共查询到20条相似文献,搜索用时 312 毫秒
1.
Julia V. Manganello 《Climate Dynamics》2008,30(6):621-641
The influence of sea surface temperature anomalies (SSTA) on multi-year persistence of the North Atlantic Oscillation (NAO)
during the second half of the twentieth century is investigated using the Center for Ocean-Land-Atmosphere Studies (COLA)
Atmospheric GCM (AGCM) with an emphasis on isolating the geographic location of the SSTA that produce this influence. The
present study focuses on calculating the atmospheric response to the SSTA averaged over 1988–1995 (1961–1968) corresponding
to the observed period of strong persistence of the positive (negative) phase of the decadal NAO. The model response to the
global 1988–1995 average SSTA shows a statistically significant large-scale pattern characteristic of the positive phase of
the NAO. Forcing with the global 1961–1968 average SSTA generates a NAO of the opposite polarity compared to observations.
However, all large-scale features both in the model and observations during this period are weaker in magnitude and less significant
compared to 1988–1995. Additional idealized experiments show that over the northern center of the NAO the non-linear component
of the forced response appears to be quite important and acts to enhance the positive NAO signal. On the other hand, over
the southern center where the model response is the strongest, it is also essentially linear. The 1988–1995 average SSTA restricted
to the western tropical Pacific region produce a positive NAO remarkably similar in structure but stronger in magnitude than
the model response to the global and tropical Indo-Pacific 1988–1995 forcing. A 200-hPa geopotential height response in these
experiments shows a positive anomaly over the southern center of the NAO embedded in the Rossby wave trains propagating from
the western tropical Pacific. Indian Ocean SSTA lead to much weaker positive NAO primarily through the effect on its northern
center. SST forcing confined to the North Atlantic north of equator does not produce a response statistically different from
the control simulation, suggesting that it is not strong enough to significantly affect the phase of the decadal NAO. Inclusion
of the South Atlantic north of 45° south does not change this result.
相似文献
Julia V. ManganelloEmail: |
2.
Remotely forced variability in the tropical Atlantic Ocean 总被引:1,自引:1,他引:1
An ensemble of eight hindcasts has been conducted using an ocean-atmosphere general circulation model fully coupled only within the Atlantic basin, with prescribed observational sea surface temperature (SST) for 1950–1998 in the global ocean outside the Atlantic basin. The purpose of these experiments is to understand the influence of the external SST anomalies on the interannual variability in the tropical Atlantic Ocean. Statistical methods, including empirical orthogonal function analysis with maximized signal-to-noise ratio, have been used to extract the remotely forced Atlantic signals from the ensemble of simulations. It is found that the leading external source on the interannual time scales is the El Niño/Southern Oscillation (ENSO) in the Pacific Ocean. The ENSO signal in the tropical Atlantic shows a distinct progression from season to season. During the boreal winter of a maturing El Niño event, the model shows a major warm center in the southern subtropical Atlantic together with warm anomalies in the northern subtropical Atlantic. The southern subtropical SST anomalies is caused by a weakening of the southeast trade winds, which are partly associated with the influence of an atmospheric wave train generated in the western Pacific Ocean and propagating into the Atlantic basin in the Southern Hemisphere during boreal fall. In the boreal spring, the northern tropical Atlantic Ocean is warmed up by a weakening of the northeast trade winds, which is also associated with a wave train generated in the central tropical Pacific during the winter season of an El Niño event. Apart from the atmospheric planetary waves, these SST anomalies are also related to the sea level pressure (SLP) increase in the eastern tropical Atlantic due to the global adjustment to the maturing El Niño in the tropical Pacific. The tropical SLP anomalies are further enhanced in boreal spring, which induce anomalous easterlies on and to the south of the equator and lead to a dynamical oceanic response that causes cold SST anomalies in the eastern and equatorial Atlantic from boreal spring to summer. Most of these SST anomalies persist into the boreal fall season.
相似文献
B. HuangEmail: |
3.
The current generations of climate models are in substantial disagreement as to the projected patterns of sea surface temperatures (SSTs) in the Tropics over the next several decades. We show that the spatial patterns of tropical ocean temperature trends have a strong influence on global mean temperature and precipitation and on global mean radiative forcing. We identify the SST patterns with the greatest influence on the global mean climate and find very different, and often opposing, sensitivities to SST changes in the tropical Indian and West Pacific Oceans. Our work stresses the need to reduce climate model biases in these sensitive regions, as they not only affect the regional climates of the nearby densely populated continents, but also have a disproportionately large effect on the global climate.
相似文献
Joseph J. BarsugliEmail: Phone: +1-303-4976042Fax: +1-303-4976449 |
4.
In this study seasonal predictability of Tier-one and Tier-two predictions are evaluated and compared. Through the comparison
of these two predictions, it is demonstrated that the air–sea coupled process is an important factor not only for climatological
simulation but also for seasonal predictability. In particular, the air–sea coupling plays a crucial role over the warm pool
region, as the atmosphere tends to lead the ocean in anomalous variability. In this region, the Tier-one prediction has better
climatology compared to the Tier-two prediction despite the presence of a climatological SST bias. Furthermore, the Tier-one
has a relatively higher seasonal predictive skill than that of the Tier-two although its SST prediction skill is relatively
poor. It is suggested that the air–sea coupled process plays a role to reduce both the climatological and anomalous biases
in the uncoupled AGCM by means of the negative feedback of the SST-heat flux-precipitation loop. Using the CliPAS and DEMETER
seasonal prediction data, the robustness of these results are demonstrated in the multi-model frame works.
This paper is a contribution to the AMIP-CMIP Diagnostic Sub-project on General Circulation Model Simulation of the East Asian
Climate, coordinated by W.-C. Wang.
相似文献
In-Sik KangEmail: |
5.
Multi-century climate simulations obtained with the GISS atmospheric general circulation model coupled to the hybrid-isopycnic
ocean model HYCOM are described. Greenhouse gas concentrations are held fixed in these experiments to investigate the coupled
model’s ability to reproduce the major features of today’s climate with minimal drift. Emphasis is placed on the realism of
the oceanic general circulation and its effect on air–sea exchange processes. Several model runs using different closures
for turbulent vertical exchange as well as improvements to reduce vertical numerical diffusion are compared with climate observations.
As in previous studies, the Southern Ocean emerges as the Achilles Heel of the ocean model; deficiencies in its physical representation
had far-reaching consequences in early experiments with the coupled model and have provided the strongest impetus for model
improvement. The overarching goal of this work is to add diversity to the pool of ocean models available for climate prediction
and thereby reduce biases that may stand in the way of assessing climate prediction uncertainty.
相似文献
Shan Sun (Corresponding author)Email: |
Rainer BleckEmail: |
6.
Guojun Gu 《Climate Dynamics》2009,32(4):457-471
Intraseasonal (30–80 days) variability in the equatorial Atlantic-West African sector during March–June is investigated using
various recently-archived satellite measurements and the NCEP/DOE AMIP-II reanalysis daily data. The global connections of
regional intraseasonal signals are first examined for the period of 1979–2006 through lag-regression analyses of convection
(OLR) and other dynamic components against a regional intraseasonal convective (OLR) index. The eastward-propagating features
of convection can readily be seen, accompanied by coherent circulation anomalies, similar to those for the global tropical
intraseasonal mode, i.e., the Madden–Julian oscillation (MJO). The regressed TRMM rainfall (3B42) anomalies during the TRMM
period (1998–2006) manifest similar propagating features as for the regressed OLR anomalies during 1979–2006. These coherent
features hence tend to suggest that the regional intraseasonal convective signals might be mostly a regional response to,
or closely associated with the MJO, and probably contribute to the MJO’s global propagation. Atmospheric and surface intraseasonal
variability during March–June of 1998–2006 are further examined using the high-quality TRMM Microwave Imager (TMI) sea surface
temperature (SST), columnar water vapor, and cloud liquid water, and the QuikSCAT oceanic winds (2000–2006). Enhanced (suppressed)
convection or positive (negative) rainfall anomalies approximately cover the entire basin (0°–10°N, 30°W–10°E) during the
passage of intraseasonal convective signals, accompanied by anomalous surface westerly (easterly) flow. Furthermore, a unique
propagating feature seems to exist within the tropical Atlantic basin. Rainfall anomalies always appear first in the northwestern
basin right off the coast of South America, and gradually extend eastward to cover the entire basin. A dipolar structure of
rainfall anomalies with cross-equatorial surface wind anomalies can thus be observed during this evolution, similar to the
anomaly patterns on the interannual time scale discovered in past studies. Coherent intraseasonal variations and patterns
can also be found in other physical components.
相似文献
Guojun GuEmail: |
7.
Extratropical control of recent tropical Pacific decadal climate variability: a relay teleconnection 总被引:2,自引:0,他引:2
Observations indicate that recent tropical Pacific decadal climate variability tends to be associated with the extratropical North Pacific through a relay teleconnection of a fast coupled ocean-atmosphere bridge and a slow oceanic tunnel. A coupled ocean-atmosphere model, forced by the observed decadal wind in the extratropical North Pacific, explicitly demonstrates that extratropical decadal sea surface temperature (SST) anomalies may propagate to the tropics through a coupled wind-evaporative-SST (WES) feedback. The WES feedback cannot only lead to a nearly synchronous change of tropical SST, but also force a delayed adjustment of the meridional overturning circulation in the upper ocean to further sustain the tropical SST change. The study further suggests that the extratropical–tropical teleconnection provides a positive feedback to sustain the decadal changes in both the tropical and extratropical North Pacific. 相似文献
8.
Joaquim G. Pinto Stefan Zacharias Andreas H. Fink Gregor C. Leckebusch Uwe Ulbrich 《Climate Dynamics》2009,32(5):739-737
The occurrence of extreme cyclones is analysed in terms of their relationship to the NAO phase and the dominating environmental
variables controlling their intensification. These are latent energy (equivalent potential temperature 850 hPa is used as
an indicator), upper-air baroclinicity, horizontal divergence and jet stream strength. Cyclones over the North Atlantic are
identified and tracked using a numerical algorithm, permitting a detailed analysis of their life cycles. Extreme cyclones
are selected as the 10% most severe in terms of intensity. Investigations focus on the main strengthening phase of each cyclone.
The environmental factors are related to the NAO, which affects the location and orientation of the cyclone tracks, thus explaining
why extreme cyclones occur more (less) frequently during strong positive (negative) NAO phases. The enhanced number of extreme
cyclones in positive NAO phases can be explained by the larger area with suitable growth conditions, which is better aligned
with the cyclone tracks and is associated with increased cyclone life time and intensity. Moreover, strong intensification
of cyclones is frequently linked to the occurrence of extreme values of growth factors in the immediate vicinity of the cyclone
centre. Similar results are found for ECHAM5/OM1 for present day conditions, demonstrating that relationships between the
environment factors and cyclones are also valid in the GCM. For future climate conditions (following the SRES A1B scenario),
the results are similar, but a small increase of the frequency of extreme values is detected near the cyclone cores. On the
other hand, total cyclone numbers decrease by 10% over the North Atlantic. An exception is the region near the British Isles,
which features increased track density and intensity of extreme cyclones irrespective of the NAO phase. These changes are
associated with an intensified jet stream close to Europe. Moreover, an enhanced frequency of explosive developments over
the British Isles is found, leading to more frequent windstorms affecting Europe.
相似文献
Joaquim G. PintoEmail: |
9.
An atmospheric general circulation model of intermediate complexity is used to investigate the origin and structure of the climate change in the second half of the twentieth century. The variability of the atmospheric flow is considered as a superposition of an internal part, due to intrinsic dynamical variability, and an external part, due to the variations of the sea surface temperature (SST) forcing. The two components are identified by performing a 50-member ensemble of atmospheric simulations with prescribed, observed SSTs in the period 1949–2002. The large number of realizations allows the estimation of statistics of the atmospheric variability with a high confidence level. The analysis performed focuses on interdecadal and interannual variability of 500 hPa geopotential height in the Northern Hemisphere (NH) during winter. The model reproduces well the structure of the observed trend (defined as the difference in the two 25-year intervals 1977–2001 and 1952–1976), particularly in the Pacific region, and about half of the amplitude of the signal. The trend in 500 hPa height projects mainly onto the second empirical orthogonal function (EOF), both in the observations and in the model ensemble. However, differences between the modelled and the observed variability are found in the pattern of the second EOF in the Atlantic sector. SST changes associated with the El Niño southern oscillation (ENSO) are responsible for about 50% of the signal of the 500 hPa height trend in the Pacific. A second 50-member ensemble is used to evaluate the sensitivity of interdecadal variability to an increase in CO2 optical depth compatible with observed concentration changes. In this second experiment, the simulated trend includes a statistically significant contribution from the positive phase of the Arctic oscillation (AO). Such a contribution is also found in observations. Furthermore, the additional CO2 forcing accounts for part of the NH trend in near-surface temperature, and brings the zonal-mean temperature changes in the stratosphere and upper-troposphere closer to observations.
相似文献
Fred KucharskiEmail: |
10.
Role of soil freezing in future boreal climate change 总被引:3,自引:0,他引:3
We introduced a simple scheme of soil freezing in the LMDz3.3 atmospheric general circulation model (AGCM) to examine the potential effects of this parameterization on simulated future boreal climate change. In this multi-layer soil scheme, soil heat capacity and conductivity are dependent on soil water content, and a parameterization of the thermal and hydrological effects of water phase changes is included. The impact of these new features is evaluated against observations. By comparing present-day and 2×CO2 AGCM simulations both with and without the parameterization of soil freezing the role of soil freezing in climate change is analysed. Soil freezing does not have significant global impacts, but regional effects on simulated climate and climate change are important. In present-day conditions, hydrological effects due to freezing lead to dryer summers. In 2×CO2 climate, thermal effects due to freeze/thaw cycles are more pronounced and contribute to enhance the expected future overall winter warming. Impact of soil freezing on climate sensitivity is not uniform: the annual mean warming is amplified in North America (+15%) and Central Siberia (+36%) whereas it is reduced in Eastern Siberia (–23%). Nevertheless, all boreal lands undergo a strong attenuation of the warming during summertime. In agreement with some previous studies, these results indicate once more that soil freezing effects are significant on regional boreal climate. But this study also demonstrates its importance on regional boreal climate change and thus the necessity to include soil freezing in regional climate change predictions.
相似文献
G. KrinnerEmail: Phone: +33-476-824241Fax: +33-476-824201 |
11.
T. J. Raddatz C. H. Reick W. Knorr J. Kattge E. Roeckner R. Schnur K.-G. Schnitzler P. Wetzel J. Jungclaus 《Climate Dynamics》2007,29(6):565-574
Global warming caused by anthropogenic CO2 emissions is expected to reduce the capability of the ocean and the land biosphere to take up carbon. This will enlarge the
fraction of the CO2 emissions remaining in the atmosphere, which in turn will reinforce future climate change. Recent model studies agree in
the existence of such a positive climate–carbon cycle feedback, but the estimates of its amplitude differ by an order of magnitude,
which considerably increases the uncertainty in future climate projections. Therefore we discuss, in how far a particular
process or component of the carbon cycle can be identified, that potentially contributes most to the positive feedback. The
discussion is based on simulations with a carbon cycle model, which is embedded in the atmosphere/ocean general circulation
model ECHAM5/MPI-OM. Two simulations covering the period 1860–2100 are conducted to determine the impact of global warming
on the carbon cycle. Forced by historical and future carbon dioxide emissions (following the scenario A2 of the Intergovernmental
Panel on Climate Change), they reveal a noticeable positive climate–carbon cycle feedback, which is mainly driven by the tropical
land biosphere. The oceans contribute much less to the positive feedback and the temperate/boreal terrestrial biosphere induces
a minor negative feedback. The contrasting behavior of the tropical and temperate/boreal land biosphere is mostly attributed
to opposite trends in their net primary productivity (NPP) under global warming conditions. As these findings depend on the
model employed they are compared with results derived from other climate–carbon cycle models, which participated in the Coupled
Climate–Carbon Cycle Model Intercomparison Project (C4MIP).
相似文献
T. J. RaddatzEmail: |
12.
Analysis of the projected regional sea-ice changes in the Southern Ocean during the twenty-first century 总被引:2,自引:1,他引:1
Using the set of simulations performed with atmosphere-ocean general circulation models (AOGCMs) for the Fourth Assessment
Report of the Intergovernmental Panel on Climate Change (IPCC AR4), the projected regional distribution of sea ice for the
twenty-first century has been investigated. Averaged over all those model simulations, the current climate is reasonably well
reproduced. However, this averaging procedure hides the errors from individual models. Over the twentieth century, the multimodel
average simulates a larger sea-ice concentration decrease around the Antarctic Peninsula compared to other regions, which
is in qualitative agreement with observations. This is likely related to the positive trend in the Southern Annular Mode (SAM)
index over the twentieth century, in both observations and in the multimodel average. Despite the simulated positive future
trend in SAM, such a regional feature around the Antarctic Peninsula is absent in the projected sea-ice change for the end
of the twenty-first century. The maximum decrease is indeed located over the central Weddell Sea and the Amundsen–Bellingshausen
Seas. In most models, changes in the oceanic currents could play a role in the regional distribution of the sea ice, especially
in the Ross Sea, where stronger southward currents could be responsible for a smaller sea-ice decrease during the twenty-first
century. Finally, changes in the mixed layer depth can be found in some models, inducing locally strong changes in the sea-ice
concentration.
相似文献
W. LefebvreEmail: |
13.
Physical Mechanism of the Impacts of the Tropical Atlantic Sea Surface Temperature on the Decadal Change of the Summer North Atlantic Oscillation 下载免费PDF全文
SUN Jian-Qi 《大气和海洋科学快报》2013,6(5):365-368
In this study,physical mechanism of the impacts of the tropical Atlantic sea surface temperature(SST)on decadal change of the summer North Atlantic Oscillation(SNAO)was explored using an atmospheric general circulation model(AGCM)developed at the International Centre for Theoretical Physics(ICTP).The simulation results indicate that the decadal warming of the SST over the tropical Atlantic after the late 1970s could have significantly enhanced the convection over the region.This enhanced convection would have strengthened the local meridional circulation over the Eastern Atlantic-North Africa-Western Europe region,exciting a meridional teleconnection.This teleconnection might have brought the signal of the tropical Atlantic SST to the Extratropics,consequently activating the variability of the eastern part of the SNAO southern center,which led to an eastward shift of the SNAO southern center around the late 1970s.Such physical processes are highly consistent with the previous observations. 相似文献
14.
This study examines the variability of the monthly average significant wave height (SWH) field in the Mediterranean Sea, in
the period 1958–2001. The analysed data are provided by simulations carried out using the WAM model (WAMDI group, 1988) forced
by the wind fields of the ERA-40 (ECMWF Re-Analysis). Comparison with buoy observations, satellite data, and simulations forced
by higher resolution wind fields shows that, though results underestimate the actual SWH, they provide a reliable representation
of its real space and time variability. Principal component analysis (PCA) shows that the annual cycle is characterised by
two main empirical orthogonal functions (EOF) patterns. Most inter-monthly variability is associated with the first EOF, whose
positive/negative phase is due to the action of Mistral/Etesian wind regimes. The second EOF is related to the action of southerly
winds (Libeccio and Sirocco). The annual cycle presents two main seasons, winter and summer characterised, the first, by the
prevalence of eastwards and southeastwards propagating waves all over the basin, and the second, by high southwards propagating
waves in the Aegean Sea and Levantin Basin. Spring and fall are transitional seasons, characterised by northwards and northeastwards
propagating waves, associated to an intense meridional atmospheric circulation, and by attenuation and amplification, respectively,
of the action of Mistral. These wave field variability patterns are associated with consistent sea level pressure (SLP) and
surface wind field structures. The intensity of the SWH field shows large inter-annual and inter-decadal variability and a
statistically significant decreasing trend of mean winter values. The winter average SWH is anti-correlated with the winter
NAO (North Atlantic Oscillation) index, which shows a correspondingly increasing trend. During summer, a minor component of
the wave field inter-annual variability (associated to the second EOF) presents a statistically significant correlation with
the Indian Monsoon reflecting its influence on the meridional Mediterranean circulation. However, the SLP patterns associated
with the SWH inter-annual variability reveal structures different from NAO and Monsoon circulation. In fact, wave field variability
is conditioned by regional storminess in combination with the effect of fetch. The latter is likely to be the most important.
Therefore, the inter-annual variability of the mean SWH is associated to SLP patterns, which present their most intense features
above or close to Mediterranean region, where they are most effective for wave generation.
相似文献
P. LionelloEmail: |
15.
Chidong Zhang Min Dong Silvio Gualdi Harry H. Hendon Eric D. Maloney Andrew Marshall Kenneth R. Sperber Wanqiu Wang 《Climate Dynamics》2006,27(6):573-592
The status of the numerical reproduction of the Madden–Julian Oscillation (MJO) by current global models was assessed through
diagnoses of four pairs of coupled and uncoupled simulations. Slow eastward propagation of the MJO, especially in low-level
zonal wind, is realistic in all these simulations. However, the simulated MJO suffers from several common problems. The MJO
signal in precipitation is generally too weak and often eroded by an unrealistic split of an equatorial maximum of precipitation
into a double ITCZ structure over the western Pacific. The MJO signal in low-level zonal wind, on the other hand, is sometimes
too strong over the eastern Pacific but too weak over the Indian Ocean. The observed phase relationship between precipitation
and low-level zonal wind associated with the MJO in the western Pacific and their coherence in general are not reproduced
by the models. The seasonal migration in latitude of MJO activity is missing in most simulations. Air–sea coupling generally
strengthens the simulated eastward propagating signal, but its effects on the phase relationship and coherence between precipitation
and low-level zonal wind, and on their geographic distributions, seasonal cycles, and interannual variability are inconsistent
among the simulations. Such inconsistency cautions generalization of results from MJO simulations using a single model. In
comparison to observations, biases in the simulated MJO appear to be related to biases in the background state of mean precipitation,
low-level zonal wind, and boundary-layer moisture convergence. This study concludes that, while the realistic simulations
of the eastward propagation of the MJO are encouraging, reproducing other fundamental features of the MJO by current global
models remains an unmet challenge.
相似文献
Chidong ZhangEmail: |
16.
Katharine Hayhoe Cameron P. Wake Thomas G. Huntington Lifeng Luo Mark D. Schwartz Justin Sheffield Eric Wood Bruce Anderson James Bradbury Art DeGaetano Tara J. Troy David Wolfe 《Climate Dynamics》2007,28(4):381-407
To assess the influence of global climate change at the regional scale, we examine past and future changes in key climate,
hydrological, and biophysical indicators across the US Northeast (NE). We first consider the extent to which simulations of
twentieth century climate from nine atmosphere-ocean general circulation models (AOGCMs) are able to reproduce observed changes
in these indicators. We then evaluate projected future trends in primary climate characteristics and indicators of change,
including seasonal temperatures, rainfall and drought, snow cover, soil moisture, streamflow, and changes in biometeorological
indicators that depend on threshold or accumulated temperatures such as growing season, frost days, and Spring Indices (SI).
Changes in indicators for which temperature-related signals have already been observed (seasonal warming patterns, advances
in high-spring streamflow, decreases in snow depth, extended growing seasons, earlier bloom dates) are generally reproduced
by past model simulations and are projected to continue in the future. Other indicators for which trends have not yet been
observed also show projected future changes consistent with a warmer climate (shrinking snow cover, more frequent droughts,
and extended low-flow periods in summer). The magnitude of temperature-driven trends in the future are generally projected
to be higher under the Special Report on Emission Scenarios (SRES) mid-high (A2) and higher (A1FI) emissions scenarios than
under the lower (B1) scenario. These results provide confidence regarding the direction of many regional climate trends, and
highlight the fundamental role of future emissions in determining the potential magnitude of changes we can expect over the
coming century.
相似文献
Katharine HayhoeEmail: |
17.
Cycles and shifts: 1,300 years of multi-decadal temperature variability in the Gulf of Alaska 总被引:2,自引:0,他引:2
The Gulf of Alaska (GOA) is highly sensitive to shifts in North Pacific climate variability. Here we present an extended tree-ring
record of January–September GOA coastal surface air temperatures using tree-ring width data from coniferous trees growing
in the mountain ranges along the GOA. The reconstruction (1514–1999), based on living trees, explains 44% of the temperature
variance, although, as the number of chronologies decreases back in time, this value decreases to, and remains around ∼30%
before 1840. Verification of the calibrated models is, however, robust. Utilizing sub-fossil wood, we extend the GOA reconstruction
back to the early eighth century. The GOA reconstruction correlates significantly (95% CL) with both the Pacific Decadal Oscillation
Index (0.53) and North Pacific Index (−0.42) and therefore likely yields important information on past climate variability
in the North Pacific region. Intervention analysis on the GOA reconstruction identifies the known twentieth century climate
shifts around the 1940s and 1970s, although the mid-1920s shift is only weakly expressed. In the context of the full 1,300 years
record, the well studied 1976 shift is not unique. Multi-taper method spectral analysis shows that the spectral properties
of the living and sub-fossil data are similar, with both records showing significant (95% CL) spectral peaks at ∼9–11, 13–14
and 18–19 years. Singular spectrum analysis identifies (in order of importance) significant oscillatory modes at 18.7, 50.4,
38.0, 91.8, 24.4, 15.3 and 14.1 years. The amplitude of these modes varies through time. It has been suggested (Minobe in
Geophys Res Lett 26:855–858, 1999) that the regime shifts during the twentieth century can be explained by the interaction between pentadecadal (50.4 years)
and bidecadal (18.7 years) oscillatory modes. Removal of these two modes of variance from our GOA time series does indeed
remove the twentieth century shifts, but many are still identified prior to the twentieth century. Our analysis suggests that
climate variability of the GOA is very complex, and that much more work is required to understand the underlying oscillatory
behavior that is observed in instrumental and proxy records from the North Pacific region.
相似文献
Rob WilsonEmail: |
18.
Simon F. B. Tett Richard Betts Thomas J. Crowley Jonathan Gregory Timothy C. Johns Andy Jones Timothy J. Osborn Elisabeth Öström David L. Roberts Margaret J. Woodage 《Climate Dynamics》2007,28(1):3-34
A climate simulation of an ocean/atmosphere general circulation model driven with natural forcings alone (constant “pre-industrial” land-cover and well-mixed greenhouse gases, changing orbital, solar and volcanic forcing) has been carried out from 1492 to 2000. Another simulation driven with natural and anthropogenic forcings (changes in greenhouse gases, ozone, the direct and first indirect effect of anthropogenic sulphate aerosol and land-cover) from 1750 to 2000 has also been carried out. These simulations suggest that since 1550, in the absence of anthropogenic forcings, climate would have warmed by about 0.1 K. Simulated response is not in equilibrium with the external forcings suggesting that both climate sensitivity and the rate at which the ocean takes up heat determine the magnitude of the response to forcings since 1550. In the simulation with natural forcings climate sensitivity is similar to other simulations of HadCM3 driven with CO2 alone. Climate sensitivity increases when anthropogenic forcings are included. The natural forcing used in our experiment increases decadal–centennial time-scale and large spatial scale climate variability, relative to internal variability, as diagnosed from a control simulation. Mean conditions in the natural simulation are cooler than in our control simulation reflecting the reduction in forcing. However, over certain regions there is significant warming, relative to control, due to an increase in forest cover. Comparing the simulation driven by anthropogenic and natural forcings with the natural-only simulation suggests that anthropogenic forcings have had a significant impact on, particularly tropical, climate since the early nineteenth century. Thus the entire instrumental temperature record may be “contaminated” by anthropogenic influences. Both the hydrological cycle and cryosphere are also affected by anthropogenic forcings. Changes in tree-cover appear to be responsible for some of the local and hydrological changes as well as an increase in northern hemisphere spring snow cover.
相似文献
Simon F. B. TettEmail: |
19.
Oscar Peralta Darrel Baumgardner Graciela B. Raga 《Journal of Atmospheric Chemistry》2007,57(2):153-169
Spectrothermography, defined as the evaluation of thermograms of carbon evolved from heated aerosol samples, is a technique
for evaluating differences in particle characteristics as they relate to emission sources and processes that modify particle
evolution. Here we describe the inherent uncertainties and demonstrate the utility of this technique with an evaluation of
samples that were collected with eight stage cascade impactors at three sites in Mexico City over a period of 5 months. The
study was implemented with statistical analysis based on tests for goodness of fit to separate thermograms with distinctive
shapes related to the relative amounts of organic and elemental carbon mass that evolves as a function of temperature. Thermograms
with unique shapes were found for particles with aerodynamic diameters of 1–10, 0.56–1, 0.32–0.56 and 0.18–0.32 μm with further
differentiation of curves related to the relative amounts of gasoline and diesel fuel that was combusted in the region of
the three sites. The common shapes fit 32–42% of samples in each particle size range and indicate that this type of analysis
can help distinguish differences in the primary sources of organic and elemental carbon.
相似文献
Darrel BaumgardnerEmail: |
20.
Transient simulation of the last glacial inception. Part I: glacial inception as a bifurcation in the climate system 总被引:2,自引:2,他引:0
Reinhard Calov Andrey Ganopolski Martin Claussen Vladimir Petoukhov Ralf Greve 《Climate Dynamics》2005,24(6):545-561
We study the mechanisms of glacial inception by using the Earth system model of intermediate complexity, CLIMBER-2, which
encompasses dynamic modules of the atmosphere, ocean, biosphere and ice sheets. Ice-sheet dynamics are described by the three-dimensional
polythermal ice-sheet model SICOPOLIS. We have performed transient experiments starting at the Eemiam interglacial, at 126 ky
BP (126,000 years before present). The model runs for 26 kyr with time-dependent orbital and CO2 forcings. The model simulates a rapid expansion of the area covered by inland ice in the Northern Hemisphere, predominantly
over Northern America, starting at about 117 kyr BP. During the next 7 kyr, the ice volume grows gradually in the model at
a rate which corresponds to a change in sea level of 10 m per millennium. We have shown that the simulated glacial inception
represents a bifurcation transition in the climate system from an interglacial to a glacial state caused by the strong snow-albedo
feedback. This transition occurs when summer insolation at high latitudes of the Northern Hemisphere drops below a threshold
value, which is only slightly lower than modern summer insolation. By performing long-term equilibrium runs, we find that
for the present-day orbital parameters at least two different equilibrium states of the climate system exist—the glacial and
the interglacial; however, for the low summer insolation corresponding to 115 kyr BP, we find only one, glacial, equilibrium
state, while for the high summer insolation corresponding to 126 kyr BP only an interglacial state exists in the model.
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Reinhard CalovEmail: |