This study focuses on the climatic impacts of the Atlantic Multidecadal Oscillation (AMO) as a mode of internal vari- ability. Given the difficulties involved in excluding the effects of external forcing from intern...This study focuses on the climatic impacts of the Atlantic Multidecadal Oscillation (AMO) as a mode of internal vari- ability. Given the difficulties involved in excluding the effects of external forcing from internal variation, i.e., owing to the short record length of instrumental observations and historical simulations, we assess and compare the AMO and its related climatic impacts both in observations and in the "Pre-industrial" experiments of models participating in CMIP5. First, we evaluate the skill of the 25 CMIP5 models' "Historical" simulations in simulating the observational AMO, and find there is generally a considerable range of skill among them in this regard. Six of the models with higher skill relative to the other models are selected to investigate the AMO-related climate impacts, and it is found that their "Pre-industrial" simulations capture the essential features of the AMO. A positive AMO favors warmer surface temperature around the North Atlantic, and the Atlantic ITCZ shifts northward leading to more rainfall in the Sahel and less rainfall in Brazil. Furthermore, the results confirm the existence of a teleconnection between the AMO and East Asian surface temperature, as well as the late withdrawal of the Indian summer monsoon, during positive AMO phases. These connections could be mainly caused by internal climate variability. Opposite patterns are true for the negative phase of the AMO.展开更多
During June-July 2020,the strongest recorded mei-yu rainfall occurred in the middle and lower reaches of the Yangtze River.The rainfall processes exhibited an obvious quasi-biweekly(biweekly in brief)variability,and t...During June-July 2020,the strongest recorded mei-yu rainfall occurred in the middle and lower reaches of the Yangtze River.The rainfall processes exhibited an obvious quasi-biweekly(biweekly in brief)variability,and there are altogether five cycles.It is found that the biweekly rainfall cycle mainly arises from the collaborative effects of biweekly variabilities from both the tropics and extratropics.As for the tropics,the biweekly meridional march and retreat of the western Pacific subtropical high(WPSH)is particularly evident.As for the extratropics,geopotential height anomalies near Lake Baikal are active.The former is attributed to the intensified biweekly activity of the southwest-northeast oriented EastAsian Pacific wave train(EAP)originating from the tropical western Pacific,while the latter is associated with the biweekly activities of the eastward propagating Eurasia mid-high latitudinal wave train and the westward propagating North Pacific wave train.Why the biweekly activities of these wave trains intensified is further diagnosed from the perspective of thermodynamical forcing and also from the modulation of interannual background on intraseasonal variability.It is found that the strongest recorded convection anchoring over the tropical western Indian Ocean(IO)triggers anomalous descent over the tropical western Pacific,which modulates the biweekly activity of the EAP.Meanwhile,the anomalous diabatic heating over the IO causes changes of the meridional thermodynamic contrast across the IO to the high latitudes,which modulates the extratropical wave trains.A further diagnosis of barotropic kinetic energy conversion suggests that the active occurrence of two extratropical biweekly wave trains is attributed to the increased efficiency of energy conversion from basic flow.The westward propagation of the extratropical North Pacific wave train is attributed to the weakened and northshifted upper-level westerly,which is caused by the SST warmth near the Kuroshio extension.展开更多
We use the Wind Farm Parameterization(WFP) scheme coupled with the Weather Research and Forecasting model under multiple resolution regimes to simulate turbulent wake dynamics generated by a real onshore wind farm and...We use the Wind Farm Parameterization(WFP) scheme coupled with the Weather Research and Forecasting model under multiple resolution regimes to simulate turbulent wake dynamics generated by a real onshore wind farm and their influence at the local meteorological scale. The model outputs are compared with earlier modeling and observation studies. It is found that higher vertical and horizontal resolutions have great impacts on the simulated wake flow dynamics. The corresponding wind speed deficit and turbulent kinetic energy results match well with previous studies. In addition, the effect of horizontal resolution on near-surface meteorology is significantly higher than that of vertical resolution. The wake flow field extends from the start of the wind farm to downstream within 10 km, where the wind speed deficit may exceed 4%. For a height of 150 m or at a distance of about 25 km downstream, the wind speed deficit is around 2%. This indicates that, at a distance of more than 25 km downstream, the impact of the wind turbines can be ignored. Analysis of near-surface meteorology indicates a night and early morning warming near the surface, and increase in near-surface water vapor mixing ratio with decreasing surface sensible and latent heat fluxes. During daytime, a slight cooling near the surface and decrease in the near-surface water vapor mixing ratio with increasing surface sensible and latent heat fluxes is noticed over the wind farm area.展开更多
In previous work, a significant relationship was identified between the meridional displacement of the Asian westerly jet (JMD) and the Silk Road Pattern (SRP) in summer. The present study reveals that this relati...In previous work, a significant relationship was identified between the meridional displacement of the Asian westerly jet (JMD) and the Silk Road Pattern (SRP) in summer. The present study reveals that this relationship is robust in northward JMD years but absent in southward JMD years. In other words, the amplitude of the SRP increases with northward displacement of the jet but shows little change with southward displacement. Further analysis indicates that, in northward JMD years, the Rossby wave source (RWS) anomalies, which are primarily contributed by the planetary vortex stretching, are significantly stronger around the entrance of the Asian jet, i.e., the Mediterranean Sea-Caspian Sea area, with the spatial distribution being consistent with that related to the SRP. By contrast, in southward JMD years, the RWS anomalies are much weaker. Therefore, this study suggests that the RWS plays a crucial role in inducing the asymmetry of the JMD-SRP relationship. The results imply that climate anomalies may be stronger in strongly northward-displaced JMD years due to the concurrence of the JMD and SRP, and thus more attention should be paid to these years.展开更多
Based on ensemble experiments with three atmospheric general circulation models(AGCMs), this study investigates the role of the Atlantic Multidecadal Oscillation(AMO) in shaping the summer nonuniform warming over the ...Based on ensemble experiments with three atmospheric general circulation models(AGCMs), this study investigates the role of the Atlantic Multidecadal Oscillation(AMO) in shaping the summer nonuniform warming over the Eurasian continent since the mid-1990 s. The results validate that the positive-phase AMO can indeed cause nonuniform warming,with predominant amplified warming over Europe–West Asia and Northeast Asia, but with much weaker warming over Central Asia. The underlying mechanism is then diagnosed from the perspective that the boundary forcing modulates the intrinsic atmospheric variability. The results highlight the role of the Silk Road Pattern(SRP), an intrinsic teleconnection pattern across the subtropical Eurasian continent propagating along the Asian jet. The SRP can not only be identified from the AGCM control experiments with the climatological sea surface temperature(SST), but can also be simulated by the AMO-related SST anomaly(SSTA) forcing. Furthermore, diagnostic linear baroclinic model experiments are conducted, and the results suggest that the SRP can be triggered by the AMO-related tropical diabatic heating. The AMO-triggered SRP-like responses feature anticyclonic circulations over Europe–West Asia and Northeast Asia, but cyclonic circulation over Central Asia. These responses cause increased warm advection towards Europe–West Asia and Northeast Asia, reduced precipitation and cloud cover, and then increased downward shortwave radiation. This increased warm advection and increased downward shortwave radiation together cause amplified warming in Europe–West Asia and Northeast Asia. The situation is opposite for Central Asia.展开更多
The role of winter sea-ice in the Labrador Sea as a precursor for precipitation anomalies over southeastern North America and Western Europe in the following spring is investigated. In general terms, as the sea ice in...The role of winter sea-ice in the Labrador Sea as a precursor for precipitation anomalies over southeastern North America and Western Europe in the following spring is investigated. In general terms, as the sea ice increases, the precipitation also increases. In more detail, however, analyses indicate that both the winter sea-ice and the sea surface temperature(SST)anomalies related to increases in winter sea-ice in the Labrador Sea can persist into the following spring. These features play a forcing role in the spring atmosphere, which may be the physical mechanism behind the observational relationship between the winter sea-ice and spring precipitation anomalies. The oceanic forcings in spring include Arctic sea-ice anomalies and SST anomalies in the tropical Pacific and high-latitude North Atlantic. Multi-model Coupled Model Intercomparison Project Phase 5 and Atmospheric Model Intercomparison Project simulation results show that the atmospheric circulation response to the combination of sea-ice and SST is similar to that observed, which suggests that the oceanic forcings are indeed the physical reason for the enhanced spring precipitation. Sensitivity experiments conducted using an atmospheric general circulation model indicate that the increases in precipitation over southeastern North America are mainly attributable to the effect of the SST anomalies, while the increases over Western Europe are mainly due to the sea-ice anomalies. Although model simulations reveal that the SST anomalies play the primary role in the precipitation anomalies over southeastern North America, the observational statistical analyses indicate that the area of sea-ice in the Labrador Sea seems to be the precursor that best predicts the spring precipitation anomaly.展开更多
This study uses linear regression and composite analyses to identify a pronounced asymmetric connection of sea surface temperature(SST)in the Tasman Sea with the two opposite phases of El Ni?o-Southern Oscillation(ENS...This study uses linear regression and composite analyses to identify a pronounced asymmetric connection of sea surface temperature(SST)in the Tasman Sea with the two opposite phases of El Ni?o-Southern Oscillation(ENSO)during austral summer.In El Ni?o years,the SST anomalies(SSTAs)in the Tasman Sea exhibit a dipolar pattern with weak warmth in the northwest and modest cooling in the southeast,while during La Ni?a years the SSTAs exhibit a basin-scale warmth with greater amplitude.Investigations into the underlying mechanism suggest that this asymmetry arises from a mechanism related to oceanic heat transport,specifically the anomalous Ekman meridional heat transport induced by the zonal wind stress anomalies,rather than the surface heat fluxes on the air-sea interface.Further analysis reveals that the asymmetry of oceanic heat transport between El Ni?o and La Ni?a years is driven by the asymmetric atmospheric circulation over the Tasman Sea stimulated by the asymmetric diabatic heating in the tropical Pacific between the two opposite ENSO phases.展开更多
Previous studies have found amplified warming over Europe-West Asia and Northeast Asia in summer since the mid- 1990s relative to elsewhere on the Eurasian continent, but the cause of the amplification in these two re...Previous studies have found amplified warming over Europe-West Asia and Northeast Asia in summer since the mid- 1990s relative to elsewhere on the Eurasian continent, but the cause of the amplification in these two regions remains unclear. In this study, we compared the individual contributions of influential factors for amplified warming over these two regions through a quantitative diagnostic analysis based on CFRAM (climate feedback-response analysis method). The changes in surface air temperature are decomposed into the partial changes due to radiative processes (including CO2 concentration, incident solar radiation at the top of the atmosphere, surface albedo, water vapor content, ozone concentration, and clouds) and non-radiative processes (including surface sensible heat flux, surface latent heat flux, and dynamical processes). Our results suggest that the enhanced warming over these two regions is primarily attributable to changes in the radiative processes, which contributed 0.62 and 0.98 K to the region-averaged warming over Europe-West Asia (1.00 K) and Northeast Asia (1.02 K), respectively. Among the radiative processes, the main drivers were clouds, CO2 concentration, and water vapor content. The cloud term alone contributed to the mean amplitude of warming by 0.40 and 0.85 K in Europe-West Asia and Northeast Asia, respectively. In comparison, the non-radiative processes made a much weaker contribution due to the combined impact of surface sensible heat flux, surface latent heat flux, and dynamical processes, accounting for only 0.38 K for the warming in Europe-West Asia and 0.05 K for the warming in Northeast Asia. The resemblance between the influential factors for the amplified warming in these two separate regions implies a common dynamical origin. Thus, this validates the possibility that they originate from the Silk Road pattern.展开更多
This study compares the impacts of interarmual Arctic sea ice loss and ENSO events on winter haze days m mare- land China through observational analyses and AGCM sensitivity experiments. The results suggest that (1)...This study compares the impacts of interarmual Arctic sea ice loss and ENSO events on winter haze days m mare- land China through observational analyses and AGCM sensitivity experiments. The results suggest that (1) Arctic sea ice loss favors an increase in haze days in central-eastern China; (2) the impact of ENSO is overall contained within southern China, with increased (reduced) haze days during La Nifia (El Nifio) winters; and (3) the impacts from sea ice loss and ENSO are linearly additive. Mechanistically, Arctic sea ice loss causes quasi-barotropic positive height anomalies over the region from northem Europe to the Ural Mountains (Urals in brief) and weak and negative height anomalies over the region from central Asia to northeastem Asia. The former favors intensified frequency of the blocking over the regions from northern Europe to the Urals, whereas the latter favors an even air pressure distribu- tion over Siberia, Mongolia, and East Asia. This large-scale circulation pattern favors more frequent occurrence of calm and steady weather in northern China and, as a consequence, increased occurrence of haze days. In comparison, La Nifia (El Nifio) exerts its influence along a tropical pathway by inducing a cyclonic (anticyclonic) lower-tropo- spheric atmospheric circulation response over the subtropical northwestern Pacific. The northeasterly (southwesterly) anomaly at the northwestern rear of the cyclone (anticyclone) causes reduced (intensified) rainfall over southeastern China, which favors increased (reduced) occurrence of haze days through the rain-washing effect.展开更多
Considering the importance of black carbon (BC), this study began by comparing the 20th century simulation of South Asian summer climate in IPCC CMIP3, based on the scenario of models with and without BC. Generally,...Considering the importance of black carbon (BC), this study began by comparing the 20th century simulation of South Asian summer climate in IPCC CMIP3, based on the scenario of models with and without BC. Generally, the multi-model mean of the models that include BC reproduced the observed climate relatively better than those that did not. Then, the 21st century South Asian summer precipitation was projected based on the IPCC CMIP3 projection simulations. The projected precipitation in the present approach exhibited a considerable difference from the multi- model ensemble mean (MME) of IPCC AR4 projection simulations, and also from the MME of the models that ig- nore the effect of BC. In particular, the present projection exhibited a dry anomaly over the central Indian Peninsula, sandwiched between wet conditions on the southern and northern sides of Pakistan and India, rather than homogen- eous wet conditions as seen in the MME of IPCC AR4. Thus, the spatial pattern of South Asian summer rainfall in the future may be more complicated than previously thought.展开更多
基金jointly supported by the National Natural Science Foundation of China(Grant No.41421004)the National Key Basic Research Development Program of China(Grant No.2016YFA0601802 and 2015CB453202)the National Natural Science Foundation of China(Grant Nos.41375085)
文摘This study focuses on the climatic impacts of the Atlantic Multidecadal Oscillation (AMO) as a mode of internal vari- ability. Given the difficulties involved in excluding the effects of external forcing from internal variation, i.e., owing to the short record length of instrumental observations and historical simulations, we assess and compare the AMO and its related climatic impacts both in observations and in the "Pre-industrial" experiments of models participating in CMIP5. First, we evaluate the skill of the 25 CMIP5 models' "Historical" simulations in simulating the observational AMO, and find there is generally a considerable range of skill among them in this regard. Six of the models with higher skill relative to the other models are selected to investigate the AMO-related climate impacts, and it is found that their "Pre-industrial" simulations capture the essential features of the AMO. A positive AMO favors warmer surface temperature around the North Atlantic, and the Atlantic ITCZ shifts northward leading to more rainfall in the Sahel and less rainfall in Brazil. Furthermore, the results confirm the existence of a teleconnection between the AMO and East Asian surface temperature, as well as the late withdrawal of the Indian summer monsoon, during positive AMO phases. These connections could be mainly caused by internal climate variability. Opposite patterns are true for the negative phase of the AMO.
基金jointly supported by a Strategic Project of the Chinese Academy of Sciences[grant number XDA19070402]the National Natural Science Foundation of China[grant number 41790473]the Post-doctoral Innovation Foundation of Hubei Province。
基金jointly supported by the National Key Research and Development Program of China(Grant No.2018YFA0606403)the National Natural Science Foundation of China(Grant Nos.41731177 and 41790473)。
文摘During June-July 2020,the strongest recorded mei-yu rainfall occurred in the middle and lower reaches of the Yangtze River.The rainfall processes exhibited an obvious quasi-biweekly(biweekly in brief)variability,and there are altogether five cycles.It is found that the biweekly rainfall cycle mainly arises from the collaborative effects of biweekly variabilities from both the tropics and extratropics.As for the tropics,the biweekly meridional march and retreat of the western Pacific subtropical high(WPSH)is particularly evident.As for the extratropics,geopotential height anomalies near Lake Baikal are active.The former is attributed to the intensified biweekly activity of the southwest-northeast oriented EastAsian Pacific wave train(EAP)originating from the tropical western Pacific,while the latter is associated with the biweekly activities of the eastward propagating Eurasia mid-high latitudinal wave train and the westward propagating North Pacific wave train.Why the biweekly activities of these wave trains intensified is further diagnosed from the perspective of thermodynamical forcing and also from the modulation of interannual background on intraseasonal variability.It is found that the strongest recorded convection anchoring over the tropical western Indian Ocean(IO)triggers anomalous descent over the tropical western Pacific,which modulates the biweekly activity of the EAP.Meanwhile,the anomalous diabatic heating over the IO causes changes of the meridional thermodynamic contrast across the IO to the high latitudes,which modulates the extratropical wave trains.A further diagnosis of barotropic kinetic energy conversion suggests that the active occurrence of two extratropical biweekly wave trains is attributed to the increased efficiency of energy conversion from basic flow.The westward propagation of the extratropical North Pacific wave train is attributed to the weakened and northshifted upper-level westerly,which is caused by the SST warmth near the Kuroshio extension.
基金the Strategic Project of the Chinese Academy of Sciences[grant number XDA19070402]the National Natural Science Foundation of China[grant number 41790473].
基金the National Key Research and Development Program of China (Grant No.2017YFA0604501)the National Natural Science Foundation of China (Grant No.41475013) for the funding support
文摘We use the Wind Farm Parameterization(WFP) scheme coupled with the Weather Research and Forecasting model under multiple resolution regimes to simulate turbulent wake dynamics generated by a real onshore wind farm and their influence at the local meteorological scale. The model outputs are compared with earlier modeling and observation studies. It is found that higher vertical and horizontal resolutions have great impacts on the simulated wake flow dynamics. The corresponding wind speed deficit and turbulent kinetic energy results match well with previous studies. In addition, the effect of horizontal resolution on near-surface meteorology is significantly higher than that of vertical resolution. The wake flow field extends from the start of the wind farm to downstream within 10 km, where the wind speed deficit may exceed 4%. For a height of 150 m or at a distance of about 25 km downstream, the wind speed deficit is around 2%. This indicates that, at a distance of more than 25 km downstream, the impact of the wind turbines can be ignored. Analysis of near-surface meteorology indicates a night and early morning warming near the surface, and increase in near-surface water vapor mixing ratio with decreasing surface sensible and latent heat fluxes. During daytime, a slight cooling near the surface and decrease in the near-surface water vapor mixing ratio with increasing surface sensible and latent heat fluxes is noticed over the wind farm area.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41320104007, 41421004, and 41731177)
文摘In previous work, a significant relationship was identified between the meridional displacement of the Asian westerly jet (JMD) and the Silk Road Pattern (SRP) in summer. The present study reveals that this relationship is robust in northward JMD years but absent in southward JMD years. In other words, the amplitude of the SRP increases with northward displacement of the jet but shows little change with southward displacement. Further analysis indicates that, in northward JMD years, the Rossby wave source (RWS) anomalies, which are primarily contributed by the planetary vortex stretching, are significantly stronger around the entrance of the Asian jet, i.e., the Mediterranean Sea-Caspian Sea area, with the spatial distribution being consistent with that related to the SRP. By contrast, in southward JMD years, the RWS anomalies are much weaker. Therefore, this study suggests that the RWS plays a crucial role in inducing the asymmetry of the JMD-SRP relationship. The results imply that climate anomalies may be stronger in strongly northward-displaced JMD years due to the concurrence of the JMD and SRP, and thus more attention should be paid to these years.
基金supported by the National Key Research and Development Program of Ministry of Science and Technology of China (Grant 2018YFA0606403 and 2015CB453202)
文摘Based on ensemble experiments with three atmospheric general circulation models(AGCMs), this study investigates the role of the Atlantic Multidecadal Oscillation(AMO) in shaping the summer nonuniform warming over the Eurasian continent since the mid-1990 s. The results validate that the positive-phase AMO can indeed cause nonuniform warming,with predominant amplified warming over Europe–West Asia and Northeast Asia, but with much weaker warming over Central Asia. The underlying mechanism is then diagnosed from the perspective that the boundary forcing modulates the intrinsic atmospheric variability. The results highlight the role of the Silk Road Pattern(SRP), an intrinsic teleconnection pattern across the subtropical Eurasian continent propagating along the Asian jet. The SRP can not only be identified from the AGCM control experiments with the climatological sea surface temperature(SST), but can also be simulated by the AMO-related SST anomaly(SSTA) forcing. Furthermore, diagnostic linear baroclinic model experiments are conducted, and the results suggest that the SRP can be triggered by the AMO-related tropical diabatic heating. The AMO-triggered SRP-like responses feature anticyclonic circulations over Europe–West Asia and Northeast Asia, but cyclonic circulation over Central Asia. These responses cause increased warm advection towards Europe–West Asia and Northeast Asia, reduced precipitation and cloud cover, and then increased downward shortwave radiation. This increased warm advection and increased downward shortwave radiation together cause amplified warming in Europe–West Asia and Northeast Asia. The situation is opposite for Central Asia.
基金supported by the Natural Science Foundation of China (Grant Nos.41305064 and 41375085)a strategic project of the Chinese Academy of Sciences (Grant No.XDA11010401)the China Scholarship Council
文摘The role of winter sea-ice in the Labrador Sea as a precursor for precipitation anomalies over southeastern North America and Western Europe in the following spring is investigated. In general terms, as the sea ice increases, the precipitation also increases. In more detail, however, analyses indicate that both the winter sea-ice and the sea surface temperature(SST)anomalies related to increases in winter sea-ice in the Labrador Sea can persist into the following spring. These features play a forcing role in the spring atmosphere, which may be the physical mechanism behind the observational relationship between the winter sea-ice and spring precipitation anomalies. The oceanic forcings in spring include Arctic sea-ice anomalies and SST anomalies in the tropical Pacific and high-latitude North Atlantic. Multi-model Coupled Model Intercomparison Project Phase 5 and Atmospheric Model Intercomparison Project simulation results show that the atmospheric circulation response to the combination of sea-ice and SST is similar to that observed, which suggests that the oceanic forcings are indeed the physical reason for the enhanced spring precipitation. Sensitivity experiments conducted using an atmospheric general circulation model indicate that the increases in precipitation over southeastern North America are mainly attributable to the effect of the SST anomalies, while the increases over Western Europe are mainly due to the sea-ice anomalies. Although model simulations reveal that the SST anomalies play the primary role in the precipitation anomalies over southeastern North America, the observational statistical analyses indicate that the area of sea-ice in the Labrador Sea seems to be the precursor that best predicts the spring precipitation anomaly.
基金jointly supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA19070402)the National Natural Science Foundation of China(Grant Nos.41790473 and 41731177)。
文摘This study uses linear regression and composite analyses to identify a pronounced asymmetric connection of sea surface temperature(SST)in the Tasman Sea with the two opposite phases of El Ni?o-Southern Oscillation(ENSO)during austral summer.In El Ni?o years,the SST anomalies(SSTAs)in the Tasman Sea exhibit a dipolar pattern with weak warmth in the northwest and modest cooling in the southeast,while during La Ni?a years the SSTAs exhibit a basin-scale warmth with greater amplitude.Investigations into the underlying mechanism suggest that this asymmetry arises from a mechanism related to oceanic heat transport,specifically the anomalous Ekman meridional heat transport induced by the zonal wind stress anomalies,rather than the surface heat fluxes on the air-sea interface.Further analysis reveals that the asymmetry of oceanic heat transport between El Ni?o and La Ni?a years is driven by the asymmetric atmospheric circulation over the Tasman Sea stimulated by the asymmetric diabatic heating in the tropical Pacific between the two opposite ENSO phases.
基金jointly supported by the National Natural Science Foundation of China [grant numbers 41790473 and41421004]the Strategic Priority Research Program of the Chinese Academy of Sciences [grant number XDA19070402]
基金supported by the National Key Research and Development Program of China(Grant Nos.2018YFA0606403 and 2015CB453202)the National Natural Science Foundation of China(Grant Nos.41790473 and 41421004)
文摘Previous studies have found amplified warming over Europe-West Asia and Northeast Asia in summer since the mid- 1990s relative to elsewhere on the Eurasian continent, but the cause of the amplification in these two regions remains unclear. In this study, we compared the individual contributions of influential factors for amplified warming over these two regions through a quantitative diagnostic analysis based on CFRAM (climate feedback-response analysis method). The changes in surface air temperature are decomposed into the partial changes due to radiative processes (including CO2 concentration, incident solar radiation at the top of the atmosphere, surface albedo, water vapor content, ozone concentration, and clouds) and non-radiative processes (including surface sensible heat flux, surface latent heat flux, and dynamical processes). Our results suggest that the enhanced warming over these two regions is primarily attributable to changes in the radiative processes, which contributed 0.62 and 0.98 K to the region-averaged warming over Europe-West Asia (1.00 K) and Northeast Asia (1.02 K), respectively. Among the radiative processes, the main drivers were clouds, CO2 concentration, and water vapor content. The cloud term alone contributed to the mean amplitude of warming by 0.40 and 0.85 K in Europe-West Asia and Northeast Asia, respectively. In comparison, the non-radiative processes made a much weaker contribution due to the combined impact of surface sensible heat flux, surface latent heat flux, and dynamical processes, accounting for only 0.38 K for the warming in Europe-West Asia and 0.05 K for the warming in Northeast Asia. The resemblance between the influential factors for the amplified warming in these two separate regions implies a common dynamical origin. Thus, this validates the possibility that they originate from the Silk Road pattern.
基金Supported by the Strategic Project of the Chinese Academy of Sciences(XDA11010401)China Meteorological Administration Special Public Welfare Research Fund(GYHY201306026)National(Key) Basic Research and Development(973)Program of China(2015CB453202 and 2016YFA0601802)
文摘This study compares the impacts of interarmual Arctic sea ice loss and ENSO events on winter haze days m mare- land China through observational analyses and AGCM sensitivity experiments. The results suggest that (1) Arctic sea ice loss favors an increase in haze days in central-eastern China; (2) the impact of ENSO is overall contained within southern China, with increased (reduced) haze days during La Nifia (El Nifio) winters; and (3) the impacts from sea ice loss and ENSO are linearly additive. Mechanistically, Arctic sea ice loss causes quasi-barotropic positive height anomalies over the region from northem Europe to the Ural Mountains (Urals in brief) and weak and negative height anomalies over the region from central Asia to northeastem Asia. The former favors intensified frequency of the blocking over the regions from northern Europe to the Urals, whereas the latter favors an even air pressure distribu- tion over Siberia, Mongolia, and East Asia. This large-scale circulation pattern favors more frequent occurrence of calm and steady weather in northern China and, as a consequence, increased occurrence of haze days. In comparison, La Nifia (El Nifio) exerts its influence along a tropical pathway by inducing a cyclonic (anticyclonic) lower-tropo- spheric atmospheric circulation response over the subtropical northwestern Pacific. The northeasterly (southwesterly) anomaly at the northwestern rear of the cyclone (anticyclone) causes reduced (intensified) rainfall over southeastern China, which favors increased (reduced) occurrence of haze days through the rain-washing effect.
基金Supported by the National(Key) Basic Research and Development(973) Program of China(2015CB453202 and 2016YFA0601802)National Natural Science Foundation of China(41421004,41528502,and 41375085)
文摘Considering the importance of black carbon (BC), this study began by comparing the 20th century simulation of South Asian summer climate in IPCC CMIP3, based on the scenario of models with and without BC. Generally, the multi-model mean of the models that include BC reproduced the observed climate relatively better than those that did not. Then, the 21st century South Asian summer precipitation was projected based on the IPCC CMIP3 projection simulations. The projected precipitation in the present approach exhibited a considerable difference from the multi- model ensemble mean (MME) of IPCC AR4 projection simulations, and also from the MME of the models that ig- nore the effect of BC. In particular, the present projection exhibited a dry anomaly over the central Indian Peninsula, sandwiched between wet conditions on the southern and northern sides of Pakistan and India, rather than homogen- eous wet conditions as seen in the MME of IPCC AR4. Thus, the spatial pattern of South Asian summer rainfall in the future may be more complicated than previously thought.