Characteristics And Causes Of The Winter Recurrence And Persistence Barrier In Global Ocean-Atmosphere Coupled System

The persistence indicates how long the memory of the system sustain,and hints at the potential predictability of the system.Therefore,a better understanding of the SSTA persistence in the air-sea coupled system should be important for studying the global climate and predicting future climate change.Although more researches have been performed to the seasonal change of the SSTA persistence,the relative studies are still inadequate,even some important questions have not been considered.This study will therefore perform a series of researches on the winter-to-winter recurrence(WWR) and the persistence barrier.First,we comprehensively analyze the temporal-spatial characteristics of the WWR of air-sea system in the Northern Hemisphere,investigate the relationships between the SSTA WWR and the WWR of the atmospheric circulation anomalies,discuss the possible causes of the WWR of air-sea system in the North Pacific,examine the interannual variability of the SSTA WWR though classifying the recurrence year and non-recurrence year.Second,the temporal-spatial characteristics of the persistence barrier of SSTA in the world's oceans are examined.And the further investigations on the summer persistence barrier in the central North Pacific and fall persistence barrier in the South China Sea and Indonesia region are performed.Finally,we evaluate the simulation ability of the WWR and the persistence barrier in the air-sea system using the IPCC 20C3M coupled model output data.The major results are as follows:(1) The temporal-spatial characteristics of the winter-to-winter recurrence(WWR) of sea surface temperature anomalies(SSTA) in the Northern Hemisphere are comprehensively studied through the lag correlation analysis.Results show that the SSTA WWR in both the North Pacific and Atlantic occurs in most of the basin,but the temporal-spatial distributions of the SSTA WWR in the two oceans are distinctly different.Further analyses indicate that,in the North Atlantic Ocean the temporal-spatial distributions of SSTA WWR are consistent with the spatial distributions of the seasonal cycle of mixed layer depth(MLD),while in the North Pacific Ocean the spatial differences of recurrence timing cannot be completely explained by those of the difference in the MLD between winter and summer in some regions,although the 'reemergence mechanism' still works there.(2) The atmospheric circulation anomalies also exhibit WWR in the Northern Hemisphere, and it is mainly located in eastern Asia,the central North Pacific and the region near Newfoundland in the North Atlantic.The linear regression analysis indicates that,the sea level pressure anomalies(SLPA) in the central North Pacific,which is one of the key areas of WWR of the atmospheric circulation anomalies,is essential for the occurrence of the SSTA WWR in the central North Pacific.Moreover,the strongest positive correlations occur when the SLPA lead SSTA in the central North Pacific by 1 month,which suggests that the force of the atmosphere on the ocean may play a dominant role in this area.Therefore,the 'reemergence mechanism' is not the only process influencing the SSTA WWR,the WWR of the atmospheric circulation anomalies may be one of the causes of the SSTA WWR in the central North Pacific. However,this relationship of the air-sea system is not notable between the SLPA in the region near Newfoundland in the North Atlantic and the SSTA in the North Atlantic.(3) The relationships between WWR in the air-sea system and ENSO, interannual-interdecadal variability,Pacific Decadal Oscillation(PDO) and sea ice in the arctic are investigated.The results indicate that,similar to the SSTA WWR,the occurrence of the WWR of the atmosphere circulation anomalies in the Northern Hemisphere is also linearly independent of ENSO,implying that ENSO might not be essential for the occurrence of the WWR of the air-sea system in the Northern Hemisphere.The analyses of different time scales of SSTA indicate that,besides interannual variability(less than ten years),the occurrence of the SSTA WWR in the Northern Hemisphere is also closely related to interdecadal variability of SSTA.In addition,it seems that PDO and the sea ice in the arctic does not influence the temporal-spatial distribution of the WWR of the ocean and atmosphere.(4) The interannual variability of the SSTA WWR is examined.Results show that SSTA WWR in the North Pacific does not occur in every year.Regardless of the recurrence year and non-recurrence year,the atmospheric forcing and the oceanic process both influence the SSTA. (1) Recurrence year:the influences of the atmospheric forcing and the oceanic reemergence mechanism are the same,because the SSTA in winter of the second year formed by the atmospheric forcing and the oceanic process have the same sign as previous winter.(2) Non-recurrence year:the influences of the atmospheric forcing and the oceanic process are opposite.Since the sign of the atmospheric circulation in the second winter is opposite to that in the previous winter,which induces a sign reversal of the SSTA in the North Pacific.In a word, the force of the atmosphere on the ocean may play a dominant role in the North Pacific, especially in winter.As the Aleutian low weakens(enhances),the westerlies also weaken (enhance),which induce a warm(cold) SSTA in the central North Pacific.(5) The temporal-spatial characteristics of the persistence barrier of SSTA in the world's oceans are examined.The presence of "the spring persistence barrier(SPB) in El Ni(?)o-Southern Oscillation(ENSO)" is well known,which refers to the persistence of ENSO anomalies show a rapid decline in April-June regardless of starting month.In addition to the central and eastern equatorial Pacific,other regions also exist persistence barriers,such as summer barrier in the central North Pacific,fall barrier in the South China Sea and Indonesia region.These are further analyzed in the next two chapters.(6) The further investigation on the summer persistence barrier in the central North Pacific (CNP) and its cause is performed.Results show that the occurrence of the summer persistence barrier of SSTA in the CNP is linearly independent of ENSO which appears spring persistence barrier.Moreover,the CNP summer persistence barrier,which occurs in the maximum phase of the annual cycle of the CNP sea surface temperature variance,does not resemble the ENSO spring barrier since the ENSO variance is minimum in spring.This suggests the major cause of the CNP summer persistence barrier is essentially different from that of the ENSO spring persistence barrier.In addition,the analyses on different time scales show that the summer persistence barrier in the CNP is closely associated with the interdecadal variability of SSTA in this area,and PDO is an essential factor influencing the occurrence of the CNP summer persistence barrier.Since they both have significant effect on the persistence characteristic of SSTA in the CNP starting from July to December,but not for January-June starting month.In fact,the persistence of the CNP SSTA starting from January to June mainly exhibits winter recurrence.Combined with the results in the chapter 3 and 5,we think that the SSTA persistence in the CNP is influenced not only by the PDO,but also by the local air-sea process. In this way,the summer persistence barrier of SSTA in the CNP occurs.(7) The possible causes for the persistence barrier of SSTA in the South China Sea(SCS) and its adjacent regions are investigated from the perspective of interannual-interdecadal time scales,and the results are compared with those of ENSO spring barrier.The occurrence of the persistence barrier in the SCS and Indonesia region is closely associated with interdecadal variability of SSTA,as well as interannual variability.The persistence barriers in these two regions do not exist alone if interdecadal variability is not considered.Moreover,the influence of interdecadal variability of SSTA on the persistence barrier of SSTA in the SCS and Indonesia region may be associated with SSTA in the Indian Ocean and Western Pacific,but is not closely associated with the Pacific Decadal Oscillation.However,compared with the ENSO SPB,the close relationship between the persistence barriers in the SCS and Indonesia region and the interdecadal variability is unique,since the ENSO SPB is not significantly affected by such variability.(8) The temporal-spatial characteristics of the SSTA WWR in the Northern Hemisphere, the characteristic of the SSTA persistence in the CNP region and the temporal-spatial characteristics of the persistence barrier of SSTA in the world's oceans are evaluated using the model output of 23 coupled models of CMIP in IPCC 4^th assessment.Results show that,most of models can simulate the basinwide winter recurrence of SSTA in the Northern Hemisphere,but they can't simulate the geographical distribution of recurrence timing well.Compared with the SST,little skill is shown in the WWR of the atmospheric Circulation in most models.Second, the characteristics of SSTA persistence in the CNP in the coupled models differ from each other, and only 8 models can simulate the characteristic in the observation.In addition,only 5 models are able to simulate ENSO spring barrier,and 3 for the fall barrier in the Indonesia region. However,there is no model can simulate the summer barrier in the CNP and fall barrier in the SCS.