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1.
R. Glowienka-Hense 《Climate Dynamics》1999,15(4):269-275
The semi-annual oscillation (SAO) of the southern hemispheric sea-level pressure (SLP) in the global atmospheric GCM ECHAM
is examined. Five model runs initiated from different atmospheric states were conducted. Monthly values of sea surface temperature
(SST) and sea-ice distribution for the period 1950–1994 are specified boundary conditions for each run. The interdecadal change
of the SAO as forced by the changing boundary conditions is compared to the internal model variability, represented by the
five runs. The performance of the SAO in the ECHAM model is much improved compared to that of its precursor the T21 Hamburg
version of the ECMWF model in 1990. Analysis of observed SLP shows that between 1973–1979 the SAO had high amplitude whereas
from 1980–89 its amplitude was low. These changes go along with significant changes in SLP, i.e. the subpolar trough does
not expand as far equatorward from September to December as in the years before. The model does not show this reduction of
SAO strength in recent years. Multivariate Hotelling-T2 statistic and analysis of variance techniques (ANOVA) are used to determine the boundary forced part of variance of SLP and
SAO in the ECHAM simulations. The result is that only a small part of the SAO seems to be externally forced mainly from the
tropics.
Received: 24 July 1998 / Accepted: 10 November 1998 相似文献
2.
M. R. Van den Broeke 《Climate Dynamics》2000,16(5):369-377
We use NCEP/NCAR reanalysis data to study the impact of the semiannual oscillation (SAO) on the annual cycle of Antarctic
near-surface temperature. When the SAO is weak, the contracted phases (March/April and September/October) are warm and the
expanded phases (December/January and June/July) cold. This pattern is explained in terms of the changing meridional fetch
of the circumpolar pressure trough. Because of the wave number three character of the SAO, large regional deviations are found.
For instance, enhanced north-westerly flow in the second expansion phase (June/July) of weak SAO years limits the growth of
the sea ice in the Amundsen and Bellingshausen seas, leading to anomalously high temperatures in the Antarctic Peninsula region.
The short (<50 year) temperature records at Antarctic stations still carry the fingerprint of decadal SAO variability. By
matching the observed monthly temperature trends to the patterns derived from the gridded re-analysis, we propose a background
Antarctic warming trend for the second expansion phase (June/July) of 4.62 ± 1.02 °C per century, four times the annual value.
Received: 23 August 1999 / Accepted: 28 October 1999 相似文献
3.
Thomas J. Bracegirdle 《Climate Dynamics》2011,37(11-12):2323-2333
The semi-annual oscillation (SAO) in sea-level pressure at high southern latitudes is the consequence of a twice-yearly contraction (and strengthening) and expansion (and weakening) of the storm track between 50 and 65°S, with the contracted phases in spring and autumn. In this study the extent to which inter-annual variability of the SAO is correlated with inter-annual variability in mid- to lower-stratospheric circulation at 60°S was determined using NCEP/NCAR Reanalysis 1 data for the period 1979?C2009. The second harmonic of the annual cycle of an SAO index was used to assess SAO amplitude and phase (the date of the first peak of the second harmonic). Zonal mean zonal wind at 60°S was used as an index for atmospheric circulation. The results show that year-to-year variability in the SAO amplitude is significantly correlated with mid-stratospheric (10?hPa) circulation variability in late summer/early autumn (February?CMarch) and late winter/early spring (August?CSeptember). However, variability in the SAO phase is significantly correlated with mid-stratospheric circulation variability in spring (September?CNovember). These maxima in significant correlations at 10?hPa propagate down to the surface in approximately one month. The characteristics of upward planetary wave propagation alone do not explain the late summer/early autumn and spring maxima in correlations. Evidence is shown that internal reflection of stationary wave-number 1 is important for explaining the strong correlations in late summer/early autumn, but that large variability during polar vortex break-up dominates the spring correlations. The results may be important for understanding seasonal differences in how stratospheric ozone depletion influences tropospheric circulation. 相似文献
4.
基于1979—2000年的NCEP/NCAR海平面气压和位势高度场资料分析了南半球大气环流的准半年振荡 (半年波) 现象。结果表明:这一现象主要出现在南半球对流层低层的中高纬度和中高层的热带地区。对南半球热带外大气而言, 40°S和65°S是低层大气环流准半年振荡最为显著的两个纬度带, 半年波的贡献都超过了70%, 低层南半球中高纬度海平面气压场季节变化的反位相也主要体现为各自半年波分量变化的反位相。在此基础上, 检验了IAP 9L AGCM (大气物理研究所9层大气环流模式) 对这一现象模拟的能力, 模拟结果显示, 模式成功模拟了65°S处海平面气压场的准半年振荡现象, 其振幅略低于观测结果, 但模式对40°S处气压场准半年振荡的模拟效果较差。 相似文献
5.
Effect of tropospheric temperature change on the zonal mean circulation and SH winter extratropical cyclones 总被引：1，自引：1，他引：0
This study aims to understand the mechanisms which cause an overall reduction of SH extratropical cyclone activity with a
slight increase in the high latitudes in a warmer climate simulated in general circulation models (GCMs) with increasing CO2. For this purpose, we conducted idealized model experiments by forcing warm temperature anomalies to the areas where climate
change models exhibit local maximum warming—the tropics in the upper troposphere and the polar regions in the lower troposphere—simultaneously
and separately. The Melbourne University atmospheric GCM (R21) coupled with prescribed SST was utilized for the experiments.
Our results demonstrate that the reduction of SH extratropical cyclone frequency and depth in the midlatitudes but the slight
increase in the high latitudes suggested in climate change models result essentially from the tropical upper tropospheric
warming. With this tropical warming, the enhanced static stability which decreases baroclinicity in the low and midlatitudes
turns out to be a major contributor to the decrease of cyclone activity equatorward of 45°S whereas the increased meridional
temperature gradient in the high latitudes seems an important mechanism for the increase of cyclone activity over 50°–60°S. 相似文献
6.
The ability of five, global coupled climate models to simulate important atmospheric circulation characteristics in the Southern
Hemisphere for the period 1960–1999 is assessed. The circulation features examined are the Southern Hemisphere annular mode
(SAM), the semi-annual oscillation (SAO) and the quasi-stationary zonal wave 3 (ZW3). The models assessed are the National
Center for Atmospheric Research Community Climate System Model Version 3 (CCSM3), the Commonwealth Scientific and Industrial
Research Organisation Mark 3, the Geophysical Fluid Dynamics Laboratory Model, the Goddard Institute for Space Studies Model
ER (GISS-ER) and the UK Meteorological Office Hadley Center Coupled Model Version 3. The simulations were compared to the
NCAR–NCEP reanalyses. The models simulate a SAO which differs spatially from the observed over the Pacific and Indian oceans.
The amplitudes are too high over the southern ocean and too low over the midlatitudes. These differences are attributed to
a circumpolar trough which is too deep and extends too far north, and to the inability of the models to simulate the middle
to high latitude temperature gradient. The SAM is well-represented spatially by most models but there are important differences
which may influence the flow over the Pacific and in the region extending from the Ross to Weddell Seas. The observed trend
towards positive polarity in the SAM is apparent in the ensemble averages of the GISS-ER and CCSM3 simulations, suggesting
that the trend is due to external forcing by changes in the concentration of ozone and greenhouse gases. ZW3 is well-represented
by the models but the observed trend towards positive phases of ZW3 is not apparent in the simulations suggesting that the
observed trend may be due to natural variability, not external forcing. 相似文献
7.
Kevin Hamilton 《大气与海洋》2013,51(4):319-354
Abstract The general circulation of the tropical stratosphere, mesosphere and lowermost thermosphere is discussed at a tutorial level. Observations of the quasi‐biennial and semiannual oscillations by both in situ and satellite techniques are first reviewed. The basic dynamics controlling the zonal‐mean component of the circulation are then discussed. The role of radiative diabatic cooling in constraining the zonal‐mean circulation in the middle atmosphere is emphasized. It is shown that the effectiveness of this radiative constraint is reduced at low latitudes, allowing for the sustained mean flow accelerations over long periods of time characteristic of the quasi‐biennial and semiannual oscillations in the tropics. The current view is that the dominant driving for the equatorial mean flow accelerations seen in the middle atmosphere derives from vertically‐propagating waves. This process is illustrated here in its simplest context, i.e. the Plumb (1977) model of the interaction of monochromatic internal gravity waves with the mean flow (based on earlier work of Lindzen and Holton, 1968; Holton and Lindzen, 1972). It is shown that the dynamics illustrated by this simple model can serve as the basis for an explanation of the quasi‐biennial oscillation. The paper then describes some of recent developments in the theory of the quasi‐biennial and semiannual oscillations, including aspects related to the interaction between tropics and midlatitudes in the middle atmosphere. The paper concludes with a discussion of the effects of the long period dynamical variations in the tropical circulation on the chemical composition of the stratosphere. 相似文献
8.
Analyses of proxy based reconstructions of surface temperatures during the past 330 years show the existence of a distinct
oscillatory mode of variability with an approximate time scale of 70 years. This variability is also seen in instrumental
records, although the oscillatory nature of the variability is difficult to assess due to the short length of the instrumental
record. The spatial pattern of this variability is hemispheric or perhaps even global in scale, but with particular emphasis
on the Atlantic region. Independent analyses of multicentury integrations of two versions of the GFDL coupled atmosphere-ocean
model also show the existence of distinct multidecadal variability in the North Atlantic region which resembles the observed
pattern. The model variability involves fluctuations in the intensity of the thermohaline circulation in the North Atlantic.
It is our intent here to provide a direct comparison of the observed variability to that simulated in a coupled ocean-atmosphere
model, making use of both existing instrumental analyses and newly available proxy based multi-century surface temperature
estimates. The analyses demonstrate a substantial agreement between the simulated and observed patterns of multidecadal variability
in sea surface temperature (SST) over the North Atlantic. There is much less agreement between the model and observations
for sea level pressure. Seasonal analyses of the variability demonstrate that for both the model and observations SST appears
to be the primary carrier of the multidecadal signal.
Received: 8 June 1999 / Accepted: 11 February 2000 相似文献
9.
W. M. Connolley 《Climate Dynamics》1997,13(10):745-756
Using a hierarchy of climate models together with observations from gridded analyses, I examine the atmosphere-only and coupled
ocean-atmosphere variability in the general circulation for the region south of 40 °S. The variability in mean sea level pressure
(MSLP) is well simulated by the coupled models. A complication is that the difference between the two analyses used for verification
is comparable to the analysis-model differences. An increase in variability is seen within the hierarchy of model runs although
even a model without interannual variations in sea surface temperatures (SSTs) captures most of the observed variability.
The temporal variation in MSLP in southern high latitudes has a white spectrum consistent with “random” forcing by weather
events and a decoupling from oceanic “integration”. In contrast, the spatial pattern of MSLP variability shows large-scale
structure that is consistent between observations and various models, even without interannual variation in SSTs. This shows
that the models are sufficiently skillful to reproduce the pattern of observed variability and suggests that the pattern of
variability is a characteristic of the land-sea distribution and topography.
Received: 18 December 1996/Accepted: 23 May 1997 相似文献
10.
G. A. Meehl P. R. Gent J. M. Arblaster B. L. Otto-Bliesner E. C. Brady A. Craig 《Climate Dynamics》2001,17(7):515-526
Historically, El Nino-like events simulated in global coupled climate models have had reduced amplitude compared to observations.
Here, El Nino-like phenomena are compared in ten sensitivity experiments using two recent global coupled models. These models
have various combinations of horizontal and vertical ocean resolution, ocean physics, and atmospheric model resolution. It
is demonstrated that the lower the value of the ocean background vertical diffusivity, the greater the amplitude of El Nino
variability which is related primarily to a sharper equatorial thermocline. Among models with low background vertical diffusivity,
stronger equatorial zonal wind stress is associated with relatively higher amplitude El Nino variability along with more realistic
east–west sea surface temperature (SST) gradient along the equator. The SST seasonal cycle in the eastern tropical Pacific
has too much of a semiannual component with a double intertropical convergence zone (ITCZ) in all experiments, and thus does
not affect, nor is it affected by, the amplitude of El Nino variability. Systematic errors affecting the spatial variability
of El Nino in the experiments are characterized by the eastern equatorial Pacific cold tongue regime extending too far westward
into the warm pool. The time scales of interannual variability (as represented by time series of Nino3 SSTs) show significant
power in the 3–4 year ENSO band and 2–2.5 year tropospheric biennial oscillation (TBO) band in the model experiments. The
TBO periods in the models agree well with the observations, while the ENSO periods are near the short end of the range of
3–6 years observed during the period 1950–94. The close association between interannual variability of equatorial eastern
Pacific SSTs and large-scale SST patterns is represented by significant correlations between Nino3 time series and the PC
time series of the first EOFs of near-global SSTs in the models and observations.
Received: 17 April 2000 / Accepted: 17 August 2000 相似文献
11.
利用中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室（LASG/IAP）发展的耦合的气候系统模式FGOALS-s2工业革命前控制试验结果研究了大西洋经向翻转流（Atlantic Meridional Overturning Circulation,AMOC）的年代际变率及其物理机制。传统AMOC是利用深度坐标下的质量流函数来表征,本文通过对密度坐标下49.5°N的AMOC指数与其余纬度的AMOC指数作相关分析,发现AMOC的变化有从深水形成区向南传播的过程,且密度坐标下的AMOC变率在北大西洋高纬度明显大于低纬度。分析进一步表明,模式模拟的AMOC具有年代际振荡,周期约为70年。这个低频振荡主要是由与AMOC变化相关的温度和盐度的变化与海表风场之间的相互作用引起,具体机制如下:格陵兰-冰岛-挪威海有异常强的海表风场,导致蒸发增强,继而使海表盐度增加,深水形成增多,从而使AMOC增强。AMOC加强后,会使得向北的热量和盐度输送增加,减弱此处的经向温度梯度,风场随之减弱,从而完成位相的反转。 相似文献
12.
R. Villalba E. R. Cook R. D. D’Arrigo G. C. Jacoby P. D. Jones M. J. Salinger J. Palmer 《Climate Dynamics》1997,13(6):375-390
A tree-ring chronology network recently developed from the subantarctic forests provides an opportunity to study long-term
climatic variability at higher latitudes in the Southern Hemisphere. Fifty long (1911–1985), homogeneous records of monthly
mean sea-level pressure (MSLP) from the southern latitudes (15–65 °S) were intercorrelated on a seasonal basis to establish the most consistent, long-term Trans-Polar teleconnections during
this century. Variations in summer MSLP between the South America-Antarctic Peninsula and the New Zealand sectors of the Southern
Ocean are significantly correlated in a negative sense (r=−0.53, P<0.001). Climatically sensitive chronologies from Tierra del Fuego (54–55°) and New Zealand (39–47°) were used to develop verifiable reconstructions of summer (November to February) MSLP for both sectors of the Southern Ocean.
These reconstructions, which explain between 37 and 43% of the instrumentally recorded pressure variance, indicate that inverse
trends in MSLP from diametrically opposite sides of Antarctica have prevailed during the past two centuries. However, the
strength of this relationship varies over time. Differences in normalized MSLP between the New Zealand and the South America-Antarctic
Peninsula sectors were used to develop a Summer Trans-Polar Index (STPI), which represents an index of sea-level pressure
wavenumber one in the Southern Hemisphere higher latitudes. Tree-ring based reconstructions of STPI show significant differences
in large-scale atmospheric circulation between the nineteenth and the twentieth centuries. Predominantly-negative STPI values
during the nineteenth century are consistent with more cyclonic activity and lower summer temperatures in the New Zealand
sector during the 1800s. In contrast, cyclonic activity appears to have been stronger in the mid-twentieth than previously
for the South American sector of the Southern Ocean. Recent variations in MSLP in both regions are seen as part of the long-term
dynamics of the atmosphere connecting opposite sides of Antarctica. A detailed analysis of the MSLP and STPI reconstructions
in the time and frequency domains indicates that much of the interannual variability is principally confined to frequency
bands with a period around 3.3–3.6 y. Cross spectral analysis between the STPI reconstruction and the Southern Oscillation
Index suggests that teleconnections between the tropical ocean and extra-tropical MSLP variations may be influencing climate
fluctuations at southern latitudes.
Received: 18 December 1996/Accepted: 10 January 1997 相似文献
13.
冬季黑潮延伸体区域海表温度锋对北太平洋风暴轴的影响 总被引：2，自引：0，他引：2
利用NOAA最优插值逐日海表温度资料和NCEP/NCAR的逐日大气再分析资料,分析了冬季黑潮延伸体区域海表温度锋的变化及其对北太平洋风暴轴的影响。结果表明,冬季黑潮延伸体区域海表温度锋强度和纬度位置既存在年际变化,也存在年代际变化,且强度和位置的变化是相互独立的。冬季黑潮延伸体区域海表温度锋强度的年际变化对北太平洋风暴轴没有显著的影响,而其年代际变化则对北太平洋风暴轴具有非常显著的影响,当冬季海表温度锋偏强时,大气斜压性在鄂霍次克海及阿拉斯加附近区域上空增强,而在海表温度锋下游至东太平洋区域上空显著减弱,平均有效位能向涡动有效位能的斜压能量转换在45°N以北的太平洋区域上空有所增多,而在30°-45°N的太平洋区域上空有所减少,涡动有效位能向涡动动能的斜压能量转换在35°N以北的西太平洋区域以及45°N以北的东太平洋区域都显著增加,而仅在其南部边缘存在东西带状的减弱区域,导致40°N以北海区北太平洋风暴轴增强,40°N以南海区北太平洋风暴轴减弱,冬季海表温度锋偏弱时则有与之相反的结果。冬季黑潮延伸体区域海表温度锋纬度位置的变化对北太平洋风暴轴也存在较显著的影响,当海表温度锋位置偏北时,在其下游45°N以南的太平洋区域上空大气斜压性减弱,45°N以南的中东太平洋区域上空区域平均有效位能向涡动有效位能、以及涡动有效位能向涡动动能的斜压能量转换都减少;而在45°N以北的太平洋区域上空大气斜压性增强,在阿拉斯加湾附近上空尤其显著,在黑潮延伸体区域附近以及45°N以北的中东太平洋上空平均有效位能向涡动有效位能、以及涡动有效位能向涡动动能的斜压能量转换都显著增加,导致北太平洋风暴轴在其气候平均态轴线两侧呈现北正南负的偶极子形态;海表温度锋位置偏南时则有与之相反的结果。冬季黑潮延伸体区域海表温度锋强度和位置的变化均对北太平洋风暴轴具有显著的影响,其具体的物理机制还需要进一步的研究。 相似文献
14.
基于1960—2017年中国国家气象信息中心整编的753站逐日平均温度资料、美国国家海洋大气中心（NOAA）重建的逐月海表温度资料以及美国国家环境预测中心/国家大气研究中心（NCEP/NCAR）提供的再分析大气环流资料,分析了ENSO对中国冬季天气尺度气温变率的影响。结果表明,ENSO与中国东部大部分地区的冬季天气尺度气温变率呈显著正相关,即厄尔尼诺年冬季,中国气温波动幅度增大,天气尺度气温变率明显较强;而拉尼娜年冬季,气温变化相对平稳,天气尺度温度变率较小。进一步研究发现,厄尔尼诺事件加强了冬季欧亚大陆中高纬度地区的经向温度梯度,根据热成风原理,局地大气斜压性增强,西伯利亚地区的风暴活动和下游东亚地区大气环流的天气尺度变异也随之加强,因而有利于中国大部分地区天气尺度温度变率的增大。拉尼娜年冬季,异常情况与之大致相反。 相似文献
15.
春季欧亚大陆积雪对春夏季南北半球大气质量交换的可能影响 总被引：2，自引：0，他引：2
本文基于春季欧亚雪盖资料与大气再分析资料的奇异值分解(SVD)分析结果,结合数值试验,研究了春季欧亚大陆积雪变化与春、夏季南北半球大气质量交换的联系。研究表明,当春季欧亚积雪异常偏多时,同期欧亚大陆中高纬大范围地区的地面气温异常偏低,这种冷却效应可能持续至夏季,同时,冷空气的堆积造成了欧亚大陆地表气压(气柱大气质量)的增加,并且对应了夏季北半球大气总质量的异常上升,而南半球大气质量却明显下降。分析发现,春季欧亚积雪异常与夏季南北半球际大气质量涛动存在显著的滞后相关,而且前者还与同期及后期包括索马里急流和对流层上部80°E~120°E区域高空急流在内的多处越赤道气流变化联系密切。从数值模拟结果分析发现,以改变春季初始积雪状况作为驱动,欧亚大陆中高纬地区的低层大气环流出现了显著响应,即当积雪增加时,同期及其后夏季地面气温显著降低,并且冷异常区域对应着气柱质量的异常升高。 相似文献
16.
The variability of near surface temperature on global and regional spatial scales and interannual time scales from a 1000
year control integration of the Hadley Centre coupled model (HADCM2-CTL) are compared with the observational record of surface
temperature. The model succeeds in reproducing the observed patterns of natural variability, with high variability over the
northern continents and low variability over much of the tropics. The model global mean variability has similar strength to
observed global mean variability on time scales less than 20 years. The warming seen in the historical record is outside the
range of natural variability as simulated in HADCM2-CTL. The model has El-Ni?o/Southern Oscillation (ENSO)-like behaviour
with a central Pacific, peak to peak, strength of approximately 3 K. Changes in near surface temperature in the central Pacific
are strongly correlated with changes in near surface temperature over most of the tropics, large regions of the extra-tropics
and changes in tropical ocean upper 250 m heat content. Tropospheric temperature changes and tropical surface pressure changes
are also strongly correlated with changes in the central Pacific surface temperature. Oceanic regions show significant departures
from an AR1 or first order Markov behaviour in the Northwest Atlantic, Northwest Pacific and Arctic oceans. The Northwest
Atlantic region has large amounts of variability over periods greater than 50 years. This variability is associated with a
jump in the strength of North Atlantic meridional stream function. The spectra of the Western European and Continental US
land regions are not significantly different from an AR1 process. The flow through the Drake Passage has an interannual standard
deviation of approximately 2.5 Sv with significant departures from an AR1 process at time scales greater than 40 years. Winter
northern hemispheric 500 hPa geopotential height shows some evidence of multiple regimes but no year to year persistence of
these regimes.
Received: 31 January 1996/Accepted: 22 July 1996 相似文献
17.
Summary Climatic fluctuations across Africa are analysed from two century+ records of rainfall at Durban, South Africa and the Nile
River flow in southern Egypt. A wavelet transform analysis is applied to the rainfall record to determine the strength of
intra-seasonal to decadal rhythms. The annual cycle constitutes 33% of variability, whilst 2.3–4 year cycles account for 10%
of the variance. A contingency analysis of flood events reveals a bimodal character with peaks in November and March. The
Durban rainfall time series is compared with remote environmental variables. Close relationships are found with the meridional
gradient of sea surface temperature in the Atlantic and the southern oscillation index. Comparisons are made between the southern
summer rainfall at Durban (November–March) and northern summer Nile River flow (July–October). Cross-wavelet analysis of the
two records indicates a matching of frequency in quasi-biennial and El Ni?o frequency bands. This suggests that the uptake
of ‘teleconnections’ governing African climate occurs in a widespread manner.
Received February 25, 2000 相似文献
18.
加强大气季节内振荡研究是发展延伸期预报能力的关键之一。研究表明低温形成与冬季风和冷空气的季节内振荡有密切联系。因此,本文利用192站日最低温度观测资料和ERA-Interim再分析环流资料,讨论了偏东路径南下冷空气造成的南方低温事件中准双周振荡特征及低频环流特征,并进行热力学诊断,希望提高对中高纬度地区持续性低温事件中低频信号的认识。结果显示:我国南方地区最低温度存在显著的10~20 d振荡周期,低温事件伴随低频振荡的加强而发生。1996年2月17~24日低温过程前后的低频环流场分析表明,西伯利亚及东亚上空的异常高/低压是影响我国大部分地区冬季温度的关键区,系统沿西北-东南向低频波列向下游移动,东移特征在中纬度带最明显,异常偏北风引导高纬冷空气向南推进是低温事件爆发的根本原因。垂直结构上,内陆以正压性为主,东亚沿岸表现出斜压性。热力学诊断发现温度局地变化主要受平流项和非绝热项作用,冷平流是维持低温过程的关键。 相似文献
19.
Changes in mid-latitude variability due to increasing greenhouse gases and sulphate aerosols 总被引：1，自引：0，他引：1
Intra-seasonal variability in the Northern Hemisphere winter is investigated in ensembles of experiments using the Hadley
Centre coupled ocean-atmosphere model. Synoptic techniques which identify low centres and blocking anticyclones have been
used in preference to time-filtered variances of geopotential height as these may not uniquely identify true synoptic systems.
Changes in mid-latitude variability are qualitatively similar in experiments that include changes in greenhouse gases only
and those that also include the direct effects of sulphate aerosols. The presence of aerosols reduces the warming of the northern
continents but the relatively larger warming of the land compared to the oceans remains in both experiments and at higher
latitudes this leads to a reduced poleward transient flux of energy. There is an increase in the transient flux of energy
at most latitudes, due to a greater transport of latent heat arising from the greater moisture availability. The total number
of Northern Hemisphere storms decreases but there is a tendency towards deeper low centres. There are fewer storms in the
North Pacific and North Atlantic source regions where the local baroclinicity is reduced. The climatological tracks from these
regions are shorter with decreases at the northeastern ends of the tracks and increases in the regions with maximum counts
towards the centre of the ocean basins. These changes are not generally statistically significant. The greatest changes in
blocking anticyclones occur in the North Pacific where there is a downstream shift in the region of maximum activity. Changes
in stationary waves show a strong increase in the PNA oscillation which may be influencing the changes in blocking as has
been found by other authors. Possible mechanisms for forcing this response are speculated but it will need further experiments
to unravel them.
Received: 10 September 1997/Accepted: 2 December 1997 相似文献
20.
Time-Frequency Characteristics of the Relationships Between Tropical Indo-Pacific SSTs 总被引：1，自引：0，他引：1
In this study, several advanced analysis methods are applied to understand the relationships between the Nino-3.4 sea surface temperatures （SST） and the SSTs related to the tropical Indian Ocean Dipole （IOD）. By analyzing a long data record, the authors focus on the time-frequency characteristics of these relationships, and of the structure of IOD. They also focus on the seasonal dependence of those characteristics in both time and frequency domains. Among the Nino-3.4 SST, IOD, and SSTs over the tropical western Indian Ocean （WIO） and eastern Indian Ocean （EIO）, the WIO SST has the strongest annual and semiannual oscillations. While the Nino-3.4 SST has large inter-annual variability that is only second to its annual variability, the IOD is characterized by the largest semiannual oscillation, which is even stronger than its annual oscillation. The IOD is strongly and stably related to the EIO SST in a wide range of frequency bands and in all seasons. However, it is less significantly related to the WIO SST in the boreal winter and spring. There exists a generally weak and unstable relationship between the WIO and EIO SSTs, especially in the biennial and higher frequency bands. The relationship is especially weak in summer and fall, when IOD is apparent, but appears highly positive in winter and spring, when the IOD is unimportantly weak and even disappears. This feature reflects a caution in the definition and application of IOD. The Nino-3.4 SST has a strong positive relationship with the WIO SST in all seasons, mainly in the biennial and longer frequency bands. However, it shows no significant relationship with the EIO SST in summer and fall, and with IOD in winter and spring. 相似文献