Mixing Layer Height Research Articles

Impact of a noon-time annular solar eclipse on the mixing layer height and vertical distribution of aerosols in the atmospheric boundary layer

Impact of the long duration noontime annular solar eclipse on 15 January 2010 on the vertical distribution of aerosols and mixing layer height ( H M ) in a well-developed convective atmospheric boundary layer (ABL) has been investigated using continuous Lidar observations over a tropical coastal station, Thumba (8.5°N, 76.9°E). This study shows that H M has decreased from its peak value of ∼1800 m at 12:00 h to ∼1000 m following the annular phase of the eclipse (13:17 h), while the corresponding decrease in the total aerosol abundance of ABL is ∼29%. The post-eclipse increase of H M is rapid compared to that during forenoon.

Comparison of lidar-derived PM<sub>10</sub> with regional modeling and ground-based observations in the frame of MEGAPOLI experiment

Abstract. An innovative approach using mobile lidar measurements was implemented to test the performances of chemistry-transport models in simulating mass concentrations (PM10) predicted by chemistry-transport models. A ground-based mobile lidar (GBML) was deployed around Paris onboard a van during the MEGAPOLI (Megacities: Emissions, urban, regional and Global Atmospheric POLlution and climate effects, and Integrated tools for assessment and mitigation) summer experiment in July 2009. The measurements performed with this Rayleigh-Mie lidar are converted into PM10 profiles using optical-to-mass relationships previously established from in situ measurements performed around Paris for urban and peri-urban aerosols. The method is described here and applied to the 10 measurements days (MD). MD of 1, 15, 16 and 26 July 2009, corresponding to different levels of pollution and atmospheric conditions, are analyzed here in more details. Lidar-derived PM10 are compared with results of simulations from POLYPHEMUS and CHIMERE chemistry-transport models (CTM) and with ground-based observations from the AIRPARIF network. GBML-derived and AIRPARIF in situ measurements have been found to be in good agreement with a mean Root Mean Square Error RMSE (and a Mean Absolute Percentage Error MAPE) of 7.2 μg m−3 (26.0%) and 8.8 μg m−3 (25.2%) with relationships assuming peri-urban and urban-type particles, respectively. The comparisons between CTMs and lidar at ~200 m height have shown that CTMs tend to underestimate wet PM10 concentrations as revealed by the mean wet PM10 observed during the 10 MD of 22.4, 20.0 and 17.5 μg m−3 for lidar with peri-urban relationship, and POLYPHEMUS and CHIMERE models, respectively. This leads to a RMSE (and a MAPE) of 6.4 μg m−3 (29.6%) and 6.4 μg m−3 (27.6%) when considering POLYPHEMUS and CHIMERE CTMs, respectively. Wet integrated PM10 computed (between the ground and 1 km above the ground level) from lidar, POLYPHEMUS and CHIMERE results have been compared and have shown similar results with a RMSE (and MAPE) of 6.3 mg m−2 (30.1%) and 5.2 mg m−2 (22.3%) with POLYPHEMUS and CHIMERE when comparing with lidar-derived PM10 with periurban relationship. The values are of the same order of magnitude than other comparisons realized in previous studies. The discrepancies observed between models and measured PM10 can be explained by difficulties to accurately model the background conditions, the positions and strengths of the plume, the vertical turbulent diffusion (as well as the limited vertical model resolutions) and chemical processes as the formation of secondary aerosols. The major advantage of using vertically resolved lidar observations in addition to surface concentrations is to overcome the problem of limited spatial representativity of surface measurements. Even for the case of a well-mixed boundary layer, vertical mixing is not complete, especially in the surface layer and near source regions. Also a bad estimation of the mixing layer height would introduce errors in simulated surface concentrations, which can be detected using lidar measurements. In addition, horizontal spatial representativity is larger for altitude integrated measurements than for surface measurements, because horizontal inhomogeneities occurring near surface sources are dampened.

Effect of Flare Stack Radiation on the Mixing Height over Olorunsogo Area of Ogun State, Nigeria

Mixed layer depth, Solar and flare stack radiations, Atmospheric boundary layer Abstract: Mixing of chemical species released from pollution sources occurs at certain heights in the atmospheric boundary layer of the troposphere. Within this height, mixing of materials occurs due to convective heat transport and mechanical (wind) actions. The mixed layer height can be estimated by analyzing measured meteorological parameters. In this study, the parameterization of meteorological variables based on established mathematical models were used to compute mixed layer height over Olorunsogo in Ogun State, Nigeria. The vertical extent through which pollutants mix occurs was described in a height-temperature profile for both the day time and nocturnal characteristics. The mixing depths were computed for two locations comprising one area with gas flaring operation present and another with no flare stack present. The findings of this study revealed that mixed layer depth for the location without flaring activities, day time ranged between 1200m and 1400m, and at night time as well as early morning ranged between 150m and 400m. In contrast with the location where gas flaring occurred, mixing height ranged between 9280m and 9310m for day time and between 9100m and 9180m for nocturnal period. In addition, it was observed that pollution trapped below the flare during the day, experience rapid vertical motion due to outgoing long wave radiation (OLR) from the surface. While above the flare a vertical motion coupled with dispersion occurs under lapse rate for pollutants, but remained trapped at the inversion layer. At night time, pollutants around the flare advect vertically and experience rapid vertical dispersed motion and after going through the flare are trapped at the inversion layer. Hence most submicron sized particulate matter hardly reaches ground level over areas where gas flaring operations occur except entrainments in wet depositions predominantly through rainfall.

Path-integrated measurements of carbon dioxide in the urban canopy layer

Continuous CO2 concentration measurements have been recorded within the city center of Essen, Germany, using a path-integrated measuring system above a typical urban area over the course of nine months (FebruaryeOctober 2010). Mean monthly urban CO2 concentrations were 396 and 446 ppm in summer and winter, respectively, which were 8.5 % in average higher than at a nearby suburban measuring site. Urban-suburban differences mainly occur due to increased CO2 emissions from traffic and industry within the urban area, as well as domestic heating in winter. Among the analyzed meteorological variables, low wind velocities increased CO2 concentrations as well as high atmospheric stability within the urban boundary layer, respectively. The influence of wind direction reflects the heterogeneous distribution of local CO2 sources at the recording sites, particularly industrial point sources. Other point sources in the vicinity of the urban site strongly influence the additional point measurements but show no significant effect on the measured CO2 concentrations by the path-integrated measuring system. Within an eight-day case study, a significant positive correlation between CO2 concentration and traffic count (R ¼0.26; p<0.05) was found on weekdays using partial correlation analysis after excluding the influence of meteorological variables. This correlation diminishes when combined with the meteorological components, and mixing layer height shows the strongest negative correlation with measured urban CO2 (R ¼� 0.59). The path-integrated system provides CO2 concentrations on a greater temporal and spatial scale than common point measurements, which can be influenced by strong adjacent local CO2 sources.

Annual cycle of aerosol backscatter coefficient and aerosol mixed layer height above Neuchâtel (Switzerland, 47.00°N, 6.95°E)

AbstractDue to the complexity of the direct and indirect effects of the atmospheric aerosols on the air quality and atmospheric radiation balance, complementary methods are necessary to assess the aerosol optical properties. In this sense the backscatter lidar methods are critical in aerosol vertical distribution study. This work presents the annual cycle of aerosol backscatter coefficient (ABC) and aerosol mixed layer (AML) height over Neuchâtel, Switzerland (47.00 N; 6.950 E, 485 m asl). The study is performed by a ground based backscatter lidar operating at 532 nm wavelength as part of EARLINET program of EU. Atmospheric layering for this study is based on a classification of lower atmosphere from 1 km to 2 km above sea level (asl) and from 2 km to 5 km asl, respectively.

Annual cycle of aerosol backscatter coefficient and aerosol mixed layer height above Neuchâtel (Switzerland, 47.00°N, 6.95°E)

Due to the complexity of the direct and indirect effects of the atmospheric aerosols on the air quality and atmospheric radiation balance, complementary methods are necessary to assess the aerosol optical properties. In this sense the backscatter lidar methods are critical in aerosol vertical distribution study. This work presents the annual cycle of aerosol backscatter coefficient (ABC) and aerosol mixed layer (AML) height over Neuchâtel, Switzerland (47.00 N; 6.950 E, 485 m asl). The study is performed by a ground based backscatter lidar operating at 532 nm wavelength as part of EARLINET program of EU. Atmospheric layering for this study is based on a classification of lower atmosphere from 1 km to 2 km above sea level (asl) and from 2 km to 5 km asl, respectively.

Variation in aerosol black carbon concentration and its emission estimates at the mega-city Delhi

Simultaneous measurements of aerosol black carbon (BC) mass concentration using an Aethalometer Model AE-42 and mixing layer height (MLH) using a monostatic sonic detection and ranging (SODAR) system were carried out from January 2006 to January 2007 at the mega-city Delhi. The BC concentration generally had a typical diurnal variation with morning and late-afternoon/night peaks. The average BC concentration during the whole period of observation was fairly high at 14.75 μg m−3. The BC concentration nearly doubled during cloudy-sky conditions compared to that during clear-sky conditions. The seasonal variation showed a maximum average concentration during the winter (25.5 μg m−3) and a minimum during the monsoon season (7.7 μg m−3), with post- and pre-monsoon values at 13.7 and 9.4 μg m−3, respectively. The average BC concentrations were strongly affected by the ventilation coefficient, a product of average wind speed (WS) and average MLH, and were found to be strongly anticorrelated. A simple model of BC concentration along with the MLH and WS was applied to estimate the average BC emission, which was found to vary in the range 11 000–17 000 kg of BC per day. The maximum emission during the day averaged every hour for different months lay in the range 1000–2100 kg h−1. The mean monthly emission varied in the range 0.35–0.52 Gg per month, giving rise to an annual estimated emission of 4.86 Gg in the year 2006 over Delhi.

Lidar remote sensing of the mixed layer height over a tropical urban Indian station

Mixed layer is an important parameter which controls meteorological conditions in the lower atmosphere. Transport and diffusion of pollutants in the lower atmosphere is highly dependant on the structure of the planetary boundary layer, one important feature of which is the height of the well-mixed layer. In the present study, continuous wave, bistatic argon ion lidar-derived scattered signal strength from different heights in the lower troposphere over Pune (18˚ 32′ N, 73˚ 51′ E, 559 m above mean sea level), India during the period April 2007–January 2008 has been recorded remotely and by employing simple statistical tools, the mixed layer height (MLH) and transition layer thickness (TLT) have been estimated. The results show that sufficient mixing of atmospheric constituents such as aerosols exists in the boundary layer in the post-sunset hours during the summer season, enabling estimation of MLH and TLT. On the other hand, during winter months as mixing ceases/weakens by late evening hours, the mixed layer depth is either low or not easily discernible. In view of the importance of mixed layer depth information for various atmospheric applications, the remote sensing tool used and the simple methodology followed here seem promising.

Inter-comparison of lidar and ceilometer retrievals for aerosol and Planetary Boundary Layer profiling over Athens, Greece

Abstract. This study presents an inter-comparison of two active remote sensors (lidar and ceilometer) to determine the mixing layer height and structure of the Planetary Boundary Layer (PBL) and to retrieve tropospheric aerosol vertical profiles over Athens, Greece. This inter-comparison was performed under various strongly different aerosol loads/types (urban air pollution, biomass burning and Saharan dust event), implementing two different lidar systems (one portable Raymetrics S.A. lidar system running at 355 nm and one multi-wavelength Raman lidar system running at 355 nm, 532 nm and 1064 nm) and one CL31 Vaisala S.A. ceilometer (running at 910 nm). Spectral conversions of the ceilometer's data were performed using the Ångström exponent estimated by ultraviolet multi-filter radiometer (UV-MFR) measurements. The inter-comparison was based on two parameters: the mixing layer height determined by the presence of the suspended aerosols and the attenuated backscatter coefficient. Additionally, radiosonde data were used to derive the PBL height. In general, a good agreement was found between the ceilometer and the lidar techniques in both inter-compared parameters in the height range from 500 m to 5000 m, while the limitations of each instrument are also examined.

Impact of Annular Solar Eclipse of 15 January 2010 on the Atmospheric Boundary Layer Characteristics Over Thumba: A Case Study

On 15 January 2010, Thumba (8.5°N, 76.9°E) witnessed one of the longest known noontime annular solar eclipses (ASEs) spanning a period of about 7 min, centered at 1314 hours local time. In this research article, we present a case study on the behaviour of the atmospheric boundary layer characteristics and its vertical structure in response to this rare celestial event by making use of a suite of different in-situ instruments. During the peak period of the ASE, the incoming solar irradiance was dimmed by about 87% of its normal values, resulting in a significant reduction in the magnitudes of turbulent kinetic energy and surface-layer turbulent fluxes of heat and momentum. The intensity and vertical thickness of the sea/land breeze circulation cell over the study domain also weakened. However, the mixed layer heights determined from balloon-borne GPS Radiosonde did not show any appreciable changes. Analysis of vertical profiles of thermodynamic parameters in association with the wind direction during ASE indicated the formation of a double mixed layer between 700 and 1500 m and is attributed to horizontal advection of a different airmass at those altitudes.

Evaluation of the Interpretation of Ceilometer Data with RASS and Radiosonde Data

Since 2006 different remote monitoring methods for determining mixing-layer height have been operated in parallel in Augsburg (Germany). One method is based on the operation of eye-safe commercial mini-lidar systems (ceilometers). The optical backscatter intensities recorded with ceilometers provide information about the range-dependent aerosol concentration; gradient minima within this profile mark the tops of mixed layers. Special software for these ceilometers provides routine retrievals of lower atmospheric layering. A second method, based on sodar observations, detects the height of a turbulent layer characterized by high acoustic backscatter intensities due to thermal fluctuations and a high variance of the vertical velocity component. This information is extended by measurements with a radio-acoustic sounding system (RASS) that directly provides the vertical temperature profile from the detection of acoustic signal propagation and thus temperature inversions that mark atmospheric layers. Ceilometer backscatter information is evaluated by comparison with parallel measurements. Data are presented from 2 years of combined ceilometer and RASS measurements at the same site and from comparison with a nearby (60 km) radiosonde for larger-scale humidity information. This evaluation is designed to ensure mixing-layer height monitoring from ceilometer data more reliable.

Particle Number Size Distribution and Weight Concentration of Background Urban Aerosol in a Po Valley Site

Measurements of particle size distributions and PM2.5 from an urban background site in the Central Po Valley are analysed; the site is one of the medium–small-size cities in the central valley, without the direct influence of the metropolitan and industrial area of Milan and of the Adriatic Sea. The data comprise number concentration of particle with diameters ranging between 10 and 700 nm, PM2.5 and main meteorological variables from February to August 2008. Daily cycles of the observed pollutants are analysed, along with auto-correlation function for particle number concentration and principal component analysis (PCA) of all the available variables; finally, the diurnal pattern of PM2.5 low-, medium- and high-pollution events has been investigated. Total particle number concentration showed a daily pattern both in winter and summer, although different between weekdays and Sundays and with wider variations during the cold season. A daily cycle is present for the geometric mean diameter of nucleation mode particles in winter and of nucleation and Aitken mode particles in summer. PM2.5 showed a slight daily pattern for weekdays and Sundays, similar, but lagged, to total particle count cycle. Mixing layer depth resulted the main process controlling PM2.5, although also human activities contribute to PM2.5 concentration and allow some deposition and (re-)mobilisation at the first hours of the day and morning rush hour, respectively, while particle number concentration responds immediately to anthropogenic sources. PCA confirmed the dependence of particle number concentration also on meteorological variables, e.g. mixing layer height, wind speed or atmospheric pressure, showing the important influence of regional meteorology on local pollution conditions. Modena can be considered a representative test area of the effect of the meteorological regime for the Central Po Valley on atmospheric particle concentration patterns, characterised by steady high-background concentration.

A measurement based analysis of the spatial distribution, temporal variation and chemical composition of particulate matter in Munich and Augsburg

The objective of the studies presented in this paper is to present an analysis of spatial distribution and temporal variation of particulate matter in Munich and Augsburg, Germany, and to identify and discuss the factors determining the aerosol pollution in both areas. Surface-based in-situ and remote sensing measurements of particle mass and particle size distribution have been performed in, around, and above the two cities. Two measurement campaigns were conducted in Munich, one in late spring and one in winter 2003. Another campaign has been on-going in Augsburg since 2004. Spatial and temporal variations are analyzed from this data (PM 10 , PM 2.5 and PM 1 ). There are higher particle mass concentrations at the urban site than at the surrounding rural sites, especially in winter. No significant difference in the major ionic composition of the particles between the urban and the rural site was detected. This is considered to be related to the spatial distribution of secondary inorganic aerosol that is more homogeneous than aerosol resulting from other sources like traffic or urban releases in general. During the measurement campaigns mixing layer heights were determined continuously by remote sensing (SODAR, ceilometer, RASS). Significant dependence of particle size distribution and particle mass concentration on mixing layer height was found. This finding paves the way to new applications of satellite remote sensing products.

Quantifying Mixing in Penetrative Convection Experiments

Penetrative convection in a stably stratified fluid has been reproduced in laboratory by employing a tank filled with water and subjected to heating from below. The goal of the experiments is predicting the mixing layer growth as a function of initial and boundary conditions and describing the fate of a tracer dissolved in the fluid phase. The equipment employed is suitable for simultaneously providing temperatures inside the domain through thermocouples and Lagrangian particle trajectories by feature tracking. The field of view is illuminated through a thin light sheet with suitable optical equipment. To fully characterize the transport feature of the phenomenon under investigation, the mixing layer growth is detected employing both temperature data and statistics of the velocity field, i.e., the vertical velocity component standard deviation. The velocity spatial correlation allows the plume horizontal dimension to be determined. This information coupled with the knowledge of the mixing layer height allows the spatial extension of the convective region to be fully described.

Mixing Depth Estimation from Operational JMA and KMA Wind-Profiler Data and its Preliminary Applications: Examples from Four Selected Sites

In this study, mixed layer (ML) height information is extracted from the range-corrected signal-to-noise ratio (SNR) data of wind profilers operated by the Japan Meteorological Agency (JMA) and the Korea Meteorological Administration (KMA). The altitude where the maximum backscattered power is received by a wind profiler is regarded as ML height. Four sites (Kumagaya and Mito in Japan; Munsan and Gangneung in Korea) were tested on clear sky days, which were chosen using a sunshine ratio. The ML height information obtained was utilized to analyze the spatiotemporal variations of ML heights over Japan and to qualitatively evaluate the model mixing depth predicted by a KMA regional numerical weather prediction model. The frequency of the wind profiler is 1.36 GHz (1.29 GHz for sites in Korea), and the temporal resolution of the SNR data is 10 min. In the vertical, the operating resolutions are 300 m for the sites in Japan and 70 m for Korea. The quantitative analysis of the mixing depths estimated by JMA shows day-to-day, seasonal, and spatial variations in the measured mixing depths. Comparison with nearby radiosonde observations, as well as surface station and satellite observations, is conducted. The estimated ML height tended to be somewhat high in the early morning presumably due to the minimum detectable range and a residual layer (RL) effect. Mean ML heights at the Kumagaya site in July and October 2001 show a seasonal difference of about 500 m. The sea breeze effect can be seen in ML heights at the Mito site located near the sea coast. On the other hand, the evaluation of model-predicted ML heights against KMA SNR data reflected the nonlocal K-profile boundary layer scheme's well-known feature of having faster development with greater depth for an ML. It is proposed in this paper that the ML heights estimated from the Munsan and Gangneung sites can be applied to the observational analysis of mixing depths and be employed as an auxiliary tool for evaluating model ML heights on an operational basis.

Characterization of the Vertical Structure of Coastal Atmospheric Boundary Layer over Thumba (, ) during Different Seasons

Vertical profiles of meteorological parameters obtained from balloon-borne GPS Radiosonde for a period of more than two years are analyzed for characterization of the coastal atmospheric boundary layer (CABL) over Thumba (, , India). The study reports seasonal variability in the thickness of three different sublayers of the CABL, namely, mixed layer, turbulent flow, and sea breeze flow. Among the three, the vertical thickness of sea breeze flow showed considerable dominance on the other two throughout the year. Mixed layer heights derived through gradients in virtual potential temperature () showed large seasonal variability with a peak in the Summer and Post-Monsoon. On the other hand, the vertical thickness of turbulent flow remained steady all through the year. Results from the present study indicate that the magnitudes of mixed layer heights are often larger than the turbulent flow thickness.

Smoke injection heights from agricultural burning in Eastern Europe as seen by CALIPSO

Abstract. High frequency of agricultural fires is observed every year during the summer months over SW Russia and Eastern Europe. This study investigates the initial injection height of aerosol generated by the fires over these regions during the biomass burning season, which determines the potential for long-range transport of the smoke. This information is critical for aerosol transport modeling, as it determines the smoke plume evolution. The study focuses on the period 2006–2008, and is based on observations made by the CALIOP instrument on board the NASA CALIPSO satellite. MODIS data are synergistically used for the detection of the fires and the characterization of their intensity. CALIPSO aerosol vertical distributions generated by the active fires are analyzed to investigate the aerosol top height which is considered dependent on the heat generated by the fires and can be associated with the initial injection height. Aerosol top heights of the vertically homogenous smoke layers are found to range between 1.6 and 5.9 km. Smoke injection heights from CALIPSO are compared with mixing layer heights taken by the European Centre for Medium-range Weather Forecast (ECMWF), to investigate the direct injection of smoke particles into the free troposphere. Our results indicate that the aerosol plumes are observed within the boundary layer for the 50% of the cases examined. For the rest of the cases, the strong updrafts generated by the fires resulted to smoke injection heights greater than the ECMWF estimated mixing layer by 0.5 to 3.0 km, indicating a direct smoke injection into the free troposphere. The smoke injection height showed a dependence on the MODIS-Land Fire Radiative Power product which is indicative of the fire intensity, especially in the cases of lower static stability in the upper part of the boundary layer and the free troposphere.

Diurnal and Seasonal Trends in Convective Mixed-Layer Heights Estimated from Two Years of Continuous Ceilometer Observations in Vancouver, BC

Twenty-six months of continuous ceilometer data are used to estimate the convective mixed-layer height for 710 days by identifying backscatter gradients associated with the entrainment zone. To accomplish this, a semi-automatic procedure is developed that removes all non-applicable data before applying a mixed-layer height algorithm to the backscatter profiles. Two different algorithms for estimating the mixed-layer height are assessed: the minimum-gradient method and the ideal-profile method. The latter of these two algorithms is found to be more robust. Comparisons of mixed-layer height values estimated from the ceilometer agree with previous observations with slightly higher estimates in the mornings and evenings. For clear days with no cumulus cloud formation, the seasonal cycle in mixed-layer heights peaks in late June to early July. Daily maximum values are suppressed by the site’s coastal location, remaining below 800 m for all but a few days. The mean daily maximum mixed-layer height increases by 384 m for days with boundary-layer clouds. The mean summer diurnal trend is found not to differ greatly from that in spring on clear days, while days with boundary-layer clouds have higher spring values than in summer. Net surface heat flux and synoptic stability likely have the largest influence on the mixed-layer heights. Additionally, large intra-monthly variability suggests a strong influence from regional dynamics.

A GIS based approach to back trajectory analysis for the source apportionment of aerosol constituents and its first application

A new method has been developed to combine back trajectory statistics with a detailed land cover analysis. It provides numeric proxies for the residence times of sampled air masses above certain land cover classes (marine, natural vegetation, agricultural lands, urban areas, and bare areas), as well as further meteorological parameters (mean trajectory length, solar radiation along trajectory, and local height of the boundary mixing layer). The method has been implemented into a GIS-enabled database system to allow for an efficient processing of large datasets with low computational demands. A principal component analysis was performed on a dataset including the modelled residence times, the modelled meteorological parameters, some measured meteorological parameters (wind speed and temperature), and the concentrations of 10 particle constituents (inorganic ions and organic and elemental carbon) in 5 particle size ranges for 29 winter- and summertime samples at an urban background site in Leipzig, Germany. Six principal components could be extracted which together explained about 80% of the total variance in the dataset. The factors could be attributed to the influence of meteorology to continental background pollution, secondary formation processes in polluted air masses, wood burning, aged sea-salt, local traffic, and long-range transported crustal material. The modelled residence times and the meteorological parameters were generally consistent with the existing knowledge of specific particle sources and thereby facilitated and strengthened the interpretation of the factors. Moreover, they allowed for a clear distinction between continental background pollution and secondary formation processes, which has not been possible in previous source apportionment studies. The results demonstrate that the combined usage of back trajectory, land cover, and meteorological data by the presented method yields valuable additional information on the history of sampled air masses, which can improve the quality of source apportionment of atmospheric aerosol constituents.

Daytime Mixed Layer over the Santiago Basin: Description of Two Years of Observations with a Lidar Ceilometer

Abstract Two years of high-resolution backscatter profiles obtained with a commercial lidar ceilometer in Santiago Basin (33.5°S, 70.6°W) are analyzed. The generally large aerosol load in the Santiago atmospheric boundary layer (ABL) facilitates the use of these backscatter profiles for the retrieval of the daytime mixed layer height (MH), especially around midday. In winter mornings, however, MH retrievals are frequently confused by upper residual aerosol layers, while in summer afternoons very low aerosol concentrations often preclude them. Based on a database formed with successful MH retrievals over Santiago, the hourly, synoptic, and seasonal variability of clear-day MHs are documented. Daytime growth rates of MH show typical values of 50 m h−1 in winter and 100 m h−1 in summer. MHs at 1200 LT (UTC − 4 h) present a fourfold change between the cold months (MH ∼200 m) and the warm months (MH ∼800 m). Interquartile ranges of the monthly distributions of MH are about 200 m, with little change along the seasons. This statistical description of MH data is supplemented with analysis of temperature, solar radiation, and wind data at selected stations located at the basin’s floor, at the basin’s entrance, and at an elevated location representative of a level about 400 m above the basin’s floor. Seasonal MH variability appears highly controlled by the surface energy budget, with about 30% of the top-of-the-atmosphere radiative energy being used in the warming and growth of the daytime MH. Advection of cool air from the marine boundary layer to the west of the basin also appears to be important in the basin’s ABL energy budget in some cases. Stability of the early morning temperature profile in the basin’s air mass is also a factor in the mixed layer growth. Under conditions of large bulk stability of the basin’s air mass, there exist cases of very shallow daytime mixed layers that appear to develop after nights in which the stability is highly enhanced near the surface. Results herein are a first step toward a better understanding of the dynamics of this complex terrain ABL.