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1.
Two regional climate model experiments for northern and central Europe are studied focussing on greenhouse gas‐induced changes in heavy precipitation. The average yearly maximum one‐day precipitation P max shows a general increase in the whole model domain in both experiments, although the mean precipitation P mean decreases in the southern part of the area, especially in one of the experiments. The average yearly maximum six‐hour precipitation increases even more than the one‐day P max , suggesting a decrease in the timescale of heavy precipitation. The contrast between the P mean and P max changes in the southern part of the domain and the lack of such a contrast further north are affected by changes in wet‐day frequency that stem, at least in part, from changes in atmospheric circulation. However, the yearly extremes of precipitation exhibit a larger percentage increase than the average wet‐day precipitation. The signal‐to‐noise aspects of the model results are also studied in some detail. The 44 km grid‐box‐scale changes in P max are very heavily affected by inter‐annual variability, with an estimated standard error of about 20% for the 10‐year mean changes. However, the noise in P max decreases sharply toward larger horizontal scales, and large‐area mean changes in P max can be estimated with similar accuracy to those in P mean . Although a horizontal averaging of model results smooths out the small‐scale details in the true climate change signal as well, this disadvantage is, in the case of P max changes, much smaller than the advantage of reduced noise. 相似文献
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Sea surface temperature (SST) anomalies associated with El Niño/Southern Oscillation (ENSO) constitute a major source of predictability in the tropics. We evaluate the ability of a regional climate model (the Rossby Centre Atmospheric Model; RCA) to downscale SST and large-scale atmospheric anomalies associated with ENSO. RCA is configured over the tropical east Pacific and tropical Americas and runs for the period 1979–2005, using European Centre for Medium-Range Weather Forecasts (ECMWF) lateral and surface boundary conditions. We study the ability of RCA to represent regional patterns of precipitation, with respect to both the climatology and interannual variability associated with ENSO. The latter is achieved by grouping the simulations into El Niño and La Niña composites and studying the delayed response of precipitation to SST forcing in four regions of Central and South America.
In this paper, we concentrate on seasonal mean timescales. We find that RCA accurately simulates the main features of the precipitation climatology over the four regions and also reproduces the majority of the documented regional responses to ENSO forcing. Furthermore, the model captures the variability in precipitation anomalies between different ENSO events. The model exhibits a wet bias over the northern Amazon and slightly overestimates the magnitude of ENSO anomalies over Central America. 相似文献
In this paper, we concentrate on seasonal mean timescales. We find that RCA accurately simulates the main features of the precipitation climatology over the four regions and also reproduces the majority of the documented regional responses to ENSO forcing. Furthermore, the model captures the variability in precipitation anomalies between different ENSO events. The model exhibits a wet bias over the northern Amazon and slightly overestimates the magnitude of ENSO anomalies over Central America. 相似文献
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What will happen to local record values of temperature and precipitation in a world with ongoing global warming? Here we first examine how many of the observed local temperature maxima of 1901–2006 occurred in the years 2001–2006 and compare the observations with model simulations. Then we study whether, and how soon, the models simulate the climate records of the 20th century to be broken in the ongoing 21st century.
In 27% of our analysis area, the highest annual mean temperatures of the whole period 1901–2006 were observed in 2001–2006. For the 22 climate models in our study, this fraction varies from 17% to 70%, with a multimodel mean of 40%. In simulations based on the SRES A1B emissions scenario, the highest annual mean temperature of the 20th century is exceeded on average in 99% of the global area by the year 2080. The same number for the highest (lowest) annual precipitation total is 60% (43%). Monthly and seasonal temperature and precipitation records are also analysed, and the geographical distributions of record value occurrence are related to the distributions of time mean climate change and magnitude of interannual variability. 相似文献
In 27% of our analysis area, the highest annual mean temperatures of the whole period 1901–2006 were observed in 2001–2006. For the 22 climate models in our study, this fraction varies from 17% to 70%, with a multimodel mean of 40%. In simulations based on the SRES A1B emissions scenario, the highest annual mean temperature of the 20th century is exceeded on average in 99% of the global area by the year 2080. The same number for the highest (lowest) annual precipitation total is 60% (43%). Monthly and seasonal temperature and precipitation records are also analysed, and the geographical distributions of record value occurrence are related to the distributions of time mean climate change and magnitude of interannual variability. 相似文献
5.
Numerical experiments with the ECHAM5 atmospheric general circulation model have been performed in order to simulate the influence of changes in the ocean surface temperature (OST) and sea ice concentration (SIC) on climate characteristics in regions of Eurasia. The sensitivity of winter and summer climates to OST and SIC variations in 1998–2006 has been investigated and compared to those in 1968–1976. These two intervals correspond to the maximum and minimum of the Atlantic Long-Period Oscillation (ALO) index. Apart from the experiments on changes in the OST and SIC global fields, the experiments on OST anomalies only in the North Atlantic and SIC anomalies in the Arctic for the specified periods have been analyzed. It is established that temperature variations in Western Europe are explained by OST and SIC variations fairly well, whereas the warmings in Eastern Europe and Western Siberia, according to model experiments, are substantially (by a factor of 2–3) smaller than according to observational data. Winter changes in the temperature regime in continental regions are controlled mainly by atmospheric circulation anomalies. The model, on the whole, reproduces the empirical structure of changes in the winter field of surface pressure, in particular, the pressure decrease in the Caspian region; however, it substantially (approximately by three times) underestimates the range of changes. Summer temperature variations in the model are characterized by a higher statistical significance than winter ones. The analysis of the sensitivity of the climate in Western Europe to SIC variations alone in the Arctic is an important result of the experiments performed. It is established that the SIC decrease and a strong warming over the Barents Sea in the winter period leads to a cooling over vast regions of the northern part of Eurasia and increases the probability of anomalously cold January months by two times and more (for regions in Western Siberia). This effect is caused by the formation of the increased-pressure region with a center over the southern boundary of the Barents Sea during the SIC decrease and an anomalous advection of cold air masses from the northeast. This result indicates that, to estimate the ALO actions (as well as other long-scale climatic variability modes) on the climate of Eurasia, it is basically important to take into account (or correctly reproduce) Arctic sea ice changes in experiments with climatic models. 相似文献
6.
Experiments are performed with the climate model of the Institute of Numerical Mathematics, Russian Academy of Sciences (INM RAS), integrated jointly with the Lund-Potsdam-Jena dynamic global vegetation model (LPJ-DGVM). It is shown that the coupled model reproduces the distribution of basic plant functional types around the world quite well. In simulations of climate for the 21st century, this model predicts changes in dominant plant types and in the total area occupied by vegetation regionally. However, it does not reproduce the significant inverse influence that vegetation succession has on the simulated climate. 相似文献
7.
When long, fast swell waves travel in approximately the same direction as the wind, the surface stress is reduced compared with under wind-sea conditions. Using measurements from the Östergarnsholm site in the Baltic Sea, new expressions of the roughness length were developed for wind sea and swell. These new expressions were implemented in the RCA3 regional climate model covering Europe. A 3-year simulation and two case studies using the wavefield from the ECMWF reanalysis (ERA-40) were analysed using the improved formulations. Wind-following swell led to a significant reduction of mean wind stress and heat fluxes. The mean surface layer wind speed was redistributed horizontally and the marine boundary layer cooled and dried slightly. This cooling was most pronounced over North Sea and the Norwegian Sea (almost 0.2 °C annually on average) whereas the drying was most pronounced over the Mediterranean Sea (almost 0.4 g kg−1 ). Somewhat less convective precipitation and low-level cloudiness over the sea areas were also indicated, in particular over the Mediterranean Sea. The impact on the atmosphere, however, is significantly locally greater in time and space. 相似文献
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The present study evaluates future storm surge risk due to tropical cyclones (typhoons) in East Asia. A state-of-the-art atmospheric general circulation model (GCM) outputs are employed as the driving force for simulating storm surges associated with the projected changes in climate. The reproducibility of tropical cyclone (TC) characteristics from the GCM in the Northwest Pacific (NWP) is confirmed by comparing with the observed best track data, and future typhoon changes were presented. Storm surge simulation is carried out for East Asia, with the finest nested domain on the Japanese coast. The probability of maximum storm surge heights with specified return periods is determined using extreme value statistics. We show a strong regional dependency on future changes of severe storm surges. 相似文献
10.
Seamounts are ubiquitous topographic units in global oceans, and their influences on local oceanic circulation have attracted great attention in physical oceanography; however, previous efforts were less made in paleoclimatology and paleoceanography. The Caiwei Guyot in the Magellan Seamounts of the western Pacific is a typical seamount, and in this study, we investigate a well-dated sediment core by magnetic properties to reveal the relationship between deep-sea sedimentary processes and global climate changes. The principal results are as follows: (1) the dominant magnetic minerals in the sediments are low-coercivity magnetite in pseudo-single domain range, probably including a biogenic contribution; (2) the variabilities of magnetic parameters can be clustered into two sections at ～500 ka, and the differences between the two units are evident in amplitudes and means; (3) changes in the grainsize-dependent magnetic parameters can be well correlated to records of global ice volume and atmospheric CO2 in the middle Pleistocene. Based on these results, a close linkage was proposed between deep-sea sedimentary processes in the Caiwei Guyot and global climate changes. This linkage likely involves different roles of biogenic magnetite in the sediments between interglacial and glacial intervals, responding to changes in marine productivity and deep-sea circulation and displaying a major change in the Mid-Brunhes climate event. Therefore, we proposed that the sedimentary archives at the bottom of the Caiwei Guyot record some key signals of global climate changes, providing a unique window to observe interactions between various environmental systems on glacial-interglacial timescales. 相似文献
11.
The main characteristics of spatial and temporal variability of the precipitation regime in Sweden were studied by using the long‐term monthly precipitation amount (1890‐1990) at 33 stations. The data were filtered by using Empirical Orthogonal Function (EOF) analysis, which provides principal modes of both spatial variability and time coefficient series describing the dominant temporal variability. Canonical correlation analysis (CCA) was used to reveal association between the atmospheric circulation and the characteristics of the climate variability. Statistically significant upward shifts in the mean precipitation have been found during cold months (March, September, November and December) and only a downward shift (less significant) for August. Simultaneous changes in the time series associated to the optimally correlated circulation patterns were found, indicating an important role of the circulation. The circulation patterns are given by the North Atlantic Oscillation (NAO) in March and December and a cyclonic structure centred over southern Scandinavia in September and November. These changes may have induced changes in the mean precipitation seasonality reflected by a shift of the maximum precipitation from August to July (after 1931 for western part and after 1961 for the southeastern coast) and after 1961 to September, October or November for other regions. Combining rotated EOF analysis with cluster analysis, 4 regions with similar climate variability were objectively identified. For these regions the standardised monthly precipitation anomalies were computed. The frequency of the extreme events (very dry/wet and dry/wet months) over 5‐year consecutive intervals was analysed. It has been concluded that extreme wet months were more frequent than extreme dry months over the entire country, especially in the northern and southeastern part. 相似文献
12.
Observational evidence indicates that in the northern North Atlantic, especially in the Labrador Sea, almost the whole column of the ocean water is fresher, and colder in late 20th century than in 1950–1960s. Here we analyze a four-member ensemble of the 20th century simulations from a coupled climate model to examine the possible causes for these observed changes. The model simulations resemble the observed changes in the northern North Atlantic. The simulated results show that a decreased meridional freshwater divergence and an increased meridional heat divergence associated with a weaker thermohaline circulation in the North Atlantic are the primary causes for the freshening and cooling in the northern North Atlantic. The increased precipitation less evaporation tends to enforce the freshening, but the reduced sea ice flux into this region tends to weaken it. On the other hand, the surface warming induced by a higher atmospheric CO2 concentration tends to heat up the northern North Atlantic, but is overcome by the cooling from increased meridional heat divergence. 相似文献
13.
Interdecadal changes in the links between European precipitation and atmospheric circulation during boreal spring and fall 总被引：2，自引：0，他引：2
IGOR I. ZVERYAEV 《地球，A辑:动力气象学与海洋学》2009,61(1):50-56
A gridded monthly terrestrial precipitation from the Climatic Research Unit (CRU), University of East Anglia data set and the UK Met Office Northern Hemisphere mean sea level pressure data are used to investigate interdecadal changes in the relationships between precipitation variability over Europe and atmospheric circulation in the Atlantic–European sector during boreal spring and fall.
Singular value decomposition (SVD) analysis, performed for the climatic periods of strong/weak links to the North Atlantic Oscillation (NAO) during spring and fall, revealed considerable interdecadal changes both in the strength and the structure of the links between European precipitation and regional atmospheric circulation. During periods of strong links to the NAO, the leading SVD mode is characterized by the NAO-like meridional dipole in sea level pressure (SLP) fields and associated opposite precipitation variations over northern/southern Europe. When the links to the NAO are weak, the leading SVD mode is represented by the tripole pattern in SLP fields over the North Atlantic–European region, driving regional precipitation variability both in spring and fall. Further correlation analysis has shown that this mode is associated with the Scandinavian teleconnection pattern (SCA). Thus, for the considered seasons during periods of weak NAO influence, the SCA plays a role of major driver of the regional precipitation variability. 相似文献
Singular value decomposition (SVD) analysis, performed for the climatic periods of strong/weak links to the North Atlantic Oscillation (NAO) during spring and fall, revealed considerable interdecadal changes both in the strength and the structure of the links between European precipitation and regional atmospheric circulation. During periods of strong links to the NAO, the leading SVD mode is characterized by the NAO-like meridional dipole in sea level pressure (SLP) fields and associated opposite precipitation variations over northern/southern Europe. When the links to the NAO are weak, the leading SVD mode is represented by the tripole pattern in SLP fields over the North Atlantic–European region, driving regional precipitation variability both in spring and fall. Further correlation analysis has shown that this mode is associated with the Scandinavian teleconnection pattern (SCA). Thus, for the considered seasons during periods of weak NAO influence, the SCA plays a role of major driver of the regional precipitation variability. 相似文献
14.
DAILIN WANG 《地球，A辑:动力气象学与海洋学》2001,53(1):27-34
Application of the accelerated convergence (or asynchronous integration) method of Bryan (1984) to climate problems with time‐dependent forcing is investigated using an ocean general circulation model (GCM), with an idealized box ocean and forced with an idealized seasonal restoring surface temperature. Numerical experiments consist of a control experiment, which is integrated synchronously for 9000 years, and 2 experiments with asynchronous integration, one with depth dependent acceleration and one with depth independent acceleration. The latter 2 cases were integrated synchronously for 9000 years after asynchronous equilibria are reached. It is found that a few thousand years of synchronous integration is needed to reach a new equilibrium after asynchronous equilibrium is obtained, consistent with a scaling argument. However, at the new equilibrium, temperature in the deep ocean only differs from that of the early stage of synchronous adjustment by about 0.01°C. So for practical purposes, 50 years of synchronous integration beyond asynchronous equilibrium is sufficient. A simple interpretation of the accelerated convergence method of Bryan is also presented. 相似文献
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The El Niño/Southern Oscillation (ENSO) constitutes a major source of potential predictability in the tropics. The majority of past seasonal prediction studies have concentrated on precipitation anomalies at the seasonal mean timescale. However, fields such as agriculture and water resource management require higher time frequency forecasts of precipitation variability. Regional climate models (RCMs), with their increased resolution, may offer one means of improving general circulation model forecasts of higher time frequency precipitation variability.
Part I of this study evaluated the ability of the Rossby Centre regional atmospheric model (RCA), forced by analysed boundary conditions, to simulate seasonal mean precipitation anomalies over the tropical Americas associated with ENSO variability. In this paper the same integrations are analysed, with the focus now on precipitation anomalies at subseasonal (pentad) timescales.
RCA simulates the climatological annual cycle of pentad-mean precipitation intensity quite accurately. The timing of the rainy season (onset, demise and length) is well simulated, with biases generally of less than 2 weeks. Changes in the timing and duration of the rainy season, associated with ENSO forcing, are also well captured. Finally, pentad-mean rainfall intensity distributions are simulated quite accurately, as are shifts in these distributions associated with ENSO forcing. 相似文献
Part I of this study evaluated the ability of the Rossby Centre regional atmospheric model (RCA), forced by analysed boundary conditions, to simulate seasonal mean precipitation anomalies over the tropical Americas associated with ENSO variability. In this paper the same integrations are analysed, with the focus now on precipitation anomalies at subseasonal (pentad) timescales.
RCA simulates the climatological annual cycle of pentad-mean precipitation intensity quite accurately. The timing of the rainy season (onset, demise and length) is well simulated, with biases generally of less than 2 weeks. Changes in the timing and duration of the rainy season, associated with ENSO forcing, are also well captured. Finally, pentad-mean rainfall intensity distributions are simulated quite accurately, as are shifts in these distributions associated with ENSO forcing. 相似文献
16.
Projections of ocean climate for northwestern Pacific Ocean 总被引：1，自引：1，他引：0
The long-term adjustment processes of atmosphere and ocean in response to gradually increased atmospheric CO2 concentration have been analyzed in 70 and 140a integrations with NCAR fully-coupled climate system model (CSM). In these experiments the CO2 concentration has been increased to double and quadruples the initial concentration, respectively. After 70a, at the time of CO2 doubling, the model predicts surface air temperature rises by 1.2 and 1.5K for the globe and the northwestern Pacific Ocean, respectively. The behavior of the quadrupling run is similar: each global and regional mean surface air temperatures increase by 2.8 and 3.0K at the time of CO2 quadrupling. From the experiments, surface air temperature changes in the northwestern Pacific Ocean will be more distinctive compared with the global average, mainly due to exceptionally large warming and sea level change near the entrance of the Kuroshio extension. 相似文献
17.
A. Dawson L. Elliott S. Noone K. Hickey T. Holt P. Wadhams I. Foster 《Marine Geology》2004,210(1-4):247-259
The existence of a well-defined climate ‘see-saw’ across the North Atlantic region and surrounding areas has been known for over 200 years. The occurrence of severe winters in western Greenland frequently coincides with mild winters in northern Europe. Conversely, mild winters in western Greenland are frequently associated with cold winters across northern Europe. Whereas this ‘see-saw’ is normally discussed in terms of air temperature and pressure differences, here we explore how the climate ‘see-saw’ is reflected in records of historic storminess from Scotland, NW Ireland and Iceland. It is concluded that the stormiest winters in these regions during the last ca. 150 years have occurred when western Greenland temperatures have been significantly below average. In contrast, winters of reduced storminess have coincided with winters when air temperatures have been significantly above average in western Greenland. This reconstruction of winter storminess implies a relationship between chronologies of coastal erosion and the history of North Atlantic climate ‘see-saw’ dynamics with sustained winter storminess, and hence increased coastal erosion, taking place when the Icelandic low pressure cell is strongly anchored within the circulation of the northern hemisphere. Considered over the last ca. 2000 years, it would appear that winter storminess and climate-driven coastal erosion was at a minimum during the Medieval Warm Period. By contrast, the time interval from ca. AD 1420 until present has been associated with sustained winter storminess across the North Atlantic that has resulted in accelerated coastal erosion and sand drift. 相似文献
18.
表面增暖形态决定了全球水汽加温度直减率反馈的不确定性 总被引：1，自引：0，他引：1
气候反馈通常是利用与全球平均表面温度升高相关的辐射效应变化来评估的。但是反馈的不确定性不仅仅是全球平均表面温度升高的函数。全球气候模式的预测表明,海表面温度变化的地域不同,给区域尺度上的大气环流和降水响应带来了重大不确定性。在本文中我们证明了表面增暖的空间格局是造成水汽-直减率综合反馈的不确定性的主要因素。基于运用辐射核理论计算的31个气候模型中,气温和相对湿度变化的全球平均辐射效应证明了这一观点。我们的结果突出了区域气候变化对气候反馈不确定性的重要贡献,并确定了世界上限制表面增暖形态对提高气候预测能力最有效的区域。 相似文献
19.
大西洋经向翻转环流（Atlantic Meridional Overturning Circulation,AMOC）是气候系统重要的组成部分,其强度变化可直接影响南北半球的热量分配,厘清其变化机理对全球变暖背景下的未来预估至关重要。海洋沉积物记录发现,在晚更新世,AMOC的变化与地球岁差周期有紧密联系,但其物理机理尚不清楚。本文利用海洋-大气耦合气候模型—COSMOS(ECHAM5/JSBACH/MPIOM)模型,通过敏感试验,分析在冰盛期冷期和间冰期暖期气候背景下,AMOC对地球岁差变化的响应机理。结果表明：岁差降低引起的北半球夏季太阳辐射增强,会导致间冰期暖期背景下的AMOC显著减弱,但对冰盛期AMOC的影响并不明显。通过进一步分析发现,在间冰期暖期,夏季太阳辐射增强,造成高低纬大西洋海表的升温,同时促进北大西洋高纬度地区的局地降水,两者导致北大西洋表层海水密度降低,共同削弱大西洋深层水生成。而在冰盛期冷期,大西洋高低纬度地区的响应对AMOC的影响反向—副热带升温触发的海盆尺度低压异常,通过其南侧的西风异常削弱大西洋向太平洋的水汽输送,导致净降水增多,海表盐度下降;同时,高纬度升... 相似文献
20.
Influence of volcanic activity on climate change in the past several centuries: Assessments with a climate model of intermediate complexity 总被引：1，自引：1，他引：0
The climate model of intermediate complexity developed at the A.M. Obukhov Institute of Atmospheric Physics of the Russian Academy of Sciences (IAP RAS CM) is supplemented by a scheme which takes into account the volcanic forcing of climate. With this model, ensemble experiments have been conducted for the 1600s–1900s, in which, along with the volcanic forcing, the anthropogenic forcing due to greenhouse gases and sulfate aerosols and the natural forcing due to variations in solar irradiance were taken into account. The model realistically reproduces the annual mean response of surface air temperature and precipitation to major eruptions both globally and regionally. In particular, the decreases in the annual mean global temperature T g in the IAP RAS CM after the largest eruptions in the latter half of the 20th century, the Mt. Agung (1963), El Chichon (1982), and Mt. Pinatubo (1991) volcanic eruptions, are 0.28, 0.27, and 0.46 K, respectively, in agreement with estimates from observational data. Moreover, in the IAP RAS CM, the volcanic eruptions result in a general precipitation decrease, especially over land in the middle and high latitudes of the Northern Hemisphere. The seasonal distribution of the response shows good agreement with observations for high-latitude eruptions and worse agreement for tropical and subtropical volcanoes. On interdecadal scales, volcanism leads to variations in T g on the order of 0.1 K. In numerical experiments with anthropogenic and natural forcings, the model reproduces a general change in surface air temperature over the past several centuries. Taking into account the volcanic forcing, along with that due to variations in solar irradiance, the model has partly reproduced the nonmonotonic global warming for the 20th century. 相似文献