Stomatal conductance was found to change from steady-state to a slate of oscillations during daytime when vapour pressure deficit (VPD) increased to a value of 1 kPa in Glycyrrhiza inflata Batalin grown under the cond...Stomatal conductance was found to change from steady-state to a slate of oscillations during daytime when vapour pressure deficit (VPD) increased to a value of 1 kPa in Glycyrrhiza inflata Batalin grown under the conditions of arid desert in north-west China. The injected metabolic inhibitors (NaN3 or carbonyl cyanide-m-chlorophenyl-hydrazone (CCCP)) slightly reduced the stomatal conductance but did not significantly decrease the intensity of stomatal oscillations (amplitude/average). The oscillation intensity was found to he significantly correlated with VPD and root resistance, but not with the respiration rate. There might exist a minimum threshold of VPD (0.8 kPa) and root resistance (1/4 relative value) that induced stomatal oscillations. These results suggested that stomatal oscillations induced by atmospheric drought stress and root resistance were mainly a type of hydropassive movement.展开更多
[Objective] The research aimed to study the rapid propagation technology and establish effective clone of Hemistepta lyrata Bunge. [Method] With tender stem of Hemistepta lyrata Bunge as material, the conditions neede...[Objective] The research aimed to study the rapid propagation technology and establish effective clone of Hemistepta lyrata Bunge. [Method] With tender stem of Hemistepta lyrata Bunge as material, the conditions needed in calluses induction and differentiation, adventitious bud differentiation and radication, test tube seedling cutting and transplantation were studied. [ Result] The results showed that the optimum medium for granulated calluses induction from tender stem was MS + BA 0.3 mg/L +2,4-D 1 -1.5 mg/L, for granulated calluses and adventitious bud differentiation was MS + AgNO31.5 mg/L + BA 0.4 mg/L + NAA 0.1 mg/L. 1/2 MS + IAA 0.6 mg/L was suitable for test tube seedling rooting and regeneration, and cinder was used as transplantation and cutting substrate. [ Conclusion]This study will provide the scientific reference for choosing the feasible medium in tissue culture of Hemistepta lyrata Bunge.展开更多
The solidified structures of horizontally continuous casting(HCC) of super-thin slab and its relations with the current were studied under the electromagnetic vibration(EMV).The results show that,under the action ...The solidified structures of horizontally continuous casting(HCC) of super-thin slab and its relations with the current were studied under the electromagnetic vibration(EMV).The results show that,under the action of the periodical forces from EMV,the solidified structures of the super-thin slab of pure tin is greatly refined,and the extent of grain refinement is increased with the magnitude of alternating current.For the Sn-10%Pb alloy,it is shown that the EMV promotes the growth of equiaxed grains in the center of super-thin slab,and the grains are refined with the alternating current increasing.This is useful to prevent some solidification defects in the horizontally continuous casting of super-thin slab,such as columnar grains butting,porosity,inclusions and gases gathering,and composition segregation in the centre of slab.展开更多
This study focuses on dynamic mechanism behind the formation of the freshwater zone around the Meimao Sandbank by use of 3D numerical simulation.The Meimao Sandbank is located along the southern bank of the South Pass...This study focuses on dynamic mechanism behind the formation of the freshwater zone around the Meimao Sandbank by use of 3D numerical simulation.The Meimao Sandbank is located along the southern bank of the South Passage in the Changjiang(Yangtze River) estuary,which is considered as a freshwater resource for Shanghai City.Interaction between runoff and tide is the main mechanism of the freshwater zone formation.However,the freshwater zone often suffers from saltwater intrusion in dry season.Tidal oscillation is stronger during spring tides,able to carry freshwater farther seaward.Therefore,it is more likely to occur during the ebb of a spring tide in dry seasons.In addition,the water zone is sensitive to runoff:when runoff decreases,it disappears,and vice versa.The northerly winds favor the formation of the freshwater zone.展开更多
The Oscillating Water Column(OWC) wave energy convertor with the advantage of its simple geometrical construction and excellent stability is widely employed.Recently,perforated breakwaters have been often used as they...The Oscillating Water Column(OWC) wave energy convertor with the advantage of its simple geometrical construction and excellent stability is widely employed.Recently,perforated breakwaters have been often used as they can effectively reduce the wave reflection from and wave forces acting on the structures.Considering the similarity between the compartment of perforated caisson and the air chamber of OWC wave energy convertor,a new perforated caisson of breakwater is designed in this paper.The ordinary caisson is modified by installing facilities similar to the air chamber of OWC converter,but here they are utilized to dissipate the wave energy inside the caisson.Such an arrangement improves the stability of the caisson and reduces the construction cost by using the compartment of perforated caisson like using an air chamber.This innovation has both academic significance and important engineering value.For a new type of caisson,reliability analysis of the structure is necessary.Linear potential flow theory is applied to calculate the horizontal wave force acting on the caisson.The calculated results are compared with experimental data,showing the feasibility of the method.The Importance Sampling Procedure(ISP) is used to analyse the reliability of this caisson breakwater.展开更多
The use of a Savonius rotor as turbine for an oscillating water column(OWC) is demonstrated.The effect of tuning the OWC using turbine duct blockage is also studied for different wave conditions.A horizontal turbine s...The use of a Savonius rotor as turbine for an oscillating water column(OWC) is demonstrated.The effect of tuning the OWC using turbine duct blockage is also studied for different wave conditions.A horizontal turbine section OWC employing a Savonius rotor was tested by varying the opening of OWC exit(0%,25%,50%,75% and 100%) to study the behavior and performance of the device.The OWC model was tested at water depth of 0.29 m at frequencies of 0.8,0.9 and 1.0 Hz while the exit openings are varied.The static pressure,dynamic pressure,rotational speed of the Savonius rotor and the coefficient of power are presented as results.The OWC with exit opening of 25% showed greater performance in terms of rotational speed and CP compared to OWC with other exit opening percentages.This proves the ability of the OWC to be tuned by regulating flow in the turbine duct.展开更多
In this paper, the impact of ENSO on the precipitation over China in the winter half-year is investigated diagnostically. The results show that positive precipitation anomalies with statistical significance appear ove...In this paper, the impact of ENSO on the precipitation over China in the winter half-year is investigated diagnostically. The results show that positive precipitation anomalies with statistical significance appear over southern China in El Nio episodes, which are caused by the enhanced warm and humid southwesterlies along the East Asian coast in the lower troposphere. The enhanced southwesterlies transport more water vapor to southern China, and the convergence of water vapor over southern China increases the precipitable water and specific humidity. In La Nia episodes,although atmospheric elements change reversely, they are not statistically significant as those in El Nio periods. The possible physical mechanism of the different impact of ENSO cycle on the precipitation over southern China is investigated by analyzing the intraseasonal oscillations(ISOs) in El Nio and La Nia winter half-years, respectively. By comparing the characteristics of ISOs in El Nio and La Nia, a physical mechanism is proposed to explain the different responses of the precipitation over China to ENSO in the winter half-year. In El Nio episodes, over western North Pacific(WNP) and South China Sea(SCS) the ISOs are inactive and exert little effect on water vapor transport and convergence, inducing positive precipitation anomalies with statistical significance over southern China in El Nio episodes. In La Nia episodes, however, the ISOs are active, which weaken the interannual variation signals of ENSO over WNP and southern China and lead to the insignificance of the interannual signals related to ENSO. Therefore, the different responses of precipitation over China to ENSO in the winter half-year are possibly caused by the difference of intraseasonal oscillations over WNP and SCS between El Nio and La Nia.展开更多
During the boreal winter,abundant persistent heavy rainfall(PHR)amount and significant rainfall variability at subseasonal timescale are generally observed over the southern sector of East China,where the large-scale ...During the boreal winter,abundant persistent heavy rainfall(PHR)amount and significant rainfall variability at subseasonal timescale are generally observed over the southern sector of East China,where the large-scale circulation and moisture transport are tightly connected with the equatorial Madden-Julian Oscillation(MJO).As the MJO convections occur over the equatorial Indian Ocean(MJO phases 1-4),the low-level moisture convergence is enhanced over southern China(SC,108°-120°E,21°-26°N)with the divergence to the north.Thus,a positive anomaly of PHR amount appears in SC but a negative anomaly of PHR amount is seen in the Yangtze River valley(YR,113°-122°E,28°-30°N).In contrast,the divergence(convergence)of moisture flux anomalies in the SC(YR)associated with the western equatorial Pacific MJO convections(phases 5-8)limits(benefits)the occurrence of PHR in the SC(YR).The wintertime PHR over southern China is found to undergo a long-term change over the past three decades(1979-2011)with a decreasing(an increasing)trend of PHR amount in the SC(YR).The change in PHR amount occurs consistently with the decadal change in MJO activity.In the earlier decade(1979-1994,E1),the active Indian Ocean(western Pacific)MJO events appeared more frequently while they became less frequent in the recent decade(1995-2011,E2).Accordingly,the Indian Ocean(western Pacific)MJO-related moisture convergence(divergence)anomalies in the SC tend to be weakened(enhanced),contributing to the decrease in PHR amount over the SC in the recent decade.展开更多
The authors explore the intraseasonal oscillation(ISO)of rainfall anomalies in South China,the related circulation regimes,and discuss the possible causes of the large variability of the positive rainfall anomalies ov...The authors explore the intraseasonal oscillation(ISO)of rainfall anomalies in South China,the related circulation regimes,and discuss the possible causes of the large variability of the positive rainfall anomalies over South China during the winter of the 1982/83,1997/98 and 2015/16 super EI Nino events.Case-by-case analysis shows that the 10–20-day ISO associated with the successive heavy rainfall events lead to the positive anomalies of winter rainfall in the three winters.Meanwhile,the 20–50-day ISO is relatively stronger in the winter of 1982/83 and 2015/16 but weaker in the winter of 1997/98.Except for a different speed,the anomalies of the 200-hPa wave train associated with the two ISOs both propagate eastward along the westerly jet between 20 N and 30 N.In the winter of 1982/83 and 2015/16,when the upper-level subseasonal wave trains in different periods pass through South China,the in-phase enhancement of upper-level divergences and the pumping effect could induce the persistent heavy rainfall events,which facilitate the stronger seasonal-mean rainfall.Although the 10–20-day ISO alone in the winter of 1997/98 could cause the higher-frequency rainfall events,the weaker 20–50-day ISO attenuates the anomalies of the South China winter rainfall.Therefore,the joint effects of the 10–20-and 20–50-day ISOs are critical for the larger amount of above-normal rainfall over South China during the mature phase of super EI Nino events.展开更多
The article studies the oscillation features of the water in the square moon pool under the circumstances of wave-flow combined conditions. Comparing with the results of experiments of the square moon pool, a series o...The article studies the oscillation features of the water in the square moon pool under the circumstances of wave-flow combined conditions. Comparing with the results of experiments of the square moon pool, a series of studies reveal that the water piston oscillation phenomenon is quite similar to that of the circular one. Two types of oscillation are exhibited under different incoming wave periods, i.e. self-excited oscillation and forced oscillation. The difference between the circular and square moon pool is that the attack angle makes greater influences on the square one. "Beating phenomenon" is also found in the square moon pool which is not mentioned of the circular one.展开更多
A series of heavy rainfall events occurred over the Yangtze River Valley(YRV)in summer 2014,which were modulated by the 10-20-day quasi-biweekly oscillation(QBWO).Thus,the strongest QBWO cycle for the period 10-24 Jul...A series of heavy rainfall events occurred over the Yangtze River Valley(YRV)in summer 2014,which were modulated by the 10-20-day quasi-biweekly oscillation(QBWO).Thus,the strongest QBWO cycle for the period 10-24 July was used as a representative case to reveal the dynamical mechanism for the QBWO of the YRV rainfall from the potential vorticity(PV)perspective and based on MERRA-2 reanalysis data.The quasi-biweekly YRV rainfall was found to depend closely on the QBWO of the upper-tropospheric South Asian high(SAH),with the SAH configuration modified by the southward-intruding midlatitude high PV stream along with southwestward-advected high PV,altering the divergent condition over the YRV.Quantitative diagnoses for the anomalous vertical motion demonstrated that,in the wet phase of the QBWO cycle,the upper-tropospheric southward-intruding high PV stream acted as a positive PV advection,while negative PV advection was generated due to the lower-tropospheric southerlies,thereby forming a positive vertical gradient of horizontal PV advection to induce evident isentropic-displacement ascending motion.On the other hand,the southward-intruding high PV stream extended downward to the middle troposphere,causing the isentropic surfaces to become more sloping,thus producing a strong isentropic-gliding ascending component.Subsequently,the stronger diabatic heating-related ascending motion was induced to generate positive rainfall anomalies over the YRV.The opposite situation arose in the dry phase,with weak descending motion in magnitude.展开更多
Previous studies have shown that the Atlantic Multidecadal Oscillation (AMO) can play an important role in modulating the variabilityoflndian summer monsoon rainfall (ISMR) over a 50-60-yr timescale. A significant...Previous studies have shown that the Atlantic Multidecadal Oscillation (AMO) can play an important role in modulating the variabilityoflndian summer monsoon rainfall (ISMR) over a 50-60-yr timescale. A significant positive correlation between the AMO and ISMR is found both in observations and models. However, instrumental records show that the relationship becomes non-significant or even of opposite sign after the mid-1990s, suggesting a weakening of the AMO-ISMR connection. The mechanism for the breakdown of the AMO-ISMR connection is investigated in the present work, and the results suggest that a substantial warming in the Indian-tropical western Pacific Ocean plays a role. The warming weakens the meridional gradient of tropospheric temperature between Eurasia and the indian Ocean, and reduces the meridional sea level pressure gradient between the Indian Subcontinent and Indian Ocean, weakening the Indian summer monsoon. Thus, warming in the Indian-tropical western Pacific Ocean seems responsible for the weakened connection between the AMO and ISM.展开更多
文摘Stomatal conductance was found to change from steady-state to a slate of oscillations during daytime when vapour pressure deficit (VPD) increased to a value of 1 kPa in Glycyrrhiza inflata Batalin grown under the conditions of arid desert in north-west China. The injected metabolic inhibitors (NaN3 or carbonyl cyanide-m-chlorophenyl-hydrazone (CCCP)) slightly reduced the stomatal conductance but did not significantly decrease the intensity of stomatal oscillations (amplitude/average). The oscillation intensity was found to he significantly correlated with VPD and root resistance, but not with the respiration rate. There might exist a minimum threshold of VPD (0.8 kPa) and root resistance (1/4 relative value) that induced stomatal oscillations. These results suggested that stomatal oscillations induced by atmospheric drought stress and root resistance were mainly a type of hydropassive movement.
文摘[Objective] The research aimed to study the rapid propagation technology and establish effective clone of Hemistepta lyrata Bunge. [Method] With tender stem of Hemistepta lyrata Bunge as material, the conditions needed in calluses induction and differentiation, adventitious bud differentiation and radication, test tube seedling cutting and transplantation were studied. [ Result] The results showed that the optimum medium for granulated calluses induction from tender stem was MS + BA 0.3 mg/L +2,4-D 1 -1.5 mg/L, for granulated calluses and adventitious bud differentiation was MS + AgNO31.5 mg/L + BA 0.4 mg/L + NAA 0.1 mg/L. 1/2 MS + IAA 0.6 mg/L was suitable for test tube seedling rooting and regeneration, and cinder was used as transplantation and cutting substrate. [ Conclusion]This study will provide the scientific reference for choosing the feasible medium in tissue culture of Hemistepta lyrata Bunge.
基金Project(50674066)supported by the National Natural Science Foundation of China
文摘The solidified structures of horizontally continuous casting(HCC) of super-thin slab and its relations with the current were studied under the electromagnetic vibration(EMV).The results show that,under the action of the periodical forces from EMV,the solidified structures of the super-thin slab of pure tin is greatly refined,and the extent of grain refinement is increased with the magnitude of alternating current.For the Sn-10%Pb alloy,it is shown that the EMV promotes the growth of equiaxed grains in the center of super-thin slab,and the grains are refined with the alternating current increasing.This is useful to prevent some solidification defects in the horizontally continuous casting of super-thin slab,such as columnar grains butting,porosity,inclusions and gases gathering,and composition segregation in the centre of slab.
基金Supported by the Funds for Creative Research Groups of China (No. 40721004)the National Natural Science Foundation of China (No. 40976056)National Major Science and Technology Project of Water Pollution Control and Countermeasures (No. 2008ZX07421-001)
文摘This study focuses on dynamic mechanism behind the formation of the freshwater zone around the Meimao Sandbank by use of 3D numerical simulation.The Meimao Sandbank is located along the southern bank of the South Passage in the Changjiang(Yangtze River) estuary,which is considered as a freshwater resource for Shanghai City.Interaction between runoff and tide is the main mechanism of the freshwater zone formation.However,the freshwater zone often suffers from saltwater intrusion in dry season.Tidal oscillation is stronger during spring tides,able to carry freshwater farther seaward.Therefore,it is more likely to occur during the ebb of a spring tide in dry seasons.In addition,the water zone is sensitive to runoff:when runoff decreases,it disappears,and vice versa.The northerly winds favor the formation of the freshwater zone.
基金supported by the National Natural Science Foundation of China (Grant No 4087-6047)
文摘The Oscillating Water Column(OWC) wave energy convertor with the advantage of its simple geometrical construction and excellent stability is widely employed.Recently,perforated breakwaters have been often used as they can effectively reduce the wave reflection from and wave forces acting on the structures.Considering the similarity between the compartment of perforated caisson and the air chamber of OWC wave energy convertor,a new perforated caisson of breakwater is designed in this paper.The ordinary caisson is modified by installing facilities similar to the air chamber of OWC converter,but here they are utilized to dissipate the wave energy inside the caisson.Such an arrangement improves the stability of the caisson and reduces the construction cost by using the compartment of perforated caisson like using an air chamber.This innovation has both academic significance and important engineering value.For a new type of caisson,reliability analysis of the structure is necessary.Linear potential flow theory is applied to calculate the horizontal wave force acting on the caisson.The calculated results are compared with experimental data,showing the feasibility of the method.The Importance Sampling Procedure(ISP) is used to analyse the reliability of this caisson breakwater.
文摘The use of a Savonius rotor as turbine for an oscillating water column(OWC) is demonstrated.The effect of tuning the OWC using turbine duct blockage is also studied for different wave conditions.A horizontal turbine section OWC employing a Savonius rotor was tested by varying the opening of OWC exit(0%,25%,50%,75% and 100%) to study the behavior and performance of the device.The OWC model was tested at water depth of 0.29 m at frequencies of 0.8,0.9 and 1.0 Hz while the exit openings are varied.The static pressure,dynamic pressure,rotational speed of the Savonius rotor and the coefficient of power are presented as results.The OWC with exit opening of 25% showed greater performance in terms of rotational speed and CP compared to OWC with other exit opening percentages.This proves the ability of the OWC to be tuned by regulating flow in the turbine duct.
基金National Natural Science Foundation of China(41221064)Specialized Scientific Research Project for Public Welfare Industries(Meteorology)(GYHY201306018)
文摘In this paper, the impact of ENSO on the precipitation over China in the winter half-year is investigated diagnostically. The results show that positive precipitation anomalies with statistical significance appear over southern China in El Nio episodes, which are caused by the enhanced warm and humid southwesterlies along the East Asian coast in the lower troposphere. The enhanced southwesterlies transport more water vapor to southern China, and the convergence of water vapor over southern China increases the precipitable water and specific humidity. In La Nia episodes,although atmospheric elements change reversely, they are not statistically significant as those in El Nio periods. The possible physical mechanism of the different impact of ENSO cycle on the precipitation over southern China is investigated by analyzing the intraseasonal oscillations(ISOs) in El Nio and La Nia winter half-years, respectively. By comparing the characteristics of ISOs in El Nio and La Nia, a physical mechanism is proposed to explain the different responses of the precipitation over China to ENSO in the winter half-year. In El Nio episodes, over western North Pacific(WNP) and South China Sea(SCS) the ISOs are inactive and exert little effect on water vapor transport and convergence, inducing positive precipitation anomalies with statistical significance over southern China in El Nio episodes. In La Nia episodes, however, the ISOs are active, which weaken the interannual variation signals of ENSO over WNP and southern China and lead to the insignificance of the interannual signals related to ENSO. Therefore, the different responses of precipitation over China to ENSO in the winter half-year are possibly caused by the difference of intraseasonal oscillations over WNP and SCS between El Nio and La Nia.
基金supported by the National Key R&D Program of China [grant number 2018YFC1505804]
文摘During the boreal winter,abundant persistent heavy rainfall(PHR)amount and significant rainfall variability at subseasonal timescale are generally observed over the southern sector of East China,where the large-scale circulation and moisture transport are tightly connected with the equatorial Madden-Julian Oscillation(MJO).As the MJO convections occur over the equatorial Indian Ocean(MJO phases 1-4),the low-level moisture convergence is enhanced over southern China(SC,108°-120°E,21°-26°N)with the divergence to the north.Thus,a positive anomaly of PHR amount appears in SC but a negative anomaly of PHR amount is seen in the Yangtze River valley(YR,113°-122°E,28°-30°N).In contrast,the divergence(convergence)of moisture flux anomalies in the SC(YR)associated with the western equatorial Pacific MJO convections(phases 5-8)limits(benefits)the occurrence of PHR in the SC(YR).The wintertime PHR over southern China is found to undergo a long-term change over the past three decades(1979-2011)with a decreasing(an increasing)trend of PHR amount in the SC(YR).The change in PHR amount occurs consistently with the decadal change in MJO activity.In the earlier decade(1979-1994,E1),the active Indian Ocean(western Pacific)MJO events appeared more frequently while they became less frequent in the recent decade(1995-2011,E2).Accordingly,the Indian Ocean(western Pacific)MJO-related moisture convergence(divergence)anomalies in the SC tend to be weakened(enhanced),contributing to the decrease in PHR amount over the SC in the recent decade.
基金jointly supported by the Special Fund for Public Welfare Industry[grant number GYHY20140619]the National Natural Science Foundation of China[grant numbers41475057,41775052 and 41505049]the Basic Scientific Research and Operation Foundation of CAMS[grant numbers2015Z001 and 2017R001]
文摘The authors explore the intraseasonal oscillation(ISO)of rainfall anomalies in South China,the related circulation regimes,and discuss the possible causes of the large variability of the positive rainfall anomalies over South China during the winter of the 1982/83,1997/98 and 2015/16 super EI Nino events.Case-by-case analysis shows that the 10–20-day ISO associated with the successive heavy rainfall events lead to the positive anomalies of winter rainfall in the three winters.Meanwhile,the 20–50-day ISO is relatively stronger in the winter of 1982/83 and 2015/16 but weaker in the winter of 1997/98.Except for a different speed,the anomalies of the 200-hPa wave train associated with the two ISOs both propagate eastward along the westerly jet between 20 N and 30 N.In the winter of 1982/83 and 2015/16,when the upper-level subseasonal wave trains in different periods pass through South China,the in-phase enhancement of upper-level divergences and the pumping effect could induce the persistent heavy rainfall events,which facilitate the stronger seasonal-mean rainfall.Although the 10–20-day ISO alone in the winter of 1997/98 could cause the higher-frequency rainfall events,the weaker 20–50-day ISO attenuates the anomalies of the South China winter rainfall.Therefore,the joint effects of the 10–20-and 20–50-day ISOs are critical for the larger amount of above-normal rainfall over South China during the mature phase of super EI Nino events.
基金support of "111" project which was from China Education Department( No. B07019)
文摘The article studies the oscillation features of the water in the square moon pool under the circumstances of wave-flow combined conditions. Comparing with the results of experiments of the square moon pool, a series of studies reveal that the water piston oscillation phenomenon is quite similar to that of the circular one. Two types of oscillation are exhibited under different incoming wave periods, i.e. self-excited oscillation and forced oscillation. The difference between the circular and square moon pool is that the attack angle makes greater influences on the square one. "Beating phenomenon" is also found in the square moon pool which is not mentioned of the circular one.
基金jointly supported by the Strategic Priority Re-search Program of the Chinese Academy of Sciences[grant number XDB40000000]the National Key Research and Development Program of China[grant number 2018YFC1506004]the National Natural Science Foundation of China[grant numbers 41730963 and 41876020].
文摘A series of heavy rainfall events occurred over the Yangtze River Valley(YRV)in summer 2014,which were modulated by the 10-20-day quasi-biweekly oscillation(QBWO).Thus,the strongest QBWO cycle for the period 10-24 July was used as a representative case to reveal the dynamical mechanism for the QBWO of the YRV rainfall from the potential vorticity(PV)perspective and based on MERRA-2 reanalysis data.The quasi-biweekly YRV rainfall was found to depend closely on the QBWO of the upper-tropospheric South Asian high(SAH),with the SAH configuration modified by the southward-intruding midlatitude high PV stream along with southwestward-advected high PV,altering the divergent condition over the YRV.Quantitative diagnoses for the anomalous vertical motion demonstrated that,in the wet phase of the QBWO cycle,the upper-tropospheric southward-intruding high PV stream acted as a positive PV advection,while negative PV advection was generated due to the lower-tropospheric southerlies,thereby forming a positive vertical gradient of horizontal PV advection to induce evident isentropic-displacement ascending motion.On the other hand,the southward-intruding high PV stream extended downward to the middle troposphere,causing the isentropic surfaces to become more sloping,thus producing a strong isentropic-gliding ascending component.Subsequently,the stronger diabatic heating-related ascending motion was induced to generate positive rainfall anomalies over the YRV.The opposite situation arose in the dry phase,with weak descending motion in magnitude.
基金supported by the National Key Research and Development Program of China[grant number 2016YFA0601802]the National Natural Science Foundation of China[grant number41375085],[grant number 421004]the Strategic Project of the Chinese Academy of Sciences[grant number XDA11010401]
文摘Previous studies have shown that the Atlantic Multidecadal Oscillation (AMO) can play an important role in modulating the variabilityoflndian summer monsoon rainfall (ISMR) over a 50-60-yr timescale. A significant positive correlation between the AMO and ISMR is found both in observations and models. However, instrumental records show that the relationship becomes non-significant or even of opposite sign after the mid-1990s, suggesting a weakening of the AMO-ISMR connection. The mechanism for the breakdown of the AMO-ISMR connection is investigated in the present work, and the results suggest that a substantial warming in the Indian-tropical western Pacific Ocean plays a role. The warming weakens the meridional gradient of tropospheric temperature between Eurasia and the indian Ocean, and reduces the meridional sea level pressure gradient between the Indian Subcontinent and Indian Ocean, weakening the Indian summer monsoon. Thus, warming in the Indian-tropical western Pacific Ocean seems responsible for the weakened connection between the AMO and ISM.