Average Summer Research Articles

Estimation of Oceanic Heat Flux Under Sea Ice in the Arctic Ocean

Oceanic heat flux (Fw) is the vertical heat flux that is transmitted to the base of sea ice. It is the main source of sea ice bottom melting. The residual method was adopted to study oceanic heat flux under sea ice. The data acquired by 28 ice mass balance buoys (IMBs) deployed over the period of 2004 to 2013 in the Arctic Ocean were used. Fw values presented striking seasonal and spatial variations. The average summer Fw values for the Canada Basin, Transpolar Drift, and Multiyear Ice area were 16.8, 7.7, and 5.9 Wm−2, respectively. The mean summer Fw for the whole Arctic was 10.1 Wm−2, which was equivalent to a bottom melt of 0.4m. Fw showed an autumn peak in November in the presence of the near-surface temperature maximum (NSTM). The average Fw for October to December was 3.7Wm−2. And the average Fw for January to March was 1.0Wm−2, which was approximately one third of the average Fw in the presence of NSTM. The summer Fw was almost wholly attributed to the incident solar radiation that enters the upper ocean through leads and the open water. Fw calculated through the residual method using IMB data was compared with that calculated through the parameterization method using Autonomous Ocean Flux Buoy data. The results revealed that the Fw provided by the two methods were consistent when the sea ice concentration exceeded 70% and mixing layer temperature departure from freezing point was less than 0.15℃. Otherwise, the Fw yielded by the residual method was approximately one third smaller than that provided by the parameterization method.

Could wearing motorcycle protective clothing compromise rider safety in hot weather?

Motorcycle protective clothing (PPE) effectively reduces the risk of injury in crashes, however in hot conditions many motorcyclists ride unprotected. Recent work found available motorcycle PPE to be thermally inefficient in hot weather with potential to cause significant thermal strain under average Australian summer conditions. The current study investigated the potential for the cognitive and psychophysical concomitants of thermal strain to compromise reaction times, mood and fatigue with potential consequences for motorcyclists’ safety. MethodVolunteers wearing motorcycle PPE participated in a 90 min trial (cycling 30 W) in 35 °C, 40%RH with overhead radiant heaters and a fan to simulate wind speed. Heart rate, core and skin temperature were recorded continuously. Reaction time and subjective ratings of thermal sensation and comfort, workload and mood were recorded at baseline, during rest breaks at 25 min intervals and on completion of the trail. Repeated measures analysis assessed each participant’s performance against their own baseline. ResultsCore temperatures increased by 2 °C (p < .0001), skin temperatures (3 °C, (p < .0001) and heart rates (66bpm, p < .0001). Reaction times fluctuated 36 ms 8% (p < .0001) over the trial. Subjective workload increased 68% (p = 0.001) and mood deteriorated 33 points (p < .0001) including feeling less alert (p = <.0001), contented (p = 0.001) and calm (p = 0.0004). Multivariate repeated measures analysis found significant associations between core temperature and workload (p = 0.01), mood (p = 0.001) and reaction time (<.0001). Skin temperature and workload (p = 0.02), mood (p = 0.01) and reaction time (<.0001). Subjective ratings of temperature sensation and wetness discomfort were associated respectively with increased workload (p = 0.0001, p = 0.004), mood change (p < .0001, p = 0.04) and reaction time (p < .0001, p < .0001). ConclusionsThe physiological impact of wearing thermally inefficient motorcycle PPE in hot conditions could impair motorcyclists cognitive and psychophysical functioning and, potentially, their riding performance and safety.These outcomes indicate an urgent need for manufacturers to develop motorcycle PPE that is effective and suitable for use, in hot conditions.

Climate Change Projections of Extreme Temperatures for the Iberian Peninsula

The comprehensive characterization of heat waves and extreme hot days is fundamental for policymakers due to its vast implications for human health. This study evaluates extreme temperature changes over the Iberian Peninsula for the present climate and future projections, considering extreme temperature indices, cold/heat waves, and a recovery factor, using the Weather Research and Forecasting model. The projected temperatures show an increase of over 6 °C. An increase in the number of summer days and tropical nights and a decrease in frost days is expected. The number of heat waves and their duration and intensity are expected to increase. The number of heat wave days are expected to increase, with much of the average summer season being under heat wave conditions. The recovery factor is expected to decrease. Cold spells are projected to decrease in terms of number, intensity, duration, and number of spell days, whereas the recovery factor is expected to increase. Heat wave analysis was combined with maximum temperature thresholds to isolate extreme heat waves. The results show an increase in extreme heat wave days, with regions experiencing over 10 heat wave days with maximum temperature surpassing 45 °C for the long-term future.

Study of the glacial flow of rivers in the Grønfjord bay basin (Western Svalbard)

The melting of glaciers in the Arctic archipelagoes provides glacier runoff, which must be considered when assessing river flow. Glacial runoff, as a component of the total river flow, directly affects the thermal and ice conditions of the bays, the productivity and species composition of the marine biota. Also, this process is broadly related to the livelihoods of the Arctic villages. Furthermore, it acts as the important factor for the development of transport and tourism. Melted water of Svalbard glaciers is a significant contribution in total runoff of the local rivers. The issue of this study is to assess this contribution. Grønfjord Bay was selected for assessment because of the fact of regular measurements of water discharge in the river estuaries from June to October. Among 7 rivers flowing into the bay, 6 have glacial runoff. Despite the fact that only small mountain glaciers are common in this area, its melting largely determines the water regime of the rivers. The value of the glacier runoff in Grønfjord Bay was calculated based on an estimation of the glaciers melting by average summer air temperature in 2017 and 2018. Comparison of the amount of glacial and total flow was carried out on the rivers flowing into the Grønfjord Bay.The comparative analysis of the glacial and total river flows size along the 6 rivers of the Grønfjord Bay: Grøndalselva, Grønfjorddalselva, Bretjørna, Aldegonda, Brydebekken, Vasstakelva showed significant differences in the glacier runoff content depending on the area of glaciation in the catchment of rivers. The content of glacial runoff in the total freshwater discharge by rivers into the bay in 2017 and 2018 vary from 20 to 90 %. The largest glacier runoff is observed on the Bretjørna river — 90 %, the Grøndalselva, Brydebekken and Vasstakelva have the smallest glacier runoff — 20 %. The average total glacial runoff of the rivers varied from 41 to 53 % of the total discharge of the rivers of the gulf.

The unprecedented coupled ocean-atmosphere summer heatwave in the New Zealand region 2017/18: drivers, mechanisms and impacts

During austral summer (DJF) 2017/18, the New Zealand region experienced an unprecedented coupled ocean-atmosphere heatwave, covering an area of 4 million km2. Regional average air temperature anomalies over land were +2.2 °C, and sea surface temperature anomalies reached +3.7 °C in the eastern Tasman Sea. This paper discusses the event, including atmospheric and oceanic drivers, the role of anthropogenic warming, and terrestrial and marine impacts. The heatwave was associated with very low wind speeds, reducing upper ocean mixing and allowing heat fluxes from the atmosphere to the ocean to cause substantial warming of the stratified surface layers of the Tasman Sea. The event persisted for the entire austral summer resulting in a 3.8 ± 0.6 km3 loss of glacier ice in the Southern Alps (the largest annual loss in records back to 1962), very early Sauvignon Blanc wine-grape maturation in Marlborough, and major species disruption in marine ecosystems. The dominant driver was positive Southern Annular Mode (SAM) conditions, with a smaller contribution from La Niña. The long-term trend towards positive SAM conditions, a result of stratospheric ozone depletion and greenhouse gas increase, is thought to have contributed through association with more frequent anticyclonic ‘blocking’ conditions in the New Zealand region and a more poleward average latitude for the Southern Ocean storm track. The unprecedented heatwave provides a good analogue for possible mean conditions in the late 21st century. The best match suggests this extreme summer may be typical of average New Zealand summer climate for 2081–2100, under the RCP4.5 or RCP6.0 scenario.

Activation of Cryogenic Processes in Central Yamal as a Result of Regional and Local Change in Climate and Thermal State of Permafrost

Various climatic parameters (average annual, winter, and summer air temperature, winter and summer total precipitation) and their temporal variability are analyzed to explain the activation of cryogenic processes in Central Yamal. The effect of fluctuations of these parameters on the thaw depth and ground temperature is analyzed. The regression analysis is carried out to reconstruct ground temperature during earlier periods of time in the years preceding the activation of thermal denudation and the formation of gas emission craters.

Mapped Hydroclimatology of Evapotranspiration and Drainage Runoff Using SMAP Brightness Temperature Observations and Precipitation Information

AbstractThe partitioning of incident precipitation into evapotranspiration, runoff, drainage, storage change, and hydrologic fluxes depends on the soil moisture state. With the availability of global remotely sensed soil moisture fields, the functional dependence of each flux on soil moisture may be identifiable. In this study we develop an observation‐driven approach to map key hydroclimatology fields using remotely sensed soil moisture and gauge‐based precipitation data only. National Aeronautics and Space Administration's Soil Moisture Active Passive (SMAP) low‐frequency microwave brightness temperature observations and precipitation fields, from the National Centers for Environmental Prediction, are the sole inputs into an adjoint‐state variational estimation framework. Furthermore, the proposed methodology does not rely on micrometeorological information, or land surface models. The approach is flexible by design so that almost any partitioning pattern can result from estimation and corresponding evapotranspiration and drainage fields can be quantified. Three‐year averaged summer season evapotranspiration estimates are compared with available vapor flux at in situ AmeriFlux eddy‐covariance sites. Basin‐averaged drainage over major U.S. hydrologic units is also compared with U.S. Geological Survey streamgages measurements. The remote sensing‐based estimated hydroclimate fields explain about 70% of the variance in the in situ measurements. This exploratory study adds to the body of evidence emerging in literature that a significant amount of hydrologic information is encoded in the dynamic fields of remotely sensed soil moisture. Observation‐driven hydroclimate data fields that are independent of land surface models can provide valuable insights into the state of the water cycle and guide future development of land surface models.

Temporal Characterization of Dust Activity in the Central Patagonia Desert (Years 1964–2017)

AbstractDust emitted from the southern end of South America (SSA) is transported long distances over the Southern Ocean and deposited over this marine ecosystem. Whether the nutrients released through dissolution have a biogeochemical impact is a question with biological as well as climate implications, yet there is no clear answer. Additionally, the provenance of dust recently found in accumulated snow in East Antarctica is still a matter of debate. The Patagonia desert in SSA is the likely source, but there are no detailed records documenting dust activity in this area, thereby preventing any definite assessments. Here we provide a survey of modern dust activity of the largest dust source in SSA, the lake Colhué Huapi in central Patagonia. We analyzed five decades (1964–2017) of surface synoptic observations (World Meteorological Weather Present weather codes) and concurrent satellite aerosol detection (UV Aerosol Index from the Total Ozone Monitoring Sensor and Ozone Monitoring Instrument detectors, 1978–2017). We assessed the seasonal, year‐to‐year variability and periods of major dust activity. Several periods of enhanced activity were found with roughly 2‐ to 10‐year duration each (1970–1976, 1989–1994, 1996–1997, and 1999–2017). While dust activity peaks during summer months, wintertime activity during the most active years can well exceed the summer average of nonactive years. For a period of coincident satellite observations, the occurrence of at least three periods of high activity is confirmed. Since satellite detection is more sensitive to mesoscale dust events, the large events that occurred during these periods brought abundant dust into the SW South Atlantic. Satellites with polar orbits tend to under detect dust events in this region. Significant cloudiness obstructs the direct view of dust, and dust activity tends to occur late in the afternoon after the overpass of polar satellites. These observations have a time span adequate for comparison with transport models and modern records of dust samples collected in East Antarctica. The results contribute to a better understanding of the dynamic of modern dust transport in the Southern Hemisphere, the provenance of dust found in Antarctica, and the provenance of eolian nutrients into the Southern Ocean.

Seed and seedling traits have strong impacts on establishment of a perennial bunchgrass in invaded semi‐arid systems

Abstract Many restoration projects use seeds to found new populations, and understanding phenotypic traits associated with seedling establishment in disturbed and invaded communities is important for restoration efforts world‐wide. Focusing on the perennial grass Elymus elymoides, a native species common to sagebrush steppe communities in the Western United States, we asked if seed and seedling traits could predict field establishment. We collected seeds from 34 populations from the western Great Basin. In greenhouse studies, we measured variation in seed and seedling characteristics of wild populations and one cultivar. We also quantified abiotic conditions at the collection location and asked if these characteristics predicted survival and other fitness metrics at five planting sites. Planting sites were all near‐monocultures of the invasive annual grass Bromus tectorum, and all sites experienced similar, below‐average precipitation during the experiment. Phenotypic traits were strongly correlated with performance across all sites, with remarkably high predictive power. Seeds from populations with longer roots, larger seeds and earlier emergence were significantly more likely to survive the first growing season (R2 = 0.66, p &lt; 0.0001). In contrast, while some abiotic variables at the collection location (e.g. 30‐year average summer precipitation and fall minimum temperatures) were associated with field performance at some sites, abiotic variables explained less variation in performance than traits (average R2 = 0.22). Despite the low predictive power of abiotic variables, populations that performed best at each field site were from locations with climate variables similar to planting sites. Synthesis and applications. The best seed sources for restoration of Elymus elymoides in invaded sites were populations with longer roots, larger seeds and earlier emergence. These easily measured traits were strong predictors of survival in disturbed field sites. While the most successful populations were found in areas with similar abiotic conditions as planting sites, there was phenotypic variation even among populations originating from locations with similar conditions. Thus, our results indicate that abiotic conditions are important considerations when selecting seeds, but these conditions may not sufficiently predict which populations will establish. Understanding population differences in seedling functional traits can improve predictions of restoration success.

Estimation of the surface ablation and mass balance of Eustre Grønfjordbreen (Spitsbergen)

Due to climatic changes in Spitsbergen the glaciation of the Nordenskjold Land (West Spitsbergen) has significantly degraded over the past 100 years. Changes in glaciers are undoubtedly associated with intensive melting caused by a rise of summer air temperatures. Based on the results of field measurements of ablation on the East Grenford glacier, data on the ice reduction were obtained since 2004. Analysis of the results showed that magnitude of the surface ablation is in a good agreement with the values calculated by the Krenke–Hodakov formula, in which the argument is the average summer air temperature. The parabolic dependence of the Krenke-Hodakov formula with the exponent of 3.25 presented the best approximation to the field measurements for all high-altitude zones of the glacier with a correlation coefficient of 0.96. The calculated values of ablation of ice and snow were used to estimate the mass balance of the East Grenford glacier since 2004. The calculations were based on the following: measured values of jump in temperature at the boundary of the glacier, averaged values of the air temperature gradient, and averaged data on snow storage on the glacier. Data on the mass balance of the glacier is indicative of its shortening during the last decade, despite the interannual variations. In 2016, the glacier mass balance reached the lowest value equal to −1990 mm, the calculated value was equal to −1960 mm. Analysis of the data demonstrated that the average summer air temperature is the major factor affecting the glacier mass balance. These results may be useful for estimating melting and mass balance of a number of mountain glaciers of the Nordenskjold Land.

Температурный режим торфяных олиготрофных почв лесостепи Западной Сибири (на примере Николаевского ряма)

Температурный режим торфяных олиготрофных почв лесостепи Западной Сибири (на примере Николаевского ряма)

Analysis of the temporal–spatial changes in surface radiation budget over the Antarctic sea ice region

The surface radiation budget (SRB) of the Antarctic sea ice region (ASIR) is important for the climate change in Antarctica, which partly explains the global warming. Long-term (1982–2015) satellite-derived (EUMETSAT Satellite Application Facility on Climate Monitoring, CLARA-A2) and reanalysis (European Centre for Medium-Range Weather Forecasts, ERA-Interim) datasets provided high quality and global coverage surface radiation products, which enabled us to quantify the SRB of the ASIR and widen our understanding of the polar climate. The downwelling longwave (LW) and shortwave (SW) radiation from the two datasets were validated at two Baseline Surface Radiation Network Stations (i.e., Neumayer and Syowa). Cloud LW emission dominated over cloud SW reflection and absorption due to high-albedo over the sea ice surface, thereby leading to a positive all-wave cloud radiative forcing (CRF) within 0–100 W m−2. This result indicated a warming effect on the surface of the ASIR, except during the austral summer. Compared with the all sky, substantial solar radiation was absorbed by the surface which under the clear sky will result in the increasing of temperature and sea ice melting during the austral summer; hence, the SW CRF had a major influence on all-wave CRF and caused more than −150 W m−2 of cooling near the edge of the sea ice. The summer averages of all-wave CRF over the ASIR surface were − 43.02 and − 35.74 W m−2 for the ERA-Interim and CLARA-A2 datasets, respectively. Contrary to the effect of CRF, the surface net LW radiation (LWnet) exhibited a cooling effect over the ASIR surface throughout the year and peaks at −47.21 W m−2 for CLARA-A2 dataset in December. Meanwhile, a warming effect was caused by the surface net SW radiation (SWnet) peaks at 101.52 and 104.09 W m−2 for the ERA-Interim and CLARA-A2 datasets, respectively. In summer, the warming effect caused by the surface net all-wave radiation in East Antarctica was deeper than that in West Antarctica. The time series and trend analysis showed that the surface net radiation and CRF over the entire ASIR basically exhibited a decreasing trend. The descending speed of SWnet (−3.652 W m−2 decade−1) about five times faster than that of LWnet (−0.722 W m−2 decade−1). Although a significant trough appeared in 1993/1994 of the time series curves of All-wave CRF, it had a deeply negative trend with about −3.443 W m−2 decade−1. Detailed analysis on the five longitudinal sectors around Antarctica (the Weddell Sea, the Indian Ocean, the Pacific Ocean, the Ross Sea, and the Bellingshausen-Amundsen Sea) can further help us understand the SRB of the ASIR.

Temperature and masting control Norway spruce growth, but with high individual tree variability

Tree growth and reproduction are subject to trade-offs in resource allocation. At the same time, they are both influenced by climate. In this study, we combined long records of reproductive effort at the individual- (29 years), population- (41 years) and regional (up to 53 years) scale, and tree ring chronologies, to investigate the effects of climate and reproductive allocation on radial growth in an Alpine Norway spruce forest.Seed and cone production was highly variable between years (mean individual CV = 1.39, population CV = 1.19), but showed high reproductive synchrony between individuals (mean inter-tree correlation = 0.72). No long-term trend in reproductive effort was detected over four decades of observations. At the stand scale, cone production was dominated by a small number of individuals (“super-producers”), who remained dominant over three decades.Individual tree growth responded positively to summer temperature, but the response to cone production varied between individual trees. Consequently, we found some evidence that mast years were associated with a divergence in growth between high and low cone producing individuals, and a decline in within-population growth synchrony.At the population level we found limited evidence of a relationship between growth and reproduction. Radial growth was lower than average in some mast years, but not in others. This was partly explained by summer temperature during the year of growth, with growth reductions restricted to mast years that coincided with colder than average summers. Regional mast records and tree ring chronologies provided some support to indicate that our results were consistent in other spruce stands, although the effect of mast years on growth appeared to vary between sites.Tree ring variation at the individual and population level, and between-tree growth synchrony are influenced by masting, and consequently dendrochronologists should consider both the occurrence of masting and the individual differences in reproductive effort when interpreting tree ring datasets. Our results also indicate that tree ring chronologies contain information to facilitate reconstruction of mast events, which will help address outstanding questions regarding the future response of masting to climate change.

Reconstructing salinity changes and environmental influence on dinoflagellate cysts in the central Baltic Sea since the late 19th century

We present a record of dinoflagellate cyst assemblage composition, abundance, and morphology from the central Baltic Sea, spanning the late 19th to the early 21st centuries. Environmental time-series were analyzed in relation to changes in community structure and diversity as inferred from the sediment record, and average summer sea surface salinity (SSS) was reconstructed based on the average process length of Protoceratium reticulatum resting cysts. The reconstructed summer SSS was compared to instrumental data for a critical evaluation of this approach. The most abundant species in this record were P. reticulatum and Biecheleria baltica, and on average ten taxa were identified per sample. The cyst record of B. baltica indicated that although this species has been present in the Gotland Basin at least since the 1880s, its concentrations have increased significantly since the 1980s, possibly linked to eutrophication. Variations in assemblage composition and P. reticulatum cyst morphology reflected patterns of major, instrumentally recorded hydrographic and environmental changes in the Baltic Sea during the past century. The variability in microfossil relative abundances was best explained by the average spring SSS as well as by the average NO3 concentrations during spring and by the combined effects of average summer SSS and NAO variability. Reconstructed summer SSS and instrumental SSS showed notable differences, depending on the year and function applied for reconstruction. Although roughly reflecting the same patterns, the reconstructed values are offset when compared to instrumental measurements. We put forward suggestions for improvement of the process-length method and recommend using the reconstructed values as an indication of relative changes in past summer sea surface salinity, preferably as part of a multiproxy approach.

Can antecedent moisture conditions modulate the increase in flood risk due to climate change in urban catchments?

Climate change coupled with the current trend in rapid urbanization is increasing the risk of flooding that can cause loss of life and damage to property. Adapting to climate change impacts and flood mitigation has become a life critical factor as well as a severe challenge. Green infrastructure and low impact development methods are common approaches that are increasingly used to address stormwater management in developed environments. The analysis and results of this study show that AMC/IC does impact flood response even in urban developed catchments and that it can significantly impact flood responses during storm events. We show that considering AMC/ICs coupled with changes in seasonal rainfall patterns that are projected for warmer climates in the future can modulate some of the increases in flood risk due to climate change.The prevailing thought is that Antecedent Moisture Conditions (AMCs) have little to no relevance in urban hydrology, particularly in relation to climate change. However, current trends in use of stormwater management methods that depend on local storage and infiltration is increasingly making AMC or Initial Conditions (IC) a factor in urban flooding. Despite this trend there is little available literature that discuss the aspect of AMC/IC that can have an implication on urban flood management. Here, we move towards filling this gap in current literature related to impacts of AMCs in flooding of developed areas by focusing on how possible changes in seasonal rainfall patterns in a warming climate might impact AMC and starting conditions in stormwater Best Management Practices (SWBMPs), and how those changed initial conditions impact flood risk in developed areas. Using a comprehensive hydrologic/hydraulic model of an urban/developed catchment and continuous simulation, we demonstrate the importance of accurately accounting for initial conditions in flood assessments. We consider average summer temperatures based on approximately 70 years of historic data to select warm and cold years. We compare the model results between the warm and cold years as a proxy to look at trends related to a future warming climate.

Variation in Summer and Winter Microclimate in Multi-Chambered Bat Boxes in Eastern Australia: Potential Eco-Physiological Implications for Bats

Bat boxes are commonly used as a conservation tool. Detailed knowledge on the influence of box elements on microclimate is lacking, despite eco-physiological implications for bats. Summer and winter box temperature and relative humidity patterns were studied in narrow multi-chambered plywood and wood-cement boxes in eastern Australia. Box exteriors were black or white and plywood boxes comprised vents. Relative humidity was higher in white boxes than black boxes and box colour, construction material, chamber sequence and vents influenced temperatures. Maximum box temperature differences between designs varied by up to 9.0 °C in summer and 8.5 °C in winter. The black plywood box consistently recorded the warmest temperatures. This design comprised a temperature gradient between chambers and within the front chamber (influenced by vent). During the 32-day summer sampling period, the front chamber rarely recorded temperatures over 40.0 °C (postulated upper thermal tolerance limit of bats), while the third and fourth chamber never reached this threshold. At the study site, the tested black boxes are considered most thermally suitable for bats during average summer conditions. However, during temperature extremes black boxes likely become too hot. Wood-cement, a durable material not previously tested in Australia should be considered as an alternative construction material.

Seasonal pattern of ammonium 15N natural abundance in precipitation at a rural forested site and implications for NH3 source partitioning

Excess ammonia (NH3) emissions and deposition can have negative effects on air quality and terrestrial ecosystems. Identifying NH3 sources is a critical step for effectively reducing NH3 emissions, which are generally unregulated around the world. Stable nitrogen isotopes (δ15N) of ammonium (NH4+) in precipitation have been directly used to partition NH3 sources. However, nitrogen isotope fractionation during atmospheric processes from NH3 sources to sinks has been previously overlooked. Here we measured δ15NNH4+ in precipitation on a daily basis at a rural forested site in Northeast China over three years to examine its seasonal pattern and attempt to constrain the NH3 sources. We found that the NH4+ concentrations in precipitation ranged from 5 to 1265 μM, and NH4+ accounted for 65% of the inorganic nitrogen deposition (20.0 kg N ha−1 yr−1) over the study period. The δ15N values of NH4+ fluctuated from −24.6 to +16.2‰ (average −6.5‰) and showed a repeatable seasonal pattern with higher values in summer (average −2.3‰) than in winter (average −16.4‰), which could not be explained by only the seasonal changes in the NH3 sources. Our results suggest that in addition to the NH3 sources, isotope equilibrium fractionation contributed to the seasonal pattern of δ15NNH4+ in precipitation, and thus, nitrogen isotope fractionation should be considered when partitioning NH3 sources based on δ15NNH4+ in precipitation.

Characterization and source estimates of primary and secondary carbonaceous aerosols at urban and suburban atmospheres of Düzce, Turkey.

Düzce is one of the cities located in the western Black Sea region of Turkey with a population of 377,610 in 2017 (TUIK, 2017). There is no satisfying scientific information available to address the contribution of primary and secondary sources of carbonaceous aerosols to the observed PM10 levels in the city. The main objective of the study is to determine the levels and sources of carbonaceous aerosols in PM10. For this purpose, PM10 samples were collected at urban and suburban locations in Düzce during winter and summer season in 2015. Average summer OC and EC concentrations in the urban area were 9.5 and 1.3μgm-3, respectively, while the corresponding concentrations were observed as 28.5 and 2.3μgm-3, respectively for winter season. Summer mean OC and EC levels at the suburban site were 5.46 and 0.37μgm-3, respectively, while those for winter were found as 6.68 and 0.61μgm-3.The contributions of OC and EC to measured PM10 levels were found in the range of 10% to 60% and 1% to 7%, respectively, at the urban station while the associated contributions were in the range of 10% to 50% and 0.6% to 6%, respectively, at the suburban station. The concentrations measured during winter months in both areas were found to be higher than those measured during summer months. The EC tracer method was used in order to estimate the SOC contribution. The contribution of SOC concentrations to the total PM10 mass was found to be higher during winter in the urban area and during summer in the suburban area.

Study of the effect of green quantity and structure on thermal comfort and air quality in an urban-like residential district by ENVI-met modelling

This study quantifies the influence of green spaces on microclimate and PM10 concentration in a typical residential district of Nanjing (China) by employing the CFD-based and microclimate model ENVI-met 4. Five green indices, related to quantity and structure of vegetation, are employed to investigate the impact of different types (grass, shrub and tree) and layouts of a green space located in the center of the residential district under an average Nanjing summer day. Results show that the thermal comfort (expressed by the mean radiant temperature MRT and the predicted mean vote PMV) is slightly enhanced with increasing green quantity, especially trees, even though more trees may increase the wind blocking effect with a consequent slight increase of pollutant concentration. In this regard, a single patch of trees located in the central part of the green space is preferable. The green indices are shown to be useful for studying the relationship between green space morphology, microclimate and air quality in cities.

Fine-scale stand structure mediates drought-induced tree mortality in pinyon-juniper woodlands.

Severe drought has resulted in widespread tree die-off events in forests and woodlands globally and is forecast to become more frequent in coming decades. Tree mortality is a complex process influenced by climate, soils, characteristics of individual trees, interactions between trees, and the dynamics of pests and pathogens. The role of stand structure and stand density in mediating the resistance of trees to drought remains poorly understood, especially in semiarid woodlands, which are expected to be highly susceptible to future severe drought. We sampled permanent plots in central Nevada woodlands dominated by single-leaf pinyon pine and Utah juniper before and after a severe multi-year drought (2013-2015) to investigate the importance of climate, tree attributes, and local-neighborhood stand structure on tree mortality and canopy dieback at the level of individual trees and 0.1-ha plots. We observed widespread tree mortality of pinyon at approximately eight times the reported background mortality rate, and substantial canopy dieback in both pinyon and juniper. Both species were more prone to mortality and dieback in hotter, drier sites. Canopy dieback was associated with both long-term average climate and the severity of recent drought, with elevated mortality on sites with higher water deficits, average summer temperatures, and vapor pressure deficits. Soils also played a role in tree dieback, with greater mortality on deeper soils. While mortality was driven largely by climate at coarse scales, fine-scale stand structure interacted with climate to mediate mortality and dieback. Neighborhood statistics showed that trees were susceptible to competitive influence, and pinyon trees were especially sensitive to neighborhood density on drier sites. Mortality and dieback were associated with diverse, co-occurring insect and parasitic plant mortality agents. Canopy dieback prior to the drought was strongly associated with tree mortality during the drought, implying that current widespread defoliation caused by these agents may foreshadow future elevated woodland decline. Fine-scale influences such as stand structure and soil characteristics play a key role in the long-term dynamics of semiarid woodlands, and these factors should be considered in predictive models of forest and woodland susceptibility to drought.