Summer Air Temperature Research Articles

Divergent shrub-cover responses driven by climate, wildfire, and permafrost interactions in Arctic tundra ecosystems.

The expansion of shrubs across the Arctic tundra may fundamentally modify land-atmosphere interactions. However, it remains unclear how shrub expansion pattern is linked with key environmental drivers, such as climate change and fire disturbance. Here we used 40+years of high-resolution (~1.0m) aerial and satellite imagery to estimate shrub-cover change in 114 study sites across four burned and unburned upland (ice-poor) and lowland (ice-rich) tundra ecosystems in northern Alaska. Validated with data from four additional upland and lowland tundra fires, our results reveal that summer precipitation was the most important climatic driver (r=0.67, p<0.001), responsible for 30.8% of shrub expansion in the upland tundra between 1971 and 2016. Shrub expansion in the uplands was largely enhanced by wildfire (p<0.001) and it exhibited positive correlation with fire severity (r=0.83, p<0.001). Three decades after fire disturbance, the upland shrub cover increased by 1077.2±83.6m2 ha-1 , ~7 times the amount identified in adjacent unburned upland tundra (155.1±55.4m2 ha-1 ). In contrast, shrub cover markedly decreased in lowland tundra after fire disturbance, which triggered thermokarst-associated water impounding and resulted in 52.4% loss of shrub cover over three decades. No correlation was found between lowland shrub cover with fire severity (r=0.01). Mean summer air temperature (MSAT) was the principal factor driving lowland shrub-cover dynamics between 1951 and 2007. Warmer MSAT facilitated shrub expansion in unburned lowlands (r=0.78, p<0.001), but accelerated shrub-cover losses in burned lowlands (r=-0.82, p<0.001). These results highlight divergent pathways of shrub-cover responses to fire disturbance and climate change, depending on near-surface permafrost and drainage conditions. Our study offers new insights into the land-atmosphere interactions as climate warming and burning intensify in high latitudes.

ФОРМИРОВАНИЕ СТРУКТУРЫ ПОСЕВА И ПРОДУКТИВНОСТИ РАСТЕНИЙ СОИ СЕВЕРНОГО ЭКОТИПА ПРИ РАЗНЫХ СПОСОБАХ ПОСЕВА В УСЛОВИЯХ ЛЕСОСТЕПИ СРЕДНЕГО ПОВОЛЖЬЯ

The studies were carried out in order to study the effect of the row spacing on the formation of the structure and productivity of plants of the early maturing soybean of Milyausha variety. In a field experiment on gray forest soils with a weakly acidic reaction and a humus content of 3.21 ... 3.83%, two sowing methods were compared: continuous sowing with a distance between rows of 15 cm and a series of rows - 30 cm. In the conditions of Kama region of the Republic of Tatarstan in dry years (2016, 2018), the duration of the growing season of the variety did not depend on the sowing methods and was 89 ... 91 days. With a moderate temperature regime and abundant precipitation (2017), with row sowing with a row spacing of 15 cm, it increased up to 105 days, in the variant with a row spacing of 30 cm - up to 109 days. An increase in the duration of the period from sowing to emergence of seedlings with a lack of heat led to a decrease in field germination according to the variants of the experiment to 70.0 ... 72.5%, plant survival - to 57.5 ... 66.0%. The maximum field germination in the experiment (95.0 and 85.0%), safety (98.2 and 94.1%) and plant survival (93.3 and 80.0%) were noted in 2018 with a high sum of air temperatures above 10 ° C and moderate moisture (total precipitation 102 mm) during the growing season. In the variant with a row spacing of 30 cm, the mass of seeds per plant in arid conditions was higher than with continuous sowing, by 2.2 ... 2.7, and in conditions of excessive moisture - by 1.7 times. An increase in the mass of seeds provided an increase in branching, the number of beans and seeds per plant. In terms of productivity and yield per unit area, there were no significant differences between the options for sowing methods. The maximum realization of the potential of productivity (289.1 and 314.7 g / m2) and yield (2.78 and 2.81 t / ha) in the experiment was achieved with the duration of the growing season 105 and 109 days (2017)

Atmospheric stilling and warming air temperatures drive long‐term changes in lake stratification in a large oligotrophic lake

AbstractLake surface temperatures are warming in many regions and have the potential to alter seasonal thermal stratification. However, the effects of climate change on thermal stratification can be difficult to characterize because trends in thermal stratification can be regulated by changes in multiple climate variables and other characteristics, such as water clarity. Here, we use long‐term (1993–2017) data from near‐pristine Crater Lake (Oregon) to understand long‐term changes in the depth and strength of summer stratification, measured by the center of buoyancy and Schmidt Stability, respectively. The depth of stratification has shoaled significantly (2.4 m decade−1), while stratification strength exhibited no long‐term trend. Empirical observations and modeling scenarios demonstrate that atmospheric stilling at Crater Lake is associated with the 25‐year shoaling trend as spring wind speeds declined over the observation period. While summer lake surface water and air temperatures warmed during the study period, spring air temperatures were variable and correlated with summer Schmidt Stability. Our results indicate that warmer spring air temperature resulted in earlier onset of stratification and stronger summer stratification. The observed shoaling of stratification depth at Crater Lake may have important ecological consequences, especially for non‐motile primary producers who can become constrained within a thinner epilimnion and exposed to higher solar radiation and reduced upwelling of nutrients. Driven by climate changes, many large lakes may be experiencing similar trends in seasonal stratification.

Extending Limited In Situ Mountain Weather Observations to the Baseline Climate: A True Verification Case Study

The availability of in situ atmospheric observations decreases with elevation and topographic complexity. Data sets based on numerical atmospheric modeling, such as reanalysis data sets, represent an alternative source of information, but they often suffer from inaccuracies, e.g., due to insufficient spatial resolution. sDoG (statistical Downscaling for Glacierized mountain environments) is a reanalysis data postprocessing tool designed to extend short-term weather station data from high mountain sites to the baseline climate. In this study, sDoG is applied to ERA-Interim predictors to produce a retrospective forecast of daily air temperature at the Vernagtbach climate monitoring site (2640 MSL) in the Central European Alps. First, sDoG is trained and cross-validated using observations from 2002 to 2012 (cross-validation period). Then, the sDoG retrospective forecast and its cross-validation-based uncertainty estimates are evaluated for the period 1979–2001 (hereafter referred to as the true evaluation period). We demonstrate the ability of sDoG to model air temperature in the true evaluation period for different temporal scales: day-to-day variations, year-to-year and season-to-season variations, and the 23-year mean seasonal cycle. sDoG adds significant value over a selection of reference data sets available for the site at different spatial resolutions, including state-of-the-art global and regional reanalysis data sets, output by a regional climate model, and an observation-based gridded product. However, we identify limitations of sDoG in modeling summer air temperature variations particularly evident in the first part of the true evaluation period. This is most probably related to changes of the microclimate around the Vernagtbach climate monitoring site that violate the stationarity assumption underlying sDoG. When comparing the performance of the considered reference data sets, we cannot demonstrate added value of the higher resolution data sets over the data sets with lower spatial resolution. For example, the global reanalyses ERA5 (31 km resolution) and ERA-Interim (80 km resolution) both clearly outperform the higher resolution data sets ERA5-Land (9 km resolution), UERRA HARMONIE (11 km resolution), and UERRA MESCAN-SURFEX (5.5 km resolution). Performance differences among ERA5 and ERA-Interim, by contrast, are comparably small. Our study highlights the importance of station-scale uncertainty assessments of atmospheric numerical model output and downscaling products for high mountain areas both for data users and model developers.

Effect of large-scale modes of total variability of the atmosphere and ocean in the Atlantic-European region on the climate of Belarus

We have established the relationships of quasicyclic components in changes of air temperature and precipitation in Belarus with large-scale modes of general variability of the atmosphere and ocean in the Atlantic-European region. When the summer air temperature changes in Belarus and in Eastern Europe, a quasi-60-year oscillation is identified, which coincides in phase with the Atlantic multi-decadal oscillation. It is shown that the time series of winter air temperature in Belarus contain a quasi-8-year component synchronized with a similar component of the North Atlantic Oscillation. Moreover, the periods of acceleration and deceleration of winter warming in Belarus coincide with the upward and downward quasi-30-year phases of the North Atlantic Oscillation, respectively. The latter are also consistent with fluctuations in moisture content in Belarus and Europe. Based on the established patterns, we have concluded that the rapid rise in winter temperatures, slowing down of summer warming and deterioration in water supply in the southern regions of Belarus observed in the last decade are part of a natural cycle lasting about 30 years, developing against the background of a long-term trend of anthropogenic global warming.

Adaptation of the technology of cultivation of different varieties of rice for ripeness when watering with sprinkling

The results of long-term scientific and industrial research are presented, which shows that the cultivation of rice during sprinkling on the lands of LLC Agrocomplex "Prikubansky" of the Krasnodar territory is possible and economically feasible. The proposed technology of irrigation of rice by sprinkling reduces the cost of irrigation water by 5-10 times compared to the traditional one, removes problems related to the environment, which depend on the continuous flooding of the cheques with a layer of water, provides high productivity and economic effect, and allows you to cultivate rice on General-purpose irrigation systems. When evaluating the varieties Volgogradskya, sonet and Novator, belonging to the early-ripe group, watered by sprinkling, the low-water-consumption variety Volgogradskya proved to be the most preferable in the experimental zone. It took 116 days to complete its life cycle with the lowest sum of average air temperatures of 2489.3 0C. It formed a yield of 5.50 t / ha of grain over the years of experiments, this is 1.50 t / ha more than the Sonet variety and 1.90 t/ha novator.

The 2020 Larsen C Ice Shelf surface melt is a 40-year record high

Abstract. Along with record-breaking summer air temperatures at an Antarctic Peninsula meteorological station in February 2020, the Larsen C ice shelf experienced an exceptionally long and extensive 2019/2020 melt season. We use a 40-year time series of passive and scatterometer satellite microwave data, which are sensitive to the presence of liquid water in the snow pack, to reveal that the extent and duration of melt observed on the ice shelf in the austral summer of 2019/2020 was the greatest on record. We find that unusual perturbations to Southern Hemisphere modes of atmospheric flow, including a persistently positive Indian Ocean Dipole in the spring and a very rare Southern Hemisphere sudden stratospheric warming in September 2019, preceded the exceptionally warm Antarctic Peninsula summer. It is likely that teleconnections between the tropics and southern high latitudes were able to bring sufficient heat via the atmosphere and ocean to the Antarctic Peninsula to drive the extreme Larsen C Ice Shelf melt. The record-breaking melt of 2019/2020 brought to an end the trend of decreasing melt that had begun in 1999/2000, will reinitiate earlier thinning of the ice shelf by depletion of the firn air content, and probably affected a much greater region than Larsen C Ice Shelf.

Improved Near‐Surface Continental Climate in IPSL‐CM6A‐LR by Combined Evolutions of Atmospheric and Land Surface Physics

AbstractThis work is motivated by the identification of the land‐atmosphere interactions as one of the key sources of uncertainty in climate change simulations. It documents new developments in related processes, namely, boundary layer/convection/clouds parameterizations and land surface parameterization in the Earth System Model of the Institut Pierre Simon Laplace (IPSL). Simulations forced by prescribed oceanic conditions are produced with different combinations of atmospheric and land surface parameterizations. They are used to explore the sensitivity to the atmospheric physics and/or soil physics of major biases in the near surface variables over continents, the energy and moisture coupling established at the soil/atmosphere interface in not too wet (energy limited) and not too dry (moisture limited) soil moisture regions also known as transition or “hot‐spot” regions, the river runoff at the outlet of major rivers. The package implemented in the IPSL‐Climate Model for the Phase 6 of the Coupled Models Intercomparison Project (CMIP6) allows us to reduce several biases in the surface albedo, the snow cover, and the continental surface air temperature in summer as well as in the temperature profile in the surface layer of the polar regions. The interactions between soil moisture and atmosphere in hotspot regions are in better agreement with the observations. Rainfall is also significantly improved in volume and seasonality in several major river basins leading to an overall improvement in river discharge. However, the lack of consideration of floodplains and human influences in the model, for example, dams and irrigation, impacts the realism of simulated discharge.

Оценка уровня адаптации лиан к воздействию неблагоприятных факторов среды в условиях г. Саратова

The article is devoted to the actual topic of expansion of assortment of lianas in vertical gardening in Saratov by the use of introduced species of tree lianas from the Far East. Currently, the studied species: Actinidia arguta; Actinidia kolomikta; Ampelopsis aconitifolia; Schisandra chinensis; Menispermum dauricum — have been distributed in individual land use areas mainly as food crops. It is noted that the far Eastern species of lianas differ in a significant amplitude of biological tolerance of adaptation, have high frost resistance and immunity against diseases. The reason for including these species in the prospective assortment for use in urban plantations is given taking into account a comprehensive assessment of their drought resistance, heat resistance, and resistance to anthropogenic impact. All species are resistant to high summer air temperatures and insufficient humidity, which is typical for the climate of Saratov. The assessment of gas resistance of lianas is given in comparison with the results of studies previously conducted with respect to other species, which allows us to determine possible combinations of plants on landscaping sites. Ranking of species showed that the studied Far Eastern species of lianas have high and medium gas resistance. The obtained data give reason to recommend the studied lianas for use in plantings of various categories in Saratov, depending on the availability of care and air quality. To prevent damage to leaves and shoots by drought, as well as to improve the gas resistance of plants, it is recommended to conduct agro-measures that improve the water-air and food regime of soils in the growing areas.

ВЛИЯНИЕ ПОГОДНЫХ УСЛОВИЙ ВЕГЕТАЦИОННОГО ПЕРИОДА НА ПРОДУКТИВНОСТЬ ЗЕРНОВОГО СОРГО

Global warming is currently having a measurable effect on Earth, so the process is bringing about significant changes in weather conditions during the vegetation period of the main field crops. This is true for the arid steppe conditions of the Donbass territory. The authors conducted a field experiment to evaluate climatic factors' effect on the productivity of various early maturing grain sorghum hybrids on ordinary chernozem in Luhansk National Agrarian university's experimental field 2015–2019. The study obtained the strongest direct correlation between the yield of hybrids and the amount of precipitation for April – September (r = 0,84–0,99) or only correlated with precipitation for August (r = 0,75–0,98). A moderate and high correlation was found between the yield of hybrids and the hydrothermal coefficient (HTC) for April – September (r = 0,53–0,89) and a high correlation with the HTC for August (r = 0,67–0,99). The average monthly air temperature in summer did not show a significant correlation with the sorghum yield. The crop yield had an average (r = 0,52–0,66) and strong (r = 0,90) direct correlation with the mass of 1000 grains, a strong correlation (r = 0,92) with the height of plants, and a strong correlation (r = 0,76–0,99) with the duration of the vegetational season of sorghum. The early-maturing hybrid Yankee and the medium-early maturing hybrid Puma Star showed the closest correlation between the sorghum crop and the amount of precipitation for August (r = 0,91–0,98) and the Selyaninov HTC for August (r = 0,87–0,99). In 2015–2019, the Puma Star hybrid demonstrated the highest grain yield, significantly higher than other hybrids (56,5–77,6 C/ha), due to the higher grain weight obtained from the panicle (42,5–49,8 g) and the weight of 1000 grains (21,8–28,2 g). The Puma Star hybrid showed an extreme dependence of the yield on the mass of 1000 grains (r = 0,96 ± 0,01).

Summer warming explains widespread but not uniform greening in the Arctic tundra biome

Arctic warming can influence tundra ecosystem function with consequences for climate feedbacks, wildlife and human communities. Yet ecological change across the Arctic tundra biome remains poorly quantified due to field measurement limitations and reliance on coarse-resolution satellite data. Here, we assess decadal changes in Arctic tundra greenness using time series from the 30 m resolution Landsat satellites. From 1985 to 2016 tundra greenness increased (greening) at ~37.3% of sampling sites and decreased (browning) at ~4.7% of sampling sites. Greening occurred most often at warm sampling sites with increased summer air temperature, soil temperature, and soil moisture, while browning occurred most often at cold sampling sites that cooled and dried. Tundra greenness was positively correlated with graminoid, shrub, and ecosystem productivity measured at field sites. Our results support the hypothesis that summer warming stimulated plant productivity across much, but not all, of the Arctic tundra biome during recent decades.

A revised chronology for the growth and demise of Loch Lomond Readvance (‘Younger Dryas’) ice lobes in the Lochaber area, Scotland

We present a revised varve chronology for the duration of ice-dammed lakes that formed in the Lochaber district, Scotland, during the Loch Lomond (‘Younger Dryas’) Stadial. We analysed new varved sequences and combined them with existing varve records to develop the Lochaber Master Varve Chronology 2019 (LMVC19), published here for the first time. It spans an interval of 518 ± 18 vyrs and is considered more secure than its predecessors because: (i) it is anchored by a more robust record of the Vedde Ash, which is dated to 12,043 ± 43 cal yr BP; and (ii) it provides revised estimates of the timings of key regional palaeoclimatic shifts that are fully compatible with those inferred from independently-dated, non-varved records obtained from neighbouring sites. The new results indicate that the Lochaber ice-dammed lakes existed between ∼12,135 and 11,618 ± 61 cal yr BP, but the pattern of glacier advance that led to lake formation was more complex than previously assumed, with some ice fronts reaching their maximal positions 300 years before others. Initiation of ice retreat at ∼11,800 cal yr BP appears to have coincided with a rise of ∼2 °C in mean July temperatures inferred from chironomid data obtained from the Abernethy Forest site in the eastern Highlands. This local climatic shift is thought to have been a delayed response (by up to 335 years) to a mid-Stadial northward migration of the North Atlantic Polar Front, the delay probably due to the influence of the SW Highland icefield. Subsequent retreat that led to the formation of ice stagnation features throughout large parts of the area was initiated by a further rise in summer air temperature of ∼3 °C at the start of the Early Holocene. Final drainage of the lake system occurred ∼190 years after the initiation of ice retreat, while it took a further 200 years for the ice to vacate the Rannoch plateau, a nearby upland glacial source.

Factors controlling long-term carbon dioxide exchange between a Douglas-fir stand and the atmosphere identified using an artificial neural network approach

It is critical to have long-term carbon dioxide (CO2) flux observations in forest ecosystems to understand how changing climate can affect forest carbon (C) stocks and CO2 exchange between forests and the atmosphere. In this study, fifteen years (2002–2016) of continuous eddy-covariance flux and climate measurements in an intermediate-aged Douglas-fir stand on the east coast of Vancouver Island, Canada, were analyzed. First, the eddy covariance-measured CO2 fluxes were partitioned into gross primary production and ecosystem respiration using two artificial neural networks. Second, the responses of net ecosystem production, gross primary production and ecosystem respiration to interannual climate variability, including five El Niño-Southern Oscillation events, were determined. Three hyper-parameters (number of layers, hidden units, and batch size) of each artificial neural network were set by Bayesian optimization using sequential model-based optimization while the remaining hyper-parameters were taken from the literature. The first artificial neural network was fitted using only nighttime CO2 flux data and applied to estimate nighttime and daytime ecosystem respiration values, and the second one was used to gap-fill gross primary production values. In addition, a predictor analysis was done to investigate the most influential predictors (i.e., environmental variables) within seasons and years. When applied to half-hourly data, the ecosystem respiration model had an R2 of 0.43, whereas the gross primary production model had an R2 of 0.80. The stand was a moderate C sink (average net ecosystem production of 118 ± 404 g C m−2 year−1) during the entire study period, except for the years 2002–2006 when the stand was a moderate C source. The mean annual values of gross primary production and ecosystem respiration were 1649 ± 157 g C m−2 year−1 and 1531 ± 410 g C m−2 year−1, respectively. Our analysis showed that soil temperature was the most important predictor for the ecosystem respiration model, and photosynthetically active irradiance was the most important predictor for the gross primary production model. However, during dry periods in late summer, soil moisture became the most important predictor. Interannual variability of net ecosystem production was only slightly affected by annual total precipitation, mean soil temperature and mean air temperature. Instead, it depended on spring mean air temperature (start of the growing season), summer total precipitation (indicative of water deficiency) and mean summer air temperature. El Niño and La Niña events generally resulted in lower and higher annual net ecosystem production, respectively.

Sensitivity of gross primary productivity to climatic drivers during the summer drought of 2018 in Europe.

In summer 2018, Europe experienced a record drought, but it remains unknown how the drought affected ecosystem carbon dynamics. Using observations from 34 eddy covariance sites in different biomes across Europe, we studied the sensitivity of gross primary productivity (GPP) to environmental drivers during the summer drought of 2018 versus the reference summer of 2016. We found a greater drought-induced decline of summer GPP in grasslands (-38%) than in forests (-10%), which coincided with reduced evapotranspiration and soil water content (SWC). As compared to the 'normal year' of 2016, GPP in different ecosystems exhibited more negative sensitivity to summer air temperature (Ta) but stronger positive sensitivity to SWC during summer drought in 2018, that is, a stronger reduction of GPP with soil moisture deficit. We found larger negative effects of Ta and vapour pressure deficit (VPD) but a lower positive effect of photosynthetic photon flux density on GPP in 2018 compared to 2016, which contributed to reduced summer GPP in 2018. Our results demonstrate that high temperature-induced increases in VPD and decreases in SWC aggravated drought impacts on GPP. This article is part of the theme issue 'Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale'.

ДЕРНООБРАЗУЮЩИЕ ЗЛАКОВЫЕ ТРАВЫ ДЛЯ ТАЕЖНОЙ ЗОНЫ

Experimental selection studies were carried out in 2016-2018. in the fields of the Narym Department of Breeding and Seed Production of the Siberian Research Institute of Agriculture and Peat (Kolpashevo, Tomsk Region). The purpose of the research was to study collection samples of lawn grasses capable of effectively using the agro-resource potential of the naturaland climatic conditions in the taiga zone of the Tomsk region. The climate in the research area is sharply continental with long, severe winters and short, but hot and often dry summers. The snow cover lasts about seven months (usually from October to April). The frost-free period is short. Annual precipitation is about 500 mm, including more than 300 mm during the growing season. The sum of air temperatures above 10° C is 1300-1600° C. The soils of the experimental plots are sod-podzolic, sandy loam in granulometric composition, with a humus content in the arable horizon of no more than 2%. As experimental material, 21 samples of bluegrass of three species were studied (8 domestic and 13 foreign varieties); 21 samples of pasture ryegrass (domestic varieties - 3, foreign - 18); 10 samples of four species of bent field of foreign origin; 12 samples of five types of fescue (domestic varieties – 5, foreign – 7). Among the experimental cultivars, the following sources of economically valuable traits were identified: high winter hardiness - all investigated cultivars of bluegrass, bent grass, fescue; grade of perennial ryegrass Yuventus (Denmark); short stature - varieties of meadow bluegrass Yaskia, Limonsine (Germany), Barkenta (Netherlands); ryegrass cultivars of pasture Sport (Poland), Fiesta (USA), Yuventus (Denmark); bentgrass wild populations from Mongolia (K14272, K-14273) and bentgrass from Ukraine (K14265); fine texture source - perennial ryegrass varieties Yuventus, Denmark, Primevere, France, K-14233, Poland.

The Best Urban Trees for Daytime Cooling Leave Nights Slightly Warmer

Summer air temperatures will continue to rise in metropolitan regions due to climate change and urbanization, intensifying daytime and nighttime air temperatures and result in greater thermal discomfort for city dwellers. Urban heat may be reduced by trees which provide shade, decreasing air and surface temperatures underneath their canopies. We asked whether tree height and canopy density can help to identify species that provide greater microclimate benefits during day and night. We also asked if increased canopy cover of street trees provides similar microclimate benefits. We used continuous measurements of near-surface air temperatures under 36 park trees and from two urban streets to assess these questions. In the park, trees were grouped according to their height (&lt;10 m, 10–20 m, &gt;20 m) and canopy density (low, high), while the effect of canopy cover was tested using streets with high (31%) and low (11%) cover. Daytime near-surface air temperature declined with increasing height and canopy density providing significant cooling benefits. However, this trend was reversed at night when tall trees with dense canopies restricted longwave radiative cooling and trapped warm air beneath their crowns. High canopy cover of street trees reduced daytime air temperatures more, resulting in a lower number of days with hot (&gt;35 °C) and extreme (&gt;40 °C) air temperatures compared to the street that had low canopy cover. These findings suggest that tree species and streetscapes with dense canopy cover improve local thermal conditions during the day but do not seem ideal to allow for nighttime cooling, creating potential discomfort for residents during hot summer nights. Our results indicate that classifying trees using a simple metric can assist in selecting tree species that can alleviate the local negative effect of urban heat during the day, but at the same time, their effect in preventing optimal longwave radiative cooling during the night must be factored into planting strategies.

Long-term relationship between air and water temperatures in Lake Paldang, South Korea

A long-term investigation into the relationship between air and water temperatures was conducted in Lake Paldang, which is the largest water source in South Korea, by studying hysteresis. From 1973 to 2018, the annual mean air temperature increased by 0.05°C/yr (seasonal Sen’s slope). The results of a numerical model (R &gt; 0.86) showed that the ratios of the air and water temperatures increased (0.71‒0.77) in the rising limb and decreased (0.70‒0.76) in the falling limb. However, the intercept values were 0.13–3.52 and 6.62–7.78 in the rising and falling limbs, respectively, and hence there was a 4–5°C increase in temperature. In particular, in 2015, 2016, and 2018, the intercept values in the falling limb were ≥ 7, exhibiting hysteresis, whereby high water temperatures were slow to decline. Lake Paldang showed stronger water temperature hysteresis than its influent rivers and stream. The rising and falling limbs did not show a large difference in the extent of water temperature change (slope). However, the water temperature did not decrease rapidly, and the decrease continued for longer due to hysteresis, which is a type of inertia where the elevated temperature persists if the summer air temperature is significantly increased.

New evidence for atmospheric mercury transformations in the marine boundary layer from stable mercury isotopes

Abstract. The marine boundary layer (MBL) is the largest transport place and reaction vessel of atmospheric mercury (Hg). The transformations of atmospheric Hg in the MBL are crucial for the global transport and deposition of Hg. Herein, Hg isotopic compositions of total gaseous mercury (TGM) and particle-bound Hg (PBM) collected during three cruises to Chinese seas in summer and winter were measured to reveal the transformation processes of atmospheric Hg in the MBL. Unlike the observation results at inland sites, isotopic compositions of TGM in the MBL were affected not only by mixing continental emissions but also largely by the oxidation of Hg0 primarily derived by Br atoms. Δ199Hg values of TGM were significantly positively correlated with air temperature in summer, indicating that processes inducing positive mass-independent fractionation of odd isotopes in TGM could be more active at low temperatures, while the relative processes might be weak in winter. In contrast, the positive Δ199Hg and high ratios of Δ199Hg∕Δ201Hg in PBM indicated that alternative oxidants other than Br or Cl atoms played a major role in the formation of Hg(II) in PBM, likely following the nuclear volume effect. Our results suggest the importance of local Hg environmental behaviors caused by an abundance of highly reactive species and provide new evidence for understanding the complicated transformations of atmospheric Hg in the MBL.

Modelling and thermo-hygrometric performance study of an underground chamber with a long vertical earth-air heat exchanger system

A study of an underground building ventilated by a long vertical earth-air heat exchanger (EAHE) system is especially of interest because it shows a mechanism to alter the thermal characteristics in the building. However, studies on this thermal configuration are rare. In this paper, based on the free-falling equation of water film and the heat and mass transfer equations of airflow, a coupled numerical solution method is proposed to predict the thermo-hygrometric performance of the system. The Heat Index (HI) is chosen as the thermal evaluation index. According to the numerical results, the long vertical EAHE system can significantly reduce the indoor air temperature in summer while it only has a lag effect on the air humidity ratio, causing a high relative humidity and making it the main reason for the indoor thermal discomfort. The indoor HI decreases by approximately 1 °C for every 6 m3/(h·p) (“p” is short for “per person”) increase of the ventilation volume, but the reduced rate gradually slows down; the diameter of ventilation pipe less than 0.25 m is not conducive for the thermal control; the EAHE system is more suitable for application with a buried depth less than 200 m.

Nutrients and warming interact to force mountain lakes into unprecedented ecological states.

While deposition of reactive nitrogen (N) in the twentieth century has been strongly linked to changes in diatom assemblages in high-elevation lakes, pronounced and contemporaneous changes in other algal groups suggest additional drivers. We explored the origin and magnitude of changes in two mountain lakes from the end of the Little Ice Age at ca 1850, to ca 2010, using lake sediments. We found dramatic changes in algal community abundance and composition. While diatoms remain the most abundant photosynthetic organisms, concentrations of diatom pigments decreased while pigments representing chlorophytes increased 200-300% since ca 1950 and total algal biomass more than doubled. Some algal changes began ca 1900 but shifts in most sedimentary proxies accelerated ca 1950 commensurate with many human-caused changes to the Earth System. In addition to N deposition, aeolian dust deposition may have contributed phosphorus. Strong increases in summer air and surface water temperatures since 1983 have direct and indirect consequences for high-elevation ecosystems. Such warming could have directly enhanced nutrient use and primary production. Indirect consequences of warming include enhanced leaching of nutrients from geologic and cryosphere sources, particularly as glaciers ablate. While we infer causal mechanisms, changes in primary producer communities appear to be without historical precedent and are commensurate with the post-1950 acceleration of global change.