北半球陆面过程对全球变暖响应特征的初步分析

利用NCAR气候系统模式CCSM3.0 IPCC AR420世纪气候（20C3M）和21世纪SRES A1B排放情景下的模拟结果,着重分析了未来北半球陆面情况对全球变暖的总体响应特征。对比分析模式对20世纪和21世纪SRES A1B情景下的模拟结果表明：北半球陆面的水、热过程在全球变暖背景下将发生显著的变化。伴随全球地面温度的持续升高,北半球陆面的净辐射通量、感热通量和潜热通量均表现出不同程度的上升趋势,其中潜热通量的增幅明显高于感热通量;伴随着全球变暖,地表的水循环也发生了明显的变化,具体表现为北半球降水持续增多,陆面蒸发明显增加,地表径流也呈现出总体增加的趋势,但土壤含水量则表现出减少的趋势。     

山西陆面过程对A1B排放情景下全球变化趋势的响应

山西地处气候过渡带,气候敏感、生态脆弱,在全球气候变暖背景下其陆面物理过程受气候波动影响十分明显。本文利用NCAR CCSM IPCC AR4陆面分量模式(CLM)20世纪气候模拟(20C3M)和21世纪SRES A1B排放情景下的模拟结果,对山西省21世纪(2001~2099年)与20世纪(1901~1999年)陆面能量和水文变量进行了对比分析。结果显示:(1)模式模拟出山西地区未来地面温度的空间及时间分布特征。未来山西省地面温度呈明显上升趋势,上升速率冬季大于夏季。空间上,增温幅度冬季自北向南递减,夏季自西向东递减;(2)未来山西省陆面各分量空间上,净辐射通量西北增幅大于东南,降水率和径流率则与其相反,潜热通量与蒸发率一致,西南部增加幅度大,土壤含水率冬夏分布相反,感热通量呈下降趋势,西南下降幅度大;时间上,净辐射通量、潜热通量均表现出不同程度的上升趋势,土壤热通量冬季上升,夏季下降;地表水循环的各分量均呈增加趋势。     

植被冠层截留对地表水分和能量平衡影响的数值模拟

利用NCAR_CLM4.0模式,通过有无植被冠层截留的试验对比分析,讨论了植被冠层截留对全球陆面水分和能量平衡产生的潜在影响.结果表明:就全球水分平衡而言,不考虑植被冠层截留时,全球平均土壤总含水量、表面径流和次表面径流增加,蒸散发减少.空间分布特征表明,低纬地区各水分平衡分量全年维持较高的差值分布,并随季节变化沿赤道南北振荡;北半球中高纬高值区有春季扩张、夏季极盛、秋冬季撤退的趋势.冠层截留消失后冠层蒸发的消失是蒸散发减弱的主要原因.对于能量平衡而言,不考虑冠层截留时,全球感热通量增加,冠层感热的增加明显大于地面感热的减少;潜热减少.此外,不同植被类型对不考虑冠层截留后产生的响应存在明显差异.     

干旱区荒漠草原过渡带快速变化的陆面过程特征观测分析

干旱区荒漠草原过渡带下垫面受降水影响而变化,在短期内由沙漠转化为草地,因而其陆面过程特征快速变化十分显著,可能对区域天气或气候造成一定影响。本文利用2012年7~9月在腾格里沙漠南缘的荒漠草原过渡带开展的"微气象蒸发观测实验"的观测资料,通过分析强降水前后土壤温度、含水量、辐射及湍流通量,研究快速变化的陆面过程特征。结果表明:40 cm以上的浅层土壤温度在降水后降低,随着降水辐射效应的消失,土壤温度升高;而深层的土壤温度变化较小。土壤含水量对降水有明显的响应,20 cm以上的浅层土壤含水量迅速增大,而后缓慢减小;30、40 cm的土壤含水量先增大后迅速下降。7、8月的净辐射变化不大,在-50~450 W·m-2间变化。降水发生后,反射辐射和地表长波辐射较干旱荒漠有所降低,2~3 d后又恢复到干旱荒漠的量级。地表反照率在降水后先降后升,荒漠草地的地表反照率日均值较大,与地表含水量、太阳高度角及植被生长参数密切相关。感热和潜热在降水前后变化显著,潜热增大而后减小,感热减小而后增大,干旱荒漠地表能量传输以感热通量为主,强降水发生后,潜热通量占主导地位,而后由于蒸散发使土壤含水量减小,潜热的主导地位逐渐被感热代替。     

NCAR_CLM系列模式对全球近50 a陆面状况的模拟及其比较分析

基于普林斯顿大学1948-2006年3h一次、1 °×1 °空间分辨率的全球陆面驱动数据,利用NCAR系列陆面模式CLM3.0、CLM3.5、CLM4.0,分别对全球近50 a的陆面状况进行了offline模拟试验.在此基础上,对比分析了不同版本模式对全球土壤温度、土壤湿度、地表感热、潜热和地表径流气候态的模拟结果,揭示了不同版本模式对全球陆面变量模拟的差异及主要特征.结果表明:1)CLM系列模式模拟的土壤温度、湿度在全球范围内存在一定差异.与CLM4.0相比,CLM3.0和CLM3.5模拟的1月、7月的浅层和深层土壤温度在北半球中高纬度存在明显的暖偏差.CLM3.0模拟的土壤湿度在北半球高纬地区均存在不同程度的偏湿,而在热带及中纬度地区则以偏干为主,尤其是对热带地区深层土壤湿度的模拟存在严重偏干的现象;相比之下,CLM3.5模拟的浅层土壤湿度仅在北半球高纬地区存在偏湿的现象;二者对深层土壤湿度的模拟差异较小.2)CLM系列模式模拟的地表能量通量和地表水文变量也存在较明显的差异.模式对潜热通量和感热通量的明显差异主要出现在热带地区,与CLM4.0相比,CLM3.0模拟的潜热(感热)通量总体偏小(大),而CLM3.5模拟的潜热(感热)通量以偏大(小)为主.CLM3.0模拟的地表径流在热带地区明显偏大,CLM3.5在一定程度上改善了上述区域径流偏大的问题,但过分低估了上述地区的地表径流.3)模式模拟结果的差异具有明显的季节变化和区域性特点.总体而言,CLM3.0对不同地区的土壤湿度和冠层蒸散的季节变化模拟都存在较大偏差,其模拟的土壤湿度明显偏低,而对冠层蒸腾作用在冠层蒸散过程中所做的贡献估计不足;CLM3.5和CLM4.0对上述结果有了较明显的改进.对于其他陆面因子的季节变化而言,CLM3.0的模拟能力也存在一定程度的不足,而CLM3.5和CLM4.0的模拟结果则更为合理.     

珠峰北坡地区地表辐射和能量季节变化的初步分析

对青藏高原地区地表能量的研究是一个十分重要的问题.利用中国科学院珠穆朗玛峰大气与环境综合观测研究站2006年5月至2007年4月一年的观测资料,分析了青藏高原珠峰地区的地表能量,即净辐射通量、感热通量、潜热通量和土壤热通量,得到了一些有关珠峰地区地表能量的结果,即太阳总辐射、大气长波辐射、地面长波辐射和净辐射呈现出明显的年变化特征,净辐射、感热通量、潜热通量和土壤热通量得到的日变化是很明显的.并且讨论了计算地表能量通量的方法及其优缺点.     

典型干旱区陆面模式模拟检验

利用2000年9月至2001年8月"我国西北干旱区陆-气相互作用试验(NWC-ALIEX)"敦煌站的陆面过程观测资料,基于已有的参数化结果,模拟了敦煌主要陆面特征。结果表明:典型干旱区敦煌夏季感热通量与潜热通量差异显著,感热几乎是潜热的4倍,冬季二者都很小。模式对地表温度模拟较好,但高估了浅层土壤湿度峰值;对向上辐射模拟较好,但对净辐射的模拟存在较大偏差;同时高估了地表能量的峰值。模式结果表明参数化方案对干旱区陆面过程模式具有一定的改进作用。     

干旱区陆面过程模型参数优化和地气相互作用特征的模拟研究

依据干旱区陆地下垫面观测结果, 对陆面过程模式Common Land Model (CoLM) 中反照率、 粗糙度长度和土壤热力性质3个方面的参数进行了优化, 并按照不同的参数组合形式设计了为加深理解干旱区地气相互作用的控制试验和研究重要参数影响的敏感性试验, 对敦煌戈壁2000年5月～2004年7月的陆面过程进行了离线 (off-line) 数值模拟分析。控制试验结果表明: 优化参数的模式在干旱区得到了更好的模拟性能, 对地表和深层土壤温度、 净短波辐射、 净长波辐射以及感热通量的模拟能力较原模式有了明显的提高。敏感性试验的结果表明: 地表温度在全年对反照率都比较敏感, 春季和夏季更为显著; 粗糙度长度和土壤热力性质分别在春夏和秋冬对地表温度有较大影响; 感热通量对反照率和粗糙度长度在夏半年比较敏感, 而土壤热力性质对感热通量的影响并不明显。对敏感性试验的结果进一步分析发现: 原模式在计算地表温度、 净辐射和感热通量的过程中存在不同形式的误差抵消的现象, 这就会掩盖模式的模拟误差, 优化参数的模式可以更好的反映干旱区地气相互作用的物理过程。针对模式输出的感热通量和地表热通量的分析发现: 感热通量的季节变化明显, 全年都有由地表向上的感热通量输送, 夏季尤为显著; 相对于感热通量而言, 潜热通量量级很小可以忽略不计。夏季, 净辐射的能量大部分以感热通量的形式返回大气, 其余的能量以地表热通量的形式进入土壤并贮存, 夏季土壤为热汇; 冬季, 夏季贮存的能量又由土壤返回大气, 此时土壤为热源。     

黄土高原半干旱区雨养农田地表辐射和能量通量的季节变化

黄土高原陇东地区有着特殊的气候背景和下垫面,对这一地区陆气相互作用特征和影响因素的观测分析对改进和发展陆面过程模式以及气候变化研究有重要意义。利用陇东平凉陆面过程与灾害天气观测研究站连续一年的陆面过程观测资料,分析了雨养农田降水量、土壤含水量、辐射、反照率和能量通量的季节变化,以及降水、土壤含水量和农业生产活动对能量分配的影响。结果表明,陇东地区降水量季节分布不均,土壤含水量有明显季节差异,随降水有明显波动;辐射通量的季节变化较为规律,短波辐射的日均值受天气状况影响,波动较大;地表反照率呈明显的季节变化,全年正午反照率最大值为0.83,出现在降雪后,生长季随着作物的生长,反照率下降至0.2以下,农作物收割以后的裸土反照率随降水变化明显,反照率与土壤体积含水量呈明显的线性相关关系;湍流能量通量日循环和季节变化明显,地表能量分配在很大程度上受降水影响,同时农业生产活动也对其有较大影响,主导能量通量有较大的月际波动,潜热通量月平均日变化峰值最大为240.8 W·m~(-2),出现在5月,感热通量为192.5 W·m~(-2),出现在4月;在年尺度上,正午净辐射多被感热通量消耗,感热通量约占35%,潜热通量约占32%,低于灌溉农田;在冬小麦快速生长季(3-5月),潜热通量约占34%,远低于灌溉的冬小麦田,研究站点的蒸散发过程受到水分限制。     

那曲高寒草地长时间地面热源特征及其气候影响因子分析

利用中国科学院那曲高寒气候环境观测研究站2002—2015年自动气象塔(AWS_Tower)和2011—2014年涡动相关系统(EC)的观测资料,基于地表能量平衡组合法和涡动相关法计算那曲高寒草地下垫面湍流通量。利用涡动相关法对地表能量平衡组合法计算的感热通量、潜热通量进行校正,并将校正规律外推得到一个长时间连续的地表通量序列,分析那曲高寒草地下垫面感热通量、潜热通量的长时间变化特征以及地面热源与气候影响因子的关系。结果表明,该序列地表能量闭合度在春、夏、秋以及全年接近1,而冬季辐射观测值偏小导致能量闭合度正偏差较大为1. 34。近14年中,感热通量在年际变化上呈上升趋势;潜热通量呈显著减弱趋势,造成地面热源呈减弱趋势。地面热源与风速、地表温度、土壤湿度以及净辐射通量资料的关系显著。其中地面热源全年对净辐射通量响应显著,对地表温度在春、秋以及冬季响应显著,与土壤湿度在春、夏以及秋季响应明显,与风速在春季响应特征较为突出。季节变化上,感热通量在4月达到全年最大值,在7月为最小值;潜热通量在7月为全年最大值,在1月为最小值。     

Asymmetry of surface climate change under RCP2.6 projections from the CMIP5 models

The multi-model ensemble (MME) of 20 models from the Coupled Model Intercomparison Project Phase Five (CMIP5) was used to analyze surface climate change in the 21st century under the representative concentration pathway RCP2.6, to reflect emission mitigation efforts. The maximum increase of surface air temperature (SAT) is 1.86°C relative to the pre-industrial level, achieving the target to limit the global warming to 2°C. Associated with the “increase-peak-decline” greenhouse gases (GHGs) concentration pathway of RCP2.6, the global mean SAT of MME shows opposite trends during two time periods: warming during 2006–55 and cooling during 2056–2100. Our results indicate that spatial distribution of the linear trend of SAT during the warming period exhibited asymmetrical features compared to that during the cooling period. The warming during 2006–55 is distributed globally, while the cooling during 2056–2100 mainly occurred in the NH, the South Indian Ocean, and the tropical South Atlantic Ocean. Different dominant roles of heat flux in the two time periods partly explain the asymmetry. During the warming period, the latent heat flux and shortwave radiation both play major roles in heating the surface air. During the cooling period, the increase of net longwave radiation partly explains the cooling in the tropics and subtropics, which is associated with the decrease of total cloud amount. The decrease of the shortwave radiation accounts for the prominent cooling in the high latitudes of the NH. The surface sensible heat flux, latent heat flux, and shortwave radiation collectively contribute to the especial warming phenomenon in the high-latitude of the SH during the cooling period.     

Estimates of climate changes in the 20th-21st centuries based on the version of the IAP RAS climate model including the model of general ocean circulation

Numerical experiments are analyzed for 1860–2100 with the version of the climate model of intermediate complexity of the Obukhov Institute of Atmospheric Physics of the Russian Academy of Sciences (IAP RAS) including the model of general ocean circulation as the oceanic module (CM IAP RAS-GOC) taking account of concentration variations of anthropogenic greenhouse gases and tropospheric sulfate aerosols from the data of observations and reconstructions for the second half of the 19th and for the 20th century and, according to SRES scenarios, in the 21st century. In the 20th century, the model simulates realistically the variations of surface atmospheric temperature, characteristics of heat absorption by the ocean, and oceanic meridional heat transport. The linear trend of global surface atmospheric temperature in the 20th century (in its last 30 years) in this version of the model amounts to 0.5 ± 0.1 K/100 years (0.22 ± 0.05 K/10 years) that is agreed with the observational data. In the 21st century, the global increase in the surface temperature amounts to 2.5 K (3.5 and 4.1 K) for SRES B1 scenario (for SRES A1B and SRES A2 scenarios, respectively). The increase in the surface temperature is the most significant in high latitudes, especially in the Northern Hemisphere and it is higher, on the whole, over the land than over the ocean. The warming near the surface is larger in winter than in summer. The maximum warming is observed in the Arctic and over the land of subpolar latitudes of the Northern Hemisphere reaching 6–10 K by the end of the 21st century in these regions as compared with the end of the 20th century depending on the anthropogenic impact scenario. At the increase in surface temperature in the 20th–21st centuries, the increase in the heat flow to the ocean and the weakening of the heat transport by the ocean from the tropics to the polar area by 1.5–2 times are registered, on the whole. At the warming, the CM IAP RAS-GOC gives the general increase in the annual precipitation amount which is especially appreciable in the tropics and in the storm-track regions. At the global averaging, the precipitation in the 21st century increase by 20–25%.     

BCC_CSM1.1对10年尺度全球及区域温度的预测研究

近期10～30年时间尺度的年代际预测是第五次耦合模式国际比较计划(CMIP5)重要内容之一。按照CMIP5试验要求, 国家气候中心利用气候系统模式BCC_CSM1.1完成并提交了年代际试验结果。本文评估了该模式年代际试验对10年尺度全球及区域地表温度的预测能力, 并通过与20世纪历史气候模拟试验的对比分析, 研究模式模拟对海洋初始观测状态的依赖程度。分析结果表明:(1)在有、无海洋初始化条件下, 模式均能模拟出1960～2005年间全球10年平均实测地表温度的变暖趋势, 但在有海洋初始化条件下, 可以明显减小BCC_CSM1.1模式模拟的全球升温趋势, 使得年代际试验比历史试验的结果更接近观测值。这一特点在观测资料相对丰富的南北纬50°以内地区更为显著。(2)在年代际试验预测前期, 通过Nudging方法, 利用SODA再分析海洋温度资料对模式进行初始化, 经过前期8～12月的协调后, 模式预测的第1年南北纬50°范围海洋、陆面的平均地表气温接近于观测值(CRUTEM3, HadSST2)。由于模式初值SODA再分析SST资料与HadSST2观测值存在明显的全球大洋系统暖偏差以及模式本身系统偏差的影响, 年代际试验模拟的地表气温在2～7年之内, 从观测SST状态逐渐恢复到模式系统本身状态。在同组Decadal试验中, 陆面和海洋恢复调整的时间长度几乎一致。(3) 从10年平均气候异常在区域尺度上的预报技巧来看, 有、无海洋初始同化对预测结果影响不大, 高预测技巧区主要分布在南半球印度洋中高纬度、热带西太平洋以及热带大西洋区域。(4)SST变化与下垫面热通量密切相关, 在热带和副热带海洋区域, 长波辐射和感热通量是影响10年时间尺度SST变化较大的物理量, 在中高纬度海洋, 洋面温度变化主要受潜热通量的影响相对较大。     

Influence of snow cover changes on surface radiation and heat balance based on the WRF model

The snow cover extent in mid-high latitude areas of the Northern Hemisphere has significantly declined corresponding to the global warming, especially since the 1970s. Snow-climate feedbacks play a critical role in regulating the global radiation balance and influencing surface heat flux exchange. However, the degree to which snow cover changes affect the radiation budget and energy balance on a regional scale and the difference between snow-climate and land use/cover change (LUCC)-climate feedbacks have been rarely studied. In this paper, we selected Heilongjiang Basin, where the snow cover has changed obviously, as our study area and used the WRF model to simulate the influences of snow cover changes on the surface radiation budget and heat balance. In the scenario simulation, the localized surface parameter data improved the accuracy by 10 % compared with the control group. The spatial and temporal analysis of the surface variables showed that the net surface radiation, sensible heat flux, Bowen ratio, temperature and percentage of snow cover were negatively correlated and that the ground heat flux and latent heat flux were positively correlated with the percentage of snow cover. The spatial analysis also showed that a significant relationship existed between the surface variables and land cover types, which was not obviously as that for snow cover changes. Finally, six typical study areas were selected to quantitatively analyse the influence of land cover types beneath the snow cover on heat absorption and transfer, which showed that when the land was snow covered, the conversion of forest to farmland can dramatically influence the net radiation and other surface variables, whereas the snow-free land showed significantly reduced influence. Furthermore, compared with typical land cover changes, e.g., the conversion of forest into farmland, the influence of snow cover changes on net radiation and sensible heat flux were 60 % higher than that of land cover changes, indicating the importance of snow cover changes in the surface-atmospheric feedback system.     

Projections of the advance in the start of the growing season during the 21st century based on CMIP5 simulations

It is well-known that global warming due to anthropogenic atmospheric greenhouse effects advanced the start of the vegetation growing season(SOS) across the globe during the 20 th century. Projections of further changes in the SOS for the 21 st century under certain emissions scenarios(Representative Concentration Pathways, RCPs) are useful for improving understanding of the consequences of global warming. In this study, we first evaluate a linear relationship between the SOS(defined using the normalized difference vegetation index) and the April temperature for most land areas of the Northern Hemisphere for 1982–2008. Based on this relationship and the ensemble projection of April temperature under RCPs from the latest state-of-the-art global coupled climate models, we show the possible changes in the SOS for most of the land areas of the Northern Hemisphere during the 21 st century. By around 2040–59, the SOS will have advanced by-4.7 days under RCP2.6,-8.4 days under RCP4.5, and-10.1 days under RCP8.5, relative to 1985–2004. By 2080–99, it will have advanced by-4.3 days under RCP2.6,-11.3 days under RCP4.5, and-21.6 days under RCP8.5. The geographic pattern of SOS advance is considerably dependent on that of the temperature sensitivity of the SOS. The larger the temperature sensitivity,the larger the date-shift-rate of the SOS.     

The Warming of the Tibetan Plateau in Response to Transient and Stabilized 2.0°C/1.5°C Global Warming Targets

As "the third pole", the Tibetan Plateau (TP) is sensitive to climate forcing and has experienced rapid warming in recent decades. This study analyzes annual and seasonal near-surface air temperature changes on the TP in response to transient and stabilized 2.0°C/1.5°C global warming targets based on simulations of the Community Earth System Model (CESM). Elevation-dependent warming (EDW) with faster warming at higher elevations is predicted. A surface energy budget analysis is adopted to uncover the mechanisms responsible for the temperature changes. Our results indicate a clear amplified warming on the TP with positive EDW in 2.0°C/1.5°C warmer futures, especially in the cold season. Mean TP warming relative to the reference period (1961–90) is dominated by an enhanced downward longwave radiation flux, while the variations in surface albedo shape the detailed pattern of EDW. For the same global warming level, the temperature changes under transient scenarios are ~0.2°C higher than those under stabilized scenarios, and the characteristics of EDW are broadly similar for both scenarios. These differences can be primarily attributed to the combined effects of differential downward longwave radiation, cloud radiative forcing, and surface sensible and latent heat fluxes. These findings contribute to a more detailed understanding of regional climate on the TP in response to the long-term climate goals of the Paris Agreement and highlight the differences between transient and stabilized warming scenarios.     

On the subarctic North Atlantic cooling due to global warming

Various ocean reanalysis data reveal that the subarctic Atlantic sea surface temperature (SST) has been cooling during the twentieth century. A similar cooling pattern is found in the doubling CO₂ experiment obtained from the CMIP3 (coupled model intercomparison project third phase) compared to the pre-industrial experiment. Here, in order to investigate the main driver of this cooling, we perform the heat budget analysis on the subarctic Atlantic upper ocean temperature. The net surface heat flux associated with the increased concentration of greenhouse gases heats the subarctic ocean surface. In the most of models, the longwave radiation, latent heat flux, and sensible heat flux exert a warming effect, and the shortwave radiation exerts a cooling effect. On the other hand, the thermal advection by the meridional current reduces the subarctic upper ocean temperature in all models. This cold advection is attributed to the weakening of the meridional overturning circulation, which is related to the reduction in the ocean surface density. In particular, greater warming of the surface air than of the sea surface results in the reduction of surface evaporation and thereby enhanced freshening of the ocean surface water, while precipitation change was smaller than evaporation change. The thermal advections by both the wind-driven Ekman current and the density-driven geostrophic current contribute to cooling in most of the models, where the heat transport by the geostrophic current tends to be larger than that by the Ekman current.     

三个陆面过程模式在西北半干旱区的模拟性能对比

利用NOAH(The Community Noah Land Surface Model)、SHAW(Simultaneous Heat and Water)和CLM(Community Land Model)3个不同的陆面过程模式及兰州大学(Semi-Arid Climate Observatory and Laboratory,SACOL)2007年的观测资料,对黄土高原半干旱区的陆面过程进行了模拟研究。通过与观测值间的对比,考察不同陆面过程模式在半干旱区的适用性。研究结果表明:3个模式在半干旱区的模拟性能有较大差异。其中,CLM模式模拟的20 cm以上的浅层土壤温度最优,SHAW模式模拟的深层土壤温度最优;SHAW模式模拟的土壤含水量与观测值最为接近,而NOAH和CLM模式模拟值有较大偏差;3个模式均能较好地模拟地表反射辐射,其中SHAW模式模拟值与观测值的偏差最小;对地表长波辐射的模拟,CLM模式的模拟最优;3个模式均能较好地反映感热、潜热通量的变化趋势,其中CLM模式对感热的模拟性能优于其他两个模式,在有降水发生后的湿润条件下,CLM模式对潜热的模拟性能最优,而无降水的干燥条件下,CLM模式的模拟偏差最大,NOAH模式对冬季潜热的模拟最优。总体而言,CLM模式能够更好地再现半干旱区地气之间的相互作用,但模式对土壤含水量及干燥条件下的潜热通量的模拟较差,模式对半干旱区陆气间的水文过程还有待进一步的研究和改进。