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1.
According to the different pattern of sea surface temperature anomaly(SSTA) in the previous year of La Nia events,we categorized La Nia events into two types to investigate the different characteristics of tropical cyclone(TC) activity over the western North Pacific(WNP) in TC peak season of two types La Nia events.One type is following the previous El Nio event(La Nia I);the other is following the previous neutral phase or developing La Nia event(La Nia II).Results show that TC genesis frequency in the WNP during TC peak season of La Nia I is less than normal year,whereas it has no differences from normal year during La Nia II.The main reason is attributed to the different amplitude SSTA in the East Indian Ocean(EIO) and the western Pacific Ocean(WPO).Similar to the capacitor effect,strongly positive SSTA in the EIO-WPO during La Nia I triggers an equatorial baroclinic Kelvin wave,which intensifies the easterly in the lower troposphere and weakens the East Asian summer monsoon,and thus the TC frequency decreased during La Nia I.However,the easterly anomaly shows a weak response to the SSTA in the EIO-WPO during La Nia II,and there is no significant change in the environmental pattern over the WNP;so is TC frequency.The modulation of strong EIO-WPO SSTA on large-scale circulation over the WNP reduces the environmental barotropic energy conversion into synoptic-scale disturbances during La Nia I,and also suppresses TC disturbances.The understanding of two different types of La Nia events could help improve the seasonal prediction of TC activity in the WNP during La Nia. 相似文献
2.
The tropical Pacific experienced a sustained warm sea surface condition that started in 2014 and a very strong El Nio event in 2015. One striking feature of this event was the horseshoe-like pattern of positive subsurface thermal anomalies that was sustained in the western-central equatorial Pacific throughout 2014–2015. Observational data and an intermediate ocean model are used to describe the sea surface temperature(SST) evolution during 2014–2015. Emphasis is placed on the processes involved in the 2015 El Nio event and their relationships with SST anomalies, including remote effects associated with the propagation and reflection of oceanic equatorial waves(as indicated in sea level(SL) signals) at the boundaries and local effects of the positive subsurface thermal anomalies. It is demonstrated that the positive subsurface thermal anomaly pattern that was sustained throughout 2014–2015 played an important role in maintaining warm SST anomalies in the equatorial Pacific. Further analyses of the SST budget revealed the dominant processes contributing to SST anomalies during 2014–2015. These analyses provide an improved understanding of the extent to which processes associated with the 2015 El Nio event are consistent with current El Nio and Southern Oscillation theories. 相似文献
3.
Recent studies have found a connection between Indian Ocean Basin Warming and the anomalous Northwest Pacific Anticyclone(ANPWA) during El Ni?o decaying year.This study focuses on the necessary condition for this connection by using observation and numerical simulation.The seasonal transition of the Indian Ocean sea surface wind is critical to the climatic effect of Indian Ocean Basin Warming.When the South Asian Summer Monsoon reaches its peak,the background wind becomes desirable for basin warming,which then affects the climate in the Northwest Pacific.Via the Kelvin waves and Ekman divergence,the wind anomalies exist in the lower atmosphere east of the Indian Ocean warm Sea Surface Temperature(SST) anomalies,and intensify and sustain the ANWPA throughout the El Nio decaying summer.This impact plays an important role in the inter-annual variability of the East Asian Summer Monsoon. 相似文献
4.
《中国科学:地球科学(英文版)》2017,(10)
We applied a season-reliant empirical orthogonal function(S-EOF) analysis based on the results of the Community Earth System Model, version 1-Biogeochemistry, to seasonal mean air-sea CO_2 flux over the western North Pacific(WNP)(0°–35°N, 110°E–150°E). The first leading mode accounts for 29% of the total interannual variance, corresponding to the evolution of the El Ni-Southern Oscillation(ENSO) from its developing to decaying phases. During the ENSO developing phase in the summer and fall, the contribution of surface seawater CO_2 partial pressure anomalies is greater than that of gas transfer/solubility anomalies, which contribute to increasing oceanic CO_2 uptake over the WNP. During the ENSO mature phase in the winter, the anomalous southwesterly northwest of the western North Pacific anticyclone(WNPAC) reduces the surface wind speed in the China marginal sea and thus decreases oceanic CO_2 uptake by reducing the gas transfer coefficient. In the subsequent spring, the WNPAC maintains with an eastward shift in position. The anomalous southwesterly warms sea surface temperatures in the China marginal sea by reducing evaporation and thus decreases oceanic CO_2 uptake by enhancing surface seawater CO_2 partial pressure. This process, rather than the effect of decreasing gas transfer coefficient, dominates CO_2 flux anomalies in the spring. 相似文献
5.
Reconstruction of Conceptual Prediction Model for the Three Rainfall Patterns in the summer of eastern China under global warming 总被引：1，自引：0，他引：1
With the influence of global warming,the global climate has undergone significant inter-decadal variation since the late 1970s.Although El Nio-Southern Oscillation(ENSO)has been the strongest signal for predicting global climate inter-annual variability,its relation with the summer rainfall in China has significantly changed,and its indicative function on the summer rainfall in China has weakened.This has led to a significant decrease in the accuracy rate of early conceptual prediction models for the Three Rainfall Patterns in the summer of eastern China.On the basis of the difference analysis of atmospheric circulation system configuration in summer,as well as the interaction of ocean and atmospheric in previous winter between two phases,i.e.before and after the significant global warming(1951 to 1978 and 1979 to 2012,respectively),we concluded that(1)Under different inter-decadal backgrounds,the atmospheric circulations that impacted the Three Rainfall Patterns in the summer of eastern China showed consistency,but in the latter phase of the global warming,the Western Pacific Subtropical High(WPSH)was on the strong side,the position of which was in the south,and the blocking high in the Eurasia mid-high latitudes was active,while the polar vortex extended to the south,and meridional circulation intensified.This circulation background may have been conducive to the increase of the circulation frequency of Patterns II and III,and the decrease of the circulation frequency of Pattern I,thus leading to more Patterns II and III and fewer Pattern I in the summer rainfall of eastern China.(2)In the former phase,the corresponding previous winter SST fields of different rainfall patterns showed visible differences.The impact of ENSO on North Pacific Oscillation(NPO)was great,and the identification ability of which on Patterns I and II of summer rainfall was effective.In the latter phase,this identification ability decreased,while the impact of ENSO on the Pacific/North American(PNA)teleconnection pattern increased,and the identification ability of the PNA on Patterns II and III also increased.Based on the new inter-decadal climate background,this study reconstructs the conceptual prediction model for the Three Rainfall Patterns in summer of eastern China by using the previous winter PNA and the Eurasian(EU)teleconnection indexes.The fitting effect was satisfying,though it is necessary to be further tested. 相似文献
6.
<正>El Nio is a remarkable climate phenomenon with a basinwide warming of sea surface temperatures(SST) in the easterncentral tropical Pacific. El Nio means The Little Boy, or Christ Child in Spanish, and on the contrary, a basinwide cooling of the tropical Pacific SST is called La Nia that means The Little Girl in Spanish. Always, a large-scale SST change in the tropical 相似文献
7.
Interdecadal change of the linkage between the North Atlantic Oscillation and the tropical cyclone frequency over the western North Pacific 总被引：2，自引：0，他引：2
The relationship between the North Atlantic Oscillation(NAO) and the tropical cyclone frequency over the western North Pacific(WNPTCF) in summer is investigated by use of observation data. It is found that their linkage appears to have an interdecadal change from weak connection to strong connection. During the period of 1948–1977, the NAO was insignificantly correlated to the WNPTCF. However, during the period of 1980–2009, they were significantly correlated with stronger(weaker) NAO corresponding to more(fewer) tropical cyclones in the western North Pacific. The possible reason for such a different relationship between the NAO and the WNPTCF during the former and latter periods is further analyzed from the perspective of large-scale atmospheric circulations. When the NAO was stronger than normal in the latter period, an anomalous cyclonic circulation prevailed in the lower troposphere of the western North Pacific and the monsoon trough was intensified, concurrent with the eastward-shifting western Pacific subtropical high as well as anomalous low-level convergence and high-level divergence over the western North Pacific. These conditions favor the genesis and development of tropical cyclones, and thus more tropical cyclones appeared over the western North Pacific. In contrast, in the former period, the impact of the NAO on the aforementioned atmospheric circulations became insignificant, thereby weakening its linkage to the WNPTCF. Further study shows that the change of the wave activity flux associated with the NAO during the former and latter periods may account for such an interdecadal shift of the NAO–WNPTCF relationship. 相似文献
8.
Most ocean-atmosphere coupled models have difficulty in predicting the El Nio-Southern Oscillation(ENSO) when starting from the boreal spring season. However, the cause of this spring predictability barrier(SPB) phenomenon remains elusive. We investigated the spatial characteristics of optimal initial errors that cause a significant SPB for El Nio events by using the monthly mean data of the pre-industrial(PI) control runs from several models in CMIP5 experiments. The results indicated that the SPB-related optimal initial errors often present an SST pattern with positive errors in the central-eastern equatorial Pacific, and a subsurface temperature pattern with positive errors in the upper layers of the eastern equatorial Pacific, and negative errors in the lower layers of the western equatorial Pacific. The SPB-related optimal initial errors exhibit a typical La Ni-a-like evolving mode, ultimately causing a large but negative prediction error of the Nio-3.4 SST anomalies for El Nio events. The negative prediction errors were found to originate from the lower layers of the western equatorial Pacific and then grow to be large in the eastern equatorial Pacific. It is therefore reasonable to suggest that the El Nio predictions may be most sensitive to the initial errors of temperature in the subsurface layers of the western equatorial Pacific and the Nio-3.4 region, thus possibly representing sensitive areas for adaptive observation. That is, if additional observations were to be preferentially deployed in these two regions, it might be possible to avoid large prediction errors for El Nio and generate a better forecast than one based on additional observations targeted elsewhere. Moreover, we also confirmed that the SPB-related optimal initial errors bear a strong resemblance to the optimal precursory disturbance for El Nio and La Nia events. This indicated that improvement of the observation network by additional observations in the identified sensitive areas would also be helpful in detecting the signals provided by the precursory disturbance, which may greatly improve the ENSO prediction skill. 相似文献
9.
Using predictions for the sea surface temperature anomaly(SSTA) generated by an intermediate coupled model(ICM)ensemble prediction system(EPS), we first explore the "spring predictability barrier"(SPB) problem for the 2015/16 strong El Nio event from the perspective of error growth. By analyzing the growth tendency of the prediction errors for ensemble forecast members, we conclude that the prediction errors for the 2015/16 El Nio event tended to show a distinct season-dependent evolution, with prominent growth in spring and/or the beginning of the summer. This finding indicates that the predictions for the 2015/16 El Nio occurred a significant SPB phenomenon. We show that the SPB occurred in the 2015/16 El Nio predictions did not arise because of the uncertainties in the initial conditions but because of model errors. As such, the mean of ensemble forecast members filtered the effect of model errors and weakened the effect of the SPB, ultimately reducing the prediction errors for the 2015/16 El Nio event. By investigating the model errors represented by the tendency errors for the SSTA component,we demonstrate the prominent features of the tendency errors that often cause an SPB for the 2015/16 El Nio event and explain why the 2015/16 El Nio was under-predicted by the ICM EPS. Moreover, we reveal the typical feature of the tendency errors that cause not only a significant SPB but also an aggressively large prediction error. The feature is that the tendency errors present a zonal dipolar pattern with the west poles of positive anomalies in the equatorial western Pacific and the east poles of negative anomalies in the equatorial eastern Pacific. This tendency error bears great similarities with that of the most sensitive nonlinear forcing singular vector(NFSV)-tendency errors reported by Duan et al. and demonstrates the existence of an NFSV tendency error in realistic predictions. For other strong El Nio events, such as those that occurred in 1982/83 and 1997/98, we obtain the tendency errors of the NFSV structure, which cause a significant SPB and yield a much larger prediction error. These results suggest that the forecast skill of the ICM EPS for strong El Nio events could be greatly enhanced by using the NFSV-like tendency error to correct the model. 相似文献
10.
《中国科学:地球科学(英文版)》2021,(8)
In this study, sea surface salinity(SSS) indexes are derived from reanalysis and observational datasets to distinguish the two types of(Central Pacific(CP) and Eastern Pacific(EP)) El Ni?o events in the tropical Pacific. Based on the SSS anomalous spatial and temporal pointwise correlations with sea surface temperature(SST) indexes of two types of El Ni?o events, the key areas with SSS variations for EP and CP El Ni?o events are identified. For EP El Ni?o events, the key areas are located over an arcuate area centered at(0°, 130°E) and in the central equatorial Pacific covering(5°S–5°N, 175°W–158°W). For CP El Ni?o events, the key areas are located in the northeastern western Pacific covering(2°N, 142°E–170°E) and in the southeastern Pacific covering(20°S–10°S, 135°W–95°W). The key areas for EP and CP El Ni?o events in this study are not located near the dateline in the equatorial Pacific and differ from those obtained from the regression or composite methods.Accordingly, these key areas are used to construct SSS indexes, termed as the CP/EP El Ni?o SSS index(CSI/ESI), to distinguish EP and CP El Ni?o events independently. The SSS indexes are verified by different datasets over varying time periods and they can be adequately used to identify the two types of El Ni?o events and serve as another useful tool for monitoring ENSO. These analyses offer novel insight into how to represent the diversity of El Ni?o events. 相似文献
11.
The 2015/16 El Nio developed from weak warm conditions in late 2014 and NINO3.4 reached 3℃ in November 2015. We describe the characteristics of the evolution of the 2015/16 El Nio using various data sets including SST, surface winds,outgoing longwave radiation and subsurface temperature from an ensemble operational ocean reanalyses, and place this event in the context of historical ENSO events since 1979. One salient feature about the 2015/16 El Nio was a large number of westerly wind bursts and downwelling oceanic Kelvin waves(DWKVs). Four DWKVs were observed in April-November 2015 that initiated and enhanced the eastern-central Pacific warming. Eastward zonal current anomalies associated with DWKVs advected the warm pool water eastward in spring/summer. An upwelling Kelvin wave(UWKV) emerged in early November 2015 leading to a rapid decline of the event. Another outstanding feature was that NINO4 reached a historical high(1.7℃), which was 1℃(0.8℃) higher than that of the 1982/83(1997/98) El Nio . Although NINO3 was comparable to that of the 1982/83 and 1997/98 El Nio , NINO1+2 was much weaker. Consistently, enhanced convection was displaced 20 degree westward, and the maximum D20 anomaly was about 1/3.1/2 of that in 1997 and 1982 near the west coast of South America. 相似文献
12.
How would typhoon activity over the western North Pacific change for various scenarios of future global warming?Using the model projections of the Coupled Model Intercomparison Project phase 3(CMIP 3)under the SRES A1B scenario,we generated summer(September)ice-free Arctic conditions,also referred to as Blue Arctic conditions,and then used the corresponding monthly sea surface temperature(SST)and a set of CO2concentrations to drive an AGCM model to simulate the resulting changes in background conditions affecting typhoon activity over the western North Pacific.Our results show that,during typhoon season(June to October),atmospheric and ocean circulations over the western North Pacific would be significantly different from the present circulations.Changes in the vertical shear of zonal wind and outgoing longwave radiation(OLR)in the western North Pacific are favorable for westward and northward shift,respectively,of the location of typhoon genesis.Moreover,changes in the above fields over the key area may be conducive to less frequent typhoons.In addition,the tropical cyclone genesis potential index(GPI)over the western North Pacific would decrease(increase)east(west)of 150°E(140°E). 相似文献
13.
North Pacific sea ice cover, a predictor for the Western North Pacific typhoon frequency? 总被引：13，自引：0，他引：13
Fan Ke 《中国科学D辑(英文版)》2007,50(8):1251-1257
The relationship between the sea ice cover in the North Pacific and the typhoon frequency has been studied in this paper. It follows that the index for the sea ice cover in the North Pacific (ISA) both in December-January-February (DJF) and in March-April-May (MAM) is negatively correlated with annual typhoon number over the western North Pacific (TNWNP) during 1965―2004, with correlation coeffi-cients of -0.42 and -0.49 respectively (above 99% significant level). Large sea ice cover in the North Pacific tends to decrease TNWNP. Positive ISA (MAM) is associated with the tropical circulation and SST anomalies in the North Pacific, which may lead to unfavorable dynamic and thermal conditions for typhoon genesis over WNP from June to October (JJASO). The variability of the atmospheric circula-tion over the North Pacific, associated with the ISA anomaly in MAM is connected to the tropical at-mospheric circulation variability in MAM via the teleconnection wave train. Besides, as the tropical circulation has strong seasonal persistency from the MAM to JJASO, thus, the ISA in MAM-related variability of the tropical atmospheric circulation as well as the SST can affect the typhoon activity over the western North Pacific. 相似文献
14.
The 2015/2016 El Nio was one of the strongest El Nio events in history, and this strong event was preceded by a weak El Nio in 2014. This study systematically analyzed the dynamical processes responsible for the genesis of these events. It was found that the weak 2014 El Nio had two warming phases, the spring-summer warming was produced by zonal advection and downwelling Kelvin waves driven by westerly wind bursts(WWBs), and the autumn-winter warming was produced by meridional advection, surface heating as well as downwelling Kelvin waves. The 2015/2016 extreme El Nio, on the other hand, was primarily a result of sustained zonal advection and downwelling Kelvin waves driven by a series of WWBs, with enhancement from the Bjerknes positive feedback. The vast difference between these two El Nio events mainly came from the different amount of WWBs in 2014 and 2015. As compared to the 1982/1983 and 1997/1998 extreme El Nio events, the 2015/2016 El Nio exhibited some distinctive characteristics in its genesis and spatial pattern. We need to include the effects of WWBs to the theoretical framework of El Nio to explain these characteristics, and to improve our understanding and prediction of El Nio. 相似文献
15.
Two interannual variability modes of the Northwestern Pacific Subtropical Anticyclone in boreal summer 总被引：3，自引：0，他引：3
Using the reanalysis data and 20th century simulation of coupled model FGOALS_gl developed by LASG/IAP, we identified two distinct interannual modes of Northwestern Pacific Subtropical Anticyclone (NWPAC) by performing Empirical Orthogonal Function (EOF) analysis on 850 hPa wind field over the northwestern Pacific in summer. Based on the associated anomalous equatorial zonal wind, these two modes are termed as "Equatorial Easterly related Mode" (EEM) and "Equatorial Westerly related Mode" (EWM), respectively. The formation mechanisms of these two modes are similar, whereas the maintenance mechanisms, dominant periods, and the relationships with ENSO are different. The EEM is associated with El Ni o decaying phase, with the anomalous anticyclone established in the preceding winter and persisted into summer through local positive air-sea feedback. By enhancing equatorial upwelling of subsurface cold water, EEM favors the transition of ENSO from El Ni o to La Ni a. The EWM is accompanied by the El Ni o events with long persistence, with the anomalous anticyclone formed in spring and strengthened in summer due to the warm Sea Surface Temperature anomalies (SSTA) forcing from the equatorial central-eastern Pacific. The model well reproduces the spatial patterns of these two modes, but fails to simulate the percentage variance accounted for by the two modes. In the NCEP reanalysis (model result), EEM (EWM) appears as the firstmode, which accounts for 35.6% (68.2%) of the total variance. 相似文献
16.
The interannual variability of the boreal winter (DJF) Hadley Cell strength during 1979-2008 is investigated using NCEP/NCAR reanalysis data. The results of AMIP simulation of LASG/IAP AGCM GAMIL2.0 are compared against the reanalysis data. Both the reanalysis data and the simulation show that the interannual variability of the Hadley Cell strength has a non-uniform spatial distribution, as evidenced by the 1st Empirical Orthogonal Function (EOF) mode. The change of Hadley cell strength in the tropics is opposite to that in the subtropical regions. Our analysis indicates that a positive phase of EOF1 is associated with an El Ni o-like warmer equatorial central and eastern Pacific and a warmer southern Indian Ocean. Above features are also seen in the results of GAMIL2.0 simulation, indicating that the interannual variability of the Hadley Cell strength is driven by the tropical ocean variability. Our analysis also demonstrates that the contribution of the warmer central-eastern Pacific to the 1st EOF mode is larger than that of the South Indian Ocean. The SST forcing enhances the local Hadley circulation strength in the central Pacific and Africa (30°S-30°N, 150°E-90°W), while it weakens the local Hadley circulation in other regions (30°S-30°N, 90°-10°W). The western Pacific anticyclone remotely driven by the El Ni o forcing leads to a weakened local Hadley cell in the Northern Hemisphere, while the South Indian Ocean anticyclone driven by the remote El Ni o forcing and the local warmer SST anomalies in the southern Indian Ocean results in a weakened local Hadley Cell in the Southern Hemisphere. The enhancement of the Pacific local Hadley Cell is stronger (weaker) than that of the Atlantic, the western Pacific, and the southern Indian Ocean in the tropical (subtropical) part, thus for the zonal mean condition the strength of the total Hadley Cell is stronger (weaker) in the tropical (subtropical) limb. The amplitude of the Hadley Cell change in the Northern Hemisphere is stronger than that in the Southern Hemisphere. Hence the leading interannual variability mode of boreal winter Hadley Cell exhibits a non-uniform spatial pattern. 相似文献
17.
Here we assessed the performances of IAP/LASG climate system model FGOALS-g2 and FGOAS-s2 in the simulation of the tropical Pacific Walker circulation(WC). Both models reasonably reproduce the climatological spatial distribution features of the tropical Pacific WC. We also investigated the changes of WC simulated by two versions of FGOALS model and discussed the mechanism responsible for WC changes. Observed Indo-Pacific sea level pressure(SLP) reveals a reduction of WC during 1900–2004 and 1950–2004, and an enhancement of WC during 1982–2004. During the three different time spans, the WC in FGOALS-g2 shows a weakening trend. In FGOALS-s2, tropical Pacific atmospheric circulation shows no significant change over the past century, but the WC strengthens during 1950–2004 and 1982–2004. The simulated bias of the WC change may be related to the phase of the multi-decadal mode in coupled models, which is not in sync with that in the observations. The change of WC is explained by the hydrological cycle constraints that precipitation must be balanced with the moisture transporting from the atmospheric boundary layer to the free troposphere. In FGOALS-g2, the increasing amplitude of the relative variability of precipitation(?P/P) is smaller(larger) than the relative variability of moisture(?q/q) over the tropical western(eastern) Pacific over the three time spans, and thus leads to a weakened WC. In FGOALS-s2, the convective mass exchange fluxes increase(decrease) over the tropical western(eastern) Pacific over the past 53 a(1950–2004) and the last 23 a(1982– 2004), and thus leads to a strengthened WC. The distributions of sea surface temperature(SST) trends dominate the change of WC. Over the past 55 a and 23 a, tropical Pacific SST shows an El Ni?o-like(a La Ni?a-like) trend pattern in FGOALS-g2(FGOALS-s2), which drives the weakening(strengthening) of WC. Therefore, a successful simulation of the tropical Pacific SST change pattern is necessary for a reasonable simulation of WC change in climate system models. This idea is further supported by the diagnosis of historical sea surface temperature driven AGCM-simulations. 相似文献
18.
Arabian Peninsula-North Pacific Oscillation and its association with the Asian summer monsoon 总被引：2，自引：0，他引：2
Using correlation and EOF analyses on sea level pressure from 57-year NCEP-NCAR reanalysis data, the Arabian Peninsula-North Pacific Oscillation (APNPO) is identified. The APNPO reflects the co-variability between the North Pacific high and South Asian summer monsoon low. This teleconnec- tion pattern is closely related to the Asian summer monsoon. On interannual timescale, it co-varies with both the East Asian summer monsoon (EASM) and South Asian summer monsoon (SASM); on decadal timescale, it co-varies with the EASM: both exhibit two abrupt climate changes in the middle 1960s and the late 1970s respectively. The possible physical process for the connections between the APNPO and Asian summer monsoon is then explored by analyzing the APNPO-related atmospheric circulations. The results show that with a strong APNPO, the Somali Jet, SASM flow, EASM flow, and South Asian high are all enhanced, and an anomalous anticyclone is produced at the upper level over northeast China via a zonal wave train. Meanwhile, the moisture transportation to the Asian monsoon regions is also strengthened in a strong APNPO year, leading to a strong moisture convergence over India and northern China. All these changes of circulations and moisture conditions finally result in an anoma- lous Asian summer monsoon and monsoon rainfall over India and northern China. In addition, the APNPO has a good persistence from spring to summer. The spring APNPO is also significantly corre- lated with Asian summer monsoon variability. The spring APNPO might therefore provide valuable in- formation for the prediction of Asian summer monsoon. 相似文献
19.
The 2018 typhoon season in the western North Pacific(WNP) was highly active, with 26 named tropical cyclones(TCs) from June to November, which exceeded the climatological mean(22) and was the second busiest season over the past twenty years. More TCs formed in the eastern region of the WNP and the northern region of the South China Sea(SCS). More TCs took the northeast quadrant in the WNP, recurving from northwestward to northward and causing heavy damages in China's Mainland(69.73 billion yuan) in 2018. Multiscale climate variability is conducive to an active season via an enhanced monsoon trough and a weakened subtropical high in the WNP. The large-scale backgrounds in 2018 showed a favorable environment for TCs established by a developing central Pacific(CP) El Ni?o and positive Pacific meridional mode(PMM)episode on interannual timescales. The tropical central Pacific(TCP) SST forcing exhibits primary control on TCs in the WNP and large-scale circulations, which are insensitive to the PMM. During CP El Ni?o years, anomalous convection associated with the TCP warming leads to significantly increased anomalous cyclonic circulation in the WNP because of a Gill-type Rossby wave response. As a result, the weakened subtropical high and enhanced monsoon trough shift eastward and northward, which favor TC genesis and development. Although such increased TC activity in 2018 might be slightly suppressed by interdecadal climate variability, it was mostly attributed to the favorable interannual background. In addition, high-frequency climate signals,such as intraseasonal oscillations(ISOs) and synoptic-scale disturbances(SSDs), interacted with the enhanced monsoon trough and strongly modulated regional TC genesis and development in 2018. 相似文献
20.
The future potential changes in precipitation and monsoon circulation in the summer in East Asia are projected using the latest generation of coupled climate models under Intergovernmental Panel on Climate Change (IPCC) Special Report on Emission Scenarios (SRES) A1B scenario (a medium emission scenario).The multi-model ensemble means show that during the period of 2010-2099,the summer precipitation in East Asia will increase and experience a prominent change around the 2040s,with a small increase (～1%) before the end of the 2040s and a large increase (～9%) afterward.This kind of two-stage evolution characteristic of precipitation change can be seen most clearly in North China,and then in South China and in the mid and lower Yangtze River Valley.In 2010-2099,the projected precipitation pattern will be dominated by a pattern of "wet East China" that explains 33.6% of EOF total variance.The corresponded time coefficient will markedly increase after the 2040s,indicating a great contribution from this mode to the enhanced precipitation across all East China.Other precipitation patterns that prevail in the current climate only contribute a small proportion to the total variance,with no prominent liner trend in the future.By the late 21st century,the monsoon circulation will be stronger in East Asia.At low level,this is due to the intensification of southwesterly airflow north of the anticyclone over the western Pacific and the SCS,and at high level,it is caused by the increased northeasterly airflow east of the anticyclone over South Asia.The enhanced monsoon circulation will also experience a two-stage evolution in 2010-2099,with a prominent increase (by ～0.6 m s-1) after the 2040s.The atmospheric water vapor content over East Asia will greatly increase (by ～9%) at the end of 21st century.The water vapor transported northward into East China will be intensified and display a prominent increase around the 2040s similar to other examined variables.These indicate that the enhanced precipitation over East Asia is caused by the increases in both monsoon circulation and water vapor,which is greatly different from South Asia.Both the dynamical and thermal dynamic variables will evolve consistently in response to the global warming in East Asia,i.e.,the intensified southwesterly monsoon airflow corresponding to the increased water vapor and southwesterly moisture transport. 相似文献