Characteristics of tropical Pacific SST predictability in coupled GCM forecasts using the NCEP CFS

The limits of predictability of El Niño and the Southern Oscillation (ENSO) in coupled models are investigated based on retrospective forecasts of sea surface temperature (SST) made with the National Centers for Environmental Prediction (NCEP) coupled forecast system (CFS). The influence of initial uncertainties and model errors associated with coupled ENSO dynamics on forecast error growth are discussed. The total forecast error has maximum values in the equatorial Pacific and its growth is a strong function of season irrespective of lead time. The largest growth of systematic error of SST occurs mainly over the equatorial central and eastern Pacific and near the southeastern coast of the Americas associated with ENSO events. After subtracting the systematic error, the root-mean-square error of the retrospective forecast SST anomaly also shows a clear seasonal dependency associated with what is called spring barrier. The predictability with respect to ENSO phase shows that the phase locking of ENSO to the mean annual cycle has an influence on the seasonal dependence of skill, since the growth phase of ENSO events is more predictable than the decay phase. The overall characteristics of predictability in the coupled system are assessed by comparing the forecast error growth and the error growth between two model forecasts whose initial conditions are 1 month apart. For the ensemble mean, there is fast growth of error associated with initial uncertainties, becoming saturated within 2 months. The subsequent error growth follows the slow coupled mode related the model’s incorrect ENSO dynamics. As a result, the Lorenz curve of the ensemble mean NINO3 index does not grow, because the systematic error is identical to the same target month. In contrast, the errors of individual members grow as fast as forecast error due to the large instability of the coupled system. Because the model errors are so systematic, their influence on the forecast skill is investigated by analyzing the erroneous features in a long simulation. For the ENSO forecasts in CFS, a constant phase shift with respect to lead month is clear, using monthly forecast composite data. This feature is related to the typical ENSO behavior produced by the model that, unlike the observations, has a long life cycle with a JJA peak. Therefore, the systematic errors in the long run are reflected in the forecast skill as a major factor limiting predictability after the impact of initial uncertainties fades out.     

Stable oxygen and hydrogen isotopic composition of bentonites from Cabo de Gata (Almería,Spain)

The aim of this study is to investigate the nature of the solutions and the temperature during the bentonite formation by using δ¹⁸O and δ²H values and the relationship between chemical and isotopic composition of smectites from Cabo de Gata region. Therefore, 36 bentonite samples had been selected. For analyses the <2 μm fraction were separated. Most of the samples contain smectite above 90 wt%. The stable oxygen and hydrogen isotopic composition of the analysed smectites is close to the “montmorillonite line”. However, from isotopic composition two types of bentonite can be distinguished. The Sierra de Gata (SG) and Serrata de Nijar (SN) types show δ¹⁸O and δ²H values above and below this line, respectively. Temperatures obtained from geothermometer equation are similar to the temperatures values obtained from the equation of Savin and Lee (1988). Estimated formation temperatures of SG type are 25 and 49 °C higher compared to those of the SN type (6 and 25 °C).Correlations between structural cations versus isotopic composition show no statistical significance concerning all samples. However, separating the samples of SG (Sierra de Gata) from SN (Serrata of Nijar) a statistical significance for the individual areas is obtained. In both cases the effect is similar for ¹⁸O and for ²H. This could be due to the different composition of the solutions forming these bentonites.     

State of knowledge of coastal aquifer management in South America

A comparative analysis of the existing hydrogeological and management information from 15 coastal aquifers in South America was performed in order to obtain insight into common features of the sub-continent coastal zones. Some knowledge from other areas has been incorporated. There is a very variable degree of knowledge and management practice, ranging from almost no data and no action (the most common case), to sound conceptual models about aquifer behaviour and comprehensive management actions such as relocation of abstractions, pumping brackish groundwater, and aquifer vulnerability mapping. Some common features are: intensive groundwater exploitation; lack of characterization studies to support resource planning and management; lack of monitoring networks; and the need for raising awareness within society and its involvement in resource planning and management action programmes. Quality and quantity problems arising in heavily populated areas associated with coastal aquifers in South America point to unsustainable groundwater development. The sustainable use of those aquifers must rely on adequate evaluation of aquifer characteristics and monitoring.     

Morphodynamic interactions of continental shelf,beach and dunes: the Cabopino dune system in southern Mediterranean Spain

The complex morphodynamic interactions between nearshore, shoreface and dune systems are usually simplified by studying these zones and their associated processes in isolation. However, the established relationships between each of them suggests that an integrated approach is required to examine the genesis, evolution and adaptation of the entire morphodynamic system. The Cabopino dune system in the southern Spanish Mediterranean Sea provides a clear example of a linked morphodynamic system in which a relatively large dune system has been generated and grown through the supply of sediments from an adjacent littoral supply environment. Here, we present a conceptual model of how the nearshore has provided suitable conditions for beach and dune development. We purport that synchronization of sediment activation in the marine and aeolian sections of the system have played a major role in this microtidal setting in which temporal aspects are not only tied to storm action, but to large sedimentary features moving alongshore. © 2019 John Wiley & Sons, Ltd.     

Planktonic foraminiferal distribution record productivity cycles: evidence from the Aptian-Albian Piobbico core (central Italy)

The Aptian-Albian 'Scisti a Fucoidi' varicoloured pelagic sediments in central Italy, show a 'couplet' alternation of carbonate-rich/carbonate-poor layers, which are interpreted as the sedimentary expression of precession (frequency 19–23 kyr). Carbonate content, chromatic variation, and planktonic foraminiferal abundance were analysed at a 1-cm spacing for a 10-m interval of the Piobbico core, specifically drilled through this formation. Spectral analysis of these parameters shows a prominent signal equated to the c . 100 kyr cycle of orbital eccentricity at a sedimentation rate of 5 mm kyr⁻¹. The coherency of the spectral response of each parameter suggests that a single mechanism controlled the whole sedimentary record. Detailed study of planktonic foraminiferal distribution of the same section at 1-mm scale resolves the Milankovitch frequencies of 41 kyr and 18 to 23 kyr, equated with the obliquity and precessional cycles. But foraminiferal abundance is not in phase with carbonate content, which was largely controlled by calcareous nannofossils, but peaked at intermediate carbonate values. The proposed model for explaining the discrepancy at the precessional level is that foraminifera thrived at intermediate values of the precession index, when the environment was only moderately fertile but stable, while during highs of the precession index, mixing of the water column increased fertility and caused calcareous nannofossil blooms and restriction of planktonic foraminifera to few and tolerant species. The resulting bimodality of foraminiferal abundance per precessional cycle appears to be recorded in the spectrum by peaks at the 11 and 14 kyr levels. Cross correlation of foraminiferal abundances with the calcium carbonate curve over 1–2 Myr intervals produces discrepant results (apparent phase lags) which we attribute to differences in the response to the fundamental eccentricity cycles.     

Modes of variability of Southern Hemisphere atmospheric circulation estimated by AGCMs

The seasonal mean variability of the atmospheric circulation is affected by processes with time scales from less than seasonal to interannual or longer. Using monthly mean data from an ensemble of Atmospheric General Circulation Model (AGCM) realisations, the interannual variability of the seasonal mean is separated into intraseasonal, and slowly varying components. For the first time, using a recently developed method, the slowly varying component in multiple AGCM ensembles is further separated into internal and externally forced components. This is done for Southern Hemisphere 500?hPa geopotential height from five AGCMs in the CLIVAR International Climate of the Twentieth Century project for the summer and winter seasons. In both seasons, the intraseasonal and slow modes of variability are qualitatively well reproduced by the models when compared with reanalysis data, with a relative metric finding little overall difference between the models. The Southern Annular Mode (SAM) is by far the dominant mode of slowly varying internal atmospheric variability. Two slow-external modes of variability are related to El Ni?o-Southern Oscillation (ENSO) variability, and a third is the atmospheric response to trends in external forcing. An ENSO-SAM relationship is found in the model slow modes of variability, similar to that found by earlier studies using reanalysis data. There is a greater spread in the representation of model slow-external modes in winter than summer, particularly in the atmospheric response to external forcing trends. This may be attributable to weaker external forcing constraints on SH atmospheric circulation in winter.     

AQD occurrence at Addis Ababa,Trivandrum and Alibag

The effect of the equatorial electrojet is sufficient to reduce the probability of an abnormal quiet day occurring at Addis Ababa, Trivandrum and Alibag. Addis Ababa AQD occurrence exhibits an anomalous or subdued relationship to solar intensity, compared to that of Alibag, Trivandrum, and Greenwich/Abinger/Hartland; this is thought to be due to some unknown characteristic of the PM electrojet. Few AQD's are common to Addis Ababa and Trivandrum, Addis Ababa and Alibag, and Trivandrum and Alibag compared to the number common to Abinger and Wingst.     

Distribution and origin of nitrate in groundwater in an urban and suburban aquifer in Mar del Plata,Argentina

The impact of urbanization on groundwater quality is of special concern for water managers dealing with the provision of drinking water to large urban centers. Nitrate is one of the most common contaminants found in urban aquifers. This paper presents a case study aiming at evaluating the distribution and sources of nitrate in an urban aquifer in the city of Mar del Plata, Argentina. Four study zones under different land uses, including a pristine, a semi-rural, an intermediate, and an urban area, were evaluated as a part of this study. The three latter zones are linked by the groundwater flow system. The average nitrate concentration in the pristine area is 6.7 mg/L as nitrate and is over the permissible level of 50 mg/L for drinking water in the other areas. In the semi-rural area it ranges from 39.2 to 107.1 mg/L with an average value of 38.2 mg/L and the nitrate concentration tends to decrease in the intermediate zone to an average value of 38.2 mg/L; however, values above 60 mg/L are also observed there. Then the nitrate concentration in the urban area water is higher than that in the intermediate zonewater ranging from 48.2 to 100.3 mg/L with an average value of 67.3 mg/L. Data on the stable isotopes 15N and 18O in nitrate show that the main sources of nitrate in the study area are manure associated to agriculture uses and cesspools in the semi-rural area, and leakage of the sewage distribution network in the urban area, respectively. This is supported by a previous study which found that 20 % of the water flooding many underground structures in the city came from leakage of the sewage network. No evidence of nitrate attenuation by denitrification was found in the groundwater. This study has shown that aquifers in urban areas can be affected by agricultural activity in the upstream areas and leakage of the sewage network in the urban area.     

Discharge variability in Romania using Palmer indices and a simple atmospheric index of large-scale circulation

ABSTRACT

The aim of this study is to analyse the seasonal characteristics of four Palmer indices calculated on the basis of data from 27 meteorological stations in Romania, and the impact of these indices on river discharges in the period 1931–1998. Our research also tests the influence of large-scale atmospheric circulation on these indices and on discharge. For each season, developments in the empirical orthogonal functions (EOF) and multivariate EOF (MEOF) are achieved. The MEOF representation highlights the overall characteristics of the four Palmer indices. It maximizes specific information for each season compared with individual information of each Palmer index. We then identify geographical areas with homogeneous distribution, taking into account both the discharge distribution and the rotated EOF components of each Palmer index. Finally, we analysed the impact of large-scale atmospheric circulation on hydro-climatic events in Romania by means of the Greenland-Balkan Oscillation Index (GBOI), which is shown to have a greater influence on southeastern Europe than the North Atlantic Oscillation Index (NAOI).