西太平洋-南海地区潜热通量长期变化趋势的南北差异及成因分析

利用1958~2014年美国伍兹霍尔海洋研究所客观分析海气通量项目(OAFlux)的月平均潜热通量和相关气象要素数据,以及NCEP/NCAR再分析表面气压数据,通过Trend-EOF分析方法,本文研究了西太平洋—南海地区潜热通量的长期变化趋势。发现西太平洋—南海地区潜热通量整体呈上升的趋势,其中冬季上升趋势最强。冬季潜热通量趋势存在明显的南北差异,特别是在南海地区,南海北部为上升趋势而南部为下降趋势。南海北部以及菲律宾海地区冬季潜热通量上升的主要原因是海气比湿差的增大,而南海南部潜热通量呈下降趋势,在东侧主要原因是风速减小,在西侧主要原因是海气比湿差减小。南海潜热通量长期趋势的南北差异是风速和海气比湿差的共同作用造成的。另外,研究发现风速变化趋势受到局地环流变化的影响,在表面气压下降中心线以北地区为上升趋势,在其以南为下降趋势,而海气比湿差的变化趋势则主要取决于海表温度的变化趋势。     

北太平洋海气界面湍流热通量的年际变化

本文采用美国伍兹霍尔海洋研究所客观分析海气通量项目提供的1958～2006年月平均的湍流热通量及相关气象场数据, 利用EOF分析、小扰动方法、线性回归、相关分析等方法研究了北太平洋海气界面湍流热通量年际变化的时空特征、 影响因子及其与大气环流的关系。结果表明, 北太平洋湍流热通量的年际变化在冬季最为显著。我国东部海域及其向中东太平洋的延伸部分为冬季潜热通量和感热通量年际变化的关键区。冬季潜热通量的年际变化在副热带太平洋和菲律宾海域主要受风速变化影响, 在北太平洋的高纬和低纬海域尤其是赤道中太平洋主要受比湿差变化影响, 而冬季感热通量的年际变化在整个北太平洋都主要受海气温差变化影响。受大尺度环流影响, 异常低压中心的东 (西) 侧海气比湿差和海气温度差偏小 (偏大), 所以异常低压中心的东 (西) 侧潜热输送和感热输送偏弱 (偏强)。     

西太平洋暖池热含量年际变化及其对东亚气候异常的影响

利用1980—2010年共31个冬季的GODAS海洋同化资料,以5～366 m次表层海温构造西太平洋暖池区域的热含量,分析了冬季西太平洋暖池次表层热含量的时空特征、持续性以及对其邻近区域的气候异常影响,结果表明:(1) 整体一致性分布是冬季西太暖池区次表层热含量年际变化的主导模态,其时间系数的年际振荡较好地代表了暖池区次表层热状况的年际异常。暖池区热含量的变化与ENSO事件联系密切,它能保持超前两季以上的显著自相关,持续性较赤道中东太平洋海温异常更为稳定。(2) 冬季暖池区热含量异常对后期春、夏季暖池热状况产生持续影响,相应的暖水体积变化导致暖水的经向输送及垂直交换,对后期春夏两季暖池及邻近区域尤其是菲律宾海的表层海温、海表热通量变化有较大影响。(3) 冬季暖池区热含量上升对应春季菲律宾海以东洋面OLR数值下降以及降水偏多,所引起的对流活动加热异常导致热带及副热带西北太平洋位势等压面抬升,进而对西太副高产生影响。之后,此区域相应的海表热通量交换加强,对流层低层形成强大的异常气旋,海气相互作用加强,加上对流加热异常,使得冬季暖池热含量异常与夏季副热带高压变化联系更加紧密。因此冬季暖池区热含量可作为春、夏季西太副高变化和西北太平洋夏季风强度的有效预测因子。      

春夏季青藏高原与伊朗高原地表热通量的时空分布特征及相互联系

伊朗高原和青藏高原热力作用对东亚区域气候具有重要影响。基于1979—2014年欧洲中心ERA-interim月平均再分析地表热通量资料,分析了春、夏季青藏高原与伊朗高原地表热通量的时、空分布特征以及春、夏季青藏高原与伊朗高原地表热通量的关系。结果表明,春、夏季青藏高原与伊朗高原地表热通量在季节、年际和年代际尺度上具有不同的时、空分布特征。对于青藏高原,春、夏季地表感热呈西部大东部小、地表潜热呈东部大西部小;地表感热在春季最大且大于地表潜热,地表潜热在夏季最大且大于地表感热。在年际时间尺度上,春、夏季青藏高原地表热通量异常的年际变化在东、西部不一致,青藏高原西部,地表感热与地表潜热有较强的负相关关系。青藏高原地表感热异常具有很强的持续性,当春季地表感热较强（弱）时,夏季高原地表感热同样较强（弱）。青藏高原东部与西部地表热通量的年代际变化有明显差异,春（夏）季青藏高原东部地表感热呈显著的年代际减弱趋势,1998（2001）年发生年代际转折,由正异常转为负异常;而青藏高原西部地表感热在春季则有显著的增大趋势,2003年发生年代际转折,由负异常转为正异常。青藏高原东部地表潜热仅在春季为显著减弱趋势,2003年出现年代际转折,由正异常转为负异常;青藏高原西部地表潜热在春、夏季都有显著减弱趋势,年代际转折出现在21世纪初,由正异常转为负异常。对于伊朗高原,春、夏季地表热通量的空间分布在整个区域较一致,地表感热在夏季最大,地表潜热在春季大、夏季小,但各季节地表感热都大于地表潜热。相对于青藏高原地表感热,伊朗高原地表感热在各月都更大。在年际时间尺度上,春、夏季伊朗高原各区域地表热通量异常的年际变化较一致;地表感热与潜热有很强的负相关关系;伊朗高原地表感热、潜热异常都具有持续性,当春季地表感热（潜热）通量较强（弱）时,夏季地表感热（潜热）通量同样较强（弱）。伊朗高原北部与南部地表热通量的年代际变化存在差异。其中,春、夏季伊朗高原北部地表感热（潜热）呈显著增强（减弱）趋势,在20世纪末发生了年代际转折,春、夏季北部地表感热（潜热）由负（正）异常转为正（负）异常。而伊朗高原南部春、夏季地表热通量无显著变化趋势,但春季地表感热、潜热与夏季地表感热同样在20世纪末存在年代际转折,地表感热（潜热）由负（正）异常转为正（负）异常。春、夏季两个高原地区地表热通量的关系主要表现为:就春季同期变化而言,伊朗高原地表感热与青藏高原西部地表感热具有同相变化关系,与青藏高原东部地表感热具有反相变化关系,伊朗高原地表潜热与青藏高原东部地表潜热具有同相变化关系;就非同期变化而言,春季伊朗高原地表感热与夏季青藏高原东部地表感热存在反相变化关系。      

热带西太平洋热状况年代际和年际变化特征分析

采用谐波分析和EOF分析方法,对比研究了暖池区域表层热状况(海表温度距平SST'表征)和浅层热状况(热含量距平HS'和次表层海温距平ST'表征)在1月和7月的年代际、年际尺度时空特征.分析结果表明:⑴不同季节的年代际、年际尺度SST'和HS'都存在两个显著模态,HS'1月的年代际、年际尺度结构最简单,而SST'7月的年代际和1月年际结构最复杂;⑵ 1970年代末和1980年代初发生的年代际跃变HS'晚于SST', 且SST'(HS')呈增温(减少)趋势;⑶ HS'的年际异常与ENSO关系密切,而SST'与ENSO关系不显著.     

耦合模式热带太平洋云—气候反馈模拟误差评估

云—气候反馈是热带海气相互作用的重要过程, 同时也是气候模拟的难点。本文利用IPCC AR4提供的耦合模式20世纪模拟试验结果和观测资料, 通过滤波和经验正交展开 (EOF) 的方法将热带太平洋海表温度的年际变化和年代际变化信号分别提取出来, 然后再分别计算观测和模式在年际和年代际时间尺度上云—辐射和热通量反馈特征, 发现在上述两个时间尺度上, 耦合模式模拟的云—辐射和热通量的反馈都要比观测和再分析资料的偏弱。反馈偏弱的可能原因是模式中热带大气对流和云对海表温度变化的敏感性比真实大气要偏弱。值得注意的是, 尽管耦合模式热带太平洋年代际热力反馈偏弱, 但是耦合模式模拟的热带太平洋南北纬10°之间海表温度的年代际增温趋势与观测相当。进一步分析表明, 只用年代际热力反馈来解释热带太平洋的气候变化是不够的, 还必须考虑动力反馈对于海表温度变化的调节作用。     

黑潮延伸体区域海表温度锋的时空变化特征分析

利用NOAA最优插值逐日海表温度资料和AVISO中心的海表高度异常资料,分析了黑潮延伸体区域的海表温度锋的时空变化特征以及导致其年代际变化可能的原因。结果表明,气候平均态的黑潮延伸体区域海表温度锋位于黑潮延伸体区域北部边缘,在143 °E和150 °E附近存在两个弯曲,SST水平梯度最大值出现在142 °E附近,强度超过4.5 ℃/(100 km),其后强度自西向东逐渐递减,在149 °E附近又出现一个较弱的大值中心,在141~153 °E范围内,海表温度锋位置的平均值为36.25 °N,强度的平均值为3.22 ℃/(100 km)。黑潮延伸体区域的海表温度锋南北位置的季节变化很弱,而其强度的季节变化非常显著。相较于较弱的季节变化,海表温度锋位置的年际和年代际的低频变化则要显著得多,其南北变化跨度超过2 °。海表温度锋强度的年际和年代际的低频变化也较强,超过4.5 ℃/(100 km)。黑潮延伸体区域的海表温度锋的变化与太平洋年代际振荡（PDO）以及北太平洋涡旋振荡（NPGO）存在显著的相关关系,NPGO和PDO在中东太平洋区域会强迫产生海表高度异常,随后向西传播,在约3年后到达黑潮延伸体区域,使该区域流场发生变化产生海洋热平流异常,最终导致海表温度锋强度发生变化。      

东亚冬季风与冬季黑潮海温异常的关系

利用统计分析方法，分析了冬季黑潮区域海表温度异常与东亚冬季风的相关关系．及其可能的机制。结果表明：东亚冬季风异常与冬季黑潮区域海温异常有密切的联系。当东亚冬季风偏强时，冬季黑潮区域海温偏低；反之，当东亚冬季风偏弱时，冬季黑潮区域海温则偏高。其过程可能是东亚冬季风异常偏强（弱）造成了黑潮区域1000hPa气温的明显下降（上升）。而由于黑潮区域海温的变化相对较小．使得黑潮区域的海气温差也发生了显著地增大（减小），从而使得该区域的海洋热通量也相应地增多（减少）。这种海洋热通量释放的增多（减少），造成该区域的海温下降（上升）。     

华南夏季极端降水时空变异及其与西北部太平洋海气异常关联性初探

基于长时间序列的观测和再分析数据,分析了1958-2008年间华南夏季极端降水的时空变异特征及其与西北部太平洋海域的海表温度、潜热通量以及水汽输送异常的联系.华南地区夏季极端降水异常变化的主要模态显示,华南绝大部分地区夏季极端降水异常呈同相变化,并以2～5年的年际变化最为显著.特别是近50年来该地区夏季极端降水趋势变化在20世纪80年代末存在明显转折,即在1989年之前华南绝大部分地区夏季极端降水频次呈减少趋势,之后表现为增多趋势.结果表明,西北部太平洋同期海气异常与我国华南地区夏季极端降水显著关联的关键区主要位于南海海域及其邻近的西太平洋暖池区.该海域的海表温度、潜热通量的异常变化可能是影响华南夏季极端降水的重要因素,而南海北部水汽经向输送的异常变化可能是引起华南夏季极端降水变异的关键因素之一.这可为我国华南地区夏季极端降水变异规律、机理及模拟预测研究提供一定的参考依据.     

利用船测近海层湍流热通量资料验证OAFlux数据集

美国伍兹霍尔海洋研究所(Woods Hole Oceanographic Institution,WHOI)的客观分析海气通量(Objectively Analyzed air-sea Fluxes,OAFlux)数据集中的近海层湍流热通量数据被公认为最可信,并被广泛地用于气候模式模拟结果检验。利用NOAA ETL(Environmental Technology Laboratory)两个固定观测站点的科学试验的船测通量数据库(TOGA COARE试验观测资料和KAWJEX试验观测资料),对OAFlux的热通量进行验证。结果表明:OAFlux的潜热通量普遍高于船测值,并且风速较大时,两者差异较大。风速对潜热通量的变化趋势起主导作用,海表和大气湿度差影响甚微。低风条件下,OAFlux的潜热通量和船测值差异则很小。海面湍流感热交换很弱,通量值本身依然受到风速的主导作用,但由于感热通量值与观测仪器误差十分接近,导致比较分析异常困难。分析结果表明:在上述两个观测试验期内,由于海表空气湿度和大气的湿度差变化不显著,海气相互作用的强度主要取决于海面风速的变化。     

Changes in Surface Energy Partitioning in China over the Past Three Decades

Surface energy balance and the partitioning of sensible heat flux(SHF) and latent heat flux(LHF) play key roles in land–atmosphere feedback. However,the lack of long-term observations of surface energy fluxes,not to mention spatially extensive ones,limits our understanding of how the surface energy distribution has responded to a warming climate over recent decades(1979–2009) at the national scale in China. Using four state-of-the-art reanalysis products with long-term surface energy outputs,we identified robust changes in surface energy partitioning,defined by the Bowen ratio(BR = SHF/LHF),over different climate regimes in China. Over the past three decades,the net radiation showed an increasing trend over almost the whole of China. The increase in available radiative energy flux,however,was balanced by differential partitioning of surface turbulent fluxes,determined by local hydrological conditions. In semi-arid areas,such as Northeast China,the radiative energy was transferred largely into SHF. A severe deficiency in near-surface and soil moistures led to a significant decreasing trend in LHF. The combined effect of increased SHF and decreased LHF resulted in significant upward trends in the BR and surface warming over Northeast China. In contrast,in the wet monsoon regions,such as southern China,increased downward net radiation favored a rise in LHF rather than in SHF,leading to a significant decreasing trend in the BR. Meanwhile,the increased LHF partly cancelled out the surface warming. The warming trend in southern China was smaller than that in Northeast China. In addition to impacts on heat-related events,the changes in the BR also reflected recent cases of extreme drought in China. Our results indicate that information regarding the BR may be valuable for drought monitoring,especially in regions prone to such conditions.     

夏季我国干旱、半干旱区陆面过程能量平衡及其局地大气环流

利用NCEP资料分析得出,夏季我国干旱,半干旱区在整个欧亚大陆上是陆面感热通量最强的地方,与此对应的陆面潜热通量则最弱.陆面所接收的太阳短波辐射主要以感热和长波辐射的能量形式释放.该区降水量很少,降水量的年际变率也很弱;因此,该区的陆面热量通量都显出很弱的年际变率;然而,这些通量的年代际变率信号则比较显著.我国干旱、半干旱区大气环流的热力过程与其陆面过程特征密切相关.该区对流层大气的辐射冷却很强,达-3 K d-1.由于缺乏水汽和上升运动,大尺度凝结加热率、深对流加热率、浅对流加热率都非常弱.因此,600hPa以上的大气以绝热下沉加热来平衡辐射冷却;600hPa以下,陆面感热引起的垂直扩散加热率非常强,多达8 K d-1,它除了平衡辐射冷却以外还制造对流层低层的对流运动,以绝热上升冷却来平衡多余的垂直扩散加热.总之,我国干旱、半干旱区的陆面过程特征决定了该区大气运动的特殊垂直结构,即对流层低层对流上升运动及其上层的下沉运动.我国干旱、半干旱区陆面能量平衡及其局地大气环流的年代际变率,是全球气候系统年代际变率的必然结果.     

Persistence of Summer Sea Surface Temperature Anomalies in the Midlatitude North Pacific and Its Interdecadal Variability

The present study investigates the persistence of summer sea surface temperature anomalies(SSTAs) in the midlatitude North Pacific and its interdecadal variability. Summer SSTAs can persist for a long time(approximately 8–14 months)around the Kuroshio Extension(KE) region. This long persistence may be strongly related to atmospheric forcing because the mixed layer is too shallow in the summer to be influenced by the anomalies at depths in the ocean. Changes in atmospheric circulation, latent heat flux, and longwave radiation flux all contribute to the long persistence of summer SSTAs. Among these factors, the longwave radiation flux has a dominant influence. The effects of sensible heat flux and shortwave radiation flux anomalies are not significant. The persistence of summer SSTAs displays pronounced interdecadal variability around the KE region, and the variability is very weak during 1950–82 but becomes stronger during 1983–2016. The changes in atmospheric circulation, latent heat flux, and longwave radiation flux are also responsible for this interdecadal variability because their forcings on the summer SSTAs are sustained for much longer after 1982.     

东亚中纬度夏季陆面增暖与土壤湿度异常的联系

利用1979—2015年ERA-Interim再分析土壤湿度、云量资料,NCEP/NCAR再分析环流资料和CPC土壤湿度资料,分析了东亚中纬度夏季陆面热力异常的时空分布特征及其与前期春季土壤湿度异常的联系,探讨了前期春季土壤湿度影响东亚中纬度夏季陆面增暖的可能途径。结果表明,东亚中纬度夏季土壤表层温度呈全区一致增暖趋势,其中贝加尔湖及以南地区温度变化最剧烈、增暖最迅速,且1990年代中期前后存在一个明显由冷向暖的年代际转变。进一步分析发现,春、夏季西西伯利亚到贝加尔湖北部地区的土壤湿度与夏季贝加尔湖及以南地区的土壤表层温度在年代际和年际尺度上均存在紧密联系:西西伯利亚到贝加尔湖北部地区土壤湿度异常偏高,通常对应贝加尔湖及南部地区夏季土壤表层温度偏高。西西伯利亚到贝加尔湖北部地区春、夏土壤湿度异常可以引起夏季大气环流异常,从而对东亚夏季中纬度陆面热力异常产生影响:春、夏土壤湿度偏高时,贝加尔湖及其南部地区上空位势高度为正异常,对应为反气旋性异常环流,云量减少,有利于东亚中纬度陆面增暖;反之,则对应为气旋性异常环流,不利于陆面增暖。     

Evidence for the role of the Atlantic multidecadal oscillation and the ocean heat uptake in hiatus prediction

The recent hiatus in global temperature at the surface has been analysed by several studies, mainly using global climate models. The common accepted picture is that since the late 1990s, the increase in anthropogenic radiative forcings has been counterbalanced by other factors, e.g., a decrease in natural forcings, augmented ocean heat storage and negative phases of ocean–atmosphere-coupled oscillation patterns. Here, simple vector autoregressive models are used for forecasting the temperature hiatus in the period 2001–2014. This gives new insight into the problem of understanding the ocean contribution (in terms of heat uptake and atmosphere–ocean-coupled oscillations) to the appearance of this recent hiatus. In particular, considering data about the ocean heat content until a depth of 700 m and the Atlantic multidecadal oscillation is necessary for correctly forecasting the hiatus, so catching both trend and interannual variability. Our models also show that the ocean heat uptake is substantially driven by the natural component of the total radiative forcing at a decadal time scale, confining the importance of the anthropogenic influences to a longer range warming of the ocean.     

Relative roles of dynamic and thermodynamic processes in causing positive and negative global mean SST trends during the past 100 years

Global mean surface temperature (GMST) during 1910–2012 experienced four alternated rapid warming and warming hiatus phases. Such a temporal variation is primarily determined by global mean sea surface temperature (SST) component. The relative roles of ocean dynamic and thermodynamic processes in causing such global mean SST variations are investigated, using two methods. The first method is ocean mixed layer heat budget analysis. The budget diagnosis result shows that the thermodynamic processes dominate in the rapid warming phases, while the ocean dynamics dominate during the hiatus phases. The second method relies on the diagnosis of a simple equilibrium state model. This model captures well the horizontal distribution of SST difference between two warmer and cooler equilibrium states during either the rapid warming or hiatus phases. It is found that the SST difference during the rapid warming phases is primarily controlled by the increase of downward longwave radiation as both column integrated water vapor and CO₂ increase during the phases. During the hiatus phases, the water vapor induced greenhouse effect offsets the CO₂ effect, and the SST cooling tendency is primarily determined by the ocean dynamics over the Southern Ocean and tropical Pacific. The SST pattern associated with the Interdecadal Pacific Oscillation (IPO) might be responsible for the remote and local ocean dynamic responses through induced wind change.     

Atmospheric Warming Slowdown during 1998?2013 Associated with Increasing Ocean Heat Content

Although atmospheric greenhouse gas concentrations continuously increased, there was relatively little change in global-averaged surface temperatures from 1998 to 2013, which is known as atmospheric warming slowdown. For further understanding the mechanism involved, we explored the energy redistribution between the atmosphere and ocean in different latitudes and depths by using data analysis as well as simulations of a coupled atmosphere–ocean box model. The results revealed that, compared with observational changes of ocean heat content (OHC) associated with rapid warming, the OHC changes related to warming slowdown are relatively larger in multiple ocean basins, particularly in the deeper layer of the Atlantic. The coupled box model also showed that there is a larger increasing trend of OHC under the warming slowdown scenario than the rapid warming scenario. Particularly, during the warming slowdown period, the heat storage in the deeper ocean increases faster than the ocean heat uptake in the surface ocean. The simulations indicated that the warming patterns under the two scenarios are accompanied by distinct outgoing longwave radiation and atmospheric meridional heat transport, as well as other related processes, thus leading to different characteristics of ocean heat uptake. Due to the global energy balance, we suggest this slowdown has a tight relationship with the accelerated heat transport into the global ocean.     

Difference in the Interdecadal Variability of Spring and Summer Sensible Heat Flux over Northwest China

The present study investigates the difference in interdecadal variability of the spring and summer sensible heat fluxes over Northwest China by using station observations from 1960 to 2000. It was found that the spring sensible heat flux over Northwest China was greater during the period from the late 1970s to the 1990s than during the period from the 1960s to the mid-1970s. The summer sensible heat flux was smaller in the late 1980s through the 1990s than it was in the 1970s through the early 1980s. Both the spring and summer land-air temperature differences over Northwest China displayed an obvious interdecadal increase in the late 1970s. Both the spring and summer surface wind speeds experienced an obvious interdecadal weakening in the late 1970s. The change in the surface wind speed played a more important role in the interdecadal variations in sensible heat flux during the summer, whereas the change in the land-air temperature difference was more important for the interdecadal variations in sensible heat flux in the spring. This difference was related to seasonal changes in the mean land-air temperature difference and the surface wind speed. Further analysis indicated that the increase in the spring land surface temperature in Northwest China was related to an increase in surface net radiation.     

Possible Impacts of the Arctic Oscillation on the Interdecadal Variation of Summer Monsoon Rainfall in East Asia

The influences of the wintertime AO (Arctic Oscillation) on the interdecadal variation of summer monsoon rainfall in East Asia were examined. An interdecadal abrupt change was found by the end of the 1970s in the variation of the AO index and the leading principal component time series of the summer rainfall in East Asia, The rainfall anomaly changed from below normal to above normal in central China, the southern part of northeastern China and the Korean peninsula around 1978. However,the opposite interdecadal variation was found in the rainfall anomaly in North China and South China.The interdecadal variation of summer rainfall is associated with the weakening of the East Asia summer monsoon circulation. It is indicated that the interdecadal variation of the AO exerts an influence on the weakening of the monsoon circulation. The recent trend in the AO toward its high-index polarity during the past two decades plays important roles in the land-sea contrast anomalies and wintertime precipitation anomaly. The mid- and high-latitude regions of the Asian continent are warming, while the low-latitude regions are cooling in winter and spring along with the AO entering its high-index polarity after the late 1970s. In the meantime, the precipitation over the Tibetan Plateau and South China is excessive, implying an increase of soil moisture. The cooling tendency of the land in the southern part of Asia will persist until summer because of the memory of soil moisture. So the warming of the Asian continent is relatively slow in summer. Moreover, the Indian Ocean and Pacific Ocean which are located southward and eastward of the Asian land, are warming from winter to summer. This suggests that the contrast between the land and sea is decreased in summer. The interdecadal decrease of the land-sea heat contrast finally leads to the weakening of the East Asia summer monsoon circulation.