Seasonal Sea Surface Temperature Research Articles

Using all data to improve seasonal sea surface temperature predictions: A combination‐based model forecast with unequal observation lengths

One way to reduce model uncertainty in climate predictions is to combine forecasts from several models. Recent multi‐model combination approaches combine model forecasts by pooling data for a time period, common across all the models, thus ignoring the additional data available or discarding altogether the models with the shorter time period. This results in the loss of some information which could otherwise be used while combining the models to possibly improve forecast skill. Our research explores this issue in the context of multi‐model sea surface temperature (SST) models predictions and proposes a novel concept that allows a framework for combining models with unequal time period. Here, the unequal time periods imply different range of start and end dates of available model forecasts. A qualitative standpoint of our multi‐model forecasting strategy is to reduce the uncertainty and improve the forecast skill. The utility of the approach is demonstrated by combining the global seasonal NDJ (November–January) SST predictions of two models and also as many as eight models, obtained using both equal and unequal time periods. The proposed approach shows improvement over 62–69% grid cells around the entire globe over the case when the common period of data length across the models is considered.

Seasonal-Temporal Variability of Sea Surface Temperature Derived from Satellite and In Situ Data: Case Study of Indian Ocean Western Part of Sumatera Island

It has been widely knowing that one of the important parameters to study about processes and phenomena in oceans is sea surface temperature (SST). This study is about the use of satellite and in situ data to find the seasonal and temporal SST value in Indian Ocean western part of Sumatera Island during 2010 to 2016. This result focuses on changes of SST and the accuracy of SST value derived from MODIS Satellite and ARGO Float. We divide the data into the dry and wet season based on a seasonal condition in Indonesia. The result shows the same pattern of SST value both from satellite and in situ data. The changes trend of SST value (Celsius) is increasing from 2010 to 2016 both in situ and satellite data. SST value increases 0.093 for in situ data and SST value increases 0.132 measured by MODIS satellite. The accuracy assessment (RMSE) value is 0,555. The coefficient of determination r2 value shows a positive correlation between MODIS and ARGO data especially in dry season, while in the wet season the R2 is smaller than in dry season.

Last Interglacial Hydroclimate Seasonality Reconstructed From Tropical Atlantic Corals

AbstractThe seasonality of hydroclimate during past periods of warmer than modern global temperatures is a critical component for understanding future climate change scenarios. Although only partially analogous to these scenarios, the last interglacial (LIG, Marine Isotope Stage 5e, ~127–117 ka) is a popular test bed. We present coral δ18O monthly resolved records from multiple Bonaire (southern Caribbean) fossil corals (Diploria strigosa) that date to between 130 and 118 ka. These records represent up to 37 years and cover a total of 105 years, offering insights into the seasonality and characteristics of LIG tropical Atlantic hydroclimate. Our coral δ18O records and available coral Sr/Ca‐sea surface temperature (SST) records reveal new insights into the variable relationship between the seasonality of tropical Atlantic seawater δ18O (δ18Oseawater) and SST. Coral δ18O seasonality is found to covary with SST and insolation seasonality throughout the LIG, culminating in significantly higher than modern values at 124 and 126 ka. At 124 ka, we reconstruct a 2 month lead of the coral δ18O versus the Sr/Ca‐SST annual cycle and increased δ18Oseawater seasonality. A fully coupled climate model simulates a concomitant increase of southern Caribbean Sea summer precipitation and depletion of summer δ18Oseawater. LIG hydroclimate at Bonaire differed from today's semiarid climate with a minor rainy season during winter. Cumulatively, our coral δ18O, δ18Oseawater, and model findings indicate a mid‐LIG northward expansion of the South American Intertropical Convergence Zone into the southern Caribbean Sea, highlighting the importance of regional aspects within model and proxy reconstructions of LIG hydroclimate seasonality.

Observed Seasonal Variations of the Upper Ocean Structure and Air‐Sea Interactions in the Andaman Sea

AbstractThe Andaman Sea (AS) is a poorly observed basin, where even the fundamental physical characteristics have not been fully documented. Here the seasonal variations of the upper ocean structure and the air‐sea interactions in the central AS were studied using a moored surface buoy. The seasonal double‐peak pattern of the sea surface temperature (SST) was identified with the corresponding mixed layer variations. Compared with the buoys in the Bay of Bengal (BOB), the thermal stratification in the central AS was much stronger in the winter to spring, when a shallower isothermal layer and a thinner barrier layer were sustained. The temperature inversion was strongest from June to July because of substantial surface heat loss and subsurface prewarming. The heat budget analysis of the mixed layer showed that the net surface heat fluxes dominated the seasonal SST cycle. Vertical entrainment was significant from April to July. It had a strong cooling effect from April to May and a striking warming effect from June to July. A sensitivity experiment highlighted the importance of salinity. The AS warmer surface water in the winter was associated with weak heat loss caused by weaker longwave radiation and latent heat losses. However, the AS latent heat loss was larger than the BOB in summer due to its lower relative humidity.

The changing relationship between the convection over the western Tibetan Plateau and the sea surface temperature in the northern Bay of Bengal

Using the National Oceanic and Atmospheric Administration (NOAA) sea surface temperature (SST) data, we found that the peak Indian summer monsoon season SST in the northern Bay of Bengal (NBOB) has been increased since late 1990s. Moreover, the NBOB SST reveals an increasing trend after 1999 (hereafter POST99), whereas prior to 1999 (PRE99) the trend is decreasing. During POST99, the NBOB SST facilitates a deep convection, while during PRE99 it does not seem so. A robust causality analysis also reveals a large impact on the convection and precipitation over the western Tibetan Plateau during POST99, whereas no significant causality is identified before 1999. Besides, regressions onto the NBOB SST result in a cyclonic circulation pattern and ascending winds on upper vertical levels over the western Tibetan Plateau during POST99, which are distinctly different from those during PRE99.

A Systematic Comparison of Particle Filter and EnKF in Assimilating Time‐Averaged Observations

AbstractThe particle filter (PF) and the ensemble Kalman filter (EnKF) are two promising and popularly adopted types of ensemble‐based data assimilation methods for paleoclimate reconstruction. However, no systematic comparison between them has been attempted. We compare these two uncertainty based methods in pseudoproxy experiments where synthetic seasonal mean sea surface temperature observations are assimilated. Their skills are evaluated with regards to local, hemispherically averaged and globally averaged analysis error, and their ability to capture large‐scale modes of variability. It is found that the EAKF (Ensemble Adjustment Kalman filter, a variant of EnKF) performs better than the PF with only one third of the ensemble size, despite PF's theoretical superiority in allowing for non‐Gaussian statistics and nonlinear dynamics. The success of the EAKF is attributed to the facts that (1) Gaussian assumption is somewhat appropriate for this application; (2) The EAKF is less sensitive to sampling errors than the PF due to the different methodological natures. Sixteen members are enough to estimate accurate covariance for the EAKF, but 48 (even 96) members still underrepresent the state space of high‐dimensional system for the PF. Our study highlights the importance of a large localization radius in the application of the EnKF to paleoclimate reconstruction due to the sparse proxy network and suggests that additional techniques, such as localization or clustered particle filter, are needed to improve the PF for paleoclimate reconstruction, in addition to the simple importance resampling currently adopted by most research.

Late-Holocene dynamics of sea-surface temperature and terrestrial hydrology in southwestern Africa

Southwest Africa is an important region for paleo-climatic studies, being influenced by both tropical and temperate climate systems and thus reflecting the interplay of variable controls. The aim of this study was to unravel the interaction of sea-surface temperature (SST) changes in the southernmost Benguela upwelling system with precipitation changes in South Africa’s winter rainfall zone (WRZ) during the late Holocene. Therefore, a marine sediment core from the southernmost Benguela upwelling system was investigated to reconstruct climate changes in this region for the past ~2000 years. Grain size and geochemical analyses were conducted to reconstruct changes in fluvial sediment discharge and weathering intensity, while SST changes were estimated using alkenone paleo-thermometry. Results show that the southernmost Benguela behaves distinctly in comparison with the rest of the Benguela system reflecting amplified SST changes. Decreasing SSTs accompanied increasing river discharge during times of increased precipitation in the WRZ, reflecting northerly shifted westerly winds during austral winter. We infer a control of past SST changes by processes not analogous to modern processes driving seasonal SST changes by changes through upwelling intensity. The findings suggest that late-Holocene SST changes in the southernmost Benguela upwelling system and the precipitation in the WRZ were both driven by latitudinal shifts of the austral westerly wind belt and associated changes in advection of cold sub-Antarctic waters and/or changes in Agulhas leakage of warm Indian Ocean waters.

Population biology of the sea star Anasterias minuta (Forcipulatida: Asteriidae) threatened by anthropogenic activities in rocky intertidal shores of San Matías Gulf, Patagonia, Argentina

In Patagonian coastal areas, intertidal benthic communities are exposed to extreme physical conditions. The interaction between harsh environment and anthropogenic pressure can generate changes in population biology of marine invertebrates, like density and reproduction. The oral brooding sea star Anasterias minuta is a key organism in food chains of Atlantic Patagonian rocky intertidals, hence changes on its population structure can negatively affect shore communities. We studied the population biology of A. minuta and assess the effect of environmental parameters and anthropogenic activities on its population on rocky intertidal shores of San Matías Gulf, Patagonia, Argentina. Seasonal sea surface temperature, pH, salinity, water velocity, desiccation rate, boulders density, and anthropogenic influence (tourists and octopus fishermen) were recorded. In sites with less tourist influence and high refuge, an increase in density was recorded, especially during the summer. Brooding individuals were found in fall and winter, while feeding individuals were observed in all seasons (12 different prey, mainly the molluscs Tegula patagonica and Perumytilus purpuratus). Environmental variables such as boulders density and water velocity were the most important predictor of variation in population structure. Tourism and pH were the most important variables negatively correlated with density. Rev. Biol. Trop. 65(Suppl. 1): S73-S84. Epub 2017 November 01.

Increased chlorophyll-a concentration in the South China Sea caused by occasional sea surface temperature fronts at peripheries of eddies

ABSTRACTThis study investigates the processes of occasional sea surface temperature (SST) fronts and their impacts on chlorophyll-a concentration (chl-a) in the South China Sea (SCS), based on satellite remote sensing and in situ observations in 2009–2013. The SST fronts were detected by an entropy-based edge detection algorithm method from satellite-derived SST images with a 0.011° grid size. Three offshore SST front case studies (S1, S2 and S3) at the peripheries of eddies in the northern SCS were studied. In case S1 in September 2013, two SST fronts were detected with gradient magnitudes (GMs) greater than 0.06°C km–1 in the cyclonic eddy and 0.08°C km–1 in the periphery waters, and the fronts only existed for one and two days, respectively. After three and seven days, the high chl-a was found in the strong SST front waters which were about 51 and 54% higher than the concentration in the surrounding waters. The depth of the maximum chl-a elevated from the subsurface (50 m) to the surface. In case S2 in August 2013, two SST fronts were detected at the periphery of an anti-cyclonic eddy with GM stronger than 0.06°C km–1 and only existed for one day. After two days, the chl-a in the SST front waters was about 40% higher than the levels in the surrounding waters. In case S3 in June 2009, the GM of the eddy-feature SST front was stronger than 0.12°C km–1 and existed for three days, which was generated by tropical cyclone Linfa. The chl-a in the eddy-feature phytoplankton bloom was 6 times higher than in the surrounding waters. The results show that, in general, occasional offshore SST fronts at peripheries of eddies have stronger influence on surface chl-a, comparing to those seasonal coastal and permanent offshore SST fronts, via ‘Wind Pump’ effects.

Isoprenoid tetraether lipids in suspended particulate matter from the East China Sea and implication for sedimentary records

A total of 90 samples of suspended particulate matter (SPM) collected in surface waters of the East China Sea (ECS) in summer and winter were studied for archaeal isoprenoid glycerol dialkyl glycerol tetraether lipids (iGDGTs) and the derived sea surface temperature (SST) proxy, i.e. TEX86H. Our data showed that in summer SPM TEX86H correlated well with in-situ measured SST, but in winter the relationship became much poorer. We found that the bottom water depth (BWD) of 70 m was a critical depth when studying the TEX86H-SST relationship in winter SPM. In locations with BWD < 70 m, concentrations of iGDGTs in SPM were > 5x higher in winter than in summer, but TEX86H showed a much weaker correlation with in-situ measured SST. This was speculated to be caused by lateral transport of SPM and resuspension of surface sediments in winter due to strong winds. Whereas in locations with BWD > 70 m, TEX86H correlated well with in-situ measured SST, suggesting a minor influence of SPM lateral transport and sediment resuspension. Moreover, although only core iGDGTs were analyzed, we found that both summer and winter TEX86H values correlated better with in-situ measured SST than with seasonal and annual mean SST, suggesting that SPM iGDGTs were dominantly produced around the sampling time rather than encompassing longer time input. The linear relationships of SPM TEX86H with in-situ measured SST were different between winter (BWD > 70 m) and summer, likely due to seasonal archaeal community change. Published sedimentary TEX86H data in the ECS were reexamined here, and a BWD of 70 m was also found to be a critical depth. At sites with BWD > 70 m, TEX86H in sediments correlated well with annual mean SST, whereas the correlation became poor at BWD < 70 m, suggesting that sedimentary GDGTs were also greatly influenced by resuspension and lateral transport, and hence complicating the application of the proxy to shallow locations in the ECS.

Persistent influence of tropical North Atlantic wintertime sea surface temperature on the subsequent Atlantic hurricane season

AbstractThis study explores the seasonally lagged impact of wintertime sea surface temperature (SST) in the Atlantic main development region (MDR) on the subsequent Atlantic hurricane season. It is found that wintertime SST anomalies in the MDR can persist into the summer, explaining 42% of the variance in the subsequent hurricane season's SST during 1951–2010. An anomalously warm wintertime in the MDR is usually followed by an anomalously active hurricane season. Analysis shows an important constraint on the seasonal evolution of the MDR SST by the water vapor feedback process, in addition to the well‐known wind‐evaporation‐SST and cloud‐SST feedback mechanisms over the tropical North Atlantic. The water vapor feedback influences the seasonal evolution of MDR SST by modulating seasonal variations of downward longwave radiation. This wintertime thermal control of hurricane activity has significant implications for seasonal predictions and long‐term projections of hurricane activity over the North Atlantic.

Spatiotemporal Decompositions of Summer Drought in China and Its Teleconnection with Global Sea Surface Temperatures during 1901–2012

The teleconnection between the summer (June–August) Palmer drought severity index (PDSI) in China and seasonal global sea surface temperatures (SSTs) is investigated at both spatial and temporal scales during 1901–2012. Three pairs of coupled spatial patterns for China’s PDSI and global SST anomalies are identified using the singular value decomposition (SVD) method. With a combination of ensemble empirical mode decomposition (EEMD) and multiple linear regression (MLR) analysis, it is found that the first mode, the sea ice loss–global warming pattern, causes wetness over north and northeastern China and drying over Inner Mongolia. The North Pacific Current (NPC) mode shows that a warmer NPC corresponds to a wetter summer over eastern China and a drier one over the Tibetan Plateau. Both NPC and Pacific decadal oscillation (PDO) affect moisture variability in northern China and over the Tibetan Plateau, with the NPC mode more important in the centennial scale, while the PDO mode is more important in the multidecadal scale.

Survey timing vs. ecosystem scheduling: Degree-days to underpin observed interannual variability in marine ecosystems

Fishery annual surveys are shifting towards integrated ecosystem surveys. However, monitoring the whole ecosystem once a year entails special attention to the interpretation of observations, because they only represent a snapshot in the seasonal dynamics of the environment, of a species, or any dynamic process of interest. The dependency of this snapshot to the timing, but also to the duration, of the survey with respect to this seasonal dynamics needs to be considered. Fish stock assessment is only little impacted by the observed timing within a given season, whereas warming, stratification, plankton bloom occurrence, or fish fecundity, are processes rapidly changing especially in spring. Firstly, from independent satellite data, we described the seasonal and interannual Sea Surface Temperature (SST) variability in the Bay of Biscay in spring around the annual PELGAS surveys. Our results revealed that the in-situ surface temperature snapshot from a given survey may be strongly misleading on the existing spatial pattern, blurring the latitudinal temperature gradient, with potential impact in e.g. species habitat modelling. Secondly, based on these survey-independent SST data, we proposed a methodology to position annual surveys in the environment spring schedule. Our temporal indicator is based on a degree-day metric, computed as the cumulated temperature from the previous winter date with minimum annual temperature. The annual degree-day is then compared to the climatology of the degree-day metric to correct the actual date of survey to an environment date. The methodology was spatialised to take into account both latitudinal shift in phasing of seasonality, and rapidly changing conditions in the environment during the survey itself. Finally, we tested the methodology to refine the description of anchovy and sardine spawning phenology, as well as spawning spatial distribution for particular years such as hot year 2003. More generally, this is an example of how synoptic, independent data from operational oceanography, as a background history of the environment dynamics, can be used to improve the interpretation of biological observations in marine ecosystems.

A late Quaternary record of seasonal sea surface temperatures off southern Africa

The southern Cape coastal region is important for understanding both the behavioural history of modern humans, and regional and global climate dynamics, because it boasts a long archaeological record and occupies a key geographical location near the intersection of two major oceans. The western boundary Agulhas Current, implicated in global heat exchange dynamics, is an important modulator of southern African climates and yet we understand its past behaviour only broadly as the Current itself scours the coastal shelf and marine sediment core records necessarily provide little detail. Numerous archaeological sites from both the late Pleistocene and Holocene provide the opportunity for reconstruction of near-shore seasonal SST records, which respond both to localized wind-driven upwellings and Agulhas temperature shifts, corresponding in turn with terrestrial precipitation trends in the near-coastal and summer rainfall regions. Here we present a record of seasonal SSTs extending over MIS5, MIS4, and the Holocene, from serial δ18O measurements of a single gastropod species, Turbo sarmaticus. The results show that mean SST shifts accord well with global SST trends, although they are larger than those recorded in the Agulhas Current from coarser-scale marine sediment records. Comparison with a record of Antarctic sea-ice suggests that annual SST amplitude responds to Antarctic sea-ice extent, reflecting the positioning of the regional wind systems that drive upwelling dynamics along the coast. Thus, near-shore SST seasonality reflects the relative dominance of the westerly and easterly wind systems. These data provide a new climate archive for an important but understudied climate system.

Spatio-temporal variability of sea surface temperature in Irish waters (1982–2015) using AVHRR sensor

Temporal and spatial variability of Sea Surface Temperature (SST), a key variable linked to climate change, was analysed using a continuous 34-year time series of Advanced Very-High-Resolution radiometer (AVHRR) data (1982–2015). The climatological analysis showed a significant latitudinal SST gradient; waters were warmer in the south and colder in the north. A seasonal effect was evident, with lowest SST values in March and highest SST in August. Results suggest that the temporal and spatial variability in Irish waters is mainly related to the Atlantic Multi-decadal Oscillation (AMO) and the warming from anthropogenic CO2 emissions. Overall, the warming trend was significant (p-value of ≤0.05) and positive (0.26°Cdecade−1) for the whole study area. However, this trend was not spatially homogeneous and varied between the International Council for the Exploration of the Seas (ICES) Divisions, having the most significant positive trends in the north (VIa, VIb, VIIb and VIIc) and east (VIId and VIIe). Seasonal SST trends were similar to the annual trends but warming was more intense in the autumn.

P CO 2 variability in the surface waters of the ultra-oligotrophic Levantine Sea: Exploring the air–sea CO 2 fluxes in a fast warming region

Abstract Seasonal p CO 2 variability was studied in the Southeast Levantine (SE-Levantine) during 2009–2015 with the aim of quantifying air–sea CO 2 fluxes in this ultra-oligotrophic, warm and highly evaporative marginal sea. Mixed layer p CO 2 varied significantly between 560 ± 9.0 μatm in August (summer) and 350 ± 8.7 μatm in March (winter). Comparison of p CO 2 to Sea Surface Temperature (SST) yielded a strong positive correlation ( n = 135, r 2 = 0.94), suggesting that the seasonal variations are the result of a thermodynamic effect on the carbonate system in seawater. Using the coupling between p CO 2 and SST, we calculated the mean monthly values and the air-sea fluxes in this region. These calculations indicated that this region is a net source of CO 2 to the atmosphere over an annual cycle, with an average flux of 845 ± 270 mmol C m 2 y − 1 (~ 0.98 Tg C y − 1 ). Flux estimation for three other sub-basins of the East Mediterranean (South of Crete) with similar oceanographic conditions, were calculated from mean seasonal SST and wind data (MEDATLAS). The results suggest that these regions may either be a weak source or sink for atmospheric CO 2 . However, considering the relatively rapid warming trends (~+1 °C/decade) observed in the Levantine basin and the anticipated thermodynamic effect on p CO 2 levels in seawater, these sub basins could become more pronounced sources for atmospheric CO 2 . Thus, with the fast warming and increased stratification of its surface water the CO 2 source of the Eastern Mediterranean is expected to expend spatially.

On the skill of seasonal sea surface temperature forecasts in the California Current System and its connection to ENSO variability

The California Current System (CCS) is a biologically productive Eastern Boundary Upwelling System that experiences considerable environmental variability on seasonal and interannual timescales. Given that this variability drives changes in ecologically and economically important living marine resources, predictive skill for regional oceanographic conditions is highly desirable. Here, we assess the skill of seasonal sea surface temperature (SST) forecasts in the CCS using output from Global Climate Forecast Systems in the North American Multi-Model Ensemble (NMME), and describe mechanisms that underlie SST predictability. A simple persistence forecast provides considerable skill for lead times up to ~4 months, while skill above persistence is mostly confined to forecasts of late winter/spring and derives primarily from predictable evolution of ENSO-related variability. Specifically, anomalously weak (strong) equatorward winds are skillfully forecast during El Niño (La Niña) events, and drive negative (positive) upwelling anomalies and consequently warm (cold) temperature anomalies. This mechanism prevails during moderate to strong ENSO events, while years of ENSO-neutral conditions are not associated with significant forecast skill in the wind or significant skill above persistence in SST. We find also a strong latitudinal gradient in predictability within the CCS; SST forecast skill is highest off the Washington/Oregon coast and lowest off southern California, consistent with variable wind forcing being the dominant driver of SST predictability. These findings have direct implications for regional downscaling of seasonal forecasts and for short-term management of living marine resources.

Upper water mass variability in the Anegada–Jungfern Passage, NE Caribbean, during the last 11,100 cal. yr

Using qualitative and quantitative analyses of planktonic foraminifera assemblages, δ18O measurements, Mg/Ca–temperature relationship ( Globigerinoides ruber pink sensu stricto) data and sea-surface temperatures (SSTs) derived from artificial neural network (ANN) transfer functions, a reconstruction was made of upper water mass variability in the Anegada–Jungfern Passage (AJP), northeastern Caribbean Sea, over the last c. 11,100 years. Our record is based on the study of two marine sediment cores and reveals three main circulation stages during the Holocene. In the early-Holocene (11,100–6300 cal. yr BP), ANN-based SST estimations indicate moderately cooler than present winter condition in the NE Caribbean with SSTs of ~25.5°C. These conditions presumably reflect advection of well-mixed upper water masses from the Guyana upwelling area associated with a strong Atlantic Meridional Overturning Circulation (AMOC) and enhanced trade wind activity, linked to a more northerly location of the inter-tropical convergence zone (ITCZ). Between 6300 and 3700 cal. yr BP, a relative warming of winter SSTs (~26.5°C) was probably related to a weaker circulation and upper water mass mixing because of less intense trade wind activity, as the ITCZ moved southwards. From 3700 cal. yr BP to the present, the region was characterised by small seasonal SST variations and generally stable winter and summer SSTs. The data suggest a minor shift in the (sub)surface inflow pattern during the last 2000 years, possibly related to changes in Northern Hemisphere large-scale atmospheric circulation also observed at higher latitude. The ANN-based temperature pattern is supported by fluctuations in the Mg/Ca-derived temperature record, although temperature maxima derived from the Mg/Ca ratio appear anomalously high. On a Holocene timescale, we conclude that the northeastern Caribbean SST and circulation regime have been mainly dependent on the position of the ITCZ, which, in turn, is controlled by changes in hemispheric solar insolation.

Alongcoast structure and interannual variability of seasonal midshelf water properties and velocity in the Northern California Current System

AbstractMoored sensors were maintained for ∼5 years on the northern California Current System (CCS) midshelf. The alongcoast sensor array spanned the area of influence of the plume from the Columbia River, several submarine canyons, as well as a coastal promontory where the equatorward coastal jet frequently separates from the shelf. Upwelling‐favorable wind stress magnitude decreases poleward by more than a factor of three over the latitudinal range and shelf width varies by a factor of two. In spite of the alongcoast structure in setting, both seasonal and interannual patterns in subsurface layer water properties were remarkably similar at all sites. Higher in the water column, freshwater forcing was substantial. Because of the near surface freshwater input, seasonal sea surface and subsurface temperatures were almost perfectly out of phase in the northernmost CCS, with a mid water column inversion in winter. Year to year differences in subsurface layer wintertime water properties were similar to spatial and temporal patterns of wind stress variability: little alongcoast structure except in salinity, but pronounced interannual differences strongly related to local wind stress. Summertime wind and subsurface property patterns were the opposite of those in winter: pronounced alongcoast wind stress structure, but little or no alongcoast or interannual variability in water properties, and only a weak relationship to local wind stress. Summertime interannual water property variability, including source waters, was shown to be more consistent with “remote forcing” via larger scale wind stress rather than with local wind stress, particularly in the northernmost CCS.

Feedback of 10–20-day intraseasonal oscillations on seasonal mean SST in the tropical Western North Pacific during boreal spring through fall

The present study documents the factors for year-to-year changes in the intensity of 10–20-day intraseasonal oscillations (ISOs) and investigates the feedback of the 10–20-day ISO intensity on seasonal mean sea surface temperature (SST) change in the tropical western North Pacific during boreal spring through fall. An analysis of local correlation reveals a significant negative correlation of the 10–20-day ISO intensity and the seasonal mean SST tendency in the tropical western North Pacific during spring, summer, and fall, suggesting a plausible feedback of the ISO intensity on seasonal mean SST anomaly. The 10–20-day ISO intensity change over the tropical western North Pacific is influenced by El Nino-Southern Oscillation (ENSO) through modulation of vertical shear of zonal winds, lower-level moisture, and upward motion. Due to the phase dependence of location of these ENSO-induced background field changes, the ISO intensity is subject to ENSO influence in different regions during the three seasons. The feedback of the 10–20-day ISO intensity on local seasonal mean SST change in the tropical western North Pacific is demonstrated by separating latent heat flux anomalies into components on different time scales. The ISO-induced latent heat flux anomalies may accumulate in a season and overcome interannual anomalies due to seasonal mean changes. Thus, the ISO-induced surface heat flux change may play an important role in the seasonal mean SST anomaly in the tropical western North Pacific.