The features of 30-60-day convection oscillations over the subtropical western North Pacific （WNP） were investigated, along with the degree of tropical-subtropical linkage between the oscillations over the WNP durin...The features of 30-60-day convection oscillations over the subtropical western North Pacific （WNP） were investigated, along with the degree of tropical-subtropical linkage between the oscillations over the WNP during summer 1998. It was found that 30-60-day oscillations were extremely strong in that summer over both the subtropical and tro]~ical WNP, providing a unique opportunity to study the behavior of subtropical oscillations and their relationship to tropical oscillations. Further analyses indicated that 30-60-day oscillations propagate westwards over the subtropical WNP and reach eastern China. In addition, 30-60-day oscillations in the subtropics are affected by those over the South China Sea （SCS） and tropical WNP through two mechanisms： （1） direct propagation from the tropics into the subtropics; and （2） a seesaw pattern between the tropics and subtropics, with the latter being predominant.展开更多
The influence of intraseasonal oscillation (ISO) on TC genesis over the northwestern Pacific is studied through comparing analyses of the more and less TC years from 1979 to 2006. It is indicated that the ISO strongly...The influence of intraseasonal oscillation (ISO) on TC genesis over the northwestern Pacific is studied through comparing analyses of the more and less TC years from 1979 to 2006. It is indicated that the ISO strongly affects the TC genesis. In the years for more TC genesis, the ISO is weak and propagates insignificantly in the area to the west of the Philippines, but the ISO is strong in the area to the east of the Philippines and propagates significantly northwestward. In this situation, the Walker cell shifts gradually westward from the tropical western Pacific to the tropical eastern Indian Ocean. Convergent winds appear in the lower atmosphere while divergent winds in the upper atmosphere, suggesting the presence of enhanced ascending flow over the 140-160°E region and a favorable condition for TC genesis. Moreover, in the years for less TC genesis, the ISO gradually becomes stronger in the area to the west of the Philippines and significant eastward propagation prevails from the eastern Indian Ocean to the area around 120°E; the ISO is weak in the area to the east of the Philippines. During these years, the Walker circulation gradually moved eastward, with convergent winds in the upper troposphere and divergent winds in the lower troposphere. Sinking motion was significant, unfavorable for the TC genesis over the Northwestern Pacific.展开更多
An atmospheric general circulation model is used in a series of three experiments to simulate the intraseasonal oscillation in the tropical atmosphere.Analyses of the model daily data show that various physical variab...An atmospheric general circulation model is used in a series of three experiments to simulate the intraseasonal oscillation in the tropical atmosphere.Analyses of the model daily data show that various physical variables,from sever- al different regions,exhibit fluctuations with a spectral peak between 30 and 60 days.This represents a 30—60 day oscillation in the tropical atmosphere and possesses several features which are consistent with observations.These in- clude a horizontal structure dominated by zonal wavenumber 1 and a vertical structure which is predominantly baroclinic. The effect of warm SST (sea surface temperature) anomalies on the 30—60 day oscillation in the tropical atmos- phere is also simulated by prescribing global SST as observed in 1983.This has the effect of weakening the oscillation while at the same time the vertical structure becomes less baroclinic. The importance of cumulus convection to the propagational characteristics of this oscillation is demonstrated by a comparison of results based on different parameterizations for convection.In one case,where the maximum convection over the Pacific is simulated to be too far east,the simulated 30—60 day oscillation shows evidence of westward propa- gation.In the second case,where the convection maximum is located near the observed position in the western Pacific, there is more clearly evidence of eastward propagation. Both results suggest that the location of maximum convection in the Pacific can have an important influence on the strength,structure and propagation of the 30—60 day oscillation.展开更多
The intraseasonal oscillation(ISO) of the South China Sea(SCS, 105-120°E, 5-20°N) convection and its influences on the genesis and track of the western North Pacific(WNP) tropical cyclones(TCs) were explored...The intraseasonal oscillation(ISO) of the South China Sea(SCS, 105-120°E, 5-20°N) convection and its influences on the genesis and track of the western North Pacific(WNP) tropical cyclones(TCs) were explored, based on the daily average of NCEP/NCAR reanalysis data, the OLR data and the western North Pacific tropical cyclone best-track data from 1979 to 2008. The mechanism of the influences of ISO on TC movement and the corresponding large-scale circulation were discussed by a trajectory model. It was found as follows.(1) During the SCS summer monsoon, the SCS convection exhibits the ISO features with active phases alternating with inactive phases. The monsoon circulation patterns are significantly different during these two phases. When the SCS convection is active(inactive), the SCS-WNP monsoon trough stretches eastward(retreats westward) due to the activity(inactivity) of SCS monsoon, and the WNP subtropical high retreats eastward(stretches westward), which enhances(suppresses) the monsoon circulation.(2) The amount of TC genesis in the active phase is much more than that in the inactive phase. A majority of TCs form west of 135 °E during the active phases but east of 135 °E in the inactive phases.(3) The TCs entering the area west of 135 °E and south of 25 °N would move straight into the SCS in the active phase, or recurve northward in the inactive phase.(4) Simulation results show that the steering flow associated with the active(inactive)phases is in favor of straight-moving(recurving) TCs. Meanwhile, the impacts of the locations of TC genesis on the characteristics of TC track cannot be ignored. TCs that occurred father westward are more likely to move straight into the SCS region.展开更多
基金supported by the National Basic Research Program of China(Grant No2010CB950403)by the National Natural Science Foundation of China(Grant No.U0933603)
文摘The features of 30-60-day convection oscillations over the subtropical western North Pacific （WNP） were investigated, along with the degree of tropical-subtropical linkage between the oscillations over the WNP during summer 1998. It was found that 30-60-day oscillations were extremely strong in that summer over both the subtropical and tro]~ical WNP, providing a unique opportunity to study the behavior of subtropical oscillations and their relationship to tropical oscillations. Further analyses indicated that 30-60-day oscillations propagate westwards over the subtropical WNP and reach eastern China. In addition, 30-60-day oscillations in the subtropics are affected by those over the South China Sea （SCS） and tropical WNP through two mechanisms： （1） direct propagation from the tropics into the subtropics; and （2） a seesaw pattern between the tropics and subtropics, with the latter being predominant.
文摘The influence of intraseasonal oscillation (ISO) on TC genesis over the northwestern Pacific is studied through comparing analyses of the more and less TC years from 1979 to 2006. It is indicated that the ISO strongly affects the TC genesis. In the years for more TC genesis, the ISO is weak and propagates insignificantly in the area to the west of the Philippines, but the ISO is strong in the area to the east of the Philippines and propagates significantly northwestward. In this situation, the Walker cell shifts gradually westward from the tropical western Pacific to the tropical eastern Indian Ocean. Convergent winds appear in the lower atmosphere while divergent winds in the upper atmosphere, suggesting the presence of enhanced ascending flow over the 140-160°E region and a favorable condition for TC genesis. Moreover, in the years for less TC genesis, the ISO gradually becomes stronger in the area to the west of the Philippines and significant eastward propagation prevails from the eastern Indian Ocean to the area around 120°E; the ISO is weak in the area to the east of the Philippines. During these years, the Walker circulation gradually moved eastward, with convergent winds in the upper troposphere and divergent winds in the lower troposphere. Sinking motion was significant, unfavorable for the TC genesis over the Northwestern Pacific.
文摘An atmospheric general circulation model is used in a series of three experiments to simulate the intraseasonal oscillation in the tropical atmosphere.Analyses of the model daily data show that various physical variables,from sever- al different regions,exhibit fluctuations with a spectral peak between 30 and 60 days.This represents a 30—60 day oscillation in the tropical atmosphere and possesses several features which are consistent with observations.These in- clude a horizontal structure dominated by zonal wavenumber 1 and a vertical structure which is predominantly baroclinic. The effect of warm SST (sea surface temperature) anomalies on the 30—60 day oscillation in the tropical atmos- phere is also simulated by prescribing global SST as observed in 1983.This has the effect of weakening the oscillation while at the same time the vertical structure becomes less baroclinic. The importance of cumulus convection to the propagational characteristics of this oscillation is demonstrated by a comparison of results based on different parameterizations for convection.In one case,where the maximum convection over the Pacific is simulated to be too far east,the simulated 30—60 day oscillation shows evidence of westward propa- gation.In the second case,where the convection maximum is located near the observed position in the western Pacific, there is more clearly evidence of eastward propagation. Both results suggest that the location of maximum convection in the Pacific can have an important influence on the strength,structure and propagation of the 30—60 day oscillation.
基金National Basic Research Program of China(2015CB953904)National Natural Science Foundation of China(41575081)+1 种基金Startup Foundation for Introducing Talent of NUIST(2015r035)Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)
文摘The intraseasonal oscillation(ISO) of the South China Sea(SCS, 105-120°E, 5-20°N) convection and its influences on the genesis and track of the western North Pacific(WNP) tropical cyclones(TCs) were explored, based on the daily average of NCEP/NCAR reanalysis data, the OLR data and the western North Pacific tropical cyclone best-track data from 1979 to 2008. The mechanism of the influences of ISO on TC movement and the corresponding large-scale circulation were discussed by a trajectory model. It was found as follows.(1) During the SCS summer monsoon, the SCS convection exhibits the ISO features with active phases alternating with inactive phases. The monsoon circulation patterns are significantly different during these two phases. When the SCS convection is active(inactive), the SCS-WNP monsoon trough stretches eastward(retreats westward) due to the activity(inactivity) of SCS monsoon, and the WNP subtropical high retreats eastward(stretches westward), which enhances(suppresses) the monsoon circulation.(2) The amount of TC genesis in the active phase is much more than that in the inactive phase. A majority of TCs form west of 135 °E during the active phases but east of 135 °E in the inactive phases.(3) The TCs entering the area west of 135 °E and south of 25 °N would move straight into the SCS in the active phase, or recurve northward in the inactive phase.(4) Simulation results show that the steering flow associated with the active(inactive)phases is in favor of straight-moving(recurving) TCs. Meanwhile, the impacts of the locations of TC genesis on the characteristics of TC track cannot be ignored. TCs that occurred father westward are more likely to move straight into the SCS region.
