A review of ENSO prediction studies   总被引：10，自引：0，他引：10  

M. Latif  T. P. Barnett  M. A. Cane  M. Flügel  N. E. Graham  H. von Storch  J. -S. Xu  S. E. Zebiak 《Climate Dynamics》1994,9(4-5):167-179

A hierarchy of ENSO (El Niño/Southern Oscillation) prediction schemes has been developed which includes statistical schemes and physical models. The statistical models are, in general, based on advanced statistical techniques and can be classified into models which use either low-frequency variations in the atmosphere (sea level pressure or surface wind) or upper ocean heat content as predictors. The physical models consist of coupled ocean-atmosphere models of varying degrees of complexity, ranging from simplified coupled models of the shallow water-type to coupled general circulation models. All models, statistical and physical, perform considerably better than the persistence forecast on predicting typical indices of ENSO on lead times of 6 to 12 months. The most successful prediction schemes, the fully physical coupled ocean-atmosphere models, show significant prediction abilities at lead times exceeding one year period. We therefore conclude that ENSO is predictable at least one year in advance. However, all of this applies to gross indices of ENSO such as the Southern Oscillation Index. Despite the demonstrated predictability, little is known about the predictability of specific features known to be associated with ENSO (e.g. Indian Monsoon rainfall, Southern African drought, or even off-equatorial sea surface temperature). Nor has the relative importance for prediction of different regional anomalies or different physical processes yet been established. A seasonal dependence in predictability is well established, but the processes responsible for it are not fully understood.  相似文献   

Walker circulation controls ENSO atmospheric feedbacks in uncoupled and coupled climate model simulations     

Tobias Bayr  Dietmar Dommenget  Mojib Latif 《Climate Dynamics》2020,54(5):2831-2846

Many climate models strongly underestimate the two most important atmospheric feedbacks operating in El Niño/Southern Oscillation (ENSO), the positive (amplifying) zonal surface wind feedback and negative (damping) surface-heat flux feedback (hereafter ENSO atmospheric feedbacks, EAF). This hampers a realistic representation of ENSO dynamics in these models. Here we show that the atmospheric components of climate models participating in the 5th phase of the Coupled Model Intercomparison Project (CMIP5) when forced by observed sea surface temperatures (SST), already underestimate EAF on average by 23%, but less than their coupled counterparts (on average by 54%). There is a pronounced tendency of atmosphere models to simulate stronger EAF, when they exhibit a stronger mean deep convection and enhanced cloud cover over the western equatorial Pacific (WEP), indicative of a stronger rising branch of the Pacific Walker Circulation (PWC). Further, differences in the mean deep convection over the WEP between the coupled and uncoupled models explain a large part of the differences in EAF, with the deep convection in the coupled models strongly depending on the equatorial Pacific SST bias. Experiments with a single atmosphere model support the relation between the equatorial Pacific atmospheric mean state, the SST bias and the EAF. An implemented cold SST bias in the observed SST forcing weakens deep convection and reduces cloud cover in the rising branch of the PWC, causing weaker EAF. A warm SST bias has the opposite effect. Our results elucidate how biases in the mean state of the PWC and equatorial SST hamper a realistic simulation of the EAF.  相似文献   

Performance of irrigation projects and their impacts on poverty reduction and its empowerment in arid environment     

A. A. Irajpoor Ph.D.  M. Latif Ph.D. 《International Journal of Environmental Science and Technology》2011,8(3):533-544

Biophysical and socioeconomic conditions of pre and post dam construction were assessed in one of the arid regions of Iran commanded by Minab dam. The methodology used in this study was drawn from the international organizations especially the World Commission on Dams and the United Nations for selection of the indicators for sustainable development relating to water resources projects. Commissioning of the dam in 1986 led to progressive expansion of the irrigated agriculture, which was almost doubled in year 2006. Results of the study revealed that there is significant positive impact of the irrigation infrastructures of the dam; for example literacy rate has increased from 41 % (pre project) to 74 % in 2006. Similarly, significant improvements were observed in health care, sanitation, education and other scopes. Nevertheless, for some of the targets only 50–60 % progress were made, whereas no significant achievements had been made in the others. Therefore, development did not match with the planned goals of the project. Deficiency in achieving the primary objectives, especially after many years of project completion, may be attributed to the management and implementation of the project. For effective project performance, a new institutional framework and guide lines are proposed in this article.  相似文献   

A parametric Markov renewal model for predicting tropical cyclones in Bangladesh     

Md. Asaduzzaman  A. H. M. Mahbub Latif 《Natural Hazards》2014,73(2):597-612

In this paper, we consider a Markov renewal process (MRP) to model tropical cyclones occurred in Bangladesh during 1877–2009. The model takes into account both the occurrence history and some physical constraints to capture the main physical characteristics of the storm surge process. We assume that the sequence of cyclones constitutes a Markov chain, and sojourn times follow a Weibull distribution. The parameters of the Weibull MRP jointly with transition probabilities are estimated using the maximum likelihood method. The model shows a good fit with the real events, and probabilities of occurrence of different types of cyclones are calculated for various lengths of time interval using the model. Stationary probabilities and mean recurrence times are also calculated. A brief comparison with a Poisson model and a marked Poisson model has also been demonstrated.  相似文献   

Composition of selected heavy metals in road dust from Kuala Lumpur city centre   总被引：1，自引：1，他引：0  

Nur Mun’im Mohd Han  Mohd Talib Latif  Murnira Othman  Doreena Dominick  Noorlin Mohamad  Hafizan Juahir  Norhayati Mohd Tahir 《Environmental Earth Sciences》2014,72(3):849-859

This study was carried out in order to determine the concentration of heavy metals, e.g., lead (Pb), cadmium (Cd), copper (Cu), zinc (Zn), iron (Fe), manganese (Mn), nickel (Ni) and chromium (Cr) in road dust in Kuala Lumpur’s city centre. Samples were collected from four sampling locations, each of which had four sampling points and three replications. Heavy metals from different fractions of particles separated by different diameter sizes: d < 63 μm (Fraction A), 63 < d < 125 μm (Fraction B) and 125 < d < 250 μm (Fraction C) were analyzed using inductively coupled plasma mass spectrometry. The results from this study showed that concentration of heavy metals was dominated by the smallest particle size: <63 μm and that Fe was the most abundant heavy metal overall, followed by Cu > Mn > Zn > Pb > Ni > Cr > Cd. The fact that Cd had the highest enrichment factor value (EF) for all particle sizes indicates that anthropogenic activities contributed to the presence of this metal. There was also a higher EF value for heavy metals in small particle (Fraction A), compared to Fraction B and C, which suggests that fine particles were being produced through anthropogenic activities. Cluster analysis and principal component analysis demonstrated the likelihood of the heavy metals detected in the road dust, originating from road traffic and industrial activities.  相似文献   

Analysis of observed and simulated SST spectra in the midlatitudes     

D. Dommenget  M. Latif 《Climate Dynamics》2002,19(3-4):277-288

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PPMXL photometric analysis of three open cluster candidates     

Ashraf Latif Tadross 《New Astronomy》2012,17(2):198-202

We present here the astrophysical parameters of three stellar open cluster candidates using PPMXL (<http://vizer.cfa.harvard.edu/viz-bin/VizieR?-source=I/317>) database. In this study, the main photometric, astrometry and statistical parameters of Ruprecht 13, Ruprecht 16 and Ruprecht 24 are estimated for the first time.  相似文献   

Cyclone life cycle characteristics over the Northern Hemisphere in coupled GCMs   总被引：4，自引：1，他引：3  

Ulrike Löptien  Olga Zolina  Sergey Gulev  Mojib Latif  Vladimir Soloviov 《Climate Dynamics》2008,31(5):507-532

Cyclone activity and life cycle are analysed in the coupled GCMs ECHAM5/OM and ECHAM4/OPYC3. First, the results for the present climate (1978–1999) are compared with ERA-40 and NCEP/NCAR reanalyses, showing a drastic improvement in the representation of cyclone activity in ECHAM5/OM compared to ECHAM4/OPYC3. The total number of cyclones, cyclone intensity, propagation velocity and deepening rates are found to be much more realistic in ECHAM5/OM relative to ECHAM4/OPYC3. Then, changes in extra tropical cyclone characteristics are compared between present day climate and future climate under the emission-scenario A1B using ECHAM5/OM. This comparison is performed using the 20-year time slices 1978–1999, 2070–2090 and 2170–2190, which were considered to be representative for the various climate conditions. The total number of cyclones does not undergo significant changes in a warmer climate. However, regional changes in cyclone numbers and frequencies are evident. One example is the Mediterranean region where the number of cyclones in summer increases almost by factor 2. Some noticeable changes are also found in cyclone life cycle characteristics (deepening rate and propagation velocity). Cyclones in the future climate scenario tend to move slower and their deepening rate becomes stronger, while cyclone intensity does not undergo significant change in a warmer climate. Generally, our results do not support the hypothesis of enhanced storminess under future climate conditions.  相似文献   

Twentieth century Walker Circulation change: data analysis and model experiments   总被引：2，自引：1，他引：1  

Qingjia Meng  Mojib Latif  Wonsun Park  Noel S. Keenlyside  Vladimir A. Semenov  Thomas Martin 《Climate Dynamics》2012,38(9-10):1757-1773

Recent studies indicate a weakening of the Walker Circulation during the twentieth century. Here, we present evidence from an atmospheric general circulation model (AGCM) forced by the history of observed sea surface temperature (SST) that the Walker Circulation may have intensified rather than weakened. Observed Equatorial Indo-Pacific Sector SST since 1870 exhibited a zonally asymmetric evolution: While the eastern part of the Equatorial Pacific showed only a weak warming, or even cooling in one SST dataset, the western part and the Equatorial Indian Ocean exhibited a rather strong warming. This has resulted in an increase of the SST gradient between the Maritime Continent and the eastern part of the Equatorial Pacific, one driving force of the Walker Circulation. The ensemble experiments with the AGCM, with and without time-varying external forcing, suggest that the enhancement of the SST gradient drove an anomalous atmospheric circulation, with an enhancement of both Walker and Hadley Circulation. Anomalously strong precipitation is simulated over the Indian Ocean and anomalously weak precipitation over the western Pacific, with corresponding changes in the surface wind pattern. Some sensitivity to the forcing SST, however, is noticed. The analysis of twentieth century integrations with global climate models driven with observed radiative forcing obtained from the Coupled Model Intercomparison Project (CMIP) database support the link between the SST gradient and Walker Circulation strength. Furthermore, control integrations with the CMIP models indicate the existence of strong internal variability on centennial timescales. The results suggest that a radiatively forced signal in the Walker Circulation during the twentieth century may have been too weak to be detectable.  相似文献   

The role of ocean dynamics in producing decadal climate variability in the North Pacific     

D. W. Pierce  T. P. Barnett  N. Schneider  R. Saravanan  D. Dommenget  M. Latif 《Climate Dynamics》2001,18(1-2):51-70

 Decadal time scale climate variability in the North Pacific has implications for climate both locally and over North America. A crucial question is the degree to which this variability arises from coupled ocean/atmosphere interactions over the North Pacific that involve ocean dynamics, as opposed to either purely thermodynamic effects of the oceanic mixed layer integrating in situ the stochastic atmospheric forcing, or the teleconnected response to tropical variability. The part of the variability that is coming from local coupled ocean/atmosphere interactions involving ocean dynamics is potentially predictable by an ocean/atmosphere general circulation model (O/A GCM), and such predictions could (depending on the achievable lead time) have distinct societal benefits. This question is examined using the results of fully coupled O/A GCMs, as well as targeted numerical experiments with stand-alone ocean and atmosphere models individually. It is found that coupled ocean/atmosphere interactions that involve ocean dynamics are important to determining the strength and frequency of a decadal-time scale peak in the spectra of several oceanic variables in the Kuroshio extension region off Japan. Local stochastic atmospheric heat flux forcing, integrated by the oceanic mixed layer into a red spectrum, provides a noise background from which the signal must be extracted. Although teleconnected ENSO responses influence the North Pacific in the 2–7 years/cycle frequency band, it is shown that some decadal-time scale processes in the North Pacific proceed without ENSO. Likewise, although the effects of stochastic atmospheric forcing on ocean dynamics are discernible, a feedback path from the ocean to the atmosphere is suggested by the results. Received: 23 January 2000 / Accepted: 10 January 2001  相似文献