Pre-reading 1.What did historians believe caused the decline of Easter Island’s population?2.How did the Rapa Nui people grow crops in a harsh environment?Easter Island,which is in the Pacific Ocean to the west of Ch...Pre-reading 1.What did historians believe caused the decline of Easter Island’s population?2.How did the Rapa Nui people grow crops in a harsh environment?Easter Island,which is in the Pacific Ocean to the west of Chile,is famous for its giant stone statues.For a long time,historians believed that the people who once lived there destroyed their environment by using too many natural resources.As the island could support fewer people,the population dwindled.However,new research suggested that this probably wasn’t true.展开更多
1.Easter is a Christian feast that the resurrection of Jesus Christ. a.commemorate b.commemorates C.will commemorate d.has to commemorate 2.It is one of holy days in the calendar of Christian churches. a.most b.the mo...1.Easter is a Christian feast that the resurrection of Jesus Christ. a.commemorate b.commemorates C.will commemorate d.has to commemorate 2.It is one of holy days in the calendar of Christian churches. a.most b.the more e.more d.the most 3.Easter symbolizes God's promise that soul is immortal. a.man b.men c.man's d.mans' 4.Easter was a pagan festival. a.original b.展开更多
Air quality in eastern China has becoming more and more worrying in recent years, and haze is now No.1 air pollution issue. Results in this study show the decreasing Arctic sea ice(ASI) is an important contributor to ...Air quality in eastern China has becoming more and more worrying in recent years, and haze is now No.1 air pollution issue. Results in this study show the decreasing Arctic sea ice(ASI) is an important contributor to the recent increased haze days in eastern China. The authors find that the number of winter haze days(WHD) in eastern China is strongly negatively correlated with the preceding autumn ASI during 1979–2012, and about 45%– 67% of the WHD interannual to interdecadal variability can be explained by ASI variability. Following previous studies on the impact of ASI loss on the northern hemisphere climate, the authors' studies further reveal that the reduction of autumn ASI leads to positive sea-level pressure anomalies in mid-latitude Eurasia, northward shift of track of cyclone activity in China, and weak Rossby wave activity in eastern China south of 40N during winter season. These atmospheric circulation changes favor less cyclone activity and more stable atmosphere in eastern China, leading to more haze days there. Furthermore, the patterns of circulation changes associated with autumn ASI and WHD are in very good agreement over the East Asia, particularly in eastern China. The authors suggest that haze pollution may continue to be a serious issue in the near future as the decline of ASI continues under global warming.展开更多
Although it is well known that the tropical easterly jet(TEJ)has a significant impact on summer weather and climate over India and Africa,whether the TEJ exerts an important impact on tropical cyclone(TC)activity over...Although it is well known that the tropical easterly jet(TEJ)has a significant impact on summer weather and climate over India and Africa,whether the TEJ exerts an important impact on tropical cyclone(TC)activity over the western North Pacific(WNP)remains unknown.In this study,we examined the impact of the TEJ on the interannual variability of TC genesis frequency over the WNP in the TC season(June-September)during 1980-2020.The results show a significant positive correlation between TC genesis frequency over the WNP and the jet intensity in the entrance region of the TEJ over the tropical western Pacific(in brief WP_TEJ),with a correlation coefficient as high as 0.66.The intensified WP_TEJ results in strong ageostrophic northerly winds in the entrance region and thus upper-level divergence to the north of the jet axis over the main TC genesis region in the WNP.This would lead to an increase in upward motion in the troposphere with enhanced low-level convergence,which are the most important factors to the increases in low-level vorticity,mid-level humidity and low-level eddy kinetic energy,and the decreases in sea level pressure and vertical wind shear in the region.All these changes are favorable for TC genesis over the WNP and vice versa.Further analyses indicate that the interannual variability of the WP_TEJ intensity is likely to be linked to the local diabatic heating over the Indian Ocean-western Pacific and the central Pacific El Ni?o-Southern Oscillation.展开更多
The low latitude easterlies at 200 hPa in summer (May-October) is analysed climatically during the 13-year period from 1968 to 1980, with a special emphasis on the relationships between the anomalous tropical easterly...The low latitude easterlies at 200 hPa in summer (May-October) is analysed climatically during the 13-year period from 1968 to 1980, with a special emphasis on the relationships between the anomalous tropical easterly jet Stream over South Asia and the low latitude atmospheric circulation, and also the summer monsoon precipitation in India. The compositing analysis shows that the tropical easterly jet stream over South Asia has five anomalous patterns at 200 hPa i.e. the western pattern, middle pattern, eastern pattern, two-branch pattern and multi-core pattern. Evidence has shown that the precipitaion in India anomalously increased during the anomalous period of the western pattern and the middle pattern, but reverse case is true in the eastern pattern. Some different anomalies of the precipitation in different area of India were found during the other two anomalous pattern.展开更多
By employing the NCEP/NCAR reanalysis data sets (1000-10hPa, 2.5°× 2.5°), the characteristics have been analyzed of the structure and evolution of an easterly vortex over the tropical upper troposphere ...By employing the NCEP/NCAR reanalysis data sets (1000-10hPa, 2.5°× 2.5°), the characteristics have been analyzed of the structure and evolution of an easterly vortex over the tropical upper troposphere relating to the east-west direction shift of the subtropical anticyclone over the Western Pacific Ocean. It is shown that there exists a westward shift simultaneously between the anticyclone and the vortex locating south of it. The anticyclone retreats eastward abnormally while the easterly encounters with the westerly around the same longitudes as they move from the opposite directions. The former is an upper weather system, extending from mid-troposphere to the height of 50 hPa with the center locating on 200 hPa. The vertical thermal distribution illustrates the characteristics of being"warm in the upper layer but cold in the lower layer". The divergence effect and the vertical motion change largely within the east and west sides of the easterly vortex and ascending branch transforms to descending branch near its center.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
This study investigates the mean kinematic characteristics of the tropical Atlantic easterly disturbances in January-March （JFM）, April-June （AM J）, July-September （JAS） and October-December （OND） from 1968-19...This study investigates the mean kinematic characteristics of the tropical Atlantic easterly disturbances in January-March （JFM）, April-June （AM J）, July-September （JAS） and October-December （OND） from 1968-1998. For each season, the preferential tracks of these disturbances in the 3--10-day band periods were computed and spatialized, as well as their associated wavelength, velocity and main period, which lies between 3-5 days and between 6-9 days depending on the track and the season. Two main tracks are highlighted over the Atlantic Ocean. During OND and JFM these two tracks are well separated and located in each hemisphere around 15°S and 12.5°N. From AMJ to JAS these tracks migrate northward; in JAS, they merge into one over the northern tropical Atlantic along 17.5°N. The associated wavelength fields exhibit a meridional gradient, with large wavelengths （greater than 4000 km） around the equator, between 5°N and 5°S, and smaller wavelengths outside of this latitude band （between 2500-3500 kin）. The phase speed is also found to exhibit poleward decreasing values from 12-6 m s^-1. Over the north Atlantic track, 6-9-day disturbances were found to occur from January to May and approximately from October to December. From June to September, the 3-5-day waves dominate the synoptic activity. Over the south Atlantic track, between May and August the synoptic variability is mainly explained by the 3-5-day disturbances but from January to April and from September to December both 3-5-day waves and 6-9-day waves can occur.展开更多
On the basis of comprehensive analysis on weather background and main influencing system of rainstorm formation,using NCEP reanalysis data,rainfall data of Shaoyang ground regional automatic station,a new generation o...On the basis of comprehensive analysis on weather background and main influencing system of rainstorm formation,using NCEP reanalysis data,rainfall data of Shaoyang ground regional automatic station,a new generation of Doppler weather radar product information,etc.,high-altitude weather situation and physical formation mechanism of local double-cyclone type of rainstorm process with easterly wave in Shaoyang area on August 14,2016 were analyzed in detail,to find out prophase signal features which had indicating significance for rainstorm forecast. The results showed that:(1) the position of zonal subtropical high pressure in east-west direction was the necessary condition for the formation of easterly wave.(2) The rainstorm formation was closely related to double tropical depressions acting in the south of subtropical high pressure,and westward movement of easterly wave over 500 hPa and low-pressure inverted trough at low layer were main impact systems of the rainstorm.(3) Continuous flow of water vapor from the South China Sea to northwest was the source of water vapor required by this rainstorm.(4) Numerical prediction model products had certain guiding significance for forecasting the heavy precipitation,with important reference value.(5) Doppler radar products had strong forecasting ability in the nowcasting of rainstorm falling zone,which was an important measure of correcting forecast errors.展开更多
The study concerns the propagation of easterly wave (EW) at tropics as west-moving soliton more steady both in ionn and velocity as evidenced in the dynamic framework.Under the impact of different circulation patterns...The study concerns the propagation of easterly wave (EW) at tropics as west-moving soliton more steady both in ionn and velocity as evidenced in the dynamic framework.Under the impact of different circulation patterns over the regions of western Pacific trade wind,South-Asia monsoon and their transition,such a soliton becomes tapering off during its westward movement and degrading to a common dispersive wave on the whole,followed by dismtegra-non when striking the South-China Sea monsoon segment,thereby indicating that the sea sector is inaccessible to the soliton When no monsoon trough is present over the South Asian monsoon area around 30癗 or the monsoon depression ]S shallow,it is likely to have west-travelling soliton,which suggests the incursion of the EW into the South-Asian monsoon region.展开更多
[Objective] The research aimed to analyze an easterly wave thunderstorm and gale weather during the latter flood season of 2010.[Method] Based on conventional observation data,data of automatic station,NCEP 1°...[Objective] The research aimed to analyze an easterly wave thunderstorm and gale weather during the latter flood season of 2010.[Method] Based on conventional observation data,data of automatic station,NCEP 1°×1° reanalysis data,Doppler radar reflectivity and radial velocity data,the easterly wave thunderstorm and gale weather process which happened during 4-5 August,2010 was analyzed.The circulation situation,wind field and dynamic & thermal structures of easterly wave,echo characteristics of Doppler radar when thunderstorm and gale happened were studied.[Result] The thunderstorm and gale weather happened in the northeaster zone in front of the deep thick easterly wave trough.When thunderstorm and gale weather happened,position of the subtropical high was by north(ridge line was at 35° N).Eastward movement of the north branch of trough compelled subtropical high splitting into east and west circles.Westward extension of the east subtropical high and saddle-type field circulation were favorable for generation and development of the easterly wave.As development and westward movement of the easterly wave,in the influence zone in front of the trough,upper easterly component transmitted downward.Then,low-level northeaster obviously strengthened,and thunderstorm and gale weather appeared.In the zone where thunderstorm and gale happened,airflow had cyclonic convergence at the middle and low layers and anti-cyclonic divergence near the ground layer.Subsidence movement was obvious.Moreover,thermal force structure that it tended to be dry and cold at the middle and high layers,warm and wet at the low layer existed.Supercell storm was at the developed stage on 4th.It had obvious mesocyclone and hooked echo characteristics(meso-and small-scale characteristics).Characteristics of the squall line,gale region and adverse wind region appeared in central west Guangdong on 5th.Doppler characteristics of the mesocyclone,hooked echo,squall line,gale region and adverse wind region had indication significance for short-imminent forecast of the thunderstorm and gale.[Conclusion] This research revealed some information which had significance for forecasting local easterly wave thunderstorm and gale weather.展开更多
In this paper, a strong 1TCZ process and an 1TCZ - absent process during FGGE in 1979 were selected for comparison to explore how they were subject to the influence of the evolution of the upper easterly jets.
Easterly waves are one of the rain-bearing systems of northeast monsoon and produce massive rainfall events over south India. In the present case study, an attempt is made to identify extreme heavy rainfall event over...Easterly waves are one of the rain-bearing systems of northeast monsoon and produce massive rainfall events over south India. In the present case study, an attempt is made to identify extreme heavy rainfall event over south India on 26th October, 2006 due to the passage of the easterly wave. Satellite images provide an inverted v-shape easterly wave. Next, circulation features at different levels clearly indicate the location, movement and speed of the easterly wave. Strong north-easterlies with a magnitude of 9.9 m/s are maintained at the surface. The convergence is mainly occupied between 12°N - 16°N, while the divergence is 5°N - 12°N on 26th October, 2006 at the surface level. On 25th, easterly wave is advected north of trough with a magnitude of 0.2 m/s and increased during the remaining days. There are two divergence cells along 5°N and 16°N before and after the event at 700 hPa level. Thus this study helps to bring out the essential characteristics of the easterly wave during northeast monsoon. The highlight of this study is that the easterly wave creates floods in the absence of tropical cyclones over south India.展开更多
Many children in America enjoy hunting forEaster eggs.Easter is a celebration associated withthe Christian religion,but Easter eggs go back toancient festivals that celebrate the coming of
The Easter Parade is a masterpiece by Richard Yates,which was published in 1976.The image of Emily,the heroine of the book,can be regarded as an iconic figure of early feminists in America.The aim of this paper is to ...The Easter Parade is a masterpiece by Richard Yates,which was published in 1976.The image of Emily,the heroine of the book,can be regarded as an iconic figure of early feminists in America.The aim of this paper is to explore Richard Yates’view of feminism,through analyzing the image of Emily in the book,and to understand the pursuits and dilemmas of feminists.Emily,as a woman in patriarchal society,who has always struggled independently on her own and fights against her fate,ends up in failure.Sarah,a typical image of“the other”who is dependent on men,eventually dies a tragic death.In front of the cruel and unpredictable fate,whether women have the sense of resistance or not,it seems that life always points to tragedy.Emily’s path of awakening is accompanied by real-life dilemmas,which is the epitome of every feminist’s experience.展开更多
In this study,the Betts-Miller-Janjic(BMJ)convective adjustment scheme in the Weather Research and Forecasting(WRF)model version 4.0 was used to investigate the effect of itsα-parameter,which influences the first-gue...In this study,the Betts-Miller-Janjic(BMJ)convective adjustment scheme in the Weather Research and Forecasting(WRF)model version 4.0 was used to investigate the effect of itsα-parameter,which influences the first-guess potential temperature reference profile on the Madden-Julian oscillation(MJO)propagation and structure.This study diagnosed the MJO active phase composites of the MJO-filtered outgoing longwave radiation(OLR)during the December-to-February(DJF)period of 2006-2016 over the Indian Ocean(IO),Maritime Continent(MC),and western Pacific(WP).The results show that the MJO-filtered OLR intensity,propagation pattern,and MJO classification(standing,jumping,and propagating clusters)are sensitive to theα-value,but the phase speeds of propagating MJOs are not.Overall,with an increasingα-value,the simulated MJO-filtered OLR intensity increases,and the simulated propagation pattern is improved.Results also show that the intensity and propagation pattern of an eastward-propagating MJO are associated with MJO circulation structures and thermodynamic structures.Asαincreases,the front Walker cell and the low-level easterly anomaly are enhanced,which premoistens the lower troposphere and triggers more active shallow and congestus clouds.The enhanced shallow and congestus convection preconditions the lower to middle troposphere,accelerating the transition from congestus to deep convection,thereby facilitating eastward propagation of the MJO.Therefore,the simulated MJO tends to transfer from standing to eastward propagating asαincreases.In summary,increasing theα-value is a possible way to improve the simulation of the structure and propagation of the MJO.展开更多
The Antarctic Slope Current(ASC)links the processes occurring in the coast area with the global ocean by modulating the flow across the continental slope,which influences global overturning circulation and the mass ba...The Antarctic Slope Current(ASC)links the processes occurring in the coast area with the global ocean by modulating the flow across the continental slope,which influences global overturning circulation and the mass balance of the Antarctic ice shelves.This paper aims to explore the effects of wind and buoyancy fluxes on the long-term changes in the ASC using observation and reanalysis datasets.From 1993 to 2022,the ASC accelerated in all seasons,particularly in austral autumn,and was accompanied with the advancement of the strong flow.The positive buoyancy flux anomaly generates a low-density anomaly,which is accumulated by the prevailing surface easterly,maintaining a sharp density front along the continental slope.The heat flux intensifies the positive trend of buoyancy flux in summer and autumn,increasing the input of the lighter density anomaly into the ocean and advancing the strong flow of ASC.Compared with the annual mean,the additional acceleration of the ASC in autumn is mainly due to the contribution of the barotropic component,which could be explained by the local momentum input from the weakly enhanced local surface wind.The acceleration of the ASC is primarily driven by the positive trend of the buoyancy flux,while the influence of the wind on its seasonal variability becomes more significant due to the contribution of the local surface wind in autumn.展开更多
文摘Pre-reading 1.What did historians believe caused the decline of Easter Island’s population?2.How did the Rapa Nui people grow crops in a harsh environment?Easter Island,which is in the Pacific Ocean to the west of Chile,is famous for its giant stone statues.For a long time,historians believed that the people who once lived there destroyed their environment by using too many natural resources.As the island could support fewer people,the population dwindled.However,new research suggested that this probably wasn’t true.
文摘1.Easter is a Christian feast that the resurrection of Jesus Christ. a.commemorate b.commemorates C.will commemorate d.has to commemorate 2.It is one of holy days in the calendar of Christian churches. a.most b.the more e.more d.the most 3.Easter symbolizes God's promise that soul is immortal. a.man b.men c.man's d.mans' 4.Easter was a pagan festival. a.original b.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41421004 and 41210007)
文摘Air quality in eastern China has becoming more and more worrying in recent years, and haze is now No.1 air pollution issue. Results in this study show the decreasing Arctic sea ice(ASI) is an important contributor to the recent increased haze days in eastern China. The authors find that the number of winter haze days(WHD) in eastern China is strongly negatively correlated with the preceding autumn ASI during 1979–2012, and about 45%– 67% of the WHD interannual to interdecadal variability can be explained by ASI variability. Following previous studies on the impact of ASI loss on the northern hemisphere climate, the authors' studies further reveal that the reduction of autumn ASI leads to positive sea-level pressure anomalies in mid-latitude Eurasia, northward shift of track of cyclone activity in China, and weak Rossby wave activity in eastern China south of 40N during winter season. These atmospheric circulation changes favor less cyclone activity and more stable atmosphere in eastern China, leading to more haze days there. Furthermore, the patterns of circulation changes associated with autumn ASI and WHD are in very good agreement over the East Asia, particularly in eastern China. The authors suggest that haze pollution may continue to be a serious issue in the near future as the decline of ASI continues under global warming.
基金supported by the Guangdong Major Project of Basic and Applied Basic Research(Grant No.2020B0301030004)the National Natural Science Foundation of China(Grant Nos.42075015,41775060,41875114)+1 种基金the Science and Technology Commission of Shanghai MunicipalityChina(Grant No.20dz1200700)。
文摘Although it is well known that the tropical easterly jet(TEJ)has a significant impact on summer weather and climate over India and Africa,whether the TEJ exerts an important impact on tropical cyclone(TC)activity over the western North Pacific(WNP)remains unknown.In this study,we examined the impact of the TEJ on the interannual variability of TC genesis frequency over the WNP in the TC season(June-September)during 1980-2020.The results show a significant positive correlation between TC genesis frequency over the WNP and the jet intensity in the entrance region of the TEJ over the tropical western Pacific(in brief WP_TEJ),with a correlation coefficient as high as 0.66.The intensified WP_TEJ results in strong ageostrophic northerly winds in the entrance region and thus upper-level divergence to the north of the jet axis over the main TC genesis region in the WNP.This would lead to an increase in upward motion in the troposphere with enhanced low-level convergence,which are the most important factors to the increases in low-level vorticity,mid-level humidity and low-level eddy kinetic energy,and the decreases in sea level pressure and vertical wind shear in the region.All these changes are favorable for TC genesis over the WNP and vice versa.Further analyses indicate that the interannual variability of the WP_TEJ intensity is likely to be linked to the local diabatic heating over the Indian Ocean-western Pacific and the central Pacific El Ni?o-Southern Oscillation.
文摘The low latitude easterlies at 200 hPa in summer (May-October) is analysed climatically during the 13-year period from 1968 to 1980, with a special emphasis on the relationships between the anomalous tropical easterly jet Stream over South Asia and the low latitude atmospheric circulation, and also the summer monsoon precipitation in India. The compositing analysis shows that the tropical easterly jet stream over South Asia has five anomalous patterns at 200 hPa i.e. the western pattern, middle pattern, eastern pattern, two-branch pattern and multi-core pattern. Evidence has shown that the precipitaion in India anomalously increased during the anomalous period of the western pattern and the middle pattern, but reverse case is true in the eastern pattern. Some different anomalies of the precipitation in different area of India were found during the other two anomalous pattern.
基金Open Research Fund for 2006 from State Key Laboratory Severe Weather, Chinese Academyof Meteorological Sciences (2006LASW08)Development and Planning Project for Key State FundamentalResearch (2006CB403607 2004CB418300)
文摘By employing the NCEP/NCAR reanalysis data sets (1000-10hPa, 2.5°× 2.5°), the characteristics have been analyzed of the structure and evolution of an easterly vortex over the tropical upper troposphere relating to the east-west direction shift of the subtropical anticyclone over the Western Pacific Ocean. It is shown that there exists a westward shift simultaneously between the anticyclone and the vortex locating south of it. The anticyclone retreats eastward abnormally while the easterly encounters with the westerly around the same longitudes as they move from the opposite directions. The former is an upper weather system, extending from mid-troposphere to the height of 50 hPa with the center locating on 200 hPa. The vertical thermal distribution illustrates the characteristics of being"warm in the upper layer but cold in the lower layer". The divergence effect and the vertical motion change largely within the east and west sides of the easterly vortex and ascending branch transforms to descending branch near its center.
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 CNPq(Conselho Nacional de Desenvolvimento Cientifico e Tecnlogico,Brazil)/IRD(Institut de Recherche pour le Développement,France)cooperative project(Grant No.910153/98-1)support from the FAPESP(Fundao de Amparo à Pesquisa do Estado de Sao Paulo)(Grant No.99/06045)
文摘This study investigates the mean kinematic characteristics of the tropical Atlantic easterly disturbances in January-March （JFM）, April-June （AM J）, July-September （JAS） and October-December （OND） from 1968-1998. For each season, the preferential tracks of these disturbances in the 3--10-day band periods were computed and spatialized, as well as their associated wavelength, velocity and main period, which lies between 3-5 days and between 6-9 days depending on the track and the season. Two main tracks are highlighted over the Atlantic Ocean. During OND and JFM these two tracks are well separated and located in each hemisphere around 15°S and 12.5°N. From AMJ to JAS these tracks migrate northward; in JAS, they merge into one over the northern tropical Atlantic along 17.5°N. The associated wavelength fields exhibit a meridional gradient, with large wavelengths （greater than 4000 km） around the equator, between 5°N and 5°S, and smaller wavelengths outside of this latitude band （between 2500-3500 kin）. The phase speed is also found to exhibit poleward decreasing values from 12-6 m s^-1. Over the north Atlantic track, 6-9-day disturbances were found to occur from January to May and approximately from October to December. From June to September, the 3-5-day waves dominate the synoptic activity. Over the south Atlantic track, between May and August the synoptic variability is mainly explained by the 3-5-day disturbances but from January to April and from September to December both 3-5-day waves and 6-9-day waves can occur.
基金Supported by Forecasters' Special Project of Hunan Meteorological Bureau(XQKJ16C008)
文摘On the basis of comprehensive analysis on weather background and main influencing system of rainstorm formation,using NCEP reanalysis data,rainfall data of Shaoyang ground regional automatic station,a new generation of Doppler weather radar product information,etc.,high-altitude weather situation and physical formation mechanism of local double-cyclone type of rainstorm process with easterly wave in Shaoyang area on August 14,2016 were analyzed in detail,to find out prophase signal features which had indicating significance for rainstorm forecast. The results showed that:(1) the position of zonal subtropical high pressure in east-west direction was the necessary condition for the formation of easterly wave.(2) The rainstorm formation was closely related to double tropical depressions acting in the south of subtropical high pressure,and westward movement of easterly wave over 500 hPa and low-pressure inverted trough at low layer were main impact systems of the rainstorm.(3) Continuous flow of water vapor from the South China Sea to northwest was the source of water vapor required by this rainstorm.(4) Numerical prediction model products had certain guiding significance for forecasting the heavy precipitation,with important reference value.(5) Doppler radar products had strong forecasting ability in the nowcasting of rainstorm falling zone,which was an important measure of correcting forecast errors.
文摘The study concerns the propagation of easterly wave (EW) at tropics as west-moving soliton more steady both in ionn and velocity as evidenced in the dynamic framework.Under the impact of different circulation patterns over the regions of western Pacific trade wind,South-Asia monsoon and their transition,such a soliton becomes tapering off during its westward movement and degrading to a common dispersive wave on the whole,followed by dismtegra-non when striking the South-China Sea monsoon segment,thereby indicating that the sea sector is inaccessible to the soliton When no monsoon trough is present over the South Asian monsoon area around 30癗 or the monsoon depression ]S shallow,it is likely to have west-travelling soliton,which suggests the incursion of the EW into the South-Asian monsoon region.
文摘[Objective] The research aimed to analyze an easterly wave thunderstorm and gale weather during the latter flood season of 2010.[Method] Based on conventional observation data,data of automatic station,NCEP 1°×1° reanalysis data,Doppler radar reflectivity and radial velocity data,the easterly wave thunderstorm and gale weather process which happened during 4-5 August,2010 was analyzed.The circulation situation,wind field and dynamic & thermal structures of easterly wave,echo characteristics of Doppler radar when thunderstorm and gale happened were studied.[Result] The thunderstorm and gale weather happened in the northeaster zone in front of the deep thick easterly wave trough.When thunderstorm and gale weather happened,position of the subtropical high was by north(ridge line was at 35° N).Eastward movement of the north branch of trough compelled subtropical high splitting into east and west circles.Westward extension of the east subtropical high and saddle-type field circulation were favorable for generation and development of the easterly wave.As development and westward movement of the easterly wave,in the influence zone in front of the trough,upper easterly component transmitted downward.Then,low-level northeaster obviously strengthened,and thunderstorm and gale weather appeared.In the zone where thunderstorm and gale happened,airflow had cyclonic convergence at the middle and low layers and anti-cyclonic divergence near the ground layer.Subsidence movement was obvious.Moreover,thermal force structure that it tended to be dry and cold at the middle and high layers,warm and wet at the low layer existed.Supercell storm was at the developed stage on 4th.It had obvious mesocyclone and hooked echo characteristics(meso-and small-scale characteristics).Characteristics of the squall line,gale region and adverse wind region appeared in central west Guangdong on 5th.Doppler characteristics of the mesocyclone,hooked echo,squall line,gale region and adverse wind region had indication significance for short-imminent forecast of the thunderstorm and gale.[Conclusion] This research revealed some information which had significance for forecasting local easterly wave thunderstorm and gale weather.
文摘In this paper, a strong 1TCZ process and an 1TCZ - absent process during FGGE in 1979 were selected for comparison to explore how they were subject to the influence of the evolution of the upper easterly jets.
文摘Easterly waves are one of the rain-bearing systems of northeast monsoon and produce massive rainfall events over south India. In the present case study, an attempt is made to identify extreme heavy rainfall event over south India on 26th October, 2006 due to the passage of the easterly wave. Satellite images provide an inverted v-shape easterly wave. Next, circulation features at different levels clearly indicate the location, movement and speed of the easterly wave. Strong north-easterlies with a magnitude of 9.9 m/s are maintained at the surface. The convergence is mainly occupied between 12°N - 16°N, while the divergence is 5°N - 12°N on 26th October, 2006 at the surface level. On 25th, easterly wave is advected north of trough with a magnitude of 0.2 m/s and increased during the remaining days. There are two divergence cells along 5°N and 16°N before and after the event at 700 hPa level. Thus this study helps to bring out the essential characteristics of the easterly wave during northeast monsoon. The highlight of this study is that the easterly wave creates floods in the absence of tropical cyclones over south India.
文摘Many children in America enjoy hunting forEaster eggs.Easter is a celebration associated withthe Christian religion,but Easter eggs go back toancient festivals that celebrate the coming of
文摘The Easter Parade is a masterpiece by Richard Yates,which was published in 1976.The image of Emily,the heroine of the book,can be regarded as an iconic figure of early feminists in America.The aim of this paper is to explore Richard Yates’view of feminism,through analyzing the image of Emily in the book,and to understand the pursuits and dilemmas of feminists.Emily,as a woman in patriarchal society,who has always struggled independently on her own and fights against her fate,ends up in failure.Sarah,a typical image of“the other”who is dependent on men,eventually dies a tragic death.In front of the cruel and unpredictable fate,whether women have the sense of resistance or not,it seems that life always points to tragedy.Emily’s path of awakening is accompanied by real-life dilemmas,which is the epitome of every feminist’s experience.
基金supported by the National Natural Science Foundation of China(Grant Nos.41975090,U2242201,42075077)the Natural Science Foundation of Hunan Province,China(2022JJ20043)the Science and Technology Innovation Program of Hunan Province,China(2022RC1239)。
文摘In this study,the Betts-Miller-Janjic(BMJ)convective adjustment scheme in the Weather Research and Forecasting(WRF)model version 4.0 was used to investigate the effect of itsα-parameter,which influences the first-guess potential temperature reference profile on the Madden-Julian oscillation(MJO)propagation and structure.This study diagnosed the MJO active phase composites of the MJO-filtered outgoing longwave radiation(OLR)during the December-to-February(DJF)period of 2006-2016 over the Indian Ocean(IO),Maritime Continent(MC),and western Pacific(WP).The results show that the MJO-filtered OLR intensity,propagation pattern,and MJO classification(standing,jumping,and propagating clusters)are sensitive to theα-value,but the phase speeds of propagating MJOs are not.Overall,with an increasingα-value,the simulated MJO-filtered OLR intensity increases,and the simulated propagation pattern is improved.Results also show that the intensity and propagation pattern of an eastward-propagating MJO are associated with MJO circulation structures and thermodynamic structures.Asαincreases,the front Walker cell and the low-level easterly anomaly are enhanced,which premoistens the lower troposphere and triggers more active shallow and congestus clouds.The enhanced shallow and congestus convection preconditions the lower to middle troposphere,accelerating the transition from congestus to deep convection,thereby facilitating eastward propagation of the MJO.Therefore,the simulated MJO tends to transfer from standing to eastward propagating asαincreases.In summary,increasing theα-value is a possible way to improve the simulation of the structure and propagation of the MJO.
基金The National Natural Science Foundation of China under contract Nos 42376256,42230405,and 41576020.
文摘The Antarctic Slope Current(ASC)links the processes occurring in the coast area with the global ocean by modulating the flow across the continental slope,which influences global overturning circulation and the mass balance of the Antarctic ice shelves.This paper aims to explore the effects of wind and buoyancy fluxes on the long-term changes in the ASC using observation and reanalysis datasets.From 1993 to 2022,the ASC accelerated in all seasons,particularly in austral autumn,and was accompanied with the advancement of the strong flow.The positive buoyancy flux anomaly generates a low-density anomaly,which is accumulated by the prevailing surface easterly,maintaining a sharp density front along the continental slope.The heat flux intensifies the positive trend of buoyancy flux in summer and autumn,increasing the input of the lighter density anomaly into the ocean and advancing the strong flow of ASC.Compared with the annual mean,the additional acceleration of the ASC in autumn is mainly due to the contribution of the barotropic component,which could be explained by the local momentum input from the weakly enhanced local surface wind.The acceleration of the ASC is primarily driven by the positive trend of the buoyancy flux,while the influence of the wind on its seasonal variability becomes more significant due to the contribution of the local surface wind in autumn.
