A Comparative Study and Evaluation of Mixing-Height Estimation Based on Sodar-RASS, Ceilometer Data and Numerical Model Simulations

Helmis, C. G.; Sgouros, G.; Tombrou, M.; Schäfer, Klaus; Münkel, Christoph; Bossioli, E.; Dandou, A.

doi:10.1007/s10546-012-9743-4

Cited by 40 publications

(27 citation statements)

References 54 publications

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“…Numerous studies (e.g. Emeis et al, 2008;Eresmaa et al, 2006;Helmis et al, 2012) show that ceilometer data are suitable for studying the vertical characteristics of the atmosphere and for using the obtained profiles to assess the height of aerosol layers and the mixing layer height.…”

Section: Ceilometer Measurements and Analytical Methodsmentioning

confidence: 99%

Investigation of the mixing layer height derived from ceilometer measurements in the Kathmandu Valley and implications for local air quality

Mues¹,

Rupakheti²,

Münkel³

et al. 2017

Preprint

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Abstract. In this study one year of ceilometer measurements taken in the Kathmandu Valley, Nepal, in the framework of the SusKat project (A Sustainable Atmosphere for the Kathmandu Valley) were analyzed to investigate the diurnal variation of the mixing layer height and its dependency on the meteorological conditions. In addition, the impact of the mixing layer height on the temporal variation and the magnitude of the measured black carbon concentrations are analysed for each season. Based on the assumption that black carbon aerosols are vertically well mixed within the mixing layer and the finding that the mixing layer varies only little during night time and morning hours, black carbon emission fluxes are estimated for these hours and per month. Even though this method is relatively simple, it can give an observationally based first estimate of the black carbon emissions in this region, especially illuminating the seasonal cycle of the emission fluxes. In all seasons the diurnal cycle of the mixing layer height is typically characterized by low heights during the night and maximum values during in the afternoon. Seasonal differences are found in the absolute mixing layer height values and the duration of the typical daytime maximum. During the monsoon season a diurnal cycle has been observed with the smallest amplitude, with the lowest daytime mixing height of all seasons, and also the highest nighttime and early morning mixing height of all seasons. These characteristics can mainly be explained with the frequently present clouds and the associated reduction in incoming solar radiation and outgoing longwave radiation. In general, the black carbon concentrations show a clear anticorrelation with mixing layer height measurements, although this relation is less pronounced in the monsoon season. The daily evolution of the black carbon diurnal cycle differs between the seasons, partly due to the different meteorological conditions including the mixing layer height. Other important reasons are the different main emission sources and their diurnal variations in the individual seasons. The estimation of the black carbon emission flux for the morning hours show a clear seasonal cycle with maximum values in December to April. Compared to the emission flux values provided by different emission databases for this region, the here estimated values are considerably higher. Several possible sources of uncertainty are considered, and even the absolute lower bound of the emissions based on our methodology is higher than in most emissions datasets, providing strong evidence that the black carbon emissions for this region have likely been underestimated in modelling studies thus far.

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Section: Ceilometer Measurements and Analytical Methodsmentioning

confidence: 99%

Investigation of the mixing layer height derived from ceilometer measurements in the Kathmandu Valley and implications for local air quality

Mues¹,

Rupakheti²,

Münkel³

et al. 2017

Preprint

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“…The depth of the convective boundary layer (CBL) was inferred from 10 min means of these data, in combination with semi-daily radiosonde ascends in nearby Xilinhot (World Meteorological Organization station 54102, http://weather.uwyo.edu/ upperair/sounding.html). For this purpose the maximum gradient method is used, which enables the detection of up to five lifted inversions (Emeis et al, 2008;Helmis et al, 2012;Münkel and Roininen, 2010). It is assumed that the aerosol number concentration, size distribution, shape and chemical composition (refractive index, absorption) adapt rapidly to the CBL structure.…”

Section: Study Areamentioning

confidence: 99%

Spatially explicit regionalization of airborne flux measurements using environmental response functions

et al. 2013

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Abstract. The goal of this study is to characterize the sensible (H) and latent (LE) heat exchange for different land covers in the heterogeneous steppe landscape of the Xilin River catchment, Inner Mongolia, China. Eddy-covariance flux measurements at 50–100 m above ground were conducted in July 2009 using a weight-shift microlight aircraft. Wavelet decomposition of the turbulence data enables a spatial discretization of 90 m of the flux measurements. For a total of 8446 flux observations during 12 flights, MODIS land surface temperature (LST) and enhanced vegetation index (EVI) in each flux footprint are determined. Boosted regression trees are then used to infer an environmental response function (ERF) between all flux observations (H, LE) and biophysical (LST, EVI) and meteorological drivers. Numerical tests show that ERF predictions covering the entire Xilin River catchment (&approx;3670 km2) are accurate to ≤18% (1 σ). The predictions are then summarized for each land cover type, providing individual estimates of source strength (36 W m−2 < H < 364 W m−2, 46 W m−2 < LE < 425 W m−2) and spatial variability (11 W m−2 < σH < 169 W m−2, 14 W m−2 < σLE < 152 W m−2) to a precision of ≤5%. Lastly, ERF predictions of land cover specific Bowen ratios are compared between subsequent flights at different locations in the Xilin River catchment. Agreement of the land cover specific Bowen ratios to within 12 &pm; 9% emphasizes the robustness of the presented approach. This study indicates the potential of ERFs for (i) extending airborne flux measurements to the catchment scale, (ii) assessing the spatial representativeness of long-term tower flux measurements, and (iii) designing, constraining and evaluating flux algorithms for remote sensing and numerical modelling applications.

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“…They found generally good agreement, but this agreement was subject to spatial representativeness errors, and the lidar estimate was systematically higher than the microwave temperature profiler estimate. Helmis et al (2012) compared two mesoscale models, a sodar-RASS (Radio Acoustic Sounding System), and a ceilometer. They found that reliable PBL depth estimates could be made using each approach only under certain meteorological conditions.…”

Section: Introductionmentioning

confidence: 99%

Comparison of GEOS-5 AGCM planetary boundary layer depths computed with various definitions

McGrath-Spangler

Molod

2014

Atmos. Chem. Phys.

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Abstract. Accurate models of planetary boundary layer (PBL) processes are important for forecasting weather and climate. The present study compares seven methods of calculating PBL depth in the GEOS-5 atmospheric general circulation model (AGCM) over land. These methods depend on the eddy diffusion coefficients, bulk and local Richardson numbers, and the turbulent kinetic energy. The computed PBL depths are aggregated to the Köppen-Geiger climate classes, and some limited comparisons are made using radiosonde profiles. Most methods produce similar midday PBL depths, although in the warm, moist climate classes the bulk Richardson number method gives midday results that are lower than those given by the eddy diffusion coefficient methods. Additional analysis revealed that methods sensitive to turbulence driven by radiative cooling produce greater PBL depths, this effect being most significant during the evening transition. Nocturnal PBLs based on Richardson number methods are generally shallower than eddy diffusion coefficient based estimates. The bulk Richardson number estimate is recommended as the PBL height to inform the choice of the turbulent length scale, based on the similarity to other methods during the day, and the improved nighttime behavior.

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A Comparative Study and Evaluation of Mixing-Height Estimation Based on Sodar-RASS, Ceilometer Data and Numerical Model Simulations

Cited by 40 publications

References 54 publications

Investigation of the mixing layer height derived from ceilometer measurements in the Kathmandu Valley and implications for local air quality

Investigation of the mixing layer height derived from ceilometer measurements in the Kathmandu Valley and implications for local air quality

Spatially explicit regionalization of airborne flux measurements using environmental response functions

Comparison of GEOS-5 AGCM planetary boundary layer depths computed with various definitions

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