共查询到20条相似文献，搜索用时 15 毫秒
1.
S. Hetzinger J. Halfar J. V. Mecking N. S. Keenlyside A. Kronz R. S. Steneck W. H. Adey P. A. Lebednik 《Climate Dynamics》2012,39(6):1447-1455
Decadal- to multidecadal variability in the extra-tropical North Pacific is evident in 20th century instrumental records and has significant impacts on Northern Hemisphere climate and marine ecosystems. Several studies have discussed a potential linkage between North Pacific and Atlantic climate on various time scales. On decadal time scales no relationship could be confirmed, potentially due to sparse instrumental observations before 1950. Proxy data are limited and no multi-centennial high-resolution marine geochemical proxy records are available from the subarctic North Pacific. Here we present an annually-resolved record (1818–1967) of Mg/Ca variations from a North Pacific/Bering Sea coralline alga that extends our knowledge in this region beyond available data. It shows for the first time a statistically significant link between decadal fluctuations in sea-level pressure in the North Pacific and North Atlantic. The record is a lagged proxy for decadal-scale variations of the Aleutian Low. It is significantly related to regional sea surface temperature and the North Atlantic Oscillation (NAO) index in late boreal winter on these time scales. Our data show that on decadal time scales a weaker Aleutian Low precedes a negative NAO by several years. This atmospheric link can explain the coherence of decadal North Pacific and Atlantic Multidecadal Variability, as suggested by earlier studies using climate models and limited instrumental data. 相似文献
2.
Yvan J. Orsolini Retish Senan Rasmus E. Benestad Arne Melsom 《Climate Dynamics》2012,38(11-12):2437-2448
The autumn and early winter atmospheric response to the record-low Arctic sea ice extent at the end of summer 2007 is examined in ensemble hindcasts with prescribed sea ice extent, made with the European Centre for Medium-Range Weather Forecasts state-of-the-art coupled ocean–atmosphere seasonal forecast model. Robust, warm anomalies over the Pacific and Siberian sectors of the Arctic, as high as 10°C at the surface, are found in October and November. A regime change occurs by December, characterized by weaker temperatures anomalies extending through the troposphere. Geopotential anomalies extend from the surface up to the stratosphere, associated to deeper Aleutian and Icelandic Lows. While the upper-level jet is weakened and shifted southward over the continents, it is intensified over both oceanic sectors, especially over the Pacific Ocean. On the American and Eurasian continents, intensified surface Highs are associated with anomalous advection of cold (warm) polar air on their eastern (western) sides, bringing cooler temperatures along the Pacific coast of Asia and Northeastern North America. Transient eddy activity is reduced over Eurasia, intensified over the entrance and exit regions of the Pacific and Atlantic storm tracks, in broad qualitative agreement with the upper-level wind anomalies. Potential predictability calculations indicate a strong influence of sea ice upon surface temperatures over the Arctic in autumn, but also along the Pacific coast of Asia in December. When the observed sea ice extent from 2007 is prescribed throughout the autumn, a higher correlation of surface temperatures with meteorological re-analyses is found at high latitudes from October until mid-November. This further emphasises the relevance of sea ice for seasonal forecasting in the Arctic region, in the autumn. 相似文献
3.
Extra-tropical cyclonic/anticyclonic activity in North-Eastern Pacific and air temperature extremes in Western North America 总被引：1，自引：1，他引：1
Synoptic extra-tropical cyclone and anticyclone trajectories have been constructed from mean daily sea level pressure (SLP) data using a new automated scheme. Frequency, intensity and trajectory characteristics of these transients have been summarized to form indices describing wintertime cyclonic and anticyclonic activity over the North-Eastern Pacific (east of 170°W) during 1950–2001. During this period, the strength of anticyclones gradually diminished and their frequency became more variable, while cyclones intensified in a discrete shift with deeper lows and further southerly trajectories occurring since the mid-1970s. These changes in synoptic transients translate into anomalously low seasonal mean SLP in the Aleutian Low, a low-level circulation anomaly consistent with the positive phase of the North Pacific Decadal Oscillation, with positive sea surface temperature (SST) anomalies along the west coast of North America and negative in the central North Pacific Ocean. A link between cyclonic/anticyclonic activity and tropical SST anomalies also exists, but this link only becomes significant after the mid-1970s, a period that coincides with more southerly cyclone trajectories. Southward excursions of mid-latitude cyclones during El Niño/positive NPO winters accomplish the northward advection of tropical air and discourage the southward penetration of polar air masses associated with transient anticyclones. Naturally, these changes in cyclonic/anticyclonic activity directly impact surface air temperatures, especially at night. We document these profound impacts on observed wintertime minimum temperatures over Western North America. 相似文献
4.
We analyzed the sea ice conditions in the Bering Sea for the time period 1979–2012, for which good data based on microwave satellite imagery, being able to look through clouds and darkness, are available. The Bering Sea, west of Alaska, is ice-free in summer, but each winter, an extensive sea ice cover is established, reaching its maximum normally in March. We found a slight increase in ice area over the time period, which is in stark contrast to the significant retreat observed in the Beaufort Sea north of Alaska and the Arctic Ocean as a whole. Possible explanation might be found in the Pacific Decadal Oscillation (PDO), which went from dominantly positive values to more negative values in the last decade. The PDO is related to the sea surface temperature (SST) in the North Pacific, negative values indicated cooler temperatures and cooler SST weakening the semipermanent Aleutian Low. When comparing the circulation pattern obtained from the National Centers for Environmental Prediction/National Center for Atmospheric Research reanalyzed data set for years of heavy ice against light ice years, an additional vectorial northerly wind component could be deduced from the pressure data. Hence, less relatively warm air is advected into the Bering Sea, which becomes of special importance in winter, when solar radiation is at its minimum. Surface observations confirmed these findings. Atmospheric pressure increased in Cold Bay, located close to the center of the semi-permanent Aleutian Low, the N–S pressure gradient (Nome–Cold Bay) in the Bering Sea decreased, wind speeds of the coastal stations became weakened, and the temperature of coastal stations decreased. 相似文献
5.
Jae-Heung Park Soon-Il An Sang-Wook Yeh Niklas Schneider 《Theoretical and Applied Climatology》2013,112(3-4):431-445
The Pacific decadal oscillation (PDO) is defined as the first empirical orthogonal function (EOF) mode of the North Pacific sea surface temperature anomalies. In this study, we reconstructed the PDO using the first-order autoregressive model from various climate indices representing the El Niño-Southern oscillation (ENSO), Aleutian Low (AL), sea surface height (SSH), and thermocline depth over the Kuroshio–Oyashio extension (KOE) region. The climate indices were obtained from observation and twentieth-century simulations of the eight coupled general circulation models (CGCMs) participating in the Climate Model Intercomparison Project Phase III (CMIP3). In this manner, we quantitatively assessed the major climate components generating the PDO using observation and models. Based on observations, the PDO pattern in the central to eastern North Pacific was accurately reconstructed by the AL and ENSO indices, and that in the western North Pacific was best reconstructed by the SSH and thermocline indices. In the CMIP3 CGCMs, the relative contribution of each component to the generation of the PDO varied greatly from model to model, and observations, although the PDO patterns from most of the models were similar to the pattern observed. In the models, the PDO pattern in the eastern and western North Pacific were well reconstructed using the AL and SSH indices, respectively. However, the PDO pattern reconstructed by the ENSO index was quite different from the observed pattern, which was possibly due to the model's common deficiency in simulating the amplitude and location of the ENSO. Furthermore, the differences in the contribution of the KOE thermocline index between the observed pattern and most of the models indicated that the PDO pattern associated with ocean wave dynamics is not properly simulated by most models. Therefore, the virtually well simulated PDO pattern by models is a result of physically inconsistent processes. 相似文献
6.
In this study, a statistical model is developed to predict the frequency of tropical cyclones (TCs) that influence Taiwan in boreal summer. Predictors are derived from large-scale environments from February to May in six regions, including four atmospheric circulation predictors over the western sea and eastern sea of Australia, the subtropical western North Pacific (SWNP), and the eastern sea of North America, and two sea surface temperature predictors in the Southeast Indian Ocean and the North Atlantic. The statistical model is verified based on statistical cross-validation tests and by contrasting the differences in the large-scale environments between high and low TC frequency years hindcasted by the model. The results show the relationships of two atmospheric circulation predictors and one SST predictor around Australia with Antarctic Oscillation (AAO) pattern, as well as the relationships of those in the SWNP and around eastern sea of North America with Pacific/North American teleconnection (PNA) pattern. When the anomalous anticyclone around Australia (positive AAO pattern) and the one over the region from eastern sea of North America and the Aleutian Islands to the SWNP (negative PNA pattern) are both strengthened from February, the trade wind in the equatorial Pacific is intensified and consequently plays an important role in steering TCs towards Taiwan during boreal summer. 相似文献
7.
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). 相似文献
8.
冬季黑潮海域异常加热与北太平洋大气环流的耦合关系 总被引：1，自引：0，他引：1
利用NCEP/NCAR和OAFlux月平均资料,采用SVD方法分析冬季黑潮海域的热通量和北太平洋500 hPa位势高度场之间的关系。第1对奇异向量占总方差的86.24%,表现为黑潮北部海域异常多的放热和北太平洋中西部的500 hPa位势高度场异常低。将正负异常年的各气象要素的距平场进行合成分析后表明：当阿留申低压增强（减弱）时,黑潮海域上空的西北风增强（减弱）,导致近地面层大气温度降低（升高）,使得热通量异常释放增加（减少）,从而降低（升高）了海表面温度。在黑潮海域及其下游,温度场在纬向垂直方向是斜压结构,位势高度场是相当正压结构,反映的是冷低压（暖脊）结构。通过分析风场无旋分量和垂直速度的距平发现,在中纬度地区存在距平的纬向环流圈：大气在北太平洋中部的低层上升（下沉）,在对流层高层（低层）分别向西、向东运动,在黑潮海域和北美西部下沉（上升）,增强（减弱）了中纬度纬向环流圈（MZC）。 相似文献
9.
Gulf of Alaska Atmosphere-Ocean Variability Over Recent Centuries Inferred from Coastal Tree-Ring Records 总被引：2，自引：0，他引：2
Eight tree-ring chronologies from coastal sites along the Gulf of Alaska (GOA) are used to develop a 227-year (1762–1988) reconstruction of spring/summer (March–September) coastal land temperatures for the region. This reconstruction explains 35% of the variance in the instrumental temperature data. The tree-ring records and reconstruction reflect the documented 1976 transition from cold to warm conditions in the North Pacific and are consistent with regional temperature compilations. Three of the eight ring-width series, from elevational timberline sites where trees are particularly stressed by temperature, extend back to A.D. 1600 and are used to identify additional occurrences of such transitions. The first principal component (PC) scores of these three longer records are positively correlated with spring (March–May) land and sea surface temperatures for the GOA region and are used to reconstruct land surface temperatures. Decadal-scale fluctuations in the reconstructions show agreement with decade-long changes in the intensity of the Aleutian Low pressure cell over the past century, suggesting that the tree-ring data may provide an index of past circulation changes for the northeast Pacific. Blackman-Tukey spectral analyses of both reconstructions indicate significant power at 7–11 years, with additional peaks at 3 years for the spring/summer reconstruction and 19 years for the longer spring temperature series. The modes of variation at about 3 and 7 years may correspond to those associated with the El Niño-Southern Oscillation bandwidth, whereas the 19-year term may relate to a proposed 20-year cycle of North Pacific circulation. The spring temperature series shows generally increased growth over the past century, coinciding with warmer spring temperatures in south coastal Alaska over this interval. Comparison with the entire spring series suggests that the recent warming exceeds temperature levels of prior centuries, extending back to A.D. 1600. 相似文献
10.
Decadal atmosphere-ocean variations in the Pacific 总被引：67，自引：7，他引：60
Considerable evidence has emerged of a substantial decade-long change in the north Pacific atmosphere and ocean lasting from about 1976 to 1988. Observed significant changes in the atmospheric circulation throughout the troposphere revealed a deeper and eastward shifted Aleutian low pressure system in the winter half year which advected warmer and moister air along the west coast of North America and into Alaska and colder air over the north Pacific. Consequently, there were increases in temperatures and sea surface temperatures (SSTs) along the west coast of North America and Alaska but decreases in SSTs over the central north Pacific, as well as changes in coastal rainfall and streamflow, and decreases in sea ice in the Bering Sea. Associated changes occurred in the surface wind stress, and, by inference, in the Sverdrup transport in the north Pacific Ocean. Changes in the monthly mean flow were accompanied by a southward shift in the storm tracks and associated synoptic eddy activity and in the surface ocean sensible and latent heat fluxes. In addition to the changes in the physical environment, the deeper Aleutian low increased the nutrient supply as seen through increases in total chlorophyll in the water column, phytoplankton and zooplankton. These changes, along with the altered ocean currents and temperatures, changed the migration patterns and increased the stock of many fish species. A north Pacific (NP) index is defined to measure the decadal variations, and the temporal variability of the index is explored on daily, annual, interannual and decadal time scales. The dominant atmosphere-ocean relation in the north Pacific is one where atmospheric changes lead SSTs by one to two months. However, strong ties are revealed with events in the tropical Pacific, with changes in tropical Pacific SSTs leading SSTs in the north Pacific by three months. Changes in the storm tracks in the north Pacific help to reinforce and maintain the anomalous circulation in the upper troposphere. A hypothesis is put forward outlining the tropical and extratropical realtionships which stresses the role of tropical forcing but with important feed-backs in the extratropics that serve to emphasize the decadal relative to interannual time scales. The Pacific decadal timescale variations are linked to recent changes in the frequency and intensity of El Niño versus La Nina events but whether climate change associated with global warming is a factor is an open question.The National Center for Atmospheric Research is sponsored by the National Science Foundation 相似文献
11.
E. Roeckner J. M. Oberhuber A. Bacher M. Christoph I. Kirchner 《Climate Dynamics》1996,12(11):737-754
The interannual variability associated with the El Ni?o/Southern Oscillation (ENSO) cycle is investigated using a relatively
high-resolution (T42) coupled general circulation model (CGCM) of the atmosphere and ocean. Although the flux correction is
restricted to annual means of heat and freshwater, the annual as well as the seasonal climate of the CGCM is in good agreement
with that of the atmospheric model component forced with observed sea surface temperatures (SSTs). During a 100-year simulation
of the present-day climate, the model is able to capture many features of the observed interannual SST variability in the
tropical Pacific. This includes amplitude, lifetime and frequency of occurrence of El Ni?o events and also the phase locking
of the SST anomalies to the annual cycle. Although the SST warming during the evolution of El Ni?os is too confined spatially,
and the warming along the Peruvian coast is much too weak, the patterns and magnitudes of key atmospheric anomalies such as
westerly wind stress and precipitation, and also their eastward migration from the western to the central equatorial Pacific
is in accord with observations. There is also a qualitative agreement with the results obtained from the atmospheric model
forced with observed SSTs from 1979 through 1994. The large-scale dynamic response during the mature phase of ENSO (December
through February) is characterized by an eastward displacement and weakening of the Walker cell in the Pacific while the Hadley
cell intensifies and moves equatorward. Similar to the observations, there is a positive correlation between tropical Pacific
SST and the winter circulation in the North Pacific. The deepening of the Aleutian low during the ENSO winters is well captured
by the model as well as the cooling in the central North Pacific and the warming over Canada and Alaska. However, there are
indications that the anomalies of both SST and atmospheric circulation are overemphasized in the North Pacific. Finally, there
is evidence of a coherent downstream effect over the North Atlantic as indicated by negative correlations between the PNA
index and the NAO index, for example. The weakening of the westerlies across the North Atlantic in ENSO winters which is related
to a weakening and southwestward displacement of the Icelandic low, is in broad agreement with the observations, as well as
the weak tendency for colder than normal winters in Europe.
Received: 31 October 1995 / Accepted: 29 May 1996 相似文献
12.
采用CAM3（Community Atmosphere Model Version3）模式中海气湍流通量参数化原方案和改进方案,利用观测海温驱动CAM3模式进行气候模拟,以分析模式对厄尔尼诺事件影响气候变化的模拟能力。结果表明,采用CAM3模式海气湍流通量参数化改进方案,模式能够更好地模拟出由厄尔尼诺事件引起的北太平洋和北美地区大气环流的变化,尤其是对厄尔尼诺年冬季阿留申低压强度和与PNA遥相关型有关的500hPa位势高度异常的模拟。 相似文献
13.
北太平洋浅层海温时空特征及区域海气相互作用的诊断分析 总被引：2，自引：1，他引：1
采用EOF(Empirical Orthogonal Function)、SVD(Singular Value Decompo—sition)、相似、相关以及合成分析等方法,探讨了北太平洋浅层海温(ST)层际间时空结构的差异,据此对浅层海温场进行分层,并研究其与海平面气压场的相互作用。结果表明：北太平洋浅层海温距平场第1模态及其时间系数基本上反映了该海区浅层海温场的时空特征。1月浅层海温场可划分为两层,7月可划分为4层,说明7月的浅层海温分布较1月复杂。海气相互作用的主要时域特征为明显的年代际变化,正负值转变主要发生在中后期。海气相互作用分析表明,当北太平洋中部ST持续偏高时,相应的1(7)月阿留中低压(北太平洋副高)偏弱,位置偏西,其西侧冬(夏)季风偏弱;反之亦然。 相似文献
14.
Kuang Xueyuan Liu Jian Zhang Yaocun Huang Danqing Huang Ying 《Asia-Pacific Journal of Atmospheric Sciences》2011,47(5):485-495
Based on the simulation results derived from ECHO-G global coupled climate model, several East Asian winter monsoon (EAWM) indices are compared in order to choose the most suitable one for signaling the intensity of winter monsoon in the last millennium. The index I_shi, which is defined with normalized sea level pressure difference between sea and land in mid and low latitudes, is selected to describe the winter monsoon intensity variation owing to its better capability for reflecting the variation of winter monsoon subsystems, such as the continental high pressure, Aleutian low, East Asian major trough, westerly jet stream, and surface air temperature than the other indices examined. Wavelet analysis on index I_shi shows that the EAWM intensity is characterized by multi-timescale variation with inter-annual, decadal, inter-decadal and inter-centennial oscillations on the background of a slight descending trend. Correlation analysis between the EAWM index and sea surface temperature (SST) at various timescales reveals that the SST in mid-latitudes might provide the background of the EAWM strength changes above decadal timescales, and a negative-feedback process lasting for about two years is found between the EAWM intensity and the SST in the eastern equatorial Pacific. According to the correlation, the El Nino occurrence in the second-half of the year leads to weaker EAWM than normal in the following winter and the weakened EAWM corresponds to lower SST in eastern equatorial Pacific after about half a year, which will then strengthen the EAWM intensity in the next winter. It is a stable feedback process and its mechanism is discussed. 相似文献
15.
CMIP5多模式对阿留申低压气候特征的模拟检验与预估 总被引：2，自引：0，他引：2
利用观测的海温资料和海平面气压资料,检验了CMIP5(Coupled Model Intercomparison Project 5,CMIP5)多模式对阿留申低压(Aleutian Low,AL)特征指数的时空分布和变化的模拟能力;从AL周期及变化趋势等方面,分析了CMIP5模式预估的未来AL的变化特征。结果表明,CMIP5模式及其集合平均能够很好地模拟AL的环流结构,对AL的气候态有着较强的模拟能力,尤其是模式对于东太平洋海表温度的模拟能力直接影响其对于AL的模拟效果。模式的集合平均对变率强度的模拟偏强,且对于变率的模拟效果逊于对气候态的模拟。22个模式中的16个模式能模拟出AL强度指数的年代际变化周期,对年代际周期有着较好的刻画能力。Historical试验下对于AL的变化趋势存在着较大的不确定性,而相对于两种不同排放情景,随着排放的增加,AL更加偏北,强度增强,年际、年代际周期变得更加显著。在两种排放情景下模式的集合平均以及多数模式模拟出AL有着向北和增强的趋势。 相似文献
16.
The Oscillation between Tropical Indian Ocean and North Pacific:Evidence and Possible Impact on Winter Climate in China 
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下载免费PDF全文 This paper provides evidence that the variation of boreal winter sea level pressure (SLP) over the North Pacific is out-of-phase with SLP fluctuation over the tropical Indian Ocean on both the interdecadal and interannual time scales.Subsequently,a SLP between tropical Indian Ocean and North Pacific (TIO-NP) oscillation index is defined to indicate the variation of such out-of-phase fluctuation.Moreover,the simultaneous surface air temperature and precipitation anomalies in China are closely related to TIO-NP oscillations.Below-normal surface air temperature anomalies in the northern and the eastern part of China,and less rainfall in southern China,correspond to positive TIO-NP oscillation phase with negative SLP anomalies in tropical Indian Ocean and positive anomalies in North Pacific.The TIO-NP oscillation affects China’s winter climate anomalies,possibly through modulating the northeast East Asia winter monsoon. 相似文献
17.
Laurent Z. X. Li 《Climate Dynamics》2006,27(5):543-552
The atmospheric response to an idealized 2 K cooling of the Mediterranean Sea is studied in a general circulation model (GCM). In the downstream region, from the eastern Mediterranean basin to the whole Asian continent (following the sub-tropical jet-stream), a baroclinic response is produced with high pressure near the surface and low pressure in the upper layers. It is the direct response to the Mediterranean cooling and it needs only a few days to be established. Teleconnections with strong zonal characteristics are found following the sub-tropical jet-stream to the North Pacific and North America, propagating further across the North Atlantic towards Northern Europe. Two remarkable remote features are the deepening of the Aleutian Low in the North Pacific and the weakening of the Icelandic Low in the North Atlantic. These two teleconnections form and grow in several days in the North Pacific and several tens of days in the North Atlantic. Both have a quasi-barotropic vertical structure. It is believed that they are the consequence of complex interactions between the mean flow and the transient eddies in the atmosphere. 相似文献
18.
利用1961—2018年中国地面气象台站2 400站中广东省和广西壮族自治区(两广地区)134站逐日降水资料、英国Hadley中心逐月海表温度资料、NCEP/NCAR逐月再分析资料,筛选了两广地区前汛期降水正(负)异常、后汛期降水负(正)异常的年份,即前、后汛期降水异常反位相年份。结果表明,近60 a来,两广地区前、后汛期降水反位相现象与热带西太平洋海温异常存在密切联系。前汛期期间,当热带西太平洋海温为负异常时,大气对该冷源的Rossby波响应引起西北太平洋反气旋环流异常,且水汽由热带西太平洋向两广地区输送并辐合,同时两广地区为水汽的湿平流区域、风场异常辐合区域,其上空受异常上升运动控制,这样的环流配置有利于两广前汛期期间降水正异常。热带西太平洋海温负异常可持续至后汛期期间,大气的Rossby波响应所致的西太平洋反气旋较前汛期偏西北,两广地区为水汽异常辐散区域,同时水汽干平流且风场异常辐散,受异常下沉运动控制,不利于两广地区降水的产生。反之亦然。 相似文献
19.
Linkages between the North Pacific Oscillation and central tropical Pacific SSTs at low frequencies 总被引：2，自引：1，他引：1
Jason C. Furtado Emanuele Di Lorenzo Bruce T. Anderson Niklas Schneider 《Climate Dynamics》2012,39(12):2833-2846
The North Pacific Oscillation (NPO) recently (re-)emerged in the literature as a key atmospheric mode in Northern Hemisphere climate variability, especially in the Pacific sector. Defined as a dipole of sea level pressure (SLP) between, roughly, Alaska and Hawaii, the NPO is connected with downstream weather conditions over North America, serves as the atmospheric forcing pattern of the North Pacific Gyre Oscillation (NPGO), and is a potential mechanism linking extratropical atmospheric variability to El Ni?o events in the tropical Pacific. This paper explores further the forcing dynamics of the NPO and, in particular, that of its individual poles. Using observational data and experiments with a simple atmospheric general circulation model (AGCM), we illustrate that the southern pole of the NPO (i.e., the one near Hawaii) contains significant power at low frequencies (7–10?years), while the northern pole (i.e., the one near Alaska) has no dominant frequencies. When examining the low-frequency content of the NPO and its poles separately, we discover that low-frequency variations (periods >7?years) of the NPO (particularly its subtropical node) are intimately tied to variability in central equatorial Pacific sea surface temperatures (SSTs) associated with the El Ni?o-Modoki/Central Pacific Warming (CPW) phenomenon. This result suggests that fluctuations in subtropical North Pacific SLP are important to monitor for Pacific low-frequency climate change. Using the simple AGCM, we also illustrate that variability in central tropical Pacific SSTs drives a significant fraction of variability of the southern node of the NPO. Taken together, the results highlight important links between secondary modes (i.e., CPW-NPO-NPGO) in Pacific decadal variability, akin to already established relationships between the primary modes of Pacific climate variability (i.e., canonical El Ni?o, the Aleutian Low, and the Pacific Decadal Oscillation). 相似文献
20.
Presented are the results of studies of the effect that oceans (the North Atlantic and Northwest Pacific) and atmospheric circulation at the midlatitudes of the Northern Hemisphere produce on forest fire conditions in the Far East. Expansion coefficients of the natural components of anomaly fields of the sea surface temperature of two oceans are proposed as the main predictors of the forest fire drought index. Characteristics of atmospheric circulation in the Aleutian low area are considered as an additional predictor. 相似文献