Evolution Of Atmospheric Boundary Layer Research Articles

Introducing the novel concept of cumulative concentration roses for studying the transport of ultrafine particles from an airport to adjacent residential areas

Abstract. Airports are often surrounded by urban residential areas, which is both a motivation and challenge for studying their potential impact on local air quality. Airports are a relevant source of ultrafine particles (UFPs), which can pose a risk to human health due to their small size (particle diameter Dp≤100 nm). However, in urban environments, UFPs originate from a multitude of biogenic and anthropogenic sources. Here, we investigate UFPs in close proximity to an airport to disentangle their impact on local air quality from other urban sources. We present observations and analyses of airborne UFP concentrations and size distributions determined at two sites in close proximity to Munich Airport. Therefore, two novel measurement stations were established north and south of the airport but were neither situated on the axis of prevailing wind directions nor impacted by fly overs. This set-up allowed us to explore a mainly advection-driven distribution of UFPs into the most populated adjacent residential areas. The observation period covered a full year from August 2021 to July 2022. We analysed the data set in three steps. (1) First, we derived UFP concentration roses using the wind data as reported at 10 m height at the airport to represent the local wind field. An increase in particle number concentrations and a shift of the modal maximum towards smaller mobility diameters became evident for wind directions, including those approaching from the airport. During the airport's operation hours during the daytime, median particle number concentrations were 2.2- and 1.6-fold compared to nighttime at the northern station and the southern station. However, our data had a high variability, and the direction-based analysis was uncertain due to other potential UFP sources in the surroundings and the assumption of a homogeneous, local wind field. (2) Next, we derived concentration roses employing the airflow observations from the two measuring stations at 5.3 m height. While the annual concentration rose in principle yielded the same conclusions as the first analysis step, a significant seasonal and diurnal variability of UFPs and wind became evident. The influencing factors were likely other urban local UFP sources, an increased surface roughness due to green vegetation, and the atmospheric boundary layer development. (3) In order to assess the possible advection of UFPs from the direction of Munich Airport relative to all other directions over the course of the year, we calculated cumulative concentration roses with both local- and site-scale wind data. Under the assumption of a homogeneous local wind field, the fraction of all UFPs sampled in airflows approaching from the airport's direction was 21 % (N322) and 40 % (S229). Considering a local background, the range of UFP advection from Munich Airport to the adjacent residential areas was up to 10 % in the north and 14 % in the south. It has to be noted that these values highlight the relative magnitude of the maximum impact of the airport on local air quality as they do not distinguish between UFP sources from the airport and other measuring sites. Additionally, they integrate over a time period during which the airport did not reach its full capacity compared to pre-COVID-19 times.

Sway of aerosol on Atmospheric Boundary Layer influencing air pollution of Delhi

Aerosols influence the development of Atmospheric Boundary Layer (ABL) ensuing aggravated air pollution in megacities. ABL Height (ABLH) and Ventilation coefficient (VC) are key aspects in the pollution study that determines the vertical extent of dispersion of pollutants. To address the intricate, multi-sectoral problem of air pollution, a cogent and considerable approach of evaluating the influence of aerosol on ABLH is vital. The data from 2019 –2021 over Delhi, presents quantitative evaluation of radiation effect of aerosol on ABL. The study demonstrates qualitatively that high aerosol loading lowers the ABLH, consecutively causes further increase in aerosol and PM2.5. Lowering of ABLH subsequently lowers the VC. The influence of aerosol on ABL and radiative forcing (RF) is critiqued with correlation coefficient (R) as −0.17 and − 0.37 respectively. The cooling effect of the surface is enhanced as Aerosol Optical Depth (AOD) rises, further impeding the development of ABL. Further, through the interdependence between Single Scattering Albedo (SSA) and ABLH, it is speculated that the absorbing aerosols (AA) tend to increase the stability, ultimately leading to lower ABLH. Assessing the link between ABL and air pollution is vital not only for preventing and combating aerosol emissions in Delhi, but also for accurate air quality prediction and numerical weather prediction.

Energy Mechanism of Atmospheric Boundary Layer Development Over the Tibetan Plateau

AbstractThe distinct thermodynamic characteristics of the atmospheric boundary layer (ABL) over the Tibetan Plateau (TP) significantly affect regional and global climate. It is well recognized that the ABL depth over the western TP can exceed 4,000 m. However, the energy mechanism of its development is less understood. In this study, the energy mechanism of ABL development of three sites on the TP was analyzed using intensive sounding observation data from the Third Tibetan Plateau Atmospheric Scientific Experiment. The results showed that the surface sensible heat flux, boundary layer entrainment energy, and heat flux at the top of the ABL affected ABL growth. The ABL depths at the Shiquanhe and Gerze stations were relatively higher, with a mean height of approximately 2,500 m above ground level (agl) and a maximum of 4,500 m agl. The ABL grew to its highest height at 20:00 Beijing Time, and its residual layer was also deep. The ABL depths at the Jiulong station were mainly below 1,200 m agl. The accumulated surface sensible heat flux (62.5%) and residual layer entrainment energy (9.7%) significantly affected the ABL development at Shiquanhe station. In addition to the accumulated sensible heat flux and residual layer entrainment energy, the latent heat flux at the top of the boundary layer also significantly impacted the ABL development at Gerze station. The energy required for the ABL growth at Jiulong station was also the smallest, owing to its lowest depth here. The accumulated sensible heat flux played the most crucial role in boundary layer development over the TP. The influences of wind shear on ABL growth cannot be ignored.

Soil Moisture-Boundary Layer Feedbacks on the Loess Plateau in China Using Radiosonde Data with 1-D Atmospheric Boundary Layer Model

The Loess Plateau is one land-atmosphere coupling hotspot. Soil moisture has an influence on atmospheric boundary layer development under specific early-morning atmospheric thermodynamic structures. This paper investigates the sensitivity of atmospheric convection to soil moisture conditions over the Loess Plateau in China by using the convective triggering potential (CTP)—humidity index (HIlow) framework. The CTP indicates atmospheric stability and the HIlow indicates atmospheric humidity in the low-level atmosphere. By comparing the model outcomes with the observations, the one-dimensional model achieves realistic daily behavior of the radiation and surface heat fluxes and the mixed layer properties with appropriate modifications. New CTP-HIlow thresholds for soil moisture-atmosphere feedbacks are found in the Loess Plateau area. By applying the new thresholds with long-time scales sounding data, we conclude that negative feedback is dominant in the north and west portion of the Loess Plateau; positive feedback is predominant in the south and east portion. In general, this framework has predictive significance for the impact of soil moisture on precipitation. By using this new CTP-HIlow framework, we can determine under what atmospheric conditions soil moisture can affect the triggering of precipitation and under what atmospheric conditions soil moisture has no influence on the triggering of precipitation.

Nocturnal surface radiation cooling modulated by cloud cover change reinforces PM2.5 accumulation: Observational study of heavy air pollution in the Sichuan Basin, Southwest China

Surface radiation is crucial to atmospheric boundary layer development and air pollution formation. Several studies have revealed that surface radiation plays a vital role in developing the daytime convective boundary layer that controls the explosive growth of PM2.5 concentration; however, less attention has been paid to the effects of changing nighttime surface radiation on the near-surface temperature inversion layer and PM2.5 accumulation. In this study, we used long-term observations of meteorological and environmental data and atmospheric boundary layer measurements during a severe PM2.5 pollution event to investigate the effect of changes in nocturnal surface radiation on the increase in PM2.5 concentrations. The results showed that surface radiation cooling was enhanced (weakened) by decreased (increased) cloud cover fraction by changing longwave radiation at night; this strengthened (weakened) near-surface temperature inversion intensity and promoted (prevented) the accumulated increase in PM2.5. This observational study using 5-year data further confirmed the cloud radiative effect on the nighttime accumulation of PM2.5 with a significant negative correlation between nighttime averages of surface PM2.5 concentrations and cloud cover fractions. This reveals an important mechanism for the impact of surface radiation cooling modulated by cloud cover change on the nighttime accumulated increase in PM2.5. This finding extends our understanding of air pollutant accumulation at night with potential implications for atmospheric environment change.

Distribution characteristics of methylsiloxanes in atmospheric environment of Saitama, Japan: Diurnal and seasonal variations and emission source apportionment

The large production volume of methylsiloxanes (MSs), combined with their high mobility/volatility and persistence, is a matter of concern from the atmospheric pollution perspective. Therefore, we evaluated of the concentrations and emission sources of MSs, including 7 cyclic methylsiloxanes (D3–D9; CMSs, the number refers to the number of Si–O bonds) and 13 linear methylsiloxanes (L3–L15; LMSs) in ambient air collected from Saitama, Japan. This is a first study regarding the evaluation of 20 methylsiloxanes in the Japanese atmosphere. We improved the air sampling methodology by determination the stability of D5 during a 7-d air sampling and arbitrary sample storage period using polystyrene-divinyl benzene copolymer sorbent (Sep-Pak plus PS-2). We analyzed air samples for MSs seasonally collected from nine locations in Saitama, including urban, suburban, rural, and mountainous areas. The mean CMS and LMS concentrations were 358 ng m−3 and 13.4 ng m−3, respectively. The D5 concentrations were distributed widely, with high concentrations in urban/suburban populous areas and dispersed at low concentrations in surrounding areas (north and mountainous areas). We analyzed 7-d air samples collected every week over a year and found apparent seasonal and periodic trends in the CMS concentrations. In the diurnal sampling campaign, we observed periodic fluctuations in ambient CMSs, with an inverse relationship with the atmospheric boundary layer development during the day. Backward trajectories and the prevailing wind direction during the sampling period indicated that the specific profiles of D4 observed in fall/winter weeks and north of Saitama could be ascribed to northwestward air-mass advection. We employed a novel approach in estimating CMSs emission sources and source apportionment by using non-negative matrix factorization (NMF). The concentration matrix was divided successfully into two factors (emission sources) namely, personal care and household products and industrial activities.

Impact of Lateral Groundwater Flow and Subsurface Lower Boundary Conditions on Atmospheric Boundary Layer Development over Complex Terrain

AbstractCredible soil moisture redistribution schemes are essential to meteorological models, as lower boundary moisture influences the balance of surface turbulent fluxes and atmospheric boundary layer (ABL) development. While land surface models (LSMs) have vastly improved in their hydrologic representation, several commonly held assumptions, such as free-draining lower boundary, one-dimensional moisture flux, and lack of groundwater representation, can bias the terrestrial water balance. This study explores the impact of LSM hydrology representation on ABL development in the Weather Research and Forecasting (WRF) meteorological model. The results of summertime WRF simulations with Noah LSM, characterized by 2-m-thick soil and one-dimensional flow, are shown for a domain in the Colorado Rocky Mountain headwaters region. A reference WRF simulation is compared to 1) the same model with soil moisture initialized by the hydrologic model ParFlow; 2) a deep, free-draining simulation; and 3) WRF coupled to ParFlow, a three-dimensional, integrated groundwater-surface water model. Results show that both lateral transport of groundwater and the rate of drainage from the lower soil layer can weaken or reverse the coupling strength between evaporative fraction and ABL over a 5-month summer period. The resulting shifts in low-level moist convection in river valleys and thermally driven airflows yield strengthened anabatic upslope winds and perturbations to regional precipitation.

Diurnal and seasonal variations of radon (222Rn) and their dependence on soil moisture and vertical stability of the lower atmosphere at Pune, India

Continuous measurements of the concentration of Radon (222Rn) and its progenies were made with a Radon detector, RTM 2200, at a tropical site, Pune (18° 31′ N, 73° 55′ E, 560 m), India from January to December 2012. Simultaneous measurements of small ions of <1.6 nm diameter were made with a Neutral Air Ion Spectrometer (NAIS). Annually - averaged diurnal variation curves of 222Rn concentration showed a peak (~9.9 Bq m−3) at 0800 Local Time (LT) and a minimum (~5.4 Bq m−3) at 1800 LT. Diurnal variations of 222Rn concentration during winter, post-monsoon, and pre-monsoon seasons were almost similar in shape but with decreasing amplitudes in these seasons. However, during monsoon season, 222Rn concentration was the lowest and remained almost constant throughout the day. Monthly mean value of 222Rn concentration was the highest in December and the lowest in June. Polonium (218Po) concentration did not show any systematic diurnal variation. Results are explained in terms of surface meteorology, soil moisture, soil temperature, vertical wind velocity, local topography and development of atmospheric boundary layer. 222Rn concentration increased with soil moisture content of <16%, rapidly dropped down to dry soil values and then remained almost constant with increasing soil moisture. On the other hand, 222Rn concentration decreased with the increase of upward vertical wind velocity in the atmospheric boundary layer. The diurnal variations of ionization rate, directly estimated from 222Rn measurements, and calculated from ion concentration measurements showed some similarities but differed in their amplitudes. Annual effective dose of 222Rn (~0.075 mSv) as estimated from our measurements at Pune was found below the value prescribed by World Health Organization.

Dual CCD detection method to retrieve aerosol extinction coefficient profile.

The profile of aerosol extinction coefficient can help understand the air pollution transportation and development of the atmospheric boundary layer. The charge-coupled device (CCD)-laser aerosol detection system (CLADS) was widely used to measure the profile of aerosol extinction coefficient, which has excellent resolution near the ground. Traditionally, a constant aerosol scattering phase function and single scattering albedo (SSA) is assumed when retrieving the profile of aerosol extinction coefficient using the measured signals from CLADS. Sensitivity studies in this research show that aerosol scattering phase function leads to an uncertainty up to 462% of the retrieved profile of aerosol extinction coefficient, while SSA leads to an uncertainty up to 25%. A new method is proposed to derive the profile of aerosol extinction coefficient by using two CCD cameras. The aerosol scattering phase function can be determined by minimizing the difference between profiles of aerosol extinction coefficient from the two CCD cameras without any assumption. The profile of aerosol extinction coefficient can be retrieved with high accuracy by using our optimized aerosol scattering phase function. This method is validated by simulation studies where the relative difference between the pre-parameterized aerosol extinction profile and retrieved aerosol extinction profile is below 6%. This dual CCD detection system is employed in a field measurement and proved to be reliable. Our proposed method can obtain more accurate profile of aerosol extinction coefficient for further works about air pollution and atmospheric boundary layer development.

Observations and Numerical Simulation of the Effects of the 21 August 2017 North American Total Solar Eclipse on Surface Conditions and Atmospheric Boundary-Layer Evolution

We present unique observations of a total solar eclipse from a small unmanned aircraft system (sUAS) platform that was operated during the 21 August 2017 North American solar eclipse. The observations were collected near Ten Mile, Tennessee, where eclipse totality lasted 2 min 38 s. A 2-m micrometeorological tripod was erected on-site to measure surface and air temperature, near-surface water vapour, incoming and outgoing shortwave and longwave radiative fluxes, and turbulent fluxes. The sUAS platform and micrometeorological tripod observations indicate significant cooling below a height of 50 m above ground level (a.g.l.) during and shortly after totality. Near-surface temperatures do not return to pre-eclipse values until about 60 min following totality. Above about 50 m a.g.l., smaller temperature changes are observed during the eclipse, as the duration of the eclipse has less influence on deeper boundary-layer turbulence. Additionally, the sensible heat flux becomes slightly negative around totality, and the turbulence kinetic energy and vertical velocity variance concurrently decrease. The evolution of the near-surface meteorological fields are investigated in more detail using a large-eddy simulation (LES) model. The simulations generally reproduce the observations well, in terms of the timing and magnitude of changes in temperature, moisture and sensible and latent heat fluxes. However, the LES model slightly underestimates the diurnal range and decrease in temperature during the eclipse while overestimating the sensible heat fluxes.

Effect of weakened diurnal evolution of atmospheric boundary layer to air pollution over eastern China associated to aerosol, cloud – ABL feedback

Upon the effect of atmospheric stability on air pollution, this study highlights the weakened diurnal evolution of atmospheric boundary layer (ABL), which is crucial to the formation of regional fog-haze and air pollution episodes over eastern China (ECN). The decrease of atmospheric visibility (Vis) during 1973–2012 is found to be related to the more stable ABL with weakened diurnal evolution that is characterized by a concurrent weakening of surface wind, a decrease in ABL height, and a reduction of diurnal temperature range (DTR, – 0.26 and – 0.092 °C/10-years in the winter and summer, respectively). With a general synchronous variation, the increase in both aerosol loading and cloud cover might work in concert to reduce solar radiation reaching the surface, stabilize ABL and weaken the diurnal ABL evolution, thereby weakening the turbulent mixing of pollutants and enhancing air pollution. This conjecture of “aerosol, cloud – ABL – air pollution” feedback, with particular emphasis on the effect of cloud (in addition to the effect of aerosol) on the ABL evolution, is supported by our analysis of 40 years trends in the cloud, Vis and DTR from surface observation, the aerosol optical depth from MODIS, and the validated MERRA-2 reanalysis aerosol, cloud and boundary layer height (by surface observation and routine radiosonde sounding). Regarding the linkage between fog-haze and diurnal evolution of the ABL, the result emphasizes the effect of a persistent high relative humidity (RH), which is found to be important to the formation of regional persistent fog-haze episodes and must be carefully considered in future study. Therefore, a chain of processes is suggested to interpret the occurrence of regional persistent fog-haze episodes over ECN. First, during a polluted day, because of aerosol radiative effects, the high ABL stability and high RH can persist throughout the day, and consequently, favoring the accumulation of pollutants as well as the secondary formation and hygroscopic growth of aerosol. Second, the maintenance of such more stable, humid and polluted ABL is in contrast to a clear day when the ABL is more convective in the afternoon and facilitates the diffusion and dilution of pollutants. Third, under a persistent stable synoptic system, the increase of air pollution associated with the weakened diurnal evolution of ABL due to the “aerosol, cloud – ABL – air pollution” feedback, as described above, can be further strengthened, thereby renders more persistent and severe air pollution events. The DTR variation in relationship with the aerosol, cloud, ABL and air pollution is also discussed.

On the diurnal cycle of surface energy fluxes in the North American monsoon region using the WRF‐Hydro modeling system

AbstractThe diurnal cycles of surface energy fluxes are important drivers of atmospheric boundary layer development and convective precipitation, particularly in regions with heterogeneous land surface conditions such as those under the influence of the North American monsoon (NAM). Characterization of diurnal surface fluxes and their controls has not been well constrained due to the paucity of observations in the NAM region. In this study, we evaluate the performance of the uncoupled WRF‐Hydro modeling system in its ability to represent soil moisture, turbulent heat fluxes, and surface temperature observations and compare these to operational analyses from other commonly used land surface models (LSMs). After a rigorous model evaluation, we quantify how the diurnal cycles of surface energy fluxes vary during the warm season for the major ecosystems in a regional basin. We find that the diurnal cycle of latent heat flux is more sensitive to ecosystem type than sensible heat flux due to the response of plant transpiration to variations in soil water content. Furthermore, the peak timing of precipitation affects the shape and magnitude of the diurnal cycle of plant transpiration in water‐stressed ecosystems, inducing mesoscale heterogeneity in land surface conditions between the major ecosystems within the basin. Comparisons to other LSMs indicate that ecosystem differences in the diurnal cycle of turbulent fluxes are underestimated in these products. While this study shows how land surface heterogeneity affects the simulated diurnal cycle of turbulent fluxes, additional coupled modeling efforts are needed to identify the potential impacts of these spatial differences on convective precipitation.

The surface-atmosphere exchange of carbon dioxide, water, and sensible heat across a dryland wheat-fallow rotation

Summer fallow – the practice of keeping a field out of production during the growing season – is a common practice in dryland wheat (Triticum aestivum L.) cropping systems to conserve soil water resources. Fallow also depletes soil carbon stocks and thereby soil quality. The area of summer fallow has decreased by tens of millions of hectares since the 1970s in the northern North American Great Plains as producers have recognized that avoiding fallow usually confers both economic and soil conservation benefits. Observed summertime cooling across parts of this region has coincided with fallow reduction, suggesting that the role of fallow in atmospheric processes needs to be ascertained. We measured carbon dioxide, latent heat, and sensible heat flux across a winter wheat – spring wheat – fallow sequence in Montana, USA to determine the effects of dryland crop management on ecosystem carbon resources and energy partitioning at the surface-atmosphere interface. Winter wheat and spring wheat fields were carbon sinks (Fc=−203±52g CCO2m−2 and −107±29g CCO2m−2), respectively, during the April to September study period, but the fallow field was a carbon source of 135±73g CCO2m−2. Evapotranspiration in the wheat crops was over 100mm greater than the 275±39mm observed in the fallow field during the study period. Modeled maximum daily atmospheric boundary layer height was on average 210m higher and up to 900m higher in fallow compared to the spring wheat field with more crossings of the modeled atmospheric boundary layer and lifted condensation level, suggesting that regional studies of the effects of fallow on near-surface temperature and moisture are necessary to understand the effects of fallow reduction on regional climate dynamics. Results demonstrate that fallow has a detrimental impact to soil carbon resources yet is less water intensive, with consequences for regional climate via its impacts on atmospheric boundary layer development and global climate via its carbon metabolism.

A Simplified Land Model (SLM) for use in cloud‐resolving models: Formulation and evaluation

AbstractA Simplified Land Model (SLM) that uses a minimalist set of parameters with a single‐layer vegetation and multilevel soil structure has been developed distinguishing canopy and undercanopy energy budgets. The primary motivation has been to design a land model for use in the System for Atmospheric Modeling (SAM) cloud‐resolving model to study land‐atmosphere interactions with a sufficient level of realism. SLM uses simplified expressions for the transport of heat, moisture, momentum, and radiation in soil‐vegetation system. The SLM performance has been evaluated over several land surface types using summertime tower observations of micrometeorological and biophysical data from three AmeriFlux sites, which include grassland, cropland, and deciduous‐broadleaf forest. In general, the SLM captures the observed diurnal cycle of surface energy budget and soil temperature reasonably well, although reproducing the evolution of soil moisture, especially after rain events, has been challenging. The SLM coupled to SAM has been applied to the case of summertime shallow cumulus convection over land based on the Atmospheric Radiation Measurements (ARM) Southern Great Plain (SGP) observations. The simulated surface latent and sensible heat fluxes as well as the evolution of thermodynamic profiles in convective boundary layer agree well with the estimates based on the observations. Sensitivity of atmospheric boundary layer development to the soil moisture and different land cover types has been also examined.

Impact of debris cover on glacier ablation and atmosphere–glacier feedbacks in the Karakoram

Abstract. The Karakoram range of the Hindu-Kush Himalaya is characterized by both extensive glaciation and a widespread prevalence of surficial debris cover on the glaciers. Surface debris exerts a strong control on glacier surface-energy and mass fluxes and, by modifying surface boundary conditions, has the potential to alter atmosphere–glacier feedbacks. To date, the influence of debris on Karakoram glaciers has only been directly assessed by a small number of glaciological measurements over short periods. Here, we include supraglacial debris in a high-resolution, interactively coupled atmosphere–glacier modeling system. To investigate glaciological and meteorological changes that arise due to the presence of debris, we perform two simulations using the coupled model from 1 May to 1 October 2004: one that treats all glacier surfaces as debris-free and one that introduces a simplified specification for the debris thickness. The basin-averaged impact of debris is a reduction in ablation of ~ 14 %, although the difference exceeds 5 m w.e. on the lowest-altitude glacier tongues. The relatively modest reduction in basin-mean mass loss results in part from non-negligible sub-debris melt rates under thicker covers and from compensating increases in melt under thinner debris, and may help to explain the lack of distinct differences in recent elevation changes between clean and debris-covered ice. The presence of debris also strongly alters the surface boundary condition and thus heat exchanges with the atmosphere; near-surface meteorological fields at lower elevations and their vertical gradients; and the atmospheric boundary layer development. These findings are relevant for glacio-hydrological studies on debris-covered glaciers and contribute towards an improved understanding of glacier behavior in the Karakoram.

A Scale-Consistent Terrestrial Systems Modeling Platform Based on COSMO, CLM, and ParFlow

AbstractA highly modular and scale-consistent Terrestrial Systems Modeling Platform (TerrSysMP) is presented. The modeling platform consists of an atmospheric model (Consortium for Small-Scale Modeling; COSMO), a land surface model (the NCAR Community Land Model, version 3.5; CLM3.5), and a 3D variably saturated groundwater flow model (ParFlow). An external coupler (Ocean Atmosphere Sea Ice Soil, version 3.0; OASIS3) with multiple executable approaches is employed to couple the three independently developed component models, which intrinsically allows for a separation of temporal–spatial modeling scales and the coupling frequencies between the component models.Idealized TerrSysMP simulations are presented, which focus on the interaction of key hydrologic processes, like runoff production (excess rainfall and saturation) at different hydrological modeling scales and the drawdown of the water table through groundwater pumping, with processes in the atmospheric boundary layer. The results show a strong linkage between integrated surface–groundwater dynamics, biogeophysical processes, and boundary layer evolution. The use of the mosaic approach for the hydrological component model (to resolve subgrid-scale topography) impacts simulated runoff production, soil moisture redistribution, and boundary layer evolution, which demonstrates the importance of hydrological modeling scales and thus the advantages of the coupling approach used in this study.Real data simulations were carried out with TerrSysMP over the Rur catchment in Germany. The inclusion of the integrated surface–groundwater flow model results in systematic patterns in the root zone soil moisture, which influence exchange flux distributions and the ensuing atmospheric boundary layer development. In a first comparison to observations, the 3D model compared to the 1D model shows slightly improved predictions of surface fluxes and a strong sensitivity to the initial soil moisture content.

Development and verification of a new wind speed forecasting system using an ensemble Kalman filter data assimilation technique in a fully coupled hydrologic and atmospheric model

Wind power is rapidly gaining prominence as a major source of renewable energy. Harnessing this promising energy source is challenging because of the chaotic nature of wind and its inherently intermittent nature. Accurate forecasting tools are critical to support the integration of wind energy into power grids and to maximize its impact on renewable energy portfolios. We have adapted the Data Assimilation Research Testbed (DART), a community software facility which includes the ensemble Kalman filter (EnKF) algorithm, to expand our capability to use observational data to improve forecasts produced with a fully coupled hydrologic and atmospheric modeling system, the ParFlow (PF) hydrologic model and the Weather Research and Forecasting (WRF) mesoscale atmospheric model, coupled via mass and energy fluxes across the land surface, and resulting in the PF.WRF model. Numerous studies have shown that soil moisture distribution and land surface vegetative processes profoundly influence atmospheric boundary layer development and weather processes on local and regional scales. We have used the PF.WRF model to explore the connections between the land surface and the atmosphere in terms of land surface energy flux partitioning and coupled variable fields including hydraulic conductivity, soil moisture, and wind speed and demonstrated that reductions in uncertainty in these coupled fields realized through assimilation of soil moisture observations propagate through the hydrologic and atmospheric system. The sensitivities found in this study will enable further studies to optimize observation strategies to maximize the utility of the PF.WRF‐DART forecasting system.

Simulation on Wind Characteristics in Extremely High Atmospheric Boundary Layer over Northwest China

Extremely high atmospheric boundary layer is observed during 29 May to 3 June 2000 over Dunhuang in Northwest China. Average height of the atmospheric boundary layer is more than 3500m during the observation. Environmental conditions such as wind related to the extremely high atmospheric boundary layer are analysed combined with numerical simulation. Of the first three days in the observation there are low-level jets and large wind shear near surface observed on 29 and 31 May. Wind speed variation in these three days agrees well with variation of the atmospheric boundary layer heights. WRF model is applied to simulate atmospheric boundary layer height and investigate wind characteristics. The model simulation ability is checked and the simulation results find a significant west jet exists over northern Dunhuang. The momentum from the jet transfers downward to Dunhuang to supply kinetic energy developing atmospheric boundary layer. At last two sensitive experiments are performed to study wind effect on the height. The sensitive experiments demonstrate that wind as a lateral boundary parameter heavily influences the atmospheric boundary layer development.

Physical and optical properties of aerosols over an urban location in Spain: seasonal and diurnal variability

Abstract. Measurements of aerosol optical properties and aerosol number size distribution obtained during the period from December 2005 to November 2007 at Granada, an urban site in south-eastern Spain, are analyzed. Large variations of the measured variables have been found, and related to variations in emissions sources and meteorological conditions. High values of aerosol absorption and scattering coefficients are obtained during winter and low values are measured during summer. This seasonal pattern in the surface aerosol optical properties is opposite to the seasonal cycle showed by columnar aerosol optical depth. The differences in the seasonal features of the surface and column-integrated data are related to seasonal variations in the aerosol vertical distribution, aerosol sources and boundary layer height. In winter the number density of "fine" particles (0.5&lt;particle diameter&lt;1 μm) is significantly larger than in summer while the number density of "coarse" particles (1&lt;particle diameter&lt;20 μm) is slightly larger during summer and spring than during winter and autumn. The scattering Angström exponent, αs, presents an evident seasonal cycle with values of 1.8±0.2, 1.6±0.3, 1.3±0.3 and 1.4±0.3 in winter, spring, summer and autumn, respectively. This suggests the presence of a large fraction of submicron particles at the site, especially during winter. The aerosols measured in this study contain a large fraction of absorbing material as indicated by the average single-scattering albedo that has values of 0.65±0.07, 0.66±0.06, 0.70±0.06 and 0.73±0.06 in autumn, winter, spring and summer, respectively. The aerosol scattering albedo obtained in the surface boundary layer of Granada is below the critical value of 0.86 that determines the shift from cooling to warming. These results put in evidence the need of efforts to reduce absorbing particles (black carbon) emissions to avoid the possible warming that would result from the reductions of the cooling aerosols only. The aerosol absorption and scattering coefficients present a clear diurnal pattern, in all seasons, with two local maxima, one early in the morning and the second one in the evening. This diurnal cycle is mainly attributed to the diurnal evolution of atmospheric boundary layer and local anthropogenic activities.

Aerosol optical properties and related chemical apportionment at Xinken in Pearl River Delta of China

Aerosol optical properties (AOPs) of sub- 10 μ m particles under dry conditions (relative humidity (RH) < 20 % ) were investigated at Xinken in Pearl River Delta of China from 4 October to 5 November 2004. Severe aerosol optical pollution has been found characterized by strongly light-absorbing particles. At 550 nm, the magnitude of the light scattering ( 333 ± 138 Mm - 1 ) and absorption ( 70 ± 42 Mm - 1 ), limited visual range ( 5.3 ± 2.5 km ), and low single scattering albedo ( 0.83 ± 0.05 ) show Xinken to be comparable to the most polluted urban cores rather than even a polluted rural site. Other presented AOPs include hemispheric backscattering fraction ( 11 ± 1 % ) and asymmetry parameter ( 0.67 ± 0.01 ) at 550 nm, and Ångström exponent ( a ˚ 450 / 700 = 1.6 ± 0.15 ). Systematic relationships exist among the various AOPs. Their diurnal variations cannot be solely explained with the development of atmospheric boundary layer, but also obviously influenced by local wind patterns, variation of sources, photochemistry and nighttime heterogeneous chemistry. The fractional contributions to extinction, scattering and absorption ( f ep ; sp ; ap ) due to sub-aerosol-populations and individual chemical compounds are derived by the Mie simulations. The sub- 1 μ m particles contribute more than 90% of the particle extinction ( σ ep , 550 nm ). Under dry conditions, f ep of non-sea-salt sulfate, particulate organic matter, elemental carbon (EC) and residual are about 44%, 17%, 17% and 15%, respectively. However, the water uptake of particles can contribute 50–60% to σ ep , 550 nm at RH 90%. So in the ambient atmosphere, sulfate, carbonaceous material and water all play very important roles, concerning the visibility impairment at Xinken. The respective mass extinction, scattering and absorption efficiencies ( α ep ; sp ; ap ) are mostly consistent with previously reported values for the polluted area. α ap , EC , 550 nm for sub- 1 μ m and sub- 10 μ m ranges are 9.3 ± 1.4 and 7.2 ± 1.0 m 2 g - 1 , respectively. Our results imply a higher α ap , EC for more internally mixed EC under the atmospheric conditions present at Xinken.