Determination Of Boundary Layer Height Research Articles

Boundary Layer Height as Estimated from Radar Wind Profilers in Four Cities in China: Relative Contributions from Aerosols and Surface Features

The turbulent mixing and dispersion of air pollutants is strongly dependent on the vertical structure of the wind, which constitutes one of the major challenges affecting the determination of boundary layer height (BLH). Here, an adaptive method is proposed to estimate BLH from measurements of radar wind profilers (RWPs) in Beijing (BJ), Nanjing (NJ), Chongqing (CQ), and Wulumuqi (WQ), China, during the summer of 2019. Validation against simultaneous BLH estimates from radiosondes (RSs) yielded a correlation coefficient of 0.66, indicating that the method can be used to derive BLH from RWPs. Diurnal variations of BLH and the ventilation coefficient (VC) at four sites were then examined. A distinct diurnal cycle of BLH was observed over all four cities; BLH gradually increased from sunset, reached a maximum in the afternoon, and then dropped sharply after sunset. The maximum hourly average BLH (1.426 ± 0.46 km) occurred in WQ, consistent with the maximum hourly mean VC larger than 5000 m2/s observed there. By comparison, the diurnal variation of VC was not strong, with values ranging between 2000 and 3000 m2/s, likely owing to the high-humidity environment. Furthermore, surface sensible heat flux, latent heat flux, and dry mass of particulate matter with aerodynamic diameter ≤2.5 µm (PM2.5) concentrations were found to somehow affect the vertical structure of wind and thermodynamic features, leading to a difference between RS and RWP BLH estimates. This indicates that the atmospheric environment can affect BLH estimates using RWP data. The BLH results from RWPs were better in some specific cases. These findings show great potential of RWP measurements in air quality research, and will provide key data references for policy-making toward emission reductions.

Boundary Layer Heights as Derived From Ground-Based Radar Wind Profiler in Beijing

The vertical structure of wind is a key factor in modulating air quality, from which the determination of boundary layer height (BLH) remains a major challenge. In this paper, we developed an improved threshold method to determine the BLH from radar wind profiler (RWP) measurements. The normalized signal-to-noise ratio (SNR) profiles were used instead of the original SNR profiles to avoid instrumental inconsistencies. Additionally, a peak filter was designed to indicate the BLH based on the maximum SNR by taking into account the multiple peaks in the SNR profile. This algorithm was then applied to the RWP measurements taken in the summer (June–July–August) of 2018 in Beijing to obtain the BLHs. Validation analyses suggested that the BLH retrievals from RWP exhibited high consistency with those from radiosondes, with an average correlation coefficient of 0.69 (0.66) and a root mean squared error of 0.39 (0.41) in the daytime (nighttime). Additionally, the major features of summertime BLHs in Beijing were examined. In particular, a distinct diurnal variation in BLH was observed with a peak (1630 ± 510 m) occurring at 0600 universal time coordinated (UTC) and a minimum (587 ± 343 m) at 2300 UTC. Therefore, the algorithm presented here has great potential to be applied to other regions to obtain reliable BLHs. The findings obtained here highlight the importance of vertical wind structure in air quality studies.

Technical note: Boundary layer height determination from lidar for improving air pollution episode modeling: development of new algorithm and evaluation

Abstract. Predicting air pollution events in the low atmosphere over megacities requires a thorough understanding of the tropospheric dynamics and chemical processes, involving, notably, continuous and accurate determination of the boundary layer height (BLH). Through intensive observations experimented over Beijing (China) and an exhaustive evaluation of existing algorithms applied to the BLH determination, persistent critical limitations are noticed, in particular during polluted episodes. Basically, under weak thermal convection with high aerosol loading, none of the retrieval algorithms is able to fully capture the diurnal cycle of the BLH due to insufficient vertical mixing of pollutants in the boundary layer associated with the impact of gravity waves on the tropospheric structure. Consequently, a new approach based on gravity wave theory (the cubic root gradient method: CRGM) is developed to overcome such weakness and accurately reproduce the fluctuations of the BLH under various atmospheric pollution conditions. Comprehensive evaluation of CRGM highlights its high performance in determining BLH from lidar. In comparison with the existing retrieval algorithms, CRGM potentially reduces related computational uncertainties and errors from BLH determination (strong increase of correlation coefficient from 0.44 to 0.91 and significant decreases of the root mean square error from 643 to 142 m). Such a newly developed technique is undoubtedly expected to contribute to improving the accuracy of air quality modeling and forecasting systems.

Improving Daytime Planetary Boundary Layer Height Determination from CALIOP: Validation Based on Ground-Based Lidar Station

An integrated algorithm by combining the advantages of the wavelet covariance method and the improved maximum variance method was developed to determine the planetary boundary layer height (PBLH) from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) measurements, and an aerosol fraction threshold was applied to the integrated algorithm considering the applicability of the two methods. We compared the CALIOP retrieval with the measurements of PBLH derived from nine years of ground-based Lidar synchronous observations located in Lille, north of France. The results indicate that a good correlation (R≥0.79) exists between the PBLHs derived from CALIOP and ground-based Lidar under clear sky conditions. The mean absolute differences of PBLHs are, respectively, of 206 m and 106 m before and after the removal of the aloft aerosol layer. The results under cloudy sky conditions show a lower agreement (R=0.48) in regard of the comparisons performed under clear sky conditions. Besides, the spatial correlation of PBLHs decreases with the increasing spatial distance between CALIOP footprint and Lille observation platform. Based on the above analysis, the PBLHs can be effectively derived by the integrated algorithm under clear sky conditions, while larger mean absolute difference (i.e., 527 m) exists under cloudy sky conditions.

Simulation of Pollutant Transport in Complex Terrain with a Numerical Weather Prediction–Particle Dispersion Model Combination

A new scaling approach, based on the convective velocity obtained from the sun-exposed eastern slopes and thus suited for steep and narrow Alpine valleys, is investigated with respect to pollutant dispersion. The capability of the new method is demonstrated with the operational emergency response system of MeteoSwiss, which consists of the COSMO (COnsortium for Small-scale MOdelling) numerical weather prediction model coupled with a Lagrangian particle dispersion model (LPDM). The new scaling approach is introduced to the interface between COSMO and LPDM, and is compared to results of a classical similarity theory approach and to the operational coupling type, which uses the turbulent kinetic energy (TKE) from the COSMO model directly. For the validation of the modelling system, the TRANSALP-89 tracer experiment is used, which was conducted in highly complex terrain in southern Switzerland. The ability of the COSMO model to simulate the valley wind system is assessed with several meteorological surface stations, and the dispersion simulation is evaluated with the measurements from 25 surface samplers. The sensitivity of the modelling system towards the soil moisture, horizontal grid resolution, and boundary-layer height determination is investigated, and it is shown that, if the flow field is correctly reproduced, the new scaling approach improves the tracer concentration simulation when compared to classical coupling methods.

Atomosphere boundary layer height determination and observation from ceilometer measurements over Hefei during the total solar on July 22, 2009 eclipse

Using an improved inexion point method (IIPM), we investigate atmosphere boundary layer (ABL) height evolution over Hefei during the total solar eclipse on July 22, 2009. A lidar ceilometer is used in ground-based observations. Estimations of ABL heights before, during, and after the solar eclipse are analyzed using the IIPM. Results indicate that the IIPM, which is less sensitive to background noise, is more suitable in detecting ABL height and temporal evolution. Data demonstrate that the total solar eclipse resultes in a decrease in ABL height, indicating a suppression of turbulence activity, similar to that observed during the sunset hours. Changes in ABL height are associated with a slow change in temperature, indicating a significant weakening of penetrative convection and a time lag between ABL response and the reduction in solar radiation.

Towards operational determination of boundary layer height using sodar/RASS soundings and surface heat flux data

A method for the derivation of boundary layer height from measurements of sodar, RASS and sonic anemometer-thermometer data is presented. Datasets of the years 2004 and 2005 measured at the Meteorological Observatory Lindenberg (Germany) are used. The time resolution is 15 min. Special emphasis is laid on air pollution issues where mixing heights shallower than 500 m are important. A difference to the numerous methods already presented in the literature is twofold. Firstly, not only single vertical profiles of measured or derived parameters are used but also bulk information, e.g. histograms and boundary layer evolution over time intervals, is considered. Secondly, the presented method analyses sodar data and confirms or corrects the results by use of temperature profiles from RASS and by sonic surface heat flux data. The results are presented as frequency distributions for the whole period and for the four seasons, stratified by the hour of the day. The additional analysis of temperature profiles and surface heat flux is particularly helpful for the detection of stable boundary layers and increases the number of shallow boundary layers particularly in the evening. The comparison with radiosonde-derived boundary layer heights shows a good agreement, deviations are mostly due to a complicated boundary layer structure. Boundary layer depths derived after a formalism given in the German administrative regulation TA-Luft show - compared to the sodar/RASS-derived values - too many very small or partly very large values. The height range between 100 m and 300 m which is essential for pollutant dispersion issues is nearly missing. Requirements for a future operational use of the method are formulated.

Planetary boundary layer height determination during Pacific 2001 using the advantage of a scanning lidar instrument

A novel method for determining the boundary layer height has been developed specifically for scanning lidar data. The Meteorological Service of Canada has recently developed a scanning lidar facility (RASCAL—Rapid Acquisition Scanning Aerosol Lidar) capable of fast azimuth and elevation scanning profiles of the lower troposphere. During the Pacific 2001 field campaign in the Lower Fraser Valley (LFV) of British Columbia, RASCAL measurements were conducted from the Langley Lochiel ground site (49.03°N, 122.60°W). Dependent on weather, measurements were made for approximately 16 h per day between 14 and 30, August 2001, to measure the early morning boundary layer growth and its collapse to the nocturnal boundary layer. The instrument was set-up to make continuous elevation scans at three different azimuths representing the “West”, “North” and “East” direction. A robust boundary layer height algorithm has been developed to exploit the advantages of high-resolution scanning lidar data. On certain days, substantial differences in boundary layer height are evident between the different directional scans. Results also show a consistent “breakdown” of the boundary layer at approximately 19:00 PDT visible on almost every day that measurements were obtained. Accurate determination of the boundary layer is a critical parameter in understanding the regional air quality within the LFV.

Developments in UHF lower tropospheric wind profiling at NOAA's Aeronomy Laboratory

Developments in UHF profiling at 915 MHz are presented. Recent advances in UHF profiling are traced to early developments beginning about 8 years ago in the Aeronomy Laboratory at 915 MHz using microstrip antennas. This paper presents an overview of the architecture of the UHF profiler system as it has evolved over the past decade including the development of radio acoustic sounding system (RASS) capabilities. Hardware and software components are described and operational performance is summarized from experience gained from many installations, primarily from those in the tropics. Applications to wind profiling, boundary layer height determination, flux measurement, and precipitation profiling are considered.