The biases and their sources in monthly turbulent heat fluxes from the Woods Hole Oceanographic Institution (WHOI) analysis, and the National Centers for Environmental Prediction-National Center for Atmospheric Rese...The biases and their sources in monthly turbulent heat fluxes from the Woods Hole Oceanographic Institution (WHOI) analysis, and the National Centers for Environmental Prediction-National Center for Atmospheric Research reanalyses 1 and 2 (NCEPI and NCEP2) are checked in the climatically representative regions in the tropical Atlantic using the fluxes from the Southampton Oceanographic Centre (SOC) and the pilot research moored array in the tropical Atlantic (PIRATA) as references. For the WHOI analysis, the biases in turbulent heat fluxes mainly exist in equatorial regions which are due to the overestimated sea surface temperature and the underestimated 2 m air humidity. For the NCEP2 reanalysis, the maximum biases, about (40±5) W/m^2, exist in southeast and northeast trade wind regions, which are mainly caused by the flux algorithm used because the biases in wind speed and air-sea humidity difference are relatively small. In the equatorial regions, the flux biases in the NCEP2 derived from both flux-related basic variables and algorithm are equally large. Although the estimations of time series trends and air-sea humidity difference of the NCEPI are improved greatly in the NCEP2, the biases of latent heat flux in the NCEP2 are about 20 W/m^2 greater than those from the NCEP1 in the trade wind regions. The result shows that the climatologies and monthly variabilities of the turbulent heat fluxes from the WHOI are more accurate than those from the NCEP1 and NCEP2 in the tropical Atlantic, especially on outside of the equatorial regions.展开更多
Previous studies suggest that spring SST anomalies over the northern tropical Atlantic(NTA) affect the tropical cyclone(TC) activity over the western North Pacific(WNP) in the following summer and fall. The pres...Previous studies suggest that spring SST anomalies over the northern tropical Atlantic(NTA) affect the tropical cyclone(TC) activity over the western North Pacific(WNP) in the following summer and fall. The present study reveals that the connection between spring NTA SST and following summer–fall WNP TC genesis frequency is not stationary. The influence of spring NTA SST on following summer–fall WNP TC genesis frequency is weak and insignificant before, but strong and significant after, the late 1980 s. Before the late 1980 s, the NTA SST anomaly-induced SST anomalies in the tropical central Pacific are weak, and the response of atmospheric circulation over the WNP is not strong. As a result, the connection between spring NTA SST and following summer–fall WNP TC genesis frequency is insignificant in the former period. In contrast,after the late 1980 s, NTA SST anomalies induce pronounced tropical central Pacific SST anomalies through an Atlantic–Pacific teleconnection. Tropical central Pacific SST anomalies further induce favorable conditions for WNP TC genesis,including vertical motion, mid-level relative humidity, and vertical zonal wind shear. Hence, the connection between NTA SST and WNP TC genesis frequency is significant in the recent period. Further analysis shows that the interdecadal change in the connection between spring NTA SST and following summer–fall WNP TC genesis frequency may be related to the climatological SST change over the NTA region.展开更多
The mean seasonal variability of turbulent heat fluxes in the tropical Atlantic Ocean is examined using the Woods Hole Oceanographic Institution (WHOI) flux product. The most turbulent heat fluxes occur during winte...The mean seasonal variability of turbulent heat fluxes in the tropical Atlantic Ocean is examined using the Woods Hole Oceanographic Institution (WHOI) flux product. The most turbulent heat fluxes occur during winter seasons in the two hemispheres, whose centers are located at 10° -20°N and 5° 15°S respectively. In climatological ITCZ, the turbulent heat fluxes are the greatest from June to August, and in equatorial cold tongue the turbulent heat fluxes are the greatest from March to May. Seasonal variability of sensible heat flux is smaller than that of latent heat flux and mainly is dominated by the variations of air-sea temperature difference. In the region with larger climatological mean wind speed (air-sea humidity difference), the variations of air-sea humidity difference (wind speed) dominate the variability of latent heat flux. The characteristics of turbulent heat flux yielded from theory analysis and WHOI dataset is consistent in physics which turns out that WHOI' s flux data are pretty reliable in the tropical Atlantic Ocean.展开更多
Early Eocene hyperthermals are geologically short-lived global warming events and represent fundamental perturbations to the global carbon cycle and the Earth’s ecosystem due to massive additions of isotopically ligh...Early Eocene hyperthermals are geologically short-lived global warming events and represent fundamental perturbations to the global carbon cycle and the Earth’s ecosystem due to massive additions of isotopically light carbon to the ocean-atmosphere system.They serve as ancient analogs for understanding how the oceanic carbonate system and surface-ocean ecosystem would respond to ongoing and future climate change.Here,we present a continuous carbonate record across the Eocene Thermal Maximum 2(ETM2 or H1,ca.54.1 Ma)and H2(ca.54 Ma)events from an expanded section at Ocean Drilling Program Site 1258 in tropical Atlantic.The abundant calcareous nannofossils and moderate carbonate content throughout the studied interval suggest this record was deposited above the calcite compensation depth(CCD),but below the lysocline and under the influence of terrestrial dilution.An Earth system model cGENIE is used to simulate the carbon cycle dynamics across the ETM2 and H2 to offer insights on the mechanism of the rapid warming and subsequent recovery in climate and ecosystem.The model suggests moderate changes in ocean pH(0.1–0.2 unit)for the two scenarios,biogenic methane from a rechargeable methane capacitor and organic matter oxidation from thawing of the permafrost.These pH changes are consistent with a recent independent pH estimate across the ETM2 using boron isotopes.The carbon emission flux during the ETM2 is at least an order of magnitude smaller than that during the Paleocene–Eocene Thermal Maximum(PETM)(0.015–0.05 Pg C yr^(-1)vs.0.3–1.7 Pg C yr^(-1)).The comparable pre-and post-event carbonate contents suggest the lysocline did not over deepen following the ETM2 at this tropical Atlantic site,indicating spatial heterogeneity in the carbonate system due to strong dilution influence from terrestrial weathering and riverine discharge at Site 1258.展开更多
Tropical waters show different regional aspects due to specificities in their nutrient biogeochemical cycles, which can affect the carbon system and influence their regional role as sinks or sources of CO<sub>2&...Tropical waters show different regional aspects due to specificities in their nutrient biogeochemical cycles, which can affect the carbon system and influence their regional role as sinks or sources of CO<sub>2</sub>. This study was performed on particular tropical areas that present a different seasonal behaviour related to the carbon cycle observed in the late rainy season (July 2013). Understanding the CO<sub>2</sub> drawdown and outgassing potential in these areas is needed to call attention to more long-term monitoring efforts and protect understudied tropical coastal systems more efficiently. This study is focused on nutrient values, hydrological data, biogeochemical carbon behaviour linked to the carbonate system and includes estimates of CO<sub>2</sub> fluxes in three contrasting areas off the northeastern Brazilian shelf: 1) an urbanised estuary (Recife-REC), 2) a coastal Island (Itamaracá-ITA) and 3) an oceanic archipelago (Fernando de Noronha-FN). In general, REC acted as a source, while ITA and FN as carbon sinks. In ITA, despite the high DIC and Total Alkalinity observed (mean ~2360 μmol·kg<sup>-1</sup>), the sink is associated with an effective cascading of atmospheric CO<sub>2</sub> associated with turbulent shallow waters coupled with biogenic removal of and precipitation of CaCO<sub>3</sub> by coralline algae. FN acted as a sink, linked to minor decreases in Total Alkalinity (mean~2295 μmol·kg<sup>-1</sup>) influenced by ammonium-based primary production, nitrogen fixation and sporadic entrainment of nutrient rich waters in the upper thermocline. More studies in different western tropical Atlantic coastal systems can improve the knowledge of tropical shelf seas and their contribution to the ocean carbon budget under specific regional trophic regimes.展开更多
The Pacific Walker circulation(PWC)was weak in the 20th century,but its strength increased in an interdecadal scale in the late 1990s.Previous studies have suggested that it could be caused by the warming of the tropi...The Pacific Walker circulation(PWC)was weak in the 20th century,but its strength increased in an interdecadal scale in the late 1990s.Previous studies have suggested that it could be caused by the warming of the tropical Atlantic Ocean,or induced by the warming of the tropical Indian Ocean.The tropical Atlantic Ocean would not only directly affect the PWC through the equatorial east Pacific to the west,but also produce an indirect effect to the east through the equatorial west Indian Ocean.Using a coupled general circulation model,we designed a series of tropical Atlantic Heating and Heating_Shut experiments with different heating rates,to detect the mechanism of the impact of tropical Atlantic warming on the PWC.Results show that the tropical Atlantic heating weakens the Atlantic Walker circulation but strengthens the PWC.Diagnostics of multiple physical variables with coherent lowereupper troposphere structure show the responses of the Indian Ocean to the Atlantic heating play a critical role in the strengthening of the PWC.The Atlanticelinked atmosphere over the tropical Indian Ocean exerts a significantly positive heat flux onto the ocean there,greatly warming the tropical Indian Ocean,especially on the west part.This produces strong convectively ascending at the equatorial West Indian Ocean,but descending at the East-central Indian Ocean,corresponding to a‘Walker’circulation and an‘antieWalker’circulation situated at the West and East equatorial Indian Ocean respectively.Meanwhile,the convergence(divergence)of the lower(upper)troposphere over the Indo‒Pacific region is also strengthened.In this way,the tropical Atlantic heating is linked to the PWC through the circulation over the equatorial Indian Ocean.This study serves as a preliminary step to understand the impact of tropical Atlantic warming on the PWC,more Atlantic heating sensitivity studies with multi-model experiments are required to further reveal the linkage of the Pacific and Atlantic.展开更多
This study investigates the mean kinematic characteristics of the tropical Atlantic easterly disturbances in January-March (JFM), April-June (AM J), July-September (JAS) and October-December (OND) from 1968-19...This study investigates the mean kinematic characteristics of the tropical Atlantic easterly disturbances in January-March (JFM), April-June (AM J), July-September (JAS) and October-December (OND) from 1968-1998. For each season, the preferential tracks of these disturbances in the 3--10-day band periods were computed and spatialized, as well as their associated wavelength, velocity and main period, which lies between 3-5 days and between 6-9 days depending on the track and the season. Two main tracks are highlighted over the Atlantic Ocean. During OND and JFM these two tracks are well separated and located in each hemisphere around 15°S and 12.5°N. From AMJ to JAS these tracks migrate northward; in JAS, they merge into one over the northern tropical Atlantic along 17.5°N. The associated wavelength fields exhibit a meridional gradient, with large wavelengths (greater than 4000 km) around the equator, between 5°N and 5°S, and smaller wavelengths outside of this latitude band (between 2500-3500 kin). The phase speed is also found to exhibit poleward decreasing values from 12-6 m s^-1. Over the north Atlantic track, 6-9-day disturbances were found to occur from January to May and approximately from October to December. From June to September, the 3-5-day waves dominate the synoptic activity. Over the south Atlantic track, between May and August the synoptic variability is mainly explained by the 3-5-day disturbances but from January to April and from September to December both 3-5-day waves and 6-9-day waves can occur.展开更多
This study examined the relationship between the boreal spring(April?May) Antarctic Oscillation(AAO) and the North American summer monsoon(NASM)(July?September) for the period of 1979?2008.The results show that these ...This study examined the relationship between the boreal spring(April?May) Antarctic Oscillation(AAO) and the North American summer monsoon(NASM)(July?September) for the period of 1979?2008.The results show that these two systems are closely related.When the spring AAO was stronger than normal,the NASM tended to be weaker,and there was less rainfall over the monsoon region.The opposite NASM situation corresponded to a weaker spring AAO.Further analysis explored the possible mechanism for the delayed impact of the boreal spring AAO on the NASM.It was found that the tropical Atlantic sea surface temperature(SST) plays an important role in the connection between the two phenomena.The variability of the boreal spring AAO can produce anomalous SSTs over the tropical Atlantic.These SST anomalies can persist from spring to summer and can influence the Bermuda High,affecting water vapor transportation to the monsoon region.Through these processes,the boreal spring AAO exerts a significantly delayed impact on the amount of NASM precipitation.Thus,information about the boreal spring AAO is valuable for the prediction of the NASM.展开更多
We investigate the interannual variability of the South Asian summer monsoon(SASM) circulation, which has experienced a significant interdecadal change since 2000. This change is primarily influenced by sea surface ...We investigate the interannual variability of the South Asian summer monsoon(SASM) circulation, which has experienced a significant interdecadal change since 2000. This change is primarily influenced by sea surface temperatures(SSTs)in the tropical Pacific and North Atlantic oceans. During the pre-2000 period examined in this study(1979-99), the SASM is negatively correlated with eastern Pacific SSTs(the canonical ENSO mode) and positively correlated with the negative phase of the North Atlantic SST tripole(NAT). During the post-2000 period(2000-14), the SASM is negatively correlated with central Pacific SSTs and positively correlated with the positive phase of the NAT pattern. The associated Pacific SSTs change from the eastern to central region, leading to the rising(subsiding) branch of the Walker circulation moving westwards to the Maritime Continent in the latter period, which can impact the interannual variability of the SASM through modulating the wind field in the troposphere. In addition to Pacific SSTs, the NAT SSTs can propagate energy from the North Atlantic to the South Asian High(SAH) region through the wave activity flux, and then further impact the SASM via the SAH.Because the SASM is intimately related with precipitation over the Asian region, we briefly discuss the features of the precipitation patterns associated with the SASM during the two periods. The westward shifting Walker circulation leads to the shrinking and weakened anomalous westerlies of the SASM in the lower level, inducing the Maritime Continent rainfall location to move westwards and more moisture to arrive in southern China from the Pacific Ocean in the latter period.展开更多
The intensity of the interannual variability(IIV)of the mean tropical cyclone(TC)genesis latitude over the western North Pacific(WNP)has been weakening significantly since the late 1990 s.It is found that the IIV of t...The intensity of the interannual variability(IIV)of the mean tropical cyclone(TC)genesis latitude over the western North Pacific(WNP)has been weakening significantly since the late 1990 s.It is found that the IIV of the mean TC genesis latitude depends largely on the strength of the out-of-phase relationship between TC genesis numbers in the north(north of 15°N)and south(south of 15°N)of the WNP.A weaker(stronger)north–south TC see-saw has led to a smaller(larger)IIV of the mean TC genesis latitude after(before)the late 1990 s.Different configurations of sea surface temperature(SST)anomalies are found to be responsible for the decadal changes in the north–south TC see-saw and dipole structure.Before the late 1990 s,the joint effect of SST anomalies over the tropical Pacific and tropical North Indian Ocean dominated,rendering the obvious north–south TC see-saw and larger IIV of the mean TC genesis latitude.After the late 1990 s,however,the dominant SST anomalies associated with TC genesis shift to the tropical central Pacific(CP)and tropical North Atlantic Ocean,which have weakened the north–south TC seesaw and reduced the IIV of the mean TC genesis latitude.These observed decadal changes in the configuration of SST anomalies are considered to be closely associated with the shift of the El Ni?o–Southern Oscillation(ENSO)from eastern Pacific(EP)type to the CP type during the recent decades.The results suggest that the increased influences from the tropical Atlantic Ocean have become more important to the variations of TC activity in the WNP during the recent decades.These results may have important implications for assessing the latitudinal distributions of TC-induced hazards.展开更多
El Niño–Southern Oscillation(ENSO)was identified as the dominant predictor for the Indian summer monsoon rainfall(ISMR)in the early 1900s.An apparent weakening of the ENSO–ISMR relationship has been observed si...El Niño–Southern Oscillation(ENSO)was identified as the dominant predictor for the Indian summer monsoon rainfall(ISMR)in the early 1900s.An apparent weakening of the ENSO–ISMR relationship has been observed since the 1970s.Here,we found a clear restoration of the ENSO–ISMR relationship since 1999/2000.This restoring relationship is closely linked to the interdecadal transition of ENSO evolution and the associated sea surface temperature anomalies(SSTAs)over the tropical Atlantic.During 1979–1997,summer ENSO events mainly continued from the previous winter,which can drive apparent Atlantic Niña SSTAs to offset ENSO's impact on ISMR and weaken the ENSO–ISMR relationship.In contrast,when ENSO events newly emerge from late spring,as they have done more recently during 2000–2018,the associated tropical Atlantic SSTAs are weak and shift to the tropical North Atlantic,which can offset the contribution of Atlantic Niña and reinforce the ENSO–ISMR relationship.We identified that the diversity of ENSO's evolution,continuing from the previous winter or emerging from late spring,is the dominant factor perturbing the ENSO–ISMR relationship in recent epochs,with tropical Atlantic SSTAs as the crucial bridge.This finding should be considered in our efforts to improve ISMR prediction.展开更多
基金This work was jointly supported by the National Natural Science Foundation of China under contract Nos 40406004 and 40490263the Study of Air-sea Fluxes and their Influence on Monsoon during Southwest Monsoon in South China Sea+1 种基金the University Doc torate Foundation under contract No.20030423004the Foundation for Open Projects of the Key Laboratory of Physical Oceanography of the Ministry of Education under contract No,200303.The authors thank Professor Yu Lisan at the Woods Hole Oceanographic Institution in USA for providing data and discussions.
文摘The biases and their sources in monthly turbulent heat fluxes from the Woods Hole Oceanographic Institution (WHOI) analysis, and the National Centers for Environmental Prediction-National Center for Atmospheric Research reanalyses 1 and 2 (NCEPI and NCEP2) are checked in the climatically representative regions in the tropical Atlantic using the fluxes from the Southampton Oceanographic Centre (SOC) and the pilot research moored array in the tropical Atlantic (PIRATA) as references. For the WHOI analysis, the biases in turbulent heat fluxes mainly exist in equatorial regions which are due to the overestimated sea surface temperature and the underestimated 2 m air humidity. For the NCEP2 reanalysis, the maximum biases, about (40±5) W/m^2, exist in southeast and northeast trade wind regions, which are mainly caused by the flux algorithm used because the biases in wind speed and air-sea humidity difference are relatively small. In the equatorial regions, the flux biases in the NCEP2 derived from both flux-related basic variables and algorithm are equally large. Although the estimations of time series trends and air-sea humidity difference of the NCEPI are improved greatly in the NCEP2, the biases of latent heat flux in the NCEP2 are about 20 W/m^2 greater than those from the NCEP1 in the trade wind regions. The result shows that the climatologies and monthly variabilities of the turbulent heat fluxes from the WHOI are more accurate than those from the NCEP1 and NCEP2 in the tropical Atlantic, especially on outside of the equatorial regions.
基金supported by the National Natural Science Foundation of China(Grant Nos.41505048,41461164005,41275001,41475074,41505061 and 41475081)the LASW State Key Laboratory Special Fund(Grant No.2015LASW-B04)
文摘Previous studies suggest that spring SST anomalies over the northern tropical Atlantic(NTA) affect the tropical cyclone(TC) activity over the western North Pacific(WNP) in the following summer and fall. The present study reveals that the connection between spring NTA SST and following summer–fall WNP TC genesis frequency is not stationary. The influence of spring NTA SST on following summer–fall WNP TC genesis frequency is weak and insignificant before, but strong and significant after, the late 1980 s. Before the late 1980 s, the NTA SST anomaly-induced SST anomalies in the tropical central Pacific are weak, and the response of atmospheric circulation over the WNP is not strong. As a result, the connection between spring NTA SST and following summer–fall WNP TC genesis frequency is insignificant in the former period. In contrast,after the late 1980 s, NTA SST anomalies induce pronounced tropical central Pacific SST anomalies through an Atlantic–Pacific teleconnection. Tropical central Pacific SST anomalies further induce favorable conditions for WNP TC genesis,including vertical motion, mid-level relative humidity, and vertical zonal wind shear. Hence, the connection between NTA SST and WNP TC genesis frequency is significant in the recent period. Further analysis shows that the interdecadal change in the connection between spring NTA SST and following summer–fall WNP TC genesis frequency may be related to the climatological SST change over the NTA region.
基金This work is jointly supported by the National Natural Science Foundation of China under contract Nos 40576012,40576008 and 90411010;the National Hi-tech Project("863"Program)of China under contract No 20060109Z1043.
文摘The mean seasonal variability of turbulent heat fluxes in the tropical Atlantic Ocean is examined using the Woods Hole Oceanographic Institution (WHOI) flux product. The most turbulent heat fluxes occur during winter seasons in the two hemispheres, whose centers are located at 10° -20°N and 5° 15°S respectively. In climatological ITCZ, the turbulent heat fluxes are the greatest from June to August, and in equatorial cold tongue the turbulent heat fluxes are the greatest from March to May. Seasonal variability of sensible heat flux is smaller than that of latent heat flux and mainly is dominated by the variations of air-sea temperature difference. In the region with larger climatological mean wind speed (air-sea humidity difference), the variations of air-sea humidity difference (wind speed) dominate the variability of latent heat flux. The characteristics of turbulent heat flux yielded from theory analysis and WHOI dataset is consistent in physics which turns out that WHOI' s flux data are pretty reliable in the tropical Atlantic Ocean.
基金This study was supported by the National Natural Science Foundation of China(Grant Nos.41976045&41888101)and the Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai)through a group research project(99147-42080024).Y.Cui is supported by the U.S.National Science Foundation award 1603051.Samples and core data were provided by ODP.ODP is sponsored by the U.S.National Science Foundation(NSF)and participating countries under management of Joint Oceanographic Institutions(JOI),Inc.
文摘Early Eocene hyperthermals are geologically short-lived global warming events and represent fundamental perturbations to the global carbon cycle and the Earth’s ecosystem due to massive additions of isotopically light carbon to the ocean-atmosphere system.They serve as ancient analogs for understanding how the oceanic carbonate system and surface-ocean ecosystem would respond to ongoing and future climate change.Here,we present a continuous carbonate record across the Eocene Thermal Maximum 2(ETM2 or H1,ca.54.1 Ma)and H2(ca.54 Ma)events from an expanded section at Ocean Drilling Program Site 1258 in tropical Atlantic.The abundant calcareous nannofossils and moderate carbonate content throughout the studied interval suggest this record was deposited above the calcite compensation depth(CCD),but below the lysocline and under the influence of terrestrial dilution.An Earth system model cGENIE is used to simulate the carbon cycle dynamics across the ETM2 and H2 to offer insights on the mechanism of the rapid warming and subsequent recovery in climate and ecosystem.The model suggests moderate changes in ocean pH(0.1–0.2 unit)for the two scenarios,biogenic methane from a rechargeable methane capacitor and organic matter oxidation from thawing of the permafrost.These pH changes are consistent with a recent independent pH estimate across the ETM2 using boron isotopes.The carbon emission flux during the ETM2 is at least an order of magnitude smaller than that during the Paleocene–Eocene Thermal Maximum(PETM)(0.015–0.05 Pg C yr^(-1)vs.0.3–1.7 Pg C yr^(-1)).The comparable pre-and post-event carbonate contents suggest the lysocline did not over deepen following the ETM2 at this tropical Atlantic site,indicating spatial heterogeneity in the carbonate system due to strong dilution influence from terrestrial weathering and riverine discharge at Site 1258.
文摘Tropical waters show different regional aspects due to specificities in their nutrient biogeochemical cycles, which can affect the carbon system and influence their regional role as sinks or sources of CO<sub>2</sub>. This study was performed on particular tropical areas that present a different seasonal behaviour related to the carbon cycle observed in the late rainy season (July 2013). Understanding the CO<sub>2</sub> drawdown and outgassing potential in these areas is needed to call attention to more long-term monitoring efforts and protect understudied tropical coastal systems more efficiently. This study is focused on nutrient values, hydrological data, biogeochemical carbon behaviour linked to the carbonate system and includes estimates of CO<sub>2</sub> fluxes in three contrasting areas off the northeastern Brazilian shelf: 1) an urbanised estuary (Recife-REC), 2) a coastal Island (Itamaracá-ITA) and 3) an oceanic archipelago (Fernando de Noronha-FN). In general, REC acted as a source, while ITA and FN as carbon sinks. In ITA, despite the high DIC and Total Alkalinity observed (mean ~2360 μmol·kg<sup>-1</sup>), the sink is associated with an effective cascading of atmospheric CO<sub>2</sub> associated with turbulent shallow waters coupled with biogenic removal of and precipitation of CaCO<sub>3</sub> by coralline algae. FN acted as a sink, linked to minor decreases in Total Alkalinity (mean~2295 μmol·kg<sup>-1</sup>) influenced by ammonium-based primary production, nitrogen fixation and sporadic entrainment of nutrient rich waters in the upper thermocline. More studies in different western tropical Atlantic coastal systems can improve the knowledge of tropical shelf seas and their contribution to the ocean carbon budget under specific regional trophic regimes.
基金This research was supported by the National Natural Sci-ence Foundation of China(41830964,41775100)the National Key R&D Program of China(2017YFC1404104 and 2017YFC1404100)+1 种基金the Shandong Province’s“Taishan”Sci-entist Project(ts201712017)Qingdao“Creative and Initiative”frontier Scientist Program(19-3-2-7-zhc)。
文摘The Pacific Walker circulation(PWC)was weak in the 20th century,but its strength increased in an interdecadal scale in the late 1990s.Previous studies have suggested that it could be caused by the warming of the tropical Atlantic Ocean,or induced by the warming of the tropical Indian Ocean.The tropical Atlantic Ocean would not only directly affect the PWC through the equatorial east Pacific to the west,but also produce an indirect effect to the east through the equatorial west Indian Ocean.Using a coupled general circulation model,we designed a series of tropical Atlantic Heating and Heating_Shut experiments with different heating rates,to detect the mechanism of the impact of tropical Atlantic warming on the PWC.Results show that the tropical Atlantic heating weakens the Atlantic Walker circulation but strengthens the PWC.Diagnostics of multiple physical variables with coherent lowereupper troposphere structure show the responses of the Indian Ocean to the Atlantic heating play a critical role in the strengthening of the PWC.The Atlanticelinked atmosphere over the tropical Indian Ocean exerts a significantly positive heat flux onto the ocean there,greatly warming the tropical Indian Ocean,especially on the west part.This produces strong convectively ascending at the equatorial West Indian Ocean,but descending at the East-central Indian Ocean,corresponding to a‘Walker’circulation and an‘antieWalker’circulation situated at the West and East equatorial Indian Ocean respectively.Meanwhile,the convergence(divergence)of the lower(upper)troposphere over the Indo‒Pacific region is also strengthened.In this way,the tropical Atlantic heating is linked to the PWC through the circulation over the equatorial Indian Ocean.This study serves as a preliminary step to understand the impact of tropical Atlantic warming on the PWC,more Atlantic heating sensitivity studies with multi-model experiments are required to further reveal the linkage of the Pacific and Atlantic.
基金supported by the CNPq(Conselho Nacional de Desenvolvimento Cientifico e Tecnlogico,Brazil)/IRD(Institut de Recherche pour le Développement,France)cooperative project(Grant No.910153/98-1)support from the FAPESP(Fundao de Amparo à Pesquisa do Estado de Sao Paulo)(Grant No.99/06045)
文摘This study investigates the mean kinematic characteristics of the tropical Atlantic easterly disturbances in January-March (JFM), April-June (AM J), July-September (JAS) and October-December (OND) from 1968-1998. For each season, the preferential tracks of these disturbances in the 3--10-day band periods were computed and spatialized, as well as their associated wavelength, velocity and main period, which lies between 3-5 days and between 6-9 days depending on the track and the season. Two main tracks are highlighted over the Atlantic Ocean. During OND and JFM these two tracks are well separated and located in each hemisphere around 15°S and 12.5°N. From AMJ to JAS these tracks migrate northward; in JAS, they merge into one over the northern tropical Atlantic along 17.5°N. The associated wavelength fields exhibit a meridional gradient, with large wavelengths (greater than 4000 km) around the equator, between 5°N and 5°S, and smaller wavelengths outside of this latitude band (between 2500-3500 kin). The phase speed is also found to exhibit poleward decreasing values from 12-6 m s^-1. Over the north Atlantic track, 6-9-day disturbances were found to occur from January to May and approximately from October to December. From June to September, the 3-5-day waves dominate the synoptic activity. Over the south Atlantic track, between May and August the synoptic variability is mainly explained by the 3-5-day disturbances but from January to April and from September to December both 3-5-day waves and 6-9-day waves can occur.
基金supported by the Key Program of theChinese Academy of Sciences (Grant No. KZCX2-YW-Q03-3)the Special Scientific Research Fund of Meteorological Public Welfare Profession of China (Grant No. GYHY200906018)the Na- tional Basic Research Program of China (Grant No. 2009CB421406)
文摘This study examined the relationship between the boreal spring(April?May) Antarctic Oscillation(AAO) and the North American summer monsoon(NASM)(July?September) for the period of 1979?2008.The results show that these two systems are closely related.When the spring AAO was stronger than normal,the NASM tended to be weaker,and there was less rainfall over the monsoon region.The opposite NASM situation corresponded to a weaker spring AAO.Further analysis explored the possible mechanism for the delayed impact of the boreal spring AAO on the NASM.It was found that the tropical Atlantic sea surface temperature(SST) plays an important role in the connection between the two phenomena.The variability of the boreal spring AAO can produce anomalous SSTs over the tropical Atlantic.These SST anomalies can persist from spring to summer and can influence the Bermuda High,affecting water vapor transportation to the monsoon region.Through these processes,the boreal spring AAO exerts a significantly delayed impact on the amount of NASM precipitation.Thus,information about the boreal spring AAO is valuable for the prediction of the NASM.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41505070 and 41421004)the CAS-PKU Joint Research Program
文摘We investigate the interannual variability of the South Asian summer monsoon(SASM) circulation, which has experienced a significant interdecadal change since 2000. This change is primarily influenced by sea surface temperatures(SSTs)in the tropical Pacific and North Atlantic oceans. During the pre-2000 period examined in this study(1979-99), the SASM is negatively correlated with eastern Pacific SSTs(the canonical ENSO mode) and positively correlated with the negative phase of the North Atlantic SST tripole(NAT). During the post-2000 period(2000-14), the SASM is negatively correlated with central Pacific SSTs and positively correlated with the positive phase of the NAT pattern. The associated Pacific SSTs change from the eastern to central region, leading to the rising(subsiding) branch of the Walker circulation moving westwards to the Maritime Continent in the latter period, which can impact the interannual variability of the SASM through modulating the wind field in the troposphere. In addition to Pacific SSTs, the NAT SSTs can propagate energy from the North Atlantic to the South Asian High(SAH) region through the wave activity flux, and then further impact the SASM via the SAH.Because the SASM is intimately related with precipitation over the Asian region, we briefly discuss the features of the precipitation patterns associated with the SASM during the two periods. The westward shifting Walker circulation leads to the shrinking and weakened anomalous westerlies of the SASM in the lower level, inducing the Maritime Continent rainfall location to move westwards and more moisture to arrive in southern China from the Pacific Ocean in the latter period.
基金the National Natural Science Foundation of China(41776031)National Key Research and Development Program of China(2018YFC1506903)+2 种基金Guangdong Natural Science Foundation(2015A030313796)Program for Scientific Research Start-Up Funds of Guangdong Ocean UniversityFoundation for Returned Scholars of the Ministry of Education of China。
文摘The intensity of the interannual variability(IIV)of the mean tropical cyclone(TC)genesis latitude over the western North Pacific(WNP)has been weakening significantly since the late 1990 s.It is found that the IIV of the mean TC genesis latitude depends largely on the strength of the out-of-phase relationship between TC genesis numbers in the north(north of 15°N)and south(south of 15°N)of the WNP.A weaker(stronger)north–south TC see-saw has led to a smaller(larger)IIV of the mean TC genesis latitude after(before)the late 1990 s.Different configurations of sea surface temperature(SST)anomalies are found to be responsible for the decadal changes in the north–south TC see-saw and dipole structure.Before the late 1990 s,the joint effect of SST anomalies over the tropical Pacific and tropical North Indian Ocean dominated,rendering the obvious north–south TC see-saw and larger IIV of the mean TC genesis latitude.After the late 1990 s,however,the dominant SST anomalies associated with TC genesis shift to the tropical central Pacific(CP)and tropical North Atlantic Ocean,which have weakened the north–south TC seesaw and reduced the IIV of the mean TC genesis latitude.These observed decadal changes in the configuration of SST anomalies are considered to be closely associated with the shift of the El Ni?o–Southern Oscillation(ENSO)from eastern Pacific(EP)type to the CP type during the recent decades.The results suggest that the increased influences from the tropical Atlantic Ocean have become more important to the variations of TC activity in the WNP during the recent decades.These results may have important implications for assessing the latitudinal distributions of TC-induced hazards.
基金This work was supported by the National Key R&D Program of China(grant 2019YFA0606703)the National Natural Science Foundation of China(grants 41722504 and 41975116)and the Youth Innovation Promotion Association of the Chinese Academy of Sciences.Data and codes will be made available upon request to X.Y.
文摘El Niño–Southern Oscillation(ENSO)was identified as the dominant predictor for the Indian summer monsoon rainfall(ISMR)in the early 1900s.An apparent weakening of the ENSO–ISMR relationship has been observed since the 1970s.Here,we found a clear restoration of the ENSO–ISMR relationship since 1999/2000.This restoring relationship is closely linked to the interdecadal transition of ENSO evolution and the associated sea surface temperature anomalies(SSTAs)over the tropical Atlantic.During 1979–1997,summer ENSO events mainly continued from the previous winter,which can drive apparent Atlantic Niña SSTAs to offset ENSO's impact on ISMR and weaken the ENSO–ISMR relationship.In contrast,when ENSO events newly emerge from late spring,as they have done more recently during 2000–2018,the associated tropical Atlantic SSTAs are weak and shift to the tropical North Atlantic,which can offset the contribution of Atlantic Niña and reinforce the ENSO–ISMR relationship.We identified that the diversity of ENSO's evolution,continuing from the previous winter or emerging from late spring,is the dominant factor perturbing the ENSO–ISMR relationship in recent epochs,with tropical Atlantic SSTAs as the crucial bridge.This finding should be considered in our efforts to improve ISMR prediction.