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1.
The features of large-scale circulation, storm tracks and the dynamical relationship between them were examined by investigating Rossby wave breaking(RWB) processes associated with Eastern Pacific(EP) and Central Pacific(CP) El-Nin o. During EP El-Nin o, the geopotential height anomaly at 500 hPa(Z500) exhibits a Pacific–North America(PNA) pattern. During CP El-Nin o, the Z500 anomaly shows a north positive–south negative pattern over the North Pacific. The anomalous distributions of baroclinicity and storm track are consistent with those of upper-level zonal wind for both EP and CP El-Nin o, suggesting impacts of mean flow on storm track variability. Anticyclonic wave breaking(AWB) occurs less frequently in EP El-Nin o years, while cyclonic wave breaking(CWB) occurs more frequently in CP El-Nin o years over the North Pacific sector. Outside the North Pacific, more CWB events occur over North America during EP El-Nin o. When AWB events occur less frequently over the North Pacific during EP El-Nin o, Z500 decreases locally and the zonal wind is strengthened(weakened) to the south(north). This is because AWB events reflect a monopole high anomaly at the centroid of breaking events. When CWB events occur more frequently over the North Pacific under CP El-Nin o conditions, and over North America under EP El-Nin o condition, Z500 increases(decreases) to the northeast(southwest), since CWB events are related to a northeast–southwest dipole Z500 anomaly. The anomalous RWB events act to invigorate and reinforce the circulation anomalies over the North Pacific–North America region linked with the two types of El-Nin o.  相似文献   

2.
Precipitation over southeastern Lake Baikal features a significant decreasing trend in July and August over 1979–2018 and is closely related to blocking occurrence over central Siberia(45°–70°N,75°–115°E).This study investigates the formation and maintenance of anticyclonic and cyclonic wave-breaking(AWB and CWB)blocking events and their climate impacts on precipitation in the southeastern Lake Baikal area.Both AWB and CWB blocking events are characterized by a cold trough deepening from the sub-Arctic region and a ridge amplifying toward its north over central Siberia,as well as an evident Rossby wave train over midlatitude Eurasia.For AWB blocking events,the ridge and trough pair tilts clockwise and the wave train exhibits a zonal distribution.In contrast,ridge and trough pair associated with CWB blocking events leans anticlockwise with larger-scale,meridional,and more anisotropic signatures.Moreover,the incoming Rossby wave energy associated with CWB blocking events is more evident than for AWB blocking events.Therefore,CWB blocking events are more persistent.AWB blocking events produce more extensive and persistent precipitation over the southeastern Lake Baikal area than CWB blocking events,in which moderate above-normal rainfall is seen in the decaying periods of blockings.A significant decreasing trend is found in terms of AWB blocking occurrence over central Siberia,which may contribute to the downward trend of precipitation over southeastern Lake Baikal.  相似文献   

3.
孙丹  薛峰  周天军 《大气科学进展》2013,30(6):1732-1742
Based on NCEP/NCAR （National Centers for Environmental Prediction/National Center for Atmo- spheric Research） reanalysis data from 1979 to 2010, the impacts of two types of E1 Nino on atmospheric circulation in the Southern Hemisphere （SH） are analyzed. It is shown thaL when a warming event occurs in the equatorial eastern Pacific （EP E1 Nino）, there is a negative sea level pressure （SLP） anomaly in the east- ern Pacific and a positive one in the western Pacific. Besides, there exists a negative anomaly between 40°S and 60°S and a positive anomaly to the south of 60°S. When a warming event in the central Pacific （CP E1 Nino） occurs, there appears a negative SLP anomaly in the central Pacific and a positive SLP anomaly in the eastern and western Pacific, but the SLP anomalies are not so evident in the SH extratropics. In particular, the Pacific-South America （PSA） pattern induced by the CP E1 Nino is located more northwestward, with a weaker anomaly compared with the EP E1 Nino. This difference is directly related with the different position of heating centers associated with the two types of E1 Nino events. Because the SST anomaly associated with CP E1 Nino is located more westward than that associated with EP El Nino, the related heating center tends to move westward and the response of SH atmospheric circulation to the tropical heating changes accordingly, thus exciting a different position of the PSA pattern. It is also noted that the local meridional cell plays a role in the SH high latitudes during EP E1 Nino. The anomalous ascending motion due to the enhancement of convection over the eastern Pacific leads to an enhancement of the local Hadley cell and the meridional cell in the middle and high latitudes, which in turn induces an anomalous descending motion and the related positive anomaly of geopotential height over the Amundsen-Bellingshausen Sea.  相似文献   

4.
The characteristics of interannual fluctuations of the surface air temperature over North America are investigated by using the surface air temperature data of 130 stations during 1941 through 1980. It is found that the surface air temperature bears about ten-year time scale oscillation over the southeastern and northwestern North America and along the west coast of the United States, and it has the characteristics of quasibiennial oscillation over the eastern North America. The ten-year scale oscillation of the surface air temperature is related to that of the sea surface temperature (SST) of North Pacific through the PNA pattern atmospheric circulation anomaly over North Pacific through North America. It is shown that the North Pacific SST has a closer association with the surface air temperature over North America than the central and eastern equatorial Pacific SST. The characteristics of the seasonal variations of the relationship between the North Pacific SST and the surface air temperature over No  相似文献   

5.
Using monthly reanalysis data of the National Center for Environmental Research/National Center for Atmospheric Research (NCEP/NCAR) and Objectively Analyzed Air–Sea Heat Flux (OAFlux) gathered during the winter, singular vector decomposition (SVD) analysis was conducted to reveal the coupled mode between the Kuroshio marine heating anomaly and the geopotential height at 500 hPa (Z500) over the North Pacific. The first SVD mode showed that when the northern Kuroshio marine heating anomaly was positive, the Z500 in the central and western sections of the North Pacific was anomalously low. By composing the meteorological field anomalies in the positive (or negative) years, it has been revealed that while the Aleutian Low deepens (or shallows), the northwesterly wind overlying the Kuroshio strengthens (or weakens) and induces the near-surface air to be cool (or warm). Furthermore, this increases (or decreases) the upward heat flux anomaly and cools (or warms) the sea surface temperature (SST) accordingly. In the vicinity of Kuroshio and its downstream region, the vertical structure of the air temperature along the latitude is baroclinic; however, the geopotential height is equivalently barotropic, which presents a cool trough (or warm ridge) spatial structure. The divergent wind and vertical velocities are introduced to show the anomalous zonal circulation cell. These are characterized by the rising (or descending) air in the central North Pacific, which flows westward and eastward toward the upper troposphere, descends (or rises) in the Kuroshio and in the western section of North America, and then strengthens (or weakens) the mid-latitude zonal cell (MZC).  相似文献   

6.
The Circum-Pacific Teleconnection Pattern (CPTP) is revealed in the meridional wind in the high troposphere via an emprirical orthogonal function (EOF) and correlation analysis on NCEP/NCAR reanalysis data. The CPTP is found to be composed of the North Pacific-North American teleconnection pattern (PNA), the South Pacific-South American teleconnection pattern (PSA), and the teleconnection patterns over the tropical western Pacific and the tropical eastern Pacific (or, Central America, or, tropical Atlantic). There is substantial interannual variability of the CPTP and a typical CPTP can be detected in some years. It is speculated that the zonal wind anomalies over the equatorial region in the western and eastern sides of the Pacific may play a role in linking the two hemispheres. The anomalous convection activities in the Tropics are plausible triggering factors for the zonal wind anomalies that are responsible for the composition of the CPTP.  相似文献   

7.
The mechanism of the locking of the E1 Nino event onset phase to boreal spring （from April to June） in an intermediate coupled ocean-atmosphere model is investigated. The results show that the seasonal variation of the zonal wind anomaly over the equatorial Pacific associated with the seasonal variation of the ITCZ is the mechanism of the locking in the model. From January to March of the E1 Nino year, the western wind anomaly over the western equatorial Pacific can excite the downwelling Kelvin wave that propagates eastward to the eastern and middle Pacific by April to June. From April to December of the year before the E1 Nifio year, the eastern wind anomaly over the equatorial Pacific forces the downwelling Rossby waves that modulate the ENSO cycle. The modulation and the reflection at the western boundary modulate the time of the transition from the cool to the warm phase to September of the year before the E1 Nifio year and cause the strongest downwelling Kelvin wave from the reflected Rossby waves at the western boundary to arrive in the middle and eastern equatorial Pacific by April to June of the E1 Nino year. The superposition of these two kinds of downwelling Kelvin waves causes the El Nino event to tend to occur from April to June.  相似文献   

8.
Three extreme cold events successively occurred across East Asia and North America in the 2020/21 winter.This study investigates the underlying mechanisms of these record-breaking persistent cold events from the isentropic mass circulation(IMC)perspective.Results show that the midlatitude cold surface temperature anomalies always co-occurred with the high-latitude warm anomalies,and this was closely related to the strengthening of the low-level equatorward cold air branch of the IMC,particularly along the climatological cold air routes over East Asia and North America.Specifically,the two cold surges over East Asia in early winter were results of intensification of cold air transport there,influenced by the Arctic sea ice loss in autumn.The weakened cold air transport over North America associated with warmer northeastern Pacific sea surface temperatures(SSTs)explained the concurrent anomalous warmth there.This enhanced a wavenumber-1 pattern and upward wave propagation,inducing a simultaneous and long-lasting stronger poleward warm air branch(WB)of the IMC in the stratosphere and hence a displacement-type Stratospheric Sudden Warming(SSW)event on 4 January.The WB-induced increase in the air mass transported into the polar stratosphere was followed by intensification of the equatorward cold branch,hence promoting the occurrence of two extreme cold events respectively over East Asia in the beginning of January and over North America in February.Results do not yield a robust direct linkage from La Ni?a to the SSW event,IMC changes,and cold events,though the extratropical warm SSTs are found to contribute to the February cold surge in North America.  相似文献   

9.
Synthesis analysis and singular value decomposition (SVD) methods were used to study the impact of surface air temperature (SAT) over Asian-Pacific region on the summertime northeastern Asian blocking high (NABH) with NCEP/NCAR Reanalysis Data.The results showed that 500 hPa geopotential height and SAT fields over Asian-Pacific region shared the similar pattern of East Asian Pacific (EAP) wave train;there was steady remote response relationship between the EAP wave train in summer and the "+-+" pattern of tropical SAT in zonal direction from former winter to summer;there were two relative negative(positive) Walker circulations over the tropical Indian Ocean and Pacific when being more(less) summertime NABH. The influence of sea surface temperature anomaly (SSTA) on the summertime NABH was possibly as follows.The special distribution of SSTA in tropical zonal direction continuously forced the tropical convection and zonal circulation from former winter to summer,and led them to act anomaly.Finally the abnormal conditions were transported to middle-high latitudes through EAP wave train and yielded the advantageous or disadvantageous atmospheric circulation background for the summertime NABH.  相似文献   

10.
Boreal wintertime extratropical circulation is studied in relation to the tropical convection during the 1982/83 El Nino and 1988/89 La Nina. The anomaly structure of 1982/83 and 1988/89 over the extratropics reveals remarkably different features as the longitudinal tropical forcing region changes. The Rossby wave source (Positive) shows the largest maximum over East Asia in both years due to the persistent heating from the western Pacific warm pool area. However, the sink term shows contrasting features over the subtropics and extratropics between the two years. In the El Nino year, enhanced tropical convection over the eastern Pacific produces the Rossby wave sink at 10?N and shifted eastward over the North Pacific, while in the La Nina year, the sink area is shifted westward over the North Pacific. The contrasting features between the two events in mean-eddy interaction appears especially over the downstream area of the East Asian Jet. The extension (retraction) of the meanflow eastward (westward) to  相似文献   

11.
The relationships between the 200-hPa westerly jet stream anomalies over the East Asian coastal water- western Pacific(WPJS),and the oceanic surface heating and synoptic-scale transient eddy(STE)activity anomalies over the North Pacific in wintertime are examined by using ERA-40 and NCEP/NCAR reanalysis data.The analysis demonstrates that the surface heating and the STE anomalies have different patterns, corresponding to the three WPJS anomalous modes,respectively.In the first WPJS anomalous mode,the WPJS main part shows no robust anomaly.The anomalous westerly wind,occurring over the mid-latitude central-eastern Pacific past the date line is associated with the anomalous heating presenting both in the tropical central-eastern Pacific past the date line and the center of the North Pacific basin.Meanwhile,the STE anomaly appears around the region of the anomalous zonal wind.The fluctuation in jet strength shown in the second WPJS mode is strongly related to the heating anomaly in the Kuroshio Current region and the STE anomaly in the jet exit region.The third mode demonstrates a northward/southward shift of the WPJS,which has a statistical connection with a south-north dipolar pattern of the heating anomaly in the western North Pacific separated at 35°N.Meanwhile,the STE spatial displacement is in conjunction with jet shifts in the same direction.The heating anomaly has a close connection with the atmospheric circulation, and thus changes the mid-latitude baroclinicity,leading to the STE anomaly,which then reinforces the WPJS anomaly via internal atmospheric dynamics.  相似文献   

12.
The East Pacific wavetrain(EPW) refers to here the intense stationary wave activity detected in the troposphere over the East Pacific and North America in 45 northern winters from 1958 to 2002.The EPW is generated in the lower troposphere over the East Pacific,propagating predominantly eastward into North America and slightly upward then eventually into the stratosphere.The intensity of the EPW varies from year to year and exhibits apparent decadal variability.For the period 1958-1964,the EPW was in its second maximum,and it was weakest for the period 1965-1975,then it was strongest for the period 1976-1987.After 1987,the EPW weakened again.The intensity and position of the members(i.e.,the Aleutian low,the North American trough,and the North American ridge) of the EPW oscillate from time to time.For an active EPW versus a weak EPW,the Aleutian low deepens abnormally and shifts its center from the west to the east of the date line,in the middle and upper troposphere the East Asian trough extends eastward,and the Canadian ridge intensifies at the same time.The opposite is true for a weak EPW.Even in the lower stratosphere,significant changes in the stationary wave pattern are also observed.Interestingly the spatial variability of the EPW assumes a Pacific-North American(PNA)-like teleconnection pattern.It is likely that the PNA low-frequency oscillation is a reflection of the oscillations of intensity and position of the members of the EPW in horizontal direction.  相似文献   

13.
A comparison of sensitivity in extratropical circulation in the Northern Hemisphere(NH)and Southern Hemisphere(SH)is conducted through observational analyses and diagnostic linear model experiments for two types of El Nio events,the traditional El Nio with the strongest warmth in the eastern tropical Pacific(EP El Nio)and the El Nio Modoki with the strongest warmth in the central tropical Pacific(CP El Nio).It is shown that CP El Nio favors the occurrence of a negative-phase Northern Annular Mode(NAM),while EP El Nio favors that of the Pacific-North American(PNA)pattern.In SH,both EP and CP El Nio induce a negative phase Southern Annular Mode(SAM).However,the former has a greater amplitude,which is consistent with the stronger sea surface temperature(SST)warmth.The difference in the two types of El Nio events in NH may originate from the dependence of heating-induced extratropical response on the location of initial heating,which may be associated with activity of the stationary wave.In SH,the lack of sensitivity to the location of heating can be associated with weaker activity of the stationary wave therein.  相似文献   

14.
Optimal precursor perturbations of El Nino in the Zebiak-Cane model were explored for three different cost functions. For the different characteristics of the eastern-Pacific （EP） El Nino and the central-Pacific （CP） El Nino, three cost functions were defined as the sea surface temperature anomaly （SSTA） evolutions at prediction time in the whole tropical Pacific, the Nino3 area, and the Nino4 area. For all three cost functions, there were two optimal precursors that developed into El Nino events, called Precursor Ⅰ and Precursor Ⅱ. For Precursor Ⅰ, the SSTA component consisted of an east-west （positive-negative） dipole spanning the entire tropical Pacific basin and the thermocline depth anomaly pattern exhibited a tendency of deepening for the whole of the equatorial Pacific. Precursor Ⅰ can develop into an EP-El Nino event, with the warmest SSTA occurring in the eastern tropical Pacific or into a mixed El Nino event that has features between EP-El Nino and CP-El Nino events. For Precursor Ⅱ, the thermocline deepened anomalously in the eastern equatorial Pacific and the amplitude of deepening was obviously larger than that of shoaling in the central and western equatorial Pacific. Precursor Ⅱ developed into a mixed El Nino event. Both the thermocline depth and wind anomaly played important roles in the development of Precursor Ⅰ and Precursor Ⅱ.  相似文献   

15.
Experimental outputs of 11 Atmospheric Model Intercomparison Project （AMIP） models from phase 5 of the Coupled Model Intercomparison Project （CMIP5） are analyzed to assess the atmospheric circulation anomaly over Northern Hemisphere induced by the anomalous rainfall over tropical Pacific and Indian Ocean during boreal winter.The analysis shows that the main features of the interannual variation of tropical rainfall anomalies,especially over the Central Pacific （CP） （5°S-5°N,175°E-135°W） and Indo-western Pacific （IWP） （20°S-20°N,110°-150°E） are well captured in all the CMIP5/AMIP models.For the IWP and western Indian Ocean （WIO） （10°S-10°N,45°-75°E）,the anomalous rainfall is weaker in the 11 CMIP5/AMIP models than in the observation.During El Ni（n）o/La Ni（n）a mature phases in boreal winter,consistent with observations,there are geopotential height anomalies known as the Pacific North American （PNA） pattern and Indo-western Pacific and East Asia （IWPEA） pattern in the upper troposphere,and the northwestern Pacific anticyclone （cyclone） （NWPA） in the lower troposphere in the models.Comparison between the models and observations shows that the ability to simulate the PNA and NWPA pattern depends on the ability to simulate the anomalous rainfall over the CP,while the ability to simulate the IWPEA pattern is related to the ability to simulate the rainfall anomaly in the IWP and WIO,as the SST anomaly is same in AMIP experiments.It is found that the tropical rainfall anomaly is important in modeling the impact of the tropical Indo-Pacific Ocean on the extratropical atmospheric circulation anomaly.  相似文献   

16.
By applying the historical-run outputs from 24 Coupled Model Intercomparison Project Phase 5（CMIP5） models and the NOAA Extended Reconstructed SST V3 b dataset（ERSST）, the characteristics of different types of ENSO in the selected CMIP5 models, including cold-season-matured Eastern Pacific（C-EP） ENSO, warmseason-matured EP（W-EP） ENSO, cold-season-matured Central Pacific（C-CP） ENSO, and warm-season-matured CP（W-CP） ENSO, were examined in comparison with those in the ERSST dataset. The results showed that, in general, consistent with observations, EP ENSO events in most of the model runs were relatively much stronger than CP ENSO events, and cold-season-matured ENSO events were relatively much more frequent than warm-season-matured ENSO events for both EP and CP ENSO events. The composite amplitudes of ENSO events in most of the models were generally weaker than in observations, particularly for EP El Ni？o and CP La Ni？a. Moreover, most of the models successfully reproduced the amplitude asymmetries between El Ni？o and La Ni？a for cold-season-matured EP and CP ENSO events, exhibiting an average stronger/weaker EP El Ni？o/La Ni？a regime and a weaker/stronger CP El Ni？o/La Ni？a regime. Most of the models, however, failed to reproduce the observed regimes of stronger/weaker W-EP El Ni？o/ La Ni？a and weaker/stronger W-CP El Ni？o/La Ni？a.  相似文献   

17.
Sea-level pressure variations over the North Pacific Ocean influence the surface climate conditions of China and western North America. Documentary records of precipitation in China data back to the mid-15th century, and a well-replicated network of tree-ring chronologies from western North America dates to the early 17th century. These proxy climate records are used separately and together to estimate sea-level pressure variations over the North Pacific back to 1600 A.D. The models are calibrated over the period 1899 to 1950 and verified over the independent period, 1951 to 1963. The best estimates, derived from predictors in China and western North America, calibrate 44.7% of summer sea-level pressure variance. The study demonstrates the potential of combining different proxy data sources to derive estimates of past climate.  相似文献   

18.
A comparative study between the output of the Flexible Global Climate Model Version 1.0 (FGCM- 1.0) and the observations is performed. At 500 hPa, the geopotential height of FGCM is similar to the observations, but in the North Pacific the model gives lower values, and the differences are most significant over the northern boundary of the Pacific. In a net heat flux comparison, the spatial patterns of the two are similar in winter, but more heat loss appears to the east of Japan in FGCM than in COADS. On the interannual timescale, strong (weak) Kuroshio transports to the east of Taiwan lead the increasing (decreasing) net heat flux, which is centered over the Kuroshio Extension region, by 1–2 months, with low (high) pressure anomaly responses appearing at 500 hPa over the North Pacific (north of 25N) in winter. The northward heat transport of the Kuroshio is one of the important heat sources to support the warming of the atmosphere by the ocean and the formation of the low pressure anomaly at 500 hPa over the North Pacific in winter.  相似文献   

19.
In the paper the 5°×10°latitude-longitude grid point data of daily 500 hPa geopotential height over the NorthernHemisphere(NH)in summer(June—August)during 1980s are used.The base point(20°N,120°E)is selected to calcu-late point correlation between the base point and other grid points.We find that the summer heat source anomaly of thetropical western Pacific causes anomaly of summer general circulation over NH and teleconnection of general circula-tion similar to PNA pattern forms from East Asia to North America.The teleconnections show great interannualchanges.  相似文献   

20.
The summer snow anomalies over the Tibetan Plateau （TP） and their effects on climate variability are often overlooked,possibly due to the fact that some datasets cannot properly capture summer snow cover over high terrain.The satellite-derived Equal-Area Scalable Earth grid （EASE-grid） dataset shows that snow still exists in summer in the western part and along the southem flank of the TP.Analysis demonstrates that the summer snow cover area proportion （SCAP） over the TP has a significant positive correlation with simultaneous precipitation over the mei-yu-baiu （MB） region on the interannual time scale.The close relationship between the summer SCAP and summer precipitation over the MB region could not be simply considered as a simultaneous response to the Silk Road pattern and the SST anomalies in the tropical Indian Ocean and tropical central-eastern Pacific.The SCAP anomaly has an independent effect and may directly modulate the land surface heating and,consequently,vertical motion over the western TP,and concurrently induce anomalous vertical motion over the North Indian Ocean via a meridional vertical circulation.Through a zonal vertical circulation over the tropics and a Kelvin wave-type response,anomalous vertical motion over the North Indian Ocean may result in an anomalous high over the western North Pacific and modulate the convective activity in the western Pacific warm pool,which stimulates the East Asia-Pacific （EAP） pattern and eventually affects summer precipitation over the MB region.  相似文献   

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