Northeast In Summer Research Articles

Variation characteristics, source analysis, and health risk assessment of carbonyl compounds in Zhangjiajie National Forest Park, China

This study presents a comprehensive analysis of carbonyls in the atmosphere of Zhangjiajie Forest from May 2016 to January 2017 following the Environmental Protection Agency (EPA) TO-11 A guidelines, including pollution characteristics, human health risks, and sources. The dominant carbonyl compounds were formaldehyde, acetaldehyde, and acetone, with average concentrations of 5.94, 1.48, and 4.24 μg/m3, respectively. A seasonal variation was observed in the total carbonyl compound concentrations in the order summer > autumn > spring > winter. The diurnal patterns showed that the concentration of the main carbonyl compounds peaked in the afternoon. The ratios of formaldehyde/acetaldehyde (C1/C2) and acetaldehyde/propionaldehyde (C2/C3) ranged from 2.82 to 5.66 and 0.76–3.14; this indicates that compared with anthropogenic sources, volatile organic compounds emitted from natural sources contributed more significantly to atmospheric carbonyl compounds in the Zhangjiajie Forest. Correlation analysis of the three main carbonyl compounds with common air pollutants revealed that formaldehyde and acetaldehyde have similar secondary sources for photochemical reactions. In autumn and winter, acetaldehyde and acetone were affected by fuel combustion and vehicle exhaust emissions. Reverse trajectory, potential source contribution function, and concentration-weighted trajectory analyses revealed that carbonyl compounds in the atmosphere of Zhangjiajie Forest were mainly polluted locally in spring and autumn and influenced by the urban air mass from the northeast in summer and winter. The health risk assessment showed that the lifetime carcinogenic risk of formaldehyde and acetaldehyde exceeded the acceptable level and that long-term exposure to this concentration poses serious carcinogenic risks. The findings of this study shed light on the characteristics of atmospheric carbonyl compound pollution in subtropical forest areas, and provide scientific basis for formulating pollution control measures.

Diversity of Diatom Algae in the Lena Delta Nature Reserve and the Adjacent Territory in the Specific Ecological Factors of the Arctic

A total of 413 diatom taxa were known for aquatic habitats of the Lena Delta Nature Reserve. We identified 385 taxa in 14 small tundra lakes near the reserve that significantly enriched the diatom diversity of the region (666 taxa including definitions to the genus level). Thus, the species composition of diatoms in the reserve and adjacent territories was increased by 278 species. We showed that the species of the genera Pinnularia (57) and Eunotia (51) have predominance at the family and generic levels. The index of intraspecific variability Ssp./Sp. for the lakes of the reserve was 1.11, and that for the lakes of the Tiksi region 1.14, which is typical for high-latitude and high-mountain communities. The number of rare or endangered species varied in different lakes from 1 to 10, totaling 42 species for the entire study area. Bioindication has shown that potentially threatened species prefer moderate temperatures, and slightly acidic or neutral environments free from organic pollution. A comparative analysis of the species composition of diatoms in the vicinity of the Lena Delta and other northern water bodies of Yakutia and the Arctic Islands showed that the species composition of each lake in the Arctic has a discernably different species distribution. The indicator characteristics show a certain response of the species composition of diatoms to changes in salinity, pH, and organic pollution. Regularities in the spatial distribution of diatoms in the study area were revealed in connection with the environmental variables of their habitat. Statistical mapping of diatom diversity data and bioindicators revealed a pronounced response to point pollution, and also let us assume the influence of summer northeast winds on species composition of the studied lake communities. We suggest that the high diversity inherent in the diatom lakes of the Tiksi coastal zone, which can even be updated in further studies, can be considered as a property of coastal biota inherent in ecotones. Since it is in the coastal Tiksi region that a surge in the number of species is observed, this region can be considered not only an ecotone, but also a hotspot of diatom diversity. The results of the study are important for developing the basis for monitoring biodiversity under the conditions of anthropogenic and climatic changes in the Arctic.

Modulation of the late summer Northeast China cold vortex by previous-winter ENSO

The modulation of the late-summer Northeast China cold vortex (NCCV) by previous-winter El Niño–Southern Oscillation (ENSO) is investigated using reanalysis data. A significant correlation dominates in the ENSO–NCCV relationship, with El Niño (La Niña) accompanied by a weak (strong) NCCV intensity. The Indian Ocean basin mode (IOBM) plays an essential role in relaying the impact of pre-winter ENSO on the following late-summer atmospheric circulation over Northeast Asia. A positive IOBM responds passively to eastern Pacific–type El Niño and can last till late summer when El Niño has already decayed. It triggers a meridional teleconnection pattern of the cyclone over central China and anticyclone over Northeast Asia, and thereby enables a background circulation adverse to the generation of the NCCV, and vice versa. In addition, the signals of the Indian Ocean during central Pacific–type El Niño and neutral years are extremely weak, which makes their effect on NCCV generation insignificant.摘要本文利用再分析资料, 研究了前冬ENSO对夏末东北冷涡 (NCCV) 的调制作用. 结果表明, 前冬ENSO与夏末NCCV强度之间存在显著的相关性, El Niño (La Niña) 对应于弱 (强) 的NCCV. 印度洋海盆模态 (IOBM) 在前冬ENSO对夏末东北亚地区大气环流的影响中起着至关重要的作用. 作为东部型El Niño的被动响应, IOBM可以从前冬一直持续至夏末, 并在夏末激发“中国中部上空气旋—东北亚地区上空反气旋”的经向遥相关模态, 从而不利于NCCV增强. 反之亦然. 此外, 印度洋的信号在中部型El Niño和中性年份相对较弱, 使得它们对于NCCV的影响不显著.

Characteristics and mechanisms of long-lasting 2021–2022 summer Northeast Pacific warm blobs

Warm blobs are persistently warmer-than-normal seawaters over the Northeast Pacific (NEP), which cause substantial impacts on marine ecosystems and climate. Recently, the warm blobs occurred consecutively in spring and summer of 2021 and 2022. The warm blob in 2021 was mostly located east of 155°W, while it shifted to west of 155°W in 2022. Based on a mixed-layer heat budget analysis, we find that atmospheric processes positively and dominantly contributed in May 2021 and July 2022. Specifically, less latent heat loss from the ocean caused by reducing background westerlies and evaporation intensified the 2021 warm blob, while more shortwave radiation heating due to decreased low clouds intensified the one in 2022. However, the positive contribution of the atmospheric processes cannot maintain a season due to their strong internal variability. The seasonal persistence of the warm blobs, instead, is owing to the offset between the atmospheric and oceanic processes. We highlight the importance of atmospheric processes in the evolution of the NEP warm blobs in spring and summer, which lacks sufficient investigation but can provide more potential predictability for the NEP warm blobs.

Transport-driven seasonal abundance of pelagic fishes in the Chukchi Sea observed with seafloor-mounted echosounders

Abstract Recent summer surveys of the northeastern Chukchi Sea found pelagic fishes were dominated by large numbers of age-0 Arctic cod (Boreogadus saida, Gadidae) and walleye pollock (Gadus chalcogrammus, Gadidae), while adult fishes were comparatively scarce. The source and fate of these young fishes remain unclear, as sampling in this region is impeded by seasonal ice cover much of the year. Seafloor-mounted echosounders were deployed at three locations in the northeastern Chukchi Sea from 2017 to 2019 to determine the movement and seasonal variability of these age-0 gadids. These observations indicated that the abundance of pelagic fishes and community composition on the Chukchi Sea shelf were highly variable on seasonal time scales, with few fish present in winter. Tracking indicated that fish movements were strongly correlated with local currents. Fishes were primarily displaced to the northeast in summer and fall, with periodic reversals towards the southwest driven by changes in regional wind patterns. The flux of fishes past the moorings indicated that the prevailing northward currents transport a large proportion of the age-0 pelagic fishes present on the Chukchi shelf in summer to the northeast by fall, leading to relatively low abundances of age-1+fishes in this environment.

New data on a hotspot of diatom diversity in the vicinity of the Lena Delta Nature Reserve in the Arctic

In 14 small tundra reservoirs in еру vicinity of Lena Delta Wildlife Reserve, we identified385 taxa, which in the compilatory list made up a significant diversity (666 taxa including definitions to the genus level) of diatoms. Thus, the species composition of diatoms in the reserve and adjacent territories was replenished by 278 species. The number of rare or endangered species is 42 for the entire study area. Statistical mapping of indicators of community and habitat diversity revealed a strong reaction to point one-time pollution and made it possible to assume the influence of summer northeast winds on the species composition. We suggest that the high diversity inherent in the diatom lakes of coastal zone, can be considered as a property of coastal biota inherent in ecotones. Comparative floristics of diatoms from Svalbard to Chukotka established a high individuality of the species composition in the lakes of the Arctic. Since it is in the coastal region that a surge in the number of species is observed, this region can be considered not only an ecotone, but also a hotspot of diatom diversity. The results of the study are important for developing the basis for monitoring biodiversity under the conditions of anthropogenic and climatic changes in the Arctic.

An Interdecadal Enhancement of the Impact of ENSO on the Summer Northeast Asian Circulation around 1999/2000 through the Silk Road Pattern

Abstract In this study, we find that the negative relationship between El Niño–Southern Oscillation (ENSO) and summer Northeast Asia (NEA; 30°–50°N, 110°–140°E) circulation, especially the geopotential height anomalies in the upper troposphere (H200), is weakened from the early 1970s, remains stable since the middle 1980s, and is strengthened dramatically after 1999/2000. The recent transitions of the ENSO–NEA H200 relationship are closely connected with the variation of circumglobal teleconnection (CGT)/Silk Road pattern (SRP), which is further modified by the interdecadal shift of the ENSO–Indian summer monsoon rainfall (ISMR) relationship and ENSO evolution. During 1980–99 when the continuing ENSOs dominate, the weakened ENSO–ISMR relationship leads to an inactive ENSO-related CGT/SRP wave train in the upper-level troposphere and then a weakened connection between ENSO and H200 over the NEA. On the other hand, when the emerging ENSOs dominate after 1999/2000, the restored ENSO–ISMR relationship reinforces the ENSO-related CGT/SRP wave train and then enhances ENSO–NEA H200 relationship. This mechanism is well simulated in the Atmospheric Model Intercomparison Project models (AMIP) and Pacific Ocean–Global Atmosphere (POGA) experiments.

Temporal and Spatial Distribution of Surface Sediment and Its Implications in the Yangtze Subaqueous Delta

Characteristics of sediments vary significantly temporally and spatially in the Yangtze subaqueous delta and adjacent East China Sea shelf due to complicated dynamic conditions. Magnetic properties of sediments are sensitive to hydrodynamics and provenance, and therefore can indicate sediment transportation and deposition. High-resolution surface sediments collected in different seasons and years from the Yangtze subaqueous delta and neighboring East China Sea shelf were subjected to environmental magnetic analyses. In combination with granulometric analysis, this paper discusses temporal and spatial variations of magnetic properties and their implications for indicating sediment transportation, sediment source identification, and hydrodynamic response. The results show that magnetic parameters SIRM and XARM/SIRM suggest sediment transportation path from the Yangtze River into the East China Sea, with majority migrating to the south and southeast and then deposited to the west of 123°E, while a little fine sediment delivered to the northeast in summer. Cluster analysis demonstrates three sedimentation districts according to magnetic properties and particle size in the study area, which represent modern Yangtze sediment, late Pleistocene relict sand, and their mixture, respectively. Temporal-spatial changes in particle size of sediments suggests erosion outside the North Branch in the past few years, while opposite trend of changes on particle size of surface sediment in the adjacent area might reflect different degrees of erosion.

Modulation of seasonal precipitation in Argentina by the South Pacific high

AbstractThe aim of this work is to quantify the influence of the position and intensity of the South Pacific High (SPH) over seasonal rainfall in Argentina. Some indices were defined to measure the position and intensity of the SPH, and they were correlated with seasonal precipitation to study the relationship between them. Results indicate that the intensity of the SPH affects precipitation mainly in northern Argentina during spring and in the southern region in autumn and winter. The latitudinal shift of the SPH has proved to have a relevant impact on precipitation in the northeast in summer and winter, and in some regions of southern and central Argentina during winter and spring. When studying the possibility to foresee precipitation behaviour with a one‐month lag, these metrics were not able to predict precipitation effectively in the northwest. On the contrary, the SPH intensity showed significant lagged correlations with rainfall mainly in the northeast, central‐east and south during spring and summer while the position of the SPH is mostly significantly correlated with summer and winter precipitation in the northeast and central Argentina. Results suggest that the situation of SPH can provide some rainfall predictability.

First-Year Migration and Natal Region Fidelity of Immature Ferruginous Hawks

From 1999 to 2014 we used satellite telemetry to address knowledge gaps in the migration of juvenile Ferruginous Hawks (Buteo regalis) related to their migration independence from adults, migration patterns, and locations of settlement ranges. Nine fledgling hawks migrated independently from their radio-tagged parents, left natal areas at different times and directions, and settled on summer ranges separated from parents by an average of 592 km. Juvenile hawks that we followed through their entire first year (n = 12) travelled about three times farther and twice as long as adults during annual migrations, and arrived an average of 11 to 38 d later on summer, winter, and spring ranges. Hawks that hatched west of the Continental Divide (n = 14) migrated northeast in summer to ranges in the northern grasslands and to winter ranges in California and the Great Plains. Hawks that hatched east of the divide (n = 17) also migrated north to summer ranges, but wintered south from the Central Plains to Mexico. At the end of their first year, hawks (n = 14) settled on spring ranges within their natal regions, an average of 350 km from their hatch locations. In their third spring, hawks (n = 6) settled an average of 123 km from hatch locations and two females nested. We ascribe differences in migration distance and timing of juvenile hawks relative to adults to juveniles’ inexperience in locating suitable feeding areas and range prospecting independently from parents. Because migration patterns and regional fidelity of juvenile Ferruginous Hawks to settlement ranges were similar to those exhibited by adult hawks, the protection of fossorial prey and their habitats on seasonal ranges that promote survival of adult hawks will afford the same benefits to the juvenile cohorts.

Air-Sea Interaction in the Bay of Bengal

Recent observations of surface meteorology and exchanges of heat, freshwater, and momentum between the ocean and the atmosphere in the Bay of Bengal are presented. These observations characterize air-sea interaction at 18 degrees N, 89.5 degrees E from December 2014 to January 2016 and also at other locations in the northern Bay of Bengal. Monsoonal variability dominated the records, with winds to the northeast in summer and to the southwest in winter. This variability included a strong annual cycle in the atmospheric forcing of the ocean in the Bay of Bengal, with the winter monsoon marked by sustained ocean heat loss resulting in ocean cooling, and the summer monsoon marked by strong storm events with dark skies and rain that also resulted in ocean cooling. The spring intermonsoon was a period of clear skies and low winds, when strong solar heating and weak wind-driven mixing led to ocean warming. The fall intermonsoon was a transitional period, with some storm events but also with enough clear skies and sunlight that ocean surface temperature rose again. Mooring and shipboard observations are used to examine the ability of model-based surface fluxes to represent air-sea interaction in the Bay of Bengal; the model-based fluxes have significant errors. The surface forcing observed at 18 degrees N is also used together with a one-dimensional ocean model to illustrate the potential for local air-sea interaction to drive upper-ocean variability in the Bay of Bengal.

An observed cyclonic eddy associated with boundary current in the northwestern South China Sea

A cyclonic eddy detected in the northwestern South China Sea during the summer of 2011 is investigated using both satellite data and several sets of in situ observations including cruise measurements and a mooring line. The eddy was generated to the west of the Zhongsha Islands in early June and then propagated northwestward. In July and August, when the cyclonic gyre originating from the offshore jet recirculation east of Vietnam matured, the eddy was absorbed into the gyre and strengthened by it. The eddy regulated the thermohaline characteristics and the currents of the entire water column. Along-slope boundary currents (toward the northeast in summer) were completely reversed from the surface to about 1300 m below. The thermohaline in deep water (660–950 m) showed a significant response to the presence of the eddy, with the isotherms and isohalines rising up to 100 m. The recurrence of the phenomenon is further explored by a statistical analysis of satellite observations. Results suggest the presence of a cyclonic eddy and abnormal offshore jets are closely associated with the El Nino Southern Oscillation events.

CYCLONE MODELS FOR A SUBMERGED BREAKWATER

Kahului Harbor, located on the north shore of Maui, Hawaii, is approached by waves from the northwest in winter and northeast in summer. Wave energy entering the harbor during large swell events has repeatedly caused damage to existing protective structures and operations. As a result, a 706-meter long breakwater on the west was constructed to provide additional tranquility inside the harbor. A breakwater on the east with an 843-meter length was constructed to protect against waves approaching from north and northeast. However, strong wave energy still damages the harbor through the 12-meter deep and 183-meter wide entrance channel. Consequently, a submerged breakwater could be constructed in order to mitigate the wave energy that continues to damage the pier. The objective of making these models is to determine the most appropriate construction approach for the project based on construction duration and related variable costs. The study also aims to see if the project can be completed within a 5-month window during calm water. Two construction approaches were proposed—(1) using one construction crew per geotextile grid, and (2) using multiple crews per geotextile grid. Sensitivity analyses were performed on both proposed construction approaches by adjusting the number of laborers hired. This report provides the proposed geotextile submerged breakwater details based on construction plans viewed through the simulation models using EZStrobe.

A decadal shift of summer surface air temperature over Northeast Asia around the mid-1990s

This study identifies a decadal shift of summer surface air temperature (SAT) over Northeast Asia, including southeastern parts of Russia, Mongolia and northern China, around the mid-1990s. The results suggest that the SAT over the Northeast Asia experienced a significant warming after 1994 relative to that before 1993. This decadal shift also extends to northern China, and leads to a warmer summer over Northeast China and North China after the mid-1990s. The decadal warming over Northeast Asia is found to concur with the enhancement of South China rainfall around the mid-1990s. On the one hand, both the Northeast Asian SAT and South China rainfall exhibit this mid-1990s decadal shift only in summer, but not in other seasons. On the other hand, both the Northeast Asian SAT and South China rainfall exhibit this mid-1990s decadal shift not only in the summer seasonal mean, but also in each month of summer (June, July and August). Furthermore, the decadal warming is found to result from an anticyclonic anomaly over Northeast Asia, which can be interpreted as the response to the increased precipitation over South China, according to previous numerical results. Thus, we conclude that the warming shift of summer Northeast Asian SAT around the mid-1990s was a remote response to the increased precipitation over South China.

Tell me, mate, what were emus like?

Tell me, mate, what were emus like?

Seasonal-to-interannual variability of chlorophyll in central western South China Sea extracted from SeaWiFS

Using 10-year (January 1998–October 2007) dataset of Sea-viewing Wide Field-of-view Sensor (SeaWiFS), we extracted the dominant spatial patterns and temporal variations of the chlorophyll distribution in the central western South China Sea (SCS) through Empirical Orthogonal Function (EOF) analysis. The results show that the first EOF mode is characterized by a high chlorophyll concentration zone along the Vietnam coast. We found two peaks in summer (July–August) and in winter (December), respectively, in normal years. The second EOF mode is characterized by a jet-shaped tongue of high chlorophyll concentration extending seaward to the northeast in summer (July–August). To investigate the interannual variability of the chlorophyll concentration, we extracted the first non-seasonal (annual cycle removed) EOF mode, which shows high spatial variability off the southeast Vietnam coast. Both spatial pattern and time coefficients correspond well with those of sea surface temperature mode, and are closely correlated to ENSO events, with a lag of 7 months.

Improving the Northeast Asian Monsoon Simulation: Remote Impact of Tropical Heating Bias Correction

Abstract This study investigates the role of model tropical diabatic heating error on the boreal summer northeast Asian monsoon (NEAM) simulation given by a general circulation model (GCM). A numerical experiment is carried out in which the GCM diabatic heating is adjusted toward more realistic values in the tropics. It is found that the seasonal mean NEAM circulation and rainfall are improved in the GCM. This can be attributed to the reduced positive heating bias in the western Pacific Ocean around 10°–15°N in the model, which in turn leads to better-simulated low-level southerly winds over eastern Asia and more moisture supply to the NEAM region. The GCM’s ability in capturing the year-to-year variation of NEAM rainfall is also markedly improved in the experiment. These results show that the diabatic heating error over the western Pacific can be one reason for poor NEAM simulations in GCMs. The authors also suggest a simple method to reduce model heating biases that can be readily applied to dynamical seasonal prediction systems.

A Mechanism for the Interannual Variation of Summer Northeast Asian Blocking High

AbstractBased on the spatial spectral functions describing the atmospheric circulation variation retrieved with observational data, the mechanism for the interannual variation of summer Northeast Asian Blocking High were studied with improved high truncated spectral model. The results showed that when the external thermal forcing distributes as El Niño pattern, there are wave‐wave interaction of wave 2 in zonal direction and wave‐mean flow interactions between wave 2 and wave 3 in meridianal direction and mean flow of wave 1 in meridianal direction. Under such case, there is positive abnormity over Northeast Asia on 500 hPa geopotential height field, which provides advantage atmospheric circulation background for the frequently occurring of Northeast Asia Blocking High during summer. When the external thermal forcing distributes as La Niña pattern, there exist wave‐wave interaction between wave 1 in zonal direction and wave‐mean flow interactions between wave 2 and wave 4 in meridianal direction and mean flow of wave 2 in meridianal direction. Under such case, there is negative abnormity over Northeast Asia on 500hPa geopotential height field, which restrains the occurring of Northeast Asia Blocking High during summer.

Effects of Reduced Yangtze River Discharge on the Circulation of Surrounding Seas

A regional model of the western Pacific Ocean with 1/6o resolution is used to investigate possible effects of reduced Yangtze River discharge on the circulation of surrounding seas. To the extent of data availability, the model is mostly driven by monthly climatological winds and inflows/outflows through open-ocean boundaries. With climatological discharge rate, the Yangtze River plume disperses to the northeast in summer but follows the China Coastal Current (CCC) to the south in winter. While a substantial amount of the summer plume is retained in the southern Yellow Sea and northern East China Sea until the arrival of winter northerly monsoon, the winter Yangtze River discharge is able to escape freely to the south through advection by the CCC. The source water of the CCC is mainly comprised of winter discharge from Yangtze River, remnants of Yangtze River plume water retained in areas northeast of the river mouth from the preceding summer, Yellow Sea water and even some of the Bohai water. The effect of reduced Yangtze River discharge is highly asymmetric between summer and winter. Summer reduction produces an expansive, positive salinity anomaly northeast of the Yangtze River mouth. The response is rather swift and directly proportional to the reduction of freshwater supply. Winter reduction of freshwater discharge from the Yangtze River leads to higher salinity in the CCC south of the river mouth. The winter insensitivity of the CCC to reduced Yangtze outflow arises because the CCC is fed by multiple sources, some of which are not related to winter discharge from Yangtze River. In the highly unlikely event that the Yangtze River discharge is terminated for multiple years, the source water of the CCC will be dominated by the Yellow Sea and even Bohai waters.

The Role of Longwave Radiation and Boundary Layer Thermodynamics in Forcing Tropical Surface Winds*

This paper reveals major deficiencies of the existing intermediate climate models for tropical surface winds and elaborates the important roles of cloud-longwave radiational forcing and boundary layer thermodynamics in driving the tropical surface winds. The heat sink associated with the cloud-longwave radiation is demonstrated as an important driving force for boreal summer northeast trades and Indian Ocean southwest monsoons. Over the western North Pacific and Atlantic Oceans, low cloudiness and high sea surface temperature enhance longwave radiation cooling, strengthening subtropical high and associated trades. On the other hand, in the regions of heavy rainfall over South Asia, reduced cloud-longwave radiation cooling enhances monsoon trough and associated southwest monsoons. The boundary layer thermodynamic processes, primarily both the surface heat fluxes and the vertical temperature advection, are shown to be critical for a realistic simulation of the intertropical convergence zone, the equatorial surface winds, and associated divergence field. To successfully simulate the tropical surface winds, it is essential for intermediate models to adequately describe the feedback of the boundary layer frictional convergence to convective heat source, cloud-longwave radiation forcing, boundary layer temperature gradient forcing, and their interactions. The capability and limitations of the intermediate tropical climate model in reproducing both climatology and interannual variations are discussed.