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1.
The ocean response to surface temperature transients is simulated with the use of the Hamburg large-scale geostrophic (LSG) ocean general circulation model (OGCM). The transition, from the present to a climate corresponding to a doubling of the atmospheric CO2 content, is compared with the reversed transition. For the Atlantic, the time scale for the deep ocean to adjust to the temperature changes was similar for both transitions. In the Pacific, the time scale is shorter for the present to warm transition than for the reverse case, a result of increased production of Antarctic bottom water (AABW) during the warm climate. While the transition from cold to warm climate shows no secular variability, the reversed transition generates considerable variability on time scales of 300–400 years. For the warm climate, oscillations with periods of 45 years are found in the Southern Ocean. Results of principal oscillation pattern (POP) analysis indicate that these oscillations are due to interaction between convection in the Southern Ocean and advected salinity anomalies in the Antarctic Circumpolar Current (ACC) and the Southern Pacific Ocean. Received: 19 September 1995 / Accepted: 15 March 1996  相似文献   

2.
A global, flux-corrected climate model is employed to predict the surface wind stress and associated wind-driven oceanic circulation for climate states corresponding to a doubling and quadrupling of the atmospheric CO2 concentration in a simple 1% per year CO2 increase scenario. The model indicates that in response to CO2 increase, the position of zero wind stress curl in the mid-latitudes of the Southern Hemisphere shifts poleward. In addition, the wind stress intensifies significantly in the mid-latitudes of the Southern Hemisphere. As a result, the rate of water circulation in the subpolar meridional overturning cell in the Southern Ocean increases by about 6 Sv (1 Sv=106 m3 s−1) for doubled CO2 and by 12 Sv for quadrupled CO2, implying an increase of deep water upwelling south of the circumpolar flow and an increase of Ekman pumping north of it. In addition, the changes in the wind stress and wind stress curl translate into changes in the horizontal mass transport, leading to a poleward expansion of the subtropical gyres in both hemispheres, and to strengthening of the Antarctic Circumpolar Current. Finally, the intensified near-surface winds over the Southern Ocean result in a substantial increase of mechanical energy supply to the ocean general circulation.  相似文献   

3.
The effect of idealized wind-driven circulation changes in the Southern Ocean on atmospheric CO2 and the ocean carbon inventory is investigated using a suite of coarse-resolution, global coupled ocean circulation and biogeochemistry experiments with parameterized eddy activity and only modest changes in surface buoyancy forcing, each experiment integrated for 5,000 years. A positive correlation is obtained between the meridional overturning or residual circulation in the Southern Ocean and atmospheric CO2: stronger or northward-shifted westerly winds in the Southern Hemisphere result in increased residual circulation, greater upwelling of carbon-rich deep waters and oceanic outgassing, which increases atmospheric pCO2 by ～20 μatm; weaker or southward-shifted winds lead to the opposing result. The ocean carbon inventory in our model varies through contrasting changes in the saturated, disequilibrium and biogenic (soft-tissue and carbonate) reservoirs, each varying by O(10–100) PgC, all of which contribute to the net anomaly in atmospheric CO2. Increased residual overturning deepens the global pycnocline, warming the upper ocean and decreasing the saturated carbon reservoir. Increased upwelling of carbon- and nutrient-rich deep waters and inefficient biological activity results in subduction of unutilized nutrients into the ocean interior, decreasing the biogenic carbon reservoir of intermediate and mode waters ventilating the Northern Hemisphere, and making the disequilibrium carbon reservoir more positive in the mode waters due to the reduced residence time at the surface. Wind-induced changes in the model carbon inventory are dominated by the response of the global pycnocline, although there is an additional abyssal response when the peak westerly winds change their latitude, altering their proximity to Drake Passage and changing the depth extent of the southward return flow of the overturning: a northward shift of the westerly winds isolates dense isopycnals, allowing biogenic carbon to accumulate in the deep ocean of the Southern Hemisphere, while a southward shift shoals dense isopycnals that outcrop in the Southern Ocean and reduces the biogenic carbon store in the deep ocean.  相似文献   

4.
The atmospheric circulation patterns in the Southern Hemisphere have had a significant impact on the climate of the Antarctic and there is much evidence that these circulation patterns have changed in the recent past. This change is thought to have contributed to the warming trend observed at the Antarctic Peninsula over the last 50 years—one of the largest trends observed in this period on the planet. The trends associated with the continental Antarctic climate are less clear but are likely to be impacted less directly by atmospheric circulation changes. The circulation changes can be put into the context of longer timescales by considering atmospheric circulation reconstructions that have been performed using data from Antarctic ice cores. In this review paper we look at the main body of work examining: Antarctic climate trends; the understanding and impact of atmospheric circulation of the mid- to high-latitudes of the Southern Hemisphere; and the usefulness and reliability of atmospheric circulation reconstructions from Antarctic ice core data. Finally, beyond several of the more quantitative reconstructions, it is deemed that an assessment of their consistency is not possible due to the variety of circulation characteristics that the various reconstructions consider.  相似文献   

5.
Joel Gunn 《Climatic change》1991,19(4):393-420
Consistent, accurate, and numerous measures of global scale atmospheric variables have been collected since about 1958. A time series of 30 years duration was assembled to investigate contributing factors to the global energy balance. The El Nino-Southern Oscillation (ENSO), CO2 changes, and variation in solar energy output account for a quarter or more each of the variability in global energy balance. Upper atmospheric aerosols contribute, but less significantly and in a more complex way. The analysis suggests a hypothesis that has bearing on global climatic stability. Global climate fortuitously passed through a shift from a warmer NH to a warmer SH during the study period. The ENSO appears to act as a hemispheric energy balancing mechanism. There were significant changes in global atmospheric function when the hemispheric energy balance shifted in favor of the Southern Hemisphere about 1966. When applied to past climates, hemispheric dominance of global climate and related patterns of periodic stability could explain the rise and fall of some complex hierarchical social systems.  相似文献   

6.
Results are first presented from an analysis of a global coupled climate model regarding changes in future mean and variability of south Asian monsoon precipitation due to increased atmospheric CO2 for doubled (2 × CO2) and quadrupled (4 × CO2) present-day amounts. Results from the coupled model show that, in agreement with previous studies, mean area-averaged south Asian monsoon precipitation increases with greater CO2 concentrations, as does the interannual variability. Mechanisms producing these changes are then examined in a series of AMIP2-style sensitivity experiments using the atmospheric model (taken from the coupled model) run with specified SSTs. Three sets of ensemble experiments are run with SST anomalies superimposed on the AMIP2 SSTs from 1979–97: (1) anomalously warm Indian Ocean SSTs, (2) anomalously warm Pacific Ocean SSTs, and (3) anomalously warm Indian and Pacific Ocean SSTs. Results from these experiments show that the greater mean monsoon precipitation is due to increased moisture source from the warmer Indian Ocean. Increased south Asian monsoon interannual variability is primarily due to warmer Pacific Ocean SSTs with enhanced evaporation variability, with the warmer Indian Ocean SSTs a contributing but secondary factor. That is, for a given interannual tropical Pacific SST fluctuation with warmer mean SSTs in the future climate, there is enhanced evaporation and precipitation variability that is communicated via the Walker Circulation in the atmosphere to the south Asian monsoon to increase interannual precipitation variability there. This enhanced monsoon variability occurs even with no change in interannual SST variability in the tropical Pacific.  相似文献   

7.
采用NCEP/NCAR再分析资料,定义了1950-2009年菲律宾越赤道气流强度指数,并研究其与南半球大气环流的关系。结果表明,菲律宾越赤道气流受南半球低层极地高压、绕极低压带和中纬度副热带高压,以及高层巨大的绕极低压影响;南半球环流对菲律宾越赤道气流的影响主要是通过南极涛动的调整,对澳大利亚高压产生影响来发挥作用,从南极涛动发生调整到对越赤道气流及北半球环流产生影响,有约4a的时滞;澳大利亚高压强度和位置的变化对菲律宾越越赤道气流有重要影响,关键区位于澳大利亚高压西北方向的洋面上。  相似文献   

8.
The Northern Hemisphere winter (DJF) stationary eddy response of a general circulation model (GCM) to a doubling of atmospheric CO2 is simulated with a linear steady state model as a response to anomalies in diabatic heating (latent, sensible and radiative), mountain and transient eddy effects. For this analysis the doubled CO2 experiment performed by Wilson and Mitchell (1987) is used. The linear simulations of the control and perturbation climate capture most of the important features of the GCMs stationary eddies. The simulation of the anomalous stationary eddy pattern in the Northern Hemisphere captures only some of the important features of the GCMs anomalies. The climate anomalies in the Southern Hemisphere are poorly simulated. In the Northern Hemisphere the climate anomalies are dominated by the effect of transient eddies and mountains. In low latitudes also the contribution of latent heating is important. The contributions of sensible and radiative heating are small.  相似文献   

9.
Four Holocene-long East Antarctic deuterium excess records are used to study past changes of the hydrological cycle in the Southern Hemisphere. We combine simple and complex isotopic models to quantify the relationships between Antarctic deuterium excess fluctuations and the sea surface temperature (SST) integrated over the moisture source areas for Antarctic snow. The common deuterium excess increasing trend during the first half of the Holocene is therefore interpreted in terms of a warming of the average ocean moisture source regions over this time. Available Southern Hemisphere SST records exhibit opposite trends at low latitudes (warming) and at high latitudes (cooling) during the Holocene. The agreement between the Antarctic deuterium excess and low-latitude SST trends supports the idea that the tropics dominate in providing moisture for Antarctic precipitation. The opposite trends in SSTs at low and high latitudes can potentially be explained by the decreasing obliquity during the Holocene inducing opposite trends in the local mean annual insolation between low and high latitudes. It also implies an increased latitudinal insolation gradient that in turn can maintain a stronger atmospheric circulation transporting more tropical moisture to Antarctica. This mechanism is supported by results from a mid-Holocene climate simulation performed using a coupled ocean-atmosphere model. Received: 7 July 1999 / Accepted: 21 July 2000  相似文献   

10.
Jinwon Kim 《Climatic change》2005,68(1-2):153-168
The effects of increased atmospheric CO2 on the frequency of extreme hydrologic events in the Western United States (WUS) for the 10-yr period of 2040–2049 are examined using dynamically downscaled regional climate change signals. For assessing the changes in the occurrence of hydrologic extremes, downscaled climate change signals in daily precipitation and runoff that are likely to indicate the occurrence of extreme events are examined. Downscaled climate change signals in the selected indicators suggest that the global warming induced by increased CO2 is likely to increase extreme hydrologic events in the WUS. The indicators for heavy precipitation events show largest increases in the mountainous regions of the northern California Coastal Range and the Sierra Nevada. Increased cold season precipitation and increased rainfall-portion of precipitation at the expense of snowfall in the projected warmer climate result in large increases in high runoff events in the Sierra Nevada river basins that are already prone to cold season flooding in todays climate. The projected changes in the hydrologic characteristics in the WUS are mainly associated with higher freezing levels in the warmer climate and increases in the cold season water vapor influx from the Pacific Ocean.  相似文献   

11.
Several studies have analysed the atmospheric response to sea-ice changes in the Arctic region, but only few have considered the Antarctic. Here, the atmospheric response to sea-ice variability in the Southern Hemisphere is investigated with the atmospheric general circulation model ECHAM5. The model is forced by the present and a projected future seasonal cycle of Antarctic sea ice. In September, the mean atmospheric response exhibits distinct similarities to the structure of the negative phase of the Southern Annular Mode, the leading mode of Southern Hemisphere variability. In the reduced Antarctic sea-ice integration, there is an equatorward shift of the Southern Hemisphere mid-latitude jet and the storm tracks. In contrast to a recent previous study, our findings indicate that a substantial impact of Southern Hemispheric future sea-ice reduction on the mid-latitude circulation cannot be ruled out.  相似文献   

12.
Results from a suite of 30-year simulations (after spin-up) of the fully coupled Community Climate System Model version 2.0.1 are analyzed to examine the impact of doubling CO2 on interactions between the global water cycle and the regional water cycles of four similar-size, but hydrologically and thermally different study regions (the Yukon, Ob, St Lawrence, and Colorado river basins and their adjacent land). A heuristic evaluation based on published climatological data shows that the model generally produces acceptable results for the control 1× CO2 concentration, except for mountainous regions where it performs like other modern climate models. After doubling CO2, the Northern Hemisphere receives significantly (95% confidence level) more moisture from the Southern Hemisphere during the boreal summer than under 1× CO2 conditions, and the phase of the annual cycle of net moisture transport to areas north of 60°N shifts to a month later than in the reference simulation. Precipitation and evapotranspiration in the doubled CO2 simulation increase for the Yukon, Ob, and St Lawrence, but decrease, on average, for the Colorado region compared to the reference simulation. For all regions, interaction between global and regional water cycles increases under doubled CO2, because the amount of moisture entering and leaving the regions increases in the warmer climate. The degree of change in this interaction depends on region and season, and is related to slight shifts in the position/strength of semi-permanent highs and lows for the Yukon, Ob, and St Lawrence; in the Colorado region, higher temperatures associated with doubling CO2 and the anticyclone located over the region increase the persistence of dry conditions.  相似文献   

13.
We investigate the large-scale oceanic features determining the future ice shelf–ocean interaction by analyzing global warming experiments in a coarse resolution climate model with a comprehensive ocean component. Heat and freshwater fluxes from basal ice shelf melting (ISM) are parameterized following Beckmann and Goosse [Ocean Model 5(2):157–170, 2003]. Melting sensitivities to the oceanic temperature outside of the ice shelf cavities are varied from linear to quadratic (Holland et al. in J Clim 21, 2008). In 1% per year CO2-increase experiments the total freshwater flux from ISM triples to 0.09 Sv in the linear case and more than quadruples to 0.15 Sv in the quadratic case after 140 years at which 4 × 280 ppm = 1,120 ppm was reached. Due to the long response time of subsurface temperature anomalies, ISM thereafter increases drastically, if CO2 concentrations are kept constant at 1,120 ppm. Varying strength of the Antarctic circumpolar current (ACC) is crucial for ISM increase, because southward advection of heat dominates the warming along the Antarctic coast. On centennial timescales the ACC accelerates due to deep ocean warming north of the current, caused by mixing of heat along isopycnals in the Southern Ocean (SO) outcropping regions. In contrast to previous studies we find an initial weakening of the ACC during the first 150 years of warming. This purely baroclinic effect is due to a freshening in the SO which is consistent with present observations. Comparison with simulations with diagnosed ISM but without its influence on the ocean circulation reveal a number of ISM-related feedbacks, of which a negative ISM-feedback, due to the ISM-related local oceanic cooling, is the dominant one.  相似文献   

14.
A multivariate analysis of Antarctic sea ice since 1979   总被引：1，自引：0，他引：1  
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15.
S. J. Kim 《Climate Dynamics》2004,22(6-7):639-651
The role of reduced atmospheric CO2 concentration and ice sheet topography plus its associated land albedo on the LGM climate is investigated using a coupled atmosphere-ocean-sea ice climate system model. The surface cooling induced by the reduced CO2 concentration is larger than that by the ice sheet topography plus other factors by about 30% for the surface air temperature and by about 100% for the sea surface temperature. A large inter-hemispheric asymmetry in surface cooling with a larger cooling in the Northern Hemisphere is found for both cases. This asymmetric inter-hemispheric temperature response is consistent in the ice sheet topography case with earlier studies using an atmospheric model coupled with a mixed-layer ocean representation, but contrasts with these results in the reduced CO2 case. The incorporation of ocean dynamics presumably leads to a larger snow and sea ice feedback as a result of the reduction in northward ocean heat transport, mainly as a consequence of the decrease in the North Atlantic overturning circulation by the substantial freshening of the North Atlantic convection regions. A reversed case is found in the Southern Ocean. Overall, the reduction in atmospheric CO2 concentration accounts for about 60% of the total LGM climate change.  相似文献   

16.
We examined the annual exchange of CO2 between the atmosphere and moist tussock and dry heath tundra ecosystems (which together account for over one-third of the low arctic land area) under ambient field conditions and under increased winter snow deposition, increased summer temperatures, or both. Our results indicate that these two arctic tundra ecosystems were net annual sources of CO2 to the atmosphere from September 1994 to September 1996 under ambient weather conditions and under our three climate change scenarios. Carbon was lost from these ecosystems in both winter and summer, although the majority of CO2 evolution took place during the short summer. Our results indicate that (1) warmer summer temperatures will increase annual CO2 efflux from both moist and dry tundra ecosystems by 45–55% compared to current ambient temperatures; (2) deeper winter snow cover will increase winter CO2 efflux in both moist and dry tundra ecosystems, but will decrease net summer CO2 efflux; and (3) deeper winter snow cover coupled with warmer summer temperatures will nearly double the annual amount of CO2 emitted from moist tundra and will result in a 24% increase in the annual CO2 efflux of dry tundra. If, as predicted, climate change alters both winter snow deposition and summer temperatures, then shifts in CO2 exchange between the biosphere and atmosphere will likely not be uniform across the Arctic tundra landscape. Increased snow deposition in dry tundra is likely to have a larger effect on annual CO2 flux than warmer summer temperatures alone or warmer temperatures coupled with increased winter snow depth. The combined effects of increased summer temperatures and winter snow deposition on annual CO2 flux in moist tundra will be much larger than the effects of either climate change scenario alone.  相似文献   

17.
Increasing concentrations of atmospheric CO2 and other greenhouse gases are expected to contribute to a global warming. This paper examines the potential implications of a climatic change corresponding to a doubling of atmospheric concentrations of CO2 on crop production opportunities throughout Ontario, a major food producing region in Canada. The climate is projected to become warmer and drier, but the extent of these shifts are expected to vary from region to region within Ontario. The effect of this altered climate on crop yields and the area of land capable of supporting specific crops varies according to region, soil quality and crop type. Most notable are the enhanced opportunities for grains and oilseeds in the northern regions, and the diminished production prospects for most crops in the most southerly parts of Ontario.  相似文献   

18.
Abstract

We use eddy life‐cycle simulations to evaluate the response of atmospheric transient eddies to a global warming caused by CO2 doubling in the CCC general circulation model. In simulations using Northern Hemisphere winter conditions, transient waves attain larger kinetic energy and encompass a wider range of latitudes in the warmer climate. This behaviour contrasts with a previous investigation that used output from the NCAR and GFDL models. Our analysis indicates two primary factors for the difference between model responses: (1) a smaller change in the mid‐latitude temperature gradient in the CCC model, which allows (2) increased atmospheric water vapour in mid‐latitudes to catalyze a more rapidly evolving life‐cycle.  相似文献   

19.
A link between the Antarctic sea-ice extent and low-frequency atmospheric variations, particularly ENSO, has been suggested by recent modeling and empirical studies. This question is examined here using a high-resolution (by week, by region) data base of Antarctic sea-ice extent for the 1973–1982 period. Although of relatively short duration by Northern Hemisphere standards, such a data base offers an opportunity rare in Southern Hemisphere climate studies. The seaice variations are examined in the context of longer-term indices of the large-scale atmospheric circulation. These are a Southern Oscillation Index (SOI) and an index of sea-level pressure (SLP) wavenumber one in the Southern Hemisphere extratropics. The indices are updated through 1982, and their associations with regional-scale pressure indices in the Australia-New Zealand sector are also examined. The 1973–1982 period is anomalous when compared with the period 1951–1972. Correlation analysis of the monthly sea ice and circulation index values reveals that much of the apparent link between the ice and the SOI suggested in previous studies arises from autocorrelations present in both data sets and the strong annual cycle of sea-ice extent. Removing these effects from the data and re-running the correlations reveals that most of the resulting significant associations between the ice and one or other of the circulation indices can probably be explained on the basis of chance. In order to reconcile these findings with previous studies that show some strong ice-circulation interactions on regional scales, only those months in which significant correlations occur between both largescale circulation indices and the sea ice are examined further. These occur preferentially in the Ross and Weddell sectors, which constitute the regions contributing most to the variability of Antarctic sea ice. The analysis suggests that the sea-ice-extent changes lag the SOI by several months but may precede changes in extratropical SLP wavenumber one. Confirmation of these tentative regional ice extent-circulation teleconnections necessarily awaits the forward extension of the high-resolution sea-ice data base beyond the 10 years available here.This paper is based on material presented at the Conference on Mechanisms of Interannual and Longer-Term Climatic Variations held at the University of Melbourne, Australia: December 8–12, 1986.  相似文献   

20.
Carbon cycle feedbacks have been shown to be very important in predicting climate change over the next century. The response of the terrestrial carbon cycle to climate change depends on the competition between increased respiration due to warmer temperatures and increased uptake due to elevated CO2levels. Whether the terrestrial carbon cycle remains a sink for anthropogenic carbon, or switches to become a source, depends particularly on the response of soil respiration to temperature. Here we use observed global atmospheric CO2concentration to constrain the behaviour of soil respiration in a coupled climate–carbon cycle GCM.  相似文献   

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