Atmosphere

24 pages, 4140 KiB

Open AccessArticle

Atmospheric Moisture Pathways to the Highlands of the Tropical Andes: Analyzing the Effects of Spectral Nudging on Different Driving Fields for Regional Climate Modeling

by Katja Trachte

Atmosphere 2018, 9(11), 456; https://doi.org/10.3390/atmos9110456 - 19 Nov 2018

Cited by 9 | Viewed by 4826

Abstract

Atmospheric moisture pathways to the highlands of the tropical Andes Mountains were investigated using the Weather Research and Forecasting (WRF) model, as well as back-trajectory analysis. To assess model uncertainties according to the initial and lateral boundary conditions (ILBCs), the effects of spectral [...] Read more.

Atmospheric moisture pathways to the highlands of the tropical Andes Mountains were investigated using the Weather Research and Forecasting (WRF) model, as well as back-trajectory analysis. To assess model uncertainties according to the initial and lateral boundary conditions (ILBCs), the effects of spectral nudging and different driving fields on regional climate modeling were tested. Based on the spatio-temporal patterns of the large-scale atmospheric features over South America, the results demonstrated that spectral nudging compared to traditional long-term integration generally produced greater consistency with the reference data (ERA5). These WRF simulations further revealed that the location of the inter-tropical convergence zone (ITCZ), as well as the precipitation over the Andes Mountains were better reproduced. To investigate the air mass pathways, the most accurate WRF simulation was used as atmospheric conditions for the back-trajectory calculations. Three subregions along the tropical Andean chain were considered. Based on mean cluster trajectories and the water vapor mixing ratio along the pathways, the contributions of eastern and western water sources were analyzed. In particular, the southernmost subregion illustrated a clear frequency of occurrences of Pacific trajectories mostly during September–November (40%) when the ITCZ is shifted to the Northern Hemisphere and the Bolivian high pressure system is weakened. In the northernmost subregion, Pacific air masses as well reached the Andes highlands with rather low frequencies regardless of the season (2–12%), but with a moisture contribution comparable to the eastern trajectories. Cross-sections of the equivalent-potential temperature as an indicator of the moisture and energy content of the atmosphere revealed a downward mixing of the moisture aloft, which was stronger in the southern subregion. Additionally, low-level onshore breezes, which developed in both subregions, indicated the transport of warm-moist marine air masses to the highlands, highlighting the importance of the representation of the terrain and, thus, the application of dynamical downscaling using regional climate models. Full article

(This article belongs to the Section Meteorology)

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16 pages, 7193 KiB

Open AccessArticle

Impacts of Pacific SSTs on Atmospheric Circulations Leading to California Winter Precipitation Variability: A Diagnostic Modeling

by Boksoon Myoung, Sang-Wook Yeh, Jinwon Kim and Menas C. Kafatos

Atmosphere 2018, 9(11), 455; https://doi.org/10.3390/atmos9110455 - 19 Nov 2018

Cited by 5 | Viewed by 3221

Abstract

One of the primary meteorological causes of the winter precipitation deficits and droughts in California (CA) is anomalous developments and maintenance of upper-tropospheric ridges over the northeastern Pacific. In order to understand and find the key factors controlling the winter precipitation variability in [...] Read more.

One of the primary meteorological causes of the winter precipitation deficits and droughts in California (CA) is anomalous developments and maintenance of upper-tropospheric ridges over the northeastern Pacific. In order to understand and find the key factors controlling the winter precipitation variability in CA, the present study examines two dominant atmospheric modes of the 500 hPa geopotential height in the Northern Hemisphere using an Empirical Orthogonal Function (EOF) and their associated large-scale circulation patterns for the last 41 winters (1974/75–2014/15). Explaining 17.5% of variability, the second mode (EOF2) shows strong anti-cyclonic circulations in the North Pacific and cyclonic circulations in the eastern USA and mid-latitude North Atlantic, similar to the atmospheric circulation observed in the 2013/14 drought of CA. EOF2 is tightly and significantly correlated with CA winter precipitation. EOF2 is associated with warm western‒cool eastern tropical Pacific, resembling a mirror image of canonical El Niño events. In particular, it is found that, since the mid-1990s, sea surface temperatures (SSTs) in the western tropical Pacific have been more tightly correlated with EOF2 and with the variability of CA precipitation. A diagnostic regression model based on the west‒east SST difference in the tropical Pacific developed for two recent decades (1994/95–2014/15) has been found to capture the slow-moving interannual variability of the CA winter precipitation (about 50%). The regression model performs well, especially for the central and northern CA precipitation, where the impacts of El Niño Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) on precipitation are indecisive. Our results emphasize the significant role of the western tropical Pacific SST forcing in the recent past, and in turn on CA droughts and potentially other precipitation extremes. Full article

(This article belongs to the Special Issue Large-Scale Atmospheric Circulation Variability and Its Climate Impacts)

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15 pages, 476 KiB

Open AccessArticle

Advanced Ultraviolet Radiation and Ozone Retrieval for Applications (AURORA): A Project Overview

by Ugo Cortesi, Simone Ceccherini, Samuele Del Bianco, Marco Gai, Cecilia Tirelli, Nicola Zoppetti, Flavio Barbara, Marc Bonazountas, Argyros Argyridis, André Bós, Edo Loenen, Antti Arola, Jukka Kujanpää, Antti Lipponen, William Wandji Nyamsi, Ronald Van der A, Jacob Van Peet, Olaf Tuinder, Vincenzo Farruggia, Andrea Masini, Emilio Simeone, Rossana Dragani, Arno Keppens, Jean-Christopher Lambert, Michel Van Roozendael, Christophe Lerot, Huan Yu and Koen Verberne Show full author list Hide full author list

Atmosphere 2018, 9(11), 454; https://doi.org/10.3390/atmos9110454 - 18 Nov 2018

Cited by 11 | Viewed by 5467

Abstract

With the launch of the Sentinel-5 Precursor (S-5P, lifted-off on 13 October 2017), Sentinel-4 (S-4) and Sentinel-5 (S-5)(from 2021 and 2023 onwards, respectively) operational missions of the ESA/EU Copernicus program, a massive amount of atmospheric composition data with unprecedented quality will become available [...] Read more.

With the launch of the Sentinel-5 Precursor (S-5P, lifted-off on 13 October 2017), Sentinel-4 (S-4) and Sentinel-5 (S-5)(from 2021 and 2023 onwards, respectively) operational missions of the ESA/EU Copernicus program, a massive amount of atmospheric composition data with unprecedented quality will become available from geostationary (GEO) and low Earth orbit (LEO) observations. Enhanced observational capabilities are expected to foster deeper insight than ever before on key issues relevant for air quality, stratospheric ozone, solar radiation, and climate. A major potential strength of the Sentinel observations lies in the exploitation of complementary information that originates from simultaneous and independent satellite measurements of the same air mass. The core purpose of the AURORA (Advanced Ultraviolet Radiation and Ozone Retrieval for Applications) project is to investigate this exploitation from a novel approach for merging data acquired in different spectral regions from on board the GEO and LEO platforms. A data processing chain is implemented and tested on synthetic observations. A new data algorithm combines the ultraviolet, visible and thermal infrared ozone products into S-4 and S-5(P) fused profiles. These fused products are then ingested into state-of-the-art data assimilation systems to obtain a unique ozone profile in analyses and forecasts mode. A comparative evaluation and validation of fused products assimilation versus the assimilation of the operational products will seek to demonstrate the improvements achieved by the proposed approach. This contribution provides a first general overview of the project, and discusses both the challenges of developing a technological infrastructure for implementing the AURORA concept, and the potential for applications of AURORA derived products, such as tropospheric ozone and UV surface radiation, in sectors such as air quality monitoring and health. Full article

(This article belongs to the Special Issue Atmospheric Composition Modeling)

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18 pages, 4449 KiB

Open AccessArticle

Expected Changes of Montenegrin Climate, Impact on the Establishment and Spread of the Asian Tiger Mosquito (Aedes albopictus), and Validation of the Model and Model-Based Field Sampling

by Mina Petrić, Branislava Lalić, Igor Pajović, Slavica Micev, Vladimir Đurđević and Dušan Petrić

Atmosphere 2018, 9(11), 453; https://doi.org/10.3390/atmos9110453 - 17 Nov 2018

Cited by 9 | Viewed by 5520

Abstract

Aedes albopictus has become established in many parts of Europe since its introduction at the end of the 20th century. It can vector a range of arboviruses, of which Chikungunya and Dengue are most significant for Europe. An analysis of the expected climate [...] Read more.

Aedes albopictus has become established in many parts of Europe since its introduction at the end of the 20th century. It can vector a range of arboviruses, of which Chikungunya and Dengue are most significant for Europe. An analysis of the expected climate change and the related shift in Köppen zones for Montenegro and impact on the establishment of Ae. albopictus was conducted. Outputs of a mechanistic Aedes albopictus model were validated by 2245 presence/absence records collected from 237 different sites between 2001 and 2014. Finally, model-based sampling was designed and performed at 48 sites in 2015, in a previously unexplored northern part of Montenegro, and results were validated. The Eta Belgrade University (EBU)-Princeton Ocean Model (POM) regional climate model was used with the A2 emissions scenario for the 2001–2030 and 2071–2100 integration periods. The results point to a significant increase in suitability for the mosquito and a vertical shift to higher altitudes by the end of the century. The model showed excellent results with the area under the receiver operating characteristic curve (AUC) of 0.94. This study provides a tool for prioritizing surveillance efforts (model-based surveillance), especially when resources are limited. This is the first published analysis of Climate Change that incorporates observations from the national synoptic grid and the subsequent impact on Ae. albopictus in Montenegro. Full article

(This article belongs to the Special Issue Weather and Climate Change Challenges in Agricultural and Forest Meteorology)

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55 pages, 4807 KiB

Open AccessReview

Comparison of Measurement-Based Methodologies to Apportion Secondary Organic Carbon (SOC) in PM_2.5: A Review of Recent Studies

by Deepchandra Srivastava, Olivier Favez, Emilie Perraudin, Eric Villenave and Alexandre Albinet

Atmosphere 2018, 9(11), 452; https://doi.org/10.3390/atmos9110452 - 16 Nov 2018

Cited by 38 | Viewed by 7242

Abstract

Secondary organic aerosol (SOA) is known to account for a major fraction of airborne particulate matter, with significant impacts on air quality and climate at the global scale. Despite the substantial amount of research studies achieved during these last decades, the source apportionment [...] Read more.

Secondary organic aerosol (SOA) is known to account for a major fraction of airborne particulate matter, with significant impacts on air quality and climate at the global scale. Despite the substantial amount of research studies achieved during these last decades, the source apportionment of the SOA fraction remains difficult due to the complexity of the physicochemical processes involved. The selection and use of appropriate approaches are a major challenge for the atmospheric science community. Several methodologies are nowadays available to perform quantitative and/or predictive assessments of the SOA amount and composition. This review summarizes the current knowledge on the most commonly used approaches to evaluate secondary organic carbon (SOC) contents: elemental carbon (EC) tracer method, chemical mass balance (CMB), SOA tracer method, radiocarbon (¹⁴C) measurement and positive matrix factorization (PMF). The principles, limitations, challenges and good practices of each of these methodologies are discussed in the present article. Based on a comprehensive—although not exhaustive—review of research papers published during the last decade (2006–2016), SOC estimates obtained using these methodologies are also summarized for different regions across the world. Conclusions of some studies which are directly comparing the performances of different methodologies are then specifically discussed. An overall picture of SOC contributions and concentrations obtained worldwide for urban sites under similar conditions (i.e., geographical and seasonal ones) is also proposed here. Finally, further needs to improve SOC apportionment methodologies are also identified and discussed. Full article

(This article belongs to the Special Issue Air Quality and Sources Apportionment)

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Graphical abstract

26 pages, 4523 KiB

Open AccessArticle

The Impact of Adverse Weather and Climate on the Width of European Beech (Fagus sylvatica L.) Tree Rings in Southeastern Europe

by Stefan Stjepanović, Bratislav Matović, Dejan Stojanović, Branislava Lalić, Tom Levanič, Saša Orlović and Marko Gutalj

Atmosphere 2018, 9(11), 451; https://doi.org/10.3390/atmos9110451 - 15 Nov 2018

Cited by 9 | Viewed by 4479

Abstract

European beech (Fagus sylvatica L.) is the most important deciduous tree species in Europe. According to different climate scenarios, there is a relatively high probability of a massive decline in and loss of beech forests in southern Europe and in the southern [...] Read more.

European beech (Fagus sylvatica L.) is the most important deciduous tree species in Europe. According to different climate scenarios, there is a relatively high probability of a massive decline in and loss of beech forests in southern Europe and in the southern part of central Europe. Thus, the authors of this study explored the dynamics of tree diameter increments and the influence of extremely dry years on the width of tree rings. This study used dendroecological methods to analyze the growth and diameter increments of European beech trees at locations in Serbia and the Republic of Srpska. The sampling was conducted along the vertical distribution of beech forests, at five sites at the lower limit of the distribution, at five optimal sites of the distribution, and at five sites at the upper limit of the distribution. Long-term analyses indicate that dry conditions during a growing season can reduce tree-ring width, but a reduction in tree growth can be expected as a result of more than one season of unfavorable conditions. Low temperatures in autumn and winter and prolonged winters can strongly affect upcoming vegetation and reduce tree development even under normal thermal conditions during a growing season. Full article

(This article belongs to the Special Issue Weather and Climate Change Challenges in Agricultural and Forest Meteorology)

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24 pages, 5264 KiB

Open AccessArticle

Sensitivity of Glacier Runoff to Winter Snow Thickness Investigated for Vatnajökull Ice Cap, Iceland, Using Numerical Models and Observations

by Louise Steffensen Schmidt, Peter L. Langen, Guðfinna Aðalgeirsdóttir, Finnur Pálsson, Sverrir Guðmundsson and Andri Gunnarsson

Atmosphere 2018, 9(11), 450; https://doi.org/10.3390/atmos9110450 - 15 Nov 2018

Cited by 10 | Viewed by 5541

Abstract

Several simulations of the surface climate and energy balance of Vatnajökull ice cap, Iceland, are used to estimate the glacier runoff for the period 1980–2015 and the sensitivity of runoff to the spring conditions (e.g., snow thickness). The simulations are calculated using the [...] Read more.

Several simulations of the surface climate and energy balance of Vatnajökull ice cap, Iceland, are used to estimate the glacier runoff for the period 1980–2015 and the sensitivity of runoff to the spring conditions (e.g., snow thickness). The simulations are calculated using the snow pack scheme from the regional climate model HIRHAM5, forced with incoming mass and energy fluxes from the numerical weather prediction model HARMONIE-AROME. The modeled runoff is compared to available observations from two outlet glaciers to assess the quality of the simulations. To test the sensitivity of the runoff to spring conditions, simulations are repeated for the spring conditions of each of the years 1980–2015, followed by the weather of all summers in the same period. We find that for the whole ice cap, the variability in runoff as a function of varying spring conditions was on average 31% of the variability due to changing summer weather. However, some outlet glaciers are very sensitive to the amount of snow in the spring, as e.g., the variation in runoff from Brúarjökull due to changing spring conditions was on average 50% of the variability due to varying summer weather. Full article

(This article belongs to the Special Issue Cryosphere in and around Regional Climate Models)

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23 pages, 4840 KiB

Open AccessEditor’s ChoiceArticle

Emission of Air Pollutants from Rice Residue Open Burning in Thailand, 2018

by Agapol Junpen, Jirataya Pansuk, Orachorn Kamnoet, Penwadee Cheewaphongphan and Savitri Garivait

Atmosphere 2018, 9(11), 449; https://doi.org/10.3390/atmos9110449 - 15 Nov 2018

Cited by 74 | Viewed by 10881

Abstract

Crop residue burning negatively impacts both the environment and human health, whether in the aspect of air pollution, regional and global climate change, or transboundary air pollution. Accordingly, this study aims to assess the level of air pollutant emissions caused by the rice [...] Read more.

Crop residue burning negatively impacts both the environment and human health, whether in the aspect of air pollution, regional and global climate change, or transboundary air pollution. Accordingly, this study aims to assess the level of air pollutant emissions caused by the rice residue open burning activities in 2018, by analyzing the remote sensing information and country specific data. This research also aims to analyze the trend of particulate matter 10 microns or less in diameter (PM₁₀) concentration air quality sites in provinces with large paddy rice planting areas from 2010–2017. According to the results, 61.87 megaton (Mt) of rice residue were generated, comprising 21.35 Mt generated from the irrigated fields and 40.53 Mt generated from the rain-fed field. Only 23.0% of the total rice residue generated were subject to open burning—of which nearly 32% were actually burned in the fields. The emissions from such rice residue burning consisted of: 5.34 ± 2.33 megaton (Mt) of CO₂, 44 ± 14 kiloton (kt) of CH₄, 422 ± 179 kt of CO, 2 ± 2 kt of NO_X, 2 ± 2 kt of SO₂, 38 ± 22 kt of PM_2.5, 43 ± 29 kt of PM₁₀, 2 ± 1 kt of black carbon (BC), and 14 ± 5 kt of organic carbon (OC). According to the air quality trends, the results shows the higher level of PM₁₀ concentration was due to the agricultural burning activities, as reflected in the higher monthly averages of the months with the agricultural burning, by around 1.9–2.1 times. The result also shows the effect of government’s policy for farmers on the crop burning activities and air quality trends. Full article

(This article belongs to the Special Issue Air Quality in the Asia-Pacific Region)

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3 pages, 148 KiB

Open AccessEditorial

Urban Design and City Microclimates

by Robert D. Brown

Atmosphere 2018, 9(11), 448; https://doi.org/10.3390/atmos9110448 - 15 Nov 2018

Cited by 1 | Viewed by 3440

Abstract

More than half of the people in the world now live in cities and this proportion is expected to continue to increase. [...] Full article

(This article belongs to the Special Issue Urban Design and City Microclimates)

18 pages, 3624 KiB

Open AccessArticle

Nitrogen Deposition on Danish Nature

by Thomas Ellermann, Jesper Nygaard, Jesper Heile Christensen, Per Løfstrøm, Camilla Geels, Ingeborg Elbæk Nielsen, Maria Bech Poulsen, Christian Monies, Steen Gyldenkærne, Jørgen Brandt and Ole Hertel

Atmosphere 2018, 9(11), 447; https://doi.org/10.3390/atmos9110447 - 14 Nov 2018

Cited by 22 | Viewed by 6419

Abstract

Eutrophication events are frequent in Inner Danish waters and critical loads are exceeded for much of the Danish sensitive terrestrial ecosystems. The Danish air quality monitoring program combines measurements and model calculations to benefit from the complementarities in data from these two sources. [...] Read more.

Eutrophication events are frequent in Inner Danish waters and critical loads are exceeded for much of the Danish sensitive terrestrial ecosystems. The Danish air quality monitoring program combines measurements and model calculations to benefit from the complementarities in data from these two sources. Measurements describe actual status, seasonal variation, and temporal trends. Model calculations extrapolate the results to the entire country and determine depositions to specific ecosystems. Measurements in 2016 show annual depositions between 7.5 and 11 kg N/ha to terrestrial ecosystems, and a load to marine waters of 5.3 kg N/ha. The deposition on Danish marine waters in 2016 was calculated to be 73,000 tons N with an average deposition of 6.9 kg N/ha. For terrestrial areas, the deposition was calculated to be 57,000 tons N with an average deposition of 13 kg N/ha. This is above critical loads for sensitive ecosystems. Long-term trends show a 35% decrease since 1990 in measured annual nitrogen deposition. At two out of four stations in nature areas, measured ammonia levels exceeded critical levels for lichens and mosses. Conclusions: Nitrogen loads and levels to Danish nature is decreasing, but critical loads and levels are still exceeded for sensitive ecosystems. Combining measurements and model calculations is a strong tool in monitoring. Full article

(This article belongs to the Special Issue Atmospheric Nutrients: Sources, Processes and Impact on Terrestrial and Marine Ecosystems)

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17 pages, 3268 KiB

Open AccessArticle

Considering Rain Gauge Uncertainty Using Kriging for Uncertain Data

by Francesca Cecinati, Antonio M. Moreno-Ródenas, Miguel A. Rico-Ramirez, Marie-claire Ten Veldhuis and Jeroen G. Langeveld

Atmosphere 2018, 9(11), 446; https://doi.org/10.3390/atmos9110446 - 14 Nov 2018

Cited by 23 | Viewed by 4731

Abstract

In urban hydrological models, rainfall is the main input and one of the main sources of uncertainty. To reach sufficient spatial coverage and resolution, the integration of several rainfall data sources, including rain gauges and weather radars, is often necessary. The uncertainty associated [...] Read more.

In urban hydrological models, rainfall is the main input and one of the main sources of uncertainty. To reach sufficient spatial coverage and resolution, the integration of several rainfall data sources, including rain gauges and weather radars, is often necessary. The uncertainty associated with rain gauge measurements is dependent on rainfall intensity and on the characteristics of the devices. Common spatial interpolation methods do not account for rain gauge uncertainty variability. Kriging for Uncertain Data (KUD) allows the handling of the uncertainty of each rain gauge independently, modelling space- and time-variant errors. The applications of KUD to rain gauge interpolation and radar-gauge rainfall merging are studied and compared. First, the methodology is studied with synthetic experiments, to evaluate its performance varying rain gauge density, accuracy and rainfall field characteristics. Subsequently, the method is applied to a case study in the Dommel catchment, the Netherlands, where high-quality automatic gauges are complemented by lower-quality tipping-bucket gauges and radar composites. The case study and the synthetic experiments show that considering measurement uncertainty in rain gauge interpolation usually improves rainfall estimations, given a sufficient rain gauge density. Considering measurement uncertainty in radar-gauge merging consistently improved the estimates in the tested cases, thanks to the additional spatial information of radar rainfall data but should still be used cautiously for convective events and low-density rain gauge networks. Full article

(This article belongs to the Special Issue Advances in Applications of Weather Radar Data)

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19 pages, 3221 KiB

Open AccessArticle

An Investigation of Optically Very Thin Ice Clouds from Ground-Based ARM Raman Lidars

by Kelly A. Balmes and Qiang Fu

Atmosphere 2018, 9(11), 445; https://doi.org/10.3390/atmos9110445 - 14 Nov 2018

Cited by 12 | Viewed by 3405

Abstract

Optically very thin ice clouds from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and ground-based Raman lidars (RL) at the atmospheric radiation measurement (ARM) sites of the Southern Great Plains (SGP) and Tropical Western Pacific (TWP) are analyzed. The optically very [...] Read more.

Optically very thin ice clouds from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and ground-based Raman lidars (RL) at the atmospheric radiation measurement (ARM) sites of the Southern Great Plains (SGP) and Tropical Western Pacific (TWP) are analyzed. The optically very thin ice clouds, with ice cloud column optical depths below 0.01, are about 23% of the transparent ice-cloudy profiles from the RL, compared to 4–7% from CALIPSO. The majority (66–76%) of optically very thin ice clouds from the RLs are found to be adjacent to ice clouds with ice cloud column optical depths greater than 0.01. The temporal structure of RL-observed optically very thin ice clouds indicates a clear sky–cloud continuum. Global cloudiness estimates from CALIPSO observations leveraged with high-sensitivity RL observations suggest that CALIPSO may underestimate the global cloud fraction when considering optically very thin ice clouds. Full article

(This article belongs to the Special Issue Cloud Radiative Processes and Effect)

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20 pages, 5859 KiB

Open AccessArticle

Performance of Adaptive Unstructured Mesh Modelling in Idealized Advection Cases over Steep Terrains

by Jinxi Li, Jie Zheng, Jiang Zhu, Fangxin Fang, Christopher. C. Pain, Jürgen Steppeler, Ionel M. Navon and Hang Xiao

Atmosphere 2018, 9(11), 444; https://doi.org/10.3390/atmos9110444 - 13 Nov 2018

Cited by 4 | Viewed by 3144

Abstract

Advection errors are common in basic terrain-following (TF) coordinates. Numerous methods, including the hybrid TF coordinate and smoothing vertical layers, have been proposed to reduce the advection errors. Advection errors are affected by the directions of velocity fields and the complexity of the [...] Read more.

Advection errors are common in basic terrain-following (TF) coordinates. Numerous methods, including the hybrid TF coordinate and smoothing vertical layers, have been proposed to reduce the advection errors. Advection errors are affected by the directions of velocity fields and the complexity of the terrain. In this study, an unstructured adaptive mesh together with the discontinuous Galerkin finite element method is employed to reduce advection errors over steep terrains. To test the capability of adaptive meshes, five two-dimensional (2D) idealized tests are conducted. Then, the results of adaptive meshes are compared with those of cut-cell and TF meshes. The results show that using adaptive meshes reduces the advection errors by one to two orders of magnitude compared to the cut-cell and TF meshes regardless of variations in velocity directions or terrain complexity. Furthermore, adaptive meshes can reduce the advection errors when the tracer moves tangentially along the terrain surface and allows the terrain to be represented without incurring in severe dispersion. Finally, the computational cost is analyzed. To achieve a given tagging criterion level, the adaptive mesh requires fewer nodes, smaller minimum mesh sizes, less runtime and lower proportion between the node numbers used for resolving the tracer and each wavelength than cut-cell and TF meshes, thus reducing the computational costs. Full article

(This article belongs to the Section Meteorology)

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32 pages, 11321 KiB

Open AccessArticle

Source Contributions to Ozone Formation in the New South Wales Greater Metropolitan Region, Australia

by Hiep Nguyen Duc, Lisa T.-C. Chang, Toan Trieu, David Salter and Yvonne Scorgie

Atmosphere 2018, 9(11), 443; https://doi.org/10.3390/atmos9110443 - 13 Nov 2018

Cited by 12 | Viewed by 4039

Abstract

Ozone and fine particles (PM_2.5) are the two main air pollutants of concern in the New South Wales Greater Metropolitan Region (NSW GMR) due to their contribution to poor air quality days in the region. This paper focuses on source contributions [...] Read more.

Ozone and fine particles (PM_2.5) are the two main air pollutants of concern in the New South Wales Greater Metropolitan Region (NSW GMR) due to their contribution to poor air quality days in the region. This paper focuses on source contributions to ambient ozone concentrations for different parts of the NSW GMR, based on source emissions across the greater Sydney region. The observation-based Integrated Empirical Rate model (IER) was applied to delineate the different regions within the GMR based on the photochemical smog profile of each region. Ozone source contribution was then modelled using the CCAM-CTM (Cubic Conformal Atmospheric model-Chemical Transport model) modelling system and the latest air emission inventory for the greater Sydney region. Source contributions to ozone varied between regions, and also varied depending on the air quality metric applied (e.g., average or maximum ozone). Biogenic volatile organic compound (VOC) emissions were found to contribute significantly to median and maximum ozone concentration in North West Sydney during summer. After commercial and domestic sources, power generation was found to be the next largest anthropogenic source of maximum ozone concentrations in North West Sydney. However, in South West Sydney, beside commercial and domestic sources, on-road vehicles were predicted to be the most significant contributor to maximum ozone levels, followed by biogenic sources and power stations. The results provide information that policy makers can use to devise various options to control ozone levels in different parts of the NSW Greater Metropolitan Region. Full article

(This article belongs to the Special Issue Air Quality in New South Wales, Australia)

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22 pages, 8474 KiB

Open AccessArticle

Application of GPU-Based Large Eddy Simulation in Urban Dispersion Studies

by Gergely Kristóf and Bálint Papp

Atmosphere 2018, 9(11), 442; https://doi.org/10.3390/atmos9110442 - 13 Nov 2018

Cited by 13 | Viewed by 6278

Abstract

While large eddy simulation has several advantages in microscale air pollutant dispersion modelling, the parametric investigation of geometries is not yet feasible because of its relatively high computational cost. By assuming an analogy between heat and mass transport processes, we utilize a Graphics [...] Read more.

While large eddy simulation has several advantages in microscale air pollutant dispersion modelling, the parametric investigation of geometries is not yet feasible because of its relatively high computational cost. By assuming an analogy between heat and mass transport processes, we utilize a Graphics Processing Unit based software—originally developed for mechanical engineering applications—to model urban dispersion. The software allows for the modification of the geometry as well as the visualization of the transient flow and concentration fields during the simulation, thus supporting the analysis and comparison of different design concepts. By placing passive turbulence generators near the inlet, a numerical wind tunnel was created, capable of producing the characteristic velocity and turbulence intensity profiles of the urban boundary layer. The model results show a satisfactory agreement with wind tunnel experiments examining single street canyons. The effect of low boundary walls placed in the middle of the road and adjacent to the walkways was investigated in a wide parameter range, along with the impact made by the roof slope angle. The presented approach can be beneficially used in the early phase of simulation driven urban design, by screening the concepts to be experimentally tested or simulated with high accuracy models. Full article

(This article belongs to the Special Issue Recent Advances in Urban Ventilation Assessment and Flow Modelling)

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17 pages, 5753 KiB

Open AccessArticle

Differences in Sulfate Aerosol Radiative Forcing between the Daytime and Nighttime over East Asia Using the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) Model

by Hongyue Zhang, Siyu Chen, Nanxuan Jiang, Xin Wang, Xiaorui Zhang, Jian Liu, Zhou Zang, Dongyou Wu, Tiangang Yuan, Yuan Luo and Dan Zhao

Atmosphere 2018, 9(11), 441; https://doi.org/10.3390/atmos9110441 - 13 Nov 2018

Cited by 3 | Viewed by 4223

Abstract

The effect of aerosols is an important indicator of climate change. Sulfate aerosols, as the major scattering aerosols, which have attracted more and more attention in recent years. The Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) were utilized to investigate the [...] Read more.

The effect of aerosols is an important indicator of climate change. Sulfate aerosols, as the major scattering aerosols, which have attracted more and more attention in recent years. The Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) were utilized to investigate the spatial distribution of sulfate aerosols and their radiative forcing characteristics over East Asia in 2010. Results showed that sulfate aerosols were mainly distributed over eastern China (24–43° N, 101–126° E), especially in the Sichuan Basin. The concentration of sulfate aerosols decreased with increasing altitude over East Asia. It also exhibited obvious seasonal variations, where the largest range of sulfate aerosol concentrations was found in summer, with a maximum of 2.4 μg kg⁻¹ over eastern China. Although sulfate aerosol concentrations varied slightly during day and night, there was still a significantly difference in the sulfate aerosol radiative forcing. Specifically, the magnitude of the direct radiative forcing induced by sulfate aerosols at the surface was approximately −3.02 W m⁻² in the daytime, while that was +0.24 W m⁻² in the nighttime. This asymmetric change that was caused by the radiative forcing of sulfate aerosols between day and night would have significant impacts on climate change at the regional scale. Full article

(This article belongs to the Special Issue Regional Scale Air Quality Modelling)

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14 pages, 2741 KiB

Open AccessArticle

On the Roles of Advection and Solar Heating in Seasonal Variation of the Migrating Diurnal Tide in the Stratosphere, Mesosphere, and Lower Thermosphere

by Hongping Gu and Jian Du

Atmosphere 2018, 9(11), 440; https://doi.org/10.3390/atmos9110440 - 12 Nov 2018

Cited by 7 | Viewed by 3899

Abstract

The migrating diurnal tide (DW1) presents a unique latitudinal structure in the stratosphere, mesosphere, and lower thermosphere. In this paper, the physical mechanisms that govern its seasonal variation are examined in these three regions using the 31.5-year (1979–2010) output from the extended Canadian [...] Read more.

The migrating diurnal tide (DW1) presents a unique latitudinal structure in the stratosphere, mesosphere, and lower thermosphere. In this paper, the physical mechanisms that govern its seasonal variation are examined in these three regions using the 31.5-year (1979–2010) output from the extended Canadian Middle Atmosphere Model (eCMAM30). DW1 annual variation in the stratosphere is mainly controlled by the short-wave heating in the high latitudes, but by both the short-wave and adiabatic heating in the low latitudes. In the mesosphere, linear and nonlinear advection play important roles in the semiannual variation of the tide whereas short-wave heating does not. In the lower thermosphere, the annual variation of DW1 is mainly governed by the short-wave heating and linear advection. This study illustrates the complexity of the main physical mechanisms modulating the seasonal variations of DW1 in different regions of the atmosphere. Full article

(This article belongs to the Special Issue Changes in the Stratosphere, Mesosphere and Lower Thermosphere Composition and Thermal Structure)

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24 pages, 9498 KiB

Open AccessEditor’s ChoiceReview

A Review of Atmosphere–Ocean Forcings Outside the Tropical Pacific on the El Niño–Southern Oscillation Occurrence

by Shangfeng Chen, Bin Yu, Wen Chen and Renguang Wu

Atmosphere 2018, 9(11), 439; https://doi.org/10.3390/atmos9110439 - 12 Nov 2018

Cited by 21 | Viewed by 6189

Abstract

The El Niño–Southern Oscillation (ENSO) is the strongest interannual air–sea coupled variability mode in the tropics, and substantially impacts the global weather and climate. Hence, it is important to improve our understanding of the ENSO variability. Besides the well-known air–sea interaction process over [...] Read more.

The El Niño–Southern Oscillation (ENSO) is the strongest interannual air–sea coupled variability mode in the tropics, and substantially impacts the global weather and climate. Hence, it is important to improve our understanding of the ENSO variability. Besides the well-known air–sea interaction process over the tropical Pacific, recent studies indicated that atmospheric and oceanic forcings outside the tropical Pacific also play important roles in impacting and modulating the ENSO occurrence. This paper reviews the impacts of the atmosphere–ocean variability outside the tropical Pacific on the ENSO variability, as well as their associated physical processes. The review begins with the contribution of the atmosphere–ocean forcings over the extratropical North Pacific, Atlantic, and Indian Ocean on the ENSO occurrence. Then, an overview of the extratropical atmospheric forcings over the Northern Hemisphere (including the Arctic Oscillation and the Asian monsoon systems) and the Southern Hemisphere (including the Antarctic Oscillation and the Pacific–South American teleconnection), on the ENSO occurrence, is presented. It is shown that the westerly (easterly) wind anomaly over the tropical western Pacific is essential for the occurrence of an El Niño (a La Niña) event. The wind anomalies over the tropical western Pacific also play a key role in relaying the impacts of the atmosphere–ocean forcings outside the tropical Pacific on the ENSO variability. Finally, some relevant questions, that remain to be explored, are discussed. Full article

(This article belongs to the Special Issue Large-Scale Atmospheric Circulation Variability and Its Climate Impacts)

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18 pages, 2523 KiB

Open AccessEditor’s ChoiceArticle

Impact of Snow Darkening by Deposition of Light-Absorbing Aerosols on Snow Cover in the Himalayas–Tibetan Plateau and Influence on the Asian Summer Monsoon: A Possible Mechanism for the Blanford Hypothesis

by William K. M. Lau and Kyu-Myong Kim

Atmosphere 2018, 9(11), 438; https://doi.org/10.3390/atmos9110438 - 12 Nov 2018

Cited by 44 | Viewed by 7351

Abstract

The impact of snow darkening by deposition of light-absorbing aerosols (LAAs) on snow cover over the Himalayas–Tibetan Plateau (HTP) and the influence on the Asian summer monsoon were investigated using the NASA Goddard Earth Observing System Model Version 5 (GEOS-5). The authors found [...] Read more.

The impact of snow darkening by deposition of light-absorbing aerosols (LAAs) on snow cover over the Himalayas–Tibetan Plateau (HTP) and the influence on the Asian summer monsoon were investigated using the NASA Goddard Earth Observing System Model Version 5 (GEOS-5). The authors found that during April–May–June, the deposition of LAAs on snow led to a reduction in surface albedo, initiating a sequence of feedback processes, starting with increased net surface solar radiation, rapid snowmelt in the HTP and warming of the surface and upper troposphere, followed by enhanced low-level southwesterlies and increased dust loading over the Himalayas–Indo-Gangetic Plain. The warming was amplified by increased dust aerosol heating, and subsequently amplified by latent heating from enhanced precipitation over the Himalayan foothills and northern India, via the elevated heat pump (EHP) effect during June–July–August. The reduced snow cover in the HTP anchored the enhanced heating over the Tibetan Plateau and its southern slopes, in conjunction with an enhancement of the Tibetan Anticyclone, and the development of an anomalous Rossby wave train over East Asia, leading to a weakening of the subtropical westerly jet, and northward displacement and intensification of the Mei-Yu rain belt. The authors’ results suggest that the atmosphere-land heating induced by LAAs, particularly desert dust, plays a fundamental role in physical processes underpinning the snow–monsoon relationship proposed by Blanford more than a century ago. Full article

(This article belongs to the Special Issue Monsoons)

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19 pages, 4371 KiB

Open AccessArticle

Precursors of September Arctic Sea-Ice Extent Based on Causal Effect Networks

by Sha Li, Muyin Wang, Nicholas A. Bond, Wenyu Huang, Yong Wang, Shiming Xu, Jiping Liu, Bin Wang and Yuqi Bai

Atmosphere 2018, 9(11), 437; https://doi.org/10.3390/atmos9110437 - 09 Nov 2018

Cited by 4 | Viewed by 4029

Abstract

Although standard statistical methods and climate models can simulate and predict sea-ice changes well, it is still very hard to distinguish some direct and robust factors associated with sea-ice changes from its internal variability and other noises. Here, with long-term observations (38 years [...] Read more.

Although standard statistical methods and climate models can simulate and predict sea-ice changes well, it is still very hard to distinguish some direct and robust factors associated with sea-ice changes from its internal variability and other noises. Here, with long-term observations (38 years from 1980 to 2017), we apply the causal effect networks algorithm to explore the direct precursors of September Arctic sea-ice extent by adjusting the maximal lead time from one to eight months. For lead time of more than three months, June downward longwave radiation flux in the Canadian Arctic Archipelago is the only one precursor. However, for lead time of 1–3 months, August sea-ice concentration in Western Arctic represents the strongest positive correlation with September sea-ice extent, while August sea-ice concentration factors in other regions have weaker influences on the marginal seas. Other precursors include August wind anomalies in the lower latitudes accompanied with an Arctic high pressure anomaly, which induces the sea-ice loss along the Eurasian coast. These robust precursors can be used to improve the seasonal predictions of Arctic sea ice and evaluate the climate models. Full article

(This article belongs to the Section Meteorology)

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31 pages, 15615 KiB

Open AccessArticle

Sensitivity of a Mediterranean Tropical-Like Cyclone to Physical Parameterizations

by Ioannis Pytharoulis, Stergios Kartsios, Ioannis Tegoulias, Haralambos Feidas, Mario Marcello Miglietta, Ioannis Matsangouras and Theodore Karacostas

Atmosphere 2018, 9(11), 436; https://doi.org/10.3390/atmos9110436 - 09 Nov 2018

Cited by 24 | Viewed by 4646

Abstract

The accurate prediction of Mediterranean tropical-like cyclones, or medicanes, is an important challenge for numerical weather prediction models due to their significant adverse impact on the environment, life, and property. The aim of this study is to investigate the sensitivity of an intense [...] Read more.

The accurate prediction of Mediterranean tropical-like cyclones, or medicanes, is an important challenge for numerical weather prediction models due to their significant adverse impact on the environment, life, and property. The aim of this study is to investigate the sensitivity of an intense medicane, which formed south of Sicily on 7 November 2014, to the microphysical, cumulus, and boundary/surface layer schemes. The non-hydrostatic Weather Research and Forecasting model (version 3.7.1) is employed. A symmetric cyclone with a deep warm core, corresponding to a medicane, develops in all of the experiments, except for the one with the Thompson microphysics. There is a significant sensitivity of different aspects of the simulated medicane to the physical parameterizations. Its intensity is mainly influenced by the boundary/surface layer scheme, while its track is mainly influenced by the representation of cumulus convection, and its duration is mainly influenced by microphysical parameterization. The modification of the drag coefficient and the roughness lengths of heat and moisture seems to improve its intensity, track, and duration. The parameterization of shallow convection, with explicitly resolved deep convection, results in a weaker medicane with a shorter lifetime. An optimum combination of physical parameterizations in order to simulate all of the characteristics of the medicane does not seem to exist. Full article

(This article belongs to the Special Issue Mediterranean Tropical-Like Cyclones (Medicanes))

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31 pages, 4888 KiB

Open AccessArticle

Linear or Nonlinear Modeling for ENSO Dynamics?

by Marco Bianucci, Antonietta Capotondi, Riccardo Mannella and Silvia Merlino

Atmosphere 2018, 9(11), 435; https://doi.org/10.3390/atmos9110435 - 08 Nov 2018

Cited by 6 | Viewed by 4159

Abstract

The observed ENSO statistics exhibits a non-Gaussian behavior, which is indicative of the presence of nonlinear processes. In this paper, we use the Recharge Oscillator Model (ROM), a largely used Low-Order Model (LOM) of ENSO, as well as methodologies borrowed from the field [...] Read more.

The observed ENSO statistics exhibits a non-Gaussian behavior, which is indicative of the presence of nonlinear processes. In this paper, we use the Recharge Oscillator Model (ROM), a largely used Low-Order Model (LOM) of ENSO, as well as methodologies borrowed from the field of statistical mechanics to identify which aspects of the system may give rise to nonlinearities that are consistent with the observed ENSO statistics. In particular, we are interested in understanding whether the nonlinearities reside in the system dynamics or in the fast atmospheric forcing. Our results indicate that one important dynamical nonlinearity often introduced in the ROM cannot justify a non-Gaussian system behavior, while the nonlinearity in the atmospheric forcing can instead produce a statistics similar to the observed. The implications of the non-Gaussian character of ENSO statistics for the frequency of extreme El Niño events is then examined. Full article

(This article belongs to the Special Issue El Niño Southern Oscillation (ENSO))

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23 pages, 6853 KiB

Open AccessArticle

Non-Monotonic Dependencies of Cloud Microphysics and Precipitation on Aerosol Loading in Deep Convective Clouds: A Case Study Using the WRF Model with Bin Microphysics

by Ye-Lim Jeon, Sungju Moon, Hyunho Lee, Jong-Jin Baik and Jambajamts Lkhamjav

Atmosphere 2018, 9(11), 434; https://doi.org/10.3390/atmos9110434 - 08 Nov 2018

Cited by 8 | Viewed by 4158

Abstract

Aerosol-cloud-precipitation interactions in deep convective clouds are investigated through numerical simulations of a heavy precipitation event over South Korea on 15–16 July 2017. The Weather Research and Forecasting model with a bin microphysics scheme is used, and various aerosol number concentrations in the [...] Read more.

Aerosol-cloud-precipitation interactions in deep convective clouds are investigated through numerical simulations of a heavy precipitation event over South Korea on 15–16 July 2017. The Weather Research and Forecasting model with a bin microphysics scheme is used, and various aerosol number concentrations in the range N₀ = 50–12,800 cm⁻³ are considered. Precipitation amount changes non-monotonically with increasing aerosol loading, with a maximum near a moderate aerosol loading (N₀ = 800 cm⁻³). Up to this optimal value, an increase in aerosol number concentration results in a greater quantity of small droplets formed by nucleation, increasing the number of ice crystals. Ice crystals grow into snow particles through deposition and riming, leading to enhanced melting and precipitation. Beyond the optimal value, a greater aerosol loading enhances generation of ice crystals while the overall growth of ice hydrometeors through deposition stagnates. Subsequently, the riming rate decreases because of the smaller size of snow particles and supercooled drops, leading to a decrease in ice melting and a slight suppression of precipitation. As aerosol loading increases, cold pool and low-level convergence strengthen monotonically, but cloud development is more strongly affected by latent heating and convection within the system that is non-monotonically reinforced. Full article

(This article belongs to the Special Issue Aerosol-Cloud Interactions)

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17 pages, 3249 KiB

Open AccessArticle

Spatial–Temporal Variability of Hydrothermal Climate Conditions in the Yellow River Basin from 1957 to 2015

by Liqun Ma, Haoming Xia, Jiulin Sun, Hao Wang, Gary Feng and Fen Qin

Atmosphere 2018, 9(11), 433; https://doi.org/10.3390/atmos9110433 - 07 Nov 2018

Cited by 12 | Viewed by 3289

Abstract

The Yellow River Basin has been affected by global climate change. Studying the spatial–temporal variability of the hydrothermal climate conditions in the Yellow River Basin is of vital importance for the development of technologies and policies related to ecological, environmental, and agricultural adaptation [...] Read more.

The Yellow River Basin has been affected by global climate change. Studying the spatial–temporal variability of the hydrothermal climate conditions in the Yellow River Basin is of vital importance for the development of technologies and policies related to ecological, environmental, and agricultural adaptation in this region. This study selected temperature and precipitation data observed from 118 meteorological stations distributed in the Yellow River Basin over the period of 1957–2015, and used the Mann–Kendall, Pettitt, and Hurst indices to investigate the spatial–temporal variability of the hydrothermal climate conditions in this area. The results indicated: (1) the annual maximum, minimum, and average temperatures have increased. The seasonal maximum, minimum, and average temperatures for the spring, summer, autumn, and winter have also increased, and this trend is statistically significant (p < 0.01) between 1957–2015. The rate of increase in the minimum temperature exceeded that of the maximum temperature, and diurnal warming was asymmetric. Annual precipitation and the total spring, summer, and autumn precipitations declined, while the total winter precipitation increased, although the trend was non-significant (p > 0.05). (2) Based on the very restrictive assumption that future changes will be similar to past changes, according to the Hurst index experiment, the future trends of temperature and precipitation in the Yellow River Basin are expected to stay the same as in the past. There will be a long-term correlation between the two trends: the temperature will continue to rise, while the precipitation will continue to decline (except in the winter). However, over the late stage of the study period, the trends slowed down to some extent. Full article

(This article belongs to the Section Meteorology)

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15 pages, 2268 KiB

Open AccessArticle

Response of Surface Ultraviolet and Visible Radiation to Stratospheric SO₂ Injections

by Sasha Madronich, Simone Tilmes, Ben Kravitz, Douglas G. MacMartin and Jadwiga H. Richter

Atmosphere 2018, 9(11), 432; https://doi.org/10.3390/atmos9110432 - 07 Nov 2018

Cited by 19 | Viewed by 6154

Abstract

Climate modification by stratospheric SO₂ injections, to form sulfate aerosols, may alter the spectral and angular distributions of the solar ultraviolet and visible radiation that reach the Earth’s surface, with potential consequences to environmental photobiology and photochemistry. We used modeling results from [...] Read more.

Climate modification by stratospheric SO₂ injections, to form sulfate aerosols, may alter the spectral and angular distributions of the solar ultraviolet and visible radiation that reach the Earth’s surface, with potential consequences to environmental photobiology and photochemistry. We used modeling results from the CESM1(WACCM) stratospheric aerosol geoengineering large ensemble (GLENS) project, following the RCP8.5 emission scenario, and one geoengineering experiment with SO₂ injections in the stratosphere, designed to keep surface temperatures at 2020 levels. Zonally and monthly averaged vertical profiles of O₃, SO₂, and sulfate aerosols, at 30 N and 70 N, served as input into a radiative transfer model, to compute biologically active irradiances for DNA damage (i_DNA), UV index (UVI), photosynthetically active radiation (PAR), and two key tropospheric photodissociation coefficients (j_O1D for O₃ + hν (λ < 330 nm) → O(¹D) + O₂; and j_NO2 for NO₂ + hν (λ < 420 nm) → O(³P) + NO). We show that the geoengineering scenario is accompanied by substantial reductions in UV radiation. For example, comparing March 2080 to March 2020, i_DNA decreased by 25% to 29% in the subtropics (30 N) and by 26% to 33% in the polar regions (70 N); UVI decreased by 19% to 20% at 30 N and 23% to 26% at 70 N; and j_O1D decreased by 22% to 24% at 30 N and 35% to 40% at 70 N, with comparable contributions from sulfate scattering and stratospheric O₃ recovery. Different responses were found for processes that depend on longer UV and visible wavelengths, as these are minimally affected by ozone; PAR and j_NO2 were only slightly lower (9–12%) at 30 N, but much lower at 70 N (35–40%). Similar reductions were estimated for other months (June, September, and December). Large increases in the PAR diffuse-direct ratio occurred in agreement with previous studies. Absorption by SO₂ gas had a small (~1%) effect on j_O1D, i_DNA, and UVI, and no effect on j_NO2 and PAR. Full article

(This article belongs to the Special Issue Radiative Transfer in the Earth Atmosphere)

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19 pages, 16451 KiB

Open AccessArticle

Influence of the Antarctic Oscillation on the South Atlantic Convergence Zone

by Flávia Venturini Rosso, Nathalie Tissot Boiaski, Simone Erotildes Teleginski Ferraz and Tiago Capello Robles

Atmosphere 2018, 9(11), 431; https://doi.org/10.3390/atmos9110431 - 07 Nov 2018

Cited by 22 | Viewed by 5088

Abstract

The South Atlantic convergence zone (SACZ) is the main summer-typical atmospheric phenomenon occurring in South America, and it is of great interest because it regulates the rainy season in the most populated regions of Brazil. Frequency variability, persistence, and geographical position of the [...] Read more.

The South Atlantic convergence zone (SACZ) is the main summer-typical atmospheric phenomenon occurring in South America, and it is of great interest because it regulates the rainy season in the most populated regions of Brazil. Frequency variability, persistence, and geographical position of the SACZ and its relationship with intraseasonal variability is well described in the literature. However, the influence of extratropical forcing on the SACZ is not well understood. Consequently, the aim of this study is to evaluate the role of the Antarctic Oscillation (AAO) in SACZ events. The persistence and frequencies of SACZ events, mean, standard deviation of total precipitation per event, lag composite of daily precipitation and geopotential height anomalies were obtained for each phase of the AAO. Therefore, frequency, persistence and total precipitation of SACZ events were higher in positive AAO (AAO+) than negative AAO (AAO−). A teleconnection mechanism between the extratropics and the SACZ region is evident in AAO+, through intensification of the polar and subtropical jets, in the days preceding SACZ. The same was not observed in the AAO−, where the anomalies were confined in the subtropical region and displaced to the South Atlantic Ocean. Full article

(This article belongs to the Special Issue Weather and Climate Extremes: Current Developments)

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17 pages, 10438 KiB

Open AccessReview

Satellite Observations of Cloud-Related Variations in Aerosol Properties

by Tamás Várnai and Alexander Marshak

Atmosphere 2018, 9(11), 430; https://doi.org/10.3390/atmos9110430 - 07 Nov 2018

Cited by 20 | Viewed by 3884

Abstract

This paper presents an overview of our efforts to characterize and better understand cloud-related changes in aerosol properties. These efforts primarily involved the statistical analysis of global or regional datasets of Moderate Resolution Imaging Spectroradiometer (MODIS) and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) [...] Read more.

This paper presents an overview of our efforts to characterize and better understand cloud-related changes in aerosol properties. These efforts primarily involved the statistical analysis of global or regional datasets of Moderate Resolution Imaging Spectroradiometer (MODIS) and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) aerosol and cloud observations. The results show that in oceanic regions, more than half of all aerosol measurements by passive satellite instruments come from near-cloud areas, where clouds and cloud-related processes may significantly modify aerosol optical depth and particle size. Aerosol optical depth is also shown to increase systematically with regional cloud amount throughout the Earth. In contrast, it is shown that effective particle size can either increase or decrease with increasing cloud cover. In bimodal aerosol populations, the sign of changes depends on whether coarse mode or small mode aerosols are most affected by clouds. The results also indicate that over large parts of Earth, undetected cloud particles are not the dominant reason for the satellite-observed changes with cloud amount, and that 3D radiative processes contribute about 30% of the observed near-cloud changes. The findings underline the need for improving our ability to accurately measure aerosols near clouds. Full article

(This article belongs to the Special Issue Radiative Transfer in the Earth Atmosphere)

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18 pages, 5092 KiB

Open AccessArticle

Impact of Meteorological Conditions on PM_2.5 Pollution in China during Winter

by Yanling Xu, Wenbo Xue, Yu Lei, Yang Zhao, Shuiyuan Cheng, Zhenhai Ren and Qing Huang

Atmosphere 2018, 9(11), 429; https://doi.org/10.3390/atmos9110429 - 06 Nov 2018

Cited by 61 | Viewed by 5689

Abstract

Fine particulate matter (PM_2.5) poses a risk to human health. In January 2017, the PM_2.5 pollution in China was severe, and the average PM_2.5 concentration had increased by 14.7% compared to that in January 2016. Meteorological conditions greatly influence [...] Read more.

Fine particulate matter (PM_2.5) poses a risk to human health. In January 2017, the PM_2.5 pollution in China was severe, and the average PM_2.5 concentration had increased by 14.7% compared to that in January 2016. Meteorological conditions greatly influence PM_2.5 pollution. The relationship between PM_2.5 and meteorological factors was assessed using monitoring data and the Community Multiscale Air Quality modeling system (CMAQ) was used to quantitatively evaluate the impacts of variations of meteorological conditions on PM_2.5 pollution. The results indicate that variations of meteorological conditions between January 2017 and January 2016 caused an increase of 13.6% in the national mean concentration of PM_2.5. Unlike the Yangtze River Delta (YRD), where meteorological conditions were favorable, unfavorable meteorological conditions (such as low wind speed, high humidity, low boundary layer height and low rainfall) contributed to PM_2.5 concentration worsening by 29.7%, 42.6% and 7.9% in the Beijing-Tianjin-Hebei (JJJ) region, the Pearl River Delta (PRD) region and the Chengdu-Chongqing (CYB) region, respectively. Given the significant influence of local meteorology on PM_2.5 concentration, more emphasis should be placed on employing meteorological means to improve local air quality. Full article

(This article belongs to the Special Issue Air Quality in China: Past, Present and Future)

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17 pages, 7965 KiB

Open AccessArticle

Improving PM_2.5 Forecasting and Emission Estimation Based on the Bayesian Optimization Method and the Coupled FLEXPART-WRF Model

by Lifeng Guo, Baozhang Chen, Huifang Zhang, Guang Xu, Lijiang Lu, Xiaofeng Lin, Yawen Kong, Fei Wang and Yanpeng Li

Atmosphere 2018, 9(11), 428; https://doi.org/10.3390/atmos9110428 - 05 Nov 2018

Cited by 17 | Viewed by 5128

Abstract

In this study, we evaluated estimates and predictions of the PM_2.5 (fine particulate matter) concentrations and emissions in Xuzhou, China, using a coupled Lagrangian particle dispersion modeling system (FLEXPART-WRF). A Bayesian inversion method was used in FLEXPART-WRF to improve the emission calculation [...] Read more.

In this study, we evaluated estimates and predictions of the PM_2.5 (fine particulate matter) concentrations and emissions in Xuzhou, China, using a coupled Lagrangian particle dispersion modeling system (FLEXPART-WRF). A Bayesian inversion method was used in FLEXPART-WRF to improve the emission calculation and mixing ratio estimation for PM_2.5. We first examined the inversion modeling performance by comparing the model predictions with PM_2.5 concentration observations from four stations in Xuzhou. The linear correlation analysis between the predicted PM_2.5 concentrations and the observations shows that our inversion forecast system is much better than the system before calibration (with correlation coefficients of R = 0.639 vs. 0.459, respectively, and root mean square errors of RMSE = 7.407 vs. 9.805 µg/m³, respectively). We also estimated the monthly average emission flux in Xuzhou to be 4188.26 Mg/month, which is much higher (by ~10.12%) than the emission flux predicted by the multiscale emission inventory data (MEIC) (3803.5 Mg/month). In addition, the monthly average emission flux shows obvious seasonal variation, with the lowest PM_2.5 flux in summer and the highest flux in winter. This pattern is mainly due to the additional heating fuels used in the cold season, resulting in many fine particulates in the atmosphere. Although the inversion and forecast results were improved to some extent, the inversion system can be improved further, e.g., by increasing the number of observation values and improving the accuracy of the a priori emission values. Further research and analysis are recommended to help improve the forecast precision of real-time PM_2.5 concentrations and the corresponding monthly emission fluxes. Full article

(This article belongs to the Section Air Quality)

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15 pages, 3644 KiB

Open AccessArticle

The Development of a Methodology for Calibrating a Large-Scale Laboratory Rainfall Simulator

by Haksoo Kim, Teakjo Ko, Hyangseon Jeong and Sungje Ye

Atmosphere 2018, 9(11), 427; https://doi.org/10.3390/atmos9110427 - 02 Nov 2018

Cited by 15 | Viewed by 3275

Abstract

The objective of this study was to establish a method to calibrate a large-scale laboratory rainfall simulator through developing and implementing an automated rainfall collection system to assess the reliability and accuracy of a rainfall simulator. The automated rainfall collection system was designed [...] Read more.

The objective of this study was to establish a method to calibrate a large-scale laboratory rainfall simulator through developing and implementing an automated rainfall collection system to assess the reliability and accuracy of a rainfall simulator. The automated rainfall collection system was designed to overcome the limitations caused by the traditional manual measurement for obtaining the rainfall intensity and the spatial rainfall distribution in a large experimental area. The developed automated rainfall collection system was implemented to calibrate a large-scale laboratory rainfall simulator. The adequacy of average rainfall intensities automatically collected from the miniature tipping bucket rain gauges was assessed by comparison with those based on the volumetric method using the flowmeter. The functional relationships between the system variables of the rainfall simulator and the simulated intensity and uniformity distribution of rainfall (i.e., operation models) were derived based on a multiple regression approach incorporating correlation analysis on linear and logarithm scales, with consideration of a significance level. The operation models exhibited high accuracy with respect to both the rainfall intensity and the uniformity coefficients. Full article

(This article belongs to the Section Meteorology)

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