The extratropical transition （ET） of tropical cyclone （TC） Haima （2004） was simulated to understand the impact of TC on midlatitude frontal systems. Two experiments were conducted using the Advanced Research ver...The extratropical transition （ET） of tropical cyclone （TC） Haima （2004） was simulated to understand the impact of TC on midlatitude frontal systems. Two experiments were conducted using the Advanced Research version of the Weather Research and Forecast （WRF） model. In the control run （CTL）, a vortex was extracted from the 24-hour pre-run output and then inserted into the National Centers for Environmental Prediction （NCEP） global final （FNL） analysis as an initial condition, while TC circulation was removed from the initial conditions in the sensitivity run （NOTC）. Comparisons of the experiments demonstrate that the midlatitude front has a wider meridional extent in the NOTC run than that in the CTL run. Furthermore, the CTL run produces convection suppression to the southern side of the front due to strong cold advection related to the TC circulation. The easterly flow north of the TC not only decelerates the eastward displacement of the front and contracts its zonal scale but also transports more moisture westward and lifts the air along equivalent potential temperature surfaces ahead of the front. As a result, the ascending motion and diabatic heating are enhanced in the northeastern edge of the front, and the anticyclonic outflow in the upper-level is intensified. The increased pressure gradient and divergent ftow aloft strengthen the upper-level jet and distort the trough axis in a northwest-southeast orientation. The thermal contrast between the two systems and the dynamic contribution related to the TC circulation can facilitate scalar and rotational frontogenesis to modulate the frontal structure.展开更多
The influence of the Arctic atmosphere on Northern Hemisphere midlatitude tropospheric weather and climate is explored by comparing the skill of two sets of 14-day weather forecast experiments using the ECMWF model wi...The influence of the Arctic atmosphere on Northern Hemisphere midlatitude tropospheric weather and climate is explored by comparing the skill of two sets of 14-day weather forecast experiments using the ECMWF model with and without relaxation of the Arctic atmosphere towards ERA-Interim reanalysis data during the integration. Two pathways are identified along which the Arctic influences midlatitude weather: a pronounced one over Asia and Eastern Europe, and a secondary one over North America. In general, linkages are found to be strongest(weakest) during boreal winter(summer) when the amplitude of stationary planetary waves over the Northern Hemisphere is strongest(weakest). No discernible Arctic impact is found over the North Atlantic and North Pacific region, which is consistent with predominantly southwesterly flow. An analysis of the flow-dependence of the linkages shows that anomalous northerly flow conditions increase the Arctic influence on midlatitude weather over the continents. Specifically, an anomalous northerly flow from the Kara Sea towards West Asia leads to cold surface temperature anomalies not only over West Asia but also over Eastern and Central Europe. Finally, the results of this study are discussed in the light of potential midlatitude benefits of improved Arctic prediction capabilities.展开更多
Three typhoon cases are selected to conduct a series of simulations that are initialized from sequential analyses. The results show that the forecast error in crucial area where a tropical cyclone(TC) interactes with ...Three typhoon cases are selected to conduct a series of simulations that are initialized from sequential analyses. The results show that the forecast error in crucial area where a tropical cyclone(TC) interactes with the upstream trough is highly correlated to the track forecast error after the TC recurvature. Furthermore, sensitivity experiments confirm that the developments of the midlatitude downstream circulations and then the TC track after its recurvature are highly sensitive to the TC intensity and its location relative to the upstream trough, which can give an example or one way of sensitivity of the TC track to the TC-trough interaction. If the TC interacts with the upstream trough more strongly(e.g., the TC being intensified or getting closer to the upstream trough), the downstream circulations will be more meridional, thus the TC track will be more northerly and westerly; otherwise, the downstream circulations will be more zonal, and the TC track will be more southerly and easterly.展开更多
Incoherent scatter radar （ISR） extra-wide coverage experiments during the period of 1978-2011 at Millstone Hill are used to investigate longitudinal differences in electron density. This work is motivated by a recen...Incoherent scatter radar （ISR） extra-wide coverage experiments during the period of 1978-2011 at Millstone Hill are used to investigate longitudinal differences in electron density. This work is motivated by a recent finding of the US east-west coast difference in TEC suggesting a combined effect of changing geomagnetic declination and zonal winds. The current study pro- vides strong supporting evidence of the longitudinal change and the plausible mechanism by examining the climatology of electron density Ne on both east and west sides of the radar with a longitude separation of up to 40% for different heights within 300-450 kin. Main findings include： 1） The east-west difference can be up to 60% and varies over the course of the day, being positive （East side Ne 〉 West side Ne） in the late evening, and negative （West side Ne 〉 East side Ne） in the pre-noon. 2） The east-west difference exists throughout the year. The positive （relative） difference is most pronounced in winter; the negative （relative） difference is most pronounced in early spring and later summer. 3） The east-west difference tends to enhance toward decreasing solar activity, however, with some seasonal dependence; the enhancements in the positive and negative differences do not take place simultaneously. 4） Both times of largest positive and largest negative east-west differences in Ne are earlier in summer and later in winter. The two times differ by 12-13 h, which remains constant throughout the year. 5） Variations at different heights from 300-450 km are similar. Zonal wind climatology above Millstone Hill is found to be perfectly consistent with what is expected based on the electron density difference between the east and west sides of the site. The magnetic declination-zonal wind mechanism is true for other longitude sectors as well, and may be used to understand longitudinal variations elsewhere. It may also be used to derive thermospheric zonal winds.展开更多
Based on June to September 1981 ECMWF grid datasets analysis is done of the characteristics of the propagation and structure of low-frequency (quasi 40 day) oscillation over eastern Asia. Results show a separating (co...Based on June to September 1981 ECMWF grid datasets analysis is done of the characteristics of the propagation and structure of low-frequency (quasi 40 day) oscillation over eastern Asia. Results show a separating (confluence) belt for the meridional propagation of low-frequency zonal (meridional) winds at higher (lower) levels over subtropical latitudes at 120°E, revealing that the oscillation of the zonal winds is quasi- geostrophic in pature and in phase in the high- and low-level. It is also found that the eastward propagation of the high-level zonal winds around 35°N in East Asia is the result of eastward march of midlatitude low- frequency waves with 60--90 longitude wavelength and speed of 1.5--2.0 longitudes per day. In addition, such low-frequency vortices, when moving over the coastwise region, tend to develop, accompanied by sharp oscil- lation in the westerly jetstream over eastern Asia.展开更多
The storm track and oceanic front play an important role in the midlatitude air–sea interaction.In this study,future changes in the impact of the North Pacific midlatitude oceanic frontal intensity on the wintertime ...The storm track and oceanic front play an important role in the midlatitude air–sea interaction.In this study,future changes in the impact of the North Pacific midlatitude oceanic frontal intensity on the wintertime storm track are projected based on climate model outputs from the Coupled Model Intercomparison Project Phase 5(CMIP5).The performance of 13 CMIP5 models is evaluated,and it is found that a majority of these models are capable of reproducing the northward intensification of the storm track in response to the strengthened oceanic front.The ensemble means of outputs from six best models under three Representative Concentration Pathway(RCP)scenarios(RCP2.6,RCP4.5,and RCP8.5)are compared with the results of the historical simulation,and future changes are projected.It is found that the impact of the oceanic frontal intensity on the storm track tends to get stronger and extends further westward in a warming climate,and the largest increase appears in the RCP8.5 run.Further analysis reveals that the stronger impact of the oceanic front on the storm track in the future may be partially attributed to the greater oceanic frontal impact on the near-surface baroclinicity,which is mainly related to the intensified oceanic frontal impact on the meridional potential temperature gradient under the climate change scenario.However,this process can hardly explain the increasing impact of the oceanic front on the upstream of the storm track.展开更多
Within the framework of forcing/dissipation KDV dynamics, the effect is numerically studied of successive east-travelling troughs on quasi-stationary high's ridges downstream. Results show that two types of low-fr...Within the framework of forcing/dissipation KDV dynamics, the effect is numerically studied of successive east-travelling troughs on quasi-stationary high's ridges downstream. Results show that two types of low-fre- quency transiency are available, depending on the intensities of down-drifting troughs. One is that transiency occurs in strength, i.e., the ridge undergoes transient change in intensity with unchanged position; the other is that transiency takes place in pattern, viz., the breakdown of the quasi-stationary character of the ridge's posi- tion, meaning that the ridge is replaced by a trough, followed by multiple transformation between ridge and trough.展开更多
The climatological characteristics and interdecadal variability of the water vapor transport and budget over the Yellow River-Huaihe River valleys （YH1） and the Yangtze River-Huaihe River valleys （YH2） of East Chi...The climatological characteristics and interdecadal variability of the water vapor transport and budget over the Yellow River-Huaihe River valleys （YH1） and the Yangtze River-Huaihe River valleys （YH2） of East China were investigated in this study,using the NCEP/NCAR monthly mean reanalysis datasets from 1979 to 2009.Changes in the water vapor transport pattern occurred during the late 1990s over YH1 （YH2） that corresponded with the recent interdecadal changes in the eastern China summer precipitation pattern.The net moisture influx in the YH1 increased and the net moisture influx in the YH2 decreased during 2000-2009 in comparison to 1979-1999.Detailed features in the moisture flux and transport changes across the four boundaries were explored.The altered water vapor transport over the two domains can be principally attributed to the additive effects of the changes in the confluent southwesterly moisture flow by the Indian summer monsoon and East Asian summer monsoon （related with the eastward recession of the western Pacific subtropical high）.The altered water vapor transport over YH1 was also partly caused by the weakened midlatitude westerlies.展开更多
This work investigates the boreal-summer intraseasonal variability(ISV)of the precipitation over the lower reaches of the Yangtze River basin(LYRB)during 1979–2016,based on daily Climate Prediction Center global prec...This work investigates the boreal-summer intraseasonal variability(ISV)of the precipitation over the lower reaches of the Yangtze River basin(LYRB)during 1979–2016,based on daily Climate Prediction Center global precipitation data.The ISV of the summer monsoon rainfall over the LYRB is mainly dominated by the lower-frequency 12–20-day variability and the higher-frequency 8–12-day variability.The lower-frequency variability is found to be related to the northwestwardpropagating quasi-biweekly oscillation(QBWO)over the western North Pacific spanning the South China Sea(SCS)and Philippine Sea,while the higher-frequency variability is related to the southeastward propagating midlatitude wave train(MLWT).Moreover,not each active QBWO(MLWT)in the SCS(East Asia)can generate ISV components of the precipitation anomaly over the LYRB.The QBWO can change the rainfall significantly with the modulation of mean state precipitation,while the quasi-11-day mode mainly depends on the intensity of the MLWT rather than the mean precipitation change.These findings should enrich our understanding of the ISV of the East Asian summer monsoon and improve its predictability.展开更多
Atmospheric circulation cells associated with anomalous East Asian Winter Monsoon （EAWM） were studied using the 1948/49 to 2002/03 NCEP/NCAR reanalysis and NCAR CAM3 AGCM simulations with monthly global sea surface ...Atmospheric circulation cells associated with anomalous East Asian Winter Monsoon （EAWM） were studied using the 1948/49 to 2002/03 NCEP/NCAR reanalysis and NCAR CAM3 AGCM simulations with monthly global sea surface temperatures from 1950 to 2000. Several atmospheric cells in the Pacific [i.e., the zonal Walker cell （ZWC） in the tropic, the Hadley cell in the western Pacific （WPHC）, the midlatitude zonal cell （MZC） over the central North Pacific, and the Hadley cell in the eastern Pacific （EPHC）] are associated with anomalous EAWM. When the EAWM is strong, ZWC, WPHC, and MZC are enhanced, as opposed to EPHC. The anomalous enhanced ZWC is characterized by air parcels rising in the western tropical Pacific, flowing eastward in the upper troposphere, and descending in the tropical central Pacific before returning to the tropical western Pacific. The enhanced MZC has characteristics opposite those of the enhanced ZWC in the central North Pacific. The anomalous WPHC shows air parcels rising in the western Pacific, as in the case of ZWC, followed by flowing northward in the upper troposphere and descending in the west North Pacific, as in the case of the enhanced MZC before returning to the western tropical Pacific. The anomalous EPHC is opposite in properties to the anomalous WPHC. Opposite characteristics are found during the weak EAWM period. The model simulations and the observations show similar characteristics and indicate the important role of sea surface temperature. A possible mechanism is proposed to link interannual variation of EAWM with the central-eastern tropical Pacific sea surface temperature anomaly （SSTA）.展开更多
This study explores the linkage between summertime temperature fluctuations over midlatitude Eurasia and the preceding Arctic sea ice concentration (SIC) by utilizing the squared norm of the temperature anomaly, the e...This study explores the linkage between summertime temperature fluctuations over midlatitude Eurasia and the preceding Arctic sea ice concentration (SIC) by utilizing the squared norm of the temperature anomaly, the essential part of local eddy available potential energy, as a metric to quantify the temperature fluctuations with weather patterns on various timescales. By comparing groups of singular value decomposition (SVD) analysis, we suggest a significant linkage between strong (weak) August 10-to-30-day temperature fluctuations over mid-west Asia and enhanced (decreased) Barents-Kara Sea ice in the previous February. We find that when the February SIC increases in the Barents-Kara Sea, a zonal dipolar pattern of SST anomalies appears in the Atlantic subpolar region and lasts from February into the summer months. Evidence suggests that in such a background state, the atmospheric circulation changes evidently from July to August, so that the August is characterized by an amplified meridional circulation over Eurasia, weakened westerlies, and high- pressure anomalies along the Arctic coast. Moreover, the 10-to-30-day wave becomes more active in the North Atlantic-Barents-Kara Sea-Central Asia regions and manifests a more evident southward propagation from the Barents- Kara Sea into the Ural region, which is responsible for the enhanced 10-to-30-day wave activity and temperature fluctuations in the region.展开更多
The authors investigate the characteristics of propagation and the influence on tropical precipitation of 9–29-day intraseasonal variation over midlatitude East Asia during boreal winter, and find that the intraseaso...The authors investigate the characteristics of propagation and the influence on tropical precipitation of 9–29-day intraseasonal variation over midlatitude East Asia during boreal winter, and find that the intraseasonal wind signal can propagate both eastward and southward. In the case of eastward propagation, the intraseasonal wind signal is mainly confined to the midlatitudes, featuring eastward migration of anomalous cyclones and anticyclones. In the case of southward propagation, intraseasonal meridional wind perturbations may extend from the mid to the low latitudes, and even the equatorial region. The accompanying wind convergence/divergence induces anomalous precipitation in the near-equatorial regions, forming a north–south dipole precipitation anomaly pattern between the southern South China Sea and the eastern China– Japan region. An anomalous meridional overturning circulation plays an important role in linking tropical and midlatitude intraseasonal wind and precipitation variations.展开更多
Phase changes in the precipitation processes of early winter and late spring in midlatitude regions represent challenges when forecasting the timing and magnitude of snowfall.On 4 April 2018,a heavy snow process occur...Phase changes in the precipitation processes of early winter and late spring in midlatitude regions represent challenges when forecasting the timing and magnitude of snowfall.On 4 April 2018,a heavy snow process occurred in Beijing and northwestern Hebei Province,becoming the most delayed occurrence of heavy spring snow ever recorded over Beijing in the last 30 years.This paper uses observational and numerical simulation data to investigate the causes for the rapid rain-to-snow(RRTS)phase transition during this process.The following results are obtained.(1)Return flows(RFs),an interesting type of easterly wind,including those at 1000,925,and 800 hPa,played an important role in this heavy snow process and presented a characteristic"sandwich"structure.The RFs,complex topography,and snow particles that dominated the clouds,were the three key factors for the RRTS transition.(2)The RRTS transition in the plains was directly related to the RF at 925 hPa,which brought about advective cooling initiated approximately 4-6 h before the onset of precipitation.Then,the RF played a role of diabatic cooling when snow particles began to fall at the onset of precipitation.(3)The RRTS transition in the northern part of the Taihang Mountains was closely related to the relatively high altitude that led to a lower surface temperature owing to the vertical temperature lapse rate.Both immediately before and after the onset of precipitation,the snow particles in clouds entrained the middle-level cold air downward,causing the melting layer(from surface to the 0℃-isotherm level)to become very thin;and thus the snow particles did not have adequate time to melt before falling to the ground.(4)The rapid RRTS over the Yanqing mountainous area in the northwest of Beijing could have involved all the three concurrent mechanisms:the advective cooling of RF,the melting cooling of cloud snow particles,and the high-altitude effect.Compared with that in the plain area with less urbanization the duration of the RRTS in the plain area with significant urbanization was extended by approximately 2 h.展开更多
The characteristic distributions of regional sand-dust storm （SDS） weather processes over Northeast Asia from 1980 to 2011 were investigated using the shared WMO surface station meteorological data, atmospheric soun...The characteristic distributions of regional sand-dust storm （SDS） weather processes over Northeast Asia from 1980 to 2011 were investigated using the shared WMO surface station meteorological data, atmospheric sounding data, China high density weather data, NCEP/NCAR reanalysis data, as well as the archived original weather maps of China. The concentration-weighted trajectory （CWT） method was used to calculate the SDS frequency from the discrete station data and to track the large-scale regional SDS weather processes in Northeast Asia. A spline trend analysis method was employed to investigate the variability of the SDS weather systems. The results show that during 1980-2011, the SDS weather processes exhibit both a historical persistence and abrupt transitions with an approximate 10-yr high-low occurrence oscillation. Through composite analysis of atmospheric circulation during high and low SDS years, it is found that the SDS occurrences are closely related to the anomalies of arctic vortex and midlatitude westerly, and the circulation patterns around the Lake Baikal. During the high frequency years, the meridianal flows in the upper and mid troposphere above the high SDS corridor in East Asia （from the Lake Balkhash along Northwest and North China, Korean Peninsula, meridianal flows during the low SDS frequency years, the midlatitude regions. and Japan Islands） are apparently stronger than the favoring the development and transport of SDSs in the midlatitude regions.展开更多
The East Asian subtropical summer monsoon（EASSM） is one component of the East Asian summer monsoon system,and its evolution determines the weather and climate over East China.In the present paper,we firstly demonstr...The East Asian subtropical summer monsoon（EASSM） is one component of the East Asian summer monsoon system,and its evolution determines the weather and climate over East China.In the present paper,we firstly demonstrate the formation and advancement of the EASSM rainbelt and its associated circulation and precipitation patterns through reviewing recent studies and our own analysis based on JRA-55（Japanese 55-yr Reanalysis） data and CMAP（CPC Merged Analysis of Precipitation）,GPCP（Global Precipitation Climatology Project）,and TRMM（Tropical Rainfall Measuring Mission） precipitation data.The results show that the rainy season of the EASSM starts over the region to the south of the Yangtze River in early April,with the establishment of strong southerly wind in situ.The EASSM rainfall,which is composed of dominant convective and minor stratiform precipitation,is always accompanied by a frontal system and separated from the tropical summer monsoon system.It moves northward following the onset of the South China Sea summer monsoon.Moreover,the role of the land-sea thermal contrast in the formation and maintenance of the EASSM is illustrated,including in particular the effect of the seasonal transition of the zonal land-sea thermal contrast and the influences from the Tibetan Plateau and midlatitudes.In addition,we reveal a possible reason for the subtropical climate difference between East Asia and East America.Finally,the multi-scale variability of the EASSM and its influential factors are summarized to uncover possible reasons for the intraseasonal,interannual,and interdecadal variability of the EASSM and their importance in climate prediction.展开更多
基金supported by National Basic Research Program of China (Grant No. 2009CB421505)National Natural Science Foundation of China (Grant No. 41275001)
文摘The extratropical transition （ET） of tropical cyclone （TC） Haima （2004） was simulated to understand the impact of TC on midlatitude frontal systems. Two experiments were conducted using the Advanced Research version of the Weather Research and Forecast （WRF） model. In the control run （CTL）, a vortex was extracted from the 24-hour pre-run output and then inserted into the National Centers for Environmental Prediction （NCEP） global final （FNL） analysis as an initial condition, while TC circulation was removed from the initial conditions in the sensitivity run （NOTC）. Comparisons of the experiments demonstrate that the midlatitude front has a wider meridional extent in the NOTC run than that in the CTL run. Furthermore, the CTL run produces convection suppression to the southern side of the front due to strong cold advection related to the TC circulation. The easterly flow north of the TC not only decelerates the eastward displacement of the front and contracts its zonal scale but also transports more moisture westward and lifts the air along equivalent potential temperature surfaces ahead of the front. As a result, the ascending motion and diabatic heating are enhanced in the northeastern edge of the front, and the anticyclonic outflow in the upper-level is intensified. The increased pressure gradient and divergent ftow aloft strengthen the upper-level jet and distort the trough axis in a northwest-southeast orientation. The thermal contrast between the two systems and the dynamic contribution related to the TC circulation can facilitate scalar and rotational frontogenesis to modulate the frontal structure.
基金the ECMWF for providing the supercomputing resources under the ECMWF special project SPDEJUNG2.S.S.benefited from funding through the Helmholtz Climate Initiative REKLIM
文摘The influence of the Arctic atmosphere on Northern Hemisphere midlatitude tropospheric weather and climate is explored by comparing the skill of two sets of 14-day weather forecast experiments using the ECMWF model with and without relaxation of the Arctic atmosphere towards ERA-Interim reanalysis data during the integration. Two pathways are identified along which the Arctic influences midlatitude weather: a pronounced one over Asia and Eastern Europe, and a secondary one over North America. In general, linkages are found to be strongest(weakest) during boreal winter(summer) when the amplitude of stationary planetary waves over the Northern Hemisphere is strongest(weakest). No discernible Arctic impact is found over the North Atlantic and North Pacific region, which is consistent with predominantly southwesterly flow. An analysis of the flow-dependence of the linkages shows that anomalous northerly flow conditions increase the Arctic influence on midlatitude weather over the continents. Specifically, an anomalous northerly flow from the Kara Sea towards West Asia leads to cold surface temperature anomalies not only over West Asia but also over Eastern and Central Europe. Finally, the results of this study are discussed in the light of potential midlatitude benefits of improved Arctic prediction capabilities.
基金International Cooperating Program of Science and Technology(2010DFA24650)National Natural Science Foundation of China(41175061)
文摘Three typhoon cases are selected to conduct a series of simulations that are initialized from sequential analyses. The results show that the forecast error in crucial area where a tropical cyclone(TC) interactes with the upstream trough is highly correlated to the track forecast error after the TC recurvature. Furthermore, sensitivity experiments confirm that the developments of the midlatitude downstream circulations and then the TC track after its recurvature are highly sensitive to the TC intensity and its location relative to the upstream trough, which can give an example or one way of sensitivity of the TC track to the TC-trough interaction. If the TC interacts with the upstream trough more strongly(e.g., the TC being intensified or getting closer to the upstream trough), the downstream circulations will be more meridional, thus the TC track will be more northerly and westerly; otherwise, the downstream circulations will be more zonal, and the TC track will be more southerly and easterly.
基金supported by the National Natural Science Foundation of China (Grant No. 40890164)the US National Science Foundation under Cooperative Agreements (Grant Nos. ATM-0733510 and ATM-6920184)
文摘Incoherent scatter radar （ISR） extra-wide coverage experiments during the period of 1978-2011 at Millstone Hill are used to investigate longitudinal differences in electron density. This work is motivated by a recent finding of the US east-west coast difference in TEC suggesting a combined effect of changing geomagnetic declination and zonal winds. The current study pro- vides strong supporting evidence of the longitudinal change and the plausible mechanism by examining the climatology of electron density Ne on both east and west sides of the radar with a longitude separation of up to 40% for different heights within 300-450 kin. Main findings include： 1） The east-west difference can be up to 60% and varies over the course of the day, being positive （East side Ne 〉 West side Ne） in the late evening, and negative （West side Ne 〉 East side Ne） in the pre-noon. 2） The east-west difference exists throughout the year. The positive （relative） difference is most pronounced in winter; the negative （relative） difference is most pronounced in early spring and later summer. 3） The east-west difference tends to enhance toward decreasing solar activity, however, with some seasonal dependence; the enhancements in the positive and negative differences do not take place simultaneously. 4） Both times of largest positive and largest negative east-west differences in Ne are earlier in summer and later in winter. The two times differ by 12-13 h, which remains constant throughout the year. 5） Variations at different heights from 300-450 km are similar. Zonal wind climatology above Millstone Hill is found to be perfectly consistent with what is expected based on the electron density difference between the east and west sides of the site. The magnetic declination-zonal wind mechanism is true for other longitude sectors as well, and may be used to understand longitudinal variations elsewhere. It may also be used to derive thermospheric zonal winds.
基金This study is supported partially by National Natural Science Foundation of Chinapartially by the State Meteorological Administration Monsoon Research Funds.
文摘Based on June to September 1981 ECMWF grid datasets analysis is done of the characteristics of the propagation and structure of low-frequency (quasi 40 day) oscillation over eastern Asia. Results show a separating (confluence) belt for the meridional propagation of low-frequency zonal (meridional) winds at higher (lower) levels over subtropical latitudes at 120°E, revealing that the oscillation of the zonal winds is quasi- geostrophic in pature and in phase in the high- and low-level. It is also found that the eastward propagation of the high-level zonal winds around 35°N in East Asia is the result of eastward march of midlatitude low- frequency waves with 60--90 longitude wavelength and speed of 1.5--2.0 longitudes per day. In addition, such low-frequency vortices, when moving over the coastwise region, tend to develop, accompanied by sharp oscil- lation in the westerly jetstream over eastern Asia.
基金Supported by the National Natural Science Foundation of China(42005025)Scientific Research Fund of National University of Defense Technology(ZK20-34)“Double-First Class”Special Fund of National University of Defense Technology(qnrc01)。
文摘The storm track and oceanic front play an important role in the midlatitude air–sea interaction.In this study,future changes in the impact of the North Pacific midlatitude oceanic frontal intensity on the wintertime storm track are projected based on climate model outputs from the Coupled Model Intercomparison Project Phase 5(CMIP5).The performance of 13 CMIP5 models is evaluated,and it is found that a majority of these models are capable of reproducing the northward intensification of the storm track in response to the strengthened oceanic front.The ensemble means of outputs from six best models under three Representative Concentration Pathway(RCP)scenarios(RCP2.6,RCP4.5,and RCP8.5)are compared with the results of the historical simulation,and future changes are projected.It is found that the impact of the oceanic frontal intensity on the storm track tends to get stronger and extends further westward in a warming climate,and the largest increase appears in the RCP8.5 run.Further analysis reveals that the stronger impact of the oceanic front on the storm track in the future may be partially attributed to the greater oceanic frontal impact on the near-surface baroclinicity,which is mainly related to the intensified oceanic frontal impact on the meridional potential temperature gradient under the climate change scenario.However,this process can hardly explain the increasing impact of the oceanic front on the upstream of the storm track.
基金This work is supported in part by National Natural Science Foundation of Chinain part by the State Meteorological Adiministration Climate Research Funds.
文摘Within the framework of forcing/dissipation KDV dynamics, the effect is numerically studied of successive east-travelling troughs on quasi-stationary high's ridges downstream. Results show that two types of low-fre- quency transiency are available, depending on the intensities of down-drifting troughs. One is that transiency occurs in strength, i.e., the ridge undergoes transient change in intensity with unchanged position; the other is that transiency takes place in pattern, viz., the breakdown of the quasi-stationary character of the ridge's posi- tion, meaning that the ridge is replaced by a trough, followed by multiple transformation between ridge and trough.
基金supported by the Major State Basic Research Development Program of China (973 Program) under Grant Nos. 2009CB421406 and 2010CB950304Chinese Academy of Sciences under Grant No. KZCX2-YW-Q1-02the National Natural Science Foundation of China under Grant Nos. 40875048 and 40821092
文摘The climatological characteristics and interdecadal variability of the water vapor transport and budget over the Yellow River-Huaihe River valleys （YH1） and the Yangtze River-Huaihe River valleys （YH2） of East China were investigated in this study,using the NCEP/NCAR monthly mean reanalysis datasets from 1979 to 2009.Changes in the water vapor transport pattern occurred during the late 1990s over YH1 （YH2） that corresponded with the recent interdecadal changes in the eastern China summer precipitation pattern.The net moisture influx in the YH1 increased and the net moisture influx in the YH2 decreased during 2000-2009 in comparison to 1979-1999.Detailed features in the moisture flux and transport changes across the four boundaries were explored.The altered water vapor transport over the two domains can be principally attributed to the additive effects of the changes in the confluent southwesterly moisture flow by the Indian summer monsoon and East Asian summer monsoon （related with the eastward recession of the western Pacific subtropical high）.The altered water vapor transport over YH1 was also partly caused by the weakened midlatitude westerlies.
基金This work was supported by the National Natural Science Foundation of China[grant number 41420104002]the Natural Science Foundation of Jiangsu Province[grant numbers BK20150907 and 14KJA170002].
文摘This work investigates the boreal-summer intraseasonal variability(ISV)of the precipitation over the lower reaches of the Yangtze River basin(LYRB)during 1979–2016,based on daily Climate Prediction Center global precipitation data.The ISV of the summer monsoon rainfall over the LYRB is mainly dominated by the lower-frequency 12–20-day variability and the higher-frequency 8–12-day variability.The lower-frequency variability is found to be related to the northwestwardpropagating quasi-biweekly oscillation(QBWO)over the western North Pacific spanning the South China Sea(SCS)and Philippine Sea,while the higher-frequency variability is related to the southeastward propagating midlatitude wave train(MLWT).Moreover,not each active QBWO(MLWT)in the SCS(East Asia)can generate ISV components of the precipitation anomaly over the LYRB.The QBWO can change the rainfall significantly with the modulation of mean state precipitation,while the quasi-11-day mode mainly depends on the intensity of the MLWT rather than the mean precipitation change.These findings should enrich our understanding of the ISV of the East Asian summer monsoon and improve its predictability.
基金supported jointly by the grant from the Office of Science (BER),U. S. Department of Energy, the Natural Science Foundation of China (Grant Nos. 40775059, 40171029, and 40905045)the Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No. IAP09312)+1 种基金a project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD)the project from Key Laboratory of Meteorological Disaster of Jiangsu Province (Grant No. KLME050104)
文摘Atmospheric circulation cells associated with anomalous East Asian Winter Monsoon （EAWM） were studied using the 1948/49 to 2002/03 NCEP/NCAR reanalysis and NCAR CAM3 AGCM simulations with monthly global sea surface temperatures from 1950 to 2000. Several atmospheric cells in the Pacific [i.e., the zonal Walker cell （ZWC） in the tropic, the Hadley cell in the western Pacific （WPHC）, the midlatitude zonal cell （MZC） over the central North Pacific, and the Hadley cell in the eastern Pacific （EPHC）] are associated with anomalous EAWM. When the EAWM is strong, ZWC, WPHC, and MZC are enhanced, as opposed to EPHC. The anomalous enhanced ZWC is characterized by air parcels rising in the western tropical Pacific, flowing eastward in the upper troposphere, and descending in the tropical central Pacific before returning to the tropical western Pacific. The enhanced MZC has characteristics opposite those of the enhanced ZWC in the central North Pacific. The anomalous WPHC shows air parcels rising in the western Pacific, as in the case of ZWC, followed by flowing northward in the upper troposphere and descending in the west North Pacific, as in the case of the enhanced MZC before returning to the western tropical Pacific. The anomalous EPHC is opposite in properties to the anomalous WPHC. Opposite characteristics are found during the weak EAWM period. The model simulations and the observations show similar characteristics and indicate the important role of sea surface temperature. A possible mechanism is proposed to link interannual variation of EAWM with the central-eastern tropical Pacific sea surface temperature anomaly （SSTA）.
基金the National Key Research and Development Program under Grant 2022YFE0106900the Strategic Priority Research Program of the Chinese Academy of Sciences under Grant XDA2010030804the National Natural Science Foundation of China under Grant No.41621005.
文摘This study explores the linkage between summertime temperature fluctuations over midlatitude Eurasia and the preceding Arctic sea ice concentration (SIC) by utilizing the squared norm of the temperature anomaly, the essential part of local eddy available potential energy, as a metric to quantify the temperature fluctuations with weather patterns on various timescales. By comparing groups of singular value decomposition (SVD) analysis, we suggest a significant linkage between strong (weak) August 10-to-30-day temperature fluctuations over mid-west Asia and enhanced (decreased) Barents-Kara Sea ice in the previous February. We find that when the February SIC increases in the Barents-Kara Sea, a zonal dipolar pattern of SST anomalies appears in the Atlantic subpolar region and lasts from February into the summer months. Evidence suggests that in such a background state, the atmospheric circulation changes evidently from July to August, so that the August is characterized by an amplified meridional circulation over Eurasia, weakened westerlies, and high- pressure anomalies along the Arctic coast. Moreover, the 10-to-30-day wave becomes more active in the North Atlantic-Barents-Kara Sea-Central Asia regions and manifests a more evident southward propagation from the Barents- Kara Sea into the Ural region, which is responsible for the enhanced 10-to-30-day wave activity and temperature fluctuations in the region.
基金supported by the National Natural Science Foundation of China [grant numbers 41530425,41721004,41475081,and 41775080]
文摘The authors investigate the characteristics of propagation and the influence on tropical precipitation of 9–29-day intraseasonal variation over midlatitude East Asia during boreal winter, and find that the intraseasonal wind signal can propagate both eastward and southward. In the case of eastward propagation, the intraseasonal wind signal is mainly confined to the midlatitudes, featuring eastward migration of anomalous cyclones and anticyclones. In the case of southward propagation, intraseasonal meridional wind perturbations may extend from the mid to the low latitudes, and even the equatorial region. The accompanying wind convergence/divergence induces anomalous precipitation in the near-equatorial regions, forming a north–south dipole precipitation anomaly pattern between the southern South China Sea and the eastern China– Japan region. An anomalous meridional overturning circulation plays an important role in linking tropical and midlatitude intraseasonal wind and precipitation variations.
基金Supported by the National Natural Science Foundation of China(41475051 and 42075008)Beijing Natural Science Foundation(8192019)Civil Aviation Administration of China Security Capacity Building Project(20600822)。
文摘Phase changes in the precipitation processes of early winter and late spring in midlatitude regions represent challenges when forecasting the timing and magnitude of snowfall.On 4 April 2018,a heavy snow process occurred in Beijing and northwestern Hebei Province,becoming the most delayed occurrence of heavy spring snow ever recorded over Beijing in the last 30 years.This paper uses observational and numerical simulation data to investigate the causes for the rapid rain-to-snow(RRTS)phase transition during this process.The following results are obtained.(1)Return flows(RFs),an interesting type of easterly wind,including those at 1000,925,and 800 hPa,played an important role in this heavy snow process and presented a characteristic"sandwich"structure.The RFs,complex topography,and snow particles that dominated the clouds,were the three key factors for the RRTS transition.(2)The RRTS transition in the plains was directly related to the RF at 925 hPa,which brought about advective cooling initiated approximately 4-6 h before the onset of precipitation.Then,the RF played a role of diabatic cooling when snow particles began to fall at the onset of precipitation.(3)The RRTS transition in the northern part of the Taihang Mountains was closely related to the relatively high altitude that led to a lower surface temperature owing to the vertical temperature lapse rate.Both immediately before and after the onset of precipitation,the snow particles in clouds entrained the middle-level cold air downward,causing the melting layer(from surface to the 0℃-isotherm level)to become very thin;and thus the snow particles did not have adequate time to melt before falling to the ground.(4)The rapid RRTS over the Yanqing mountainous area in the northwest of Beijing could have involved all the three concurrent mechanisms:the advective cooling of RF,the melting cooling of cloud snow particles,and the high-altitude effect.Compared with that in the plain area with less urbanization the duration of the RRTS in the plain area with significant urbanization was extended by approximately 2 h.
基金Supported by the Special Project on Public Welfare of Forestry(200804020)National Science and Technology Support Program of China(2008BAC40B02)+2 种基金National Natural Science Foundation of China(40875077)National Basic Research and Development(973)Program of China(2011CB403404 and 2011CB403401)Projects of the Chinese Academy of Meteorological Sciences(2010Z002,2009Z001,and 2009Y002)
文摘The characteristic distributions of regional sand-dust storm （SDS） weather processes over Northeast Asia from 1980 to 2011 were investigated using the shared WMO surface station meteorological data, atmospheric sounding data, China high density weather data, NCEP/NCAR reanalysis data, as well as the archived original weather maps of China. The concentration-weighted trajectory （CWT） method was used to calculate the SDS frequency from the discrete station data and to track the large-scale regional SDS weather processes in Northeast Asia. A spline trend analysis method was employed to investigate the variability of the SDS weather systems. The results show that during 1980-2011, the SDS weather processes exhibit both a historical persistence and abrupt transitions with an approximate 10-yr high-low occurrence oscillation. Through composite analysis of atmospheric circulation during high and low SDS years, it is found that the SDS occurrences are closely related to the anomalies of arctic vortex and midlatitude westerly, and the circulation patterns around the Lake Baikal. During the high frequency years, the meridianal flows in the upper and mid troposphere above the high SDS corridor in East Asia （from the Lake Balkhash along Northwest and North China, Korean Peninsula, meridianal flows during the low SDS frequency years, the midlatitude regions. and Japan Islands） are apparently stronger than the favoring the development and transport of SDSs in the midlatitude regions.
基金Supported by the National(Key)Basic Research and Development(973)Program of China(2015CB453202)National Natural Science Foundation of China(41505049,41475057,and 41175083)+2 种基金Basic Research and Operation Fund of the Chinese Academy of Meteorological Sciences(2015Z001)Program for Changjiang Scholars and Innovative Research Team in Universities(PCSIRT)Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)
文摘The East Asian subtropical summer monsoon（EASSM） is one component of the East Asian summer monsoon system,and its evolution determines the weather and climate over East China.In the present paper,we firstly demonstrate the formation and advancement of the EASSM rainbelt and its associated circulation and precipitation patterns through reviewing recent studies and our own analysis based on JRA-55（Japanese 55-yr Reanalysis） data and CMAP（CPC Merged Analysis of Precipitation）,GPCP（Global Precipitation Climatology Project）,and TRMM（Tropical Rainfall Measuring Mission） precipitation data.The results show that the rainy season of the EASSM starts over the region to the south of the Yangtze River in early April,with the establishment of strong southerly wind in situ.The EASSM rainfall,which is composed of dominant convective and minor stratiform precipitation,is always accompanied by a frontal system and separated from the tropical summer monsoon system.It moves northward following the onset of the South China Sea summer monsoon.Moreover,the role of the land-sea thermal contrast in the formation and maintenance of the EASSM is illustrated,including in particular the effect of the seasonal transition of the zonal land-sea thermal contrast and the influences from the Tibetan Plateau and midlatitudes.In addition,we reveal a possible reason for the subtropical climate difference between East Asia and East America.Finally,the multi-scale variability of the EASSM and its influential factors are summarized to uncover possible reasons for the intraseasonal,interannual,and interdecadal variability of the EASSM and their importance in climate prediction.
