Vertical Layer Structure Research Articles

Evaluation of the Coupled Arctic Forecast System’s representation of the Arctic atmospheric boundary layer vertical structure during MOSAiC

Observations from the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) were used to evaluate the Coupled Arctic Forecast System (CAFS) model’s ability to simulate the atmospheric boundary layer (ABL) structure in the central Arctic. MOSAiC observations of the lower atmosphere from radiosondes, downwelling longwave radiation (LWD) from a pyranometer, and near-surface wind conditions from a meteorological tower were compared to 6-hourly CAFS output. A self-organizing map (SOM) analysis reveals that CAFS reproduces the range of stability structures identified by the SOM trained with MOSAiC observations of virtual potential temperature (θv) profiles, but not necessarily with the correct frequency or at the correct time. Additionally, the wind speed profiles corresponding to a particular θv profile are not consistent between CAFS and the observations. When categorizing profiles by static stability, it was revealed that CAFS simulates all observed stability regimes, but overrepresents the frequency of near-surface strong stability, and underrepresents the frequency of strong stability between the top of the ABL and 1 km. The 10 m wind speeds corresponding to each stability regime consistently have larger values in CAFS versus observed, and this offset increases with decreasing stability. Whether LWD is over or underestimated in CAFS is dependent on stability regime. Both variables are most greatly overestimated in spring, leading to the largest near-surface θv bias, and the greatest underrepresentation of strong stability in spring. The results of this article serve to highlight the positive aspects of CAFS for representing the ABL and reveal impacts of misrepresentations of physical processes dictating energy, moisture, and momentum transfer in the lower troposphere on the simulation of central Arctic ABL structure and stability. This highlights potential areas for improvement in CAFS and other numerical weather prediction models. The SOM-based analysis especially provides a unique opportunity for process-based model evaluation.

Revealing the antipolar order in the antiferroelectric SmZA phase by means of circular alignment

Many ferroelectric nematic liquid crystals, like one of the archetype materials, DIO, do not have a direct paraelectric N to ferroelectric NF phase transition, but exhibit yet another phase between N and NF. This phase has recently been proposed to be antiferroelectric, with a layered structure of alternating polarization normal to the average director and is sometimes referred to as Smectic ZA (SmZA). We have examined the SmZA phase in circularly rubbed (CR) cells, known to discriminate between the polar NF and the non-polar N phase from the configuration of disclination lines formed. We find that the ground state of SmZA has the same disclination configuration as the non-polar N phase, demonstrating that the SmZA phase is also non-polar, i.e., it has no net ferroelectric polarization. At the same time, the SmZA texture generally has a grainy appearance, which we suggest is partly a result of the frustration related to layered order combined with the imposed twist in CR cells. We discuss possible orientations of the smectic layers, depending on the alignment conditions. While a horizontal SmZA layer structure is always compatible with surface-induced twist, a vertical layer structure would tend to break up in a twisted bookshelf structure to match non-parallel alignment directions at the two surfaces.

In situ construction of PtSe2/Ge Schottky junction array with interface passivation for broadband infrared photodetection and imaging

AbstractInfrared (IR) detection is vital for various military and civilian applications. Recent research has highlighted the potential of two‐dimensional (2D) topological semimetals in IR detection due to their distinctive advantages, including van der Waals (vdW) stacking, gapless electronic structure, and Van Hove singularities in the electronic density of states. However, challenges such as large‐scale patterning, poor photoresponsivity, and high dark current of photodetectors based on 2D topological semimetals significantly impede their wider applications in low‐energy photon sensing. Here, we demonstrate the in situ fabrication of PtSe2/Ge Schottky junction by directly depositing 2D PtSe2 films with a vertical layer structure on a Ge substrate with an ultrathin AlOx layer. Due to high quality junction, the photodetector features a broadband response of up to 4.6 μm, along with a high specific detectivity of ~1012 Jones, and operates with remarkable stability in ambient conditions as well. Moreover, the highly integrated device arrays based on PtSe2/AlOx/Ge Schottky junction showcases excellent Mid‐IR (MIR) imaging capability at room temperature. These findings highlight the promising prospects of 2D topological semimetals for uncooled IR photodetection and imaging applications.image

Martian Atmospheric Aerosols Composition and Distribution Retrievals During the First Martian Year of NOMAD/TGO Solar Occultation Measurements: 2. Extended Results, End of MY 34 and First Half of MY 35

AbstractThis is the second part of Stolzenbach et al. (2023, https://doi.org/10.1029/2022JE007276), named hereafter Paper I, extends the period to the end of MY 34 and the first half of MY 35. This encompasses the end phase of the MY 34 Global Dust Storm (GDS), the MY 34 C‐Storm, the Aphelion Cloud Belt (ACB) season of MY 35, and an unusual early dust event of MY 35 from LS 30° to LS 55°. The end of MY 34 overall aerosol size distribution shows the same parameters for dust and water ice to what was seen during the MY 34 GDS. Interestingly, the layered water ice vertical structure of MY 34 GDS disappears. The MY 34 C‐Storm maintains condition like the MY 34 GDS. A high latitude layer of bigger water ice particles, close to 1 μm, is seen from 50 to 60 km. This layered structure is linked to an enhanced meridional transport characteristic of high intensity dust event which put the MY 34 C‐Storm as particularly intense compared to non‐GDS years C‐Storms as previously suggested by Holmes et al. (2021, https://doi.org/10.1016/j.epsl.2021.117109). Surprisingly, MY 35 began with an unusually large dust event (Kass et al., 2020, https://ui.adsabs.harvard.edu/abs/2020AGUFMP039…01K) found in the Northern hemisphere during LS 35° to LS 50°. During this dust event, the altitude of aerosol first detection is roughly equal to 20 km. This is close to the values encountered during the MY 34 GDS, its decay phase and the C‐Storm of the same year. Nonetheless, no vertical layered structure was observed.

Molybdenum disulfide (MoS[formula omitted]) and reduced graphene oxide (rGO) nanocomposite based electrochemical sensor for detecting mercury(II) ions

In this study, a two-dimensional (2D) layered nanocomposite of molybdenum disulfide and reduced graphene oxide (rGO) was synthesized through a facile single-step hydrothermal method. Internal structure and morphological studies have shown that the vertical layered structure of MoS2 has grown over the horizontally aligned layer of reduced graphene oxide. The XRD analysis proved that the structure is multi-layered with 68.8 % crystallinity. Despite the highly crystalline nanocomposite structure, very few defects are also present in the network, as shown through Raman spectroscopy. Further, the presence of CS, RSR, CO, CO, MoO and MoS bonds, identified through XPS, indicates the successful synthesis of the MoS2-rGO nanocomposite. The nanocomposite was further evaluated for its electrochemical properties and applications regarding the sensing of mercury ions. Cyclic voltammetry shows that the oxidation peak current response increased by ∼103 % with the MoS2-rGO modified electrode compared to a bare electrode. The sensor has shown an excellent detection limit (LOD) of 1.6 μM, while the sensitivity and limit of quantification obtained from the sensor are 76.302 μM μA−1 cm−2 and 5.4 μM, respectively. The enhanced sensing performance of the MoS2-rGO modified sensor is attributed to the synergistic effect of MoS2 and rGO. The as-synthesized sensor also exhibits excellent stability, as only a 13% drop in current was observed after 60 days. This work proves that MoS2-rGO possesses enormous potential for developing next-generation heavy metal ion sensors.

Characteristics of atmospheric boundary layer and its relation with PM2.5 during winter in Shihezi, an Oasis city in Northwest China

Based on low-level atmospheric meteorological elemental and pollutant data in the vertical direction observed during a tethered sonde sounding experiment from December 27, 2019 to January 14, 2020 this study analysed the atmospheric boundary layer vertical structure and its influence on winter PM2.5 concentrations in Shihezi City, Xinjiang, using Richardson number (Ri) profiling and correlation analysis to better understand the correlation between the atmospheric boundary layer structure and continuous heavy pollution in Shihezi City during winter. The results showed that heavy pollution continued during the observational period, and the diurnal variation in the atmospheric boundary layer disappeared. The atmospheric boundary layer structure tended to remain stable, and the average boundary layer height was only 109 m. The lengthy temperature inversion lifespan, high humidity, and low-wind layer near the surface primarily contributed to the sustained heavy pollution during winter in Shihezi City. Temperature and wind speed during heavy pollution events were negatively correlated with the PM2.5 concentrations in the near-surface layer. Stable atmospheric thermodynamic stratification with a cold lower layer and a warm upper layer in the atmospheric boundary layer weakens vertical atmospheric pollutant diffusion. Moreover, increased relative humidity (RH) is beneficial for hygroscopic aerosol particle growth and liquid-phase chemical reactions, thus worsening heavy pollution.

Propagation Characteristics of Lightning Radiation Field on Three-Layer Vertical Layered Ground Based on CPML Absorption Boundary

The perfectly matched layer absorbing boundary condition based on coordinate scaling transformation (CPML) has a good absorption effect in finite-difference time-domain method (FDTD) calculation. In this study, we derive the CPML update equations in the 2-D cylindrical coordinate system by setting an appropriate coordinate-stretching variable, which can more easily achieve CPML and obtain good results in the calculation of lightning electromagnetic field. Then, the propagation characteristics of the lightning return stroke radiation field on the three-layer vertical layered ground structure are studied. The results show the following: 1) at 10 m above the ground, the vertical electric field and azimuthal magnetic field are almost not affected by the vertically layered ground structure, while the horizontal electric field is slightly affected by the vertical layered ground structure and 2) at 3 m below the ground, the lightning radiation fields are all affected by the vertically layered ground structure, which the vertical electric field is the most affected, and it can also use two-layer vertical layered ground structure instead of three-layer vertical layered ground structure for FDTD calculation under certain conditions, which can simplify the calculation model. All the results are obtained at a close distance from the lighting channel.

Ridge waveguide lasers with vertically stacked quantum wells and tunnel junctions

We report on the fabrication and electro-optical performance of ridge waveguide (RW) lasers emitting near 905 nm based on a vertical layer structure consisting of three single quantum wells (SQWs) as active regions separated by two tunnel junctions (TJs). The single waveguide core is designed in such a way that the third vertical mode is lasing. The width of the ridge is varied between 3 µm and 200 µm. Deep- and shallow-etched ridges were fabricated. The shallow etching stopped slightly above the topmost SQW, whereas the deep etch went through all TJs and stopped slightly above the lowest SQW. For comparison, we also fabricated conventional shallow-etched RW lasers based on a similar vertical structure having only one SQW and no TJs. The TJ RW lasers with deep-etched ridges provide the highest output power, lowest threshold current and best slope efficiency of 2.4 W A−1 for a ridge width of 6 µm. The performance of shallow-etched TJ RW lasers is lowest for small ridge widths but surpasses the performance of the conventional RW lasers when the ridge width is increased. The lateral far field angle of deep-etched TJ RW lasers is about 2° larger compared to the shallow etched ones.

SOLS: An Open-Source Spaceborne Oceanic Lidar Simulator

In recent years, oceanic lidar has seen a wide range of oceanic applications, such as optical profiling and detecting bathymetry. Furthermore, spaceborne lidars, CALIOP and ICESat-2, designed for atmospheric and ice science applications, have been used for ocean backscattering retrievals, but, until now, there has been no spaceborne lidar specifically designed for ocean detection. There is a demand for an effective lidar simulator to study the detection potential capability of spaceborne oceanic lidar. In this study, an open-source spaceborne oceanic lidar simulator named SOLS was developed, which is available freely. Moreover, the maximum detectable depth and corresponding optimal wavelength for spaceborne lidar were analyzed at a global scale by using SOLS. The factors controlling detection limits of a spaceborne ocean profiling lidar in different cases were discussed. Then, the maximum detectable depths with different relative measurement errors and the influence of solar background radiance were estimated. Subsequently, the effects of laser and detector parameters on maximum detectable depths were studied. The relationship between the lidar detectable depth and the ocean mixed layer depth was also discussed. Preliminary results show that the maximum detectable depth could reach deeper than 120 m in the oligotrophic sea at low latitudes. We found that 490 nm is the optimal wavelength for most of the open seawater. For coastal water, 532 nm is a more suitable choice considering both the technical maturity and geophysical parameters. If possible, a lidar equipped with 440 nm could achieve the greatest depth in oligotrophic seawater in subtropical gyres north and south of the equator. The upper mixed layer vertical structure in most of the global open ocean is within the lidar maximum detectable depth. These results show that SOLS can help the design of future spaceborne oceanic lidar systems a lot.

Vertical Profiles of Ozone Concentrations in the Lower Troposphere Downwind of New York City During LISTOS 2018–2019

AbstractWhile surface concentrations of ozone are routinely monitored, ozone aloft is infrequently measured, but critical for a full understanding of ozone production and transport. In this study, twenty‐six balloon‐borne ozonesondes were launched near the north shore of central Long Island in the summers of 2018 and 2019 as part of the Long Island Sound Tropospheric Ozone Study (LISTOS). The observed vertical ozone profiles are presented and analyzed with additional data sources and modeling tools, including lidar wind profiles from the New York State Mesonet, back trajectories based on 3 km resolution high‐resolution rapid refresh model data, and surface data, aircraft observations, sonde, and ozone lidar measurements from other LISTOS participants. Special attention is given to the region of interest for ozone pollution in the lower troposphere, from the surface to 2 km altitude. Cases analyzed in detail illustrate events with high ozone levels observed in the lower troposphere, often with pronounced vertical structure in the profile. Specifically, easily discernible layers are identified with ozone excursions of up to 40 ppb over short vertical distances. Analysis indicates that synoptic and local meteorological processes can combine to generate the observed vertical profiles. Hot, sunny days with high‐pressure systems are accompanied by high precursor emissions due to increased power demands, plentiful radiation for photochemistry, and stagnation of synoptic winds. Under these conditions, meso‐ and smaller‐scale flows like low‐level jets and sea/bay/land breeze circulations may dominate synoptic flow to produce shearing and the complex vertical layered structure observed.

Mode engineering of semiconductor lasers with vertical periodic layered structures

High-power and low-divergence semiconductor lasers are useful in light detection and ranging, as well as material processing and so on. In this paper, an efficient approach is presented to explain the physics of mode selection in semiconductor lasers with vertical periodic layers for high power and low vertical beam divergence. The transmission matrix method is used to obtain the allowed band and forbidden band of the vertical periodic layered structure, and the band diagram of the layered structure of the semiconductor laser. The fundamental mode of the layered structure of the semiconductor laser lies in the forbidden band of the vertical periodic layered structure. Tapered lasers based on the designed layered structure are fabricated and can achieve an output power of 2.45 W. The measured vertical divergence angle of the tapered laser is below 10°, consistent well with the calculated result of 9.5°.

Impacts of Atmospheric Boundary Layer Vertical Structure on Haze Pollution Observed by Tethered Balloon and Lidar

In this paper, the characteristics of the atmospheric boundary layer (ABL) vertical structure over the North China Plain (NCP) during a comprehensive observation experiment conducted during 15–21 December 2018 were investigated. Observational data were obtained with a large tethered balloon, Doppler wind lidar, and ground-level instruments. The maximum concentration of PM2.5 exceeded 200 µg m−3, and the ratio of PM2.5/PM10 was approximately 0.4 (its maxi-mum was approximately 0.8) during the whole observation period, indicating the explosive growth of dominant fine-mode aerosols in the winter heating season. Elevated concentrations of pollutants decreased the solar irradiance received by the ground, resulting in lower temperature at ground level. Our results illustrate three distinct types of vertical profiles: Type 1 (convective state)—the concentration of PM2.5 decreased nearly linearly with increase of the height below approximately 600 m; Type 2 (stable state)—the PM2.5 concentration sharply decreased from the ground to approximately 200 m; and Type 3 (multilayer structure)—some pollutants were suspended aloft in the upper air layer. Diurnal evolution of the vertical profiles of PM2.5 and their relationship with the changes in meteorological factors were identified. From daytime to nighttime, the vertical profiles evolved from Type 1 to Type 2 or Type 3. All the 33 vertical PM2.5 profiles that we obtained showed a strong relationship with elements of the ABL structure, such as the distributions of winds, the inversion layer, and turbulence activities. A light-wind layer and weak turbulence activity, especially within the inversion layer, contributed greatly to the accumulation of pollutants. Vertical PM2.5 concentration patterns were also greatly affected by local ground-level emission sources and regional transport processes.

Biomass of green filamentous alga Cladophora (Chlorophyta) from a hypersaline lake in Crimea as a prospective source of lutein and other pigments

The filamentous green alga Cladophora spp. is one of the most common plants to be found in various water bodies, from fresh to hypersaline ones. The goals of this work are to determine the pigment composition and content in the green filamentous alga Cladophora spp. occurring in the hypersaline Lake Khersonesskoye (the Crimean Peninsula) and to assess the potential use of Cladophora mats as a cheap raw material for the pharmaceutical and food industries. Cladophora mats were found to have vertical stratification with pronounced morphological and biochemical characters of the layers. In the vertical layered structure of the mat, the floating and bottom mats are clearly distinguishable. Using HPLC, MS/MS, MS and UV–Vis methods, the contents of all-trans lutein (0.55 ± 0.25 mg·g−1 dry weight, d.w.), lutein cis-isomers (0.17 ± 0.07 mg·g−1 d.w.), and siphonaxanthin (0.057 ± 0.026 mg·g−1 d.w.) were determined in the lower layer of the Cladophora floating mat. A comparative analysis of the literature data as regards the content of lutein and siphonaxanthin in various natural sources showed the promise of producing these carotenoids industrially from Cladophora spp., taking into account the large and renewable resources of these algae in Crimean lakes.

Investigation on the lateral anti-seepage capacity of a vertical soil sand layer (VSSL) in a sunken lawn

The use of a sunken lawn is an emerging Low Impact Development (LID) technique to effectively control storm runoffs. However, the random infiltration of rainwater that occurs due to the construction of a sunken lawn in an area of collapsible loess seriously threatens the safety of buildings around it. Setting up a vertical soil sand layer (VSSL) structure next to a sunken lawn as an anti-permeate method has been proposed in this study. To analyze the lateral anti-seepage effects of a VSSL, a sunken lawn model around a building was established based on soil physical parameters, and water seepage in the sunken lawn was investigated using a infiltration experiment and HYDRUS-2D software. The results show that the anti-seepage effects of a VSSL can significantly reduce the average wetting front migration length and water content at the observation points behind the sand layer. The Nash-Sutcliff Efficiency (NSE) index was used to evaluate the accuracy and reliability of the HYDRUS-2D model. The values of the NSE index obtained were greater than 0.82 (varied between 0.82 and 0.98) which confirmed the applicability of the HYDRUS-2D software in accurately describing the hydraulic behavior of the lateral anti-seepage effects of the VSSL in a sunken lawn. Simulation infiltration tests showed that, on the side of the VSSL, the wetting front migration length was reduced by 55.5% on average, and the water content of the observation points behind the sand layer was reduced by 40.5%, increasing the stability of the loess around the building infrastructure. The results are of value in practical applications, such as for devising engineering or non-engineering measures to avoid loess collapsibility around sunken lawns.

Elucidating roles of near-surface vertical layer structure in different stages of PM2.5 pollution episodes over urban Beijing during 2004–2016

Local weather conditions play important roles in surface fine particulate matter (PM2.5) pollution episodes in metropolitan areas. Relative to surface meteorological factors, the roles of near-surface vertical structure of urban boundary layer in air pollution has yet to be fully understood, due to limitation of vertical observation. By using surface PM2.5 observations and multi-layer (15 levels) vertical meteorological elements from a 325-m meteorological tower during 2004–2016, we investigated the different stages of 456 PM2.5 Pollution Episodes (PPEs) and their associations with vertical urban boundary layer structure in Beijing. The average PM2.5 concentration during PPEs is 141.2 μg m−3, twice the 13-year average (70.3 μg m−3). PPEs are more frequent and severe in autumn and winter, showing significant seasonal variations. For vertical wind, southerly (southwesterly) winds prevailed from 80 m to 320 m in the early stage of pollution episodes, transporting pollutants to Beijing. While strong northerly (northwesterly) winds prevailed in near-surface layer in the dissipation stages (DSs) and after PPEs, effectively removing pollutants. Owing to different thermal dynamic conditions, the starting hours of PPEs are various, showing that PPEs with stable atmospheric stratification occur most frequently at 1800 LST. Particularly, for long-lasting PPEs, shortwave (longwave) radiation at near-surface layer is weakened (enhanced) due to the existence of clouds and pollutant aerosols, attenuating the momentum flux and sensible heat flux, which further aggravates the accumulation of pollutants. Our findings provide a better understanding of the physical formation mechanism of high concentrations of the PM2.5 pollution episodes and may aid in designing effective mitigation strategies for the urban environment and health.

Study on plasma characteristics and gas analysis before and after recovery using liquid-fluorocarbon precursor

Perfluorocarbon (PFC) gas is a representative greenhouse gas with high global warming potential (GWP) and is mainly used in the etching processes applicable to the manufacture of semiconductor devices. High capacity and high integration have been achieved in recent years as semiconductor device structures have been replaced by vertical layer structures, and the consumption of PFC gas has exploded due to the increase in high aspect ratio and patterning processes. In this study, the etching and recovery process were performed using C5F8 in L-FC which is in liquid phase at room temperature. This is because the ratio of F and C constituting C4F8, which is a PFC gas used for conventional etching, is similar. In addition, the recovered C5F8 was injected back into the chamber to confirm its reusability, and the electron temperature, plasma density, and ion energy distribution were analyzed. In addition, based on these data, the Si and SiO2 etching process requiring high selectivity was applied using the gas obtained before and after recovery. An analysis of the surface composition of Si and SiO2 after the etching process confirmed the possibility of recovering and reusing the exhaust gas during the process.

Adsorption and Recovery using Vaporization of Liquid Fluorocarbon Precursor

PFC gas is primarily used during the etching process in the manufacture of ULSIs and in cleaning after CVD processes. PFC is classified as a greenhouse gas that stays in the atmosphere for a long time and has a high GWP. High capacity and high integration have been achieved in recent years as semiconductor device structures have been replaced by vertical layer structures, and the consumption of PFC gas has exploded due to the increase in high aspect ratio and patterning processes. Therefore, many researchers have been working on methods to decompose, recover, and reuse the gas after the etching process to reduce the emissions of PFC gas. In this study, etching and recovery processes were performed using C5F8 in L-FC which is in liquid phase at room temperature. Among the L-FCs, C5F8 gas has a high C/F ratio, similar to that of the C4F8 gas, which is a conventional PFC gas. In addition, to confirm its reusability, the recovered C5F8 was injected back into the chamber, and the electron temperature, plasma density, and ion energy distribution were analyzed. Based on these experimental data, the reliability of the etch processes performed with recovered C5F8 gas was evaluated, and the possibility of reusing the recovered C5F8 gas was confirmed.

Two Inversion Layers and Their Impacts on PM2.5 Concentration over the Yangtze River Delta, China

AbstractAn integrated winter field campaign was conducted to investigate the atmospheric boundary layer structure and PM2.5 concentration at three sites over the Yangtze River delta (YRD) in China: Shouxian (a rural area), a site in a northern suburb of Nanjing, and Dongshan (a residential area). Two temperature inversion layers and air pollution events occurred simultaneously from 30 to 31 December 2016, local time, over the YRD. It was found that the two inversion layers were related to the presence of a high pressure system, resulting in divergence in the upper boundary layer and radiative cooling near the ground at night. Dominated by agricultural and residential biomass burning, the surface emission sources from the Shouxian rural area were moderately strong. After the formation of the two inversions, the vertical distribution of PM2.5 concentration below the upper inversion layer was uniform as a result of thorough boundary layer mixing in the earlier hours. During nighttime at the Nanjing site, air pollutant plumes from nearby elevated point sources could not easily diffuse downward/upward between the two inversion layers, which led to a distinct peak in the PM2.5 concentration. At the Dongshan site, the emission sources were weak and the nighttime PM2.5 concentration above 100 m was high. The surface PM2.5 concentration gradually increased from early morning to noon, which was attributed to emissions related to the local residents. The results indicated that the vertical distribution of pollutants was affected by a combination of local emissions, vertical boundary layer structure, and horizontal and vertical transports.

Investigation of the atmospheric boundary layer during an unexpected summertime persistent severe haze pollution period in Beijing

Persistent severe haze pollution seldom happens in summer in Beijing. In this study, a persistent severe haze pollution event, defined as daily PM2.5 concentration higher than 150 μg m−3 on 5 consecutive days, was observed in Beijing from 26 to 30 in July 2010. It was not caused by crop residue burning during the harvest period. Weak pressure systems dominated at surface and implicated weak advection. Regional weak southerly winds with speeds of 2–3 m s−1 consistently brought pollutants from southern large-emission regions to Beijing. Surface convergence resulted from northerly winds prevailing in northern regions induced pollutants remaining in Beijing, which contributed to the maximum daily PM2.5 concentration on 26 in July. A continental high-pressure system persisted in the northwest of Beijing at 500 hPa, which led to significant sinking motion. Elevated inversion was found in the form of subsidence inversion, and this was confirmed by a skew T-logp diagram and vertical velocity analysis. It is much different from the vertical boundary layer structure in wintertime pollution period that surface-based inversion dominates. The subsidence inversion was an extremely stable layer with an average depth of hundred meters and strength of 1.4 °C. The capping effect of the inversion layer at low altitude of average 720 m limited vertical diffusion of pollutants and trapped them in a shallow layer, and thus, extremely high concentration of PM2.5 remained. WRF-Chem model simulation demonstrated that about 70% of PM2.5 was transported to Beijing from its southern regions.

Four dimensional data assimilation (FDDA) impacts on WRF performance in simulating inversion layer structure and distributions of CMAQ-simulated winter ozone concentrations in Uintah Basin

Four-dimensional data assimilation (FDDA) was applied in WRF-CMAQ model sensitivity tests to study the impact of observational and analysis nudging on model performance in simulating inversion layers and O3 concentration distributions within the Uintah Basin, Utah, U.S.A. in winter 2013. Observational nudging substantially improved WRF model performance in simulating surface wind fields, correcting a 10 °C warm surface temperature bias, correcting overestimation of the planetary boundary layer height (PBLH) and correcting underestimation of inversion strengths produced by regular WRF model physics without nudging. However, the combined effects of poor performance of WRF meteorological model physical parameterization schemes in simulating low clouds, and warm and moist biases in the temperature and moisture initialization and subsequent simulation fields, likely amplified the overestimation of warm clouds during inversion days when observational nudging was applied, impacting the resulting O3 photochemical formation in the chemistry model. To reduce the impact of a moist bias in the simulations on warm cloud formation, nudging with the analysis water mixing ratio above the planetary boundary layer (PBL) was applied. However, due to poor analysis vertical temperature profiles, applying analysis nudging also increased the errors in the modeled inversion layer vertical structure compared to observational nudging. Combining both observational and analysis nudging methods resulted in unrealistically extreme stratified stability that trapped pollutants at the lowest elevations at the center of the Uintah Basin and yielded the worst WRF performance in simulating inversion layer structure among the four sensitivity tests. The results of this study illustrate the importance of carefully considering the representativeness and quality of the observational and model analysis data sets when applying nudging techniques within stable PBLs, and the need to evaluate model results on a basin-wide scale.