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Chandran A.,Masdar Institute of Science and Technology | Basha G.,Masdar Institute of Science and Technology | Ouarda T.B.M.J.,Masdar Institute of Science and Technology | Ouarda T.B.M.J.,National Institute of Scientific Research
International Journal of Climatology | Year: 2016

In this study, we investigate the influence of global climate oscillations on the local temperature and precipitation over the United Arab Emirates (UAE), which is one of the driest regions in the world with very high temperatures and low precipitation. The identification and assessment of remote interactions (teleconnections) are carried out by using ground station and gridded data sets. Monthly rainfall data from six ground stations over the UAE for the period of 1982-2010 is used in this study along with the long-term gridded precipitation and temperature data from the Global Precipitation Climatology Center and Global Historic Climatic Network. Linear correlations, wavelet analysis, and cross-wavelet analysis have been applied to identify the relation between climate indices and precipitation (temperature). The analysis reveals that the strong variability in precipitation is closely associated with the Southern Oscillation Index (SOI) and the Indian Ocean Dipole Index (IOD) during the months of August-March, September-January, respectively. In case of temperature, the strong variability is associated with the North Atlantic Oscillation Index (NAO) and the East Atlantic Oscillation Index (EAO) during the months of April-October, July-December. Spatial analysis of cross-wavelet reveals that the winter precipitation is significantly influenced by SOI and temperature during summer by the NAO. This research concludes that the negative phases of SOI (NAO) play a significant role in the increase of precipitation (decrease in summer temperatures) over the UAE region. © 2016 Royal Meteorological Society.

Niranjan Kumar K.,Masdar Institute of Science and Technology | Ouarda T.B.M.J.,Masdar Institute of Science and Technology | Ouarda T.B.M.J.,National Institute of Scientific Research | Sandeep S.,Abu Dhabi University | Ajayamohan R.S.,Abu Dhabi University
Climate Dynamics | Year: 2016

The climate variability on Earth is strongly influenced by the changes in the Sea Surface Temperature (SST) anomalies in the tropical oceans. More specifically, the inter-annual climate variability in the tropics as well as extra-tropical areas has large impact due to the anomalous SSTs in the tropical Pacific coupled with the El Niño Southern Oscillation (ENSO) through atmospheric teleconnections. However, the effect of ENSO on Middle Eastern region, specifically the Arabian Peninsula (AP) is marginally explored in previous studies. Hence, this study explicitly focuses on the assessment of ENSO variability and its winter climate teleconnections to the AP using the Community Atmospheric Model Version 4.0 (CAM4) simulations and Reanalysis datasets. ENSO teleconnections are also evaluated based on two sensitivity experiments (ENSO-related and ENSO-unrelated) using the CAM4 model. It is observed that during El Niño years the peninsular region receives more rainfall through enhanced moisture transport associated with anomalous westerly winds from adjoining Seas. The Rossby wave energy propagation in the atmosphere underlies important teleconnections involving ENSO. It is also noticed that there exist a distinct change in the phase of the Rossby wave pattern during El Niño and La Niña years which further causes the shift in the position of the jet stream over the Middle East. © 2016 Springer-Verlag Berlin Heidelberg

Esmaeilzadeh H.,University of Tehran | Arzi E.,University of Tehran | Mozafari M.,Niroo Research Institute | Hassani A.,National Institute of Scientific Research
Sensors and Actuators, A: Physical | Year: 2012

A broadband optical fiber based inline polarizer (OFIP) for telecom wavelength division multiplexing (WDM) systems is fabricated by coating of Al and Au layers on opposite sides of an etched multimode fiber. We demonstrated that the cladding residual thickness δ = 0 μm optimizes the OFIP design for the maximum extinction ratio (ER) of 17.1 dB/cm, at both telecom wavelengths of 1550 nm and 1310 nm. In addition to the broadband characteristics of this OFIP, the optimal ER value which is identical for both telecom regimes makes our OFIP even more desirable for WDM systems. Finally, our OFIP is very cheap and miniaturized which also makes it very attractive in commercialization point of view. © 2012 Elsevier B.V.

Charron C.,Masdar Institute of Science and Technology | Ouarda T.B.M.J.,Masdar Institute of Science and Technology | Ouarda T.B.M.J.,National Institute of Scientific Research
Journal of Hydrology | Year: 2015

Several studies have shown that improvements in the regional prediction of low-flow characteristics can be obtained through the inclusion of a parameter characterising catchment baseflow recession. Usually, a linear reservoir model is assumed to define recession characteristics used as predictors in regional models. We propose in this study to adopt instead a non-linear model. Predictors derived from the linear model and the non-linear model are used separately in low-flow regional models along with other predictors representing physiographical and meteorological characteristics. These models are applied to selected gaged catchments. Results show that better performances are obtained with the parameter from the non-linear model. One drawback of using recession parameters for regional estimation is that a streamflow record is required at the site of interest. However, recession parameters can be estimated with short streamflow records. In this study, to simulate the performances obtained at partially gaged catchments, the recession parameters are estimated with very short streamflow records at target sites. Results indicate that, with a streamflow record as short as one year, a model with a recession parameter from the non-linear model leads to better performances than a model with only physiographical and meteorological characteristics. © 2015 Elsevier B.V.

Ouarda T.B.M.J.,Masdar Institute of Science and Technology | Ouarda T.B.M.J.,National Institute of Scientific Research | Charron C.,Masdar Institute of Science and Technology | Niranjan Kumar K.,Masdar Institute of Science and Technology | And 4 more authors.
Journal of Hydrology | Year: 2014

•Rainfall series in the UAE are analyzed for detection of trends and change points.•The modified M-K test is applied for the assessment of the significance of trends.•The original results lead towards a general decreasing trend in precipitations.•Bayesian analysis reveals an increasing trend with a downward shift in 1999.•Results indicate a seasonality change with rain occurring earlier in the winter. Arid and semiarid climates occupy more than 1/4 of the land surface of our planet, and are characterized by a strongly intermittent hydrologic regime, posing a major threat to the development of these regions. Despite this fact, a limited number of studies have focused on the climatic dynamics of precipitation in desert environments, assuming the rainfall input - and their temporal trends - as marginal compared with the evaporative component. Rainfall series at four meteorological stations in the United Arab Emirates (UAE) were analyzed for assessment of trends and detection of change points. The considered variables were total annual, seasonal and monthly rainfall; annual, seasonal and monthly maximum rainfall; and the number of rainy days per year, season and month. For the assessment of the significance of trends, the modified Mann-Kendall test and Theil-Sen's test were applied. Results show that most annual series present decreasing trends, although not statistically significant at the 5% level. The analysis of monthly time series reveals strong decreasing trends mainly occurring in February and March. Many trends for these months are statistically significant at the 10% level and some trends are significant at the 5% level. These two months account for most of the total annual rainfall in the UAE. To investigate the presence of sudden changes in rainfall time-series, the cumulative sum method and a Bayesian multiple change point detection procedure were applied to annual rainfall series. Results indicate that a change point happened around 1999 at all stations. Analyses were performed to evaluate the evolution of characteristics before and after 1999. Student's t-test and Levene's test were applied to determine if a change in the mean and/or in the variance occurred at the change point. Results show that a decreasing shift in the mean has occurred in the total annual rainfall and the number of rainy days at all four stations, and that the variance has decreased for the total annual rainfall at two stations. Frequency analysis was also performed on data before and after the change point. Results show that rainfall quantile values are significantly lower after 1999. The change point around the year 1999 is linked to various global climate indices. It is observed that the change of phase of the Southern Oscillation Index (SOI) has strong impact over the UAE precipitation. A brief discussion is presented on dynamical basis, the teleconnections connecting the SOI and the change in precipitation regime in the UAE around the year 1999. © 2014.

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