The Twain-Hu Basin(THB),located in Central China,serves as a key juncture where the northerly“polluted”airflows of the East Asian winter monsoon meet the southerly warm and humid airflows.Using the T-PCA(T-mode Prin...The Twain-Hu Basin(THB),located in Central China,serves as a key juncture where the northerly“polluted”airflows of the East Asian winter monsoon meet the southerly warm and humid airflows.Using the T-PCA(T-mode Principal Component Analysis)objective synoptic pattern classification,Flexible Particle-Weather Research and Forecasting(FLEXPARTWRF)model,and Random Forest model,we investigate the influences of synoptic circulations on regional transport,local accumulation,and chemical transformation of PM_(2.5)during heavy air pollution over the THB in January of 2015-2022.The results show that the transport-type synoptic pattern accounts for 65.16%of heavy PM_(2.5)pollution,indicating that regional transport of PM_(2.5)dominates the THB’s heavy air pollution.The PM_(2.5)/CO ratio is higher in the transport-type pattern and positively correlated with PM_(2.5)concentrations,reflecting a higher efficiency of chemical transformation to secondary PM_(2.5)in transport-type pollution compared with the accumulation-type pollution.Transport-type heavy PM_(2.5)pollution is predominantly influenced by upstream anomalous northerly and easterly airflows at the bottom of the high-pressure system,converging with the southern wind in the receptor area over the THB.Accumulation-type heavy pollution exhibits weak wind anomalies in central and eastern China under the control of a uniform pressure field.Furthermore,thermally-induced vertical circulations with sinking airflows in the middle and lower troposphere suppress the vertical air pollutant dispersions.The relative contributions of atmospheric factors for transport-type PM_(2.5)heavy pollution events are 38.0%for dynamical driver,26.8%for thermal driver,and 35.1%for chemical transformation,while in accumulation-type,the contribution rates are 33.9%,36.3%,and 29.7%,respectively.This study elucidates the influences of synoptic patterns on regional transport,local accumulation,and chemical transformation of PM_(2.5)for heavy air pollution,with implications for understanding changes of air quality in the receptor region of regional transport.展开更多
To understand the spatio-temporal variability of precipitation(P)in the Third Pole region(centered on the Tibetan Plateau-TP),it is necessary to quantify the interannual periodicity of P and its relationship with larg...To understand the spatio-temporal variability of precipitation(P)in the Third Pole region(centered on the Tibetan Plateau-TP),it is necessary to quantify the interannual periodicity of P and its relationship with large-scale circulations.In this study,Morlet wavelet transform was used to detect significant(p<0.05)periodic characteristics in P data from meteorological stations in four climate domains in the Third Pole,and to reveal the major large-scale circulations that triggered the variability of periodic P,in addition to bringing large amounts of water vapour.The wavelet transform results were as follows.(1)Significant quasiperiodicity varied from 2 to 11 years.The high-frequency variability mode(2 to 6 years quasi-periods)was universal,and the low-frequency variability mode(7 to 11 years quasi-periods)was rare,occurring mainly in the westerlies and Indian monsoon domains.(2)The majority of periods were base periods(53%),followed by two-base periods.Almost all stations in the Third Pole(95%)showed one or two periods.(3)Periodicity was widely detected in the majority of years(84%).(4)The power spectra of P in the four domains were dominated by statistically significant high-frequency oscillations(ie.,with short periodicity).(5)Large-scale circulations directly and indirectly influenced the periodic P variability in the different domains.The mode of P variability in the different domains was influenced by interactions between large-scale circulation features and not only by the dominant circulation and its control of water vapour transport.The results of this study will contribute to better understanding of the causal mechanisms associated with P variability,which is important for hydrological science and waterresourcemanagement.展开更多
Haze pollution in early winter(December and January) in the Yangtze River Delta(YRD) and in North China(NC)are both severe;however, their monthly variations are significantly different. In this study, the dominant lar...Haze pollution in early winter(December and January) in the Yangtze River Delta(YRD) and in North China(NC)are both severe;however, their monthly variations are significantly different. In this study, the dominant large-scale atmospheric circulations and local meteorological conditions were investigated and compared over the YRD and NC in each month. Results showed that the YRD(NC) is dominated by the so-called Scandinavia(East Atlantic/West Russia)pattern in December, and these circulations weaken in January. The East Asian December and January monsoons over the YRD and NC have negative correlations with the number of haze days. The local descending motion facilitates less removal of haze pollution over the YRD, while the local ascending motion facilitates less removal of haze pollution over NC in January, despite a weaker relationship in December. Additionally, the monthly variations of atmospheric circulations showed that adverse meteorological conditions restrict the vertical(horizontal) dispersion of haze pollution in December(January) over the YRD, while the associated local weather conditions are similar in these two months over NC.展开更多
Initial mesoscale vortex effects on the tropical cyclone （TC） motion in a system where three components coexist （i.e., an environmental vortex （EV）, a TC, and mesoscale vortices） were examined using a barotropic...Initial mesoscale vortex effects on the tropical cyclone （TC） motion in a system where three components coexist （i.e., an environmental vortex （EV）, a TC, and mesoscale vortices） were examined using a barotropic vorticity equation model with initial fields where mesoscale vortices were generated stochastically. Results of these simulations indicate that the deflection of the TC track derived from the initial mesoscale vortices was clearly smaller than that from the beta effect in 60% of the cases. However, they may have a more significant impact on the TC track under the following circumstances. First, the interaction between an adjacent mesoscale vortex and the TC causes the emergence of a complicated structure with two centers in the TC inner region. This configuration may last for 8 h, and the two centers undergo a cyclonic rotation to make the change in direction of the TC motion. Second, two mesoscale vortices located in the EV circulation may merge, and the merged vortex shifts into the EV inner region, intensifying both the EV and steering flow for the TC, increasing speed of the TC.展开更多
Insufficient vertical mixing in the upper ocean during summer is a common problem of oceanic circulation and climate models.The turbulence associated with non-breaking waves is widely believed to effectively solve thi...Insufficient vertical mixing in the upper ocean during summer is a common problem of oceanic circulation and climate models.The turbulence associated with non-breaking waves is widely believed to effectively solve this problem.In many studies,non-breaking surface wave processes are attributed to the effects of Langmuir circulations(LCs).In the present work,the influences of LCs on the upper-ocean thermal structure are examined by using one-and three-dimensional ocean circulation,as well as climate,models.The results indicated that the effect of vertical mixing enhanced by LCs is limited to the upper ocean.The models evaluated,including those considering LC effects alone and the combined effects of LCs and wave breaking,failed to produce a reasonable summertime thermocline,resulting in a large cold bias in the subsurface layer.Therefore,while they can slightly reduce the biases of mixed layer depths and sea surface temperatures in models,LCs are insufficient to solve the problem of insufficient vertical mixing.Moreover,restriction of non-breaking surface wave-induced processes in LCs may be questionable.展开更多
The Pacific Ocean circulations were simulated based on the global warming from 1960 to 1999 by using the Non-Boussinesq POP model and the data of wind stress and temperature at 1 000 hPa from the NCEP. The results sho...The Pacific Ocean circulations were simulated based on the global warming from 1960 to 1999 by using the Non-Boussinesq POP model and the data of wind stress and temperature at 1 000 hPa from the NCEP. The results show that the circulation in the tropical Pacific Ocean was weakening during the past 40 years. The heat transported to the tropical western Pacific Ocean coast by the north equatorial current and the heat transported to middle and high latitudes in the southem hemisphere by the south equatorial current decreased with time due to the global warming, while the heat transported to middle and high latitudes in the northern hemisphere by the north equatorial current increased with time due to the global warming.展开更多
The internal flow of a droplet in the nonlinear extensional flow field will exhibit more than two internal circulations with the variation of nonlinear intensity(E).In this paper,the effect of positions and sizes of i...The internal flow of a droplet in the nonlinear extensional flow field will exhibit more than two internal circulations with the variation of nonlinear intensity(E).In this paper,the effect of positions and sizes of internal circulations on internal mass transfer rate of a single spherical droplet in a nonlinear extensional flow field is studied and compared with that in a linear extensional flow field.The simulation results show that when E≥0,there are two symmetrical internal circulations in the droplet,which is the same with that in a linear extensional flow.The limit value of mass transfer rate Sh is 15,which is equal to that in a linear extensional flow,no matter how large E is.When E≤-3/7,the number of internal flow circulation of a droplet increase to four and the transfer rate Sh increases.When E=-1,the maximum internal transfer rate Sh equals 30 which is twice of that in a linear extensional flow.The generation of new flow circulations in droplets and the circulation positions will enhance mass transfer when E≤-3/7,which provides a new idea for enhancing the internal mass transfer rate of droplets.展开更多
Based on the National Centers for Environmental Prediction and National Center for Atmospheric Research （NCEP/NCAR） reanalysis data from 1950-1999, interdecadal variability of the East Asian Summer Monsoon （EASM） ...Based on the National Centers for Environmental Prediction and National Center for Atmospheric Research （NCEP/NCAR） reanalysis data from 1950-1999, interdecadal variability of the East Asian Summer Monsoon （EASM） and its associated atmospheric circulations are investigated. The EASM exhibits a distinct interdecadal variation, with stronger （weaker） summer monsoon maintained from 1950-1964 （1976-1997）. In the former case, there is an enhanced Walker cell in the eastern Pacific and an anti-Walker cell in the western Pacific. The associated ascending motion resides in the central Pacific, which flows eastward and westward in the upper troposphere, descending in the eastern and western ends of the Pacific basin. At the same time, an anomalous East Asian Hadley Cell （EAHC） is found to connect the low-latitude and mid-latitude systems in East Asia, which strengthens the EASM. The descending branch of the EAHC lies in the west part of the anti-Walker cell, flowing northward in the lower troposphere and then ascending at the south of Lake Baikal （40°-50°N, 95°- 115°E） before returning to low latitudes in the upper troposphere, thus strengthening the EASM. The relationship between the EASM and SST in the eastern tropical Pacific is also discussed. A possible mechanism is proposed to link interdecadal variation of the EASM with the eastern tropical Pacific SST. A warmer sea surface temperature anomaly （SSTA） therein induces anomalous ascending motion in the eastern Pacific, resulting in a weaker Walker cell, and at the same time inducing an anomalous Walker cell in the western Pacific and an enhanced EAHC, leading to a weaker EASM. Furthermore, the interdecadal variation of summer precipitation over North China is found to be the south of Lake Baikal through enhancing and reducing strongly regulated by the velocity potential over the regional vertical motions.展开更多
In the context of 1958–1997 NCEP/ NCAR re-analyses, the South Asia high (SAH) was divided into two components, barotropic and baroclinic, the former based on mass weighed vertical integration and the latter on the di...In the context of 1958–1997 NCEP/ NCAR re-analyses, the South Asia high (SAH) was divided into two components, barotropic and baroclinic, the former based on mass weighed vertical integration and the latter on the difference between the measured circulation and the barotropic component counterpart, whereupon the barotropic and baroclinic circulation conversion features were addressed of the research SAH during its seasonal variation. Evidence suggests that i) in summer (winter), the SAH is a thermal (dynamical) system, with dominant baroclinicity (barotropicity), either of the components accounting for approximately 70% of the total contribution; ii) as time progresses from winter to summer, accompanied by the barotropic SAH evolving into its baroclinic analog, the SAH is moving under the “ thermal guidance” of its baroclinic component circulation, suggesting that the component circulation precedes the system itself in variation; iii) the reversal happens when it goes from summer to winter, with the SAH displacement under the “ dynamic steering” of its barotropic component circulation. Key words SAH (South Asia high) - Barotropic circulation - Baroclinic circulation - Seasonal variation (1)This work is supported by the National Natural Sciences Foundation of China under Grant No.49735170.展开更多
The spatial distribution and seasonal variation of the tide-induced Lagrangian Residual Circulations （LRC hereafter）, wind-driven LRC, and the coupling dynamic characteristics were simulated using ECOM, given the He...The spatial distribution and seasonal variation of the tide-induced Lagrangian Residual Circulations （LRC hereafter）, wind-driven LRC, and the coupling dynamic characteristics were simulated using ECOM, given the Hellerman and Rosenstein global monthly-mean wind stresses. The results showed that the tide-induced LRC of the harmonic constituent M2 bears an identical pattern in four seasons in the Bohai Sea： the surface one is weak with random directions; however, there exist a southeast current from the Bohai Strait to the Laizhou bay, and a weakly anticlockwise gyre in the south of the Bohai Strait for the bottom layer LRC. The magnitude of bottom layer tide-induced LRC is larger than the surface one, and moreover, it contributes significantly to the whole LRC in the Bohai Sea. Unlike the identical structure of the tide-induced LRC, the wind driven LRC varies seasonally under the prevailing monsoon. It forms a distinct gyre under the summer and winter monsoons in July and January respectively, but it seems weak and non-directional in April and September.展开更多
Since the South China Sea (SCS) summer monsoon (SCSSM) is pronouncedly featured by abruptly intensified southwesterly and obviously increased precipitation over the SCS,the lower-tropospheric winds and/or convection i...Since the South China Sea (SCS) summer monsoon (SCSSM) is pronouncedly featured by abruptly intensified southwesterly and obviously increased precipitation over the SCS,the lower-tropospheric winds and/or convection intensities are widely used to determine the SCSSM onset.The methods can be used successfully in most of the years but not in 2006.Due to the intrusion of Typhoon Chanchu(0601)that year,the usual method of determining SCSSM onset date by utilizing the SCS regional indices is less capable of pinpointing the real onset date.In order to solve the problem,larger-scale situations have to be taken into account.Zonal and meridional circulations would be better to determine the break-out date of SCSSM in 2006.The result indicates that its onset date is May 16.Moreover,similar onset dates for other years can be obtained using various methods,implying that large-scale zonal and meridional circulations can be used as an alternative method for determining the SCSSM onset date.展开更多
A modified inverse method is used to compute the circulations east of Taiwan and in the East China Sec and east of the Ryukyu Islands with hydrographic data obtained during early summer of 1985. The computational regi...A modified inverse method is used to compute the circulations east of Taiwan and in the East China Sec and east of the Ryukyu Islands with hydrographic data obtained during early summer of 1985. The computational region covers an area west of 129°E and from 21°45'N to 35°N. The computed results show that: (1 ) The net volume transport (VT ) of the Kuroshio through 21°45'N Section east of Ta Taiwan and west of 123°E is about 45 × 10￣6 m￣3/sduring early summer of 1985. The Kuroshio has. two current cores. One is located near Taiwan, and its velocity isvery large and its maximum velocity is 226 cm/s at the 100 m level, which is close to the maximum velocity of the beginning of the Kuroshio east of the Philippines. The other is located further to the east, and its maximum velocity is159 cm/s at the 100m level; (2) through a transect northwest Of Miyakojima Island and a transect southwest of Okinawa laaed the volume transports of the Kuroshio in the East China Sea both are about 25 × 10￣6 m￣3/s. The maximumvelocity of the Kuroshio at these two sections is 194 and 128 cm/s, respectively, and both are located on the shelfbreak; (3) beneath and east of the Kurohio there are the countercurrent (4) southeast of Okinawa Island there is anortheastward current, and its VT at Section HI is about 12. 6 × 10￣6 m￣3/s, and it comes from a westward flow at 129° This project was supported by the National Natural Science Foundation of China under contract No. 49476278.(Second Institute of Oceanography, State Oceanic Administration, Hongzhou310012, China) (Institute of Oceanography, Taiwan University, Taipei, China)E Section and the recirculating gyre, and does not originate from the Kuroshio east of Taiwan during early summer of 1985. There is a southwestward abyssal current east of Okinawa Islands (5) there are several different scale eddies in this computational region. For example, there is a meso-scale strong cyclonic eddy east of Miyakojima Island.展开更多
Currently, the Chinese central government is considering plans to build a trilateral economic sphere in the Bohai Bay area, including Beijing, Tianjin and Hebei（BTH）, where haze pollution frequently occurs. To achie...Currently, the Chinese central government is considering plans to build a trilateral economic sphere in the Bohai Bay area, including Beijing, Tianjin and Hebei（BTH）, where haze pollution frequently occurs. To achieve sustainable development, it is necessary to understand the physical mechanism of the haze pollution there. Therefore, the pollutant transport mechanisms of a haze event over the BTH region from 23 to 24 September 2011 were studied using the Weather Research and Forecasting model and the FLEXible-PARTicle dispersion model to understand the effects of the local atmospheric circulations and atmospheric boundary layer structure. Results suggested that the penetration by sea-breeze could strengthen the vertical dispersion by lifting up the planetary boundary layer height（PBLH） and carry the local pollutants to the downstream areas; in the early night, two elevated pollution layers（EPLs） may be generated over the mountain areas： the pollutants in the upper EPL at the altitude of 2–2.5 km were favored to disperse by long-range transport, while the lower EPL at the altitude of 1 km may serve as a reservoir, and the pollutants there could be transported downward and contribute to the surface air pollution.The intensity of the sea–land and mountain–valley breeze circulations played an important role in the vertical transport and distribution of pollutants. It was also found that the diurnal evolution of the PBLH is important for the vertical dispersion of the pollutants,which is strongly affected by the local atmospheric circulations and the distribution of urban areas.展开更多
This paper examines the dominant submonthly variability of zonally symmetrical atmospheric circula- tion in the Northern Hemisphere （NH） winter within the context of the Northern Annular Mode （NAM）, with particula...This paper examines the dominant submonthly variability of zonally symmetrical atmospheric circula- tion in the Northern Hemisphere （NH） winter within the context of the Northern Annular Mode （NAM）, with particular emphasis on interactive stratosphere-troposphere processes. The submonthly variability is identified and measured using a daily NAM index, which concentrates primarily on zonally symmetrical circulation. A schematic lifecycle of submonthly variability is developed that reveals a two-way coupling pro- cess between the stratosphere and troposphere in the NH polar region. Specifically, anomalous tropospheric zonal winds in the Atlantic and Pacific sectors of the Arctic propagate upwards to the low stratosphere, disturbing the polar vortex, and resulting in an anomalous stratospheric geopotential height （HGT） that subsequently propagates down into the troposphere and changes the sign of the surface circulations. From the standpoint of planetary-scale wave activities, a feedback loop is also evident when the anoma- lous planetary-scale waves （with wavenumbers 2 and 3） propagate upwards, which disturbs the anomalous zonally symmetrical flow in the low stratosphere, and induces the anomalous HGT to move poleward in the low stratosphere, and then propagates down into the troposphere. This increases the energy of waves at wavenumbers 2 and 3 in the low troposphere in middle latitudes by enhancing the land-sea contrast of the anomalous HGT field. Thus, this study supports the viewpoint that the downward propagation of stratospheric NAM signals may not originate in the stratosphere.展开更多
The circulations off the Changjiang mouth in May and November were simulated by a three dimension numerical model with monthly averaged parameters of dynamic factors in this paper. The area covers the East China Sea (...The circulations off the Changjiang mouth in May and November were simulated by a three dimension numerical model with monthly averaged parameters of dynamic factors in this paper. The area covers the East China Sea (ECS), Yellow Sea and Bohai Sea. Simulated results show that the circulation off the Changjiang mouth in spring and autumn is mainly the Changjiang runoff and Taiwan Warm Current (TWC). The Changjiang discharge is much larger in May than in November, and the wind is westward in May, and southward in November off the Changjiang mouth. The runoff in May branches in three parts, one eastward flows, the other two flow northward and southward along the Subei and Zhejiang coast respectively. The Changjiang diluted water expands eastward off the mouth, and forms a strong salinity front near the mouth. Surface circulation in autumn is similar to that in winter, the runoff southward flows along the coast, and the northward flowing TWC becomes weaker compared to that in spring and summer. The bottom circulations in May and November are mainly the runoffnear the mouth and the TWC offthe mouth, and the runoff and TWC are greater in May than in November.展开更多
Based on the simulations of 31 global models in CMIP5, the performance of the models in simulating the Hadley and Walker circulations is evaluated. In addition, their change in intensity by the end of the 21st century...Based on the simulations of 31 global models in CMIP5, the performance of the models in simulating the Hadley and Walker circulations is evaluated. In addition, their change in intensity by the end of the 21st century （2080-2099） under the RCP4.5 and RCP8.5 scenarios, relative to 1986-2005, is analyzed from the perspective of 200 hPa velocity potential. Validation shows good performance of the individual CMIP5 models and the multi-model ensemble mean （MME） in re- producing the meridional （zonal） structure and magnitude of Hadley （Walker） circulation. The MME can also capture the observed strengthening tendency of the winter Hadley circulation and weakening tendency of the Walker circulation. Such secular trends can be simulated by 39% and 74% of the models, respectively. The MME projection indicates that the winter Hadley circulation and the Walker circulation will weaken under both scenarios by the end of the 21st century. The weak- ening amplitude is larger under RCP8.5 than RCP4.5, due to stronger external forcing. The majority of the CMIP5 models show the same projection as the MME. However, for the summer Hadley circulation, the MME shows little change under RCP4.5 and large intermodel spread is apparent. Around half of the models project an increase, and the other half project a decrease. Under the RCP8.5 scenario, the MME and 65% of the models project a weakening of the summer southern Hadley circulation.展开更多
Data obtained from a comprehensive multidisciplinary oceanographic survey in the central and northern parts of the Taiwan Strait, 24°20′-26°00′N, 118°45°-121°00′E by the Fujian Institute of...Data obtained from a comprehensive multidisciplinary oceanographic survey in the central and northern parts of the Taiwan Strait, 24°20′-26°00′N, 118°45°-121°00′E by the Fujian Institute of Oceanology during the period May, 1983 through May, 1984, showed that the distributions of dissolved oxygen (DO), nitrate, dissolved inorganic phosphate and silicate concentrations here had obvious areal and seasonal characteristics that were mainly influenced by the seasonal circulation ofthree major water systems in the Taiwan Strait-- the Taiwan Strait Warm Water (TSWW), theZhejiang-Fujian Coastal Water (ZFCW), and the Northeastern Strait Warm Water (NESWW).展开更多
基金supported by the National Natural Science Foundation of China(Nos.42075186 and 41830965).
文摘The Twain-Hu Basin(THB),located in Central China,serves as a key juncture where the northerly“polluted”airflows of the East Asian winter monsoon meet the southerly warm and humid airflows.Using the T-PCA(T-mode Principal Component Analysis)objective synoptic pattern classification,Flexible Particle-Weather Research and Forecasting(FLEXPARTWRF)model,and Random Forest model,we investigate the influences of synoptic circulations on regional transport,local accumulation,and chemical transformation of PM_(2.5)during heavy air pollution over the THB in January of 2015-2022.The results show that the transport-type synoptic pattern accounts for 65.16%of heavy PM_(2.5)pollution,indicating that regional transport of PM_(2.5)dominates the THB’s heavy air pollution.The PM_(2.5)/CO ratio is higher in the transport-type pattern and positively correlated with PM_(2.5)concentrations,reflecting a higher efficiency of chemical transformation to secondary PM_(2.5)in transport-type pollution compared with the accumulation-type pollution.Transport-type heavy PM_(2.5)pollution is predominantly influenced by upstream anomalous northerly and easterly airflows at the bottom of the high-pressure system,converging with the southern wind in the receptor area over the THB.Accumulation-type heavy pollution exhibits weak wind anomalies in central and eastern China under the control of a uniform pressure field.Furthermore,thermally-induced vertical circulations with sinking airflows in the middle and lower troposphere suppress the vertical air pollutant dispersions.The relative contributions of atmospheric factors for transport-type PM_(2.5)heavy pollution events are 38.0%for dynamical driver,26.8%for thermal driver,and 35.1%for chemical transformation,while in accumulation-type,the contribution rates are 33.9%,36.3%,and 29.7%,respectively.This study elucidates the influences of synoptic patterns on regional transport,local accumulation,and chemical transformation of PM_(2.5)for heavy air pollution,with implications for understanding changes of air quality in the receptor region of regional transport.
基金National Natural Science Foundation of China,No.42271141,No.42071129National Key Basic Research and Development Project,No.2022YFF1300902。
文摘To understand the spatio-temporal variability of precipitation(P)in the Third Pole region(centered on the Tibetan Plateau-TP),it is necessary to quantify the interannual periodicity of P and its relationship with large-scale circulations.In this study,Morlet wavelet transform was used to detect significant(p<0.05)periodic characteristics in P data from meteorological stations in four climate domains in the Third Pole,and to reveal the major large-scale circulations that triggered the variability of periodic P,in addition to bringing large amounts of water vapour.The wavelet transform results were as follows.(1)Significant quasiperiodicity varied from 2 to 11 years.The high-frequency variability mode(2 to 6 years quasi-periods)was universal,and the low-frequency variability mode(7 to 11 years quasi-periods)was rare,occurring mainly in the westerlies and Indian monsoon domains.(2)The majority of periods were base periods(53%),followed by two-base periods.Almost all stations in the Third Pole(95%)showed one or two periods.(3)Periodicity was widely detected in the majority of years(84%).(4)The power spectra of P in the four domains were dominated by statistically significant high-frequency oscillations(ie.,with short periodicity).(5)Large-scale circulations directly and indirectly influenced the periodic P variability in the different domains.The mode of P variability in the different domains was influenced by interactions between large-scale circulation features and not only by the dominant circulation and its control of water vapour transport.The results of this study will contribute to better understanding of the causal mechanisms associated with P variability,which is important for hydrological science and waterresourcemanagement.
基金supported by the National Key Research and Development Plan (Grant No. 2016YFA0600703)the National Natural Science Foundation of China (Grant Nos. 91744311, 41991283 and 41705058)the funding of the Jiangsu Innovation & Entrepreneurship Team。
文摘Haze pollution in early winter(December and January) in the Yangtze River Delta(YRD) and in North China(NC)are both severe;however, their monthly variations are significantly different. In this study, the dominant large-scale atmospheric circulations and local meteorological conditions were investigated and compared over the YRD and NC in each month. Results showed that the YRD(NC) is dominated by the so-called Scandinavia(East Atlantic/West Russia)pattern in December, and these circulations weaken in January. The East Asian December and January monsoons over the YRD and NC have negative correlations with the number of haze days. The local descending motion facilitates less removal of haze pollution over the YRD, while the local ascending motion facilitates less removal of haze pollution over NC in January, despite a weaker relationship in December. Additionally, the monthly variations of atmospheric circulations showed that adverse meteorological conditions restrict the vertical(horizontal) dispersion of haze pollution in December(January) over the YRD, while the associated local weather conditions are similar in these two months over NC.
基金supported by the National Natural Science Foundation of China (Grant Nos. 40775038,40875031 and 40975036)
文摘Initial mesoscale vortex effects on the tropical cyclone （TC） motion in a system where three components coexist （i.e., an environmental vortex （EV）, a TC, and mesoscale vortices） were examined using a barotropic vorticity equation model with initial fields where mesoscale vortices were generated stochastically. Results of these simulations indicate that the deflection of the TC track derived from the initial mesoscale vortices was clearly smaller than that from the beta effect in 60% of the cases. However, they may have a more significant impact on the TC track under the following circumstances. First, the interaction between an adjacent mesoscale vortex and the TC causes the emergence of a complicated structure with two centers in the TC inner region. This configuration may last for 8 h, and the two centers undergo a cyclonic rotation to make the change in direction of the TC motion. Second, two mesoscale vortices located in the EV circulation may merge, and the merged vortex shifts into the EV inner region, intensifying both the EV and steering flow for the TC, increasing speed of the TC.
基金the National Key Research and Development Program of China(No.2017YFC1404000)the Basic Scientific Fund for National Public Research Institutes of China(No.2018S03)+1 种基金the National Natural Science Foundation of China(Nos.41776038 and 41376036)Dr.Fangli Qiao was supported by the Natural Science Foundation of China(Nos.41821004).
文摘Insufficient vertical mixing in the upper ocean during summer is a common problem of oceanic circulation and climate models.The turbulence associated with non-breaking waves is widely believed to effectively solve this problem.In many studies,non-breaking surface wave processes are attributed to the effects of Langmuir circulations(LCs).In the present work,the influences of LCs on the upper-ocean thermal structure are examined by using one-and three-dimensional ocean circulation,as well as climate,models.The results indicated that the effect of vertical mixing enhanced by LCs is limited to the upper ocean.The models evaluated,including those considering LC effects alone and the combined effects of LCs and wave breaking,failed to produce a reasonable summertime thermocline,resulting in a large cold bias in the subsurface layer.Therefore,while they can slightly reduce the biases of mixed layer depths and sea surface temperatures in models,LCs are insufficient to solve the problem of insufficient vertical mixing.Moreover,restriction of non-breaking surface wave-induced processes in LCs may be questionable.
基金supported by Natural Science Foundation of China (No. 40976015)National Science Foundation for Youth (No. 40906014)
文摘The Pacific Ocean circulations were simulated based on the global warming from 1960 to 1999 by using the Non-Boussinesq POP model and the data of wind stress and temperature at 1 000 hPa from the NCEP. The results show that the circulation in the tropical Pacific Ocean was weakening during the past 40 years. The heat transported to the tropical western Pacific Ocean coast by the north equatorial current and the heat transported to middle and high latitudes in the southem hemisphere by the south equatorial current decreased with time due to the global warming, while the heat transported to middle and high latitudes in the northern hemisphere by the north equatorial current increased with time due to the global warming.
基金supported by the National Key Research and Development Program of China(2021YFC2902502)the National Natural Science Foundation of China(22078320,22035007)+4 种基金the NSFC-EU project(31961133018)the Shandong Provincial Key Research and Development Program(2022CXGC020106)the Shandong Key Research and Development Program(International Cooperation Office)(2019GHZ018)the Shandong Province Postdoctoral Innovative Talents Support Plan(SDBX2020018)the External Cooperation Program of BIC,Chinese Academy of Sciences(122111KYSB20190032)。
文摘The internal flow of a droplet in the nonlinear extensional flow field will exhibit more than two internal circulations with the variation of nonlinear intensity(E).In this paper,the effect of positions and sizes of internal circulations on internal mass transfer rate of a single spherical droplet in a nonlinear extensional flow field is studied and compared with that in a linear extensional flow field.The simulation results show that when E≥0,there are two symmetrical internal circulations in the droplet,which is the same with that in a linear extensional flow.The limit value of mass transfer rate Sh is 15,which is equal to that in a linear extensional flow,no matter how large E is.When E≤-3/7,the number of internal flow circulation of a droplet increase to four and the transfer rate Sh increases.When E=-1,the maximum internal transfer rate Sh equals 30 which is twice of that in a linear extensional flow.The generation of new flow circulations in droplets and the circulation positions will enhance mass transfer when E≤-3/7,which provides a new idea for enhancing the internal mass transfer rate of droplets.
文摘Based on the National Centers for Environmental Prediction and National Center for Atmospheric Research （NCEP/NCAR） reanalysis data from 1950-1999, interdecadal variability of the East Asian Summer Monsoon （EASM） and its associated atmospheric circulations are investigated. The EASM exhibits a distinct interdecadal variation, with stronger （weaker） summer monsoon maintained from 1950-1964 （1976-1997）. In the former case, there is an enhanced Walker cell in the eastern Pacific and an anti-Walker cell in the western Pacific. The associated ascending motion resides in the central Pacific, which flows eastward and westward in the upper troposphere, descending in the eastern and western ends of the Pacific basin. At the same time, an anomalous East Asian Hadley Cell （EAHC） is found to connect the low-latitude and mid-latitude systems in East Asia, which strengthens the EASM. The descending branch of the EAHC lies in the west part of the anti-Walker cell, flowing northward in the lower troposphere and then ascending at the south of Lake Baikal （40°-50°N, 95°- 115°E） before returning to low latitudes in the upper troposphere, thus strengthening the EASM. The relationship between the EASM and SST in the eastern tropical Pacific is also discussed. A possible mechanism is proposed to link interdecadal variation of the EASM with the eastern tropical Pacific SST. A warmer sea surface temperature anomaly （SSTA） therein induces anomalous ascending motion in the eastern Pacific, resulting in a weaker Walker cell, and at the same time inducing an anomalous Walker cell in the western Pacific and an enhanced EAHC, leading to a weaker EASM. Furthermore, the interdecadal variation of summer precipitation over North China is found to be the south of Lake Baikal through enhancing and reducing strongly regulated by the velocity potential over the regional vertical motions.
文摘In the context of 1958–1997 NCEP/ NCAR re-analyses, the South Asia high (SAH) was divided into two components, barotropic and baroclinic, the former based on mass weighed vertical integration and the latter on the difference between the measured circulation and the barotropic component counterpart, whereupon the barotropic and baroclinic circulation conversion features were addressed of the research SAH during its seasonal variation. Evidence suggests that i) in summer (winter), the SAH is a thermal (dynamical) system, with dominant baroclinicity (barotropicity), either of the components accounting for approximately 70% of the total contribution; ii) as time progresses from winter to summer, accompanied by the barotropic SAH evolving into its baroclinic analog, the SAH is moving under the “ thermal guidance” of its baroclinic component circulation, suggesting that the component circulation precedes the system itself in variation; iii) the reversal happens when it goes from summer to winter, with the SAH displacement under the “ dynamic steering” of its barotropic component circulation. Key words SAH (South Asia high) - Barotropic circulation - Baroclinic circulation - Seasonal variation (1)This work is supported by the National Natural Sciences Foundation of China under Grant No.49735170.
基金N ational N atural Science Foundation of China, N o.40271020 K now ledge Innovation Project of the Institute ofG eographic Sciences and N aturalResources Research,CA S,N o.CX IO G -A 04-09
文摘The spatial distribution and seasonal variation of the tide-induced Lagrangian Residual Circulations （LRC hereafter）, wind-driven LRC, and the coupling dynamic characteristics were simulated using ECOM, given the Hellerman and Rosenstein global monthly-mean wind stresses. The results showed that the tide-induced LRC of the harmonic constituent M2 bears an identical pattern in four seasons in the Bohai Sea： the surface one is weak with random directions; however, there exist a southeast current from the Bohai Strait to the Laizhou bay, and a weakly anticlockwise gyre in the south of the Bohai Strait for the bottom layer LRC. The magnitude of bottom layer tide-induced LRC is larger than the surface one, and moreover, it contributes significantly to the whole LRC in the Bohai Sea. Unlike the identical structure of the tide-induced LRC, the wind driven LRC varies seasonally under the prevailing monsoon. It forms a distinct gyre under the summer and winter monsoons in July and January respectively, but it seems weak and non-directional in April and September.
基金Major State Basic Research Development Program of China(973 Program)(2010CB950304)
文摘Since the South China Sea (SCS) summer monsoon (SCSSM) is pronouncedly featured by abruptly intensified southwesterly and obviously increased precipitation over the SCS,the lower-tropospheric winds and/or convection intensities are widely used to determine the SCSSM onset.The methods can be used successfully in most of the years but not in 2006.Due to the intrusion of Typhoon Chanchu(0601)that year,the usual method of determining SCSSM onset date by utilizing the SCS regional indices is less capable of pinpointing the real onset date.In order to solve the problem,larger-scale situations have to be taken into account.Zonal and meridional circulations would be better to determine the break-out date of SCSSM in 2006.The result indicates that its onset date is May 16.Moreover,similar onset dates for other years can be obtained using various methods,implying that large-scale zonal and meridional circulations can be used as an alternative method for determining the SCSSM onset date.
文摘A modified inverse method is used to compute the circulations east of Taiwan and in the East China Sec and east of the Ryukyu Islands with hydrographic data obtained during early summer of 1985. The computational region covers an area west of 129°E and from 21°45'N to 35°N. The computed results show that: (1 ) The net volume transport (VT ) of the Kuroshio through 21°45'N Section east of Ta Taiwan and west of 123°E is about 45 × 10￣6 m￣3/sduring early summer of 1985. The Kuroshio has. two current cores. One is located near Taiwan, and its velocity isvery large and its maximum velocity is 226 cm/s at the 100 m level, which is close to the maximum velocity of the beginning of the Kuroshio east of the Philippines. The other is located further to the east, and its maximum velocity is159 cm/s at the 100m level; (2) through a transect northwest Of Miyakojima Island and a transect southwest of Okinawa laaed the volume transports of the Kuroshio in the East China Sea both are about 25 × 10￣6 m￣3/s. The maximumvelocity of the Kuroshio at these two sections is 194 and 128 cm/s, respectively, and both are located on the shelfbreak; (3) beneath and east of the Kurohio there are the countercurrent (4) southeast of Okinawa Island there is anortheastward current, and its VT at Section HI is about 12. 6 × 10￣6 m￣3/s, and it comes from a westward flow at 129° This project was supported by the National Natural Science Foundation of China under contract No. 49476278.(Second Institute of Oceanography, State Oceanic Administration, Hongzhou310012, China) (Institute of Oceanography, Taiwan University, Taipei, China)E Section and the recirculating gyre, and does not originate from the Kuroshio east of Taiwan during early summer of 1985. There is a southwestward abyssal current east of Okinawa Islands (5) there are several different scale eddies in this computational region. For example, there is a meso-scale strong cyclonic eddy east of Miyakojima Island.
基金This work was supported by the National Natural Science Foundation of China(Grants No.51979071,51779073,and 51809073)the Jiangsu Provincial Natural Science Fund for Distinguished Young Scholars(Grant No.BK20180021)the National Ten Thousand Talent Program for Young Top-Notch Talents,and the Six Talent Peaks Project of Jiangsu Province.
基金supported by the National Natural Science Foundation of China (No. 41175004)the China Meteorological Administration Special Public Welfare Research Fund (No. GYHY201106033)
文摘Currently, the Chinese central government is considering plans to build a trilateral economic sphere in the Bohai Bay area, including Beijing, Tianjin and Hebei（BTH）, where haze pollution frequently occurs. To achieve sustainable development, it is necessary to understand the physical mechanism of the haze pollution there. Therefore, the pollutant transport mechanisms of a haze event over the BTH region from 23 to 24 September 2011 were studied using the Weather Research and Forecasting model and the FLEXible-PARTicle dispersion model to understand the effects of the local atmospheric circulations and atmospheric boundary layer structure. Results suggested that the penetration by sea-breeze could strengthen the vertical dispersion by lifting up the planetary boundary layer height（PBLH） and carry the local pollutants to the downstream areas; in the early night, two elevated pollution layers（EPLs） may be generated over the mountain areas： the pollutants in the upper EPL at the altitude of 2–2.5 km were favored to disperse by long-range transport, while the lower EPL at the altitude of 1 km may serve as a reservoir, and the pollutants there could be transported downward and contribute to the surface air pollution.The intensity of the sea–land and mountain–valley breeze circulations played an important role in the vertical transport and distribution of pollutants. It was also found that the diurnal evolution of the PBLH is important for the vertical dispersion of the pollutants,which is strongly affected by the local atmospheric circulations and the distribution of urban areas.
基金jointly supported by the R&D Special Fund for Public Welfare Industry(meteorology)of China(Grant No.GYHY201306031)the National Natural Science Foundation of China(Grant No.40905040)the National Science Foundation of United States(Grant No.1107509)
文摘This paper examines the dominant submonthly variability of zonally symmetrical atmospheric circula- tion in the Northern Hemisphere （NH） winter within the context of the Northern Annular Mode （NAM）, with particular emphasis on interactive stratosphere-troposphere processes. The submonthly variability is identified and measured using a daily NAM index, which concentrates primarily on zonally symmetrical circulation. A schematic lifecycle of submonthly variability is developed that reveals a two-way coupling pro- cess between the stratosphere and troposphere in the NH polar region. Specifically, anomalous tropospheric zonal winds in the Atlantic and Pacific sectors of the Arctic propagate upwards to the low stratosphere, disturbing the polar vortex, and resulting in an anomalous stratospheric geopotential height （HGT） that subsequently propagates down into the troposphere and changes the sign of the surface circulations. From the standpoint of planetary-scale wave activities, a feedback loop is also evident when the anoma- lous planetary-scale waves （with wavenumbers 2 and 3） propagate upwards, which disturbs the anomalous zonally symmetrical flow in the low stratosphere, and induces the anomalous HGT to move poleward in the low stratosphere, and then propagates down into the troposphere. This increases the energy of waves at wavenumbers 2 and 3 in the low troposphere in middle latitudes by enhancing the land-sea contrast of the anomalous HGT field. Thus, this study supports the viewpoint that the downward propagation of stratospheric NAM signals may not originate in the stratosphere.
文摘The circulations off the Changjiang mouth in May and November were simulated by a three dimension numerical model with monthly averaged parameters of dynamic factors in this paper. The area covers the East China Sea (ECS), Yellow Sea and Bohai Sea. Simulated results show that the circulation off the Changjiang mouth in spring and autumn is mainly the Changjiang runoff and Taiwan Warm Current (TWC). The Changjiang discharge is much larger in May than in November, and the wind is westward in May, and southward in November off the Changjiang mouth. The runoff in May branches in three parts, one eastward flows, the other two flow northward and southward along the Subei and Zhejiang coast respectively. The Changjiang diluted water expands eastward off the mouth, and forms a strong salinity front near the mouth. Surface circulation in autumn is similar to that in winter, the runoff southward flows along the coast, and the northward flowing TWC becomes weaker compared to that in spring and summer. The bottom circulations in May and November are mainly the runoffnear the mouth and the TWC offthe mouth, and the runoff and TWC are greater in May than in November.
基金supported by the National Natural Science Foundation (Grant No. 41275078)the Special Fund for Public Welfare Industry (Meteorology) (Grant No. GYHY201306026)the National Science & Technology Pillar Program (Grant No. 2012BAC20B05) of China
文摘Based on the simulations of 31 global models in CMIP5, the performance of the models in simulating the Hadley and Walker circulations is evaluated. In addition, their change in intensity by the end of the 21st century （2080-2099） under the RCP4.5 and RCP8.5 scenarios, relative to 1986-2005, is analyzed from the perspective of 200 hPa velocity potential. Validation shows good performance of the individual CMIP5 models and the multi-model ensemble mean （MME） in re- producing the meridional （zonal） structure and magnitude of Hadley （Walker） circulation. The MME can also capture the observed strengthening tendency of the winter Hadley circulation and weakening tendency of the Walker circulation. Such secular trends can be simulated by 39% and 74% of the models, respectively. The MME projection indicates that the winter Hadley circulation and the Walker circulation will weaken under both scenarios by the end of the 21st century. The weak- ening amplitude is larger under RCP8.5 than RCP4.5, due to stronger external forcing. The majority of the CMIP5 models show the same projection as the MME. However, for the summer Hadley circulation, the MME shows little change under RCP4.5 and large intermodel spread is apparent. Around half of the models project an increase, and the other half project a decrease. Under the RCP8.5 scenario, the MME and 65% of the models project a weakening of the summer southern Hadley circulation.
文摘Data obtained from a comprehensive multidisciplinary oceanographic survey in the central and northern parts of the Taiwan Strait, 24°20′-26°00′N, 118°45°-121°00′E by the Fujian Institute of Oceanology during the period May, 1983 through May, 1984, showed that the distributions of dissolved oxygen (DO), nitrate, dissolved inorganic phosphate and silicate concentrations here had obvious areal and seasonal characteristics that were mainly influenced by the seasonal circulation ofthree major water systems in the Taiwan Strait-- the Taiwan Strait Warm Water (TSWW), theZhejiang-Fujian Coastal Water (ZFCW), and the Northeastern Strait Warm Water (NESWW).
