SEASONAL HEAT BUDGET IN THE TROPICAL WESTERN PACIFIC OCEAN IN A GLOBAL GCMⅠ.GENERAL DESCRIPTION

This paper describes the large scale aspects of the seasonal surface heat budget and discusses itsmain forcing mechanisms in the tropical Western Pacific Ocean.The high-resolution generalcirculation model (Semtner & Chervin,1992)used in this study reproduced well the observed upper-layer thermal structure and circulation.It is shown that at least on the average of the study region(20°S-20°N,west boundary-160°E)the semiannual variation is a dominant signal for all heat budgetcomponents and is presumably due to the sun’s passing across the equator twice a year,but that thecomponents have substantial differences in amplitude.The local Ekman divergence in the region doesnot change significantly through the year.As a result,the change in surface heat content is roughlyhalf due to ocean-atmosphere heat exchange and half due to heat advection by remotely forced verti-cal motion.Horizontal currents do not play a significant role directly by advection,because the wat-er which enters the region is not very muc     

Seasonal variation of the surface North Equatorial Countercurrent (NECC) in the western Pacific Ocean

The North Equatorial Countercurrent(NECC) is an important zonal fl ow in the upper circulation of the tropical Pacifi c Ocean, which plays a vital role in the heat budget of the western Pacifi c warm pool. Using satellite-derived data of ocean surface currents and sea surface heights(SSHs) from 1992 to 2011, the seasonal variation of the surface NECC in the western tropical Pacifi c Ocean was investigated. It was found that the intensity(INT) and axis position(Y_(CM)) of the surface NECC exhibit strikingly different seasonal fl uctuations in the upstream(128°–136°E) and downstream(145°–160°E) regions. Of the two regions, the seasonal cycle of the upstream NECC shows the greater interannual variability. Its INT and Y CM are greatly infl uenced by variations of the Mindanao Eddy, Mindanao Dome(MD), and equatorial Rossby waves to its south. Both INT and YC M also show semiannual signals induced by the combined effects of equatorial Rossby waves from the Central Pacifi c and local wind forcing in the western Pacifi c Ocean. In the downstream region, the variability of the NECC is affected by SSH anomalies in the MD and the central equatorial Pacifi c Ocean. Those in the MD region are especially important in modulating the Y CM of the downstream NECC. In addition to the SSH-related geostrophic fl ow, zonal Ekman fl ow driven by meridional wind stress also plays a role, having considerable impact on INT variability of the surface NECC. The contrasting features of the variability of the NECC in the upstream and downstream regions refl ect the high complexity of regional ocean dynamics.     

A THREE-LAYER OCEAN CIRCULATION MODEL APPLICATION TO NUMERICAL STUDIES ON THE NORTH PACIFIC OCEAN CIRCULATION

The formulation and justification of a three-layer baroclinic ocean model developed to simulate thegeneral circulation of the ocean are described in this paper.Test of the model in simulating the annualmean circulation patterns in the North Pacific under the prescribed atmospheric forcing,which consists ofthe climatological surface wind stress and sea surface heat flux,and comparison of the results withobservations showed that the model basically simulated the large scale features of the annual meancirculation patterns in the North Pacific Ocean such as those of the intensified western boundary currentsand the North Equatorial Currents and Undercurrents.But due to the coarse resolution of the model,some details of these currents were poorly reproduced.The seasonal variations of the North Pacific Oceancirculation driven by the seasonal mean sea surface wind stress was calculated,the different aspects of theseresults were analyzed and the main current(the intensified western boundary currents)transports we     

NUMERICAL SIMULATION OF THE MINDANAO EDDY AND TROPICAL CURRENTS OF PACIFIC OCEAN

Results of numerical simulation of currents in the western North Tropical Pacific Ocean by using a barotropic primitive equation model with fine horizontal resolution agreed well with observations and showed that the Mindanao Cyclonic Eddy located north of the equator and east of Mindanao Island exists during most of the year with monthly (and large seasonal) variations in scope . strength and central location . In June , an anticyclonic eddy occurs northeast of Halmahera Island, strengthens to maximum in August , exists until October and then disappears . The observed large-scale circulation systems such as the North Equatorial Current . the Mindanao Current and the North Equatorial Countercurrent are all very well reproduced in the simulations.     

CURRENT STRUCTURE AND ITS VARIATION IN THE EQUATORIAL AREA OF THE WESTERN NORTH PACIFIC OCEAN

Based on the current measurement data from the R/V Ryofu Maru of JMA in the equatorial area along 137°E (1972-83) and 155°E (1972-79) the structures of the zonal velocity of the Equatorial Undercurrent (EUC) and the North Equatorial Countercurrent (NECC) and their variations are systematically analyzed in detail.At 155°E, the current at the equator and 100-300 m depth was a typical eastward EUC, it intensified in 1973-75, i.e., in the non-El Nino period. While the corresponding current at 137°E was mostly westward, and the origin of the EUC shifted to north of the equator around 0.5-1.5°N owing to the influence of the New Guinea Coast. The EUC origin disappeared in early July, 1982. Comparing with the EUC disappearance at 159°W, the average speed of an eastward travelling wave would be~1.1m/s.The velocity core of the NECC at 137 E generally shifted northward in winter and southward in summer, and was stronger in summer and weaker in winter. The fluctuations of the NECC were closely related to thos     

Seasonal variability of zonal heat advection in the mixed layer of the tropical Pacific

Zonal heat advection （ZHA） plays an important role in the variability of the thermal structure in the tropical Pacific Ocean, especially in the western Pacific warm pool （WPWP）. Using the Simple Ocean Data Assimilation （SODA） Version 2.02/4 for the period 1958-2007, this paper presents a detailed analysis of the climatological and seasonal ZHA in the tropical Pacific Ocean. Climatologically, ZHA shows a zonal- band spatial pattern associated with equatorial currents and contributes to forming the irregular eastern boundary of the WPWP （EBWP）. Seasonal variation of ZHA with a positive peak from February to July is most prominent in the Nifio3.4 region, where the EBWP is located. The physical mechanism of the seasonal cycle in this region is examined. The mean advection of anomalous temperature, anomalous advection of mean temperature and eddy advection account for 31%, 51%, and 18% of the total seasonal variations, respectively. This suggests that seasonal changes of the South Equatorial Current induced by variability of the trade winds are the dominant contributor to the anomalous advection of mean temperature and hence, the seasonality of ZHA. Heat budget analysis shows that ZHA and surface heat flux make comparable contributions to the seasonal heat variation in the Nifio3.4 region, and that ZHA cools the upper ocean throughout the calendar year except in late boreal spring. The connection between ZHA and EBWP is further explored and a statistical relationship between EBWP, ZHA and surface heat flux is established based on least squares fitting.     

RESPONSE OF THE EQUATORIAL WESTERN PACIFIC THERMOHALINE STRUCTURE TO WIND VARIATION

During the Global Weather Experiment oceanographic measurements were recorded during winter and summer in the western Pacific region 5°S-5°N,160°E-175°E. The variations of the upper ocean temperature and salinity fields were produced by the large seasonal and spatial wind fluctuations. The vertical temperature structure of the thermocline at the equator, the meridional slope of the thermocline south of the equator, and the northward penetration of high salinity water were related to the direction and intensity of the zonal wind-stress.     

Circulation and Heat Flux along the Western Boundary of the North Pacific

On the basis of the conductivity temperature depth(CTD)observation data off the coast of the Philippines(7.5°–18°N,130°E–the east coast of the Philippines)in the fall of 2005,the water mass distribution,geostrophic flow field,and heat budget are examined.Four water masses are present:the North Pacific Tropical Surface Water,the North Pacific Sub-surface Water,the North Pacific Intermediate Water,and the Antarctic Intermediate Water(AAIW).The previous three corresponded with the North Equatorial Current(NEC),the Kuroshio Current(KC),and the Mindanao Current(MC),respectively.AAIW is the source of the Mindanao Undercurrent.The mass transport of NEC,KC,and MC is 58.7,15,and 27.95Sv,respectively(relative to 1500db).NEC can be balanced by the transport across the whole transect 18°N(31.81 Sv)and 7.5°N(26.11 Sv)but not simply by KC and MC.Direct calculation is used to study the heat flux.In sum,1.45PW heat is transported outwards the observed region,which is much more than that released from the ocean to the air at the surface(0.05PW).The net heat lost decreased the water temperature by 0.75℃each month on average,and the trend agreed well with the SST change.Vertically,the heat transported by the currents is mainly completed in the upper 500 m.     

Interannual variability of transport and bifurcation of the North Equatorial Current in the tropical North Pacific Ocean

The relationship of the interannual variability of the transport and bifurcation latitude of the North Equatorial Current (NEC) to the El Ni o-Southern Oscillation (ENSO) is investigated. This is done through composite analysis of sea surface height (SSH) observed by satellite altimeter during October 1992-July 2009, and correspondingly derived sea surface geostrophic currents. During El Nio/La Ni a years, the SSH in the tropical North Pacific Ocean falls/rises, with maximum changes in the region 0-15°N, 130°E-160°E. The decrease/increase in SSH induces a cyclonic/anticyclonic anomaly in the western tropical gyre. The cyclonic/anticyclonic anomaly in the gyre results in an increase/decrease of NEC transport, and a northward/southward shift of the NEC bifurcation latitude near the Philippine coast. The variations are mainly in response to anomalous wind forcing in the west-central tropical North Pacific Ocean, related to ENSO events.     

DISTRIBUTIONS OF CHEMICAL ELEMENTS WITH RELATION TO MAJOR WATER CIRCULATIONS IN THE CENTRAL AND NORTHERN PARTS OF THE TAIWAN STRAIT

Data obtained from a comprehensive multidisciplinary oceanographic survey in the central and northern parts of the Taiwan Strait, 24°20′-26°00′N, 118°45°-121°00′E by the Fujian Institute of Oceanology during the period May, 1983 through May, 1984, showed that the distributions of dissolved oxygen (DO), nitrate, dissolved inorganic phosphate and silicate concentrations here had obvious areal and seasonal characteristics that were mainly influenced by the seasonal circulation ofthree major water systems in the Taiwan Strait-- the Taiwan Strait Warm Water (TSWW), theZhejiang-Fujian Coastal Water (ZFCW), and the Northeastern Strait Warm Water (NESWW).     

A heat budget study on the mechanism of SST variations in the Indian ocean dipole regions

By using a new heat budget equation that is closely related to the sea surface temperature （SST） and a dataset from an ocean general circulation model （MOM2） with 10-a integration （1987-1996）, the relative importance of various processes determining SST variations in two regions of the Indian Ocean is compared. These regions are defined by the Indian Ocean Dipole Index and will be referred to hereafter as the eastern （0^＊-10^＊S, 90^＊-110^＊E） and western regions （10^＊S- 10^＊N, 50^＊-70^＊E）, respectively. It is shown that in each region there is a falling of SST in boreal summer and a rising in most months of other seasons, but the phases are quite different. In the eastern region, maximum cooling rate occurs in July, whereas in the western region it occurs in June with much larger magnitude. Maximum heating rate occurs in November in the eastern region, but in March in the western one. The western region exhibits another peak of increasing rate of SST in October, indicating a typical half-year period. Net surface heat flux and entrainment show roughly the same phases as the time-varying term, but the former has much larger contribution in most of a year, whereas the latter is important in the boreal summer. Horizontal advection, however, shows completely different seasonal variations as compared with any other terms in the heat budget equation. In the eastern region, it has a maximum in June/November and a minimum in March/ September, manifesting a half-year period; in the western region, it reaches the maximum in August and the minimum in November. Further investigation of the horizontal advection indicates that the zonal advection has almost the opposite sign to the meridional advection. In the eastern region, the zonal advection is negative with a peak in August, whereas the meridional one is positive with two peaks in June and October. In the western region, the zonal advection is negative from March to November with two peaks in June and November, whereas the meridional one is positive with one peak in July. Different phases can be clearly seen between the two regions for each component of the horizontal advection. A detailed analysis of the data of 1994, a year identified when the Indian Ocean dipole event happened, indicates that the horizontal advection plays a dominant role in the remarkable cooling of the eastern region, in which zonal and meridional advections have the same sign of anomaly. However, in the western region in 1994 no any specialty was shown as compared with other years, for the SST anomaly is not positive in large part of this region. All these imply that the eastern and western regions may be related in a quite complex way and have many differences in dynamics. Further study is needed.     

Northward expansion of the western Pacific Warm Pool in late 1990s and early 2000s

Based on 48-year (1958-2006) ocean reanalysis data of Simple Ocean Data Assimilation and 23-year (1984-2006) global ocean-surface heat flux products developed by the Objectively Analyzed Air-Sea Heat Flux Project, meridional variation of the western Pacific Warm Pool (WPWP) is addressed. The results show that there is a significant expansion of the northern edge of the WPWP in the late 1990s and early 2000s. This variation is mainly within 120°E-160°E by 8°N-20°N, we define this region (120°E-160°E by 8°N-20°N) as the core region. Furthermore, analyses on upper ocean heat budget show that the short wave radiation plays a key role in the northward expansion of the northern edge of the WPWP in the core region. It is proved that the northward expansion may be caused by the change of the mixed layer which became shallower in 1994-2006 compared with 1984-1993 in the study region. The short wave radiation flux distribution within the shallower mixed layer leads to a positive anomaly in seawater temperature, promoting the northward expansion of the WPWP.     

Sea surface height variations in the Mindanao Dome region in response to the northern tropical Pacific winds

Sea surface height (SSH) variability in the Mindanao Dome (MD) region is found to be one of the strong variations in the northern Pacific. It is only weaker than that in the Kuroshio Extension area, and is comparable to that in the North Pacific Subtropical Countercurrent region. Based on a 1.5-layer reduced gravity model, we analyzed SSH variations in this region and their responses to northern tropical Pacific winds. The average SSH anomaly in the region varies mainly on a seasonal scale, with significant periods of 0.5 and 1 year, ENSO time scale2-7years, and time scale in excess of 8 years. Annual and long-term variabilities are comparably stronger. These variations are essentially a response to the northern tropical Pacific winds. On seasonal and ENSO time scales, they are mainly caused by wind anomalies east of the region, which generate westward-propagating, long Rossby waves. On time scales longer than 8 years, they are mostly induced by local Ekman pumping. Long-term SSH variations in the MD region and their responses to local winds are examined and discussed for the first time .     

Interannual variability of the southern Yellow Sea Cold Water Mass

Temperature data collected in the sections of 34°N, 35°N and 36°N in August from 1975 through 2003 were analyzed using Empirical Orthogonal Function (EOF) to investigate interannual variability of the southern Yellow Sea Cold Water Mass (YSCWM). The first mode (EOF1) reveals variations of basin-wide thermocline depth, which is mainly caused by surface heating. The second mode (EOF2) presents fluctuations of vertical circulation, resulting mainly from interannual variability of cold front intensity. In addition, it is found that the upward extent of upwelling in the cold front is basically determined by wind stress curl and the zonal position of the warm water center in the southern Yellow Sea is correlated with spatial difference of net heat flux.     

A THEORETICAL SOLUTION FOR THE THERMOHALINE CIRCULATION IN THE SOUTHERN YELLOW SEA

Application of the thermocline equations in the thermocline areas and the boundary layer and the asymptotic matching techniques in each boundary in order to satisfy the surface and bottom conditions yielded a theoretical 2- D solution of the vertical thermohaline circulation of the Southern Yellow Sea in summer when the quasi-statically varying seasonal thermocline (density layer) is the background density structure , the deviations from which cause the secondary vertical circulation . The results show that the thermocline can be considered as an internal boundary or a barrier to the vertical heat advection so that in the central areas of the Southern Yellow Sea or the center of the Yellow Sea Cold Water Mass(YCWM)> the downwelling in the upper layer and upwelling in the lower or bottom layer form a double cell vertical circulation . The solution is similar to Hu's conceptual model ( 1986) in the central areas of the YCWM and is consistent with observed temperature . salinity and dissolved oxygen distri     

Variabilities of Surface Current in the Tropical Pacific Ocean

The Simple Ocean Data Assimilation (SODA) package is used to better understand the variabilities of surface current transport in the Tropical Pacific Ocean from 1950 to 1999. Seasonal variation, interannual and decadal variability analyses are conducted on the three major surface currents of the Tropical Pacific Ocean: the North Equatorial Current (NEC), the North Equatorial Countercurrent (NECC), and the South Equatorial Current (SEC). The transport of SEC is quite larger than those of NEC and NECC. The SEC has two maximums in February and August. The NEC has a small annual variation. The NECC has a maximum in October and is very weak in March and April. All currents have remarkable interannual and decadal variabilities. The variabilities of the NEC and the SEC relate to the winds over them well, but the relationship between the NECC and the wind over it is not close. Analysis related to El Nin^-o-Southern Oscillation (ENSO) suggests that before El Nifio (La Nin^-a) the SEC is weaker (stronger) and the NECC is stronger (weaker), after El Nifio (La Nifia) the SEC is stronger (weaker) and the SEC is weaker (stronger). There is no notable relationship between the NEC and ENSO.     

Statistic characteristics of thermal structure in the southern Yellow Sea in summer

Based on the temperature data along 34°N, 35°N and 36°N sections in August from 1977 to 2003, the structure and formation of the Southern Yellow Sea Cold Water Mass (SYSCWM) and its responses to El Nino events are analyzed. Results show that: (1) There exist double cold cores under the main thermocline along the 35°N and 36°N sections. Also, double warm cores exist above the main thermocline along the 36°N section. (2) Thermocline dome by upwelling separates the upper warm water into two parts, the eastern and western warm waters. Additionally, the circulation structure caused by upwelling along the cold front and northeastward current along the coast in summer is the main reasons of double warm cores along the 36°N section. The intermediate cold water is formed in early spring and moves eastward slowly, which results in the formation of the western one of double cold cores. (3) Position of the thermocline dome and its intensity vary interannually, which is related to El Nino events. However, the     

Subtropical sea surface salinity maxima in the South Indian Ocean

Subtropical sea surface salinity(SSS) maximum is formed in the subtropical South Indian Ocean(SIO) by excessive evaporation over precipitation and serves as the primary salt source of the SIO. Spaceborne SSS measurements by Aquarius satellite during September 2011–May 2015 detect three disconnected SSS maximum regions(35.6) in the eastern(105°E–115°E, 38°S–28°S), central(60°E–100°E, 35°S–25°S), and western(25°E–40°E, 38°S–20°S) parts of the subtropical SIO, respectively. Such structure is however not seen in gridded Argo data. Analysis of Argo pro?le data con?rms the existence of the eastern maximum patch and also reveals SSS overestimations of Aquarius near the western and eastern boundaries. Although subjected to large uncertainties, a mixed-layer budget analysis is employed to explain the seasonal cycle of SSS. The eastern and central regions reach the highest salinity in February–March and lowest salinity in August–September, which can be well explained by surface freshwater forcing(SFF) term. SFF is however not controlled by evaporation( E) or precipitation( P). Instead, the large seasonal undulations of mixed layer depth(MLD) is the key factor. The shallow(deep) MLD in austral summer(winter) ampli?es(attenuates) the forcing ef fect of local positive E-P and causes SSS rising(decreasing). Ocean dynamics also play a role. Particularly, activity of mesoscale eddies is a critical factor regulating SSS variability in the eastern and western regions.     

PREDICTION OF OCEAN SURFACE CURRENT VELOCITY AND APPLICATION TO METEOROLOGICAL NAVIGATION IN THE NORTH PACIFIC

On the basis of an understanding of the ocean current produced under the combined forces of wind stress over the sea surface and horizontal pressure gradient force caused by the uneven distribution of seawater density and the elevation of sea surface , we obtained the unsteady analytic solution of the variation with time of ocean surface current velocity corresponding to the time variation of the above two forces , and the unsteady analytic solution for variation of seawater density with time by considering only the vertical turbulence . To meet different needs, the above solutions may be written in two forms for short and long time predictions . After some simplification the analytic solution was used to predict surface ocean current velocity for meteorological -navigation in the North Pacific . The monthly average current field was first obtained to get the necessary parameters for selecting the initial shipping route in the North Pacific and Bohai and Yellow Seas . The wind current field was then cal