Atmosphere — Open Access Journal

Modeling hyper-dimensional spatial variability is a complex task from both practical and theoretical standpoints. In this paper we develop a method for modeling hyper-dimensional covariance (variogram) structures using the product-sum covariance model initially developed to model spatio-temporal variability. We show that the product-sum model can be used recursively up to an arbitrarily large number of dimensions while preserving relative modeling simplicity and yielding valid covariance models. The method can be used to model variability in anisotropic conditions with multiple axes of anisotropy or when temporal evolution is involved, and thus is applicable to “full anisotropic 3D+time” situations often encountered in environmental sciences. It requires fewer assumptions than the traditional product-sum modeling approach. The new method also presents an alternative to classical approaches to modeling zonal anisotropy and requires fewer parameters to be estimated from data. We present an example by applying the method in conjunction with ordinary kriging to map photosynthetically-active radiation (PAR) for 2006, in Oklahoma, CA, USA and to explore effects of spatio-temporal variability in PAR on gross primary productivity (GPP). Full article

In this study, using the fourth version of the Community Atmosphere Model (CAM4) with a bulk aerosol model parameterization (BAM) for dust size distribution (CAM4-BAM), East Asian dust and its direct radiative feedbacks (DRF) during the Last Glacial Maximum are analyzed by intercomparing results between the experiments with (Active) and without (Passive) the DRF. This CAM4-BAM captures the expected characteristics that the dust aerosol optical depth and loading over East Asia during the Last Glacial Maximum (LGM) were significantly greater compared to the current climate. A comparative analysis of the Active and Passive experiments reveals that consideration of the dust–radiation interaction can significantly reduce dust emissions and then weaken the whole dust cycle, including loading, transport, and dry and wet depositions over East Asia. Further analysis of the dust–radiation feedback shows that the DRF decreases surface sensible heat, mainly owing to the negative surface forcing induced by dust with a value of −11.8 W m⁻². The decreased surface sensible heat weakens the turbulent energy within the planetary boundary layer and the surface wind speed, and then reduces the regional dust emissions. This process creates a negative DRF–emission feedback loop to affect the dust cycle during the LGM. Further analysis reveals that the dust emissions in the LGM over East Asia were more reduced, with amounts of −77.2 Tg season⁻¹ by the negative DRF–emission feedback, compared to the current climate with −6.8 Tg season⁻¹. The two ratios of this reduction to their emissions are close to −10.7% for the LGM and −7.5% for the current climate. Full article

The objective of this study is to analyze the present and future climate-tourism conditions in Milos Island, Cyclades, Greece, by means of the assessment of the three climate components (physical, thermal, and aesthetic), which interprets the so-called climatic tourism potential. Milos Island is chosen as a representative island of the Cyclades complex in the Aegean Sea. Future climate change conditions are analyzed using the high-resolution simulations (grid size 0.11° × 0.11°) of the Regional Climate Model ALADIN 5.2 from Centre National de Recherche Meteorologiques, Meteo France (CNRM). The climate simulations concern the future periods 2021–2050 and 2071–2100 against the reference period 1961–1990, under two Representative Concentration Pathways, RCP4.5 and RCP8.5. Based on regional climate simulations, the tourism potential can be described in a meaningful and simple way by applying the Climate-Tourism-Information-Scheme (CTIS), which depicts detailed climate information that could be used by tourists to foresee the thermal comfort, aesthetic, and physical conditions for planning their vacations. More specifically, the thermal climate component is interpreted by the Physiologically Equivalent Temperature (PET), which is one of the most popular physiological thermal indices based on the human energy balance. The findings of the analysis could be used by stakeholders and the tourism industry in decision-making regarding the destination of Milos for tourism planning and touristic infrastructure development. Full article

We herein present the spectral linear particle depolarization ratios (δ_p) from an Aerosol Robotics NETwork (AERONET) sun/sky radiometer with respect to the aerosol type. AERONET observation sites, which are representative of each aerosol type, were selected for our study. The observation data were filtered using the Ångström exponent (Å), fine-mode fraction (FMF) and single scattering albedo (ω) to ensure that the obtained values of δ_p were representative of each aerosol condition. We report the spectral δ_p values provided in the recently released AERONET version 3 inversion product for observation of the following aerosol types: dust, polluted dust, smoke, non-absorbing, moderately-absorbing and high-absorbing pollution. The AERONET-derived δ_p values were generally within the range of the δ_p values measured from lidar observations for each aerosol type. In addition, it was found that the spectral variation of δ_p differed according to the aerosol type. From the obtained results, we concluded that our findings provide potential insight into the identification and classification of aerosol types using remote sensing techniques. Full article

The new generation of atmospheric composition sensors such as TROPOMI is capable of providing spectra of high spatial and spectral resolution. To process this vast amount of spectral information, fast radiative transfer models (RTMs) are required. In this regard, we analyzed the efficiency of two acceleration techniques based on the principal component analysis (PCA) for simulating the Hartley-Huggins band spectra. In the first one, the PCA is used to map the data set of optical properties of the atmosphere to a lower-dimensional subspace, in which the correction function for an approximate but fast RTM is derived. The second technique is based on the dimensionality reduction of the data set of spectral radiances. Once the empirical orthogonal functions are found, the whole spectrum can be reconstructed by performing radiative transfer computations only for a specific subset of spectral points. We considered a clear-sky atmosphere where the optical properties are defined by Rayleigh scattering and trace gas absorption. Clouds can be integrated into the model as Lambertian reflectors. High computational performance is achieved by combining both techniques without losing accuracy. We found that for the Hartley-Huggins band, the combined use of these techniques yields an accuracy better than 0.05% while the speedup factor is about 20. This innovative combination of both PCA-based techniques can be applied in future works as an efficient approach for simulating the spectral radiances in other spectral regions. Full article

General characteristics of K-changes, including their duration and probability of occurrence associated with ground flashes in Sri Lanka in the tropics, together with their fine structure, are presented. In 98 ground flashes where the small step changes associated with K-changes are clearly visible, there were about two K-changes per flash on average. The mean K-change time duration observed in this study is 0.38 ms. In 53 of the ground flashes, there were 120 consecutive K-changes. In these cases, the geometric mean of the time interval between K-changes was 12 ms. Analysis of the fine structure of the K-changes reveals the K-changes are always associated with either a chaotic pulse train or a combination of chaotic and regular pulse trains. The results suggest that the small step-like static electric fields identified in the literature as K-changes are the step-like static fields associated with the processes that generate chaotic or a combination of chaotic and regular pulse trains. Thus, at larger distances where the static fields are negligible, K-changes may appear as a chaotic pulse train or a combination of chaotic and regular pulse trains. Full article

Marginal seas are fundamental to humans for their importance in mariculture resources and commerce. Based on the NOAA 0.25 degree daily Optimum Interpolation (OI) sea surface temperature (SST) data set, spatiotemporal changes in mean and extreme SST in the East China Seas (ECSs) were examined for from 1982 to 2017. As a regional average, the annual mean SST has notably increased at a rate of 0.21 ± 0.08 °C per decade. The warming SST during 1982–2017 is probably related to the influence from a recent strengthening and westward extension of the WPSH. There are also notable warming trends in annual minimum and maximum SST. Spatially, the rapid warming of annual mean SSTs are located in the vicinity of the Yangtze Estuary, exceeding 0.2 °C per decade and part of the ECS-Kuroshio. This pattern may be largely affected by the spatial changes of minimum SST. Rapid warming of maximum SST can be found across the region, from the northern East China Sea (ECS) to the Bohai Sea. Since 1982, extreme hot days (EHDs) have undergone an obvious increasing trend, at a rate of 15.2 days per decade. Conversely, extreme cold days (ECDs) have been decreasing. Notably, the largest increase of EHDs appears in the western ECS and the Bohai Sea, which both have rich marine ecosystems. The trend of EHDs has a significant relationship to mean SST, suggesting that there will be a further increase in EHDs under continued warming in the ECSs. These findings emphasize the importance and urgency of strategies which should be planned for the adaptation and mitigation of specific types of extreme hot events in this region. Full article

El Niño–Southern Oscillation (ENSO) has large impacts on Australia’s rainfall. A composite analysis technique was utilized to distinguish the impact of onset time of El Niño on summer rainfall over southeastern Australia. Summer rainfall tended to be lower than normal in austral autumn El Niño events during December–January–February (DJF) and higher than normal in austral winter El Niño events, in 1980–2017. During autumn El Niño events, the Walker circulation and meridional cells served as a bridge, linking the warmer sea surface temperature (SST) in the eastern equatorial Pacific (EEP) and lower summer rainfall over southeastern Australia. This physical process can be described as follows: During DJF, a positive SST anomaly in the EEP was concurrent with anomalous downdraft over southeastern Australia via zonal anomalous Walker circulation, meridional anomalous cells along 170° E–170° W, and a Pacific South American (PSA) teleconnection wave train at 500 hPa. In addition, an anomalous convergence at 200 hPa depressed the convection. Meanwhile, an 850 hPa abnormal westerly was not conducive to transport marine water vapor into this area. These factors resulted in below-normal rainfall. During winter El Niño events, a positive SST anomaly in the central equatorial Pacific (CEP) and the changes in Walker circulation and meridional cells were weaker. The PSA teleconnection wave train shifted westward and northward, and there was a low-level anomalous ascent over southeastern Australia. At the western flank of the anomalous anticyclone, northerly transported water vapor from the ocean to southeastern Australia resulted in a sink of water vapor over this area. The development of low-level convective activity and the plentiful water vapor supply favored more rainfall over southeastern Australia. Onset time of El Niño may be a useful metric for improving the low predictive skill of southeastern Australian summer rainfall. Full article

The coupled Conformal Cubic Atmospheric Model (CCAM) and Chemical Transport Model (CTM) (CCAM-CTM) was undertaken with eleven emission scenarios segregated from the 2008 New South Wales Greater Metropolitan Region (NSW GMR) Air Emission Inventory to predict major source contributions to ambient PM_2.5 and exposure in the NSW GMR. Model results illustrate that populated areas in the NSW GMR are characterised with annual average PM_2.5 of 6–7 µg/m³, while natural sources including biogenic emissions, sea salt and wind-blown dust contribute 2–4 µg/m³ to it. Summer and winter regional average PM_2.5 ranges from 5.2–6.1 µg/m³ and 3.7–7.7 µg/m³ across Sydney East, Sydney Northwest, Sydney Southwest, Illawarra and Newcastle regions. Secondary inorganic aerosols (particulate nitrate, sulphate and ammonium) and sodium account for up to 23% and 18% of total PM_2.5 mass in both summer and winter. The increase in elemental carbon (EC) mass from summer to winter is found across all regions but particularly remarkable in the Sydney East region. Among human-made sources, “wood heaters” is the first or second major source contributing to total PM_2.5 and EC mass across Sydney in winter. “On-road mobile vehicles” is the top contributor to EC mass across regions, and it also has significant contributions to total PM_2.5 mass, particulate nitrate and sulphate mass in the Sydney East region. “Power stations” is identified to be the third major contributor to the summer total PM_2.5 mass across regions, and the first or second contributor to sulphate and ammonium mass in both summer and winter. “Non-road diesel and marine” plays a relatively important role in EC mass across regions except Illawarra. “Industry” is identified to be the first or second major contributor to sulphate and ammonium mass, and the second or third major contributor to total PM_2.5 mass across regions. By multiplying modelled predictions with Australian Bureau of Statistics 1-km resolution gridded population data, the natural and human-made sources are found to contribute 60% (3.55 µg/m³) and 40% (2.41 µg/m³) to the population-weighted annual average PM_2.5 (5.96 µg/m³). Major source groups “wood heaters”, “industry”, “on-road motor vehicles”, “power stations” and “non-road diesel and marine” accounts for 31%, 26%, 19%, 17% and 6% of the total human-made sources contribution, respectively. The results in this study enhance the quantitative understanding of major source contributions to ambient PM_2.5 and its major chemical components. A greater understanding of the contribution of the major sources to PM_2.5 exposures is the basis for air quality management interventions aiming to deliver improved public health outcomes. Full article

This study looked at the variation in air quality during the periods of fireworks as assessed from the change in ambient concentrations of air pollutants like particulate matter (PM₁₀), O₃, and NO₂ for pre-, post-, and Vishu days for four consecutive years in 2015, 2016, 2017, and 2018 in Kannur, India. Enhanced levels of O₃, NO₂, NO, and PM₁₀ were observed during the intense usage of fireworks. The concentration of metals in PM₁₀ increased and the percent increase was found to be different for metal traces. A pronounced increase in the aerosol optical depth (AOD) in the lower wavelength region of solar radiation reveals the abundance of fine mode particles. The concentrations of O₃ and NO₂ were observed to increase by more than 100% on Vishu day than the control days for the observational period. Simulation using the National Center for Atmospheric Research (NCAR) Master Mechanism photochemical box model indicates a more than 100% enhancement in NO₂ photolysis rates during the fireworks episode, which leads to a 100% increase in the surface ozone production. Observations as well as model simulations indicate that the enhanced photochemical ozone production from NO₂ photolysis is possibly the main driver of ozone production during the Vishu at this site. The air quality index (AQI) revealed the deterioration of air quality at the observational site during the period of Vishu. Full article

The interpretation of lichen bioaccumulation data is of paramount importance in environmental forensics and decision-making processes. By implementing basic ideas underlying previous interpretative scales, new dimensionless, species-independent “bioaccumulation scales” for native and transplanted lichens are proposed. Methodologically consistent element concentration datasets were populated with data from biomonitoring studies relying on native and transplanted lichens. The scale for native lichens was built up by analyzing the distribution of ratios between element concentration data and species-specific background concentration references (B ratios), herein provided for Flavoparmelia caperata and Xanthoria parietina (foliose lichens). The scale for transplants was built up by analyzing the distribution of ratios between element concentration in exposed and unexposed samples (EU ratio) of Evernia prunastri and Pseudevernia furfuracea (fruticose lichens). Both scales consist of five percentile-based classes; namely, “Absence of”, “Low”, “Moderate”, “High”, and “Severe” bioaccumulation. A comparative analysis of extant interpretative tools showed that previous ones for native lichens suffered from the obsolescence of source data, whereas the previous expert-assessed scale for transplants failed in describing noticeable element concentration variations. The new scales, based on the concept that pollution can be quantified by dimensionless ratios between experimental and benchmark values, overcome most critical points affecting the previous scales. Full article

Dust particles in the atmosphere play an important role in air pollution, climate change, and biogeochemical cycles. Some of the dominant sources of dust in mid-latitude regions are in Asia. An intense dust storm engulfed Northern China at the beginning of May 2017, and PM₁₀ mass concentrations of 1500–2000 μg m⁻³ were measured near the dust source region. We combined numerical simulations, air quality monitoring data, and satellite retrievals to investigate dust emission and transport during this event. We found that the event was closely related to cold front activity, characterized by increased wind speed, which increased dust emission. We improved the dust scheme using a local dust size distribution to better simulate the dust emission flux. We found that accurate parametrization of the dust size distribution was important to effectively simulate both dust emission and ambient particle concentration. We showed that using a local dust size distribution substantially improved the accuracy of the simulation, allowing both the spatial distribution of pollution caused by the dust storm and temporal variability in the pollution to be captured. Full article

Using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model, we tracked the paths of 46 autumn cold surges affecting North China from 1961 to 2014, and classified them by clustering analysis, thereby investigating their changes and associated atmospheric circulation evolution. Our results indicate that autumn cold surges affecting North China can be classified into three types according to their paths: the north type, west type, and northwest type, with occurrences of 12, 16, and 18 respectively. Different types of cold surges have different atmospheric circulation characteristics. The north type is associated with a blocking type of atmospheric circulation pattern, with an enhanced stretching northeast ridge over the Ural Mountains and a transverse trough over Lake Baikal. However, the northwest type is characterized by a ridge–trough–ridge wave-train pattern that is located over the Barents Sea, West Siberian Plain, and Sakhalin Island, respectively. The west-type cold surge is related to a conversion type: a blocking system over the Ural Mountains forms four days before the cold surge occurrence, after which it becomes a wave-train type. The atmospheric signals detected prior to the occurrences of the three types of cold surges are also explored. The main signal of the north-path cold surges is that the energy propagates eastward from the Azores Islands to the Ural Mountains, and then forms a blocking high over the Urals. However, for the northwest-path cold surges, there is a weak trough over the Ural Mountains that gradually strengthens because the blocking high collapses over the Norwegian Sea. The key signal of the formation of the west-path cold surges is a blocking high over the Norwegian Sea’s continuous enhancement and extension to Novaya Zemlya, which results in a transmission of energy to the Ural Mountains and leads to the formation of a blocking system over here. When the above-mentioned different types of atmospheric circulation characteristics appear, the type of cold surge path and its impact area can be potentially forecasted in advance, which may reduce the losses that result from cold surges. Full article

The impact of extreme weather events on the navigation environment in the inland waterways of the Yangtze River is an interdisciplinary hotspot in subjects of maritime traffic safety and maritime meteorology, and it is also a difficult point for the implementation of decision-making and management by maritime and meteorological departments in China. The objective of this study is to review the variation trends and distribution patterns in the periods of adverse and extreme weather events that are expected to impact on inland waterways transport (IWT) on the Yangtze River. The frequency of severe weather events, together with the changes in their spatial extension and intensity, is analyzed based on the ERA-Interim datasets (1979–2017) and the GHCNDEX dataset (1979–2017), as well as the research progresses and important events (2004–2016) affecting the navigation environment. The impacts of extreme weather events on IWT accidents and phenomena of extreme weather (e.g., thunderstorms, lightning, hail, and tornadoes) that affect the navigation environment are also analyzed and discussed. The results show that: (1) the sections located in the plain climate zone is affected by extreme weather in every season, especially strong winds and heat waves; (2) the sections located in the hilly mountain climate zone is affected particularly by spring extreme phenomena, especially heat waves; (3) the sections located in the Sichuan Basin climate zone is dominated by the extreme weather phenomena in autumn, except cold waves; (4) the occurrence frequency of potential flood risk events is relatively high under rainstorm conditions and wind gusts almost affect the navigation environment of the Jiangsu and Shanghai sections in every year; (5) the heat wave indices (TXx, TR, and WSDI) tend to increase and the temperature of the coldest day of the year gradually increases; (6) the high occurrences of IWT accidents need to be emphasized by relevant departments, caused by extreme weather during the dry season; and (7) the trends and the degree of attention of extreme weather events affecting IWT are ranked as: heat wave > heavy rainfall > wind gust > cold spell > storm. Understanding the seasonal and annual frequency of occurrence of extreme weather events has reference significance for regional management of the Yangtze River. Full article

The influence of the heights of low-level jets (LLJs) on the rotor power and aerodynamic loads of a horizontal axis wind turbine were investigated using the fatigue, aerodynamics, structures, and turbulence code. The LLJ and shear inflow wind fields were generated using an existing wind speed spectral model. We found that the rotor power predicted by the average wind speed of the hub height is higher than the actual power in relatively weak and shallow LLJ inflow conditions, especially when the LLJ height is located inside the rotor-swept area. In terms of aerodynamic loads, when the LLJ height is located inside the rotor-swept area, the root mean square (RMS) rotor thrust coefficient and torque coefficient increase, while the RMS rotor unbalanced aerodynamic load coefficients, including lateral force, longitudinal force, tilt moment, and yaw moment, decreased. This means that the presence of both positive and negative wind shear in the rotor-swept area not only increases the rotor power but also reduces the unbalanced aerodynamic loads, which is beneficial to the operation of wind turbine. Power spectrum analysis shows no obvious difference in the power spectrum characteristics of the rotor torque and thrust in LLJ inflow conditions with different heights. Full article

A two-dimensional mathematical model of moist air convection in the sub-cloud and cloud layers is proposed. A theoretical analysis of the influence of near ground atmospheric parameters on the development of sub-cloud and cloud convection is provided, and the criteria of convection development are considered. As a rule, this relationship is parameterized in general circulation, regional or mesoscale models of the atmosphere. Therefore, achieving a more complete and correct understanding of this relationship can lead to an improvement in the accuracy of weather forecasts. The mathematical model describes the system of the equations of motion, heat conductivity and the continuity equations for a two-dimensional vertical plane. The approximate analytical solution of the system of equations is obtained. Expressions for the estimation of the convection height and height of maximum velocity are derived for vertical and horizontal components of updraft wind and for vertical distribution of temperature. From the expressions obtained, the criterion of sub-cloud convection development is derived. The expressions for the convection parameters at a condensation level have also been formulated, from which the criterion of cloud development through convection is derived. It is established that the development of cloud convection depends on absolute values of the dew point deficit in a near-surface layer and, in a greater degree, on vertical gradients of water vapor mass fraction. It is shown that at certain critical values of a vertical gradient of water vapor mass fraction “explosive convective growth” is observed. The application of the obtained results to artificial stimulation of convection by means of air heating in the near-ground atmosphere has shown that the success of such an application and the required air heating-up depend on: (i) the vertical temperature gradient; (ii) the vertical dew-point gradient; and (iii) the value of the dew point deficit in the near-ground layer. The analysis performed has shown the possibility of successful stimulation of artificial convection under specific favorable atmospheric conditions. Full article

Extreme events such as rainstorms and floods are likely to increase in frequency due to the influence of global warming, which is expected to put considerable pressure on water resources. This paper presents a regional frequency analysis of precipitation extremes and its spatio-temporal pattern characteristics based on well-known index-flood L-moments methods and the application of advanced statistical tests and spatial analysis techniques. The results indicate the following conclusions. First, during the period between 1969 and 2015, the annual precipitation extremes at Fengjie station show a decreasing trend, but the Wuhan station shows an increasing trend, and the other 24 stations have no significant trend at a 5% confidence level. Secondly, the Hanjiang River Basin can be categorized into three homogenous regions by hierarchical clustering analysis with the consideration of topography and mean precipitation in these areas. The GEV, GNO, GPA and P III distributions fit better for most of the basin and MARE values range from 3.19% to 6.41% demonstrating that the best-fit distributions for each homogenous region is adequate in predicting the quantiles estimates. Thirdly, quantile estimates are reliable enough when the return period is less than 100 years, however estimates for a higher return period (e.g., 1000 years) become unreliable. Further, the uncertainty of quantiles estimations is growing with the growing return periods and the estimates based on R95P series have a smaller uncertainty to describe the extreme precipitation in the Hanjiang river basin (HJRB). Furthermore, In the HJRB, most of the extreme precipitation events (more than 90%) occur during the rainy season between May and October, and more than 30% of these extreme events concentrate in July, which is mainly impacted by the sub-tropical monsoon climate. Finally, precipitation extremes are mainly concentrated in the areas of Du River, South River and Daba Mountain in region I and Tianmen, Wuhan and Zhongxiang stations in region III, located in the upstream of Danjiangkou Reservoir and Jianghan Plain respectively. There areas provide sufficient climate conditions (e.g., humidity and precipitation) responsible for the occurring floods and will increase the risk of natural hazards to these areas. Full article