Sensitivity of the Upper Ocean Temperature and Circulation in the Equatorial Pacific to Solar Radiation Penetration Due to Phytoplankton

Solar radiation penetration in the upper ocean is strongly modulated by phytoplankton, which impacts the upper ocean temperature structure, especially in the regions abundant with phytoplankton. In the paper, a new solar radiation penetration scheme, based on the concentration of chlorophyll-a, was introduced into the LASG/IAP （State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics/Institute of Atmospheric Physics） Climate system Ocean Model （LICOM）. By comparing the simulations using this new scheme with those using the old scheme that included the constant e-folding attenuation depths in LICOM, it was found that the sea surface temperature （SST） and circulation in the central and eastern equatorial Pacific were both sensitive to the amount of phytoplankton present. Distinct from other regions, the increase of chlorophyll-a concentration would lead to SST decrease in the central and eastern equatorial Pacific. The higher chlorophyll-a concentration at the equator in comparison to the off-equator regions can enlarge the subsurface temperature gradient, which in turn strengthens the upper current near the equator and induces an enhancing upwelling. The enhancing upwelling can then lead to a decrease in the SST in the central and eastern equatorial Pacific. The results of these two sensitive experiments testify to the fact that the meridional gradient in the chlorophyll-a concentration can result in an enhancement in the upper current and a decrease in the SST, along with the observation that a high chlorophyll-a concentration at the equator is one of the predominant reasons leading to a decrease in the SST. This study points out that these results can be qualitatively different simply because of the choice of the solar radiation penetration schemes for comparison. This can help explain previously reported contradictory conclusions.

Effects of adjusting vertical resolution on the eastern equatorial Pacific cold tongue

The vertical resolution of LICOM1.0 (LASG/IAP Climate System Ocean Model, version 1.0) is adjusted by increasing the level amount within the upper 150 m while keeping the total of levels. It is found that the eastern equatorial Pacific cold tongue is sensitive to the adjustment. Compared with the simulation of the original level scheme, the adjusting yields a more realistic structure of cold tongue extending from the coast of Peru to the equator, as well as a temperature minimum at Costa Rica coast, north of the cold tongue. In the original scheme experiment, the sharp heating by net surface heat flux at the beginning of spin-up leads to a great warm- ing in the eastern equatorial Pacific Ocean. The weak vertical advection due to a too thick mixed layer in the coarse vertical structure also accounts for the warm bias. The fact that most significant improvements of the upper 50 m temperature appear at the region of the thinnest mixed layer indicates the necessity of fine vertical resolution for the eastern equatorial Pacific Ocean. However, the westward extension of equatorial cold tongue, a defect in the original scheme, gets even more serious in the adjusting scheme due to the intensi- fied vertical velocity and hence vertical advection in the central-eastern equatorial Pacific Ocean.

Combined Impacts of Warm Central Equatorial Pacific Sea Surface Temperatures and Anthropogenic Warming on the 2019 Severe Drought in East China

A severe drought occurred in East China(EC)from August to October 2019 against a background of long-term significant warming and caused widespread impacts on agriculture and society,emphasizing the urgent need to understand the mechanism responsible for this drought and its linkage to global warming.Our results show that the warm central equatorial Pacific(CEP)sea surface temperature(SST)and anthropogenic warming were possibly responsible for this drought event.The warm CEP SST anomaly resulted in an anomalous cyclone over the western North Pacific,where enhanced northerly winds in the northwestern sector led to decreased water vapor transport from the South China Sea and enhanced descending air motion,preventing local convection and favoring a precipitation deficiency over EC.Model simulations in the Community Earth System Model Large Ensemble Project confirmed the physical connection between the warm CEP SST anomaly and the drought in EC.The extremely warm CEP SST from August to October 2019,which was largely the result of natural internal variability,played a crucial role in the simultaneous severe drought in EC.The model simulations showed that anthropogenic warming has greatly increased the frequency of extreme droughts in EC.They indicated an approximate twofold increase in extremely low rainfall events,high temperature events,and concurrently dry and hot events analogous to the event in 2019.Therefore,the persistent severe drought over EC in 2019 can be attributed to the combined impacts of warm CEP SST and anthropogenic warming.

An extended variable-grid global ocean circulation model and its preliminary results of the equatorial Pacific circulation

To investigate the interaction between the tropical Pacific and China seas a variable-grid global ocean circulation model with fine grid covering the area from 20°S to 50°N and from 99° to 150°E is developed. Numerical computation of the annually cyclic circulation fields is performed. The results of the annual mean zonal currents and deep to abyssal western boundary currents in the equatorial Pacific Ocean are reported. The North Equatorial Current,the North Equatorial Countercurrent, the South Equatorial Current and the Equatorial Undercurrent are fairly well simulated. The model well reproduces the northward flowing abyssal western boundary current.From the model results a lower deep western boundary current east of the Bismarck-Solomon-New Hebrides Island chain at depths around 2 000 m has been found. The model results also show that the currents in the equatorial Pacific Ocean have multi-layer structures both in zonal currents and western boundary currents, indicating that the global ocean overturning thermohaline circulation appears of multi-layer pattern.

Eastern equatorial Pacific SST seasonal cycle in global climate models: from CMIP5 to CMIP6

The sea surface temperature(SST)seasonal cycle in the eastern equatorial Pacific(EEP)plays an important role in the El Nino–Southern Oscillation(ENSO)phenomenon.However,the reasonable simulation of SST seasonal cycle in the EEP is still a challenge for climate models.In this paper,we evaluated the performance of 17 CMIP6 climate models in simulating the seasonal cycle in the EEP and compared them with 43 CMIP5 climate models.In general,only CESM2 and SAM0-UNICON are able to successfully capture the annual mean SST characteristics,and the results showed that CMIP6 models have no fundamental improvement in the model annual mean bias.For the seasonal cycle,14 out of 17 climate models are able to represent the major characteristics of the observed SST annual evolution.In spring,12 models capture the 1–2 months leading the eastern equatorial Pacific region 1(EP1;5°S–5°N,110°–85°W)against the eastern equatorial Pacific region 2(EP2;5°S–5°N,140°–110°W).In autumn,only two models,GISS-E2-G and SAM0-UNICON,correctly show that the EP1 and EP2 SSTs vary in phase.For the CMIP6 MME SST simulation in EP1,both the cold bias along the equator in the warm phase and the warm bias in the cold phase lead to a weaker annual SST cycle in the CGCMs,which is similar to the CMIP5 results.However,both the seasonal cold bias and warm bias are considerably decreased for CMIP6,which leads the annual SST cycle to more closely reflect the observation.For the CMIP6 MME SST simulation in EP2,the amplitude is similar to the observed value due to the quasi-constant cold bias throughout the year,although the cold bias is clearly improved after August compared with CMIP5 models.Overall,although SAM0-UNICON successfully captured the seasonal cycle characteristics in the EEP and the improvement from CMIP5 to CMIP6 in simulating EEP SST is clear,the fundamental climate models simulated biases still exist.

Dimethyl sulfide in the atmospheric surface layer of the Equatorial Pacific Ocean

This paper reports a case study of atmospheric stability effect on dimethyl sulfide(DMS) concentration in the air. Investigation includes model simulation and field measurements over the Pacific Ocean. DMS concentration in surface sea water and in the air were measured during a research cruise from Hawaii to Tahiti. The diurnal variation of air temperature over the sea surface differed from the diurnal cycle of sea surface temperature because of the high heat capacity of sea water. The diurnal cycle of average DMS concentration in the air was studied in relation to the atmospheric stability parameter and surface heat flux. All these parameters had minima at noon and maxima in the early morning. The correlation coefficient of the air DMS concentration with wind speed (at 15 m high) was 0. 64. The observed concentrations of DMS in the equatorial marine surface layer and their diurnal variability agree well with model simulations. The simulated results indicate that the amplitude of the cycle and the mean concentration of DMS are dependent on the atmospheric stratifications and wind speed.

Numerical simulation of influence of the anomalies of theCentral-eastern Equatorial Pacific SST and Arctic seaice cover in summer on the atmospheric circulation

A series of numerical experiments have been conducted with a perpetual July, nine-level general circulation spectral model to determine the effect of variation of the Arctic sea ice cover extent and the joint effect of anomalies of both the Arctic sea ice cover and the Central-eastern Equatorial Pacific sea surface temperature on the summer general circulation. Results show that the two factors,anomalously large extent of the Arctic sea ice cover and anomalously warm sea surface temperature over the Central-eastern Equatorial Pacific Ocean, play substantially the equal role in the effect on the summer general circulation, and either of them can notably induce the atmospheric anomalies. The main dynamical processes determining the effect of the Arctic sea ice and the equatorial SST anomalies are associated with two leading teleconnection patterns, i. e. the Asia North/American and Eurasian patterns observed in atmosphere. The results presented in this paper again prove that the general circulation is fundamentally motivated by the non-uniform heating between the equator and the pole on the rotating earth.

Evaluating the Formation Mechanisms of the Equatorial Pacific SST Warming Pattern in CMIP5 Models

Based on the historical and RCP8.5 runs of the multi-model ensemble of 32 models participating in CMIP5, the present study evaluates the formation mechanisms for the patterns of changes in equatorial Pacific SST under global warming. Two features with complex formation processes, the zonal E1 Nifio-like pattern and the meridional equatorial peak warm- ing （EPW）, are investigated. The climatological evaporation is the main contributor to the E1 Nifio-like pattern, while the ocean dynamical thermostat effect plays a comparable negative role. The cloud-shortwave-radiation-SST feedback and the weakened Walker circulation play a small positive role in the E1 Nifio-like pattern. The processes associated with ocean dynamics are confined to the equator. The climatological evaporation is also the dominant contributor to the EPW pattern, as suggested in previous studies. However, the effects of some processes are inconsistent with previous studies. For example, changes in the zonal heat advection due to the weakened Walker circulation have a remarkable positive contribution to the EPW pattern, and changes in the shortwave radiation play a negative role in the EPW pattern.

The Role of the Halted Baroclinic Mode at the Central Equatorial Pacific in El Nifn Event

The role of halted ＂baroclinic modes＂ in the central equatorial Pacific is analyzed. It is found that dominant anomaly signals corresponding to ＂baroclinic modes＂ occur in the upper layer of the equatorial Pacific, in a two-and-a-half layer oceanic model, in assimilated results of a simple OGCM and in the ADCP observation of TAO. A second ＂baroclinic mode＂ is halted in the central equatorial Pacific corresponding to a positive SST anomaly while the first ＂baroclinic mode＂ propagates eastwards in the eastern equatorial Pacific. The role of the halted second ＂baroclinic mode＂ in the central equatorial Pacific is explained by a staged ocean-atmosphere interaction mechanism in the formation of El Nifio： the westerly bursts in boreal winter over the western equatorial Pacific generate the halted second ＂baroclinic mode＂ in the central equatorial Pacific, leading to the increase of heat content and temperature in the upper layer of the central Pacific which induces the shift of convection from over the western equatorial Pacific to the central equatorial Pacific; another wider, westerly anomaly burst is induced over the western region of convection above the central equatorial Pacific and the westerly anomaly burst generates the first ＂baroclinic mode＂ propagating to the eastern equatorial Pacific, resulting in a warm event in the eastern equatorial Pacific. The mechanism presented in this paper reveals that the central equatorial Pacific is a key region in detecting the possibility of ENSO and, by analyzing TAO observation data of ocean currents and temperature in the central equatorial Pacific, in predicting the coming of an El Nino several months ahead.

Correlations between Sea Surface Temperature in Eastern Equatorial Pacific and Rain Days over China in Summer

Sea-surface temperature (SST) in the eastern, equatorial Pacific and rain days over China in summer are analysed using correlation moments that is proposed by author and principal component analysis(PCA). Occurrences of the strong rain-day anomalies over China are associated with extreme SSTs in some years. Areas significantly affected by the phenomena include North and Northeast China.

Heat Budget of the South-Central Equatorial Pacific in CMIP3 Models

ABSTRACT Using data from 17 coupled models and nine sets of corresponding Atmospheric Model Intercomparison Project （AMIP） results, we investigated annual and seasonal variation biases in the upper 50 m of the south-central equatorial Pacific, with a focus on the double-ITCZ bias, and examined the causes for the amplitude biases by using heat budget analysis. The results showed that, in the research region, most of the models simulate SSTs that are higher than or similar to observed. The simulated seasonal phase is close to that observed, but the amplitudes of more than half of the model results are larger than or equal to observations. Heat budget analysis demonstrated that strong shortwave radiation in individual atmospheric models is the main factor that leads to high SST values and that weak southward cold advection is an important mechanism for maintaining a high SST. For seasonal circulation, large surface shortwave radiation amplitudes cause large SST amplitudes.

Dissimilarity among Ocean Reanalyses in Equatorial Pacific Upper-Ocean Heat Content and Its Relationship with ENSO

This study focuses on the temporal variation of dissimilarity in heat content(HC)anomalies in the upper 300 m of ocean(HC300A)in the equatorial Pacific(±10°N)and its response to the El Ni?o-Southern Oscillation(ENSO).The HC300A anomalies are derived from four ocean reanalyses that are commonly used in ENSO studies and are compared using a simple differencing method.The dissimilarity in HC300A is found to vary closely with the magnitude of ENSO(regardless of phase),meaning that it tends to be greater during strong ENSO events.However,the dissimilarity among ocean reanalyses persists after the event decays.This effect is more pronounced after strong events.The persistence of the dissimilarity after ENSO events is a result of a late maturation of the ENSO signal,its persistence,and the interruption of the signal decay due to follow-up ENSO events.The combined effect of these three factors slows down the decay of HC300A in the region and hence results in the slow decay of dissimilarity.It is also found that areas with a significant spread in vertical temperature profiles collocate with the ENSO signal during warm ENSO phases.Thus,differences in subsurface process reconstruction are a significant factor in the dissimilarity among ocean reanalyses during warm ENSO events.

Intraseasonal variability of the equatorial Pacific Ocean and its relationship with ENSO based on Self-Organizing Maps analysis

We investigated the intraseasonal variability of equatorial Pacific subsurface temperature and its relationship with El Nino-Southern Oscillation(ENSO) using Self-Organizing Maps(SOM) analysis.Variation in intraseasonal subsurface temperature is mainly found along the thermocline.The SOM patterns concentrate in basin-wide seesaw or sandwich structures along an east-west axis.Both the seesaw and sandwich SOM patterns oscillate with periods of 55 to 90 days,with the sequence of them showing features of equatorial intraseasonal Kelvin wave,and have marked interannual variations in their occurrence frequencies.Further examination shows that the interannual variability of the SOM patterns is closely related to ENSO;and maxima in composite interannual variability of the SOM patterns are located in the central Pacific during CP El Nino and in the eastern Pacific during EP El Nino.The se results imply that some of the ENSO forcing is manife sted through changes in the occurrence frequency of intraseasonal patterns,in which the change of the intraseasonal Kelvin wave plays an important role.

Response of western equatorial Pacificto a westerly wind burst

Atmospheric jets-with shear-can induce a vertical oceanic circulation with upwelling and down -welling even over the open ocean in regions where the Coriolis parameter can be regarded as a constant. Winds with nosheard that bloe parallel to the equator can also induce a vertical oceanic circulation with upwelling and downwellingwithin an equatorial radius of deformation. This study concerns the oceanic response to a westerly wind burst, in theform of an atmospheric jet, similar to those that occur over the western equatorial Pacific . It is shown that the shear ofthe wind, if it is within an equatorial radius of deformation, can alter the vertical circulation substantially, especially ifthere are westerly and easterly winds near the equator. A commentary on measurements amde during a westerly windburst over the western equatorial Pacific has been given.

Effects of horizontal mixing on the upper ocean temperature in the equatorial Pacific Ocean

The influence of horizontal mixing on the thermal structure of the equatorial Pacific Ocean is examined based on a sigma coordinate model. In general, the distributions of the temperature and currents simulated by the sigma coordinate model are very close to the climatology. However, the simulated thermocline along the equator is slightly diffusive so that there is a cold bias above the main thermocline, while there is a warm bias under the main thermocline. Both horizontal diffusivity and viscosity have important effects on the upper thermal structure in the equatorial Pacific Ocean, while their detailed dynamics are different. Horizontal diffusivity affects the thermal structure in the upper ocean mainly through regulating the vertical diffusivity, while the horizontal viscosity does mainly through regulating directly the circulate system. A large horizontal diffusivity or a small horizontal viscosity can be in favor of simulating a more realistically thermal structure in the equatorial Pacific Ocean.

East-west oscillation of sea temperature in the Equatorial Pacific and its modelling

In this paper, by analyzing the data of sea temperature in the Equatorial Western Pacific (EWP), we found that the sea temperature at sensitive district (WSST) (about at 6° N, depth of 125-150 m) is correlated negatively to the sea temperature in the Equatorial Eastern Pacific (EEP). On the basis of basic characteristics of Equatorial Pacific atmosphere and ocean, we designed a simple air-sea coupled model. Using this model,an ocean circulation was simulated. The east-west oscillation of sea temperature in Equatorial Pacific is related to this ocean circulation.

Geochemical characteristics of sediments from the COMRA registered pioneer area (CRPA),equatorial northeastern Pacific Ocean

COMRA(China Ocean Mineral Resources Association) registered pioneer area (CRPA) is located in the western part of the area between the Clarion and Clipperton Fraction Zones (CCFZs). Based on distinctive color and bio-disturbing properties, two layers are recognized in the sediment columns from the CRPA: a pale brown layer (Unit A) on the top and a dark for layer (Unit B) in the lower part. Color division between them can be explained as a hiatus. As a resu1t, the two units are different to each other in chemical composition and sediment properties. It is found that contents of P2O5, MnO2, CaO, Na2O in sediments of older Unit B are higher, but SiO2 content is slightly lower. Based on correlation analysis, Mn and Fe in the sediments have different origins. The former is mainly precipitated in authigenic process, whilst the latter is closely related to terrigenous detritus. Therefore, the differences in chemical composition of the sediments are caused by different sedimentation settings.

ON 3.5-YEAR COUPLED OSCILLATION BETWEEN NORTHERN OSCILLATION AND SEA SURFACE TEMPERATURE OF THE EQUATORIAL PACIFIC

In this paper, we have analyzed the processes of temporal and spatial development in the interaction be- tween the Northern Oscillation and the sea surface temperature of the cquatorial Pacific. It is revealed that between them there is a closed negative feedback process and the whole period including their influence, feedback and adjustment to each other is about 3.5 years. Furthermore, we have discussed the physical processes responsible for various links between the Northern Oscillation and the sea surface temperature of the equatorial Pacific. A physical model on 3.5-year coupled oscillation caused by the air-sea interaction in the tropical Pacific is postulated.

Study on the characteristics of the marine boundary layer in the Equatorial Pacific

In this paper the variations of the wind, temperature,humidity and turbulence in the atmospheric boundary layer over the tropical ocean are analysed by use of observational data with tethersonde over the Equatorial Pacific of 165°E from November 17, 1989 to June 29, 1990. According to the analyses, it is pointed out that generally the thermodynamic structure of the Marine boundary layer in the tropical ocean area remains in a state of convective boundary layer owing to higher temperature of the sea water. Generally, the cumulus generated by local convection easts in the mixed layer, and the cloud top is the top of the mixed layer. The turbulent kinetic energy in the surface layer (less 0. 4 Zi)and in the capping inversion layer is in exceedingly unbalanced state.

Water masses classification of the upper layer in the Equatorial Western Pacific using ISODATA of fuzzy cluster

-In this paper,by using ISODATA of fuzzy cluster,the water masses classification of the upper layer in the E-quatorial Western Pacific is carried out. On the basis of the degree of the membership in the obtained optima) classification matrix, the solid distribution of the detailed structure of water masses is made. The water of the upper layer,consisting of six water masses,may be divided into three layers,i, e. ,the surface,subsurface and intermediate layer. Besides analyzing the features of various water masses,a discussion on their distribution structure and formation mechanism is also made.