2020 Vol. 37, No. 6
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2020, 37(6): 557-568.
doi: 10.1007/s00376-020-9238-z
Abstract:
Mole fractions of atmospheric CO2 (XCO2) have been continuously measured from October 2014 to March 2016 at the Guangzhou Panyu Atmospheric Composition Site (23.00°N, 113.21°E; 140 m MSL) in the Pearl River Delta (PRD) region using a cavity ring-down spectrometer. Approximately 66.63%, 19.28%, and 14.09% of the observed values were filtered as background, pollutant source, and sink due to biospheric uptake, respectively, by applying a robust local regression procedure. Their corresponding mean values were 424.12 ± 10.12 ppm (×10−6 mol mol−1), 447.83 ± 13.63 ppm, and 408.83 ± 7.75 ppm. The background XCO2 levels were highest in spring and winter, moderate in autumn, and lowest in summer. The diurnal XCO2 was at a minimum from 1400–1600 LST (Local Standard Time) and a maximum at 0500 LST the next day. The increase of XCO2 in spring and summer was mainly associated with polluted air masses from south coastal Vietnam, the South China Sea, and the southeast Pearl River Estuary. With the exception of summer, airflow primarily from marine regions southeast of Taiwan that passed over the Pearl River Estuary had a greater impact on XCO2, suggesting an important potential source region.
Mole fractions of atmospheric CO2 (XCO2) have been continuously measured from October 2014 to March 2016 at the Guangzhou Panyu Atmospheric Composition Site (23.00°N, 113.21°E; 140 m MSL) in the Pearl River Delta (PRD) region using a cavity ring-down spectrometer. Approximately 66.63%, 19.28%, and 14.09% of the observed values were filtered as background, pollutant source, and sink due to biospheric uptake, respectively, by applying a robust local regression procedure. Their corresponding mean values were 424.12 ± 10.12 ppm (×10−6 mol mol−1), 447.83 ± 13.63 ppm, and 408.83 ± 7.75 ppm. The background XCO2 levels were highest in spring and winter, moderate in autumn, and lowest in summer. The diurnal XCO2 was at a minimum from 1400–1600 LST (Local Standard Time) and a maximum at 0500 LST the next day. The increase of XCO2 in spring and summer was mainly associated with polluted air masses from south coastal Vietnam, the South China Sea, and the southeast Pearl River Estuary. With the exception of summer, airflow primarily from marine regions southeast of Taiwan that passed over the Pearl River Estuary had a greater impact on XCO2, suggesting an important potential source region.
2020, 37(6): 569-575.
doi: 10.1007/s00376-020-9241-4
Abstract:
The need for atmospheric carbon dioxide (CO2) reduction in the context of global warming is widely acknowledged by the global scientific community. Fossil fuel CO2 (CO2ff) emissions occur mainly in cities, and can be monitored directly with radiocarbon (14C). In this research, annual plants [Setaria viridis (L.) Beauv.] were collected from 26 sites in 2013 and 2014 in the central urban district of Xi'an City. The Δ14C content of the samples were analyzed using a 3 MV Accelerator Mass Spectrometer, and CO2ff concentrations were calculated based on mass balance equations. The results showed that the CO2ff mixing ratio ranged from 15.9 to 25.0 ppm (part per million, equivalent to μmol mol−1), with an average of 20.5 ppm in 2013. The range of measured values became larger in 2014, from 13.9 ppm to 33.1 ppm, with an average of 23.5 ppm. The differences among the average CO2ff concentrations between the central area and outer urban areas were not statistically significant. Although the year-to-year variation of the CO2ff concentration was significant (P < 0.01), there was a distinctly low CO2ff value observed in the northeast corner of the city. CO2ff emissions from vehicle exhaust and residential sources appeared to be more significant than two thermal power plants, according to our observed CO2ff spatial distribution. The variation of pollution source transport recorded in our observations was likely controlled by southwesterly winds. These results could assist in the optimal placement of regional CO2 monitoring stations, and benefit the local government in the implementation of efficient carbon emission reduction measures.
The need for atmospheric carbon dioxide (CO2) reduction in the context of global warming is widely acknowledged by the global scientific community. Fossil fuel CO2 (CO2ff) emissions occur mainly in cities, and can be monitored directly with radiocarbon (14C). In this research, annual plants [Setaria viridis (L.) Beauv.] were collected from 26 sites in 2013 and 2014 in the central urban district of Xi'an City. The Δ14C content of the samples were analyzed using a 3 MV Accelerator Mass Spectrometer, and CO2ff concentrations were calculated based on mass balance equations. The results showed that the CO2ff mixing ratio ranged from 15.9 to 25.0 ppm (part per million, equivalent to μmol mol−1), with an average of 20.5 ppm in 2013. The range of measured values became larger in 2014, from 13.9 ppm to 33.1 ppm, with an average of 23.5 ppm. The differences among the average CO2ff concentrations between the central area and outer urban areas were not statistically significant. Although the year-to-year variation of the CO2ff concentration was significant (P < 0.01), there was a distinctly low CO2ff value observed in the northeast corner of the city. CO2ff emissions from vehicle exhaust and residential sources appeared to be more significant than two thermal power plants, according to our observed CO2ff spatial distribution. The variation of pollution source transport recorded in our observations was likely controlled by southwesterly winds. These results could assist in the optimal placement of regional CO2 monitoring stations, and benefit the local government in the implementation of efficient carbon emission reduction measures.
2020, 37(6): 576-585.
doi: 10.1007/s00376-020-9242-3
Abstract:
Hydrofluorocarbons (HFCs) have been widely used in China as substitutes for ozone-depleting substances, the production and use of which are being phased out under the Montreal Protocol. China is a major consumer of HFCs around the world, with its HFC emissions in CO2-equivalent contributing to about 18% of the global emissions for the period 2012–16. Three methods are widely used to estimate the emissions of HFCs—namely, the bottom-up method, top-down method and tracer ratio method. In this study, the tracer ratio method was adopted to estimate HFC emissions in the Yangtze River Delta (YRD), using CO as a tracer. The YRD region might make a significant contribution to Chinese totals owing to its rapid economic growth. Weekly flask measurements for ten HFCs (HFC-23, HFC-32, HFC-125, HFC-134a, HFC-143a, HFC-152a, HFC-227ea, HFC-236fa, HFC-245fa and HFC-365mfc) were conducted at Lin’an Regional Background Station in the YRD over the period 2012–16, and the HFC emissions were 2.4±1.4 Gg yr−1 for HFC-23, 2.8±1.2 Gg yr−1 for HFC-32, 2.2±1.2 Gg yr−1 for HFC-125, 4.8±4.8 Gg yr−1 for HFC-134a, 0.9±0.6 Gg yr−1 for HFC-152a, 0.3±0.3 Gg yr−1 for HFC-227ea and 0.3±0.2 Gg yr−1 for HFC-245fa. The YRD total HFC emissions reached 53 Gg CO2-e yr−1, contributing 34% of the national total. The per capita HFC CO2-equivalent emissions rate was 240 kg yr−1, while the values of per unit area emissions and per million GDP emissions reached 150 Mg km−2 yr−1 and 3500 kg yr−1 (million CNY GDP)−1, which were much higher than national or global levels.
Hydrofluorocarbons (HFCs) have been widely used in China as substitutes for ozone-depleting substances, the production and use of which are being phased out under the Montreal Protocol. China is a major consumer of HFCs around the world, with its HFC emissions in CO2-equivalent contributing to about 18% of the global emissions for the period 2012–16. Three methods are widely used to estimate the emissions of HFCs—namely, the bottom-up method, top-down method and tracer ratio method. In this study, the tracer ratio method was adopted to estimate HFC emissions in the Yangtze River Delta (YRD), using CO as a tracer. The YRD region might make a significant contribution to Chinese totals owing to its rapid economic growth. Weekly flask measurements for ten HFCs (HFC-23, HFC-32, HFC-125, HFC-134a, HFC-143a, HFC-152a, HFC-227ea, HFC-236fa, HFC-245fa and HFC-365mfc) were conducted at Lin’an Regional Background Station in the YRD over the period 2012–16, and the HFC emissions were 2.4±1.4 Gg yr−1 for HFC-23, 2.8±1.2 Gg yr−1 for HFC-32, 2.2±1.2 Gg yr−1 for HFC-125, 4.8±4.8 Gg yr−1 for HFC-134a, 0.9±0.6 Gg yr−1 for HFC-152a, 0.3±0.3 Gg yr−1 for HFC-227ea and 0.3±0.2 Gg yr−1 for HFC-245fa. The YRD total HFC emissions reached 53 Gg CO2-e yr−1, contributing 34% of the national total. The per capita HFC CO2-equivalent emissions rate was 240 kg yr−1, while the values of per unit area emissions and per million GDP emissions reached 150 Mg km−2 yr−1 and 3500 kg yr−1 (million CNY GDP)−1, which were much higher than national or global levels.
2020, 37(6): 586-596.
doi: 10.1007/s00376-020-9217-4
Abstract:
Ozone (O3) fluxes were measured over a maize field using the eddy covariance (EC) technique and gradient methods. The main objective was to evaluate the performance of the gradient methods for measuring the O3 flux by comparing them with the EC O3 flux. In this study, turbulent exchange coefficients (K) calculated with three methods were compared. These methods were the aerodynamic gradient (AG) method (in which K is calculated by using wind speed and temperature gradients), the aerodynamic gradient combined with EC (AGEC) method, in which the friction velocity and other variables are based on EC measurements, and the modified Bowen ratio using the EC sensible heat flux and temperature gradient (MBR) method. Meanwhile, the effects of the measurement and calculation methods of the O3 concentration gradient were analyzed. The results showed that: (1) on average, the transfer coefficient computed by the MBR method was 40% lower, and the coefficient determined with the AG method was 25% higher, than that determined with the AGEC method. (2) The gradient method’s O3 fluxes with the MBR, AGEC, and AG methods were 30.4% lower, 11.7% higher, and 45.6% higher than the EC O3 flux, respectively. (3) The effect of asynchronous O3 concentration measurements on the O3 gradient must be eliminated when using one analyzer to cyclically measure two-level O3 concentrations. The accuracy of gradient methods for O3 flux is related to the exchange coefficient calculation method, and its precision mainly depends on the quality of the O3 gradient.
Ozone (O3) fluxes were measured over a maize field using the eddy covariance (EC) technique and gradient methods. The main objective was to evaluate the performance of the gradient methods for measuring the O3 flux by comparing them with the EC O3 flux. In this study, turbulent exchange coefficients (K) calculated with three methods were compared. These methods were the aerodynamic gradient (AG) method (in which K is calculated by using wind speed and temperature gradients), the aerodynamic gradient combined with EC (AGEC) method, in which the friction velocity and other variables are based on EC measurements, and the modified Bowen ratio using the EC sensible heat flux and temperature gradient (MBR) method. Meanwhile, the effects of the measurement and calculation methods of the O3 concentration gradient were analyzed. The results showed that: (1) on average, the transfer coefficient computed by the MBR method was 40% lower, and the coefficient determined with the AG method was 25% higher, than that determined with the AGEC method. (2) The gradient method’s O3 fluxes with the MBR, AGEC, and AG methods were 30.4% lower, 11.7% higher, and 45.6% higher than the EC O3 flux, respectively. (3) The effect of asynchronous O3 concentration measurements on the O3 gradient must be eliminated when using one analyzer to cyclically measure two-level O3 concentrations. The accuracy of gradient methods for O3 flux is related to the exchange coefficient calculation method, and its precision mainly depends on the quality of the O3 gradient.
2020, 37(6): 597-607.
doi: 10.1007/s00376-020-9233-4
Abstract:
Methane (CH4) is one of the most important greenhouse gases in the atmosphere, making it worthwhile to study its temporal and vertical distributions in source areas, e.g., North China. For this purpose, a ground-based high-resolution Fourier transform infrared spectrometer (FTIR), the Bruker IFS 125HR, along with an in-situ instrument, the Picarro G2301, were deployed in Xianghe County (39.8°N,117.0°E), Hebei Province, China. Data have been recorded since June 2018. For the FTIR measurements, we used two observation modes to retrieve the mole fraction of CH4: the Total Carbon Column Observing Network (TCCON) method (retrieval algorithm: GGG2014), and the Network for the Detection of Atmospheric Composition Change (NDACC) method (retrieval algorithm: SFIT4). Combining FTIR with in-situ measurements, we found the temporal and vertical distributions of atmospheric CH4 within three vertical layers (near the ground, in the troposphere, and in the stratosphere), and throughout the whole atmosphere. Regarding the diurnal variation of CH4 near the ground, the concentration at night was higher than during the daytime. Regarding the seasonal variation, CH4 was low in spring and high in summer, for all three vertical layers. In addition, there was a peak of CH4 in winter near the ground, both in the troposphere and the whole atmosphere. We found that variation of CH4 in the tropospheric column was close to that of the in-situ measurements near the ground. Furthermore, the variations of CH4 in the stratospheric column could be influenced by vertical motions, since it was higher in summer and lower in winter.
Methane (CH4) is one of the most important greenhouse gases in the atmosphere, making it worthwhile to study its temporal and vertical distributions in source areas, e.g., North China. For this purpose, a ground-based high-resolution Fourier transform infrared spectrometer (FTIR), the Bruker IFS 125HR, along with an in-situ instrument, the Picarro G2301, were deployed in Xianghe County (39.8°N,117.0°E), Hebei Province, China. Data have been recorded since June 2018. For the FTIR measurements, we used two observation modes to retrieve the mole fraction of CH4: the Total Carbon Column Observing Network (TCCON) method (retrieval algorithm: GGG2014), and the Network for the Detection of Atmospheric Composition Change (NDACC) method (retrieval algorithm: SFIT4). Combining FTIR with in-situ measurements, we found the temporal and vertical distributions of atmospheric CH4 within three vertical layers (near the ground, in the troposphere, and in the stratosphere), and throughout the whole atmosphere. Regarding the diurnal variation of CH4 near the ground, the concentration at night was higher than during the daytime. Regarding the seasonal variation, CH4 was low in spring and high in summer, for all three vertical layers. In addition, there was a peak of CH4 in winter near the ground, both in the troposphere and the whole atmosphere. We found that variation of CH4 in the tropospheric column was close to that of the in-situ measurements near the ground. Furthermore, the variations of CH4 in the stratospheric column could be influenced by vertical motions, since it was higher in summer and lower in winter.
2020, 37(6): 608-616.
doi: 10.1007/s00376-020-9227-2
Abstract:
The balloon-borne Aircore campaign was conducted in Inner Mongolia, China, on June 13 and 14 2018, which detected carbon dioxide (CO2) and carbon monoxide (CO) profiles from surface to 24 km, showing strong positive and negative correlations between 8 km and 10 km on 13 and 14 June, respectively. Backward trajectories, meteorological analyses, and CO2 horizontal distributions were combined to interpret this phenomenon. The results indicated that the source region experienced a stratospheric intrusion and exhibited a large horizontal CO2 gradient; namely, lower CO concentrations corresponded to higher CO2 concentrations and vice versa. The laminar structure with multiple origins resulted in the highly negative correlation between CO2 and CO in the upper troposphere on 14 June. The contribution of stratospheric air mass to the upper troposphere and that of tropospheric air mass to the lower stratosphere were 26.7% and 24.3%, respectively, based on a mass balance approach. Another interesting phenomenon is that CO2 and CO concentrations increased substantially at approximately 8 km on 13 June. An analysis based on the backward trajectory implied that the air mass possibly came from anthropogenic sources. The slope of CO2/CO representing the anthropogenic sources was 87.3 ppm ppm−1. In addition, the CO2 profile showed that there was a large CO2 gradient of 4 ppm km−1 within the boundary layer on 13 June, and this gradient disappeared on 14 June.
The balloon-borne Aircore campaign was conducted in Inner Mongolia, China, on June 13 and 14 2018, which detected carbon dioxide (CO2) and carbon monoxide (CO) profiles from surface to 24 km, showing strong positive and negative correlations between 8 km and 10 km on 13 and 14 June, respectively. Backward trajectories, meteorological analyses, and CO2 horizontal distributions were combined to interpret this phenomenon. The results indicated that the source region experienced a stratospheric intrusion and exhibited a large horizontal CO2 gradient; namely, lower CO concentrations corresponded to higher CO2 concentrations and vice versa. The laminar structure with multiple origins resulted in the highly negative correlation between CO2 and CO in the upper troposphere on 14 June. The contribution of stratospheric air mass to the upper troposphere and that of tropospheric air mass to the lower stratosphere were 26.7% and 24.3%, respectively, based on a mass balance approach. Another interesting phenomenon is that CO2 and CO concentrations increased substantially at approximately 8 km on 13 June. An analysis based on the backward trajectory implied that the air mass possibly came from anthropogenic sources. The slope of CO2/CO representing the anthropogenic sources was 87.3 ppm ppm−1. In addition, the CO2 profile showed that there was a large CO2 gradient of 4 ppm km−1 within the boundary layer on 13 June, and this gradient disappeared on 14 June.
2020, 37(6): 617-633.
doi: 10.1007/s00376-020-9058-1
Abstract:
The importance of a national or regional network of meteorological stations for improving weather predictions has been recognized for many years. Ground-based automatic weather stations typically observe weather at a height of 2−10 m above ground level (AGL); however, these observations may have two major shortcomings. Large portions of data cannot be used if the station height is significantly lower than the model surface level; and such observations may contain large representativity errors as near-surface observations are often affected by the local environment, such as nearby buildings and tall trees. With the recent introduction of a significant number of mobile communication towers that are typically over 40 m AGL in China, a campaign has been proposed to use such towers to build a future observing system with an observing height of 40 m. A series of observing system simulation experiments has been conducted to assess the potential utility of such a future observing system as part of a feasibility study. The experiments were conducted using the Weather Research and Forecasting model and its Rapid Update Cycle data assimilation system. The results revealed the possibility of improving weather forecasting by raising present weather stations to a height of 40 m; this would not only enable more observations to pass the terrain check, but should also reduce interpolation errors. Additionally, improvements for temperature, humidity and wind forecasting could be achieved as the accuracy of the initial conditions increases.
The importance of a national or regional network of meteorological stations for improving weather predictions has been recognized for many years. Ground-based automatic weather stations typically observe weather at a height of 2−10 m above ground level (AGL); however, these observations may have two major shortcomings. Large portions of data cannot be used if the station height is significantly lower than the model surface level; and such observations may contain large representativity errors as near-surface observations are often affected by the local environment, such as nearby buildings and tall trees. With the recent introduction of a significant number of mobile communication towers that are typically over 40 m AGL in China, a campaign has been proposed to use such towers to build a future observing system with an observing height of 40 m. A series of observing system simulation experiments has been conducted to assess the potential utility of such a future observing system as part of a feasibility study. The experiments were conducted using the Weather Research and Forecasting model and its Rapid Update Cycle data assimilation system. The results revealed the possibility of improving weather forecasting by raising present weather stations to a height of 40 m; this would not only enable more observations to pass the terrain check, but should also reduce interpolation errors. Additionally, improvements for temperature, humidity and wind forecasting could be achieved as the accuracy of the initial conditions increases.
2020, 37(6): 634-651.
doi: 10.1007/s00376-020-9070-5
Abstract:
In this paper we examine the epochal changes in the frequency of cyclones over the North Indian Ocean during the pre-onset and onset phases of the monsoon. We consider three epochs; namely, the early (1955−74), middle (1975−94) and recent (1995−2014) epochs. It is found that the number of cyclones in the Bay of Bengal (BOB) decreases throughout the three epochs. Over the Arabian Sea (ARB), however, there is a decrease in the early epoch, before then reaching a minimum in the middle epoch followed by an increase in the recent epoch, thus exhibiting epochal variability. Dynamic and thermodynamic parameters along with Genesis Potential Index (GPI) are examined to understand the frequency variation in cyclogenesis over the ARB and BOB. Over the ARB, thermodynamic factors such as mid-level moisture, surface latent heat flux and sensible heat flux, and dynamic parameters such as lower-level convergence and upper-level divergence, are favorable during the early and recent epochs but unfavorable during the middle epoch, and these results are found to be consistent with the observed epochal variability in the frequency of cyclogenesis. However, all these influential parameters are found to have decreased over the BOB during the entire 60-year period.
In this paper we examine the epochal changes in the frequency of cyclones over the North Indian Ocean during the pre-onset and onset phases of the monsoon. We consider three epochs; namely, the early (1955−74), middle (1975−94) and recent (1995−2014) epochs. It is found that the number of cyclones in the Bay of Bengal (BOB) decreases throughout the three epochs. Over the Arabian Sea (ARB), however, there is a decrease in the early epoch, before then reaching a minimum in the middle epoch followed by an increase in the recent epoch, thus exhibiting epochal variability. Dynamic and thermodynamic parameters along with Genesis Potential Index (GPI) are examined to understand the frequency variation in cyclogenesis over the ARB and BOB. Over the ARB, thermodynamic factors such as mid-level moisture, surface latent heat flux and sensible heat flux, and dynamic parameters such as lower-level convergence and upper-level divergence, are favorable during the early and recent epochs but unfavorable during the middle epoch, and these results are found to be consistent with the observed epochal variability in the frequency of cyclogenesis. However, all these influential parameters are found to have decreased over the BOB during the entire 60-year period.
2020, 37(6): 652-661.
doi: 10.1007/s00376-020-9153-3
Abstract:
The profound impact of solar irradiance variations on the decadal variability of Earth’s climate has been investigated by previous studies. However, it remains a challenge to quantify the energetic particle precipitation (EPP) influence on the surface climate, which is an emerging research topic. The solar wind is a source of magnetospheric EPP, and the total energy input from the solar wind into Earth’s magnetosphere (Ein) shows remarkable interdecadal and interannual variability. Based on the new Ein index, this study reveals a significant interannual relationship between the annual mean Ein and Eurasian cold extremes in the subsequent winter. Less frequent cold events are observed over Eurasia (primarily north of 50°N) following the higher-than-normal Ein activity in the previous year, accompanied by more frequent cold events over northern Africa, and vice versa. This response pattern shows great resemblance to the first empirical orthogonal function of the variability of cold extremes over Eurasia, with a spatial correlation coefficient of 0.79. The pronounced intensification of the positive North Atlantic Oscillation events and poleward shift of the North Atlantic storm track associated with the anomalously higher Ein favor the anomalous extreme atmospheric circulation events, and thus less frequent extreme cold temperatures over northern Eurasia on the interannual time scale. It is further hypothesized that the wave−mean flow interaction in the stratosphere and troposphere is favorable for the connection of Ein signals to tropospheric circulation and climate in the following winter.
The profound impact of solar irradiance variations on the decadal variability of Earth’s climate has been investigated by previous studies. However, it remains a challenge to quantify the energetic particle precipitation (EPP) influence on the surface climate, which is an emerging research topic. The solar wind is a source of magnetospheric EPP, and the total energy input from the solar wind into Earth’s magnetosphere (Ein) shows remarkable interdecadal and interannual variability. Based on the new Ein index, this study reveals a significant interannual relationship between the annual mean Ein and Eurasian cold extremes in the subsequent winter. Less frequent cold events are observed over Eurasia (primarily north of 50°N) following the higher-than-normal Ein activity in the previous year, accompanied by more frequent cold events over northern Africa, and vice versa. This response pattern shows great resemblance to the first empirical orthogonal function of the variability of cold extremes over Eurasia, with a spatial correlation coefficient of 0.79. The pronounced intensification of the positive North Atlantic Oscillation events and poleward shift of the North Atlantic storm track associated with the anomalously higher Ein favor the anomalous extreme atmospheric circulation events, and thus less frequent extreme cold temperatures over northern Eurasia on the interannual time scale. It is further hypothesized that the wave−mean flow interaction in the stratosphere and troposphere is favorable for the connection of Ein signals to tropospheric circulation and climate in the following winter.
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