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All Abstracts of Session OS29

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Oral Presentations

OS29 - Climate Processes And Climate Change Over The Maritime Continent And Surrounding Region
Tuesday, August 02, 2016 | 303A (L3S) | 08:30-10:30
1.
OS29-D2-AM1-303A(L3S)-001 (OS29-A003)
 
Decadal Variability of the IOD-ENSO Teleconnection in the CMIP5 Climate Models
Dongliang YUAN#+, Peng XU, Tengfei XU, Xia ZHAO
Chinese Academy of Sciences, China
#Corresponding author: dyuan@ms.qdio.ac.cn +Presenter

The correlations between the Dipole Mode Index and the Niño3.4 index at the one-year time lag are found to have decadal variability in the observations. The dynamics of this decadal variability is investigated using the CMIP5 model simulations, which are found to be able to reproduce this decadal variability.  The composed lag correlations between the oceanic anomalies across the Indo-Pacific Ocean are calculated during the positive and negative phases of the decadal variability, separately. The results suggest that the oceanic channel, i.e. the variability of the ITF, play an important role in the IOD-ENSO precursory relation at the one-year time lag during the positive phase of the decadal variability. In contrast, the lag correlations between the surface zonal wind anomalies (SZWA) over the far western equatorial Pacific in fall and the Indo-Pacific SZWA are insignificant, suggesting that the atmospheric bridge is not responsible for the IOD-ENSO teleconnection at the one-year time lag during the positive phase of the decadal variability.  Analyses also suggest that the lag correlations between the western Pacific SZWA in fall and the oceanic anomalies in the equatorial Pacific cold tongue at the one-year lag are artificial in most of the CMIP5 historical simulations, suggesting model deficiencies in simulating the atmospheric bridge over the Indo-Pacific Oceans.

During the negative phases of the decadal variability, the thermocline depth of the eastern equatorial Pacific is deeper so that the IOD-induced anomalies in the equatorial Pacific Ocean are present at a deeper depth than in the positive phases of the decadal variability.  This has resulted in lack of response in the cold tongue SSTA to the oceanic channel dynamics.  Analyses have shown that the oceanic channel dynamics are overwhelmed by the ocean-atmosphere coupling over the equatorial Pacific Ocean during the negative phases of the decadal variability.

2.
OS29-D2-AM1-303A(L3S)-002 (OS29-A015)
 
Diurnal Cycle of Convection and Surface Forcing over the Maritime Continent and Variability Associated with the MJO
Shuyi S. CHEN#+
University of Miami, United States
#Corresponding author: schen@rsmas.miami.edu +Presenter

It has been well documented that the diurnal maximum of convection and precipitation is observed during the morning hours (AM) over the ocean, whereas the maximum is during the afternoon hours (PM) over land.  However, the difference between AM and PM precipitation in the coastal/adjacent seas over the Maritime Continent (MC) is 2-3 times larger than anywhere else in the tropics. Most large mesoscale convective systems (MCSs) during the local active phases of the MJO are over water of the MC. This makes the convective signals of the Madden-Julian Oscillation (MJO) much larger over the water than over the islands when the MJO moves through the MC. In this study, we examine the diurnal cycle of formation, propagation, and dissipation of MCSs by tracking cloud clusters in time and space using hourly satellite IR data and 3-hourly TRMM data. It is found that the large AM precipitation over the adjacent seas is a result of the propagating MCSs from the islands to the sea during the night, which are forced by the enhanced land breeze from the high mountains of the islands in the MC. MCSs can also initiate over the seas during the diurnal maximum of SST in the afternoon and continue to grow into the night and maximize during the early morning. The diurnal cycle of convection is modulated by the MJO. The two factors together may explain the large diurnal amplitude over the adjacent seas of the MC than that of the open ocean. The complex interactions of the convection, local and large-scale circulation, and the unique land-sea geography of the MC are further investigated using a high-resolution, coupled atmosphere-ocean model. The result indicates that the diurnal cycle of SST is affected by the tidal mixing in the ocean, which may be an important factor contributing to the air-sea interaction on the diurnal and MJO time scales. 

3.
OS29-D2-AM1-303A(L3S)-003 (OS29-A014)
 
Intraseasonal Variability Over Indian Ocean and Maritime Continent
Chung-Hsiung SUI#+, Ching-Shu HUNG
National Taiwan University, Taiwan
#Corresponding author: sui@as.ntu.edu.tw +Presenter

The intraseasonal variability and its associated moistening processes over Indian Ocean (IO) and Maritime Continent (MC) are investigated through a diagnosis of ECMWF Re-analysis (ERA-Interim) data in Nov.-April, 1982-2011. During this period, 27 MJO events with strong magnitude and clear propagation are identified and further classified as either primary, or successive, according to the existence of preceding event. A composite of scale-separated moisture (qv) budget is analyzed in four stages: suppressed, cloud developing, convective and decaying, for IO and MC, respectively. In the suppressed stage, the dominant moisture source over both region is surface evaporation/shallow convection (-Q2). Nonlinear zonal (meridional) advection by synoptic disturbances also has non-negligible contribution over IO (MC). In the cloud developing stage, qv approaches maximum with moistening tendency to its east. This moistening is contributed by the advection of mean moisture by anomalous easterlies associated with downstream Rossby wave response of the dry anomaly and boundary layer frictional moisture convergence. In the convective stage, while the zonal advection of anomalous westerlies and intense precipitation dries the atmosphere, the moistening of meridional advection by downstream Rossby anti-cyclonic gyres leads to the eastward propagation of deep convection. In the decaying stage, the strong westerlies bring in dry air from the west causing widespread drying. Overall, the moisture evolution of MC is consistent with IO expect meridional component is more essential in suppressed stage. A column-integrated moist static energy (MSE) budget analysis shows that longwave heating is the dominant term in convective stage and latent heat flux is more prominent in decaying stage when the westerly is strong. The in-phase relation of longwave heating with column-integrated MSE suggests that longwave heating acts to maintain MSE and retard the propagation. Latent heat flux also slows down the propagation due to the phase lag.

4.
OS29-D2-AM1-303A(L3S)-004 (OS29-A010)
 
Role of MJO-Diurnal Cycle Interaction in the Barrier Effect on the MJO by the Maritime Continent
Chidong ZHANG#+
University of Miami, United States
#Corresponding author: czhang@rsmas.miami.edu +Presenter

It has been known that the diurnal cycle of rainfall in the Maritime Continent (MC) is modulated by the MJO. Possible feedback from the diurnal cycle to the MJO is mush less clear. In this presentation, a hypothesis is proposed in which land-locked diurnal convection acts as a possible barrier effect on the MJO by the MC. This hypothesis centers at a premise that convective signals of MJO propagation through the MC are mainly over the water of the Indonesian Seas. Landlocked diurnal convection in the MC tends to disrupt the structural evolution of the cloud population, moisture supply, and large-scale circulation of the MJO, hence a barrier effect on the MJO. Several processes related to the MJO may help overcome this barrier effect, so some MJO events may propagate through the MC. An observational plan during the field campaign of Years of the Maritime Continent (YMC) is introduced. 

5.
OS29-D2-AM1-303A(L3S)-005 (OS29-A008)
 
The Variation Patterns of SST in the Tropical Western Pacific and Their Roles in Bridging the Across-Seasonal Connections Between IOD and East Asian Climate
Shuanglin LI#+
Chinese Academy of Sciences, China
#Corresponding author: shuanglin.li@mail.iap.ac.cn +Presenter

Previous Studies suggest a connection between the Indian Ocean SST Dipole (IOD) and following-winter East Asian climate. Due to the involvement and the dominance of ENSO signals in the observations, the underlying mechanism for the connection is unclear. In the study we analyzed the IOD-related SST variation patterns in the western tropical Pacific, and explored their roles in bridging the across-seasonal connection between the IOD and East Asian winter climate. Our results suggest the substantial importance of the tropical western Pacific SST, and provide an alternative explanation to the unsteady connection of East Asian winter climate with IOD.

6.
OS29-D2-AM1-303A(L3S)-006 (OS29-A005)
 
Low-Frequency Variability of the Shallow Meridional Overturning Circulation in the South China Sea
Zhitong YANG1+, Yiyong LUO2#
1 Ocean University of China, China, 2 Ocean University of China, China
#Corresponding author: yiyongluo@ouc.edu.cn +Presenter

The low-frequency variability of the shallow meridional overturning circulation (MOC) in the South China Sea(SCS) is investigated using a Simple Ocean Data Assimilation (SODA) product for the period of 1900–2010. A dynamical decomposition method is used in which the MOC is decomposed into the Ekman, external mode, and vertical shear components. Results show that all the three dynamical components contribute to the formation of the seasonal and annual mean shallow MOC in the SCS. The shallow MOC in the SCS consists of two cells: a clockwise cell in the south and an anticlockwise cell in the north; the former is controlled by the Ekman flow and the latter is dominated by the external barotropic flow, with the contribution of the vertical shear being to reduce the magnitude of both cells. In addition, the strength of the MOC in the south is found to have a falling trend over the past century, due mainly to a weakening of the Luzon Strait transport (LST) that reduces the transport of the external component. Further analysis suggests that the weakening of the LST is closely related to a weakening of the westerly wind anomalies over the equatorial Pacific, which leads to a southward shift of the North Equatorial Current (NEC) bifurcation and thus a stronger transport of the Kuroshio east of Luzon.

7.
OS29-D2-AM1-303A(L3S)-007 (OS29-A011)
 
Anomalous Behaviors of Wyrtki Jets Over the Equatorial Indian Ocean in 2013
Lin LIU#+, Yongliang DUAN
State Oceanic Administration, China
#Corresponding author: liul@fio.org.cn +Presenter

In-situ measurement of the upper ocean velocity discloses significant abnormal behaviors of two Wyrtki Jet (WJ), boreal spring WJ and fall WJ, over the tropical Indian Ocean in 2013. The two WJs occur within upper 130 m depth and persistent over than one month time. Unlike the climatological peak time of the fall WJ in November, the fall WJ in 2013 unexpectedly peaks in December, one month later than its normal condition, and the exceptional spring jet in May is also unusually stronger than the one in fall. Further analysis illustrates that the anomalous changes in the equatorial zonal wind forcing, associated with obvious intraseasonal oscillation events, primary contribute to the anomalous WJs activities. 

8.
OS29-D2-AM1-303A(L3S)-008 (OS29-A018)
 
Modulation of the South China Sea Througflow on Seasonal and Interannual Variability of the Indonesian Throughflow
Jun WEI#+
Peking University, China
#Corresponding author: junwei@pku.edu.cn +Presenter

Using a high-resolution (0.1° × 0.1°) regional ocean model, this study investigated potential roles of the South China Sea Throughflow (SCSTF) on seasonal and interannual variability of the Indonesian Throughflow (ITF) through the Karimata Strait and Mindoro–Sibutu passages. The model’s effectiveness in simulating the general circulation and SCSTF/ITF through internal seas/straits was validated against observations, SODA re-analysis, and previous results. It is found that although the total ITF transport is primarily formed by Mindanao Current leakage into the Sulawesi Sea (up to 83%), its seasonal variability is jointly determined by the Mindanao–Sulawesi flow and SCSTF through the Karimata Strait and Mindoro–Sibutu passages. The Mindanao–Sulawesi flow reaches maximum westward transport during summer with a seasonal cycle of 5.6 Sv, and the Mindoro–Sibutu flow has an opposite seasonality of 3.6 Sv with maximum transport during winter. The two flows merge in the Sulawesi Sea and produce a 2.8-Sv subdued seasonality within the Makassar Strait. The ENSO signal (transmitted into SCS and the Indonesian seas) is important in regulating SCSTF/ITF interannual variability. The Mindoro–Sibutu flow is enhanced during El Niño as more Pacific water intrudes into SCS via the Luzon Strait. This flow forces more buoyant SCS water into the Sulawesi Sea, producing a positive sea surface height gradient anomaly against the Mindanao–Sulawesi flow, thereby inhibiting Mindanao Current leakage into the Sulawesi Sea. This situation is absent during La Niña years. Conversely, SCSTF through the Karimata Strait is mostly driven by seasonal monsoons and is therefore insignificant in ITF interannual variability.

OS29 - Climate Processes And Climate Change Over The Maritime Continent And Surrounding Region
Tuesday, August 02, 2016 | 303A (L3S) | 16:00-18:00
1.
OS29-D2-PM2-303A(L3S)-009 (OS29-A016)
 
The Madden-Julian Oscillation Imprint on the Indonesian Throughflow
Asmi NAPITU1,2#+, Arnold L. GORDON1, Kandaga PUJIANA3
1 Columbia University, United States, 2 Ministry of Marine Affairs and Fisheries, Indonesia, 3 Oregon State University, United States
#Corresponding author: asminapitu@gmail.com +Presenter

Air-sea heat flux associated with the Madden-Julian Oscillation (MJO) affects sea surface temperature (SST) at intraseasonal timescales in some major basins of the Indonesian Seas (Napitu et. al., 2015). The MJO demonstrates seasonality and strongly projects on intraseasonal SST during boreal winter. Seasonal SST variations over the Indonesian Seas are also regulated by the Indonesian Throughflow (ITF), the flow of Pacific water into the Indian Ocean. Here, we investigate the impact of strong MJO events on the ITF variability during 2004-mid 2015. Observations at some ITF channels reveal that the MJO relaxes the ITF transport through two mechanisms: 1. Westerly wind bursts attributed to the MJO drives Ekman transport within the upper 100 m of the ITF passages, resulting in the weakening or reversing the ITF transport; 2. The MJO forced-oceanic Kelvin waves generated over the equatorial Indian Ocean penetrate into the ITF passages and propagate against and relax the ITF transport, a couple of weeks after the MJO’s westerly wind bursts cease over the Indonesian Seas. The first mechanism appears to cool SST, while the second one accelerates SST recovery over the Indonesian Seas. Moreover near-inertial motions are also evident in the ITF variability in the wake of the MJO events. This near-inertial variability increases sheared currents within the upper 100-m which potentially intensifies vertical mixing and prolongs SST cooling following the MJO passages.

2.
OS29-D2-PM2-303A(L3S)-010 (OS29-A009)
 
Maritime Continent - The Barrier of the Eastward Propagation of Madden Julian Oscillation
Jian LING#+
Chinese Academy of Sciences, China
#Corresponding author: lingjian@lasg.iap.ac.cn +Presenter

A newly developed method was used to identify the MJO events from 1998 to 2013 using TRMM precipitation data. Several characteristics of MJO can be retrieved using this method, such as its west and east propagation boundaries as well as their corresponding date, the averaged propagation speed and amplitude. Each MJO event was then classified into two catalogs based on whether it can propagate through the Maritime Continent (MC). The results show that whether MJO propagates through the MC has notable seasonal dependence. There were only 15% of MJO events fail to propagate through MC during the boreal winter while almost 40% during the boreal summer from 1998 to 2013. The fundamental difference between the boreal winter and summer for MJO events across the MC was diagnosed and key factor for determining whether MJO propagates through the MC was also revealed.

3.
OS29-D2-PM2-303A(L3S)-011 (OS29-A001)
 
The Variations of South China Sea Summer Monsoon Onset
Lei YANG#+
South China Sea Institute of Oceanology, China
#Corresponding author: leiyang@scsio.ac.cn +Presenter

South China Sea summer monsoon (SCSSM) is an important component of the Asian summer monsoon. One of the most important features of the SCSSM is its abrupt climatological onset across the SCS basin in the middle of May. The onset date has strong interanual variability, with the earliest of 23rd pentad (21-26 April) in 1975 and 1985, and the latest of 33rd pentad (11-16 June) in 1973 during 1958-2014. The onset date varies with different methods. The physical mechanism for the variation of monsoon onset maybe related to the anomaly of intraseasonal variability, thermal precondition of atmosphere or upper ocean heat content.  NCEP reanalysis data and CMIP5 models will be used to access whether this extreme event is related to anthropogenic climate change. 

4.
OS29-D2-PM2-303A(L3S)-012 (OS29-A006)
 
Impacts of Typhoons on Upper-Ocean Mixing and the Kuroshio in the Northwestern Pacific Ocean
Hiroaki TADA#+, Yusuke UCHIYAMA
Kobe University, Japan
#Corresponding author: hiroaki1174226@gmail.com +Presenter

Typhoons alter the upper ocean dynamics and thermal structure, resulting in feedback on the atmosphere. For rigorous oceanic modeling under typhoon conditions, we implement the inverse barometer effect and the COAMPS bulk formula into ROMS (Shchepetkin and McWilliams, 2005). A submesoscale eddy-permitting oceanic modeling is configured at a horizontal resolution of 2 km based on the JCOPE2-ROMS downscaling system forced by the JMA GPV-MSM atmospheric reanalysis. A retrospective, synoptic reanalysis is carried out with a particular attention to the two consecutive super typhoons Phanfone (#1418, Category 4, the lowest pressure was 935 hPa) and Vongfong (#1419, Cat. 5, 900 hPa) in the fall 2014. The model successfully reproduces increased eddy kinetic energy below the typhoons with intense cyclonic positive vorticity driven by torque of the wind stress curl, not only at surface but also at depth down to 100 m deep. These cyclones are cold-core mesoscale eddies with SST decrease by about 3oC associated with prominent mixed layer deepening. On the Pacific side of Japan off Shikoku Island, the Kuroshio main body oscillates horizontally and vertically upon collisions with near-inertial gravity waves maintained by inertial resonance in the mixed layer, followed by substantial alteration of the Kuroshio path in the downstream region. Velocity rotary spectra extract asymmetric responses in frequency and rotating direction. A distinct peak appears in the near-inertial frequency band on the offshore side of the Kuroshio path with clockwise rotation due to near-inertial oscillations caused by the typhoons. On the coastal side, it peaks at around periods of 3-4 days with counter-clockwise rotation, which correspond to the shedding frequency of cyclonic eddies shed from Cape Ashizuri in Shikoku Island. These eddies are enhanced by the typhoons to promote oscillations of the Kuroshio axis at around 3-day period.

5.
OS29-D2-PM2-303A(L3S)-013 (OS29-A007)
 
Different Responses of Sea Surface Temperature in the South China Sea to Various El Niño Events During Boreal Autumn
Xin WANG#+
Chinese Academy of Sciences, China
#Corresponding author: wangxin@scsio.ac.cn +Presenter

This study investigates variations of sea surface temperature (SST) anomalies in the South China Sea (SCS) during developing autumn of various El Niño events. The warm SST anomalies are observed in the SCS for canonical El Niño and El Niño Modoki I, whereas the cold SST anomalies are found for El Niño Modoki II. The ocean heat budget analyses show that the latent heat flux change induced by various types of El Niño events is a major contributor to the SCS SST variations. An anomalous anticyclone resides near the Philippine Sea for canonical El Niño and El Niño Modoki I, which induces the southerly wind anomalies over the SCS and thus weakens the climatological northeasterly in boreal autumn. The weakened surface wind speed reduces heat loss from the ocean, leading to a warmer state in the SCS. However, for El Niño Modoki II, the anomalous anticyclone shifts westward to the west of the SCS, and thus the northeasterly wind anomalies appear in the SCS. The northeasterly anomalies enhance the climatological northeasterly monsoon, increase the wind speed, and increase heat loss from the ocean, thus resulting in a cooling in the SCS. The anomalous anticyclone associated with El Niño events also increases shortwave radiation. The increases of the shortwave radiation can also contribute to the SCS warming for canonical El Niño and El Niño Modoki I in addition to the warm effect from the latent heat flux. Because the cooling effect from the latent heat flux is larger than that of the shortwave radiation for El Niño Modoki II, the SCS for El Niño Modoki II tends to be cool.

6.
OS29-D2-PM2-303A(L3S)-014 (OS29-A012)
 
Summer SST Anomalies in the Indian Ocean and the Seasonal Timing of ENSO Decay Phase
Shuyue SUN+, Rongcai REN#, Yang YANG
Chinese Academy of Sciences, China
#Corresponding author: rrc@lasg.iap.ac.cn +Presenter

ENSO affects the tropical Indian Ocean (TIO) SST in winter-spring in ENSO decay years through an ENSO-induced ‘atmospheric-bridge’ and subsequent air-sea coupling processes. The interdecadal delay of El Niño decay phase has been related to a warming change in the summer TIO since 1970s. A physical linkage between the summer SST anomalies over the TIO and the timing of ENSO decay phase is however still unclear. This study uses multi-source data to distinguish ‘later-decay’ from ‘normal-decay’ El Niño/La Niña events, and performs diagnostic analysis of the changes in various thermodynamic and dynamic processes due to later-decay ENSO for quantifying the partial contribution by each of these processes to the summer SST changes over the TIO. The results show that, at both the interannual and interdecadal timescales, the significant warmer and colder SST anomalies in the spring TIO in later-decay El Niño and La Niña years respectively can persist into summer. Most of the ENSO-induced atmospheric-bridge-related processes contribute positively to the TIO SST changes in summer due to later-decay of ENSO, as they do in spring during normal-delay ENSO year. The exceptions are the surface wind-evaporation-mechanism (WEM) and sensible heat-flux anomalies in summer, which always contribute negatively to the summer SST anomalies over most parts of the TIO. The negative contributions from these two processes in summer exist no matter whether there is a weakening or strengthening surface wind due to later-decay of ENSO events. Generally, the presence of five later-decay El Niño events after the 1970s is mainly responsible for the observed interdecadal summer TIO warming in recent decades.

7.
OS29-D2-PM2-303A(L3S)-015 (OS29-A019)
 
Detection of Southern Sri Lankan Upwelling Front and Its Variations
Anushika Iroshanie RUPPEGODA GAMAGE1,2#+, Dongxiao WANG1, Huang KE1
1 South China Sea Institute of Oceanology, China, 2 University of Ruhuna, Sri Lanka
#Corresponding author: anushikagamage@gmail.com +Presenter

In this study, the satellite imagery from Moderate-resolution Imaging Spectroradiometer Aqua (MODISA) and Sea-viewing Wide Field-of-view Sensor (SeaWiFS), and the outputs from the Navy Coastal Ocean Model (NCOM) are investigated to understand the Southern Sri Lankan upwelling front and its dynamics. Sri Lankan is a Northern Indian Ocean Island which lies between High salinity Arabian Sea on the western side and Low salinity Bay of Bengal on the eastern side, respectively. This equatorial island experiences the Southwest Monsoon (SWM) in summer and Northeast Monsoon (NEM) in winter. Both the satellite imagery and model results could reproduce the current systems along the Southern Sri Lanka during the SWM and NEM, transporting water eastward and westward, respectively, and forming the Southern Monsoon Current (SMC) and Northeast Monsoon Current (NMC). Southern upwelling front is more visible during the SWM with high Chlorophyll concentration. The location of upwelling center depends on the wind strength along the coast either eastward or westward during SWM and NEM. The strength of the upwelling front influences by the climate oscillations such as ENSO and Indian Ocean Dipole (IOD) and other extreme climate conditions.

8.
OS29-D2-PM2-303A(L3S)-016 (OS29-A020)
 
IOD and ENSO Influences on Indonesian Rainfall Variability: Role of Atmosphere–Ocean Interaction in Indo-Pacific Sector
Rahmat HIDAYAT#+, Murni Ngestu NUR'UTAMI
Bogor Agricultural University, Indonesia
#Corresponding author: rahmat.hidayat.asad@gmail.com +Presenter

The relative influences of Indian Ocean dipole (IOD) and El Nino–Southern Oscillation (ENSO) on Indonesian rainfall are investigated for seasonal time scales. For the period 1960–2011, observations and reanalysis products during September to November (SON) are used to assess the impacts of ENSO and IOD in Indonesia region. Composite of SSTs and Indonesia rainfall anomalies show detailed features in the different phases of ENSO and IOD. A distinct impact on rainfall anomalies is found during years when an El Nino and a positive IOD event or La Nina and a negative IOD event co-occur indicating the interplay of El Niño and the positive IOD in generating rainfall anomalies in Indonesian region. The atmospheric circulation and sea surface temperatures associated with these responses are discussed. Using composite analysis of anomalies of rainfall, sea surface temperature (SSTs), and circulation at any atmospheric levels, it is shown that positive anomalies of rainfall over Indonesia start to be decreased when SSTs surrounding Indonesia are cool and the Walker circulation is weakened, resulting in anomalous surface easterlies across Indonesia. The composite analysis of rainfall anomalies and the SSTs shown that rainfall variability in Indonesia is clearly influenced by IOD and ENSO phenomena. This study highlights the atmosphere–ocean interaction in Indo-Pacific sector plays an important role on Indonesian rainfall variability.

Poster Presentations

  OS29-D4-PM2-P-017 (OS29-A002)
 
Seasonal and Interannual Variability of the Eastern and Western Hainan Upwelling Systems in the South China Sea, China
Jia WANG1#+, Zhiyou JING2, Yineng LI3, Shiqiu PENG3, Yi YANG4, Daoru WANG4
1 National Oceanic and Atmospheric Administration, United States, 2 Chinese Academy of Sciences, China, 3 South China Sea Institute of Oceanology, China, 4 Hainan Marine Development and Design Institute, Hainan, China
#Corresponding author: Jia.Wang@noaa.gov +Presenter

This study investigates the variation of eastern Hainan (or Qiongdong)  and western Hainan upwelling systems during the East Asia summer monsoon (EASM) season using a state-of-the-art finite volume coastal model and Princeton Ocean Model (POM), and reveals the impacts of tidal mixing, surface wind-wave mixing, and river runoff on the Hainan upwellings in terms of the spatial and temporal variations, intensification, and vertical structure. On the seasonal time scale, it is found that 1) river runoff, a stabilizer of the water column, suppresses the upwelling beneath it from reaching the surface, although strong upwelling still occurs in the lower layer of the water column; 2) tidal mixing, a mechanism of forming bottom mixed layer, promotes upwelling, leading to strengthening of the upwelling; 3) surface wind-wave mixing, a major mechanism for formation of the upper mixed layer and a sharp thermocline, inhibits the upwelling from crossing the thermocline to reach the surface; and 4) unlike the east coast upwelling, the upwelling on the west coast is tidally induced. On the interannual time scales, it is found that 1) El Nino onset has significant impacts on the upwelling system because of the wind curl anomaly, and 2) the timing of the onset of the EASM is a key factor to the timing of the upwelling systems.

  OS29-D4-PM2-P-018 (OS29-A013)
 
Evaluation of Latent Heat Flux Products for ERA-Interim, NCEP2, OAFlux, JRA55 and TropFlux with In Situ Observations in South China Sea
Rongwang ZHANG1+, Xin WANG2#, Jian HUANG3, Lili ZENG2
1 Ocean University of China, China, 2 Chinese Academy of Sciences, China, 3 Guangzhou Institute of Tropical and Marine Meteorology, CMA, China
#Corresponding author: wangxin@scsio.ac.cn +Presenter

Various latent heat flux (LHF) products are evaluated based on in situ observations in South China Sea, in which the widely used reanalysis ERA-interim and NCEP2, the objectively analysed fluxes OAFlux, and the newly released JRA55 and TropFlux are included. Statistically, the results show that there are sound correlations between flux products and observations overall, which range from 0.68 to 0.74. For total bias, a deviation of -4 to 35 W m-2 for flux products exists with respect to observations. In terms of individual flux product, the OAFlux performs more close to observations, followed by ERA-interim and TropFlux. However, both of NCEP2 and JRA55 have the biggest errors and are consistently higher than observations. The bulk-variable-caused uncertainty dominates the LHF biases since bulk algorithm are applied by all of the flux products. It is shown that humidity errors are most correlated with LHF biases, followed by wind, air temperature, sea surface temperature (SST) errors, respectively. Both for flux products and observations, the LHF present obvious seasonal variations, which peak in winter and reach their lowest point in summer. The seasonal variation of LHF results in the differences between flux products and their errors to observations to be also strong in winter and weak in summer. Using the tendency equation for SST, the possible errors of SST caused by LHF biases from flux products are estimated. It is shown the errors of SST are significant in winter. It is noteworthy that the SST errors are still obvious in summer, since a thinner mixed layer depth in that season will enlarge the effect of even relatively small errors of LHF.

  OS29-D4-PM2-P-019 (OS29-A017)
 
An Interdecadal Change in the Intensity of Interannual Variability in Summer Rainfall Over Southern China Around Early 1990s
Jiepeng CHEN1#+, Zhiping WEN2, Xin WANG3
1 South China Sea Institute of Oceanology, China, 2 Sun Yat-sen University, China, 3 Chinese Academy of Sciences, China
#Corresponding author: chenjiep@mail3.sysu.edu.cn +Presenter

The intensity of interannual variability (IIV) in southern China (SC) summer rainfall experienced a remarkable increase in early 1990s, concurrent with the interdecadal increase in SC summer rainfall. Two factors are proposed for this interdecadal change. One is the interdecadal increase of IIV in tropical eastern Indian Ocean (TEIO) sea surface temperature (SST) after early 1990s. Anomalous warmer (cooler) TEIO SST triggers anomalous ascending (descending) motion and lower-level cyclonic (anticyclone) circulation in situ, which in turn induces anomalous descent (ascent) over SC through an anomalous meridional vertical circulation. This contributes to interannual summer rainfall variability over SC. The increase in the amplitude of TEIO SST anomalies in early 1990s led to an intensified interannual variability of summer rainfall over SC. The other is the strengthened influence of a coupled mode of the North Atlantic Oscillation (NAO) and North Atlantic triple SST anomaly on interannual variability in summer rainfall over SC after early 1990s. The leading EOF mode of the North Atlantic SST is characterized by a stripe pattern during 1979-1992, while during 1993-2008 the dominant mode of the North Atlantic SST is a triple pattern. The triple pattern of North Atlantic SST may exert positive effect on the NAO after early 1990s. Compared to the period 1979-1992, the relationship between the NAO and interannual summer rainfall over SC is enhanced during 1993-2008. The NAO coupled with North Atlantic SST triple exerts an important impact on SC summer rainfall variability through Eurasian wave-like train (EUW).

  OS29-D4-PM2-P-020 (OS29-A022)
 
Hydrography and Circulation of the Eastern Indian Ocean During Boreal Spring (2010-2016)
Ke HUANG1#+, Weiqiang WANG2, Dongxiao WANG1
1 South China Sea Institute of Oceanology, China, 2 Chinese Academy of Sciences, China
#Corresponding author: kehuang@scsio.ac.cn +Presenter

The distributions of circulation, temperature, salinity and density, and their temporal variability in the Eastern Indian Ocean (EIO) are reviewed on the basis of results from the analysis of hydrographic data collected during periods of boreal spring from 2010 to 2016 (before the onset of summer monsoon) which now includes seven SY1 cruises and six moorings. Salinity variability is focused on the inter-annual time scale over the EIO. At the mouth of the Bay of Bengal (BOB), the variations of Low-salinity surface water and its temperature inversion, interacting with the equatorial circulation, are investigated. In addition, three-dimensional changes of homogeneous of the warm water (>28C) along the equator Indian Ocean is manifested during the observation periods. An attempt has been made to associate these temporal differences with variations in climatic conditions over the area, the river runoff, the Arabian Sea high-salinity water and the equatorial waves.