUCM?simulate a lower PBLH from 00:00 to 07:00;in the stage of PBLH rising after sunrise,the simulation results are consistent with the actual observation;in the period of the most vigorous development of boundary layer in the afternoon,PBLH is overestimated,and the difference range is between 500m and 600m;after sunset,the simulation results of the different PBL scheme show obvious differences.Among them,the using of SLUCM makes PBLH of Chaoyang Station and Daxing station increase by 15%and 2%in daytime,81%and 22%in nighttime.5.The sensitivity test of numerical simulation shows that urbanization makes the PBLH increase both in daytime and at night,which has a good corresponding relationship with the temperature field of 2m.The increase is weak in daytime and strong at night.PBLH rises significantly at night,with a maximum increase of 972m. |
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