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1.
Simulated variability and trends in Northern Hemisphere seasonal snow cover are analyzed in large ensembles of climate integrations of the National Center for Atmospheric Research’s Community Earth System Model. Two 40-member ensembles driven by historical radiative forcings are generated, one coupled to a dynamical ocean and the other driven by observed sea surface temperatures (SSTs) over the period 1981–2010. The simulations reproduce many aspects of the observed climatology and variability of snow cover extent as characterized by the NOAA snow chart climate data record. Major features of the simulated snow water equivalent (SWE) also agree with observations (GlobSnow Northern Hemisphere SWE data record), although with a lesser degree of fidelity. Ensemble spread in the climate response quantifies the impact of natural climate variability in the presence and absence of coupling to the ocean. Both coupled and uncoupled ensembles indicate an overall decrease in springtime snow cover that is consistent with observations, although springtime trends in most climate realizations are weaker than observed. In the coupled ensemble, a tendency towards excessive warming in wintertime leads to a strong wintertime snow cover loss that is not found in observations. The wintertime warming bias and snow cover reduction trends are reduced in the uncoupled ensemble with observed SSTs. Natural climate variability generates widely different regional patterns of snow trends across realizations; these patterns are related in an intuitive way to temperature, precipitation and circulation trends in individual realizations. In particular, regional snow loss over North America in individual realizations is strongly influenced by North Pacific SST trends (manifested as Pacific Decadal Oscillation variability) and by sea level pressure trends in the North Pacific/North Atlantic sectors.  相似文献   

2.
Greenland ice cores, as well as many other paleo-archives from the northern hemisphere, recorded a series of 25 warm interstadial events, the so-called Dansgaard-Oeschger (D-O) events, during the last glacial period. We use the three-dimensional coupled global ocean–atmosphere–sea ice model ECBILT-CLIO and force it with freshwater input into the North Atlantic to simulate abrupt glacial climate events, which we use as analogues for D-O events. We focus our analysis on the Northern Hemisphere. The simulated events show large differences in the regional and seasonal distribution of the temperature and precipitation changes. While the temperature changes in high northern latitudes and in the North Atlantic region are dominated by winter changes, the largest temperature increases in most other land regions are seen in spring. Smallest changes over land are found during the summer months. Our model simulations also demonstrate that the temperature and precipitation change patterns for different intensifications of the Atlantic meridional overturning circulation are not linear. The extent of the transitions varies, and local non-linearities influence the amplitude of the annual mean response as well as the response in different seasons. Implications for the interpretation of paleo-records are discussed.  相似文献   

3.
Results from a two-dimensional energy balance model with a realistic land-ocean distribution show that the small ice cap instability exists in the Southern Hemisphere, but not in the Northern Hemisphere. A series of experiments with a one-dimensional energy balance model with idealized geography are used to study the roles of the seasonal cycle and the land-ocean distribution. The results indicate that the seasonal cycle and land-ocean distribution can influence the strength of the albedo feedback, which is responsible for the small ice cap instability, through two factors: the temperature gradient and the amplitude of the seasonal cycle. The land-ocean distribution in the Southern Hemisphere favors the small ice cap instability, while the land-ocean distribution in the Northern Hemisphere does not. Because of the longitudinal variations of land-ocean distribution in the Northern Hemisphere, the behavior of ice lines in the Northern Hemisphere cannot be simulated and explained by the model with zonally symmetric land-ocean distribution. Model results suggest that the small ice cap instability may be a possible mechanism for the formation of the Antarctic icesheet. The model results cast doubt, however, on the role of the small ice cap instability in Northern Hemisphere glaciations. Offprint requests to: J Huang  相似文献   

4.
The Chinese Academy of Meteorological Sciences Climate System Model (CAMS-CSM) is a newly developed global climate model that will participate in the Coupled Model Intercomparison Project phase 6. Based on historical simulations (1900?2013), we evaluate the model performance in simulating the observed characteristics of the Arctic climate system, which includes air temperature, precipitation, the Arctic Oscillation (AO), ocean temperature/salinity, the Atlantic meridional overturning circulation (AMOC), snow cover, and sea ice. The model?data comparisons indicate that the CAMS-CSM reproduces spatial patterns of climatological mean air temperature over the Arctic (60°?90°N) and a rapid warming trend from 1979 to 2013. However, the warming trend is overestimated south of the Arctic Circle, implying a subdued Arctic amplification. The distribution of climatological precipitation in the Arctic is broadly captured in the model, whereas it shows limited skills in depicting the overall increasing trend. The AO can be reproduced by the CAMS-CSM in terms of reasonable patterns and variability. Regarding the ocean simulation, the model underestimates the AMOC and zonally averaged ocean temperatures and salinity above a depth of 500 m, and it fails to reproduce the observed increasing trend in the upper ocean heat content in the Arctic. The large-scale distribution of the snow cover extent (SCE) in the Northern Hemisphere and the overall decreasing trend in the spring SCE are captured by the CAMS-CSM, while the biased magnitudes exist. Due to the underestimation of the AMOC and the poor quantification of air–sea interaction, the CAMS-CSM overestimates regional sea ice and underestimates the observed decreasing trend in Arctic sea–ice area in September. Overall, the CAMS-CSM reproduces a climatological distribution of the Arctic climate system and general trends from 1979 to 2013 compared with the observations, but it shows limited skills in modeling local trends and interannual variability.  相似文献   

5.
北极海冰面积变化与大气遥相关型   总被引：4，自引：0，他引：4  
蒋全荣  王春红 《气象科学》1995,15(4):158-165
本文综述了北极海注面积变化与大气遥相关型研究工作中的一些主要结果。诊断分析表明，北极海冰面积变化具有３－４年的振荡周期，大气中的遥相关型不仅与海冰面积变化的区域有关，还与海冰面积的振荡频率有关。海冰面积变化与大气遥相关型是互相维持的，一方的加强有利于另一方的加强，本文最后还对北极海冰和赤道中，东太平洋海温对北半年冬半年中纬度大气环流影响的相似性等问题进行了讨论。  相似文献   

6.
BCC_CSM对全球海冰面积和厚度模拟及其误差成因分析   总被引：3，自引：0，他引：3  
本文评估了国家气候中心发展的BCC_CSM模式对全球海冰的模拟能力,结果表明:该气候系统模式能够较好地模拟出全球海冰面积和厚度的时空分布特征,且南半球海冰模拟能力优于北半球。通过对比分析发现:年平均海冰面积模拟误差最大的区域位于鄂霍次克海、白令海和巴伦支海等海区,年平均海冰厚度分布与观测相近,在北半球冬季模拟的厚度偏薄;从海冰季节变化来看,模拟的夏季海冰面积偏低,冬季偏高;从海冰年际变化来看,近60年南北半球海冰面积模拟都比观测偏多,但南半球偏多幅度较小,然而北半球海冰年际变化趋势的模拟却好于南半球。另外,通过对海冰模拟误差成因分析,发现模拟的净辐射能量收入偏低使得海温异常偏冷,是导致北半球冬季海冰模拟偏多的主要原因。  相似文献   

7.
l.Introducti0nTheclimateformationandvariabilityisnotonlythereflectionofatmosphericinternalbe-havi0rbutalsotheinnuencefromtheinteractionexistSintheclimatesystem.Becausetherela-tivecooIingandheatingsourcesofatmospherearelocatedinthePOlarandtropicalregionrespectively,itiseasytounderstandthattheArcticseaicecoverandSSTanomalieswhichim-pocttheatmosphericheatingtosomeextentcanexerttheirinfluenceontheremotCatmosphericcirculation-Inthisregard,thefocusrelatedtheinflueneeofArcticseaicecoverandtropica…  相似文献   

8.
Emphasizing the model‘s ability in mean climate reproduction in high northern latitudes, resultsfrom an ocean-sea ice-atmosphere coupled model are analyzed. It is shown that the coupled model cansimulate the main characteristics of annual mean global sea surface temperature and sea level pressurewell, but the extent of ice coverage produced in the Southern Hemisphere is not large enough. The maindistribution characteristics of simulated sea level pressure and temperature at 850 hPa in high northernlatitudes agree well with their counterparts in the NCEP reanalysis dataset, and the model can reproducethe Arctic Oscillation (AO) mode successfully. The simulated seasonal variation of sea ice in the NorthernHemisphere is rational and its main distribution features in winter agree well with those from observations.But the ice concentration in the sea ice edge area close to the Eurasian continent in the inner Arctic Oceanis much larger than the observation. There are significant interannual variation signals in the simulated seaice concentration in winter in high northern latitudes and the most significant area lies in the GreenlandSea, followed by the Barents Sea. All of these features agree well with the results from observations.  相似文献   

9.
Interannual and seasonal variability of regional distribution of Antarctic sea ice extent is studied using monthly mean data on sea ice concentration in 1970-2012. The correlation is estimated between the variations in the area of floating ice in West and East Antarctica as well as in the Atlantic, Pacific, and Indian sectors of the Southern Ocean and the indices of atmospheric circuiation in the Southern Hemisphere.  相似文献   

10.
In this research, we studied the effects of black carbon (BC) aerosol radiative forcing on seasonal variation in the Northern Hemisphere (NH) using numerical simulations with the NASA finite-volume General Circulation Model (fvGCM) forced with monthly varying three-dimensional aerosol distributions from the Goddard Ozone Chemistry Aerosol Radiation and Transport Model (GOCART). The results show that atmospheric warming due to black carbon aerosols subsequently warm the atmosphere and land surfaces, especially those over Eurasia. As a result, the snow depth in Eurasia was greatly reduced in late winter and spring, and the reduction in snow cover decreased the surface albedo. Our surface energy balance analysis shows that the surface warming due to aerosol absorption causes early snow melting and further increases surface-atmosphere warming through snow/ice albedo feedback. Therefore, BC aerosol forcing may be an important factor affecting the snow/ice albedo in the NH.  相似文献   

11.
Conflicting results have been presented regarding the link between Arctic sea-ice loss and midlatitude cooling, particularly over Eurasia. This study analyzes uncoupled(atmosphere-only) and coupled(ocean–atmosphere) simulations by the Climate Forecast System, version 2(CFSv2), to examine this linkage during the Northern Hemisphere winter, focusing on the simulation of the observed surface cooling trend over Eurasia during the last three decades. The uncoupled simulations are Atmospheric Model Intercomparison Project(AMIP) runs forced with mean seasonal cycles of sea surface temperature(SST)and sea ice, using combinations of SST and sea ice from different time periods to assess the role that each plays individually,and to assess the role of atmospheric internal variability. Coupled runs are used to further investigate the role of internal variability via the analysis of initialized predictions and the evolution of the forecast with lead time.The AMIP simulations show a mean warming response over Eurasia due to SST changes, but little response to changes in sea ice. Individual runs simulate cooler periods over Eurasia, and this is shown to be concurrent with a stronger Siberian high and warming over Greenland. No substantial differences in the variability of Eurasian surface temperatures are found between the different model configurations. In the coupled runs, the region of significant warming over Eurasia is small at short leads, but increases at longer leads. It is concluded that, although the models have some capability in highlighting the temperature variability over Eurasia, the observed cooling may still be a consequence of internal variability.  相似文献   

12.
在以前工作的基础上,本文进一步分析了各个季节北方涛动和与其相联系的北太平洋海温同北半球温带大气环流遥相关的特征,并与南方涛动和赤道太平洋海温的结果进行了比较,发现它们同北半球温带大气环流的遥相关,不仅具有很强的地区性,而且具有明显的季节变化。 冬季,北方涛动和北太平洋海温与PNA型相关非常明显,且比南方涛动和赤道太平洋海温的更密切。除PNA型外,北方涛动还同500hPa高度的亚洲-北美(ANA)流型有联系。 夏季,PNA遥相关型的表现仍然非常清楚,但位置较冬季偏酉和偏北,并在北美西海岸具有特殊的分叉现象。  相似文献   

13.
By the utilization of monthly precipitation data from all stations in the Northern Hemisphere annexed to the “World Survey of climatology, Vol. 1-15, the distributions of the maximum precipitation months (MPM), the annual relative precipitation (ARP) and the monthly relative precipitation (percent of annual) in January and July are respectively mapped. Moreover the distributions of intermonthly relative precipitation variabilities from January to December are plotted as well. From these figures, the precipitation in the Northern Hemisphere may be classified into three types (continental, oceanic and transitional types) and 17 regions. The precipitation regime may also be divided into two patterns, the global and regional patterns. The global pattern consists of planetary front system and ITCZ and its inter-monthly variation shows the north-and-south shift of the rain belt; the regional pattern consists of the sea-land monsoon and plateau monsoon regime, in which the inter-monthly variation of rain belt shows a east- and-west shift.  相似文献   

14.
This work examines the near-surface responses, in the Southern Hemisphere atmosphere, to a reduction and an excess of sea ice cover in the Ross Sea. Large ensembles (60 members) of the Atmospheric General Circulation Model of the Center for Weather Forecast and Climate Studies (AGCM-CPTEC) are used for this purpose. Locally, when the sea ice cover decreases (increases), heat fluxes, temperature, and pressure increase (decreases). A principal component analysis of temperature and geopotential height identifies the potential remote connections. We have found three main results: first, an association between the sea ice cover in the Ross Sea and a wave train that resembles the Pacific South American (PSA) pattern; second, a relationship between temperatures in the Ross Sea and in the southern South America; and third, an apparent correspondence between reduced sea ice cover in the Ross Sea and the subtropical jet over Australia.  相似文献   

15.
Declining sea ice area in the Canadian Arctic has gained significant attention with respect to the prospect of increased shipping activities. To investigate relationships between recent declines in sea ice area with Arctic maritime activity, trend and correlation analysis was performed on sea ice area data for total, first-year ice (FYI), and multi-year ice (MYI), and on a comprehensive shipping dataset of observed vessel transits through the Vessel Traffic Reporting Arctic Canada Traffic Zone (NORDREG zone) from 1990 to 2012. Links to surface air temperature (SAT) and the satellite derived melt season length were also investigated. Between 1990 and 2012, statistically significant increases in vessel traffic were observed within the NORDREG zone on monthly and annual time-scales coincident with declines in sea ice area (FYI, MYI, and total ice) during the shipping season and on a monthly basis. Similarly, the NORDREG zone is experiencing increased shoulder season shipping activity, alongside an increasing melt season length and warming surface air temperatures (SAT). Despite these trends, only weak correlations between the variables were identified, although a step increase in shipping activity is apparent following the former summer sea ice extent minimum in 2007. Other non-environmental factors have also likely contributed to the observed increase in Arctic shipping activity within the Canadian Arctic, such as tourism demand, community re-supply needs, and resource exploration trends.  相似文献   

16.
The monthly and seasonal anomalies of temperature and precipitation over the Arctic are considered depending on the global and regional patterns of atmospheric circulation. Ñlimate indices are used to identify patterns. The composite analysis allowed identifying the geographic regions where the influence of atmospheric circulation modes on temperature and precipitation is statistically significant. The contingency of atmospheric circulation patterns in the Northern Hemisphere was statistically estimated. Special attention is paid to the case studies where the extreme episodes of circulation indices are associated with the significant anomalies of air temperature and precipitation. The potential is demonstrated of the numerical simulation of extreme episodes on monthly and seasonal timescales with the global semi-Lagrangian model SL-AV developed in the Institute of Numerical Mathematics jointly with the Hydrometcenter of Russia.  相似文献   

17.
利用1948—2010年NCEP/NCAR逐月位势高度再分析资料、美国国家海洋局提供的1948—2010年逐月海温再分析资料,分别定义了1 000—500 hPa和500—200 hPa厚度,利用EOF、SVD等方法研究了北半球对流层厚度时空演变特征及其与大气环流和海面温度的关系。结果表明,冬季平均厚度EOF第一模态均具有北太平洋及附近高纬度亚洲大陆地区与北美大陆高纬地区反位相变化的特点,而夏季第一模态则是北半球范围内较一致的位相分布;冬、夏季平均厚度EOF第二模态均突出体现了欧亚大陆及附近地区与北半球其他地区反位相变化的特点;冬、夏季厚度场的变化形势与大气环流及海面温度具有密切联系。  相似文献   

18.
Organic carbon buried under the great ice sheets of the Northern Hemisphere is suggested to be the missing link in the atmospheric CO2 change over the glacial-interglacial cycles. At glaciation, the advancement of continental ice sheets buries vegetation and soil carbon accumulated during warmer pe-riods. At deglaciation, this burial carbon is released back into the atmosphere. In a simulation over two glacial-interglacial cycles using a synchronously coupled atmosphere-land-ocean carbon model forced by reconstructed climate change, it is found that there is a 547-Gt terrestrial carbon release from glacial maximum to interglacial, resulting in a 60-Gt (about 30-ppmv) increase in the atmospheric CO2, with the remainder absorbed by the ocean in a scenario in which ocean acts as a passive buffer. This is in contrast to previous estimates of a land uptake at deglaciation. This carbon source originates from glacial burial,continental shelf, and other land areas in response to changes in ice cover, sea level, and climate. The input of light isotope enriched terrestrial carbon causes atmospheric δ^13C to drop by about 0.3‰ at deglaciation,followed by a rapid rise towards a high interglacial value in response to oceanic warming and regrowth on land. Together with other ocean based mechanisms such as change in ocean temperature, the glacial burial hypothesis may offer a full explanation of the observed 80-100-ppmv atmospheric CO2 change.  相似文献   

19.
The history of early meteorological observations using instruments in the Czech Lands is described (the longest temperature series for Prague-Klementinum starts in 1775, precipitation series for Brno in 1803). Using the PRODIGE method, long-term monthly temperature and precipitation series from selected secular stations were homogenised (for 10 and 12 stations, respectively). All the seasonal and annual temperature series for the common period 1882–2010 show a significant positive linear trend with accelerated warming from the 1970s onwards. No significant linear trends were disclosed in the series of seasonal and annual precipitation totals. Correlation coefficients between the Czech series analysed decrease as distances between measuring stations increase. A sharper decrease of correlations for precipitation totals displays much weaker spatial relationships than those for mean temperatures. The highest correlations between all stations appeared in 1921–1950, the lowest in 1891–1920 (temperature) and 1981–2010 (precipitation). Wavelet analysis reveals that very distinct annual cycles as well as the slightly weaker semi-annual ones are better expressed for temperature series than for precipitation. Statistically significant cycles longer than 1?year are temporally unstable and sporadic for precipitation, while in the temperature series cycles of 7.4–7.7 and 17.9–18.4?years were recorded as significant by all stations in 1882–2010 (quasi-biennial cycle of 2.1–2.2?years for half the stations). Czech homogenous temperature series correlate best with those of the Northern Hemisphere for annual, spring and summer values (with significant correlation coefficients between 0.60 and 0.70), but this relation is temporally unstable. Circulation indices, such as the North Atlantic Oscillation Index (NAOI) and the Central European Zonal Index (CEZI), may explain the greater part of Czech temperature variability, especially from December to March and for the winter; however, this relationship is much weaker, or even random, for precipitation series. Further, relationships with the Southern Oscillation Index (SOI) are weak and random. Relatively weak coincidences exist between statistically significant cycles in the Czech series and those detected in NAOI, CEZI and SOI series.  相似文献   

20.
南极海冰首要模态呈现偶极子型异常,正负异常中心分别位于别林斯高晋海/阿蒙森海和威德尔海。过去研究表明冬春季节南极海冰涛动异常对后期南极涛动（Antarctic Oscillation,AAO）型大气环流有显著影响,而AAO可以通过经向遥相关等机制影响北半球大气环流和东亚气候。本文中我们利用观测分析发现南极海冰涛动从5～7月（May–July,MJJ）到8～10月（August–October, ASO）有很好的持续性,并进一步分析其对北半球夏季大气环流的可能影响及其物理过程。结果表明,MJJ南极海冰涛动首先通过冰气相互作用在南半球激发持续性的AAO型大气环流异常,使得南半球中纬度和极地及热带之间的气压梯度加大,在MJJ至JAS,纬向平均纬向风呈现显著的正负相间的从南极到北极的经向遥相关型分布。对流层中层位势高度场上,在澳大利亚北部到海洋性大陆区域,出现显著的负异常,在东亚沿岸从低纬到高纬呈现南北走向的“? + ?”太平洋—日本（Pacific–Japan,PJ）遥相关波列,其对应赤道中部太平洋及赤道印度洋存在显著的降水和海温负异常,西北太平洋至我国东部沿海地区存在显著降水正异常和温度负异常;低纬度北美洲到大西洋一带存在的负位势高度异常和北大西洋附近存在的正位势高度异常中心,构成一个类似于西大西洋型遥相关（Western Atlantic,WA）的结构,对应赤道南大西洋降水增加和南撒哈拉地区降水减少。从物理过程来看,南极海冰涛动首先通过局地效应影响Ferrel环流,进而通过经圈环流调整使得海洋性大陆区域和热带大西洋上方的Hadley环流上升支得到增强,海洋性大陆区域特别是菲律宾附近的热带对流活动偏强,激发类似于负位相的PJ波列,影响东亚北太平洋地区的大气环流,而热带大西洋对流增强和北传特征,则通过激发WA遥相关影响大西洋和欧洲地区的大气环流。以上两种通道将持续性MJJ至ASO南极海冰涛动强迫的大气环流信号从南半球中高纬度经热带地区传递到北半球中高纬地区,从而对热带和北半球夏季大气环流产生显著影响。  相似文献   

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