The studies in China on the formation of the summertime subtropical anticyclone on the climate timescale are reviewed. New insights in resent studies are introduced. It is stressed that either in the free atmosphere o...The studies in China on the formation of the summertime subtropical anticyclone on the climate timescale are reviewed. New insights in resent studies are introduced. It is stressed that either in the free atmosphere or in the planetary boundary, the descending arm of the Hadley cell cannot be considered as a mechanism for the formation of the subtropical anticyclone. Then the theories of thermal adaptation of the atmosphere to external thermal forcing and the potential vorticity forcing are developed to understand the formation of the subtropical anticyclone in the three-dimensional domain. Numerical experiments are designed to verify these theories. Results show that in the boreal summer, the formation of the strong South Asian High in the upper troposphere and the subtropical anticyclone over the western Pacific in the middle and lower troposphere is, to a great extent, due to the convective latent heating associated with the Asian monsoon, but affected by orography and the surface sensible heating over the continents. On the other hand, the formation of the subtropical anticyclone at the surface over the northern Pacific and in the upper troposphere over North America is mainly due to the strong surface sensible heating over North America, but affected by radiation cooling over the eastern North Pacific. Moreover, in the real atmosphere such individual thermal forcing is well organized. By considering the different diabatic heating in synthesis, a quadruple heating pattern is found over each subtropical continent and its adjacent oceans in summer. A distinct circulation pattern accompanies this heating pattern. The global summer subtropical heating and circulation may be viewed as 'mosaics' of such quadruplet heating and circulation patterns respectively. At last, some important issues for further research in understanding and predicting the variations of the subtropical anticyclone are raised.展开更多
The Asian summer monsoon （ASM） anticyclone is a dominant feature of the circulation in the upper troposphere- lower stratosphere （UTLS） during boreal summer, which is found to have persistent maxima in carbon mono...The Asian summer monsoon （ASM） anticyclone is a dominant feature of the circulation in the upper troposphere- lower stratosphere （UTLS） during boreal summer, which is found to have persistent maxima in carbon monoxide （CO）. This enhancement is due to the upward transport of air with high CO from the planetary boundary layer （PBL）, and confinement within the anticyclonic circulation. With rapid urbanization and industrialization, CO surface emissions are relatively high in the ASM region, especially in India and East China. To reveal the transport pathway of CO surface emissions over these two regions, and investigate the contribution of these to the CO distribution within the ASM anticyclone, a source sensitivity experiment was performed using the Weather Research and Forecasting （WRF） with chemistry model （WRF- Chem）. According to the experiment results, the CO within the ASM anticyclone mostly comes from India, while the contribution from East China is insignificant. The result is mainly caused by the different transportation mechanisms. In India, CO transportation is primarily affected by convection. The surface air with high CO over India is directly transported to the upper troposphere, and then confined within the ASM anticyclone, leading to a maximum value in the UTLS region. The CO transportation over East China is affected by deep convection and large-scale circulation, resulting mainly in transportation to Korea, Japan, and the North Pacific Ocean, with little upward transport to the anticyclone, leading to a high CO value at 215 hPa over these regions.展开更多
The simulation characteristics of the seasonal evolution of subtropical anticyclones in the Northern Hemisphere are documented for the Flexible Global Ocean-Atmosphere-Land System model, Spectral Version 2 （FGOALS-s2...The simulation characteristics of the seasonal evolution of subtropical anticyclones in the Northern Hemisphere are documented for the Flexible Global Ocean-Atmosphere-Land System model, Spectral Version 2 （FGOALS-s2）, developed at the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, the Institute of Atmospheric Physics. An understanding of the seasonal evolution of the subtropical anticyclones is also addressed. Compared with the global analysis established by the European Centre for Medium-Range Forecasts, the ERA-40 global reanalysis data, the general features of subtropical anticyclones and their evolution are simulated well in both winter and summer, while in spring a pronounced bias in the generation of the South Asia Anticyclone（SAA） exists. Its main deviation in geopotential height from the reanalysis is consistent with the bias of temperature in the troposphere. It is found that condensation heating （CO） plays a dominant role in the seasonal development of the SAA and the subtropical anticyclone over the western Pacific （SAWP） in the middle troposphere. The CO biases in the model account for the biases in the establishment of the SAA in spring and the weaker strength of the SAA and the SAWP from spring to summer. CO is persistently overestimated in the central-east tropical Pacific from winter to summer, while it is underestimated over the area from the South China Sea to the western Pacific from spring to summer. Such biases generate an illusive anticyclonic gyre in the upper troposphere above the middle Pacific and delay the generation of the SAA over South Asia in April. In mid- summer, the simulated SAA is located farther north than in the ERA-40 data owing to excessively strong surface sensible heating （SE） to the north of the Tibetan Plateau. Whereas, the two surface subtropical anticyclones in the eastern oceans during spring to summer are controlled mainly by the surface SE over the two continents in the Northern Hemisphere, which are simulated reasonably well, albeit with their centers shifted westwards owing to the weaker longwave radiation cooling in the simulation associated with much weaker local stratiform cloud. Further improvements in the related parameterization of physical processes are therefore identified.展开更多
The deep reason of severe disaster weather with the relationship among the earth nutation,rotation and atmospheric change is explored based on the effective results about the disaster weather prediction of the long te...The deep reason of severe disaster weather with the relationship among the earth nutation,rotation and atmospheric change is explored based on the effective results about the disaster weather prediction of the long term made by the variation of the earth rotation in near 10 years. It is discussed the relationship between the subtropical anticyclone and subtropical easterlies to aim at the problem of high temperature and drought in the globe,further more,the comparison analysis has been made to the earth nutation and the variation of rotation. The research results show that the reasons of severe disaster weather not only are due to atmosphere itself,but have some variation information of earth movement which could be used for the weather forecast.展开更多
Sea ice outflow through Fram Strait is a vital component of the sea ice mass balance of the Arctic Ocean.Previous studies have examined the role of large-scale modes of atmospheric circulation variability such as the ...Sea ice outflow through Fram Strait is a vital component of the sea ice mass balance of the Arctic Ocean.Previous studies have examined the role of large-scale modes of atmospheric circulation variability such as the Arctic Oscillation,North Atlantic Oscillation,and Dipole Anomaly in the movement of sea ice.This review emphasizes the distinct impacts of synoptic weather on sea ice export as well as on other relevant fields(i.e.,sea ice concentration and sea ice drift).We identify deficiencies in previous studies that should be addressed,and we summarize potential research subjects that should be investigated to further our understanding of the relationship between synoptic weather and sea ice export via Fram Strait.For example,the connection between summertime anticyclones and weakened potential vorticity related to the observed extensive spring Eurasian snow and Siberian Ocean sea ice loss is of considerable interest.In-depth exploration of this type of geophysical mechanism will be particularly useful in assessment of the robustness of such linkages inferred through statistical analyses.展开更多
Based on the actual circulation structure as well as weather characters over East_Asia subtropical region in summer, by using three_dimension non_linear forced/dissipated dynamic model, the activities of subtropical a...Based on the actual circulation structure as well as weather characters over East_Asia subtropical region in summer, by using three_dimension non_linear forced/dissipated dynamic model, the activities of subtropical anticyclone over East_Asia have been studied and discussed. The potential enstrophy criteria of system stability have been derived and also been analysed. The criterion can provide useful reference for analysing and predicting subtropical anticyclone's extending/shrinking as well as corresponding weather over East_Asia in summer.展开更多
By employing the NCEP/NCAR reanalysis data sets(1 000 to 10 hPa,2.5°× 2.5°),the thermal forcing impacts are analyzed of an easterly vortex(shortened as EV) over the tropical upper troposphere on the qua...By employing the NCEP/NCAR reanalysis data sets(1 000 to 10 hPa,2.5°× 2.5°),the thermal forcing impacts are analyzed of an easterly vortex(shortened as EV) over the tropical upper troposphere on the quasi-horizontal movement of the Western Pacific Subtropical Anticyclone(shortened as WPS A) during 22-25 June 2003.The relevant mechanisms are discussed as well.It is shown that the distribution and intensity of the non-adiabatic effect near the EV result in the anomalous eastward retreat of the WPSA.The WPSA prefers extending to the colder region,i.e.,it moves toward the region in which the non-adiabatic heating is weakening or the cooling is strengthening.During the WPSA retreat,the apparent changes of non-adiabatic heating illustrate the characteristics of enhanced cooling in the east side of the EV.Meanwhile,the cooling in the west side exhibits a weakened eastward trend,most prominently at 300 hPa in the troposphere.The evidence on the factors causing the change in thermal condition is found:the most important contribution to the heating-rate trend is the vertical transport term,followed in turn by the local change in the heating rate term and the horizontal advection term.As a result,the atmospheric non-adiabatic heating generated by the vertical transport and local change discussed above is mainly connected to the retreat of the WPSA.展开更多
By employing NCEP−NCAR 1°×1°reanalysis datasets,the mechanism of the easterlies vortex(EV)affecting the short-term movement of the subtropical anticyclone over the western Pacific(WPSA)in the mei-yu per...By employing NCEP−NCAR 1°×1°reanalysis datasets,the mechanism of the easterlies vortex(EV)affecting the short-term movement of the subtropical anticyclone over the western Pacific(WPSA)in the mei-yu period is examined using potential vorticity(PV)theory.The results show that when the EV and the westerlies vortex(WV)travel west/east to the same longitude of 120°E,the WPSA suddenly retreats.The EV and WV manifest as the downward transport of PV in the upper troposphere,and the variation of the corresponding high-value regions of PV significantly reflects the intensity changes of the EV and WV.The meridional propagation of PV causes the intensity change of the EV.The vertical movement on both sides of the EV is related to the position of the EV relative to the WPSA and the South Asian high(SAH).When the high PV in the easterlies and westerlies arrive at the same longitude in the meridional direction,the special circulation pattern will lower the position of PV isolines at the ridge line of the WPSA.Thus,the cyclonic circulation at the lower level will be strengthened,causing the abnormally eastward retreat of the WPSA.Analysis of the PV equation at the isentropic surface indicates that when the positive PV variation west of the EV intensifies,it connects with the positive PV variation east of the WV,forming a positive PV band and making the WPSA retreat abnormally.The horizontal advection of the PV has the greatest effect.The contribution of the vertical advection of PV and the vertical differential of heating is also positive,but the values are relatively small.The contribution of the residual was negative and it becomes smaller before and after the WPSA retreats.展开更多
During the Asian summer monsoon(ASM)season,the process of stratosphere-troposphere exchange significantly affects the concentration and spatial distribution of chemical constituents in the upper troposphere and lower ...During the Asian summer monsoon(ASM)season,the process of stratosphere-troposphere exchange significantly affects the concentration and spatial distribution of chemical constituents in the upper troposphere and lower stratosphere(UTLS).However,the effect of the intensity of the Asian summer monsoon anticyclone(ASMA)on the horizontal distribution of chemical species within and around the ASMA,especially on the daily time scale,remains unclear.Here,the authors use the MERRA-2 reanalysis dataset and Aura Microwave Limb Sounder observations to study the impact of ASMA intensity on chemical distributions at 100 hPa during the ASM season.The intraseasonal variation of ASMA is classified into a strong period(SP)and weak period(WP),which refer to the periods when the intensity of ASMA remains strong and weak,respectively.The relatively low ozone(O_(3))region is found to be larger at 100 hPa during SPs,while its mixing ratio is lower than during WPs in summer.In June,analysis shows that the O_(3) horizontal distribution is mainly related to the intensity of AMSA,especially during SPs in June,while deep convections also impact the O_(3) horizontal distribution in July and August.These results indicate that the intraseasonal variation of the ASMA intensity coupled to deep convection can significantly affect the chemical distribution in the UTLS region during the ASM season.展开更多
The onset of South China Sea summer monsoon in 1998 occurred on May 21st. Using the U.S. National Centers for Environmental Prediction reanalysis data, this paper examines the physical process of the weakening of a su...The onset of South China Sea summer monsoon in 1998 occurred on May 21st. Using the U.S. National Centers for Environmental Prediction reanalysis data, this paper examines the physical process of the weakening of a subtropical anticyclone in West Pacific during the onset period using the Zwack-Okossi vorticity equation. Results show that during the pre-onset period, the positive vorticity advection in front of an upper tropospheric trough was the most dominant physical mechanism for the increase of the cyclonic vorticity on the 850-hPa layer over the South China Sea and its nearby region. The secondary contribution to the increase of the cyclonic vorticity was the warm-air advection. After the onset, the magnitude of the latent-heat warming term rapidly increased and its effect on the increase of the cyclonic vorticity was about the same as the positive-vorticity advection. The adiabatic term and divergence term contributed negatively to the increase of the cyclonic vorticity most of the time. Thus, the positive vorticity advection is the most important physical mechanism for the weakening of the West Pacific subtropical anticyclone over the South China Sea during the onset period.展开更多
The task of vortex boundaries setting is one of the most complexes in examination of factors influencing on the vortex (circulation system) development and destruction. In this study a new approach of vortex analysis ...The task of vortex boundaries setting is one of the most complexes in examination of factors influencing on the vortex (circulation system) development and destruction. In this study a new approach of vortex analysis as a whole system is proposed. It is based on vorticity equation where vorticity (left part of the equation) is defined as time coefficients of EOF-decomposition, which is integrated indexes characterizing individual vortex dynamics. Right part of the vorticity equation depicts internal and external factors influencing on the vortex. It's approbation is done on the example of an arctic-subarctic circulation system including blocking anticyclone in winter 2012 which persisted for a long time over the Atlantic sector of the Arctic and led to the formation of the largest positive air temperature anomalies and the minimum ice cover area in the Barents and Kara seas in the entire history of regular observations. It is shown that the main factor in long-term maintenance of the blocking anticyclone over the Arctic was vorticity advection, which was stabilized by horizontal heat advection.展开更多
Tropical storms(TSs)can induce sea surface cooling,freshening,and phytoplankton blooms.The dissolved oxygen(DO)concentration response to TSs within an anticyclone is still unclear due to the rarity of in situ observat...Tropical storms(TSs)can induce sea surface cooling,freshening,and phytoplankton blooms.The dissolved oxygen(DO)concentration response to TSs within an anticyclone is still unclear due to the rarity of in situ observations.In this study,we investi-gate the variations in DO concentration attributed to TS‘Haitang’within an anticyclonic eddy in the northern South China Sea based on Chinese underwater glider data.DO concentrations have a higher value at the edge of eddy than at the core.Influenced by TS,DO concentrations decrease remarkably in the subsurface layer in all three regions(inside,edge,and outside of the anticyclonic eddy).The mean DO concentrations decrease more at the edge of the anticyclone than those inside the anticyclone.The recovery time of DO concentration after TS is around one week at the edge of the anticyclone and is>10 days within the eddy.Our observations show that the DO concentrations decrease above the subsurface chlorophyll a maxima layer.Quantitative analysis shows that variations in DO concentration are dominated by horizontal advection and vertical advection terms in the subsurface layer.展开更多
This research analyzes the variations of the South Asian Summer Monsoon Rainfall Anomaly(SASMRA)between the first development year(Y0)and the following year(Y1)of all multi-year La Ni?a events from 1958 to 2022.During...This research analyzes the variations of the South Asian Summer Monsoon Rainfall Anomaly(SASMRA)between the first development year(Y0)and the following year(Y1)of all multi-year La Ni?a events from 1958 to 2022.During Y0,monsoon precipitation surpasses climatological values,presenting a tripole spatial pattern,whereas Y1 is characterized by below-normal precipitation with a dipole pattern.In certain regions,the difference in precipitation between Y0 and Y1 reaches up to 3 mm day–1.This work provides further insight into the key tropical ocean regions driving the precipitation distinction,and elucidates their coupling mechanisms with large-scale atmospheric circulation anomalies.Influenced by the development of earlier ocean-atmosphere anomaly patterns,the Tropical Indian Ocean and Western Pacific(TIO-WP)warming(cooling)is significant during the summer of Y0(Y1).The elevated sea surface temperature(SST)in Y0 supports an anomalous Western North Pacific(WNP)anticyclone via a Kelvin-wave-induced Ekman divergence mechanism.This anomalous anticyclone intensifies the suppressed convection over the WNP,which results in increased divergence in the upper-level troposphere over the Indian Ocean and South Asian regions,thereby boosting convection.Simultaneously,the easterly winds associated with the strengthened equatorial latitude SST anomaly(SSTA)gradient and the anomalous anticyclone intensified,transporting a large amount of water vapor to the west.The combined moisture and dynamic conditions support the enhanced precipitation in the South Asian region.展开更多
The western Noah Pacific anomalous anticyclone （WNPAC） is an important atmospheric circulation system that conveys El Nifio impact on East Asian climate. In this review paper, various theories on the formation and m...The western Noah Pacific anomalous anticyclone （WNPAC） is an important atmospheric circulation system that conveys El Nifio impact on East Asian climate. In this review paper, various theories on the formation and maintenance of the WNPAC, including warm pool atmosphere-ocean interaction, Indian Ocean capacitor, a combination mode that emphasizes nonlinear interaction between ENSO and annual cycle, moist enthalpy advecfion/Rossby wave modulation, and central Pacific SST forcing, are discussed. It is concluded that local atmosphere-ocean interaction and moist enthalpy advection/Rossby wave modulation mechanisms are essential for the initial development and maintenance of the WNPAC during El Nifio mature winter and subsequent spring. The Indian Ocean capacitor mechanism does not contribute to the earlier development but helps maintain the WNPAC in El Nifio decaying summer. The cold SST anomaly in the western North Pacific, although damped in the summer, also plays a role. An inter- basin atmosphere-ocean interaction across the Indo-Pacific warm pool emerges as a new mechanism in summer. In addition, the central Pacific cold SST anomaly may induce the WNPAC during rapid El Nifio decaying/La Nina developing or La Nifia persisting summer. The near-annual periods predicted by the combination mode theory are hardly detected from observations and thus do not contribute to the formation of the WNPAC. The tropical Atlantic may have a capacitor effect similar to the tropical Indian Ocean.展开更多
This paper presents a review on the impact of El Nio on the interannual variability of atmospheric circulations over East Asia and rainfall in China through the anomalous anticyclone over western North Pacific(WNPAC)....This paper presents a review on the impact of El Nio on the interannual variability of atmospheric circulations over East Asia and rainfall in China through the anomalous anticyclone over western North Pacific(WNPAC). It explains the formation mechanisms of the WNPAC and physical processes by which the WNPAC affects the rainfall in China. During the mature phase of El Nio, the convective cooling anomalies over western tropical Pacific caused by the weakened convections trigger up an atmospheric Rossby wave response, resulting in the generation of the WNPAC. The WNPAC can persist from the winter when the El Nio is in its peak to subsequent summer, which is maintained by multiple factors including the sustained presence of convective cooling anomalies and the local air-sea interaction over western tropical Pacific, and the persistence of sea surface temperature anomalies(SSTA) in tropical Indian and tropical North Atlantic. The WNPAC can influence the atmospheric circulations over East Asia and rainfall in China not only simultaneously, but also in the subsequent summer after an El Nio year, leading to more rainfall over southern China. The current paper also points out that significant anomalies of atmospheric circulations over East Asia and rainfall over southern China occur in El Nio winter but not in La Nio winter, suggesting that El Nio and La Nio have an asymmetric effect. Other issues, including the impact of El Nio diversity and its impact as well as the relations of the factors affecting the persistence of the WNPAC with summer rainfall anomalies in China, are also discussed. At the end of this paper some issues calling for further investigation are discussed.展开更多
In this paper, characteristics of precipitating clouds in a thermal convective system （TCS） occurred in the southeastern mainland of China at 15：00 BT （Beijing time） on August 2, 2003 in the central western subtr...In this paper, characteristics of precipitating clouds in a thermal convective system （TCS） occurred in the southeastern mainland of China at 15：00 BT （Beijing time） on August 2, 2003 in the central western subtropical Pacific anticyclone （WSPA） is studied by using TRMM tropical rainfallmeasuring mission PR （precipitution radar） and IR Infrared radiation measurements. The precipitating cloud structures in both horizontal and vertical, relationship among storm top, cloud top, and surface rain rate are particularly analyzed. Results show that a strong ascending air at 500 hPa and a strong convergence of moisture flux at 850 hPa in the central WSPA supply necessary conditions both in dynamics and moisture for the happening of the TCS precipitation. The TRMM PR observation shows that the horizontal scale of the most TCS precipitating clouds is about 30-40 kin, their averaged vertical scale is above 10 kin, and the maximum reaches 17.5 kin. The maximum rain rate near surface of those TCS clouds is beyond 50 mm h^-1. The mean rain profile of the TCS clouds shows that its maximum rain rate at 5 km altitude is i km lower than the estimated freezing level of the environment. Compared with the mesoscale convective system （MCS） of ＂98.7.20＂, both systems have the same altitude of the maximum rain rate displayed from both mean rain profiles, but the TCS is much deeper than the MCS. From the altitude of the maximum rain rate to near surface, profiles show that rain rate reducing in the TCS is faster than that in the MCS, which implies a strong droplet evaporation process occurring in the TCS. Relationship among cloud top, storm top, and surface rain rate analysis indicates a large variation of cloud top when storm top is lower. On the contrary, the higher the storm top, the more consistent both cloud top and storm top. And, the larger the surface rain rate, the higher and more consistent for both cloud top and storm top. At the end, results expose that area fractions of non-precipitating clouds and clear sky are 86% and 2%, respectively. The area fraction of precipitating clouds is only about 1/8 that of non-precipitating clouds.展开更多
Climatological characteristics of subtropical anticyclone structure during seasonal transition are investigated based on NCEP/NCAR reanalysis data.The ridge-surface of subtropical anticyclone is defined by the boundar...Climatological characteristics of subtropical anticyclone structure during seasonal transition are investigated based on NCEP/NCAR reanalysis data.The ridge-surface of subtropical anticyclone is defined by the boundary surface between westerly to the north and easterly to the south (WEB in brief).In Afro-Asian monsoon area,the subtropical high in troposphere whose ridgelines are consecutive in wintertime takes on relatively symmetrical and zonal structure,the WEB tilts southward with increasing height.In summer,the subtropical high ridgelines are discontinuous at low levels and continuous at upper levels,the WEB tilts northward from the bottom up.Under the constraint of thermal wind relation,the WEB usually tilts toward warmer zone.May is the period when subtropical high modality most significantly varies.The structure and properties of subtropical high during seasonal transition are different from area to area.A new concept 'seasonal transition axis' is proposed based on formation and variation of the vertical ridge axis of subtropical anticyclone.The subtropical high of summer pattern firstly occurs over eastern Bay of Bengal in the beginning of May.then stabilizes over eastern Bay of Bengal,Indo-China,and western South China Sea in the 3rd pentad of May,it exists over the South China Sea in the 4th- 5th pentad of May and establishes over central India in the 1st-2nd pentad of June.The three consequential stages when summer modal subtropical high occurs correspond to that of Asian summer monsoon onset,respectively.To a great extent,the summer monsoon onset over the Bay of Bengal depends on the reversal of meridional temperature gradient in vicinity of the WEB in upper troposphere.The meridional temperature gradient at middle-upper levels in troposphere can be used as a good indicator for measuring the seasonal transition and Asian monsoon onset.展开更多
Using the reanalysis data and 20th century simulation of coupled model FGOALS_gl developed by LASG/IAP, we identified two distinct interannual modes of Northwestern Pacific Subtropical Anticyclone （NWPAC） by perform...Using the reanalysis data and 20th century simulation of coupled model FGOALS_gl developed by LASG/IAP, we identified two distinct interannual modes of Northwestern Pacific Subtropical Anticyclone （NWPAC） by performing Empirical Orthogonal Function （EOF） analysis on 850 hPa wind field over the northwestern Pacific in summer. Based on the associated anoma- lous equatorial zonal wind, these two modes are termed as ＂Equatorial Easterly related Mode＂ （EEM） and ＂Equatorial Westerly related Mode＂ （EWM）, respectively. The formation mechanisms of these two modes are similar, whereas the maintenance mechanisms, dominant periods, and the relationships with ENSO are different. The EEM is associated with E1 Nifio decaying phase, with the anomalous anticyclone established in the preceding winter and persisted into summer through local positive air-sea feedback. By enhancing equatorial upwelling of subsurface cold water, EEM favors the transition of ENSO from E1 Nifio to La Nifia. The EWM is accompanied by the E1 Nifio events with long persistence, with the anomalous anticyclone formed in spring and strengthened in summer due to the warm Sea Surface Temperature anomalies （SSTA） forcing from the equatorial central-eastern Pacific. The model well reproduces the spatial patterns of these two modes, but fails to simulate the percentage variance accounted for by the two modes. In the NCEP reanalysis （model result）, EEM （EWM） appears as the first mode, which accounts for 35.6% （68.2%） of the total variance.展开更多
Four observed blocking anticyclones in different regions of the Northern Hemisphere are in- vestigated.Analyses show that there exist distinct differences in the maintenance of the time-mean quasi-geostrophic potentia...Four observed blocking anticyclones in different regions of the Northern Hemisphere are in- vestigated.Analyses show that there exist distinct differences in the maintenance of the time-mean quasi-geostrophic potential vorticity(PV)low in 300 hPa within blocking areas.In two Pacific blocking cases,the PV advection by time-mean flow tends to flow the PV low to northwestern part of the blocking highs,and thus is beneficial to the maintenance of the blockings'strength.The transfer by transient eddies acts to balance the effect of the time-mean flow.In the Atlantic and Alaska blocking cases,however,the advection of mean flow tends to flow the PV low eastward. The PV transfer by transient eddies acts to flow potential vorticity low to the western part of the blocking ridges and also to balance the time-mean flow's effect.Thus,in the latter two cases,it is the transfer by the transient eddies that acts to maintain the blockings.展开更多
By employing the NCEP/NCAR reanalysis data （1000-10 hPa, 2.5°×2.5°）, the impact of the vortex in the easterlies （EV） over the tropical upper troposphere on the zonal movement of the western Pacific ...By employing the NCEP/NCAR reanalysis data （1000-10 hPa, 2.5°×2.5°）, the impact of the vortex in the easterlies （EV） over the tropical upper troposphere on the zonal movement of the western Pacific subtropical anticyclone （WPSA） during 19-25 June 2003 is analyzed in this paper. It is shown that the EV can extend from middle troposphere to the height of 50 hPa, reaching a maximum at 200 hPa. The vertical thermal distribution appears to be ＂warmer in the upper layer and colder in the lower layer＂. The WPSA retreats eastward abnormally when the EV and the vortex in the westerlies （WV） encounter around the same longitude while they move toward each other. It is also shown that the vorticity variation extends from the troposphere to the height of 50 hPa, with the most prominent change occurring at 200 hPa by the diagnostic analyses of the vertical vorticity equation. The WPSA appears to retreat abnormally eastward while the negative/positive vorticity change becomes stronger near the east/west side of the EV, and the areas with positive vorticity tendency both in the EV and WV join together into one belt along 130°E during the process of the EV and the WV moving toward each other. In the vorticity equation, the positive contribution caused by the horizontal advection term is the maximum, and the minimum is caused by theβ effect. It is also found that enhanced horizontal vorticity advection andβ effect, as well as the ＂barotropic development＂ resulted from the in-phase superposition of the southerly and the northerly winds in the easterlies and westerlies near 130~E, are in agreement with the WPSA eastward retreat.展开更多
基金supported by the Chinese Academy of Sciences(Grant No.ZKCX2 SW-210)the National Natural Science Foundation of China(Grant Nos.40135020,40221503,and 40023001).
文摘The studies in China on the formation of the summertime subtropical anticyclone on the climate timescale are reviewed. New insights in resent studies are introduced. It is stressed that either in the free atmosphere or in the planetary boundary, the descending arm of the Hadley cell cannot be considered as a mechanism for the formation of the subtropical anticyclone. Then the theories of thermal adaptation of the atmosphere to external thermal forcing and the potential vorticity forcing are developed to understand the formation of the subtropical anticyclone in the three-dimensional domain. Numerical experiments are designed to verify these theories. Results show that in the boreal summer, the formation of the strong South Asian High in the upper troposphere and the subtropical anticyclone over the western Pacific in the middle and lower troposphere is, to a great extent, due to the convective latent heating associated with the Asian monsoon, but affected by orography and the surface sensible heating over the continents. On the other hand, the formation of the subtropical anticyclone at the surface over the northern Pacific and in the upper troposphere over North America is mainly due to the strong surface sensible heating over North America, but affected by radiation cooling over the eastern North Pacific. Moreover, in the real atmosphere such individual thermal forcing is well organized. By considering the different diabatic heating in synthesis, a quadruple heating pattern is found over each subtropical continent and its adjacent oceans in summer. A distinct circulation pattern accompanies this heating pattern. The global summer subtropical heating and circulation may be viewed as 'mosaics' of such quadruplet heating and circulation patterns respectively. At last, some important issues for further research in understanding and predicting the variations of the subtropical anticyclone are raised.
基金supported by the National Basic Research Program of China (Grant No. 2010CB428602)the National Natural Science Foundation of China (Grant Nos. 41175040 and 91337214)
文摘The Asian summer monsoon （ASM） anticyclone is a dominant feature of the circulation in the upper troposphere- lower stratosphere （UTLS） during boreal summer, which is found to have persistent maxima in carbon monoxide （CO）. This enhancement is due to the upward transport of air with high CO from the planetary boundary layer （PBL）, and confinement within the anticyclonic circulation. With rapid urbanization and industrialization, CO surface emissions are relatively high in the ASM region, especially in India and East China. To reveal the transport pathway of CO surface emissions over these two regions, and investigate the contribution of these to the CO distribution within the ASM anticyclone, a source sensitivity experiment was performed using the Weather Research and Forecasting （WRF） with chemistry model （WRF- Chem）. According to the experiment results, the CO within the ASM anticyclone mostly comes from India, while the contribution from East China is insignificant. The result is mainly caused by the different transportation mechanisms. In India, CO transportation is primarily affected by convection. The surface air with high CO over India is directly transported to the upper troposphere, and then confined within the ASM anticyclone, leading to a maximum value in the UTLS region. The CO transportation over East China is affected by deep convection and large-scale circulation, resulting mainly in transportation to Korea, Japan, and the North Pacific Ocean, with little upward transport to the anticyclone, leading to a high CO value at 215 hPa over these regions.
基金supported by the National Natural Science Foundation of China(Grant No.40925015)the CAS Strategic Priority Research Program(Grant No.XDA01020303)the National Program on Key Basic Research Project(Grant No.2010CB950400)
文摘The simulation characteristics of the seasonal evolution of subtropical anticyclones in the Northern Hemisphere are documented for the Flexible Global Ocean-Atmosphere-Land System model, Spectral Version 2 （FGOALS-s2）, developed at the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, the Institute of Atmospheric Physics. An understanding of the seasonal evolution of the subtropical anticyclones is also addressed. Compared with the global analysis established by the European Centre for Medium-Range Forecasts, the ERA-40 global reanalysis data, the general features of subtropical anticyclones and their evolution are simulated well in both winter and summer, while in spring a pronounced bias in the generation of the South Asia Anticyclone（SAA） exists. Its main deviation in geopotential height from the reanalysis is consistent with the bias of temperature in the troposphere. It is found that condensation heating （CO） plays a dominant role in the seasonal development of the SAA and the subtropical anticyclone over the western Pacific （SAWP） in the middle troposphere. The CO biases in the model account for the biases in the establishment of the SAA in spring and the weaker strength of the SAA and the SAWP from spring to summer. CO is persistently overestimated in the central-east tropical Pacific from winter to summer, while it is underestimated over the area from the South China Sea to the western Pacific from spring to summer. Such biases generate an illusive anticyclonic gyre in the upper troposphere above the middle Pacific and delay the generation of the SAA over South Asia in April. In mid- summer, the simulated SAA is located farther north than in the ERA-40 data owing to excessively strong surface sensible heating （SE） to the north of the Tibetan Plateau. Whereas, the two surface subtropical anticyclones in the eastern oceans during spring to summer are controlled mainly by the surface SE over the two continents in the Northern Hemisphere, which are simulated reasonably well, albeit with their centers shifted westwards owing to the weaker longwave radiation cooling in the simulation associated with much weaker local stratiform cloud. Further improvements in the related parameterization of physical processes are therefore identified.
基金supported by National Natural Science Foundation of China through Grant( 60674074 )the foundation projects of 2008 LASW-B11,GYHY(QX)2007-6-26,GYHY(QX)2007-6-2, IHR2007K02,FiDAF-2-01, BJG200801,2007AA061901,QD62,KF(2006)11
文摘The deep reason of severe disaster weather with the relationship among the earth nutation,rotation and atmospheric change is explored based on the effective results about the disaster weather prediction of the long term made by the variation of the earth rotation in near 10 years. It is discussed the relationship between the subtropical anticyclone and subtropical easterlies to aim at the problem of high temperature and drought in the globe,further more,the comparison analysis has been made to the earth nutation and the variation of rotation. The research results show that the reasons of severe disaster weather not only are due to atmosphere itself,but have some variation information of earth movement which could be used for the weather forecast.
基金This work was funded by the Natural Science Foundation of China(Grant no.41406215)The authors thank the two anonymous reviewers for their constructive comments.
文摘Sea ice outflow through Fram Strait is a vital component of the sea ice mass balance of the Arctic Ocean.Previous studies have examined the role of large-scale modes of atmospheric circulation variability such as the Arctic Oscillation,North Atlantic Oscillation,and Dipole Anomaly in the movement of sea ice.This review emphasizes the distinct impacts of synoptic weather on sea ice export as well as on other relevant fields(i.e.,sea ice concentration and sea ice drift).We identify deficiencies in previous studies that should be addressed,and we summarize potential research subjects that should be investigated to further our understanding of the relationship between synoptic weather and sea ice export via Fram Strait.For example,the connection between summertime anticyclones and weakened potential vorticity related to the observed extensive spring Eurasian snow and Siberian Ocean sea ice loss is of considerable interest.In-depth exploration of this type of geophysical mechanism will be particularly useful in assessment of the robustness of such linkages inferred through statistical analyses.
文摘Based on the actual circulation structure as well as weather characters over East_Asia subtropical region in summer, by using three_dimension non_linear forced/dissipated dynamic model, the activities of subtropical anticyclone over East_Asia have been studied and discussed. The potential enstrophy criteria of system stability have been derived and also been analysed. The criterion can provide useful reference for analysing and predicting subtropical anticyclone's extending/shrinking as well as corresponding weather over East_Asia in summer.
基金LASW State Key Laboratory Special Fund(2014LASW-A03)National Science Foundation of China(41475041)
文摘By employing the NCEP/NCAR reanalysis data sets(1 000 to 10 hPa,2.5°× 2.5°),the thermal forcing impacts are analyzed of an easterly vortex(shortened as EV) over the tropical upper troposphere on the quasi-horizontal movement of the Western Pacific Subtropical Anticyclone(shortened as WPS A) during 22-25 June 2003.The relevant mechanisms are discussed as well.It is shown that the distribution and intensity of the non-adiabatic effect near the EV result in the anomalous eastward retreat of the WPSA.The WPSA prefers extending to the colder region,i.e.,it moves toward the region in which the non-adiabatic heating is weakening or the cooling is strengthening.During the WPSA retreat,the apparent changes of non-adiabatic heating illustrate the characteristics of enhanced cooling in the east side of the EV.Meanwhile,the cooling in the west side exhibits a weakened eastward trend,most prominently at 300 hPa in the troposphere.The evidence on the factors causing the change in thermal condition is found:the most important contribution to the heating-rate trend is the vertical transport term,followed in turn by the local change in the heating rate term and the horizontal advection term.As a result,the atmospheric non-adiabatic heating generated by the vertical transport and local change discussed above is mainly connected to the retreat of the WPSA.
基金supported by the National Natural Science Foundation of China(Grant Nos.41775048,91937301,41775050 and 91637105)the National Key R&D Program of China(Grant No.2018YFC1507804)the Second Tibetan Plateau Scientific Expedition and Research(STEP)program(Grant No.2019QZKK0105).
文摘By employing NCEP−NCAR 1°×1°reanalysis datasets,the mechanism of the easterlies vortex(EV)affecting the short-term movement of the subtropical anticyclone over the western Pacific(WPSA)in the mei-yu period is examined using potential vorticity(PV)theory.The results show that when the EV and the westerlies vortex(WV)travel west/east to the same longitude of 120°E,the WPSA suddenly retreats.The EV and WV manifest as the downward transport of PV in the upper troposphere,and the variation of the corresponding high-value regions of PV significantly reflects the intensity changes of the EV and WV.The meridional propagation of PV causes the intensity change of the EV.The vertical movement on both sides of the EV is related to the position of the EV relative to the WPSA and the South Asian high(SAH).When the high PV in the easterlies and westerlies arrive at the same longitude in the meridional direction,the special circulation pattern will lower the position of PV isolines at the ridge line of the WPSA.Thus,the cyclonic circulation at the lower level will be strengthened,causing the abnormally eastward retreat of the WPSA.Analysis of the PV equation at the isentropic surface indicates that when the positive PV variation west of the EV intensifies,it connects with the positive PV variation east of the WV,forming a positive PV band and making the WPSA retreat abnormally.The horizontal advection of the PV has the greatest effect.The contribution of the vertical advection of PV and the vertical differential of heating is also positive,but the values are relatively small.The contribution of the residual was negative and it becomes smaller before and after the WPSA retreats.
基金sponsored by Strategic Priority Research Program of the Chinese Academy of Science[grant No.XDA17010106]the National Key Research and Development Program of China[grant Nos.2018YFC1505703 and 2018YFC1506704].
文摘During the Asian summer monsoon(ASM)season,the process of stratosphere-troposphere exchange significantly affects the concentration and spatial distribution of chemical constituents in the upper troposphere and lower stratosphere(UTLS).However,the effect of the intensity of the Asian summer monsoon anticyclone(ASMA)on the horizontal distribution of chemical species within and around the ASMA,especially on the daily time scale,remains unclear.Here,the authors use the MERRA-2 reanalysis dataset and Aura Microwave Limb Sounder observations to study the impact of ASMA intensity on chemical distributions at 100 hPa during the ASM season.The intraseasonal variation of ASMA is classified into a strong period(SP)and weak period(WP),which refer to the periods when the intensity of ASMA remains strong and weak,respectively.The relatively low ozone(O_(3))region is found to be larger at 100 hPa during SPs,while its mixing ratio is lower than during WPs in summer.In June,analysis shows that the O_(3) horizontal distribution is mainly related to the intensity of AMSA,especially during SPs in June,while deep convections also impact the O_(3) horizontal distribution in July and August.These results indicate that the intraseasonal variation of the ASMA intensity coupled to deep convection can significantly affect the chemical distribution in the UTLS region during the ASM season.
文摘The onset of South China Sea summer monsoon in 1998 occurred on May 21st. Using the U.S. National Centers for Environmental Prediction reanalysis data, this paper examines the physical process of the weakening of a subtropical anticyclone in West Pacific during the onset period using the Zwack-Okossi vorticity equation. Results show that during the pre-onset period, the positive vorticity advection in front of an upper tropospheric trough was the most dominant physical mechanism for the increase of the cyclonic vorticity on the 850-hPa layer over the South China Sea and its nearby region. The secondary contribution to the increase of the cyclonic vorticity was the warm-air advection. After the onset, the magnitude of the latent-heat warming term rapidly increased and its effect on the increase of the cyclonic vorticity was about the same as the positive-vorticity advection. The adiabatic term and divergence term contributed negatively to the increase of the cyclonic vorticity most of the time. Thus, the positive vorticity advection is the most important physical mechanism for the weakening of the West Pacific subtropical anticyclone over the South China Sea during the onset period.
文摘The task of vortex boundaries setting is one of the most complexes in examination of factors influencing on the vortex (circulation system) development and destruction. In this study a new approach of vortex analysis as a whole system is proposed. It is based on vorticity equation where vorticity (left part of the equation) is defined as time coefficients of EOF-decomposition, which is integrated indexes characterizing individual vortex dynamics. Right part of the vorticity equation depicts internal and external factors influencing on the vortex. It's approbation is done on the example of an arctic-subarctic circulation system including blocking anticyclone in winter 2012 which persisted for a long time over the Atlantic sector of the Arctic and led to the formation of the largest positive air temperature anomalies and the minimum ice cover area in the Barents and Kara seas in the entire history of regular observations. It is shown that the main factor in long-term maintenance of the blocking anticyclone over the Arctic was vorticity advection, which was stabilized by horizontal heat advection.
基金supported by the National Natural Science Foundation of China(No.41976002)the National Key R&D Plan of China(Nos.2017YFC0305904,2016YFC0301201).
文摘Tropical storms(TSs)can induce sea surface cooling,freshening,and phytoplankton blooms.The dissolved oxygen(DO)concentration response to TSs within an anticyclone is still unclear due to the rarity of in situ observations.In this study,we investi-gate the variations in DO concentration attributed to TS‘Haitang’within an anticyclonic eddy in the northern South China Sea based on Chinese underwater glider data.DO concentrations have a higher value at the edge of eddy than at the core.Influenced by TS,DO concentrations decrease remarkably in the subsurface layer in all three regions(inside,edge,and outside of the anticyclonic eddy).The mean DO concentrations decrease more at the edge of the anticyclone than those inside the anticyclone.The recovery time of DO concentration after TS is around one week at the edge of the anticyclone and is>10 days within the eddy.Our observations show that the DO concentrations decrease above the subsurface chlorophyll a maxima layer.Quantitative analysis shows that variations in DO concentration are dominated by horizontal advection and vertical advection terms in the subsurface layer.
基金Guangdong Major Project of Basic and Applied Basic Research(2020B0301030004)National Key Research and Development Program of China(2023YFF0805300)Civilian Space Programme of China(D040305)。
文摘This research analyzes the variations of the South Asian Summer Monsoon Rainfall Anomaly(SASMRA)between the first development year(Y0)and the following year(Y1)of all multi-year La Ni?a events from 1958 to 2022.During Y0,monsoon precipitation surpasses climatological values,presenting a tripole spatial pattern,whereas Y1 is characterized by below-normal precipitation with a dipole pattern.In certain regions,the difference in precipitation between Y0 and Y1 reaches up to 3 mm day–1.This work provides further insight into the key tropical ocean regions driving the precipitation distinction,and elucidates their coupling mechanisms with large-scale atmospheric circulation anomalies.Influenced by the development of earlier ocean-atmosphere anomaly patterns,the Tropical Indian Ocean and Western Pacific(TIO-WP)warming(cooling)is significant during the summer of Y0(Y1).The elevated sea surface temperature(SST)in Y0 supports an anomalous Western North Pacific(WNP)anticyclone via a Kelvin-wave-induced Ekman divergence mechanism.This anomalous anticyclone intensifies the suppressed convection over the WNP,which results in increased divergence in the upper-level troposphere over the Indian Ocean and South Asian regions,thereby boosting convection.Simultaneously,the easterly winds associated with the strengthened equatorial latitude SST anomaly(SSTA)gradient and the anomalous anticyclone intensified,transporting a large amount of water vapor to the west.The combined moisture and dynamic conditions support the enhanced precipitation in the South Asian region.
基金Supported by the National Key Research and Development Program(2017YFA0603802,2015CB453200)National Natural Science Foundation of China(41630423,41475084,41575043,41375095)+3 种基金United States National Science Foundation(AGS-1565653)Jiangsu Province Natural Science Foundation Key Project(BK20150062)Jiangsu Shuang-Chuang Team Fund(R2014SCT001)Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)
文摘The western Noah Pacific anomalous anticyclone （WNPAC） is an important atmospheric circulation system that conveys El Nifio impact on East Asian climate. In this review paper, various theories on the formation and maintenance of the WNPAC, including warm pool atmosphere-ocean interaction, Indian Ocean capacitor, a combination mode that emphasizes nonlinear interaction between ENSO and annual cycle, moist enthalpy advecfion/Rossby wave modulation, and central Pacific SST forcing, are discussed. It is concluded that local atmosphere-ocean interaction and moist enthalpy advection/Rossby wave modulation mechanisms are essential for the initial development and maintenance of the WNPAC during El Nifio mature winter and subsequent spring. The Indian Ocean capacitor mechanism does not contribute to the earlier development but helps maintain the WNPAC in El Nifio decaying summer. The cold SST anomaly in the western North Pacific, although damped in the summer, also plays a role. An inter- basin atmosphere-ocean interaction across the Indo-Pacific warm pool emerges as a new mechanism in summer. In addition, the central Pacific cold SST anomaly may induce the WNPAC during rapid El Nifio decaying/La Nina developing or La Nifia persisting summer. The near-annual periods predicted by the combination mode theory are hardly detected from observations and thus do not contribute to the formation of the WNPAC. The tropical Atlantic may have a capacitor effect similar to the tropical Indian Ocean.
基金supported by the National Key Project for Basic Science Development (Grant No. 2015CB453203)the National Key Research and Development Program (Grant No. 2016YFA0600602)the National Natural Science Foundation of China (Grant No. 41661144017)
文摘This paper presents a review on the impact of El Nio on the interannual variability of atmospheric circulations over East Asia and rainfall in China through the anomalous anticyclone over western North Pacific(WNPAC). It explains the formation mechanisms of the WNPAC and physical processes by which the WNPAC affects the rainfall in China. During the mature phase of El Nio, the convective cooling anomalies over western tropical Pacific caused by the weakened convections trigger up an atmospheric Rossby wave response, resulting in the generation of the WNPAC. The WNPAC can persist from the winter when the El Nio is in its peak to subsequent summer, which is maintained by multiple factors including the sustained presence of convective cooling anomalies and the local air-sea interaction over western tropical Pacific, and the persistence of sea surface temperature anomalies(SSTA) in tropical Indian and tropical North Atlantic. The WNPAC can influence the atmospheric circulations over East Asia and rainfall in China not only simultaneously, but also in the subsequent summer after an El Nio year, leading to more rainfall over southern China. The current paper also points out that significant anomalies of atmospheric circulations over East Asia and rainfall over southern China occur in El Nio winter but not in La Nio winter, suggesting that El Nio and La Nio have an asymmetric effect. Other issues, including the impact of El Nio diversity and its impact as well as the relations of the factors affecting the persistence of the WNPAC with summer rainfall anomalies in China, are also discussed. At the end of this paper some issues calling for further investigation are discussed.
基金Supported by grants of NKBRDPC (No. 2004CB418304) NSFC (Nos. 40175015 and 40375018)NSFC grant of the Joint Research Fund for Overseas Chinese Young Scholars (No. 40428006)EORC/JAXA (No. 206)
文摘In this paper, characteristics of precipitating clouds in a thermal convective system （TCS） occurred in the southeastern mainland of China at 15：00 BT （Beijing time） on August 2, 2003 in the central western subtropical Pacific anticyclone （WSPA） is studied by using TRMM tropical rainfallmeasuring mission PR （precipitution radar） and IR Infrared radiation measurements. The precipitating cloud structures in both horizontal and vertical, relationship among storm top, cloud top, and surface rain rate are particularly analyzed. Results show that a strong ascending air at 500 hPa and a strong convergence of moisture flux at 850 hPa in the central WSPA supply necessary conditions both in dynamics and moisture for the happening of the TCS precipitation. The TRMM PR observation shows that the horizontal scale of the most TCS precipitating clouds is about 30-40 kin, their averaged vertical scale is above 10 kin, and the maximum reaches 17.5 kin. The maximum rain rate near surface of those TCS clouds is beyond 50 mm h^-1. The mean rain profile of the TCS clouds shows that its maximum rain rate at 5 km altitude is i km lower than the estimated freezing level of the environment. Compared with the mesoscale convective system （MCS） of ＂98.7.20＂, both systems have the same altitude of the maximum rain rate displayed from both mean rain profiles, but the TCS is much deeper than the MCS. From the altitude of the maximum rain rate to near surface, profiles show that rain rate reducing in the TCS is faster than that in the MCS, which implies a strong droplet evaporation process occurring in the TCS. Relationship among cloud top, storm top, and surface rain rate analysis indicates a large variation of cloud top when storm top is lower. On the contrary, the higher the storm top, the more consistent both cloud top and storm top. And, the larger the surface rain rate, the higher and more consistent for both cloud top and storm top. At the end, results expose that area fractions of non-precipitating clouds and clear sky are 86% and 2%, respectively. The area fraction of precipitating clouds is only about 1/8 that of non-precipitating clouds.
基金National Key Program for Developing Basic Sciences(G1998040900)National Natural Science Foundation of China(40135020,49905002)+1 种基金Chinese Academy of Sciences(ZKCX2-SW-210)LASG Foundation(40023001)
文摘Climatological characteristics of subtropical anticyclone structure during seasonal transition are investigated based on NCEP/NCAR reanalysis data.The ridge-surface of subtropical anticyclone is defined by the boundary surface between westerly to the north and easterly to the south (WEB in brief).In Afro-Asian monsoon area,the subtropical high in troposphere whose ridgelines are consecutive in wintertime takes on relatively symmetrical and zonal structure,the WEB tilts southward with increasing height.In summer,the subtropical high ridgelines are discontinuous at low levels and continuous at upper levels,the WEB tilts northward from the bottom up.Under the constraint of thermal wind relation,the WEB usually tilts toward warmer zone.May is the period when subtropical high modality most significantly varies.The structure and properties of subtropical high during seasonal transition are different from area to area.A new concept 'seasonal transition axis' is proposed based on formation and variation of the vertical ridge axis of subtropical anticyclone.The subtropical high of summer pattern firstly occurs over eastern Bay of Bengal in the beginning of May.then stabilizes over eastern Bay of Bengal,Indo-China,and western South China Sea in the 3rd pentad of May,it exists over the South China Sea in the 4th- 5th pentad of May and establishes over central India in the 1st-2nd pentad of June.The three consequential stages when summer modal subtropical high occurs correspond to that of Asian summer monsoon onset,respectively.To a great extent,the summer monsoon onset over the Bay of Bengal depends on the reversal of meridional temperature gradient in vicinity of the WEB in upper troposphere.The meridional temperature gradient at middle-upper levels in troposphere can be used as a good indicator for measuring the seasonal transition and Asian monsoon onset.
基金supported by National Natural Science Foundation of China (Grant Nos.40890054 and 41125017)
文摘Using the reanalysis data and 20th century simulation of coupled model FGOALS_gl developed by LASG/IAP, we identified two distinct interannual modes of Northwestern Pacific Subtropical Anticyclone （NWPAC） by performing Empirical Orthogonal Function （EOF） analysis on 850 hPa wind field over the northwestern Pacific in summer. Based on the associated anoma- lous equatorial zonal wind, these two modes are termed as ＂Equatorial Easterly related Mode＂ （EEM） and ＂Equatorial Westerly related Mode＂ （EWM）, respectively. The formation mechanisms of these two modes are similar, whereas the maintenance mechanisms, dominant periods, and the relationships with ENSO are different. The EEM is associated with E1 Nifio decaying phase, with the anomalous anticyclone established in the preceding winter and persisted into summer through local positive air-sea feedback. By enhancing equatorial upwelling of subsurface cold water, EEM favors the transition of ENSO from E1 Nifio to La Nifia. The EWM is accompanied by the E1 Nifio events with long persistence, with the anomalous anticyclone formed in spring and strengthened in summer due to the warm Sea Surface Temperature anomalies （SSTA） forcing from the equatorial central-eastern Pacific. The model well reproduces the spatial patterns of these two modes, but fails to simulate the percentage variance accounted for by the two modes. In the NCEP reanalysis （model result）, EEM （EWM） appears as the first mode, which accounts for 35.6% （68.2%） of the total variance.
文摘Four observed blocking anticyclones in different regions of the Northern Hemisphere are in- vestigated.Analyses show that there exist distinct differences in the maintenance of the time-mean quasi-geostrophic potential vorticity(PV)low in 300 hPa within blocking areas.In two Pacific blocking cases,the PV advection by time-mean flow tends to flow the PV low to northwestern part of the blocking highs,and thus is beneficial to the maintenance of the blockings'strength.The transfer by transient eddies acts to balance the effect of the time-mean flow.In the Atlantic and Alaska blocking cases,however,the advection of mean flow tends to flow the PV low eastward. The PV transfer by transient eddies acts to flow potential vorticity low to the western part of the blocking ridges and also to balance the time-mean flow's effect.Thus,in the latter two cases,it is the transfer by the transient eddies that acts to maintain the blockings.
基金Supported by the National Natural Science Foundation of China under Grant No. 40875030Heavy Rain Opening Foun-dation under Grant No. IHR2005K04
文摘By employing the NCEP/NCAR reanalysis data （1000-10 hPa, 2.5°×2.5°）, the impact of the vortex in the easterlies （EV） over the tropical upper troposphere on the zonal movement of the western Pacific subtropical anticyclone （WPSA） during 19-25 June 2003 is analyzed in this paper. It is shown that the EV can extend from middle troposphere to the height of 50 hPa, reaching a maximum at 200 hPa. The vertical thermal distribution appears to be ＂warmer in the upper layer and colder in the lower layer＂. The WPSA retreats eastward abnormally when the EV and the vortex in the westerlies （WV） encounter around the same longitude while they move toward each other. It is also shown that the vorticity variation extends from the troposphere to the height of 50 hPa, with the most prominent change occurring at 200 hPa by the diagnostic analyses of the vertical vorticity equation. The WPSA appears to retreat abnormally eastward while the negative/positive vorticity change becomes stronger near the east/west side of the EV, and the areas with positive vorticity tendency both in the EV and WV join together into one belt along 130°E during the process of the EV and the WV moving toward each other. In the vorticity equation, the positive contribution caused by the horizontal advection term is the maximum, and the minimum is caused by theβ effect. It is also found that enhanced horizontal vorticity advection andβ effect, as well as the ＂barotropic development＂ resulted from the in-phase superposition of the southerly and the northerly winds in the easterlies and westerlies near 130~E, are in agreement with the WPSA eastward retreat.
