Interannual Sea Surface Temperature Variability Research Articles

The Impact of Air‐Sea Interactions on the Representation of Tropical Precipitation Extremes

AbstractThe impacts of air‐sea interactions on the representation of tropical precipitation extremes are investigated using an atmosphere‐ocean‐mixed‐layer coupled model. The coupled model is compared to two atmosphere‐only simulations driven by the coupled‐model sea‐surface temperatures (SSTs): one with 31 day running means (31 d), the other with a repeating mean annual cycle. This allows separation of the effects of interannual SST variability from those of coupled feedbacks on shorter timescales. Crucially, all simulations have a consistent mean state with very small SST biases against present‐day climatology. 31d overestimates the frequency, intensity, and persistence of extreme tropical precipitation relative to the coupled model, likely due to excessive SST‐forced precipitation variability. This implies that atmosphere‐only attribution and time‐slice experiments may overestimate the strength and duration of precipitation extremes. In the coupled model, air‐sea feedbacks damp extreme precipitation, through negative local thermodynamic feedbacks between convection, surface fluxes, and SST.

Role of Weddell Sea ice in South Atlantic atmospheric variability

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 74:171-184 (2017) - DOI: https://doi.org/10.3354/cr01495 Role of Weddell Sea ice in South Atlantic atmospheric variability Yushi Morioka1,*, Francois Engelbrecht2,3, Swadhin K. Behera1 1Application Laboratory, JAMSTEC, Yokohama, Japan 2Natural Resources & the Environment, CSIR, Pretoria, South Africa 3School of Geography, Archaeology and Environmental Sciences, University of the Witwatersrand, South Africa *Corresponding author: morioka@jamstec.go.jp ABSTRACT: We investigated the role of Weddell Sea ice in atmospheric variability over the South Atlantic by conducting observational data analysis and coupled general circulation model (CGCM) experiments. Weddell Sea ice exhibits a pronounced interannual variability in early austral summer (November-January). Low sea-ice concentration (SIC) anomalies in the Weddell Sea are strongly associated with anticyclonic atmospheric circulation anomalies in the South Atlantic. Composite analysis reveals that the low SIC anomalies in the Weddell Sea may be attributed to increased solar radiation and northwesterly wind anomalies. The low SIC anomalies, in turn, contribute to warmer skin temperature in the band of 60-70°S and enhance the near-surface atmospheric stability north of this band, implying favorable conditions for sustaining the anticyclonic circulation anomalies in the South Atlantic. This intriguing association between the SIC and atmospheric circulation anomalies is also simulated in CGCM experiments, e.g. when the interannual sea surface temperature variability in the tropics and mid-latitudes is suppressed. These results suggest that Weddell Sea ice, which may undergo interannual variation via air-sea-ice interactions in the high latitudes, influences atmospheric variability over the South Atlantic. KEY WORDS: Air–sea–ice interaction · Interannual variability · South Atlantic · Atmospheric teleconnection · Coupled general circulation model Full text in pdf format Supplementary material PreviousCite this article as: Morioka Y, Engelbrecht F, Behera SK (2017) Role of Weddell Sea ice in South Atlantic atmospheric variability. Clim Res 74:171-184. https://doi.org/10.3354/cr01495 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 74, No. 2. Online publication date: December 27, 2017 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2017 Inter-Research.

Intrinsic precursors and timescale of the tropical Indian Ocean Dipole: insights from partially decoupled numerical experiment

The intrinsic precursors and timescale of the tropical Indian Ocean Dipole (IOD) are examined with the help of a partially coupled global experiment with decoupled SST over the tropical Pacific. The IOD does exist in the absence of sea surface temperature interannual variability in the tropical Pacific in our modeling framework, but has weaker amplitude and damped Bjerknes feedback. However, IOD variability is much more biennial in the absence than presence of El Nino Southern Oscillation, especially in the eastern equatorial Indian Ocean (IO). Such biennial rhythm results mainly from two mechanisms internal to the IO. The tropical ocean dynamics play a key role in the biennial anomalies during boreal winter with a sudden reversal of thermocline anomalies in the eastern equatorial IO forced by intraseasonal disturbances reminiscent of the Madden–Julian Oscillation (MJO). However, this preconditioning is not sufficient for triggering IOD events in the next boreal spring per se. The main trigger for pure IODs relates to tropical–extratropical interactions within the IO. Convection and diabating heating associated with negative IODs promote a Gill-type tropical response, excite mid-latitude wave-trains and subtropical blocking in the Southern Hemisphere that trigger positive subtropical IOD events during boreal winter. The latter promotes cold SST and anticyclonic circulation anomalies over the southeast IO that persist and migrate northeastward, triggering positive IOD events during the next boreal spring. Accounting for the complementary influence of tropical ocean dynamics coupled to MJO and tropical-extratropical ocean–atmosphere interactions may thus help improving IOD predictability.

Long-term observation on sea surface temperature variability in the Taiwan Strait during the northeast monsoon season

ABSTRACTThe sea surface temperature (SST) in the Taiwan Strait (TS) during autumn and winter (October–March) is strongly influenced by the northeast monsoon, which drives the cold China Coastal Current to flow southward into the TS, where it encounters the warm Kuroshio Branch Current coming from the south to form a quasi-steady front. Using Advanced Very High Resolution Radiometer data, this study investigated long-term SST warming phenomena in the TS during the northeast monsoon season in the years 1980–2012. The SST trend demonstrated significant temporal and spatial variations; the SST of the TS increased during the period 1980–2000 and warmed faster in winter and early spring (January–March) than in autumn. Warming of the spatial average SST of the TS in March during this period reached 3°C. The highest warming trend was noted in the SST frontal region, indicating a northwestward movement of the winter fronts; however, the SST of the TS exhibited a decreasing trend after 2000. The interannual and decadal SST variations in the TS are partly in response to a large-scale wind field anomaly during the northeast monsoon season.

An assessment of TropFlux and NCEP air-sea fluxes on ROMS simulations over the Bay of Bengal region

This study presents an assessment of the TropFlux and the National Centers for Environmental Prediction (NCEP) reanalysis air-sea fluxes in simulating the surface and subsurface oceanic parameters over the Bay of Bengal (BoB) region during 2002–2014 using the Regional Ocean Modelling System (ROMS). The assessment has been made by comparing the simulated fields with in-situ and satellite observations. The simulated surface and subsurface temperatures in the TropFlux forced experiment (TropFlux-E) show better agreement with the Research Moored Array for African-Asian-Australian Monsoon Analysis (RAMA) and Argo observations than the NCEP forced experiment (NCEP-E). The BoB domain averaged sea surface temperature (SST) simulated in the NCEP-E is consistently cooler than the satellite SST, with a root mean square error (RMSE) of 0.79°C. Moreover, NCEP-E shows a limitation in simulating the observed seasonal cycle of the SST due to substantial underestimation of the pre-monsoon SST peak. These limitations are mostly due to the lower values of the NCEP net heat flux. The seasonal and interannual variations of SST in the TropFlux-E are better comparable to the observations with correlations and skills more than 0.80 and 0.90 respectively. However, SST is overestimated during summer monsoon periods mainly due to higher net heat flux. The superiority of TropFlux forcing over the NCEP reanalysis can also be seen when simulating the interannual variabilities of the magnitude and vertical extent of Wyrtki jets at two equatorial RAMA buoy locations. The jet is weaker in the NCEP-E relative to the TropFlux-E and observations. The simulated sea surface height anomalies (SSHA) from both the experiments are able to capture the regions of positive and negative SSHA with respect to satellite-derived altimeter data with better performance in the TropFlux-E. The speed of the westward propagating Rossby wave along 18°N in the TropFlux-E is found to be about 4.7cm/s, which is close to the theoretical phase speed of Rossby waves.

Environmental Variability and Oceanographic Dynamics of the Central and Southern Coastal Zone of Sonora in the Gulf of California

This study analyzed monthly and inter-annual variability of mesoscale phenomena, including the El Niño Southern Oscillation (ENSO), the Pacific Decadal Oscillation (PDO) climate indexes and wind intensity considering their influence on sea surface temperature (SST) and chlorophyll a (Chl-a). These analyses were performed to determine the effects, if any, of climate indexes and oceanographic and environmental variability on the central and southern coastal ecosystem of Sonora in the Gulf of California (GC). Monthly satellite images of SST (°C) and Chl-a concentration were used with a 1-km resolution for oceanographic and environmental description, as well as monthly data of the climate indexes and wind intensity from 2002–2015. Significant differences (p > 0.05) were observed while analyzing the monthly variability results of mesoscale phenomena, SST and Chl-a, where the greatest percentage of anti-cyclonic gyres and filaments was correlated with a greater Chl-a concentration in the area of study, low temperatures and, thus, greater productivity. Moreover, the greatest percentage of intrusion was correlated with the increase in temperature and cyclonic gyres and a strong decrease of Chl-a concentration values, causing oligotrophic conditions in the ecosystem and a decrease in upwelling and filament occurrence. As for the analysis of the interannual variability of mesoscales phenomena, SST, Chl-a and winds, the variability between years was not significant (p > 0.05), so no correlation was observed between variabilities or phenomena. The results of the monthly analyses of climate indexes, environmental variables and wind intensity did not show significant differences for the ENSO and PDO indexes (p > 0.05). Nonetheless, an important correlation could be observed between the months of negative anomalies of the ENSO with high Chl-a concentration values and intense winds, as well as with low SST values. The months with positive ENSO anomalies were correlated with high SST values, low Chl-a concentration and moderate winds. Significant inter-annual differences were observed for climate indexes where the years with high SST values were related to the greatest positive anomaly of ENSO, of which 2002 and 2009 stood out, characterized as moderate Niño years, and 2015 as a strong El Niño year. The years with the negative ENSO anomaly were related to the years of lower SST values, of which 2007–2008 and 2010–2011 stood out, characterized as moderate Niñas. Thus, variability associated with mesoscale oceanographic phenomena and seasonal and inter-annual variations of climate indexes had a great influence on the environmental conditions of the coastal ecosystem of Sonora in the Gulf of California.

Interannual Variability of Sea Surface Temperature in the Southwest Pacific and the Role of Ocean Dynamics

Abstract This paper investigates the mechanisms causing interannual variability of upper ocean heat content and sea surface temperature (SST) in the southwest Pacific. Using the ECCOv4 ocean reanalysis it is shown that air–sea heat flux and ocean heat transport convergence due to ocean dynamics both contribute to the variability of upper ocean temperatures around New Zealand. The ocean dynamics responsible for the ocean heat transport convergence are investigated. It is shown that SSTs are significantly correlated with the arrival of barotropic Rossby waves estimated from the South Pacific wind stress over the latitudes of New Zealand. Both Argo observations and the ECCOv4 reanalysis show deep isotherms fluctuate coherently around the country. The authors suggest that the depth of the thermocline around New Zealand adjusts to changes in the South Pacific winds, modifies the vertical advection of heat into the upper ocean, and contributes to the interannual variability of SST in the region.

Potential impact of sea surface temperature on rainfall over the western Philippines

ᅟThe study used a 5 km-resolution regional climate model, the Advanced Research Weather Research and Forecasting Model, to quantify the potential impact of sea surface temperature (SST) west of the Philippines on summer monsoon rainfall on the northwestern coast of the country. A set of control simulations (CTL) driven by ERA-Interim reanalysis data and the monthly National Oceanic and Atmospheric Administration Optimum Interpolation SST dataset was performed for the months of June to August of 1982–2012. A second set of simulations driven by climatological SST values was performed for the same period. The difference between these two simulation sets is analyzed to determine the sensitivity of rainfall to interannual variations in local SST, not remote SST, via a regional climate model. The CTL simulations represented spatial and temporal variations in rainfall well, yielding realistic climatological rainfall values with high spatial correlations with observations. The interannual correlation of monthly rainfall over the northwestern region of the Philippines was also high when compared to observations. The results showed that positive SST anomalies west of the Philippines induced positive rainfall anomalies in the northwestern Philippines via an increase in latent heat flux from the sea surface, implying that summer monsoon rainfall in the northwestern Philippines is modulated by interannual variations in SST west of the Philippines. The impact of SST on latent heat flux and rainfall were 20–40%, greatly exceeding the 7% approximation from the Clausius–Clapeyron equation, which can be explained by the enhancement of low-level winds and a weak warming of surface air temperature over the ocean.

Alleviating tropical Atlantic sector biases in the Kiel climate model by enhancing horizontal and vertical atmosphere model resolution: climatology and interannual variability

We investigate the quality of simulating tropical Atlantic (TA) sector climatology and interannual variability in integrations of the Kiel climate model (KCM) with varying atmosphere model resolution. The ocean model resolution is kept fixed. A reasonable simulation of TA sector annual-mean climate, seasonal cycle and interannual variability can only be achieved at sufficiently high horizontal and vertical atmospheric resolution. Two major reasons for the improvements are identified. First, the western equatorial Atlantic westerly surface wind bias in spring can be largely eliminated, which is explained by a better representation of meridional and especially vertical zonal momentum transport. The enhanced atmospheric circulation along the equator in turn greatly improves the thermal structure of the upper equatorial Atlantic with much reduced warm sea surface temperature (SST) biases. Second, the coastline in the southeastern TA and steep orography are better resolved at high resolution, which improves wind structure and in turn reduces warm SST biases in the Benguela upwelling region. The strongly diminished wind and SST biases at high atmosphere model resolution allow for a more realistic latitudinal position of the intertropical convergence zone. Resulting stronger cross-equatorial winds, in conjunction with a shallower thermocline, enable a rapid cold tongue development in the eastern TA in boreal spring. This enables simulation of realistic interannual SST variability and its seasonal phase locking in the KCM, which primarily is the result of a stronger thermocline feedback. Our findings suggest that enhanced atmospheric resolution, both vertical and horizontal, could be a key to achieving more realistic simulation of TA climatology and interannual variability in climate models.

CMIP5 analysis of the interannual variability of the Pacific SST and its association with the Asian–Pacific oscillation

This study analyzed the interannual variability of sea surface temperature (SST) over the Pacific in the historical simulation and under the Representative Concentration Pathways (RCPs, including R...

Role of Mixed Layer Dynamics in Tropical North Atlantic Interannual Sea Surface Temperature Variability

Abstract This study examines the causes of observed sea surface temperature (SST) anomalies in the tropical North Atlantic between 1982 and 2015. The emphasis is on the boreal winter and spring seasons, when tropical Atlantic SSTs project strongly onto the Atlantic meridional mode (AMM). Results from a composite analysis of satellite and reanalysis data show important forcing of SST anomalies by wind-driven changes in mixed layer depth and shortwave radiation between 5° and 10°N, in addition to the well-known positive wind–evaporation–SST and shortwave radiation–SST feedbacks between 5° and 20°N. Anomalous surface winds also drive pronounced thermocline depth anomalies of opposite signs in the eastern equatorial Atlantic and intertropical convergence zone (ITCZ; 2°–8°N). A major new finding is that there is strong event-to-event variability in the impact of thermocline depth on SST in the ITCZ region, in contrast to the more consistent relationship in the eastern equatorial Atlantic. Much stronger anomalies of meridional wind stress, thermocline depth, and vertical turbulent cooling are found in the ITCZ region during a negative AMM event in 2009 compared to a negative event in 2015 and a positive event in 2010, despite SST anomalies of similar magnitude in the early stages of each event. The larger anomalies in 2009 led to a much stronger and longer-lived event. Possible causes of the inconsistent relationship between thermocline depth and SST in the ITCZ region are discussed, including the preconditioning role of the winter cross-equatorial SST gradient.

Modulation of SST Interannual Variability in the Agulhas Leakage Region Associated with ENSO

Abstract The Agulhas leakage transports warm and saline water from the Indian Ocean into the South Atlantic Ocean, forming part of the upper returning arm of the meridional overturning circulation, which can influence climate. Ocean–atmosphere interactions and the strength of Agulhas leakage control sea surface temperature (SST) in the Agulhas leakage corridor, which may in turn affect regional climate variability. In a high-resolution run of the Community Climate System Model (version 3.5; CCSM3.5), it is found that the interannual variability of Agulhas leakage SST is linked to El Niño–Southern Oscillation (ENSO). Anomalous wind stress curl over the south Indian Ocean associated with ENSO excites westward-propagating oceanic Rossby waves that initiate southwestward-propagating anomalies along the coast of Africa. It takes approximately 2 years for this signal to reach the southern tip of South Africa and enter the South Atlantic, where it accounts for 20%–30% of the interannual SSH variability in the Agulhas leakage region. The authors find a similar propagation of anomalies with satellite observations. A similar ENSO cycle along with Rossby wave adjustment is detected in an analogous low-resolution CCSM3.5 run. However, the signal does not propagate all the way along the boundary to affect Agulhas leakage SST. Hence, it is found that high-resolution coupled climate models are necessary to resolve the tropical–subtropical oceanic teleconnection between ENSO and Agulhas leakage SST.

Phase locking of equatorial Atlantic variability through the seasonal migration of the ITCZ

The equatorial Atlantic is marked by significant interannual variability in sea-surface temperature (SST) that is phase-locked to late boreal spring and early summer. The role of the atmosphere in this phase locking is examined using observations, reanalysis data, and model output. The results show that equatorial zonal surface wind anomalies, which are a main driver of warm and cold events, typically start decreasing in June, despite SST and sea-level pressure gradient anomalies being at their peak during this month. This behavior is explained by the seasonal northward migration of the intertropical convergence zone (ITCZ) in early summer. The north-equatorial position of the Atlantic ITCZ contributes to the decay of wind anomalies in three ways: (1) horizontal advection associated with the cross-equatorial winds transports air masses of comparatively low zonal momentum anomalies from the southeast toward the equator. (2) The absence of deep convection leads to changes in vertical momentum transport that reduce the equatorial wind anomalies at the surface, while anomalies aloft remain relatively strong. (3) The cross-equatorial flow is associated with increased total wind speed, which increases surface drag and deposit of momentum into the ocean. Previous studies have shown that convection enhances the surface wind response to SST anomalies. The present study indicates that convection also amplifies the surface zonal wind response to sea-level pressure gradients in the western equatorial Atlantic, where SST anomalies are small. This introduces a new element into coupled air-sea interaction of the tropical Atlantic.

On the Observed Relationships between Variability in Gulf Stream Sea Surface Temperatures and the Atmospheric Circulation over the North Atlantic

Abstract The advent of increasingly high-resolution satellite observations and numerical models has led to a series of advances in understanding the role of midlatitude sea surface temperature (SST) in climate variability, especially near western boundary currents (WBC). Observational analyses suggest that ocean dynamics play a central role in driving interannual SST variability over the Kuroshio–Oyashio and Gulf Stream extensions. Numerical experiments suggest that variations in the SST field within these WBC regions may have a much more pronounced influence on the atmospheric circulation than previously thought. In this study, the authors examine the observational support for (or against) a robust atmospheric response to midlatitude SST variability in the Gulf Stream extension. To do so, they apply lead–lag analysis based on daily mean data to assess the evidence for two-way coupling between SST anomalies and the atmospheric circulation on transient time scales, building off of previous studies that have utilized weekly data. A novel decomposition approach is employed to demonstrate that atmospheric circulation anomalies over the Gulf Stream extension can be separated into two distinct patterns of midlatitude atmosphere–ocean interaction: 1) a pattern that peaks 2–3 weeks before the largest SST anomalies in the Gulf Stream extension, which can be viewed as the “atmospheric forcing,” and 2) a pattern that peaks several weeks after the largest SST anomalies, which the authors argue can be viewed as the “atmospheric response.” The latter pattern is linearly independent of the former and is interpreted as the potential response of the atmospheric circulation to SST variability in the Gulf Stream extension.

Reconstruction and analysis of long-term satellite-derived sea surface temperature for the South China Sea

Sea surface temperature (SST) is one of the key variables often used to investigate ocean dynamics, ocean-atmosphere interaction, and climate change. Unfortunately, the SST data sources in the South China Sea (SCS) are not abundant due to sparse measurements of in situ SST and a high percentage of missing data in the satellite-derived SST. Therefore, SST data sets with low resolution and/or a short-term period have often been used in previous researches. Here we used Data INterpolating Empirical Orthogonal Functions, a self-consistent and parameter-free method for filling in missing data, to reconstruct the daily nighttime 4-km AVHRR Pathfinder SST for the long-term period spanning from 1989 to 2009. In addition to the reconstructed field, we also estimated the local error map for each reconstructed image. Comparisons between the reconstructed and other data sets (satellite-derived microwave and in situ SSTs) show that the results are reliable for use in many different researches, such as validating numerical models, or identifying and tracking meso-scale oceanic features. Moreover, the Empirical Orthogonal Function (EOF) analysis of the reconstructed SST and the reconstructed SST anomalies clearly shows the subseasonal, seasonal, and interannual variability of SST under the influence of monsoon and El Nino-Southern Oscillation (ENSO), as well as reveals some oceanic features that could not be captured well in previous EOF analyses. The SCS SST often lags ENSO by about half a year. However, in this study, we see that the time lag changes with the frequencies of the SST variability, from 1 to 6 months.

Clouds–SST relationship and interannual variability modes of Indian summer monsoon in the context of clouds and SSTs: observational and modelling aspects

ABSTRACTThis study examines the relationship between clouds and sea surface temperatures (SSTs) during Indian Summer Monsoon (ISM). Observation reveals dominance of high‐level clouds in the monsoon region. NCEP Climate Forecast System version 2 (CFSv2) is able to replicate the observed high‐level cloud fractions although it underestimates the magnitude. Cloud–SST relationship for observation depicts dominance of positive correlation over equatorial Indian Ocean region which is well recapitulated in CFSv2 simulations. To investigate the most dominating patterns of interannual variability of rainfall, SST and clouds, empirical orthogonal function (EOF) analysis is performed on seasonal JJAS (June–September) dataset. EOF analysis signifies that high‐level clouds are highly correlated with rainfall for observations during ISM season. This study has also investigated relationship of clouds and El Niño Southern Oscillations (ENSO) and Indian Ocean Dipole (IOD) during ISM period. Interannual variations of clouds connote significant correlation with ENSO index (Nino 3/Nino 3.4). First principal component (PC1) of high‐level clouds and ENSO index indicate significant negative correlation. EOF analysis based on observation also connotes that first mode (second) of EOF analysis is associated with ENSO (IOD). It is also confirmed by maximum covariance analysis (MCA). CFSv2 is also able to depict the significant negative correlation between PC1 of high‐level clouds and ENSO index. Observation based second principal component (PC2) of high‐level clouds and IOD index exhibits significant positive correlation. It gives indication that PC2 of observed high‐level clouds can be associated with IOD. In contrast, PC2 of CFSv2 simulated high‐level cloud and IOD index are not correlated. EOF analysis based on CFSv2 shows that the first mode of EOF analysis is associated with ENSO; however, second mode of EOF is not related with IOD. MCA analysis also supports these findings. It means that CFSv2 has good ability to represent ENSO as compared with IOD.

Spatial and Temporal Variability of Sea Surface Temperature in Eastern Marginal Seas of China

Spatial mean value evolution, long-term mean pattern, and seasonal as well as interannual variability of sea surface temperature (SST) in Eastern Marginal Seas of China (EMSC) are reanalyzed based on thirty years’ NOAA optimum interpolation (OI) 1/4 degrees’ daily SST data. Temporal evolution of the spatial mean value shows a very marked annual cycle and a weak warming tendency (0.03437°C/year). Spatial distribution of the long-term mean value shows some more fine spatial structure of SST compared to previous studies. Over 90% of the temporal variability can be explained by the annual harmonic whose amplitude is one order larger than that of the semiannual harmonic. In addition, the annual harmonic amplitude distribution is consistent with that of the value of standard deviation. In order to investigate the interannual variation of SST, the EMSC SST interannual index was constructed. Based on wavelet analysis, a significant peak around 3.3 years was found in the EMSC SST interannual index. Further analysis demonstrated that the interannual variability of SST is linked with El Niño-Southern Oscillation (ENSO) teleconnection, through which anomalous surface heat flux warms or cools the EMSC during El Niño or La Niña events.

Variation Characteristics of Rainfall in the Pre-Flood Season of South China and Its Correlation with Sea Surface Temperature of Pacific

The characteristics of rainfall variation in the pre-flood season of South China (PFSSC) and its correlation with the sea surface temperature (SST) of the Pacific are studied in this paper. The results show that in the last 50 years, rainfall in PFSSC clearly has interannual and interdecadal oscillations, primarily in the 4a and 8a cycles. Interannual correlation analysis indicate that the rainfall in PFSSC displays a significantly negative correlation with the SST of the warm pool region in January–March and April–June. The interdecadal correlation analysis reveals that the rainfall in PFSSC is negatively correlated to the SST of the warm pool region, but has a significant positive interdecadal correlation with the Middle Eastern Pacific Ocean. For NINO1 + 2 and NINO3 regions, when the background ocean temperature is warm, the SST is significantly positively correlated to the rainfall in PFSSC; however, when the background ocean temperature is cold, there is no significant correlation between the two, even the correlation coefficients are negative. For the warm pool region, the SST demonstrates a significantly negative correlation to the rainfall in PFSSC, which is not dependent on the background SST. It is a remarkable fact that under the different SST backgrounds, the interannual variation of SST will bring different atmospheric response, and it is the reason that under the warm SST background, the correlation is more significant between the SST in tropical Pacific and the rainfall in PFSSC. Under the background of global warming, more attention should be given to study the rainfall in PFSSC and its correlation with the SST in the eastern tropical Pacific.

Multi-model ensemble analysis of Pacific and Atlantic SST variability in unperturbed climate simulations

We assess internally-generated climate variability expressed by a multi-model ensemble of unperturbed climate simulations. We focus on basin-scale annual-average sea surface temperatures (SSTs) from twenty multicentennial pre-industrial control simulations contributing to the fifth phase of the Coupled Model Intercomparison Project. Ensemble spatial patterns of regional modes of variability and ensemble (cross-)wavelet-based phase-frequency diagrams of corresponding paired indices summarize the ensemble characteristics of inter-basin and regional-to-global SST interactions on a broad range of timescales. Results reveal that tropical and North Pacific SSTs are a source of simulated interannual global SST variability. The North Atlantic-average SST fluctuates in rough co-phase with the global-average SST on multidecadal timescales, which makes it difficult to discern the Atlantic Multidecadal Variability (AMV) signal from the global signal. The two leading modes of tropical and North Pacific SST variability converge towards co-phase in the multi-model ensemble, indicating that the Pacific Decadal Oscillation (PDO) results from a combination of tropical and extra-tropical processes. No robust inter- or multi-decadal inter-basin SST interaction arises from our ensemble analysis between the Pacific and Atlantic oceans, though specific phase-locked fluctuations occur between Pacific and Atlantic modes of SST variability in individual simulations and/or periods within individual simulations. The multidecadal modulation of PDO by the AMV identified in observations appears to be a recurrent but not typical feature of ensemble-simulated internal variability. Understanding the mechanism(s) and circumstances favoring such inter-basin SST phasing and related uncertainties in their simulated representation could help constraining uncertainty in decadal climate predictions.

El Niño influence on potential maize yield in Iberian Peninsula

El Nino phenomenon is the leading mode of sea surface temperature interannual variability. It can affect weather patterns worldwide and therefore crop production. Crop models are useful tools for impact and predictability applications, allowing to obtain long time series of potential and attainable crop yield, unlike to available time series of observed crop yield for many countries. Using this tool, crop yield variability in a location of Iberia Peninsula (IP) has been previously studied, finding predictability from Pacific El Nino conditions. Nevertheless, the work has not been done for an extended area. The present work carries out an analysis of maize yield variability in IP for the whole twenty century, using a calibrated crop model at five contrasting Spanish locations and reanalyses climate datasets to obtain long time series of potential yield. The study tests the use of reanalysis data for obtaining only climate dependent time series of crop yield for the whole region, and to use these yield to analyze the influences of oceanic and atmospheric patterns. The results show a good reliability of reanalysis data. The spatial distribution of the leading principal component of yield variability shows a similar behaviour over all the studied locations in the IP. The strong linear correlation between El Nino index and yield is remarkable, being this relation non-stationary on time, although the air temperature-yield relationship remains on time, being the highest influences during grain filling period. Regarding atmospheric patterns, the summer Scandinavian pattern has significant influence on yield in IP. The potential usefulness of this study is to apply the relationships found to improving crop forecasting in IP.