Shallow Inversion Research Articles

Vertical Profiles of Aerosol Optical Properties (VIS/NIR) over Wetland Environment: POLIMOS-2018 Field Campaign

This study aims to present the benefits of unmanned aircraft systems (UAS) in atmospheric aerosol research, specifically to obtain information on the vertical variability of aerosol single-scattering properties in the lower troposphere. The results discussed in this paper were obtained during the Polish Radar and Lidar Mobile Observation System (POLIMOS) field campaign in 2018 at a wetland and rural site located in the Rzecin (Poland). UAS was equipped with miniaturised devices (low-cost aerosol optical counter, aethalometer AE-51, RS41 radiosonde) to measure aerosol properties (scattering and absorption coefficient) and air thermodynamic parameters. Typical UAS vertical profiles were conducted up to approximately 1000 m agl. During nighttime, UAS measurements show a very shallow inversion surface layer up to about 100–200 m agl, with significant enhancement of aerosol scattering and absorption coefficient. In this case, the Pearson correlation coefficient between aerosol single-scattering properties measured by ground-based equipment and UAS devices significantly decreases with altitude. In such conditions, aerosol properties at 200 m agl are independent of the ground-based observation. On the contrary, the ground observations are better correlated with UAS measurements at higher altitudes during daytime and under well-mixed conditions. During long-range transport of biomass burning from fire in North America, the aerosol absorption coefficient increases with altitude, probably due to entrainment of such particles into the PBL.

Effects of occasional tillage on soil physical and chemical properties and weed infestation in a 10-year no-till system

Few studies have investigated how one-time targeted tillage of long-term no-till fields impacts topsoil properties and weed dynamics. An on-farm trial was implemented in 2020 to test the effects of occasional tillage (OT) in Morocco with a long-term no-tillage (NT) system and rainfed field crops: durum wheat (Triticum durum), faba bean (Vicia faba minor), and chickpea (Cicer arietinum). Four treatments were established, namely, continuous NT with crop residues maintained (“NT + residue”); continuous NT with crop residues not maintained (“NT-residue”); shallow inversion tillage (“shallow OT”); and deep non-inversion tillage (“deep OT”). We assessed the effect of these treatments on soil physical and chemical properties in 0–10 and 10–20 cm soil depths after crop harvest of the 2020–2021 (year 1) and 2021–2022 (year 2) growing seasons corresponding to 1 and 2 years after OT, respectively. In addition, we evaluated the effect of the treatments on weed populations and the effect of the legume crop rotated with wheat on soil nitrogen (N) and weed density. In year 1, deep OT reduced the water content at field capacity and available water capacity at 0–10 cm compared to continuous NT; the cation-exchange capacity (CEC) under deep OT was lower than in NT-residue and NT + residue at 0–10 cm and 10–20 cm, respectively. Furthermore, deep OT increased ammonium-N (NH4-N) at 0–10 and 10–20 cm compared to NT + residue but reduced exchangeable potassium (K) at 10–20 cm depth compared to NT-residue. In year 2, shallow OT had lower total porosity at 10–20 cm than NT + residue, while shallow and deep OT recorded higher water-stable aggregates at 0–10 cm than NT + residue; at 10–20 cm, deep OT recorded lower CEC than NT + residue. However, deep OT had higher nitrate-N (NO3-N) and available sulfur (S) than NT-residue at 10–20 cm. Occasional tillage did not significantly affect 10 out of 19 of the soil properties evaluated, including soil organic matter (SOM), in all the years and did not help reduce the stratification of soil nutrients in NT. In year 1, 50 days after OT, deep OT reduced the weed density by 46% compared to NT + residue, while in year 2, 406 days after OT, shallow OT reduced weed density by 53% compared to NT-residue. Regarding the effect of the legume rotated with wheat, faba bean appeared to be the better preceding or following wheat crop as it resulted in higher residual soil mineral N and lower weed infestation than chickpea.

PM10 aerosol enhancement in the anticyclonic anomalies caused by the East Asian spring warming of 2021

This study analyzed the PM10 aerosol enhancement caused by East Asian atmospheric warming during transboundary transport in March of 2021. It was found to be cooled near the north polar area and to have shifted the polar vortices northward over the East Asian region in the mid-troposphere. The Siberian high was weakened and the East Asian region was characterized by a positive air temperature anomaly and negative zonal wind speeds. The increasing rate of air temperature anomalies at 2 m was higher in the high latitude areas over 40°N in Mongolia and northeastern China, causing a decrease in zonal wind speeds at 10 m over eastern China and Korea. The anomalous variations of the MODIS-induced aerosol optical depth (AOD) were found to be positive with the highest value of +0.93 in the area ranging from northeastern China to Korea, despite the recent decreasing trends. The positive anomalous region of the MODIS-induced AOD was correlated with positive air temperatures and negative zonal wind speeds, causing enhanced formations of secondary aerosols in the atmosphere. As cold northerly winds were suppressed in the East Asian region, anomalous high pressures (anticyclonic anomalies) developed frequently in eastern China and moved to Korea. The Weather Research and Forecasting model to which meteorological and climate data were applied coupled with Chemistry (WRF-Chem) simulations on increases in the PM10 enhancement ratio, indicating enhanced formation amounts, during transboundary transport for the period of March 13–15, 2021. An air mass near the high terrain surface over eastern China under the backward side of an anticyclone warmed and moved toward the relatively low terrain of the Yellow Sea and Korea in keeping with the height. Air temperature inversion developed in the anomalous warmer center in the mid-troposphere, reaching the surface of the Yellow Sea and Korea. High PM10 concentrations were constrained near the shallow inversion layer. Furthermore, the PM10 enhancement ratio showed a positive level over the Yellow Sea with nearly zero anthropogenic emissions on the surface, gradually increasing at a rate of approximately 60% in Korea. The hourly contribution by the warming-induced PM10 enhancement (PM10 CbWIE) was calculated and found to be at the highest level of 70% in Seoul, Korea. Among PM10 secondary inorganic aerosols, nitrate formations were enhanced during transboundary transport in the warming-induced anticyclone with reactions rich in ammonium. While the sulfate enhancement ratio reached a positive level over the Yellow Sea, the gradual decrease during transboundary transport may be reflected by the decreased emissions of sulfur dioxide in eastern China.

Historical trends in the trade wind inversion in the tropical North Atlantic Ocean and Caribbean

AbstractThe trade wind inversion (TWI) serves as an important stabilizing mechanism in the tropical North Atlantic (TNA) region, including the Caribbean basin. Previous studies have diagnosed the TWI using in situ observations and radiosondes, typically over tropical islands. However, studies relying on these point measurements are unable to discern the climatology and evolution of the TWI over the rest of the TNA. This study addresses this gap in the literature through the use of high‐resolution ERA5 reanalysis model level data. Due to the advances in the ERA line of reanalysis products, ERA5 now provides vertical level resolution as fine as ~4 mb in the lower troposphere, enabling the identification of shallow inversions, such as the TWI, consistently on a climatological time scale in remote regions of the world. While still coarser than observed soundings, this reanalysis‐based approach provides a first attempt in understanding TNA TWI variability and its strength and frequency trends from 1979 to 2019. The TWI climatology constructed here finds consilience with previous modelling and observational studies in terms of the spatial variability of the TWI base and strength across this domain. Stronger and more frequent TWIs are noted across the central TNA across all seasons. Results from a Mann–Kendall analysis reveals increasing trends in TWI frequency and strength that vary spatially across the domain based on season. The most widespread and strongest increasing TWI frequency and strength signal is over the central TNA from December to July. Due to the regionalization of trends noted, potential regional forcing mechanisms responsible for these changes are discussed.

High-resolution vertical distribution and sources of HONO and NO<sub>2</sub> in the nocturnal boundary layer in urban Beijing, China

Abstract. Nitrous acid (HONO), an important precursor of the hydroxyl radical (OH), plays a key role in atmospheric chemistry, but its sources are still debated. The production of HONO on aerosol surfaces or on ground surfaces in nocturnal atmospheres remains controversial. The vertical profile provides vertical information on HONO and NO2 to understand the nocturnal HONO production and loss. In this study, we report the first high-resolution (<2.5 m) nocturnal vertical profiles of HONO and NO2 measured from in situ instruments on a movable container that was lifted on the side wiring of a 325 m meteorological tower in Beijing, China. High-resolution vertical profiles revealed the negative gradients of HONO and NO2 in nocturnal boundary layers, and a shallow inversion layer affected the vertical distribution of HONO. The vertical distribution of HONO was consistent with stratification and layering in the nocturnal urban atmosphere below 250 m. The increase in the HONO ∕ NO2 ratio was observed throughout the column from the clean episode to the haze episode, and relatively constant HONO∕NO2 ratios in the residual layer were observed during the haze episode. Direct HONO emissions from traffic contributed 29.3 % ± 12.4 % to the ambient HONO concentrations at night. The ground surface dominates HONO production by heterogeneous uptake of NO2 during clean episodes. In contrast, the HONO production on aerosol surfaces (30–300 ppt) explained the observed HONO increases (15–368 ppt) in the residual layer, suggesting that the aerosol surface dominates HONO production aloft during haze episodes, while the surface production of HONO and direct emissions into the overlying air are minor contributors. Average dry deposition rates of 0.74±0.31 and 1.55±0.32 ppb h−1 were estimated during the clean and haze episodes, respectively, implying that significant quantities of HONO could be deposited to the ground surface at night. Our results highlight the ever-changing contributions of aerosol and ground surfaces in nocturnal HONO production at different pollution levels and encourage more vertical gradient observations to evaluate the contributions from varied HONO sources.

Temperature and Relative Humidity Vertical Profiles within Planetary Boundary Layer in Winter Urban Airshed

The planetary boundary layer is a dynamic system with turbulent flow where horizontal and vertical air mixing depends mainly on the weather conditions and geomorphology. Normally, air temperature from the Earth surface decreases with height but inversion situation may occur, mainly during winter. Pollutant dispersion is poor during inversions so air pollutant concentration can quickly rise, especially in urban closed valleys. Air pollution was evaluated by WHO as a human carcinogen (mostly by polycyclic aromatic hydrocarbons) and health effects are obvious. Knowledge about inversion layer height is important for estimation of the pollution impact and it can give us also information about the air pollution sources. Temperature and relative humidity vertical profiles complement ground measurements. Ground measurements were conducted to characterize comprehensively urban airshed in Svermov, residential district of the city of Kladno, about 30 km NW of Prague, from the 2nd Feb. to the 3rd of March 2016. The Svermov is an air pollution hot-spot for long time benzo[a]pyrene (B[a]P) limit exceedances, reaching the highest B[a]P annual concentration in Bohemia – west part of the Czech Republic. Since the Svermov sits in a shallow valley, frequent vertical temperature inversion in winter and low emission heights of pollution sources prevent pollutant dispersal off the valley. Such orography is common to numerous small settlements in the Czech Republic. Ground measurements at the sports field in the Svermov were complemented by temperature and humidity vertical profiles acquired by a Vaisala radiosonde positioned at tethered He-filled balloon. Total number of 53 series of vertical profiles up to the height of 300 m was conducted. Meteorology parameters were acquired with 4 Hz frequency. The measurements confirmed frequent early-morning and night formation of temperature inversion within boundary layer up to the height of 50 m. This rather shallow inversion had significant influence on air quality due to inversion cap over the valley. Nevertheless, formation of an inversion showed strong diurnal variability. For example, on the 18th Feb. early morning shallow inversion quickly disappeared within less than 2 hours. According to this study tethered balloon measurements has proved to be a good tool for completion comprehensive ground air quality measurements.

Surface energy fluxes during the total solar eclipse over Ny-Ålesund, Svalbard, on 20 March 2015

On 20 March 2015, a total solar eclipse occurred over Ny-Alesund (78.9° N, 11.9° E), Svalbard, under ideal conditions with clear sky. The cycle of the radiation fluxes is comparable with other experiments during eclipses, with even the upward longwave radiation showing significant changes, with a delay to the shortwave radiation and a slowly linear increase after the totality. Also, under polar conditions, an increase of the wind velocity before and a decrease after the totality was found, which is an indicator of the generation of an “Eclipse cyclone”. This change of the wind direction generated a local wind system with a near-surface-layer katabatic flow. During the eclipse, a remarkably large sensible heat flux was observed. The turbulent fluxes were analysed using a wavelet technique with 1-minute time resolution, which is the ideal method for investigating these highly non-steady conditions. No influences on the boundary layer structure as measured with radiosondes were found, with the exception of a wind direction change during the eclipse cyclone below the shallow inversion layer.

Identification and intercomparison of surface‐based inversions over Antarctica from IASI, ERA‐Interim, and Concordiasi dropsonde data

AbstractSurface‐based temperature inversions (SBIs) occur frequently over Antarctica and play an important role in climate and weather. Antarctic SBIs are examined during the austral spring of 2010 using measurements from dropsondes, ERA‐Interim Atmospheric Reanalysis Model, and the recently released version 6 of the Infrared Atmospheric Sounding Interferometer (IASI) level 2 product. A SBI detection algorithm is applied to temperature profiles from these data sets. The results will be used to determine if satellite and reanalysis products can accurately characterize SBIs, and if so, then they may be used to study SBIs outside of the spring 2010 study period. From the dropsonde data, SBIs occur in 20% of profiles over sea ice and 54% of profiles over land. IASI and ERA‐Interim surface air temperatures are found to be significantly warmer than dropsonde observations at high plateau regions, while IASI surface air temperatures are colder over sea ice. IASI and ERA‐Interim have a cold bias at nearly all levels above the surface when compared to the dropsonde. SBIs are characterized by their frequency, depth, and intensity. It is found that SBIs are more prevalent, deeper, and more intense over the continent than over sea ice, especially at higher surface elevations. Using IASI and ERA‐Interim data the detection algorithm has a high probability of detection of SBIs but is found to severely overestimate the depth and underestimate the intensity for both data sets. These overestimation and underestimation are primarily due to the existence of extremely shallow inversion layers that neither satellite nor reanalysis products can resolve.

Shallow non-inversion tillage in organic farming maintains crop yields and increases soil C stocks: a meta-analysis

Reduced tillage is increasingly promoted to improve sustainability and productivity of agricultural systems. Nonetheless, adoption of reduced tillage by organic farmers has been slow due to concerns about nutrient supply, soil structure, and weeds that may limit yields. Here, we compiled the results from both published and unpublished research comparing deep or shallow inversion tillage, with various categories of reduced tillage under organic management. Shallow refers to less than 25 cm. We found that (1) division of reduced tillage practices into different classes with varying degrees of intensity allowed us to assess the trade-offs between reductions in tillage intensity, crop yields, weed incidence, and soil C stocks. (2) Reducing tillage intensity in organic systems reduced crop yields by an average of 7.6 % relative to deep inversion tillage with no significant reduction in yield relative to shallow inversion tillage. (3) Among the different classes of reduced tillage practice, shallow non-inversion tillage resulted in non-significant reductions in yield relative to deep inversion; whereas deep non-inversion tillage resulted in the largest yield reduction, of 11.6 %. (4) Using inversion tillage to only a shallow depth resulted in minimal reductions in yield, of 5.5 %, but significantly higher soil C stocks and better weed control. This finding suggests that this is a good option for organic farmers wanting to improve soil quality while minimizing impacts on yields. (5) Weeds were consistently higher, by about 50 %, when tillage intensity was reduced, although this did not always result in reduced yields.

Observed Thermal Impacts of Wind Farms Over Northern Illinois.

This paper assesses impacts of three wind farms in northern Illinois using land surface temperature (LST) data from the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments onboard the Terra and Aqua satellites for the period 2003–2013. Changes in LST between two periods (before and after construction of the wind turbines) and between wind farm pixels and nearby non-wind-farm pixels are quantified. An areal mean increase in LST by 0.18–0.39 °C is observed at nighttime over the wind farms, with the geographic distribution of this warming effect generally spatially coupled with the layout of the wind turbines (referred to as the spatial coupling), while there is no apparent impact on daytime LST. The nighttime LST warming effect varies with seasons, with the strongest warming in winter months of December-February, and the tightest spatial coupling in summer months of June-August. Analysis of seasonal variations in wind speed and direction from weather balloon sounding data and Automated Surface Observing System hourly observations from nearby stations suggest stronger winds correspond to seasons with greater warming and larger downwind impacts. The early morning soundings in Illinois are representative of the nighttime boundary layer and exhibit strong temperature inversions across all seasons. The strong and relatively shallow inversion in summer leaves warm air readily available to be mixed down and spatially well coupled with the turbine. Although the warming effect is strongest in winter, the spatial coupling is more erratic and spread out than in summer. These results suggest that the observed warming signal at nighttime is likely due to the net downward transport of heat from warmer air aloft to the surface, caused by the turbulent mixing in the wakes of the spinning turbine rotor blades.

Multiple sites HFSWR ocean shallow water depth and current inversion

In order to extract the ocean dynamic parameters from shallow water, water depth, and current inversion at multiple (three or more) sites, HFSWR (high frequency surface wave radar) sea echo is developed. In this paper the inversion principle and theoretical model are presented in detail, and the proposed idea is verified for three or more than three sites, which shows prospects in practice. By analyzing the data collected from three HFSWR detection experiments in northern Jiangsu province, the inversion results show good performance, which is promising for extracting ocean water depth in inner zone and shallow water by HFSWR in engineering application.

High‐resolution simulations of the night‐time stable boundary layer over snow

AbstractThe nocturnal stable boundary layer (SBL) over snow was studied via 1‐D clear‐sky simulations at 67oN. Three wind regimes could be identified. A windy SBL was relatively well‐mixed, turbulent cooling rates being moderate and long‐wave (LW) cooling rates weak as gradients of temperature and moisture (T,q) remained small. In calm and near‐calm cases the surface temperature Ts dropped rapidly in the evening, leading to a strong shallow inversion dominated by strong LW cooling. During weak winds (geostrophic wind Vg ∼ 3 m s−1), Ts decreased fairly rapidly in the evening with T2m closely coupled. The nocturnal inversion was moderately strong with strong turbulent cooling in the surface layer. The T,q‐profiles induced moderate LW cooling at mid‐inversion levels but LW heating in the lowest metres, which resisted the strong turbulent cooling. Thus the heating/cooling rates were fairly sensitive to the wind, especially near the surface.The snow surface was coldest after a calm night and warmer at windy sunrises, whereas the coldest air temperatures were obtained during weak winds, provided that the model's stability functions were of the ‘short tails’ type. A maximum in the downward sensible heat flux was associated with this. When the model's multilayer snow scheme was replaced by a coarse scheme, the nocturnal Ts and T2m stayed too warm. The use of old snow properties instead of typical snow produced relatively warm nocturnal temperatures whereas fresh snow led to quite cold temperatures. These aspects may have relevance to the SBL warm biases of large‐scale models.

Observations of atmospheric boundary layer temperature profiles with a small unmanned aerial vehicle

AbstractSmall Unmanned Meteorological Observer (SUMO) unmanned aerial vehicles (UAVs) were used to observe atmospheric boundary layer temperature profiles in the vicinity of McMurdo Station, Antarctica during January and September 2012. The observations from four flight days are shown and exhibit a variety of boundary layer temperature profiles ranging from deep, well-mixed conditions to strong, shallow inversions. Repeat UAV profiles over short periods of time (tens of minutes to several hours) revealed rapid changes in boundary layer structure. The success of the SUMO flights described here demonstrates the potential for using small UAVs for Antarctic research.

Particulate matter sources on an hourly timescale in a rural community during the winter

Particulate matter (PM) sources at four different monitoring sites in Alexandra, New Zealand, were investigated on an hourly timescale. Three of the sites were located on a horizontal transect, upwind, central, and downwind of the general katabatic flow pathway. The fourth monitoring site was located at the central site, but at a height of 26 m, using a knuckleboom, when wind conditions permitted. Average hourly PM10 (PM with an aerodynamic diameter <10 μm) concentrations in Alexandra showed slightly different diurnal profiles depending on the sampling site location. Each location did, however, feature a large evening peak and smaller morning peak in PM10 concentrations. The central site in Alexandra experienced the highest PM10 concentrations as a result of PM transport along a number of katabatic flow pathways. A significant difference in PM10 concentrations between the central and elevated sites indicated that a shallow inversion layer formed below the elevated site, limiting the vertical dispersion of pollutants. Four PM10 sources were identified at each of the sites: biomass combustion, vehicles, crustal matter, and marine aerosol. Biomass combustion was identified as the most significant source of PM10, contributing up to 91% of the measured PM10. Plots of the average hourly source contributions to each site revealed that biomass combustion was responsible for both the evening and morning peaks in PM10 concentrations observed at each of the sites, suggesting that Alexandra residents were relighting their fires when they rose in the morning. The identification of PM sources on an hourly timescale can have significant implications for air quality management.Implications: Monitoring the sources of PM10 on an hourly timescale at multiple sites within an airshed provides extremely useful information for air quality management. Sources responsible for observed peaks in measured diurnal PM10 concentration profiles can be easily identified and targeted for reduction. Also, hourly PM10 sampling can provide crucial information on the role meteorology plays in the development of elevated PM10 concentrations.

An image-based effective-medium modeling of near-surface anomalies

Near-surface modeling for statics corrections is an integral part of a land seismic data processing workflow. The methods for near-surface modeling can be categorized into five groups: (1) uphole surveys, (2) shallow seismic surveys, (3) traveltime inversion, (4) waveform inversion, and (5) joint inversion of seismic and nonseismic data. The first two are past methods, the third, usually referred to as traveltime tomography, is at present the most widely accepted method, and the last two methods are future methods with several practical aspects yet to be resolved.

Seasonal Influence on the Ambient Air Quality in Al Jahra City for Year 2010

Eight primary criteria air contaminants were measured continuously for the year 2010 to evaluate ambient air quality in Al Jahra, which is one of the oldest and busiest cities in the state of Kuwait. The state of the art instrumentation was used to record the pollutants concentration to ppb levels maintaining quality control and quality assurance. Hourly base data for Non-Methane Hydrocarons (NM-HC), CH4, CO, CO2, O3, SO2, NO2 and Particulate Matter (PM10) were analyzed for year 2010. Meteorological parameters contributing to air pollution, such as (temperature, solar intensity, wind speed and direction) have also been considered. The effect of winter and summer seasonal changes on pollutant concentration levels were analyzed to identify the most probable sources for the application of the futuristic mitigation methods for pollution abatement. The obtained results consistently suggest that the foregoing pollutant concentration levels are higher in winter than summer due to poor dispersion and shallow inversion layer with the exception of O3, CO2 and PM10. However, all of the pollutant concentrations are below the allowable standards limits except for NM-HC.

An Alternative Eddy-Viscosity Model for the Horizontally Uniform Atmospheric Boundary Layer

This paper explores the utility of specifying the eddy viscosity for the horizontally uniform boundary layer as the product \({K=\sigma_w^2 \tau_w}\) of the variance of vertical velocity and an empirical time scale τ w , as opposed to the more usual formulation \({K = \sqrt{\alpha k}\lambda_k}\) where k is the turbulent kinetic energy (TKE), λ k is a length scale and α is a dimensionless coefficient. Simulations were compared with the observations on Day 33 of the Wangara experiment, and with a plausible specification of τ w (or λ k ) each model simulated convective boundary-layer development reasonably well, although the \({K=\sqrt{\alpha k}\lambda_k}\) closure produced a more realistic width for the entrainment layer. Under the light winds of Day 33, and with the onset of evening cooling, an excessively shallow and strongly-stratified nocturnal inversion developed, and limited its own further deepening. Boundary-layer models that neglect radiative heat transport and parametrize convective transport by eddy viscosity closure are prone to this runaway (unstable) feedback when forced by a negative (i.e. downward) surface flux of sensible heat.

Unraveling the complex local-scale flows influencing ozone patterns in the southern Great Lakes of North America

Abstract. This study examines the complexity of various processes influencing summertime ozone levels in the southern Great Lakes region of North America. Results from the Border Air Quality and Meteorology (BAQS-Met) field campaign in the summer of 2007 are examined with respect to land-lake differences and local meteorology using a large array of ground-based measurements, aircraft data, and simulation results from a high resolution (2.5 km) regional air-quality model, AURAMS. Analyses of average ozone mixing ratio from the entire BAQS-Met intensive campaign period support previous findings that ozone levels are higher over the southern Great Lakes than over the adjacent land. However, there is great heterogeneity in the spatial distribution of surface ozone over the lakes, particularly over Lake Erie during the day, with higher levels located over the southwestern end of the lake. Model results suggest that some of these increased ozone levels are due to local emission sources in large nearby urban centers. While an ozone reservoir layer is predicted by the AURAMS model over Lake Erie at night, the land-lake differences in ozone mixing ratios are most pronounced during the night in a shallow inversion layer of about 200 m above the surface. After sunrise, these differences have a limited effect on the total mass of ozone over the lakes and land during the day, though they do cause elevated ozone levels in the lake-breeze air in some locations. The model also predicts a mean vertical circulation during the day with an updraft over Detroit-Windsor and downdraft over Lake St. Clair, which transports ozone up to 1500 m above ground and results in high ozone over the lake. Oscillations in ground-level ozone mixing ratios were observed on several nights and at several ground monitoring sites, with amplitudes of up to 40 ppbv and time periods of 15–40 min. Several possible mechanisms for these oscillations are discussed, but a complete understanding of their causes is not possible given current data and knowledge.

Spatial distribution of aerosols in the Inn Valley atmosphere during wintertime

This study analyzes the structure of the wintertime boundary layer in an Alpine valley (Inn Valley, Austria) for a case of high air pollution. We present airborne aerosol observations collected with particle counters and a backscatter lidar. The effect of upslope winds on the spatial distribution of pollutants is investigated. An asymmetry in the aerosol distribution is observed in the cross-valley direction which presumably is related to differences in orientation and albedo of the two valley slopes. A one-sided thermal circulation, which develops above the sun-exposed slope, is most likely responsible for the observed redistribution of aerosols during daytime. Elevated aerosol layers form at the height of shallow inversion layers. Despite this vertical transport of pollutants by slope winds, no effective vertical venting of the polluted air mass into the free atmosphere can be achieved.

Manifestation of remote response over the equatorial Pacific in a climate model

In this paper we examine the simulations over the tropical Pacific Ocean from long‐term simulations of two different versions of the Center for Ocean‐Land‐Atmosphere Studies (COLA) coupled climate model that have a different global distribution of the inversion clouds. We find that subtle changes made to the numerics of an empirical parameterization of the inversion clouds can result in a significant change in the coupled climate of the equatorial Pacific Ocean. In one coupled simulation of this study we enforce a simple linear spatial filtering of the diagnostic inversion clouds to ameliorate its spatial incoherency (as a result of the Gibbs effect) while in the other we conduct no such filtering. It is found from the comparison of these two simulations that changing the distribution of the shallow inversion clouds prevalent in the subsidence region of the subtropical high over the eastern oceans in this manner has a direct bearing on the surface wind stress through surface pressure modifications. The SST in the warm pool region responds to this modulation of the wind stress, thus affecting the convective activity over the warm pool region and also the large‐scale Walker and Hadley circulation. The interannual variability of SST in the eastern equatorial Pacific Ocean is also modulated by this change to the inversion clouds. Consequently, this sensitivity has a bearing on the midlatitude height response. The same set of two experiments were conducted with the respective versions of the atmosphere general circulation model uncoupled to the ocean general circulation model but forced with observed SST to demonstrate that this sensitivity of the mean climate of the equatorial Pacific Ocean is unique to the coupled climate model where atmosphere, ocean and land interact. Therefore a strong case is made for adopting coupled ocean‐land‐atmosphere framework to develop climate models as against the usual practice of developing component models independent of each other.