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Equatorial Pacific (equatorial + pacific)
Selected AbstractsThe use of SST and SOI anomalies as indicators of crop yield variabilityINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 1 2009Maria I. Travasso Abstract Interannual climate variability accounts for most of the observed crop yield fluctuations in the main agricultural region of Argentina. Moreover, in this region climatic variations are related to sea surface temperatures (SST) and the Southern Oscillation Index (SOI). In the present study, we aimed to obtain indicators of crop yield variability based on these drivers. For this purpose, monthly anomalies corresponding to SSTs from the Equatorial Pacific (SSTN3) and South Atlantic (SSTSA) Oceans and the SOI were related to maize, sunflower and soybean grain yield anomalies. Historical data (1923,2000 for maize, 1934,2000 for sunflower and 1969,2000 for soybean) were used to obtain grain yield anomalies at the county level after removing technology trends by smoothing techniques. By means of correlation analysis, we obtained the counties presenting significant association (p < 0.05) between monthly SST/SOI anomalies and yield anomalies, for the period 1950,1997. Those indicators showing spatial consistency were classified in percentiles, and the values corresponding to the upper and lower terciles showed to be useful to discriminate between positive and negative yield anomalies (high and low yields). In general, SOI for maize and SSTSA for soybean and sunflower were the best indicators of crop yield variability. SOI corresponding to September and May were useful in counties contributing to 71% of maize production. SSTa_SA (June) was the best for soybean in the main producing region, which includes 72% of the total production. SSTa_SA (March) could be useful for sunflower in the northern part of the region, which accounts for 27% of the regional production. Copyright © 2008 Royal Meteorological Society [source] Interannual variability of lower-tropospheric moisture transport during the Australian monsoonINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 5 2002Christopher R. Godfred-Spenning Abstract The interannual variability of the horizontal lower-tropospheric moisture transport associated with the Australian summer monsoon has been analysed for the 1958,99 period. The 41-season climatology of moisture flux integrated between the surface and 450 hPa showed moderate levels of westerly transport in the month before Australian monsoon onset, associated with cross-equatorial flow in the Sulawesi Sea and west of Borneo. In the month after onset the westerly moisture transport strengthened dramatically in a zonal belt stretching from the Timor Sea to the Western Equatorial Pacific, constrained between the latitudes 5 and 15 °S, and associated with a poleward shift in the Intertropical Convergence Zone and deepening of the monsoon trough. Vertical cross-sections showed this transport extending from the surface to the 500 hPa level. In the second and third months after onset the horizontal flow pattern remained similar, although flux magnitudes progressively decreased, and the influence of trade winds became more pronounced over northern Australia. Nine El Niño and six La Niña seasons were identified from the data set, and composite plots of the affected years revealed distinct, and in some cases surprising, alterations to the large-scale moisture transport in the tropical Australian,Indonesian region. During an El Niño it was shown that the month prior to onset, in which the moisture flux was weaker than average, yielded to a dramatically stronger than average flux during the following month, with a zone of westerly flux anomalies stretching across the north Australian coast and Arafura Sea. The period of enhanced moisture flux during an El Niño is relatively short-lived, with drier easterly anomalies asserting themselves during the following 2 months, suggesting a shorter than usual monsoon period in north Australia. In the La Niña composite, the initial month after onset shows a tendency to weaker horizontal moisture transport over the Northern Territory and Western Australia. The subsequent 2 months show positive anomalies in flux magnitude over these areas; the overall effect is to prolong the monsoon. Comparison of these results with past research has led us to suggest that the tendency for stronger (weaker) circulations to arise in the initial month of El Niño (La Niña) events is a result of mesoscale changes in soil moisture anomalies on land and offshore sea surface temperature (SST) anomalies, brought about by the large-scale alterations to SST and circulation patterns during the El Niño,Southern Oscillation. The soil moisture and SST anomalies initially act to enhance (suppress) the conditions necessary for deep convection in the El Niño (La Niña) cases via changes in land,sea thermal contrast and cloud cover. Copyright © 2002 Royal Meteorological Society. [source] Potential changes in skipjack tuna (Katsuwonus pelamis) habitat from a global warming scenario: modelling approach and preliminary resultsFISHERIES OCEANOGRAPHY, Issue 4-5 2003Harilaos Loukos Abstract Recent studies suggest a reduction of primary production in the tropical oceans because of changes in oceanic circulation under global warming conditions caused by increasing atmospheric CO2 concentration. This might affect the productivity of medium and higher trophic levels with potential consequences on marine resources such as tropical tuna. Here we combine the projections of up-to-date climate and ocean biogeochemical models with recent concepts of representation of fish habitat based on prey abundance and ambient temperature to gain some insight into the impact of climate change on skipjack tuna (Katsuwonus pelamis), the species that dominates present-day tuna catch. For a world with doubled atmospheric CO2 concentration, our results suggest significant large-scale changes of skipjack habitat in the equatorial Pacific. East of the date line, conditions could be improved by an extension of the present favourable habitat zones of the western equatorial Pacific, a feature reminiscent of warming conditions associated with El Niño events. Despite its simplicity and the associated underlying hypothesis, this first simulation is used to stress future research directions and key issues for modelling developments associated to global change. [source] Trend patterns in global sea surface temperatureINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 14 2009Susana M. Barbosa Abstract Isolating long-term trend in sea surface temperature (SST) from El Niño southern oscillation (ENSO) variability is fundamental for climate studies. In the present study, trend-empirical orthogonal function (EOF) analysis, a robust space-time method for extracting trend patterns, is applied to isolate low-frequency variability from time series of SST anomalies for the 1982,2006 period. The first derived trend pattern reflects a systematic decrease in SST during the 25-year period in the equatorial Pacific and an increase in most of the global ocean. The second trend pattern reflects mainly ENSO variability in the Pacific Ocean. The examination of the contribution of these low-frequency modes to the globally averaged SST fluctuations indicates that they are able to account for most (>90%) of the variability observed in global mean SST. Trend-EOFs perform better than conventional EOFs when the interest is on low-frequency rather than on maximum variance patterns, particularly for short time series such as the ones resulting from satellite retrievals. Copyright © 2009 Royal Meteorological Society [source] Impact of global warming on ENSO variability using the coupled giss GCM/ZC modelINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 10 2006Dr. Timothy Eichler Research Scientist Abstract This study uses a hybrid coupled model (referred to as the general-circulation model (GCM)/Zebiak/Cane (ZC) model), which consists of the Goddard Institute for Space Studies' (GISS) Atmospheric general-circulation model (AGCM) coupled to the oceanic component of the ZC intermediate model to assess the impact of global warming on El Niño behavior, with and without the influence of heat introduced from the subtropical Pacific (via subtropical cell (STC) pathway). The baseline GCM/ZC model produces El Niño variability with a two year periodicity and an amplitude of approximately half the magnitude of observed El Niño. The GCM/ZC model also produces an appropriate atmospheric global response to El Niño/southern oscillation (ENSO) as shown by composites of 500 hPa heights, sea-level pressure (SLP), 200 hPa wind, and precipitation during El Niño and La Niña periods. To evaluate the importance of global warming on ENSO variability, 2× CO2 and 4× CO2 transient simulations were done increasing the atmospheric CO2 one percent per year, then extending the runs for an additional 70 years to obtain equilibrium climates for each run. An additional set of global-warming simulations was run after including a STC parameterization generated by computing 5-year running means of the sea-surface temperature (SST) difference between a transient run and the 1× CO2 GCM/ZC run at the anticipated subduction zones (160,130°W, 20,40°N and 20,44°S, 160,130°W) and adding it to the base of the equatorial mixed-layer of the ZC model with a time lag of 15 years. This effectively alters the vertical temperature gradient of the ZC model, which affects SST via upwelling. Two features of the GCM/ZC response to global warming are emphasized. Firstly, the inclusion of the STC results in a major redistribution of heat across the equatorial Pacific, leading to an El Niño-like response in the final equilibrium solution with less variability about the mean. The global warming aspect due to the El Niño-like response results in a positive feedback on global warming, which causes a higher global surface-air temperature (SAT) than identical transient simulations without inclusion of the STC. Secondly, including the STC effect produces a far greater magnitude of global ENSO-like impact because of the reduction of, or even the reversal of, the equatorial Pacific longitudinal SST gradient. The implications of such an extreme climate scenario are discussed. Copyright © 2006 Royal Meteorological Society [source] Variability of the impact of El Niño,southern oscillation on sea-level pressure anomalies over the North Atlantic in January to March (1874,1996)INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 13 2003I. Gouirand Abstract Sea-level pressure (SLP) anomalies over the North Atlantic and European (NAE) sector (25,70°N, 100°W,50°E) and over a larger domain encompassing the entire North Pacific domain are studied to demonstrate that SLP anomalies (SLPAs) during boreal winter (January,March) vary widely between years characterized by the same El Niño,southern oscillation (ENSO) phase. The typical cold ENSO signal tends to be more stable than the warm one during the 1874,1996 period. The typical cold ENSO pattern (e.g. positive SLPA south of 55°N across the North Atlantic and negative SLPA in the northern North Atlantic) is similar to the positive phase of the North Atlantic oscillation (NAO) and occurs throughout the 20th century, except during the 1950s and 1960s when the basinwide westerlies are particularly slow. On the contrary, the typical warm ENSO pattern (e.g. positive SLPA from central Canada to Scandinavia and negative SLPA from the southeastern USA to central Europe, corresponding to the negative phase of the NAO) occurs mainly from 1930 to 1970. Another robust warm ENSO pattern is associated with a large positive (negative) SLPA between Newfoundland and western Europe (between Greenland and Scandinavia), and occurs mainly at the beginning and the end of the 20th century when the basinwide North Atlantic westerlies are strengthened. All these patterns stay statistically significant when the multi-decadal variability is removed from the North Atlantic SLPA. It is shown that the low-frequency variability of the north tropical Atlantic sea-surface temperature anomalies could exert a modulating effect on the ENSO teleconnection. NAE SLPAs tend to be strong during warm (cold) ENSO winters and consistent with a negative (positive) phase of the NAO when the north tropical Atlantic is anomalously warm (cold). Lastly, the magnitude of the SLPA patterns over the NAE sector appears poorly related to the intensity of sea-surface temperature anomalies in the central and eastern equatorial Pacific. Copyright © 2003 Royal Meteorological Society [source] The impact of El Niño,southern oscillation upon weather regimes over Europe and the North Atlantic during boreal winterINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 4 2003Vincent Moron Abstract The influence of the warm and cold sea-surface temperatures in the eastern and central equatorial Pacific associated with El Niño,southern oscillation (ENSO) on the probability of occurrence of weather regimes (WRs) over the North Atlantic sector is investigated for the period November,March. Five WRs are identified from daily sea-level pressure anomalies (SLPAs) during 119 winters (1882,2000) over this sector by applying cluster analysis: the positive North Atlantic oscillation (NAO; called ZO for zonal) and negative NAO (called WBL for west blocking) patterns; GA (for Greenland anticyclone), with a positive SLPA shifted north of 60° N; EA (for European anticyclone) with a positive SLPA over Europe but enhanced north,south SLPA gradient over the western and central North Atlantic; and AR (for Atlantic Ridge) with a positive (negative) SLPA over the central North Atlantic (northern and central Europe). El Niño winters are associated with a significant increase (decrease) in the prevalence of ZO (WBL) in November,December and a significant increase (decrease) in the prevalence of GA and WBL (EA and ZO) in January,March. During La Niña winters, ZO (WBL and AR) occurs significantly less (more) frequently in November,December, and GA and WBL (EA and AR) are less (more) frequent in January,March. So, the anomalies of the WR frequencies are almost inverted between November,December and January,March. The response of the WR frequencies to ENSO extremes is most pronounced in February. On the inter- and multi-decadal time scales, the typical ENSO signals tend to be stronger during preferred phases of the basinwide westerlies, especially in January,March. The typical El Niño signal in January,March (e.g. more GA and WBL and less ZO and EA than normal) is strong when westerlies are slower than normal, around 1900, 1915 and mainly from 1930 to 1970. The generally reversed association during La Niña winters (e.g. more EA and AR and less GA and WBL than normal) in January,March is strong mainly when westerlies are faster than normal. Anomalies are weaker and quite different during ,slow westerlies,La Niña' and ,fast westerlies,El Niño' January,March winters. Such a modulation also appears in November,December with reversed association (i.e. stronger ENSO signal during ,slow westerlies,La Niña' and ,fast westerlies,El Niño' November,December winters), but the difference between the slow and fast westerlies phases is weaker than in January,March. Copyright © 2003 Royal Meteorological Society [source] Evolution of tropical and extratropical precipitation anomalies during the 1997,1999 ENSO cycleINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 8 2001Scott Curtis Abstract The 1997,1999 El Niño,Southern Oscillation (ENSO) period was very powerful, but also well observed. Multiple satellite rainfall estimates combined with gauge observations allow for a quantitative analysis of precipitation anomalies in the tropics and elsewhere accompanying the 1997,1999 ENSO cycle. An examination of the evolution of the El Niño and accompanying precipitation anomalies revealed that a dry Maritime Continent (MC) preceded the formation of positive sea-surface temperature (SST) anomalies in the eastern Pacific Ocean. Thirty- to sixty-day oscillations in the winter of 1996,1997 may have contributed to this lag relationship. Furthermore, westerly wind burst events may have maintained the drought over the MC. The warming of the equatorial Pacific was then followed by an increase in convection. A rapid transition from El Niño to La Niña occurred in May 1998, but as early as October,November 1997, precipitation indices captured substantial changes in Pacific rainfall anomalies. The global precipitation patterns for this event were in good agreement with the strong consistent ENSO-related precipitation signals identified in earlier studies. Differences included a shift in precipitation anomalies over Africa during the 1997,1998 El Niño and unusually wet conditions over northeast Australia during the later stages of the El Niño. Also, the typically wet region in the north tropical Pacific was mostly dry during the 1998,1999 La Niña. Reanalysis precipitation was compared with observations during this time period and substantial differences were noted. In particular, the model had a bias towards positive precipitation anomalies and the magnitudes of the anomalies in the equatorial Pacific were small compared with the observations. Also, the evolution of the precipitation field, including the drying of the MC and eastward progression of rainfall in the equatorial Pacific, was less pronounced for the model compared with the observations. Copyright © 2001 Royal Meteorological Society [source] Retro-active skill of multi-tiered forecasts of summer rainfall over southern AfricaINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 1 2001Willem A. Landman Abstract Sea-surface temperature (SST) variations of the oceans surrounding southern Africa are associated with seasonal rainfall variability, especially during austral summer when the tropical atmospheric circulation is dominant over the region. Because of instabilities in the linear association between summer rainfall over southern Africa and SSTs of the tropical Indian Ocean, the skilful prediction of seasonal rainfall may best be achieved using physically based models. A two-tiered retro-active forecast procedure for the December,February (DJF) season is employed over a 10-year period starting from 1987/1988. Rainfall forecasts are produced for a number of homogeneous regions over part of southern Africa. Categorized (below-normal, near-normal and above-normal) statistical DJF rainfall predictions are made for the region to form the baseline skill level that has to be outscored by more elaborate methods involving general circulation models (GCMs). The GCM used here is the Centre for Ocean,Land,Atmosphere Studies (COLA) T30, with predicted global SST fields as boundary forcing and initial conditions derived from the National Centres for Environmental Prediction (NCEP) reanalysis data. Bias-corrected GCM simulations of circulation and moisture at certain standard pressure levels are downscaled to produce rainfall forecasts at the regional level using the perfect prognosis approach. In the two-tiered forecasting system, SST predictions for the global oceans are made first. SST anomalies of the equatorial Pacific (NIÑO3.4) and Indian oceans are predicted skilfully at 1- and 3-month lead-times using a statistical model. These retro-active SST forecasts are accurate for pre-1990 conditions, but predictability seems to have weakened during the 1990s. Skilful multi-tiered rainfall forecasts are obtained when the amplitudes of large events in the global oceans (such as El Niño and La Niña episodes) are described adequately by the predicted SST fields. GCM simulations using persisted August SST anomalies instead of forecast SSTs produce skill levels similar to those of the baseline for longer lead-times. Given high-skill SST forecasts, the scheme has the potential to provide climate forecasts that outscore the baseline skill level substantially. Copyright © 2001 Royal Meteorological Society [source] GIOTTO: A coupled atmosphere-ocean general-circulation model: The tropical PacificTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 567 2000Martin Fischer Abstract A new coupled general-circulation model (GIOTTO) has been developed. The individual components are composed of the atmosphere model, ECHAM-4, and the ocean model, MOM (Modular Ocean Model)-1.2. The model domain is global, and no flux correction is applied. The coupling is active between 60°N and 60° S. Poleward of 60° the atmosphere is forced by the climatological sea surface temperature (SST), and the ocean is relaxed towards the climatological SST and sea surface salinity. Further, the sea-ice coverage is prescribed. The coupling interval is set to two hours to resolve the diurnal cycle. In this paper we describe the design of the model, and discuss results of a coupled 20-year integration. The representation of the mean state is realistic, although there is an overall cold SST bias of about one degree centigrade in the tropics, and a tendency to simulate a double Inter Tropical Convergence Zone. The annual cycle, as simulated in the equatorial Pacific, is too weak in the east Pacific and too strong in the warm-pool region. The phase, however, is well captured. The SST variability in the equatorial Pacific is underestimated by about 30%, and the anomalies are too confined to the equator. The main features of El Niño-Southern Oscillation (ENSO) dynamics, like propagation of heat-content anomalies, reflection of equatorial Kelvin and Rossby waves, and westerly wind bursts, however, are correctly represented by the model. A variability analysis based on empirical orthogonal functions indicates that the ENSO mechanisms are simulated correctly. The model also appears to be well balanced with a remarkably low SST drift (0.5 degC decade,1), and a realistic equatorial thermal structure. We are, therefore, confident that the model can be used for experimental seasonal predictions. [source] | ||||||||||