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Two climatic states and feedbacks on thermohaline circulation in an Earth system model of intermediate complexity 总被引:5,自引:0,他引:5
Zhaomin Wang 《Climate Dynamics》2005,25(2-3):299-314
The McGill Paleoclimate Model-2 (MPM-2) is employed to study climate–thermohaline circulation (THC) interactions in a pre
-industrial climate, with a special focus on the feedbacks on the THC from other climate system components. The MPM-2, a new
version of the MPM, has an extended model domain from 90S to 90N, active winds and no oceanic heat and freshwater flux adjustments.
In the MPM-2, there are mainly two stable modes for the Atlantic meridional overturning circulation (MOC) under the ‘present-day’
forcing (present-day solar forcing and the pre-industrial atmospheric CO2 level of 280 ppm). The ‘on’ mode has an active North Atlantic deep water formation, while the ‘off’ mode has no such deep
water formation. By comparing the ‘off’ mode climate state with its ‘on’ mode analogue, we find that there exist many large
differences between the two climate states, which originate from large changes in the oceanic meridional heat transports.
By suppressing or isolating each process associated with a continental ice sheet over North America, sea ice, the atmospheric
hydrological cycle and vegetation, feedbacks from these components on the Atlantic MOC are investigated. Sensitivity studies
investigating the role of varying continental ice growth and sea ice meridional transport in the resumption of the Atlantic
MOC are also carried out. The results show that a fast ice sheet growth and an enhanced southward sea ice transport significantly
favor the resumption of the Atlantic MOC in the MPM-2. In contrast to this, the feedback from the atmospheric hydrological
cycle is a weak positive one. The vegetation-albedo feedback could enhance continental ice sheet growth and thus could also
favor the resumption of the Atlantic MOC. However, before the shut-down of the Atlantic MOC, feedbacks from these components
on the Atlantic MOC are very weak. 相似文献
3.
S. M. Vakulovskii M. G. Germenchuk O. M. Zhukova 《Russian Meteorology and Hydrology》2011,36(4):265-268
A long-range atmosphere transfer of radionuclides from nuclear explosions and nuclear plant accidents is considered. Data
on radionuclide transport in the Yenisey, Pripet, Sozh, Iput’, and Besed’ rivers are presented. The time of the radionuclide
transport from the Irish Sea to the Baltic and Barents seas is defined using changes in the cesium 134/cesium 137 isotope
ratio. 相似文献
4.
K. P. Tyshko 《Russian Meteorology and Hydrology》2009,34(8):534-540
Structural-genetic types of hummocks formed on the Arctic seas’ ice cover are considered. A method of the laboratory physical
modeling was used for understanding kinematic schemes of the hummocks’ formation processes. A methodology of computation of
the hummock consolidation intensity for different hummocks’ structural types was proposed. The performed computations showed
good coherence of the laboratory experiments results and field studies of hummocks’ structure in the Barents and Kara seas. 相似文献
5.
The river ice regime is considered a sensitive indicator of climate change and within this study long term changes (in case of River Daugava starting from 1530, but for other studied rivers starting from first half of twentieth century) river ice regimes in the Baltic region have been studied. The ice cover duration on the rivers (17 rivers) in the Baltic countries and Belarus has decreased during the recent decades. In addition to this, long term observational records of ice break on the rivers of the studied region exhibit a pattern of periodic changes in the intensity of ice regime. Both the ice regime and the seasonal river discharge are shown to be strongly influenced by large-scale atmospheric circulation processes over North Atlantic that manifests through close correlation with North Atlantic Oscillation index. 相似文献
6.
Mahmoud Ahmadi Abbasali Dadashi-Roudbari Tayebeh Akbari-Azirani Behnaz Nasiri-Khuzani 《Theoretical and Applied Climatology》2020,140(3):963-982
Efficient and proper understanding of the state of the clouds regarding different seasons of the year will have profound effects on different economic and environmental sectors. The purpose of this study is to determine the hourly dissociation of ice and liquid clouds in Iran. To this end, cloud optical thickness (COT) data, as well as optical depth of clouds in two phases of liquid and ice were obtained and processed from 31 synoptic meteorological stations (1960–2015), MODIS data from Terra satellite during the years 2001 to 2011, and they were processed then. Next, using the RegCM4 model, the cloud fraction (clt) was simulated to accurately identify the cloud cover situation in Iran. The results showed that the maximum annual mean abundance of liquid and ice clouds was 18.95 days for the time 15:00 and 3.99 days for the time 06:00, respectively. Climatic zones of the Caspian and Persian Gulf coasts at 15 o’clock had the highest decreasing trend of liquid clouds. Ice clouds in all parts of Iran’s climate, with the exception of the eastern plateau, also declined. From south to north and east to west of Iran, the occurrence of ice and liquid clouds is increasing. Therefore, the spatio-temporal distribution of liquid and ice clouds in the country was also dependent on spatial components and latitude had the greatest impact. From the satellite and modeled data, the RegCM4 model has been able to detect the Monsoon phenomenon in southeastern Iran during the summer. CLT simulation in Iran has also shown that cloud cover in Iran fluctuates between 28 and 65% on average, with 81.5% of Iranian stations having a significant change in the amount of annual cloud cover. Correlation of liquid and ice clouds with precipitation showed that liquid clouds in summer and ice clouds in spring had higher correlation with precipitation in Iran. Northern coasts of Iran due to greater ascent mechanisms such as coastal compressors, north latitude atmospheric circulation systems, and maximum winds in the north and west of Iran due to the location of western systems entry and sufficient thermal gradient, had maximum ice clouds in the last half century. Also, south of Iran, despite having extended and great water-bodies, is less cloudy due to descending air in Hadley’s circulation (Hadley cell) of air. 相似文献
7.
Salvador Pueyo 《Climatic change》2007,82(1-2):131-161
Here I present a new approach to forecasting the effects of climate change on catastrophic events, based on the ‘self-organised
criticality’ concept from statistical physics. In particular, I develop the ‘self-organised critical fuel succession model’
(SOCFUS), which deals with wildland fires. I show that there is good agreement between model and data for the response pattern
of the whole fire size statistical distribution to weather fluctuations in a boreal forest region. I tentatively predict the
fire regime in this region for an instance of possible climate change scenario. I show that the immediate response is sharper
than usually thought, but part of the added burning rate might not persist indefinitely. A large fraction of the extra burning
in the transition period is likely to be concentrated in a few ‘climate change fires’, much larger than the largest fires
that could currently occur. I also suggest that the major fire events recently observed in some tropical rainforest regions
belong to a qualitatively different, even more abrupt type of response, which is also predicted by the model.
Electronic supplementary material Electronic supplementary material is available for this article at 相似文献
8.
Ramdane Alkama M. Kageyama G. Ramstein O. Marti P. Ribstein D. Swingedouw 《Climate Dynamics》2008,30(7-8):855-869
The presence of large ice sheets over North America and North Europe at the Last Glacial Maximum (LGM) strongly impacted Northern
hemisphere river pathways. Despite the fact that such changes may significantly alter the freshwater input to the ocean, modified
surface hydrology has never been accounted for in coupled ocean–atmosphere general circulation model simulations of the LGM
climate. To reconstruct the LGM river routing, we use the ICE-5G LGM topography. Because of the uncertainties in the extent
of the Fennoscandian ice sheet in the Eastern part of the Kara Sea, we consider two more realistic river routing scenarios.
The first scenario is characterised by the presence of an ice dammed lake south of the Fennoscandian ice sheet, and corresponds
to the ICE-5G topography. This lake is fed by the Ob and Yenisei rivers. In the second scenario, both these rivers flow directly
into the Arctic Ocean, which is more consistent with the latest QUEEN ice sheet margin reconstructions. We study the impact
of these changes on the LGM climate as simulated by the IPSL_CM4 model and focus on the overturning thermohaline circulation.
A comparison with a classical LGM simulation performed using the same model and modern river basins as designed in the PMIP2
exercise leads to the following conclusions: (1) The discharge into the North Atlantic Ocean is increased by 2,000 m3/s between 38° and 54°N in both simulations that contain LGM river routing, compared to the classical LGM experiment. (2)
The ice dammed lake is shown to have a weak impact, relative to the classical simulation, both in terms of climate and ocean
circulation. (3) In contrast, the North Atlantic deep convection and meridional overturning are weaker than during the classical
LGM run if the Ob and Yenisei rivers flow directly into the Arctic Ocean. The total discharge into the Arctic Ocean is increased
by 31,000 m3/s, relative to the classical LGM simulation. Consequentially, northward ocean heat transport is weaker, and sea ice more
extensive, in better agreement with existing proxy data. 相似文献
9.
Gareth S. Jones Jonathan M. Gregory Peter A. Stott Simon F. B. Tett Robert B. Thorpe 《Climate Dynamics》2005,25(7-8):725-738
Volcanic ‘super-eruptions’ have been suggested to have significantly influenced the Earth’s climate, perhaps causing glaciations
and impacting on the human population. Climatic changes following a hypothetical ‘super-eruption’ are simulated using a coupled
atmosphere ocean general circulation model, incorporating scaled volcanic stratospheric aerosols. Assumptions are made about
the stratospheric sulphate aerosol loading, size distribution, lifetime, chemical make up and spatial distribution. As this
study is concentrating on the physical climatological impacts over long timescales, microphysics and chemical interactive
processes are not simulated. Near-surface temperatures fall by as much as 10 K globally for a few months and a considerable
deviation from normal temperatures continues for several decades. A warming pattern is evident over northern land masses during
the winter due to increased longwave forcing and a positive AO mode. The overturning rate of the North Atlantic thermohaline
circulation doubles in intensity. Snow and ice increases in extent to a maximum coverage of 35% of the Earth. Despite these
and other impacts longer term climatic changes that could lead to a transition to a glaciation do not occur, for present day
boundary conditions and one possible plausible aerosol loading. 相似文献
10.
H.-S. Liu 《Theoretical and Applied Climatology》1998,61(3-4):217-229
Summary For astronomical seasons, Rubincam insolation deviations at latitude 65° N varied from 218.50 Wm−2 to 225.75 Wm−2 (3%). The periodicity of the insolation cycles varied from 36.7 Kyr to 44.7 Kyr (20%) due to phase shift. Phase shift of
insolation variations can induce asymmetry of the insolation cycles, permitting rapid melting and prolonged glaciation of
ice sheets to occur. For instance, an abnormal decrease of the insolation frequency during the longer period of glacial interval
would prolong glaciation into deep ice age. In this study, we apply Rubincam’s insolation equations to investigate the phase
shift effect of insolation variations on climate change. Using complex transforms of the changing insolation, we have detected
a phase modulation signal in the insolation variations. As a result, an especially new and interesting series of the phase-related
insolation pulsation is established. The phase modulated insolation is then introduced as a forcing function into energy balance
climate models. Results of model computations shed new insights into the spectrum of the paleoclimatic proxy-data. It is shown
that phase modulation of the insolation may provide an appropriate and complete external forcing mechanism to which the climate
system would respond. The 100 Kyr cycle of the frequency modulation of the Rubincam’s insolation variations does seem adequate
to change the climate.
Received July 16, 1997 Revised May 18, 1998 相似文献
11.
The effect of snow on Antarctic sea ice simulations in a coupled atmosphere-sea ice model 总被引:1,自引:0,他引:1
The effect of a snow cover on sea ice accretion and ablation is estimated based on the ‘zero-layer’ version sea ice model
of Semtner, and is examined using a coupled atmosphere-sea ice model including feedbacks and ice dynamics effects. When snow
is disregarded in the coupled model the averaged Antarctic sea ice becomes thicker. When only half of the snowfall predicted
by the atmospheric model is allowed to land on the ice surface sea ice gets thicker in most of the Weddell and Ross Seas but
thinner in East Antarctic in winter, with the average slightly thicker. When twice as much snowfall as predicted by the atmospheric
model is assumed to land on the ice surface sea ice also gets much thicker due to the large increase of snow-ice formation.
These results indicate the importance of the correct simulation of the snow cover over sea ice and snow-ice formation in the
Antarctic. Our results also illustrate the complex feedback effects of the snow cover in global climate models. In this study
we have also tested the use of a mean value of 0.16 Wm-1 K-1 instead of 0.31 for the thermal conductivity of snow in the coupled model, based on the most recent observations in the eastern
Antarctic and Bellingshausen and Amundsen Seas, and have found that the sea ice distribution changes greatly, with the ice
becoming much thinner by about 0.2 m in the Antarctic and about 0.4 m in the Arctic on average. This implies that the magnitude
of the thermal conductivity of snow is of considerable importance for the simulation of the sea ice distribution. An appropriate
value of the thermal conductivity of snow is as crucial as the depth of the snow layer and the snowfall rate in a sea ice
model. The coupled climate models require accurate values of the effective thermal conductivity of snow from observations
for validating the simulated sea ice distribution under the present climate conditions.
Received: 20 November 1997/Accepted: 27 July 1998 相似文献
12.
The relationship between winter sea ice variability and the North Atlantic Oscillation (NAO) is examined for the time period
1860–2300. This study uses model output to extend recently reported observational results to multi-century time scales. Nine
ensemble members are used in two Global Climate Models with forcing evolving from pre-industrial conditions through the so-called
A1B scenario in which carbon dioxide stabilizes at 720 ppm by 2100. Throughout, the NAO generates an east-west dipole pattern
of sea ice concentration (SIC) anomalies with oppositely signed centers of action over the Labrador and Barents Seas. During
the positive polarity of the NAO, SIC increases over the Labrador Sea due to wind-driven equatorward advection of ice, and
SIC decreases over the Barents Sea due to wind-driven poleward transport of heat within the mixed layer of the ocean. Although
this NAO-driven SIC variability pattern can always be detected, it accounts for a markedly varying fraction of the total sea
ice variability depending on the strength of the forced sea ice extent trend. For the first half of the 20th century or 1990
control conditions, the NAO-driven SIC pattern accounts for almost a third of the total SIC variance. In the context of the
long term winter sea ice retreat from 1860 to 2300, the NAO-driven SIC pattern is robustly observable, but accounts for only
2% of the total SIC variance. The NAO-driven SIC dipole retreats poleward with the retreating marginal ice zone, and its Barents
Sea center of action weakens. Results presented here underscore the idea that the NAO’s influence on Arctic climate is robustly
observable, but time dependent in its form and statistical importance. 相似文献
13.
Based on dynamical energy transport and thermodynamic energy balance in the earth’s atmosphere-ocean system a steady two-dimensional climate model with residual circulation is proposed. In the model, we include some important physical processes with feedbacks such as ice caps-albedo, water vapor-tempera-ture, etc. The simulated steady temperature field is very close to that of the real atmosphere. The numerical experiments show that doubling of the atmospheric carbon dioxide results in temperature increase of 1~2oC at the low latitude surface and 6~8oC at the high latitude surface. It is shown that a 6% decrease in the solar constant is required for the -10oC ice edge to move from its present latitude ~70o to~50o. 相似文献
14.
Relationships between the ice cover thickness alimentation and negative temperatures sums are defined for several ice profiles in the Votkinsk reservoir. Possibility of their using for the ice cover thickness forecasting is considered. Criteria of the acceptable errors of the ice cover forecasts and computations are studied. A new way of their improvement is proposed. 相似文献
15.
Abstract A coupled ice, ocean model for forecasting ice conditions on the Newfoundland shelf region is assessed by comparing hindcasts with satellite‐tracked ice beacon displacements and with changes in offshore ice edge location, ice thickness and southern ice extent derived from ice charts. The beacon velocity fields contain short timescale fluctuations which are not resolved by the model. The ratio of rms displacement error divided by the rms beacon displacement is 0.48 after 1 day and 0.23 after 8 days. The decrease in the scaled displacement error with increasing time is related to the short timescale motions. The skill in modelling displacement of the offshore ice edge is lower than in modelling ice displacement. Between mid‐February and mid‐April 1997, the effect of ice melt on the ice edge was a mean onshore displacement of 35 km overcoming an offshore advection of 24 km in 5 days. 相似文献
16.
We investigate the causes for a strong high latitude imposed ice (land or sea) influence on the marine Intertropical Convergence
Zone (ITCZ) in the Community Climate Model version 3 coupled to a 50-m slab ocean. The marine ITCZ in all the ocean basins
shift meridionally away from the hemisphere with an imposed added ice cover, altering the global Hadley circulation with an
increased tropical subsidence in the hemisphere with imposed ice and uplift in the other. The effect appears to be independent
of the longitudinal position of imposed ice. The anomalous ice induces a rapid cooling and drying of the air and surface over
the entire high- and midlatitudes; subsequent progression of cold anomalies occurs in the Pacific and Atlantic northeasterly
trade regions, where a wind-evaporation-sea surface temperature (SST) feedback initiates progression of a cold SST ‘front’
towards the ITCZ latitudes. Once the cooler SST reaches the ITCZ latitude, the ITCZ shifts southwards, aided by positive feedbacks
associated with the displacement. The ITCZ displacement transports moisture away from the colder and drier hemisphere into
the other hemisphere, resulting in a pronounced hemispheric asymmetric response in anomalous specific humidity; we speculate
that the atmospheric humidity plays a central role in the hemispheric asymmetric nature of the climate response to high latitude
ice cover anomalies. From an energy balance viewpoint, the increased outgoing radiative flux at the latitudes of the imposed
ice is compensated by an increased radiative energy flux at the tropical latitudes occupied by the displaced ITCZ, and subsequently
transported by the altered Hadley and eddy circulations to the imposed ice latitudes. The situation investigated here may
be applicable to past climates like the Last Glacial Maximum where hemispheric asymmetric changes to ice cover occurred. Major
caveats to the conclusions drawn include omission of interactive sea ice physics and ocean dynamical feedback and sensitivity
to atmospheric physics parameterizations across different models. 相似文献
17.
Long-term variations of ice formation dates are studied using the long (more than 100 years) series of observations of ice regime on the rivers of the Votkinsk Reservoir catchment. Proposed is the methodological approach to assessing the long-term variability of these dates using both parametric and nonparametric statistical criteria. 相似文献
18.
Lazar Lazić 《Meteorology and Atmospheric Physics》2000,75(1-2):121-130
Summary Following a recent approach of Fox-Rabinovitz an iterative Matsuno or a “Super-Matsuno” style scheme is applied as a filter
in the Eta Model. In contrast to Fox-Rabinovitz, we however apply the scheme not for all of the model’s time-differencing
but for its adjustment terms only. These distinctions compared to the original Fox-Rabinovitz’-method are made easy to implement
by the split time differencing approach of the Eta, and at the same time would appear clearly appropriate for the “initialization”
purpose. In addition, while Fox-Rabinovitz emphasizes the use of the method within a long time-scale data assimilation framework,
we are focusing on the impact of the method in a short-range forecasting environment/time-scale.
After a short one hour “initialization” procedure is completed, standard model integration is continued, now very much free
of noise. The Super-Matsuno style scheme is found to balance initially unbalanced external and internal modes and to significantly
reduce the high-frequency noise during the first 6 time steps. In a control case noise also reduces in amplitude as integration
proceeds, but at a much slower rate. The model integration results with and without “initialization” after 6 hours are however
very similar. Even so, it is to be expected that small differences, given that they have resulted from the removal of spurious
initial noise, have to be beneficial.
Received July 5, 1999/Revised January 11, 2000 相似文献
19.
V. S. Tambovskii E. A. Tikhonchuk G. V. Shevchenko 《Russian Meteorology and Hydrology》2010,35(3):197-205
The ice drift data obtained with the Furuno radar using a special methodology simultaneously at seven fixed points around
the Molikpaq oil-drilling platform on the northeastern shelf of Sakhalin Island in the period from May 14 to 28, 2003 are
analyzed. It is shown that at different distances from the shore significant variations are observed both in the alongshore
and, especially, transverse components of the tidal seaice drift, which are responsible for the ice cover deformation, whose
indices are of a substantial magnitude. The divergence has the maximum positive values (the ice opening is observed) at comparatively
low drift velocities of southern bearings soon after the tidal flow direction changed. The ice cover compression was accordingly
observed under opposite conditions. The dependence of deformation indices on the tidal cycle phase is well agreed with the
results earlier obtained at the coastal Odoptu radar station (RS), where the measurements were carried out using a similar
methodology under alike physico-geographic conditions. A steady character of the results obtained allows forecasting the tide-induced
ice cover extension and compression, which is of a practical value for providing the ship operations in the region of the
Molikpaq platform in the ice season. 相似文献
20.
L. Chapman J. E. Thornes Y. Huang X. Cai V. L. Sanderson S. P. White 《Theoretical and Applied Climatology》2008,92(1-2):121-131
Summary Variations in rail temperature are responsible for a large proportion of weather related delays on the rail network. Tracks
are pre-stressed to withstand a specified range of temperature, but once the range is breached the rail can distort causing
tension cracks in cold weather and buckling in hot weather. Currently, blanket speed restrictions are imposed at certain temperature
thresholds to ensure passenger safety. This paper discusses the measurement and modelling of rail temperature data at both
a specially constructed test track and a ‘live’ main-line track. Although, empirical techniques are presently used to derive
rail temperatures from air temperatures, this approach is limited as it fails to take into account other ambient weather conditions.
To address this, a road weather model was converted to model the energy balance of a rail. This enables rail temperatures
to be forecasted for the entire diurnal cycle and at a variety of synoptic conditions. The physical model shows significant
forecasting ability, outperforming empirical techniques with a mean bias of 0.2 °C (RMSE = 2.56°) for a 200 day measurement
campaign.
Authors’ address: L. Chapman, J. E. Thornes, Y. Huang, X. Cai, V. L. Sanderson, S. P. White, Entice Technology Ltd, School
of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham B15 2TT, U.K. 相似文献