耦合模式FGOALS-s2海洋同化试验模拟的西北太平洋海气相互作用特征

观测发现,西北太平洋区域夏季降水—SST存在显著的负相关,主要是由于El Ni?o衰减年西北太平洋异常反气旋持续至夏季,该过程是检验耦合模式性能的重要参照标准。本文利用中国科学院大气物理研究所近期气候预测系统IAP-DecPreS,通过海洋同化试验、大气模式AMIP试验与观测结果的比较,评估海洋同化试验对西北太平洋夏季局地海气相互作用特征的模拟影响。结果表明,海洋同化试验能够模拟出西北太平洋区域夏季降水—SST负相关,但负相关区域范围偏小。其与观测之间的最大差异出现在8月,西北太平洋负降水异常及异常反气旋位置偏东,强度偏弱。这是由于其模拟的El Ni?o衰减年夏季赤道东印度洋正降水异常偏弱且移动至赤道南侧,对流层增温偏弱,对西太平洋的遥相关作用偏弱。AMIP试验未考虑大气对海洋的反馈作用,不能再现西北太平洋降水—SST负相关,无法模拟出El Ni?o衰减年夏季西北太平洋异常反气旋。研究表明,海洋同化试验对西北太平洋区域局地海气相互作用特征的模拟能力较AMIP试验有所提升,其对8月西北太平洋降水与环流场的模拟偏差与东赤道印度洋降水模拟偏差有关。     

A New Ocean Mixed-Layer Model Coupled into WRF

A new mesoscale air-sea coupled model (WRF- OMLM-Noh) was constructed based on the Weather Research and Forecasting (WRF) model and an improved Mellor-Yamada ocean mixed-layer model from Noh and Kim (OMLM-Noh). Through off-line tests and a simulation of a real typhoon, the authors compared the performance of the WRF-OMLM-Noh with another existing ocean mixed-layer coupled model (WRF-OMLM-Pollard). In the off-line tests with Tropical Ocean Global Atmosphere Program’s Coupled Ocean Atmosphere Response Experiment (TOGA-COARE) observational data, the results show that OMLM-Noh is better able to simulate sea surface temperature (SST) variational trends than OMLM -Pollard. Moreover, OMLM-Noh can sufficiently reproduce the diurnal cycle of SST. Regarding the typhoon case study, SST cooling due to wind-driven ocean mixing is underestimated in WRF-OMLM-Pollard, which artificially increases the intensity of the typhoon due to more simulated air-sea heat fluxes. Compared to the WRF- OMLM-Pollard, the performance of WRF-OMLM-Noh is superior in terms of both the spatial distribution and temporal variation of SST and air-sea heat fluxes.     

Upper ocean response of the South China Sea to Typhoon Krovanh (2003)

To quantitatively investigate the dynamic and thermal responses of the South China Sea (SCS) during and subsequent to the passage of a real typhoon, a three-dimensional, regional coupled air–sea model is developed to study the upper ocean response of the SCS to Typhoon Krovanh (2003). Owing to the scarcity of ocean observations, the three-dimensional numerical modeling with high resolution, as a powerful tool, offers a valuable opportunity to investigate how the air–sea process proceeds under such extreme conditions. The amplitude and distribution of the cold path produced by the coupled model compare reasonably well with the TRMM/TMI-derived data. The maximum SST cooling is 5.3 °C, about 80 km to the right of the typhoon track, which is consistent with the well-documented rightward bias in the SST response to typhoons. In correspondence to the SST cooling, the mixed layer depth exhibits an increase; the increases in the mixed layer depth on the right of typhoon track are significantly higher than those on the left, with maxima of 58 m. This correspondence indicates that the SST cooling is caused mainly by entrainment. Under the influence of typhoon, a cyclonic, near-surface current field is generated in the upper ocean layer, which moves with the typhoon. The typhoon-induced horizontal currents in the wake of the storm have strong near-inertial oscillation, which gradually propagates downward. The unique features of the SCS response to Typhoon Krovanh are also discussed, such as Kuroshio intrusion and coastal subsurface jets.     

SEA SURFACE TEMPERATURE RESPONSE TEMPERATURE TO TYPHOON MORAKOT (2009) AND ITS INFLUENCE

While previous studies indicate that typhoons can decrease sea surface temperature(SST) along their tracks, a few studies suggest that the cooling patterns in coastal areas are different from those in the open sea. However, little is known about how the induced cooling coupled with the complex ocean circulation in the coastal areas can affect tropical cyclone track and intensity. The sea surface responses to the land falling process of Typhoon Morakot(2009) are examined observationally and its influences on the activity of the typhoon are numerically simulated with the WRF model. The present study shows that the maximum SST cooling associated with Morakot occurred on the left-hand side of the typhoon track during its landfall. Numerical simulations show that, together with the SST gradients associated with the coastal upwelling and mesoscale oceanic vortices, the resulting SST cooling can cause significant difference in the typhoon track, comparable to the current 24-hour track forecasting error. It is strongly suggested that it is essential to include the non-uniform SST distribution in the coastal areas for further improvement in typhoon track forecast.     

SEA SURFACE TEMPERATURE RESPONSE TO TYPHOON MORAKOT(2009) AND ITS INFLUENCE

While previous studies indicate that typhoons can decrease sea surface temperature(SST) along their tracks, a few studies suggest that the cooling patterns in coastal areas are different from those in the open sea. However, little is known about how the induced cooling coupled with the complex ocean circulation in the coastal areas can affect tropical cyclone track and intensity. The sea surface responses to the land falling process of Typhoon Morakot(2009) are examined observationally and its influences on the activity of the typhoon are numerically simulated with the WRF model. The present study shows that the maximum SST cooling associated with Morakot occurred on the left-hand side of the typhoon track during its landfall. Numerical simulations show that, together with the SST gradients associated with the coastal upwelling and mesoscale oceanic vortices, the resulting SST cooling can cause significant difference in the typhoon track, comparable to the current 24-hour track forecasting error. It is strongly suggested that it is essential to include the non-uniform SST distribution in the coastal areas for further improvement in typhoon track forecast.     

中尺度海-气耦合模式GRAPES_OMLM对台风珍珠的模拟研究

利用全球/区域同化与预报系统GRAPES(Global/Regional Assimilation and Prediction System)和改进的Mellor-Yamada型海洋混合层模式OMLM(Ocean Mixed Layer Model),建立了一个新的中尺度海-气耦合模式GRAPES_OMLM,并利用该模式对发生于南海的台风珍珠(0601)进行了模拟研究,检验了GRAPES_OMLM对台风的模拟性能,并分析了局地海-气相互作用对台风的影响。结果表明,GRAPES_OMLM基本能模拟出台风天气过程中的主要物理过程。考虑了海-气相互作用的耦合试验所模拟出的台风强度、近台风中心最大风速以及台风后期移动路径,相对于两组控制试验(单独大气模式)的模拟结果都有较大的改进。而且,采用逐日变化海表温度作为下边界条件的控制试验2的模拟结果相对于SST不变的控制试验1更接近观测。耦合模式GRAPES_OMLM能较好地模拟出台风过境海表温度的变化,台风珍珠在其路径右侧有超过4.0℃的降温。SST的变化和海表风应力的变化呈反相关系,风应力的增大伴随着海洋近表层湍流动能(TKE)的加强,大风动力作用是SST降低的主要原因。SST的降低致使海洋向台风输送的热通量减少,进而削弱了台风的强度并改变台风环流结构,同时通过改变位势涡度趋势的一波结构(WN-1)来影响台风的移动路径。     

Indo-Pacific remote forcing in summer rainfall variability over the South China Sea

This study investigates summer rainfall variability in the South China Sea (SCS) region and the roles of remote sea surface temperature (SST) forcing in the tropical Indian and Pacific Ocean regions. The SCS summer rainfall displays a positive and negative relationship with simultaneous SST in the equatorial central Pacific (ECP) and the North Indian Ocean (NIO), respectively. Positive ECP SST anomalies induce an anomalous low-level cyclone over the SCS-western North Pacific as a Rossby-wave type response, leading to above-normal precipitation over northern SCS. Negative NIO SST anomalies contribute to anomalous cyclonic winds over the western North Pacific by an anomalous east–west vertical circulation north of the equator, favoring more rainfall over northern SCS. These NIO SST anomalies are closely related to preceding La Niña and El Niño events through the “atmospheric bridge”. Thus, the NIO SST anomalies serve as a medium for an indirect impact of preceding ECP SST anomalies on the SCS summer rainfall variability. The ECP SST influence is identified to be dominant after 1990 and the NIO SST impact is relatively more important during 1980s. These Indo-Pacific SST effects are further investigated by conducting numerical experiments with an atmospheric general circulation model. The consistency between the numerical experiments and the observations enhances the credibility of the Indo-Pacific SST influence on the SCS summer rainfall variability.     

利用一个海气耦合模式对台风Krovanh的模拟

采用中尺度大气模式MM5和区域海洋模式POM构造了中尺度海气耦合模式, 模拟了Krovanh (0312) 台风过程中台风－海洋相互作用, 分析了台风引起的海面降温影响台风强度的机制和海洋对台风响应的特征。试验结果显示: 考虑台风引起的海面降温使台风强度模拟有了较大改进, 模拟的台风中心气压和近中心最大风速均与实况较符合。POM模拟的海表面温度与TRMM/TMI观测的海表面温度也较为一致, 台风Krovanh在其路径右侧95 km处引起较大的海面降温, 最大降温幅度达5.8℃。与海表面温度降低相对应的是混合层深度的增加, 较大的海面降温对应较大的混合层加深, 表明大风夹卷在海表面温度的降低中起主要作用。分析表明, 台风引起的海面降温降低海洋向大气输送的潜热通量和感热通量, 特别是在台风内核区, 平均总热通量减少了32.1%。热通量的减少使得湿静力能及湿静力能径向梯度减小, 削弱了台风强度。     

Response of the tropical Indian Ocean SST to decay phase of La Niña and associated processes

Delayed impact of El Niño on Tropical Indian Ocean (TIO) Sea Surface Temperature (SST) variations and associated physical mechanisms are well documented by several studies. However, TIO SST evolution during the decay phase of La Niña and related processes are not adequately addressed before. Strong cooling associated with La Niña decay over the TIO could influence climate over the Indian Oceanic rim including Indian summer monsoon circulation and remotely northwest Pacific circulation. Thus understanding the TIO basin-wide cooling and related physical mechanisms during decaying La Niña years is important. Composite analyses revealed that negative SST anomalies allied to La Niña gradually dissipate from its mature phase (winter) till subsequent summer in central and eastern Pacific. In contrast, magnitude of negative SST anomalies in TIO, induced by La Niña, starts increasing from winter and attains their peak values in early summer. It is found that variations in heat flux play an important role in SST cooling over the central and eastern equatorial Indian Ocean, Bay of Bengal and part of Arabian Sea from late winter to early summer during the decay phase of La Niña. Ocean dynamical processes are mainly responsible for the evolution of southern TIO SST cooling. Strong signals of westward propagating upwelling Rossby waves between 10°S to 20°S are noted throughout (the decaying phase of La Niña) spring and summer. Anomalous cyclonic wind stress curl to the south of the equator is responsible for triggering upwelling Rossby waves over the southeastern TIO. Further, upwelling Rossby waves are also apparent in the Arabian Sea from spring to summer and partly contributing to the SST cooling. Heat budget analysis reveals that negative SST/MLT (mixed layer temperature) anomalies over the Arabian Sea are mostly controlled by heat flux from winter to spring and vertical advection plays an important role during early summer. Vertical and horizontal advection terms primarily contribute to the SST cooling anomalies over southern TIO and the Bay of Bengal cooling is primarily dominated by heat flux. Further we have discussed influence of TIO cooling on local rainfall variations.     

APPLIED STUDY ON ATMOSPHERE-OCEAN-WAVE COUPLED MODEL IN SOUTH CHINA SEA

Based on MM5,POM,and WW3,a regional atmosphere-ocean-wave coupled system is developed in this work under the environment of Message Passing Interface.The coupled system is applied in a study of two typhoon processes in the South China Sea(SCS).The results show that the coupled model operates steadily and efficiently and exhibits good capability in simulating typhoon processes.It improves the simulation accuracy of the track and intensity of the typhoon.The response of ocean surface to the typhoon is remarkable,especially on the right side of the typhoon track.The sea surface temperature(SST)declines,and the ocean current and wave height are intensified.In the coupling experiment,the decline of SST intensifies and the inertial oscillation amplitude of the ocean current increases when the ocean-wave effect is considered.Therefore,the atmosphere-ocean-wave coupled system can help in the study of air-sea interaction and improve the capability of predicting and preventing weather and oceanic disasters in SCS.     

Influence of the South China Sea Biweekly Sea Surface Temperature on the South China Sea Summer Monsoon Especially during the Indian Ocean Dipole

The influence of the biweekly sea surface temperature (SST) in the South China Sea (SCS) on the SCS summer monsoon, especially during the Indian Ocean Dipole (IOD) is presented using the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) SST and rainfall data for April to June from 1999 to 2013. During positive IOD (PIOD) years the biweekly SST anomalies over the SCS lead the rain anomalies by three days, with a significant correlation (r?=?0.8, at the 99% confidence level), whereas during negative IOD (NIOD) years, the correlation is only 0.2. The biweekly SST is observed to influence the westward and northward propagating rainfall anomalies over the SCS and, hence, affect the SCS summer monsoon, especially during PIOD years. No such propagation was seen during NIOD years. The biweekly intraseasonal oscillation of SST in the SCS results in enhanced sea level pressure and surface shortwave radiation, especially during PIOD years. The potential findings here indicate that the biweekly SST in the SCS is strongly (weakly) influenced during PIOD (NIOD) years. Further, it is observed that SST in the SCS has a strong (weak) effect on the SCS summer monsoon by westward and northward propagation of rainfall, especially during PIOD (NIOD) years. When a PIOD or NIOD exists over the tropical Indian Ocean, the SCS SST will be strongly (r?=?0.6, at the 99% confidence level) or weakly correlated with the residual index, respectively.     

Individual and combined impacts of ENSO and East Asian winter monsoon on the South China Sea cold tongue intensity

A region of low sea surface temperature (SST) extends southward in the central part of southern South China Sea during boreal winter, which is called the South China Sea cold tongue (SCS CT). The present study investigates the factors of interannual variation of SST in the SCS CT region and explores the individual and combined impacts of El Niño-Southern Oscillation (ENSO) and East Asian winter monsoon (EAWM) on the SCS CT intensity. During years with ENSO alone or with co-existing ENSO and anomalous EAWM, shortwave radiation and ocean horizontal advection play major roles in the interannual variation of the SCS CT intensity. Ocean advection contributes largely to the SST change in the region southeast of Vietnam. In strong CT years with anomalous EAWM alone, surface wind-related latent heat flux has a major role and shortwave radiation is secondary to the EAWM-induced change of the SCS CT intensity, whereas the role of ocean horizontal advection is relatively small. The above differences in the roles of ocean advection and latent heat flux are associated with the distribution of low level wind anomalies. In anomalous CT years with ENSO, low level anomalous cyclone/anticyclone-related wind speed change leads to latent heat flux anomalies with effects opposite to shortwave radiation. In strong CT years with anomalous EAWM alone, surface wind-related latent heat flux anomalies are large as anomalous winds are aligned with climatological winds.

     

Contribution of tropical cyclones to abnormal sea surface temperature warming in the Yellow Sea in December 2004

Unusual sea surface temperature (SST) warming occurred over the Yellow Sea (YS) in December 2004. To identify the causes of the abnormal SST warming, we conducted an analysis on atmospheric circulation anomalies induced by tropical cyclones (TCs) and their impacts on upper ocean characteristics using multiple datasets. With the analysis of various datasets, we explored a new aspect of the relationship between TC activity and SST. The results show that there is a significant link between TC activity over the Northwest Pacific (NWP) and SST in the YS. The integrated effect of consecutive TCs activity induces a large-scale atmospheric cyclonic circulation anomaly over the NWP and consequently anomalous easterly winds over the YS and East China Sea. The mechanism of the unusually warm SST in the YS can be explained by considering TCs acting as an important source of Ekman heat transport that results in substantial intrusion of relatively warm surface water into the YS interior. Furthermore, TC-related circulation anomalies contribute to the retention of the resulting warm SST anomalies in the entire YS.     

Contrasting Indian Ocean SST variability with and without ENSO influence: A coupled atmosphere-ocean GCM study

Summary In this study, we perform experiments with a coupled atmosphere-ocean general circulation model (CGCM) to examine ENSO’s influence on the interannual sea-surface temperature (SST) variability of the tropical Indian Ocean. The control experiment includes both the Indian and Pacific Oceans in the ocean model component of the CGCM (the Indo-Pacific Run). The anomaly experiment excludes ENSO’s influence by including only the Indian Ocean while prescribing monthly-varying climatological SSTs for the Pacific Ocean (the Indian-Ocean Run). In the Indo-Pacific Run, an oscillatory mode of the Indian Ocean SST variability is identified by a multi-channel singular spectral analysis (MSSA). The oscillatory mode comprises two patterns that can be identified with the Indian Ocean Zonal Mode (IOZM) and a basin-wide warming/cooling mode respectively. In the model, the IOZM peaks about 3–5 months after ENSO reaches its maximum intensity. The basin mode peaks 8 months after the IOZM. The timing and associated SST patterns suggests that the IOZM is related to ENSO, and the basin-wide warming/cooling develops as a result of the decay of the IOZM spreading SST anomalies from western Indian Ocean to the eastern Indian Ocean. In contrast, in the Indian-Ocean Run, no oscillatory modes can be identified by the MSSA, even though the Indian Ocean SST variability is characterized by east–west SST contrast patterns similar to the IOZM. In both control and anomaly runs, IOZM-like SST variability appears to be associated with forcings from fluctuations of the Indian monsoon. Our modeling results suggest that the oscillatory feature of the IOZM is primarily forced by ENSO.     

Decadal predictions of the cooling and freshening of the North Atlantic in the 1960s and the role of ocean circulation

In the 1960s North Atlantic sea surface temperatures (SST) cooled rapidly. The magnitude of the cooling was largest in the North Atlantic subpolar gyre (SPG), and was coincident with a rapid freshening of the SPG. Here we analyze hindcasts of the 1960s North Atlantic cooling made with the UK Met Office’s decadal prediction system (DePreSys), which is initialised using observations. It is shown that DePreSys captures—with a lead time of several years—the observed cooling and freshening of the North Atlantic SPG. DePreSys also captures changes in SST over the wider North Atlantic and surface climate impacts over the wider region, such as changes in atmospheric circulation in winter and sea ice extent. We show that initialisation of an anomalously weak Atlantic Meridional Overturning Circulation (AMOC), and hence weak northward heat transport, is crucial for DePreSys to predict the magnitude of the observed cooling. Such an anomalously weak AMOC is not captured when ocean observations are not assimilated (i.e. it is not a forced response in this model). The freshening of the SPG is also dominated by ocean salt transport changes in DePreSys; in particular, the simulation of advective freshwater anomalies analogous to the Great Salinity Anomaly were key. Therefore, DePreSys suggests that ocean dynamics played an important role in the cooling of the North Atlantic in the 1960s, and that this event was predictable.     

THE WARMING MECHANISM IN THE SOUTHERN ARABIAN SEA DURING THE DEVELOPMENT OF INDIAN OCEAN DIPOLE EVENTS

This study aims to explore the relative role of oceanic dynamics and surface heat fluxes in the warming of southern Arabian Sea and southwest Indian Ocean during the development of Indian Ocean Dipole (IOD) events by using National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) daily reanalysis data and Global Ocean Data Assimilation System (GODAS) monthly mean ocean reanalysis data from 1982 to 2013, based on regression analysis, Empirical Orthogonal Function (EOF) analysis and combined with a 2? layer dynamic upper-ocean model. The results show that during the initial stage of IOD events, warm downwelling Rossby waves excited by an anomalous anticyclone over the west Indian Peninsula, southwest Indian Ocean and southeast Indian Ocean lead to the warming of the mixed layer by reducing entrainment cooling. An anomalous anticyclone over the west Indian Peninsula weakens the wind over the Arabian Sea and Somali coast, which helps decrease the sea surface heat loss and shallow the surface mixed layer, and also contributes to the sea surface temperature (SST) warming in the southern Arabian Sea by inhibiting entrainment. The weakened winds increase the SST along the Somali coast by inhibiting upwelling and zonal advection. The wind and net sea surface heat flux anomalies are not significant over the southwest Indian Ocean. During the antecedent stage of IOD events, the warming of the southern Arabian Sea is closely connected with the reduction of entrainment cooling caused by the Rossby waves and the weakened wind. With the appearance of an equatorial easterly wind anomaly, the warming of the southwest Indian Ocean is not only driven by weaker entrainment cooling caused by the Rossby waves, but also by the meridional heat transport carried by Ekman flow. The anomalous sea surface heat flux plays a key role to damp the warming of the west pole of the IOD.     

The rendition of the Atlantic Warm Pool in the reanalyses

The Atlantic Warm Pool (AWP) region, which is comprised of the Gulf of Mexico, Caribbean Sea and parts of the northwestern tropical Atlantic Ocean, is one of the most poorly observed parts of the global oceans. This study compares three ocean reanalyses, namely the Global Ocean Data Assimilation System of National Centers for Environmental Prediction (NCEP), the Climate Forecast System Reanalysis (CFSR) of NCEP, and the Simple Ocean Data Assimilation (SODA) for its AWP variation. The surface temperature in these ocean reanalyses is also compared with that from the Extended Range SST version 3 and Optimally Interpolated SST version 2 SST analyses. In addition we also compare three atmospheric reanalyses: NCEP-NCAR (R1), NCEP-DOE (R2), and CFSR for the associated atmospheric variability with the AWP. The comparison shows that there are important differences in the climatology of the AWP and its interannual variations. There are considerable differences in the subsurface ocean manifestation of the AWP with SODA (CFSR) showing the least (largest) modulation of the subsurface ocean temperatures. The remote teleconnections with the tropical Indian Ocean are also different across the reanalyses. However, all three oceanic reanalyses consistently show the absence of any teleconnection with the eastern equatorial Pacific Ocean. The influence of the AWP on the tropospheric temperature anomalies last for up to a one season lead and it is found to be relatively weak in R1 reanalyses. A simplified SST anomaly equation initially derived for diagnosing El Niño Southern Oscillation variability is adapted for the AWP variations in this study. The analysis of this equation reveals that the main contribution of the SST variation in the AWP region is from the variability of the net heat flux. All three reanalyses consistently show that the role of the ocean advective terms, including that associated with upwelling in the AWP region, is comparatively much smaller. The covariance of the SST tendency in the AWP with the net heat flux is large, with significant contributions from the variations of the surface shortwave and longwave fluxes.     

Study of the Air-Sea Interaction During Typhoon Kaemi (2006)

The high-resolution Weather Research and Forecasting (WRF) model is coupled to the Princeton Ocean Model (POM) to investigate the effect of air-sea interaction during Typhoon Kaemi that formed in the Northwest Pacific at 0000 UTC 19 July 2006. The coupled model can reasonably reproduce the major features of ocean response to the moving tropical cyclone (TC) forcing, including the deepening of ocean mixed layer (ML), cooling of sea surface temperature (SST), and decaying of typhoon.     

Indian summer monsoon rainfall predictability and variability associated with Northwest Pacific circulation in a suit of coupled model hindcasts

The Northwest Pacific (NWP) circulation (subtropical high) is an important component of the East Asian summer monsoon system. During summer (June–August), anomalous lower tropospheric anticyclonic (cyclonic) circulation appears over NWP in some years, which is an indicative of stronger (weaker) than normal subtropical high. The anomalous NWP cyclonic (anticyclonic) circulation years are associated with negative (positive) precipitation anomalies over most of Indian summer monsoon rainfall (ISMR) region. This indicates concurrent relationship between NWP circulation and convection over the ISMR region. Dry wind advection from subtropical land regions and moisture divergence over the southern peninsular India during the NWP cyclonic circulation years are mainly responsible for the negative rainfall anomalies over the ISMR region. In contrast, during anticyclonic years, warm north Indian Ocean and moisture divergence over the head Bay of Bengal-Gangetic Plain region support moisture instability and convergence in the southern flank of ridge region, which favors positive rainfall over most of the ISMR region. The interaction between NWP circulation (anticyclonic or cyclonic) and ISMR and their predictability during these anomalous years are examined in the present study. Seven coupled ocean–atmosphere general circulation models from the Asia-Pacific Economic Cooperation Climate Center and their multimodel ensemble mean skills in predicting the seasonal rainfall and circulation anomalies over the ISMR region and NWP for the period 1982–2004 are assessed. Analysis reveals that three (two) out of seven models are unable to predict negative (positive) precipitation anomalies over the Indian subcontinent during the NWP cyclonic (anticyclonic) circulation years at 1-month lead (model is initialized on 1 May). The limited westward extension of the NWP circulation and misrepresentation of SST anomalies over the north Indian Ocean are found to be the main reasons for the poor skill (of some models) in rainfall prediction over the Indian subcontinent. This study demonstrates the importance of the NWP circulation variability in predicting summer monsoon precipitation over South Asia. Considering the predictability of the NWP circulation, the current study provides an insight into the predictability of ISMR. Long lead prediction of the ISMR associated with anomalous NWP circulation is also discussed.     

The Effect of Intensity： Typhoon-Induced SST Cooling on Typhoon The Case of Typhoon Chanchu （2006）

In order to investigate air-sea interactions during the life cycle of typhoons and the quantificational effects of typhoon-induced SST cooling on typhoon intensity, a mesoscale coupled air-sea model is developed based on the non-hydrostatic mesoscale model MM5 and the regional ocean model POM, which is used to simulate the life cycle of Typhoon Chanchu （2006） from a tropical depression to a typhoon followed by a steady weakening. The results show that improved intensity prediction is achieved after considering typhoon-induced SST cooling; the trend of the typhoon intensity change simulated by the coupled model is consistent with observations. The weakening stage of Typhoon Chanchu from 1200 UTC 15 May to 1800 UTC 16 May can be well reproduced, and it is the typhoon-induced SST cooling that makes Chanchu weaken during this period. Analysis reveals that the typhoon-induced SST cooling reduces the sensible and latent heat fluxes from the ocean to the typhoon＇s vortex, especially in the inner-core region. In this study, the average total heat flux in the inner-core region of the typhoon decrease by 57.2%, whereas typhoon intensity weakens by 46%. It is shown that incorporation of the typhoon-induced cooling, with an average value of 2.17℃, causes a 46-hPa weakening of the typhoon, which is about 20 hPa per 1℃ change in SST.