A new version of regional ocean reanalysis for coastal waters of China and adjacent seas

A new regional ocean reanalysis over multiple decades (1958–2008) for the coastal waters of China and adjacent seas has been completed by the National Marine Data and Information Service (NMDIS) under the CORA (China Ocean ReAnalysis) project. Evaluations were performed on three aspects: (1) the improvement of general reanalysis quality; (2) eddy structures; and (3) decadal variability of sea surface height anomalies (SSHAs). Results showed that the quality of the new reanalysis has been enhanced beyond ～40% (39% for temperature, 44% for salinity) in terms of the reduction of root mean squared errors (RMSEs) for which the reanalysis values were compared to observed values in the observational space. Compared to the trial version released to public in 2009, the new reanalysis is able to reproduce more detailed eddy structures as seen in satellite and in situ observations. EOF analysis of the reanalysis SSHAs showed that the new reanalysis reconstructs the leading modes of SSHAs much better than the old version. These evaluations suggest that the new CORA regional reanalysis represents a much more useful dataset for the community of the coastal waters of China and adjacent seas.     

2009-18年西北太平洋区域海洋再分析CORA1.0产品研制及检验

在51年(1958-2008)西北太平洋区域海洋再分析CORA1.0产品的基础上,改进了模式配置和同化方法,研制了2009-18年的CORA产品并对其进行以下检验:(1)温盐和海表高度异常均方根误差分布检验;(2)35°N处温度断面分布检验;(3)再分析流场和表漂浮标轨迹对比检验.结果显示,2009-18年的CORA产品可以再现海洋要素长时间序列,时空多尺度的变化特征,为研究特征海洋现象和过程提供背景信息.     

A Regional Ocean Reanalysis System for Coastal Waters of China and Adjacent Seas

A regional ocean reanalysis system for the coastal waters of China and adjacent seas has been developed by the National Marine Data and Information Service(NMDIS).It produces a dataset package called CORA (China ocean reanalysis).The regional ocean model used is based on the Princeton Ocean Model with a generalized coordinate system(POMgcs).The model is parallelized by NMDIS with the addition of the wave breaking and tidal mixing processes into model parameterizations.Data assimilation is a sequential three-dimensional variational(3D-Var) scheme implemented within a multigrid framework.Observations include satellite remote sensing sea surface temperature(SST),altimetry sea level anomaly(SLA),and temperature/salinity profiles.The reanalysis fields of sea surface height,temperature,salinity,and currents begin with January 1986 and are currently updated every year. Error statistics and error distributions of temperature,salinity and currents are presented as a primary evaluation of the reanalysis fields using sea level data from tidal gauges,temperature profiles,as well as the trajectories of Argo floats.Some case studies offer the opportunity to verify the evolution of certain local circulations.These evaluations show that the reanalysis data produced provide a good representation of the ocean processes and phenomena in the coastal waters of China and adjacent seas.     

南海海域海-气耦合模式及其数值模拟试验

在ＮＣＡＲ区域气候模式ＲｅｇＧＭ２和普林斯顿海洋模式ＰＯＭ基础上发展适用于区域海－气相互作用研究的区域海－气耦合模式,模式采用同步耦合、海洋模式将海表温度提供给大气模式,大气模式为海洋模式提供太阳短波辐射、感热能量、潜热通量。海洋与大气模式每１５ｍｉｎ交换一次通量。耦合过程没有使用通量校正。使用该模式对中国南海区域１９９５年５－７月大气和海洋进行了模拟试验,将模拟结果与ＣＯＡＤＳ通量强迫的模拟结果     

Interdecadal Change of the Relationship Between the Tropical Indian Ocean Dipole Mode and the Summer Climate Anomaly in China

The interdecadal change of the relationship between the tropical Indian Ocean dipole(IOD) mode and the summer climate anomaly in China is investigated by using monthly precipitation and temperature records at 210 stations in China and the NCEP/NCAR reanalysis data for 1957-2005.The results indicate that along with the interdecadal shift in the large-scale general circulation around the late 1970s,the relationship between the IOD mode and the summer climate anomaly in some regions of China has significantly changed.Before the late 1970s,a developing IOD event is associated with an enhanced East Asian summer monsoon,which tends to decrease summer precipitation and increase summer temperature in South China;while after the late 1970s,it is associated with a weakened East Asian summer monsoon,which tends to increase(decrease) precipitation and decrease(increase) temperature in the south(north) of the Yangtze River.During the next summer,following a positive IOD event,precipitation is increased in most of China before the late 1970s,while it is decreased(increased) south(north) of the Yangtze River after the late 1970s.There is no significant correlation between the IOD and surface air temperature anomaly in most of China in the next summer before the late 1970s;however,the IOD tends to increase the next summer temperature south of the Yellow River after the late 1970s.     

(Re)Framing ocean acidification in the context of the United Nations Framework Convention on Climate Change (UNFCCC) and Paris Agreement

ABSTRACT

Ocean acidification is most frequently framed by the scientific community as a concurrent threat to climate change, rather than an effect of it. This separation of the two phenomena has long been deemed as a way of garnering heightened policy attention for ocean acidification rather than having it bound up in the often contested politics of climate change. This effort, however, appears to have resulted in the inadvertent placing of ocean acidification outside of the mandate of the United Nations Framework Convention on Climate Change (UNFCCC). This has created a significant gap in the global governance of this issue with no multilateral agreement understood as having jurisdiction over the mitigation of rising ocean acidity. For these reasons this paper argues that an alternative framing of ocean acidification as an effect of climate change is warranted. This would include ocean acidification in the core obligations of the Convention, thereby filling the mitigation governance gap and avoiding perverse implementation outcomes. It is contended that interpreting the UNFCCC in this way is more consistent with its objective and purpose than the existing interpretations that place ocean acidification beyond the remit of the Convention.

Key policy insights

• Ocean acidification is best understood as an effect of climate change in the context of the UNFCCC, and therefore is included in its obligations to combat climate change and its adverse effects.

• An obligation to address ocean acidification has implications for the way that the provisions of the Convention, particularly on mitigation, are implemented. Mitigation activities that exacerbate ocean acidification or lead to emission reduction pathways that do not prevent dangerous acidification should be deemed inconsistent with the Convention.

• Protection, conservation and restoration of coastal and marine ecosystems should become a priority area for action within the UNFCCC.

     

我国近海和邻近海的海洋环境对最近全球气候变化的响应

鉴于全球气候变暖对海洋环境和海洋生态及对经济和社会可持续发展影响的严重性,作者首先利用ERA-40再分析的风场资料以及HadISST 和SODA等海洋高分辨率再分析资料,分析了近50年来全球气候变化对中国近海(包括渤海、黄海、东海和南海)和邻近海(主要是热带和副热带西太平洋)海面附近的风力、海表纬向和经向风应力和海表温度的影响.分析结果表明: 由于受全球气候变暖的影响,1976年之后中国近海和邻近海上空的冬、夏季风变弱,从而引起中国近海冬、夏季海表风应力减弱(尤其是经向风应力),而海表水温明显上升; 并且,冬、夏季海表风应力的减弱和海水温度的上升在中国东海反映尤其明显,这些为中国近海赤潮的频繁发生提供了有利的海洋环境.此外,从中国近海上空环流散度分布的变化可见,中国近海上空从1976年之后大气环流辐散增强,这不利于中国近海上升流的形成,从而会对沿岸水域营养盐的输送产生影响.     

印度洋海温异常和南海夏季风建立迟早的关系I.耦合分析

运用CSVD和联合CSVD等较新颖的统计方法,在去除/未去除ENSO影响的思路下,探讨了印度洋海温异常和南海夏季风建立迟早的关系,结果表明:在没有去除ENSO信号(外部作用)影响的情况下,全区一致型的海温异常分布对南海夏季风建立迟早起着重要的作用。当全区温度距平为正(负)时,南海夏季风建立较晚(早)。在去除了ENSO信号的影响后,非ENSO全区一致型和SIODM型是影响南海夏季风建立早晚的两个主要的印度洋海温分布型。对于非ENSO全区一致型的海温分布,当前期海温全区为负(正)距平时,南海夏季风建立较早(晚)。而对于SIODM型的海温分布,则当前期海温距平为西负东正(西正东负)的SIODM型时,南海夏季风建立较早(晚)。     

Role of the Land Plume in the Transport of Ozone Over the Ocean During Indoex (1999)

Observations from aircraft, an island station, and tworesearch vessels are used to investigate the development of an elevated mixed layeror land plume over the Arabian sea during the Indian Ocean Experiment Intensive FieldPhase 1999 (INDOEX) through air mass modification. Much of the transport of aerosolsand gases occurs in this plume located above a well-mixed convective marine boundary layerwith a depth of 800–1000 m. The depth of the land plume isapproximately 2000 m with the peak ozone concentrations occurring near the centre of this land plume.Significant latitudinal variations in the concentration of ozone occur in the marineboundary layer and in the plume. Mean ozone concentrations in the land plume decreasedwith distance from the Indian coastline.     

华北春季降水及其与前期印度洋海温的关系

利用华北17站1951-2002年春季（3-5月）逐月降水资料和NOAA再分析海表温度资料，研究了华北地区春季降水特征及其与海温的关系。得知华北春季降水偏少年出现频次比偏多年频次高，但是年际变化明显，强度没有偏多年严重。华北地区春季降水有一定的年代际变化和周期性，降水周期在20世纪70年代中期以前为4-6a，在70年代中期以后为6-8a。同时用相关分析方法找出了影响华北地区春季降水的海温关键区为印度洋，发现印度洋在前一年11月到当年1月存在一个相关系数较高海区。用SVD方法证实了前期冬季印度洋海温正是与华北春季降水相关最显著的时段和地区。并用合成分析初步得到印度洋海温异常强迫影响大气环流，并通过遥相关影响华北地区降水。     

SVD揭示的印度洋海气相互作用模态及其与中国降水的联系

利用1958-1999年6-8月平均的GISST(Global Indian Sea Surface Temperature)海表温度资料和同期850 hPa水平风场等NCEP/NCAR再分析资料,作了向量奇异值分解,并对各个模态作了相应分析,发现前两个模态可以很好地表示出印度洋海气耦合的主要部分:第1模态是印度洋海温对ENSO信号的滞后响应;第2模态反映了存在于印度洋的海-气相互作用现象,是ENSO和IOD(Indian Ocean Dipole,印度洋偶极子)的混合模态.讨论了前两个模态与中国夏季降水等变化的联系,发现印度洋海温单极模态与我国华南夏季降水存在负相关,与长江流域及其以北地区存在正相关;印度洋偶极型海温与我国降水的关系不典型.     

中国夏季降水对南印度洋偶极子的响应研究

分析了春季印度洋海表温度（SST）与中国160个站夏季降水的关系,得到:印度洋全海盆的增温趋势与我国夏季降水的气候线性变化趋势是十分一致的。另外,热带外南印度洋出现西南印度洋为正（负）、其东北部出现（负）正海温异常的分布模态时,定义为正（负）南印度洋偶极子PSIOD（NSIOD）事件。SIOD事件对中国夏季降水具有重要影响,PSIOD年,5月份中国江南和西南以及长江中下游的降水偏多;6～8月份华北、东北区域、长江中游以及华南地区降水增多,华南与华北之间的区域降水偏少,即主要为两条雨带的分布。NSIOD年,5月份中国大部降水偏少; 6～8月中国西南、江南地区以及黄淮地区降水偏多。不同时段SIOD所起的作用是不同的,5月,SIOD主要通过改变马斯克林局地环流的变化,影响印度洋低层越赤道的水汽通量输送;6～8月,通过改变海洋大陆下垫面SST热状态,改变其上空对流强度以及水汽输送方向,并间接影响西北太平洋副热带高压的强度和南北位置,进而对中国雨带的分布产生影响。     

A ＂Dressed＂ Ensemble Kalman Filter Using the Hybrid Coordinate Ocean Model in the Pacific

The computational cost required by the Ensemble Kalman Filter (EnKF) is much larger than that of some simpler assimilation schemes, such as Optimal Interpolation (OI) or three-dimension variational assimilation (3DVAR). Ensemble optimal interpolation (EnOI), a crudely simplified implementation of EnKF, is sometimes used as a substitute in some oceanic applications and requires much less computational time than EnKF. In this paper, to compromise between computational cost and dynamic covariance, we use the idea of ``dressing' a small size dynamical ensemble with a larger number of static ensembles in order to form an approximate dynamic covariance. The term ``dressing' means that a dynamical ensemble seed from model runs is perturbed by adding the anomalies of some static ensembles. This dressing EnKF (DrEnKF for short) scheme is tested in assimilation of real altimetry data in the Pacific using the HYbrid Coordinate Ocean Model (HYCOM) over a four-year period. Ten dynamical ensemble seeds are each dressed by 10 static ensemble members selected from a 100-member static ensemble. Results are compared to two EnKF assimilation runs that use 10 and 100 dynamical ensemble members. Both temperature and salinity fields from the DrEnKF and the EnKF are compared to observations from Argo floats and an OI SST dataset. The results show that the DrEnKF and the 100-member EnKF yield similar root mean square errors (RMSE) at every model level. Error covariance matrices from the DrEnKF and the 100-member EnKF are also compared and show good agreement.     

Warming in the Northwestern Indian Ocean Associated with the El Ni(n)o Event

This paper investigates possible warming effects of an El Ni(n)o event on the sea surface temperature anomaly(SSTA)in the northwestern Indian Ocean.Most pure positive Indian Ocean dipole(IOD)events (without an El Ni(n)o event co-occurring) have a maximum positive SSTA mainly in the central Indian Ocean south of the equator.while most co-occurrences with an El Ni(n)o event exhibit a northwest-southeast typical dipole mode.It is therefore inferred that warming in the northwestern Indian Ocean is closely related to the El Ni(n)o event.Based on the atmospheric bridge theory,warming in the northwestern Indian Ocean during co-occurring cases may be primarily caused by relatively less latent heat loss from the ocean due to reduced wind speed.The deepened thermocline also contributes to the warming along the east coast of Africa through the suppressed upwelling of the cold water.Therefore,the El Ni(n)o event is suggested to have a modulating effect on the structure of the dipole mode in the tropical Indian Ocean.     

2014年春季我国主要气候特征及成因简析

提2014年春季（3-5月）,我国大部气温偏高,与2013年春季并列为1961年以来历史同期第二高值。全国平均降水量较常年同期略偏多,其中东北地区降水显著偏多。分析表明,东北降水偏多时段主要发生在5月2-28日,这期间较强的东北冷涡活动是导致东北地区降水偏多的重要原因,其水汽主要来源于东北冷涡从日本海带来的水汽以及偏强偏西的西太平洋副热带高压（简称西太副高）西侧的转向水汽输送。文章还初步探讨了2014年春末南海夏季风爆发偏晚的可能原因。2014年南海夏季风于6月2候爆发,是历史上南海夏季风爆发最晚年之一。导致其爆发偏晚的直接因素是西太副高在4月下旬至5月底持续偏强偏西。进一步的分析结果表明,西太副高在此期间的偏强偏西可能主要由热带印度洋海表迅速增暖所致。     

夏季中国华北降水、印度降水与太平洋海表面温度的耦合关系

本文基于1951~2014年的站点观测资料以及再分析资料,应用多变量经验正交分解法（MEOF）研究了年际尺度上华北夏季降水、印度夏季降水与海表面温度之间的耦合关系（主要模态）。结果表明:当印度夏季降水偏强时,若同期夏季赤道中东太平洋海温表现为La Ni?a位相,则西太平洋暖池对流加强,副热带高压偏西偏北,有利于华北夏季降水与印度夏季降水一致增强。反之,当印度大部降水偏弱时,若同期夏季赤道中东太平洋海温表现为El Ni?o位相,则华北夏季降水和印度夏季降水一致减弱。然而,两地夏季降水的协同变化关系并不总是成立。当赤道中东太平洋海温异常随时间演变表现为冬春El Ni?o衰减型时,伴随着印度洋偶极子（IOD）正位相的衰减过程,这会减弱东亚夏季风,使得华北夏季降水偏少。此时印度半岛夏季降水增强区集中在其西部,无法形成连接印度和华北夏季降水异常的环半球遥相关（CGT）波列,可能使得华北夏季降水异常与全印度夏季降水异常成相反形势。这些结论揭示了中国华北夏季降水、印度夏季降水和海表面温度之间的耦合关系,有助于进一步理解海温外强迫对两地夏季降水之间相关关系的作用,从而对华北夏季降水的预测具有参考意义。     

中-吉-乌铁路(中国段)设计洪水的研究

根据中—吉—乌铁路(中国段)沿线近10个水文观测站40多年(建站一2000年)最大洪峰流量资料，对中—吉—乌铁路(中国段)最大洪峰流量设计值进行系统的研究。应用统计学导出的P—Ⅲ分布，预测了中—吉—乌铁路(中国段)最大洪峰流量不同概率设计值。这对于中—吉—乌铁路(中国段)工程设计和施工及未来铁路养护等具有重要的科学意义和工程价值。     

Forecast Performance of the Pre-operational CMA-TRAMS (EPS) in South China During April - September 2020

The mesoscale ensemble prediction system based on the Tropical Regional Atmosphere Model for the South China Sea (CMA-TRAMS (EPS)) has been pre-operational since April 2020 at South China Regional Meteorological Center (SCRMC), which was developed by the Guangzhou Institute of Tropical and Marine Meteorology (GITMM). To better understand the performance of the CMA-TRAMS (EPS) and provide guidance to forecasters, we assess the performance of this system on both deterministic and probabilistic forecasts from April to September 2020 in this study through objective verification. Compared with the control (deterministic) forecasts, the ensemble mean of the CMATRAMS (EPS) shows advantages in most non-precipitation variables. In addition, the threat score indicates that the CMA-TRAMS (EPS) obviously improves light and heavy rainfall forecasts in terms of the probability-matched mean. Compared with the European Center for Medium-range Weather Forecasts operational ensemble prediction system (ECMWF-EPS), the CMA-TRAMS (EPS) improves the probabilistic forecasts of light rainfall in terms of accuracy, reliability and discrimination, and this system also improves the heavy rainfall forecasts in terms of discrimination. Moreover, two typical heavy rainfall cases in south China during the pre-summer rainy season are investigated to visually demonstrate the deterministic and probabilistic forecasts, and the results of these two cases indicate the differences and advantages (deficiencies) of the two ensemble systems.     

South China Sea Monsoon Experiment （SCSMEX） and the East Asian Monsoon

The SCSMEX is a joint atmospheric and oceanic experiment by international efforts, aiming at studying the onset, maintenance, and variability of the South China Sea (SCS) summer monsoon, thus improving the monsoon prediction in Southeast and East Asian regions. The field experiment carried out in May-August 1998 was fully successful, with a large amount of meteorological and oceanographic data acquired that have been used in four dimensional data assimilations by several countries, in order to improve their numerical simulations and prediction. These datasets are also widely used in the follow-up SCS and East Asian monsoon study. The present paper has summarized the main research results obtained by Chinese meteorologists which cover six aspects: (1) onset processes and mechanism of the SCS summer monsoon; (2) development of convection and mesoscale convective systems (MCSs) during the onset phase and their interaction with large-scale circulation; (3) low-frequency oscillation and teleconnection effect; (4) measurements of surface fluxes over the SCS and their relationship with the monsoon activity; (5) oceanic thermodynamic structures, circulation, and mesoscale eddies in the SCS during the summer monsoon and their relationship with ENSO events; and (6) numerical simulations of the SCS and East Asian monsoon.     

A study of track deflection associated with the landfall of Tropical Cyclone Sidr (2007) over the Bay of Bengal and Bangladesh

In this study, the dynamics of track deflection associated with Tropical Cyclone (TC) Sidr (2007) are explored using a numerical weather prediction model. It is found that (a) the simulated track of Sidr is sensitive to flow, orographic, and model vertical structure that change the environmental steering flow leading to the track deflection. In particular, the track of TC Sidr is deflected northwestward for cases with lower domain height, horizontal domain covering only part of Himalaya mountains, and varying mountain heights; (b) the simulated track of TC Sidr, when compared with GFS reanalysis data, is mainly controlled by its deep-layer environmental steering flow as a point vortex; (c) the northwestward deflection with lower domain height is caused by an artificially larger high pressure at lower levels in the vicinity of the Himalayas, due to the upward propagation of wave energy being reflected by the upper domain boundary; (d) the significant northwestward deflection associated with the varying mountain height cases is due to the cyclone vortex being advected by the northeasterly monsoonal flow, which is blocked by the mountains in the corresponding cases with mountains; (e) the northeastward track deflection after the landfall of Sidr is explained by the addition of the frictional force.In summary, the model vertical domain height and the Himalaya mountain representation play key roles in influencing the accuracy of TC Sidr track simulation, compared with other factors, such as the vertical resolution, at least for TC Sidr.