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Abstract
Consistency and discrepancy of air–sea latent and sensible heat fluxes (LHF and SHF, respectively) in the Southern Ocean for current-day flux products are analyzed from climatology and interannual-to-decadal variability perspectives. Five flux products are examined, including the National Oceanography Centre, Southampton flux dataset version 2 (NOCS2), the National Centers for Environmental Prediction/Department of Energy Global Reanalysis 2 (NCEP-2), the 40-yr European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA-40), the Hamburg Ocean Atmosphere Parameters and Fluxes from Satellite Data version 3 (HOAPS-3), and the objectively analyzed air–sea fluxes (OAFlux).
Comparisons suggest that most datasets show encouraging agreement in the spatial distribution of the annual-mean LHF, the meridional profile of the zonal-averaged LHF, the leading empirical orthogonal function (EOF) mode of the LHF and SHF, and the large-scale response of the LHF and SHF to the Antarctic Oscillation (AAO) and El Niño–Southern Oscillation (ENSO). However, substantial spatiotemporal discrepancies are noteworthy. The largest across-data scatter is found in the central Indian sector of the Antarctic Circumpolar Current (ACC) for the annual-mean LHF, and in the Atlantic and Indian sectors of the ACC for the annual-mean SHF, which is comparable to and even larger than their respective interannual variability. The zonal mean of the SHF varies widely across the datasets in the ACC. There is a large spread in the seasonal cycle for the LHF and SHF among the datasets, particularly in the cold season. The datasets show interannual variability of various amplitudes and decadal trends of different signs. The flux variability of the NOCS2 is substantially different from the other datasets. Possible attributions of the identified discrepancies for these flux products are discussed based on the availability of the input meteorological state variables.
Abstract
Consistency and discrepancy of air–sea latent and sensible heat fluxes (LHF and SHF, respectively) in the Southern Ocean for current-day flux products are analyzed from climatology and interannual-to-decadal variability perspectives. Five flux products are examined, including the National Oceanography Centre, Southampton flux dataset version 2 (NOCS2), the National Centers for Environmental Prediction/Department of Energy Global Reanalysis 2 (NCEP-2), the 40-yr European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA-40), the Hamburg Ocean Atmosphere Parameters and Fluxes from Satellite Data version 3 (HOAPS-3), and the objectively analyzed air–sea fluxes (OAFlux).
Comparisons suggest that most datasets show encouraging agreement in the spatial distribution of the annual-mean LHF, the meridional profile of the zonal-averaged LHF, the leading empirical orthogonal function (EOF) mode of the LHF and SHF, and the large-scale response of the LHF and SHF to the Antarctic Oscillation (AAO) and El Niño–Southern Oscillation (ENSO). However, substantial spatiotemporal discrepancies are noteworthy. The largest across-data scatter is found in the central Indian sector of the Antarctic Circumpolar Current (ACC) for the annual-mean LHF, and in the Atlantic and Indian sectors of the ACC for the annual-mean SHF, which is comparable to and even larger than their respective interannual variability. The zonal mean of the SHF varies widely across the datasets in the ACC. There is a large spread in the seasonal cycle for the LHF and SHF among the datasets, particularly in the cold season. The datasets show interannual variability of various amplitudes and decadal trends of different signs. The flux variability of the NOCS2 is substantially different from the other datasets. Possible attributions of the identified discrepancies for these flux products are discussed based on the availability of the input meteorological state variables.
Linking Phytoplankton Activity in Polynyas and Sulfur Aerosols over Zhongshan Station, East AntarcticaAbstract
Multiple year-round aerosol samplings were conducted from February 2005 to October 2008 at Zhongshan Station, a research base in East Antarctica, to study methanesulfonic acid (MSA) and non-sea-salt sulfate (nss-SO4 2−). The concentrations of atmospheric sulfur species exhibited a seasonal cycle; the maximum and minimum concentrations occurred in austral summer and austral winter, respectively. Significant correlations between chlorophyll a (Chl a) in offshore polynyas and both MSA (r = 0.726, n = 52, and p < 0.01) and nss-SO4 2− (r = 0.724, n = 48, and p < 0.01) were found, indicating that the phytoplankton activity had a crucial effect on the sulfur aerosols. The sea ice dynamics in the polynyas and the variations in the polynya area may indirectly influence the sulfur aerosols in austral spring and summer. In austral winter, the sulfur compounds in the atmosphere are primarily originating in long-range transported by-products from remote regions because nearly no phytoplankton activity occurred in the offshore polynyas.
Abstract
Multiple year-round aerosol samplings were conducted from February 2005 to October 2008 at Zhongshan Station, a research base in East Antarctica, to study methanesulfonic acid (MSA) and non-sea-salt sulfate (nss-SO4 2−). The concentrations of atmospheric sulfur species exhibited a seasonal cycle; the maximum and minimum concentrations occurred in austral summer and austral winter, respectively. Significant correlations between chlorophyll a (Chl a) in offshore polynyas and both MSA (r = 0.726, n = 52, and p < 0.01) and nss-SO4 2− (r = 0.724, n = 48, and p < 0.01) were found, indicating that the phytoplankton activity had a crucial effect on the sulfur aerosols. The sea ice dynamics in the polynyas and the variations in the polynya area may indirectly influence the sulfur aerosols in austral spring and summer. In austral winter, the sulfur compounds in the atmosphere are primarily originating in long-range transported by-products from remote regions because nearly no phytoplankton activity occurred in the offshore polynyas.
Abstract
Although bacteria are an important biological component of aerosol particles, studies of bacterial communities in remote marine aerosol are largely lacking. In this study, aerosol samples were collected over the western Pacific Ocean, the northern Pacific Ocean, the Arctic Ocean, and the Norwegian Sea during the Fifth Chinese National Arctic Research Expedition (CHINARE 5). The diversity and structure of aerosol bacterial communities, based on 454 pyrosequencing, were explored in these samples. The bacterial community in the aerosols collected over the Pacific Ocean was more diverse than over the Norwegian Sea. Both temporal and spatial variations in aerosol bacterial communities were observed based on phylogenetic analysis. These results suggest that the source of air masses shape bacterial communities in aerosol particles over remote marine regions. Aerosols are clearly important for long-range transport of bacteria. Since potential human pathogens (e.g., Streptococcus sp.) were retrieved in this study, further investigation is needed to evaluate the potential for their long-distance migration via aerosol.
Abstract
Although bacteria are an important biological component of aerosol particles, studies of bacterial communities in remote marine aerosol are largely lacking. In this study, aerosol samples were collected over the western Pacific Ocean, the northern Pacific Ocean, the Arctic Ocean, and the Norwegian Sea during the Fifth Chinese National Arctic Research Expedition (CHINARE 5). The diversity and structure of aerosol bacterial communities, based on 454 pyrosequencing, were explored in these samples. The bacterial community in the aerosols collected over the Pacific Ocean was more diverse than over the Norwegian Sea. Both temporal and spatial variations in aerosol bacterial communities were observed based on phylogenetic analysis. These results suggest that the source of air masses shape bacterial communities in aerosol particles over remote marine regions. Aerosols are clearly important for long-range transport of bacteria. Since potential human pathogens (e.g., Streptococcus sp.) were retrieved in this study, further investigation is needed to evaluate the potential for their long-distance migration via aerosol.
Increase in Aerosol Black Carbon in the 2000s over Ny-Ålesund in the SummerAbstract
To investigate the concentrations, sources, and temporal variations of atmospheric black carbon (BC) in the summer Arctic, routine ground-level observations of BC by optical absorption were made in the summer from 2005 to 2008 at the Chinese Arctic “Yellow River” Station (78°55′N, 11°56′E) at Ny-Ålesund on the island of Spitsbergen in the Svalbard Archipelago. Methods of the ensemble empirical-mode decomposition analysis and back-trajectory analysis were employed to assess temporal variation embedded in the BC datasets and airmass transport patterns. The 10th-percentile and median values of BC concentrations were 7.2 and 14.6 ng m−3, respectively, and hourly average BC concentrations ranged from 2.5 to 54.6 ng m−3. A gradual increase was found by 4 ng m−3 a−1. This increase was not seen in the Zeppelin Station and it seemed to contrast with the prevalent conception of generally decreasing BC concentration since 1989 in the Arctic. Factors responsible for this increase such as changes in emissions and atmospheric transport were taken into consideration. The result indicated that BC from local emissions was mostly responsible for the observed increase from 2005 to 2008. BC temporal variation in the summer was controlled by the atmospheric circulation, which presented a significant 6–14-day variation and coherent with 1–3- and 2–5-day and longer cycle variation. Although the atmospheric circulation changes from 2005 to 2008, there was not a marked trend in long-range transportation of BC. This study suggested that local emissions might have significant implication for the regional radiative energy balance at Ny-Ålesund.
Abstract
To investigate the concentrations, sources, and temporal variations of atmospheric black carbon (BC) in the summer Arctic, routine ground-level observations of BC by optical absorption were made in the summer from 2005 to 2008 at the Chinese Arctic “Yellow River” Station (78°55′N, 11°56′E) at Ny-Ålesund on the island of Spitsbergen in the Svalbard Archipelago. Methods of the ensemble empirical-mode decomposition analysis and back-trajectory analysis were employed to assess temporal variation embedded in the BC datasets and airmass transport patterns. The 10th-percentile and median values of BC concentrations were 7.2 and 14.6 ng m−3, respectively, and hourly average BC concentrations ranged from 2.5 to 54.6 ng m−3. A gradual increase was found by 4 ng m−3 a−1. This increase was not seen in the Zeppelin Station and it seemed to contrast with the prevalent conception of generally decreasing BC concentration since 1989 in the Arctic. Factors responsible for this increase such as changes in emissions and atmospheric transport were taken into consideration. The result indicated that BC from local emissions was mostly responsible for the observed increase from 2005 to 2008. BC temporal variation in the summer was controlled by the atmospheric circulation, which presented a significant 6–14-day variation and coherent with 1–3- and 2–5-day and longer cycle variation. Although the atmospheric circulation changes from 2005 to 2008, there was not a marked trend in long-range transportation of BC. This study suggested that local emissions might have significant implication for the regional radiative energy balance at Ny-Ålesund.
Abstract
Fujian Province in southeastern coastal China is a relatively clean region with low emissions, as its high altitude isolates it from the rest of the country. However, the region experienced haze episodes on 3–14 December 2013. The authors performed simulations using the Weather Research and Forecasting Model coupled with chemistry (WRF-Chem) to examine the impacts of meteorological conditions, aerosol radiative feedbacks (ARFs; including aerosol direct and nearly first indirect effect), and internal and external emissions reduction scenarios on particulate matter smaller than 2.5 μm (PM2.5) concentrations. To the best of the authors’ knowledge, this is the first time the WRF-Chem model has been used to study air quality in this region. The model reasonably reproduced the meteorological conditions and PM2.5 concentrations. The analysis demonstrated that the highest-PM2.5 event was associated with a cold surge that promoted the impingement of northern pollutants on the region, and PM2.5 concentrations were sensitive to the emissions from the Yangtze River delta (16.6%) and the North China Plain (12.1%). This suggests that efforts toward coastal air quality improvement require regional cooperation to reduce emissions. Noticeably, ARFs were unlikely to increase PM2.5 concentrations in the coastal region, which was in contrast to the case in northern China. ARFs induced strong clean wind anomalies in the coastal region and also lowered the inland planetary boundary layer, which enhanced the blocking of northern pollutants crossing the high terrain in the north of Fujian Province. This indicates that ARFs tend to weaken the haze intensity in the southeastern coastal region.
Abstract
Fujian Province in southeastern coastal China is a relatively clean region with low emissions, as its high altitude isolates it from the rest of the country. However, the region experienced haze episodes on 3–14 December 2013. The authors performed simulations using the Weather Research and Forecasting Model coupled with chemistry (WRF-Chem) to examine the impacts of meteorological conditions, aerosol radiative feedbacks (ARFs; including aerosol direct and nearly first indirect effect), and internal and external emissions reduction scenarios on particulate matter smaller than 2.5 μm (PM2.5) concentrations. To the best of the authors’ knowledge, this is the first time the WRF-Chem model has been used to study air quality in this region. The model reasonably reproduced the meteorological conditions and PM2.5 concentrations. The analysis demonstrated that the highest-PM2.5 event was associated with a cold surge that promoted the impingement of northern pollutants on the region, and PM2.5 concentrations were sensitive to the emissions from the Yangtze River delta (16.6%) and the North China Plain (12.1%). This suggests that efforts toward coastal air quality improvement require regional cooperation to reduce emissions. Noticeably, ARFs were unlikely to increase PM2.5 concentrations in the coastal region, which was in contrast to the case in northern China. ARFs induced strong clean wind anomalies in the coastal region and also lowered the inland planetary boundary layer, which enhanced the blocking of northern pollutants crossing the high terrain in the north of Fujian Province. This indicates that ARFs tend to weaken the haze intensity in the southeastern coastal region.
