Atmosphere, Volume 10, Issue 8 (August 2019) – 55 articles

An intensive winter campaign was organized for measuring the surface air pollutants in southeastern Europe. For a three months period, the gas concentrations of NO ${}_x$ , SO ${}_2$ , CO, O ${}_3$ , and CH ${}_4$ as well as meteorological parameters were simultaneously sampled to evaluate the variations and characteristic reactions between the gases during winter at the measuring site. The photochemical production of the ozone was observed through the diurnal variation of ozone and the solar radiation, the maximum concentration for ozone being reached one hour after the maximum value for solar radiation. A non-parametric wind regression method was used to highlight the sources of the air pollutants. The long-range transport of SO ${}_2$ and two hotspots for CO from traffic and from residential heating emissions were emphasized. The traffic hotspot situated north of the measuring site, close to the city ring road, is also a hotspot for NO ${}_x$ . The air quality during the cold season was evaluated by comparing the measured gas concentration with the European limits. During the measuring period, the values for NO ${}_2$ , CO, and SO ${}_2$ concentration were at least two times lower than the European Union pollution limits. Only twice during the study period was the concentration of O ${}_3$ higher than the established limits. Full article

The prediction skill of the Climate Forecast System, version 2 (CFSv2), for the North Atlantic Oscillation (NAO) is evaluated in three winter months (December, January, and February). The results show that the CFSv2 model can skillfully predict the December NAO one month in advance. There are two main contributors to NAO predictability in December. One is the predictability of the relationship between the North Atlantic sea surface temperature anomaly (SSTA) tripole and the NAO and the other is the second empirical orthogonal function (EOF) mode of the geopotential height at 50 hPa (Z50-EOF2). The relationship between the NAO and SSTA tripole index in December is the most significant in the three winter months. The significant monthly differences of surface heat fluxes in December over the whole North Atlantic are favorable for promoting the interaction between the NAO and North Atlantic SSTAs, in addition to improving the predictability of the December NAO. When the NAO is in a positive phase, easterly anomalies are located at the low and high latitudes and westerly anomalies prevail in the mid-latitudes of the troposphere. The correlation between the December Z50-EOF2 and zonal-mean zonal wind anomalies shows a similar spatial structure to that for the NAO. The possible reason why the CFSv2 model can predict the December NAO one month ahead is that it can reasonably reproduce the relationship between the December NAO and both the North Atlantic SST and stratospheric circulation. Full article

China and India are not only the two most populous nations on Earth, they are also two of the most rapidly growing economies. Historically, economic and social development have been subsidized by cheap and abundant fossil-fuels. Climate change from fossil-fuel emissions has resulted in the need to reduce fossil-fuel emissions in order to avoid catastrophic warming. If climate goals are achieved, China and India will have been the first major economies to develop via renewable energy sources. In this article, we examine the factors of projected population growth, available fossil-fuel reserves, and renewable energy installations required to develop scenarios in which both China and India may increase per capita energy consumption while remaining on trach to meet ambitious climate goals. Here, we show that China and India will have to expand their renewable energy infrastructure at unprecedented rates in order to support both population growth and development goals. In the larger scope of the literature, we recommend community-based approaches to microgrid and cookstove development in both China and India. Full article

Ocean salinity variability provides a new way to study the evolution of the the El Niño-Southern Oscillation (ENSO). Comparisons between the salinity variation and related processes responsible for sea surface temperature anomaly (SSTA) were extensively examined for the two strong El Niño (EN) events in 1997/1998 and 2015/2016, and a special EN event in 2014/2015. The results show that the development of EN is significantly correlated with a sea surface salinity anomaly (SSSA) in the tropical western-central Pacific. In the spring of 1997 and 2015 with strong EN events, the western-central equatorial Pacific exhibited significant negative SSSA that propagated eastward to the west of the dateline. The negative SSSA induced increased barrier layer thickness (BLT) which enhanced sea surface temperature (SST) warming in the tropical central Pacific. In contrast, although a negative SSSA occurred during April of the 2014/2015 weak EN event in the western-central equatorial Pacific, this SSSA was mainly confined to between 160° E and 180° E without significant eastward movement, resulting in a weakened BLT thickening process and a weak modulation effect on SST. We also confirm that the surface forcing associated with fresh water flux (FWF: evaporation (E) minus precipitation (P)) plays a prominent role in the surface salinity tendency in the tropical Pacific during EN events. Moreover, the negative FWF anomaly leads a strong negative SSSA by two months. Compared with the two strong ENs, the early negative FWF anomaly in the weak 2014/2015 EN did not present distinct development and eastward propagation and weakened rapidly in the summer of 2015. We demonstrate that change in salinity can modulate the ENSO, and the variation of SSSA and associated physical processes in the tropical western-central Pacific and could be used as an indicator for predicting the development of ENSO. Full article

Contribution of extra-tropical synoptic cyclones to the formation of mean summer atmospheric circulation patterns in the Arctic domain (≥60° N) was investigated by clustering dominant Arctic circulation patterns based on daily mean sea-level pressure using self-organizing maps (SOMs). Three SOM patterns were identified; one pattern had prevalent low-pressure anomalies in the Arctic Circle (SOM1), while two exhibited opposite dipoles with primary high-pressure anomalies covering the Arctic Ocean (SOM2 and SOM3). The time series of their occurrence frequencies demonstrated the largest inter-annual variation in SOM1, a slight decreasing trend in SOM2, and the abrupt upswing after 2007 in SOM3. Analyses of synoptic cyclone activity using the cyclone track data confirmed the vital contribution of synoptic cyclones to the formation of large-scale patterns. Arctic cyclone activity was enhanced in the SOM1, which was consistent with the meridional temperature gradient increases over the land–Arctic ocean boundaries co-located with major cyclone pathways. The composite daily synoptic evolution of each SOM revealed that all three SOMs persisted for less than five days on average. These evolutionary short-term weather patterns have substantial variability at inter-annual and longer timescales. Therefore, the synoptic-scale activity is central to forming the seasonal-mean climate of the Arctic. Full article

The divergence problem, which manifests as an unstable response relationship between tree-ring growth and climatic factors under the background of global warming, poses a challenge to both the traditional theory of dendroclimatology and the reliability of climatic reconstructions based on tree-ring data. Although Schrenk spruce, as the dominant tree species in the Tianshan Mountains, is frequently applied in the dendrochronological studies, the understanding of the divergence problem of this tree species is still limited. This study conducted correlation analysis between climatic factors and tree-ring width chronologies from 51 living and healthy specimens of Schrenk spruce at sites of high and low elevation in the Alatau Mountains to determine the stability of the response. The results revealed that the tree-ring width of the spruce specimens was correlated positively with precipitation and correlated negatively with temperature. Although the variations of the two tree-ring chronologies were similar, the radial growth of the spruce at the low elevation was found more sensitive to climatic factors. Furthermore, the sensitivity of tree growth to climate demonstrated an obvious increase after an abrupt change of climate under the background of the recent warming and wetting trend. Increased drought stress, calculated based on climatic data, was regarded as the main reason for this phenomenon. The results supply the gap of the stability of climatic response of tree growth in Central Asia to some extent. Full article

Subway air pollution mainly refers to inhalable particulate matter (PM) pollution, organic pollution, and microbial pollution. Based on the investigation and calculation of the existing researches, this paper summarizes the sources of air pollutants, chemical compositions, and driving factors of PM variations in subway. It evaluates the toxicity and health risks of pollutants. In this paper, the problems and challenges during the deployment of air pollution governance are discussed. Results show that the global PM compliance rate of subway is about 30%. Subway air pollution is endogenous, which means that pollutants mainly come from mechanical wear and building materials erosions. Particles are mainly metal particles, black carbon, and floating dust. The health risks of some chemical elements in the subway have reached critical levels. The variations of PM concentrations show spatial-temporal characteristics, which are mainly controlled by train age, brakes types, and environmental control systems. The authors then analyze the dynamics of interactions among government, companies and public during the air pollution governance by adding the following questions: (a) who pays the bill; (b) how to evaluate the cost-effectiveness of policies; (c) how the public moves from risk perception to actions; (d) how to develop clean air technology better so as to ultimately incentivize stakeholders and to facilitate the implementation of subway clean air programme in a resilient mode. Full article

Nature has been adversely affected by increasing industrialization, especially during the latter part of the last century, as a result of accelerating technological development, unplanned urbanization, incorrect agricultural policies and deforestation, which have contributed to the elevated concentration of the greenhouse gases (GHGs) in the environment. GHG accumulation has an adverse impact on meteorological and hydro-meteorological parameters, particularly temperature. Temperature plays a prominent and well-known role in evaporation, transpiration and changes in water demand, and thus significantly affects both water availability and food security. Therefore, a systematic understanding of temperature is important for fighting food insecurity and household poverty. Variations in temperature are often assessed and characterized through trend analysis. Hence, the objective of this paper is to determine long-term trends in mean monthly maximum and minimum air temperatures for the Maloti-Drakensberg region. The Mann–Kendall test, a non-parametric test, was applied on mean air temperature for the 1960–2016 period. A significant rising trend (p < 0.001) was detected with a yearly change in the long term annual mean maximum and mean minimum temperature by 0.03 °C/annum and 0.01 °C/annum, respectively. This knowledge has important implications for both the state of the environment and livelihoods in the region, since its use can be useful in planning and policymaking in water resource management, biodiversity conservation, agriculture, tourism and other sectors of the economy within the region. Full article

The measured concentrations of inorganic pollutants, such as ozone (2015–2018), sulfur, and nitrogen oxides (2012–2018) at air monitoring sites in the south of Eastern Siberia were sampled, following the passive sampling method, and analyzed. The spatial inhomogeneity of atmospheric gas concentrations is presented. The ozone concentration is lower in urban areas than those in rural areas and the background level. However, the nitrogen and sulfur oxide concentrations are higher in the atmosphere over the city site. The seasonal dependence of the ozone concentration was determined using its maximum (March–April) and minimum (September–October) levels. The dynamics of the nitrogen and sulfur oxide concentrations indicate that they are at their highest in December–June and their lowest in July–August. To verify the validity of the pollutant concentration measurements sampled by passive sampling, we compared our results with those obtained following the automatic and filter pack methods. A linear regression analysis and a pairwise modification of Student’s t test evaluated the concentrations of the air pollutant, sampled and measured using different methods, and they correlate well (r = 0.7–0.9). Full validation of the passive sampling method is not possible for some sites; therefore it is necessary to remove the remaining systematic errors in future work. Full article

Four cross-coupled models were used to investigate the relative contributions of atmospheric and oceanic components to the asymmetry of the El Niño–Southern Oscillation (ENSO). Strong El Niño and La Niña events related to the negative heat flux feedbacks were found to be determined mainly by the atmospheric component, and the stronger sea surface temperature (SST) anomalies in the warm phase did not lead to an increased SST asymmetry. The skewness of the four models could be affected by both atmospheric and oceanic components; the atmospheric component determines the strength of positive and negative SST anomalies, and the oceanic component affects the strength of the negative SST anomalies in the cold phase under the same atmospheric component group. The Bjerknes stability index (BJ index) of warm and cold phases contributed to the El Niño–La Niña SSTA asymmetries in observation, but the BJ index did not necessarily explain the El Niño–La Niña SSTA asymmetries in climate model simulations. The SST asymmetries in these four models were closely associated with convective precipitation and wind stress asymmetries, which are also determined by both the atmospheric and oceanic components. Full article

This work focuses on the interaction of a Coronal Mass Ejection (CME) with the ambient solar corona, by studying the spatial and temporal evolution of the density fluctuations observed by the SOHO/UV Coronagraph Spectrometer (UVCS) during the CME. The investigation is performed by applying a wavelet analysis to the HI Ly $\alpha$ 1216 Å line intensity fluctuations observed with UVCS during the CME occurred on 24 December 2006. Strong and coherent fluctuations, with a significant spatial periodicity of about 84 Mm $\simeq 0.12$ R ${}_{\odot }$ , are shown to develop in about an hour along the front of the CME. The results seem to indicate the Rayleigh-Taylor (RT) instability, susceptible to the deceleration of the heavier fluid of the CME front into the lighter surrounding coronal plasma, as the likely mechanism underlying the generation of the observed plasma fluctuations. This could be the first inference of the RT instability in the outer solar corona in UV, due to the transit of a CME front in the quiet coronal plasma; this interpretation is also supported by a linear magnetohydrodynamic analysis of the RT instability. Full article

Exploring the mechanism that influences the choice of urban public travel mode is an important policy research topic that can promote urban residents’ pro-environment travel (PET) behaviour and relieve the pressure on urban traffic and environmental problems. By expanding the theory of planned behaviour by considering the effects of the quality of public transport service and individual behaviour, this paper establishes a mixed PET behaviour model. Grounded theory is used to analyse data obtained from in-depth interviews, with the aim of determining the relationships among different attributes of the quality of public transport service and PET. An empirical examination in the form of a questionnaire was conducted in Changsha, China, to obtain the intensity and mechanism of various factors influencing pro-environment behaviour decision-making. The results reveal three new pieces of information. First, the influence of many psychological variables (except subjective norms) is consistent with the prediction results of the theory of planned behaviour (TPB), and the predictions of the model are accurate. More specifically, intention (0.535) and habit (0.354) are key factors in PET behaviour, while attitude (0.527) has the most significant effect on intention towards PET behaviour. Second, the perceived service quality of public transport has a direct and significant impact on intention towards PET behaviour. Satisfaction with public transport service quality exerts a mediating effect on perceived service quality and PET behaviour. More specifically, operation and management (0.808) and vehicle environment (0.809) have the most important influence on intention towards PET behaviour. Last but not least, the extent of the influence of PET behaviour varies based on travellers’ demographic characteristics. The driving age, income and ownership of private cars show the greatest impact. The perceived service quality of public transport and travellers’ social and economic characteristics all play roles in the psychology of travel decisions, and are associated with PET behaviour on several distinct levels. From the perspectives of passenger psychology, public transport service quality and personal attributes of passengers, this paper provides a scientific basis for decision-making in transportation systems and the formulation of traffic intervention strategies to promote voluntary public reductions in carbon-intensive travel behaviour. Full article

This study aims to address hydrological processes and impacts of an atmospheric river (AR) event that occurred during 15–18 February 2004 in the Russian River basin in California. The National Water Model (NWM), a fully distributed hydrologic model, was used to evaluate the hydrological processes including soil moisture flux, overland flow, and streamflow. Observed streamflow and volumetric soil water content data were used to evaluate the performance of the NWM using various error metrics. The simulation results showed that this AR event (15–18 February 2004) with a long duration of precipitation could cause not only deep soil saturation, but also high direct runoff depth. Taken together, the analysis revealed the complex interaction between precipitation and land surface response to the AR event. The results emphasize the significance of a change of water contents in various soil layers and suggest that soil water content monitoring could aid in improving flood forecasting accuracy caused by the extreme events such as the AR. Full article

Low-level warm clouds are a major component in multilayered cloud systems and they are generally hidden from the top-down view of satellites with passive measurements. This study conducts an investigation on oceanic warm clouds embedded in multilayered structures by using spaceborne radar data with fine vertical resolution. The occurrences of warm cloud overlapping and the geometric features of several kinds of warm cloud layers are examined. It is found that there are three main types of cloud systems that involve warm cloud layers, including warm single layer clouds, cold-warm double layer clouds, and warm-warm double layer clouds. The two types of double layer clouds account for 23% and in the double layer occurrences warm-warm double layer subsets contribute about 13%. The global distribution patterns of these three types differ from each other. Single-layer warm clouds and the lower warm clouds in the cold-warm double layer system they have nearly identical geometric parameters, while the upper and lower layer warm clouds in the warm-warm double layer system are distinct from the previous two forms of warm cloud layers. In contrast to the independence of the two cloud layers in cold-warm double layer system, the two kinds of warm cloud layers in the warm-warm double layer system may be coupled. The distance between the two layers in the warm-warm double layer system is weakly dependent on cloud thickness. Given the upper and lower cloud layer with moderate thickness of around 1 km, the cloudless gap reaches its maximum when exceeding 600 m. The cloudless gap decreases in thickness as the two cloud layers become even thinner or thicker. Full article

Prescribed pasture burning plays a critical role in ecosystem maintenance in tallgrass prairie ecosystems and may contribute to agricultural productivity but can also have negative impacts on air quality. Volatile organic compound (VOC) concentrations were measured immediately downwind of prescribed tallgrass prairie fires in the Flint Hills region of Kansas, United States. The VOC mixture is dominated by alkenes and oxygenated VOCs, which are highly reactive and can drive photochemical production of ozone downwind of the fires. The computed emission factors are comparable to those previous measured from pasture maintenance fires in Brazil. In addition to the emission of large amounts of particulate matter, hazardous air pollutants such as benzene and acrolein are emitted in significant amounts and could contribute to adverse health effects in exposed populations. Full article

The recent development of high-resolution climate models offers a promising approach in improving the simulation of precipitation, clouds and temperature. However, higher grid spacing is also a promising feature to improve the simulation of snow cover. In particular, it provides a refined representation of topography and allows for an explicit simulation of convective precipitation processes. In this study we analyze the snow cover in a set of decade-long high-resolution climate simulation with horizontal grid spacing of 2.2 km over the greater Alpine region. Results are compared against observations and lower resolution models (12 and 50 km), which use parameterized convection. The simulations are integrated using the COSMO (Consortium for Small-Scale Modeling) model. The evaluation of snow water equivalent (SWE) in the simulation of present-day climate, driven by the ERA-Interim reanalysis, against an observational dataset, reveals that the high-resolution simulation clearly outperforms simulations with grid spacing of 12 and 50 km. The latter simulations underestimate the cumulative amount of SWE over Switzerland over the whole annual cycle by 33% (12 km simulation) and 56% (50 km simulation) while the high-resolution simulation shows a spatially and temporally averaged difference of less than 1%. Scenario simulations driven by GCM MPI-ESM-LR (2081–2090 RCP8.5 vs. 1991–2000) reveal a strong decrease of SWE over the Alps, consistent with previous studies. Previous studies had found that the relative decrease becomes gradually smaller with elevation, but this finding was limited to low and intermediate altitudes (as a 12 km simulation resolves the topography up to 2500 m). In the current study we find that the height gradient reverses sign, and relative reductions in snow cover increases above 3000 m asl, where important parts of the cryosphere are present. In addition, the simulations project a transition from permanent to seasonal snow cover at high altitudes, with potentially important impacts to Alpine permafrost. This transition and the more pronounced decline of SWE emphasize the value of the higher grid spacing. Overall, we show that high-resolution climate models offer a promising approach in improving the simulation of snow cover in Alpine terrain. Full article

In this study, based on daily precipitation records during 1958–2017 from 28 meteorological stations in the Beijing-Tianjin-Hebei (BTH) region, the spatio-temporal variations in precipitation extremes defined by twelve indices are analyzed by the methods of linear regression, Mann-Kendall test and continuous wavelet transform. The results showed that the spatial patterns of all the indices except for consecutive dry days (CDD) and consecutive wet days (CWD) were similar to that of annual total precipitation with the high values in the east and the low value in the west. Regionally averaged precipitation extremes were characterized by decreasing trends, of which five indices (i.e., very heavy precipitation days (R50), very wet precipitation (R95p), extreme wet precipitation (R99p), max one-day precipitation (R × 1day), and max five-day precipitation (R × 5day)) exhibited significantly decreasing trends at 5% level. From monthly and seasonal scale, almost all of the highest values in R × 1day and R × 5day occurred in summer, especially in July and August due to the impacts of East Asian monsoon climate on inter-annual uneven distribution of precipitation. The significant decreasing trends in annual R×1day and R×5day were mainly caused by the significant descend in summer. Besides, the possible associations between precipitation extremes and large-scale climate anomalies (e.g., ENSO (El Niño Southern Oscillation), NAO (North Atlantic Oscillation), IOD (Indian Ocean Dipole), and PDO (Pacific Decadal Oscillation)) were also investigated using the correlation analysis. The results showed that the precipitation extremes were significantly influenced by ENSO with one-year ahead, and the converse correlations between the precipitation extremes and climate indices with one-year ahead and 0-year ahead were observed. Moreover, all the indices show significant two- to four-year periodic oscillation during the entire period of 1958–2017, and most of indices show significant four- to eight-year periodic oscillation during certain periods. The influences of climate anomalies on precipitation extremes were composed by different periodic components, with most of higher correlations occurring in low-frequency components. Full article

China is experiencing severe PM_2.5 (fine particles with a diameter of 2.5 μg or smaller) pollution problem. Little is known, however, about how the increasing concentration trend is spatially distributed, nor whether there are some areas that experience a stable or decreasing concentration trend. Managers and policymakers require such information to make strategic decisions and monitor progress towards management objectives. Here, we present a pixel-based linear trend analysis of annual PM_2.5 concentration variation in China during the period 1999–2016, and our results provide guidance about where to prioritize management efforts and affirm the importance of controlling coal energy consumption. We show that 87.9% of the whole China area had an increasing trend. The drastic increasing trends of PM_2.5 concentration during the last 18 years in the Beijing–Tianjin–Hebei region, Shandong province, and the Three Northeastern Provinces are discussed. Furthermore, by exploring regional PM_2.5 pollution, we find that Tarim Basin endures a high PM_2.5 concentration, and this should have some relationship with oil exploration. The relationship between PM_2.5 pollution and energy consumption is also discussed. Not only energy structure reconstruction should be repeatedly emphasized, the amount of coal burned should be strictly controlled. Full article

In ultrasonic equipment (anemometers and thermometers), for the measurement of parameters of atmospheric turbulence, a standard algorithm that calculates parameters from temporary structural functions constructed on the registered data is usually used. The algorithm is based on the Kolmogorov–Obukhov law. The experience of using ultrasonic meters shows that such an approach can lead to significant errors. Therefore, an improved algorithm for calculating the parameters is developed, which allows more accurate estimation of the structural characteristics of turbulent fluctuations, with an error that is not more than 10%. The algorithm was used in the development of a new ultrasonic hardware-software complex, autonomous meteorological complex AMK-03-4, which differs from similar measuring instruments of turbulent atmosphere parameters by the presence of four identical ultrasonic anemometers. The design of the complex allows not only registration of the characteristics of turbulence, but also measurement of the statistical characteristics of the spatial derivatives of turbulent temperature fluctuations and orthogonal components of wind speed along each of the axes of the Cartesian coordinate system. This makes it possible to investigate the space–time structure of turbulent meteorological fields of the surface layer of the atmosphere for subsequent applications in the Monin–Obukhov similarity theory and to study turbulent coherent structures. The new measurement data of the spatial derivatives of temperature at stable stratification (at positive Monin–Obukhov parameters) were obtained, at which the behavior of the derivatives was been investigated earlier. In the most part of the interval of positive Monin–Obukhov parameters, the vertical derivative of the temperature is close to a constant value. This fact can be considered as a new significant result in similarity theory. Full article

In this study, a hybrid large-eddy simulation (LES) model is developed and applied to simulate the transport of oil droplet aerosols in wind over progressive water waves. The LES model employs a hybrid spectral and finite difference method for simulating the wind turbulence and a bounded finite-volume method for modeling the oil aerosol transport. Using a wave-following coordinate system and computational grid, the LES model captures the turbulent flow and oil aerosol fields in the region adjacent to the unsteady wave surface. A flat-surface case with prescribed roughness (representing a pure wind-sea) and a wavy-surface case with regular plane progressive 100 m long waves (representing long-crest long-wavelength ocean swells) are considered to illustrate the capability of the LES model and study the effects of long progressive waves on the transport of oil droplet aerosols with four different droplet diameters. The simulation results and statistical analysis reveal enhanced suspension of oil droplets in wind turbulence due to strong disturbance from the long progressive waves. The spatial distribution of the aerosol concentration also exhibits considerable streamwise variations that correlate with the phase of the long progressive waves. Full article

Radar rainfall nowcasts are subject to many sources of uncertainty and these uncertainties change with the characteristics of a storm. The predictive skill of a radar rainfall nowcasting model can be difficult to understand as sometimes it appears to be perfect but at other times it is highly inaccurate. This hinders the decision making required for the early warning of natural hazards caused by rainfall. In this study we define radar spatial and temporal rainfall variability and relate them to the predictive skill of a nowcasting model. The short-term ensemble prediction system model is configured to predict 731 events with lead times of one, two, and three hours. The nowcasting skill is expressed in terms of six well-known indicators. The results show that the quality of radar rainfall nowcasts increases with the rainfall autocorrelation and decreases with the rainfall variability coefficient. The uncertainty of radar rainfall nowcasts also shows a positive connection with rainfall variability. In addition, the spatial variability is more important than the temporal variability. Based on these results, we recommend that the lead time for radar rainfall nowcasting models should change depending on the storm and that it should be determined according to the rainfall variability. Such measures could improve trust in the rainfall nowcast products that are used for hydrological and meteorological applications. Full article

In this study, the atmospheric moisture transport involved in the East Asian summer monsoon (EASM) water cycle is examined. Observational estimates are contrasted with the Met Office Unified Model (MetUM) climate simulations to evaluate the model’s ability to capture this transport. We explore the role of large circulation in determining the regional water cycle by analyzing key systematic errors in the model. MetUM exhibits robust errors in its representation of the summer Asian-Pacific monsoon system, including dry biases in the Indian peninsula and wet biases in the tropical Indian Ocean and tropical West Pacific. Such errors are consistent with errors in the atmospheric moisture convergence in the area. Diabatic heating biases in the Maritime Continent domain are shown, via nudging sensitivity experiments, to play a crucial role in remotely forcing the model circulation and moisture transport errors in the East Asian area. We also examine changes in the regional water cycle in response to interannual variability of the West Pacific subtropical high (WPSH). It is shown by water budget analysis that, although the model in general is not able to faithfully reproduce the response on a month to month basis, it gives comparable seasonal trends in regional moisture convergence and precipitation associated with shifts of the WPSH. Full article

The same prescribed anthropogenic aerosol forcing was implemented into three climate models. The atmosphere components of these participating climate models were the GAMIL, ECHAM, and CAM models. Ensemble simulations were carried out to obtain a reliable estimate of anthropogenic aerosol effective radiative forcing (ERF). The ensemble mean ERFs from these three participating models with this aerosol forcing were −0.27, −0.63, and −0.54 W∙m⁻². The model diversity in ERF is clearly reduced as compared with those based on the models’ own default approaches (−1.98, −0.21, and −2.22 W∙m⁻²). This is consistent with the design of this aerosol forcing. The modeled ERF can be decomposed into two basic components, i.e., the instantaneous radiative forcing (RF) from aerosol–radiation interactions (RFari) and the aerosol-induced changes in cloud forcing (△Fcloud^*). For the three participating models, the model diversity in RFari (−0.21, −0.33, and −0.29 W∙m⁻²) could be constrained by reducing the differences in natural aerosol radiative forcings. However, it was difficult to figure out the reason for the model diversity in △Fcloud^* (−0.05, −0.28, and −0.24 W∙m⁻²), which was the dominant source of the model diversity in ERF. The variability of modeled ERF was also studied. Ensemble simulations showed that the modeled RFs were very stable. The rapid adjustments (ERF − RF) had an important role to play in the quantification of the perturbation of ERF. Fortunately, the contribution from the rapid adjustments to the mean ERF was very small. This study also showed that we should pay attention to the difference between the aerosol climate effects we want and the aerosol climate effects we calculate. Full article

The present paper aims to elucidate impacts of climate change on the availability and security of water and energy in the Middle East and North Africa region (MENA region; including the Eastern Mediterranean) in the context of the water–energy nexus. It largely builds on existing knowledge and understanding and aims to present a review of existing information on this topic. The region is particularly challenged by a number of factors, including the large variability of bio-geographical characteristics, extreme population growth over the last few decades, and substantial societal and economical transitions, as well as armed conflicts in some of the countries in the region. Anticipated changes in climate conditions will exacerbate the challenges regarding water and energy security in the region. Major impacts of climate change include a significant increase in summer temperatures, which will lead to a growing number of heat waves, primarily in urban structures. A general decrease in precipitation in many of the MENA countries is foreseen, resulting in enhanced droughts and a growing number of dry spells. In addressing energy and water scarcities and their mutual interrelationships, an integrated water–energy nexus concept offers promising prospects to improve environmental, climate, human, and political security. However, only very few countries in the MENA region have presently implemented such a concept. Mitigation and adaptation strategies addressing water and energy scarcity include enhanced efficiency of resource use, integrated technology assessments regarding electricity generation, and a stronger reliance on renewable/solar technologies. While looking at the MENA region as a whole, some emphasis will be given to Cyprus and the Eastern Mediterranean. Full article

Transparent exopolymer particles (TEP) act as a major transport mechanism for organic matter (OM) to the sea surface microlayer (SML) via bubble scavenging, and into the atmosphere via bubble bursting. However; little is known about the effects of bubble scavenging on TEP enrichment in the SML. This study examined the effects of several bubbling conditions and algae species on the enrichment of TEP in the SML. TEP enrichment in the SML was enhanced by bubbling, with a larger impact from bubbling rate than bubble size and increasing enrichment over time. Depth profiles showed that any TEP aggregates formed in the underlying water (ULW) were rapidly (<2 min) transported to the SML, and that TEP was entrained in the SML by bubbling. Species experiments determined that the presence of different phytoplankton species and their subsequent release of precursor material further enhance the effectiveness of TEP enrichment via bubble scavenging. Full article

Evapotranspiration (ET) is an important element in the water and energy cycle. Potential evapotranspiration (PET) is an important measurement of ET. Its accuracy has significant influence on agricultural water management, irrigation planning, and hydrological modelling. However, whether current PET models are applicable under climate change or not, is still a question. In this study, five frequently used PET models were chosen, including one combination model (the FAO Penman-Monteith model, FAO-PM), two temperature-based models (the Blaney-Criddle and the Hargreaves models) and two radiation-based models (the Makkink and the Priestley-Taylor models), to estimate their appropriateness in the historical and future periods under climate change impact on the Yarlung Zangbo river basin, China. Bias correction methods were not only applied to the temperature output of Global Climate Models (GCMs), but also for radiation, humidity, and wind speed. It was demonstrated that the results from the Blaney-Criddle and Makkink models provided better agreement with the PET obtained by the FAO-PM model in the historical period. In the future period, monthly PET estimated by all five models show positive trends. The changes of PET under RCP8.5 are much higher than under RCP2.6. The radiation-based models show better appropriateness than the temperature-based models in the future, as the root mean square error (RMSE) value of the former models is almost half of the latter models. The radiation-based models are recommended for use to estimate PET under climate change in the Yarlung Zangbo river basin. Full article

Desert dust is now recognized as a major health hazard. However, there still exists a lack of measurements of desert dust atmospheric loads in regions located in the vicinity of the major desert areas, where a growing part of the world population is living. Dust emission is a sporadic and intense phenomenon so that the classical air quality standards should not be appropriate to reflect the real population exposure to desert dust. In order to give some insight to answer this question, PM₁₀ concentrations were continuously measured at a five-minute time step in southern Tunisia from February 2014 to February 2019. The daily and annual PM₁₀ concentrations were first discussed according to the Tunisian air quality standards: In this relatively remote area, close to dust source, these standards were respected at the annual, but no longer at the daily scale. Measurements performed at a high temporal resolution (five minutes) allowed to discriminate the different situations that led to exceed Tunisian daily standards in southern Tunisia. In particular, intense (five-minute PM₁₀ concentrations up to more than 1500 µg m⁻³) and short-lived (a few hours) dust outbreaks were regularly observed. This result raises the question of the necessity of defining specific air quality standards at the sub-daily scale in countries affected by intense desert dust outbreaks. Full article

A better knowledge of the local and regional sources of the atmospheric particulate matter provides policy makers with the proper awareness when acting to improve air quality, in order to protect public health. A source apportionment study of the carbonaceous aerosol in Naples (Italy) is presented here, in order to improve this understanding in a vulnerable urban area. The aim of this study is quantifying directly fossil and non-fossil contributions to carbonaceous aerosol, by means of radiocarbon measurements. This is the first time that such an approach is implemented in this area. Fine particles with diameter ≤ 2.5 µm (PM_2.5) were collected daily on top of a building in the city center, from November 2016 until January 2017. The carbonaceous aerosol was separated into organic carbon (OC) and elemental carbon (EC), by a two-step thermal desorption method. Subsequent radiocarbon analysis enabled the partitioning of the major sources of carbonaceous aerosol into fossil and non-fossil ones by applying radiocarbon isotopic mass balance. The PM_2.5 concentration was on average 29 ± 3 µg⁄m³ (mean ± standard error; n = 18), with a maximum of 68.6 ± 0.7 µg⁄m³ on a day when air masses back-trajectories suggest a local origin and stagnant airflow conditions in the region. The carbonaceous component accounts for roughly half of the PM_2.5 mass. Fossil fuel emissions are a minor source of OC (23%), but the dominant source of EC (66%), which is directly emitted during combustion processes. However, overall only 30% of the total carbon is of fossil origin, accounting for 14% of PM_2.5 mass. Surprisingly, a comparable contribution is due to primary biomass burning carbon, which accounts in total for 15% of PM_2.5 mass. Traffic pollution, the main cause of fossil fuel emissions in urban areas, is a significant, but not the predominant source of carbonaceous particle concentration. These findings support the conclusion of a predominant contribution from non-fossil sources to the carbon in airborne particulate matter, which policy makers should take into account when planning mitigation strategies to improve urban air quality. Full article

We present results of the studies of internal gravity waves based on altitude-time dependences of the temperature and the density of the neutral component and the velocity of the vertical plasma motion at altitudes of the lower ionosphere (60–130 km). The vertical plasma velocity, which in the specified altitude range is equal to the velocity of the neutral component, the temperature, and the density of the neutral atmosphere are determined by the method of the resonant scattering of radio waves by artificial periodic irregularities (APIs) of the ionosphere plasma. We have developed an API technique and now we are evolving it for studying the ionosphere and the neutral atmosphere using the Sura heating facility (56.1 N; 46.1 E), Nizhny Novgorod, Russia. An advantage of the API technique is the opportunity to determine the parameters of the undisturbed natural environment under a disturbance of the ionosphere by a field of powerful high frequency radio waves. Analysis of altitude-time variations of the neutral temperature, the density, and the vertical plasma velocity allows one to estimate periods of atmospheric waves propagation. Wavelike variations with a period from 5 min to 3 h and more are clearly determined. Full article

A 10-year study of elevated severe thunderstorms was performed using The National Centers for Environmental Information Storm Events Database. A total of 80 elevated thunderstorm cases were identified, verified, and divided into “Prolific” and “Marginal” classes. These severe cases occurred at least 80 km away from, and on the cold side of, a surface boundary. The downdraft convective available potential energy (DCAPE), downdraft convective inhibition (DCIN), and their ratio are tools to help estimate the potential for a downdraft to penetrate through the depth of a stable surface layer. The hypothesis is that as the DCIN/DCAPE ratio decreases, there exists enhanced possibility of severe surface winds. Using the initial fields from the Rapid Refresh numerical weather prediction model, datasets of DCIN, DCAPE, and their ratio were created. Mann-Whitney U tests on the Prolific versus Marginal case sets were undertaken to determine if the DCAPE and DCIN values come from different populations for the two different case sets. Results show that the Prolific cases have values of DCIN closer to zero, suggesting the downdraft is able to penetrate to the surface causing severe winds. Thus, comparing DCIN and DCAPE is a viable tool in determining if downdrafts will reach the surface from elevated thunderstorms. Full article