The impact of el Nino‐Southern oscillation on the temperature field over Canada: Research note     

Amir Shabbar  Madhav Khandekar 《大气与海洋》2013,51(2):401-416

Abstract

The impact of the two phases of El Niño‐Southern Oscillation (ENSO), namely El Niño and La Niña, on the surface and lower tropospheric temperature fields over Canada is documented. Gridded surface temperature data for 91 years (1900–1990) and 500–1000 hPa thickness data for 49 years (1946–1994) have been analyzed statistically in the context of El Niño, La Niña and normal years.

Using a composite analysis, the present study conclusively demonstrates that significant positive surface temperature anomalies spread eastward from the west coast of Canada to the Labrador coast from the late fall to early spring (November through May) following the onset of El Niño episodes. The accompanying temperatures in the lower troposphere show a transition from the Pacific/North American (PNA) pattern to the Tropical/Northern Hemisphere (TNH) pattern over the North American sector during the same period. Conversely, significant negative surface temperature anomalies spread southeastward from the Yukon and extend into the upper Great Lakes region by the winter season following the onset of La Niña episodes. Furthermore, the lower tropospheric temperatures show a negatively‐phased PNA‐like pattern in early winter which weakens considerably by May of the following year. Thus, while western Canadian surface temperatures are influenced during both phases of ENSO, eastern Canadian surface temperature effects are found during the El Niño phase only. The impact of ENSO on the Canadian surface temperatures is the strongest during the winter season and nearly disappears by spring (April and May). The largest positive (negative) anomalies are found to be centred over two separate regions, one over the Yukon and the other just west of Hudson Bay in the El Niño (La Niña) years. Over western Canada, mean wintertime temperature distribution of the El Niño (La Niña) years is found to be shifted towards warmer (colder) values relative to the distribution of the normal years.

This study suggests the possibility of developing a long‐range forecasting technique for Canada using ENSO related indices.  相似文献   

An investigation of near surface wind speed trends in arid and semiarid regions of Iran   总被引：1，自引：0，他引：1  

Mohammad Reza Kousari  Hossein Ahani  Hemila Hakimelahi 《Theoretical and Applied Climatology》2013,114(1-2):153-168

Wind plays an important role on the ecosystems and hydrological cycles besides other meteorological parameters such as temperature, precipitation, sunshine, and relative humidity. It strongly affects evapotranspiration, especially in arid and semiarid regions where there are serious problems in regard to water resource management. Evaluating the wind speed trend can provide good information for future agricultural planning. This study was conducted in order to investigate the wind speed trends over 24 synoptic meteorological stations located in arid and semiarid regions of Iran from 1975 to 2005. Near-surface wind speed was trended by nonparametric Mann–Kendall test spatially and temporally in three time scales (annual, seasonal, and monthly). Then, Sen’s slope estimator was used to determine the amount of the changes; furthermore, 10-year moving average low-pass filter was applied to show general trends. Finally, the smoothed time series derived from the mentioned filter were classified in three clusters for each time series and then mapped to show their spatial distribution pattern. Results showed insignificant and significant, increasing and decreasing trends during the surveyed time. Wind speeds in less than 50 % of stations changed statistically in all time scales, and in most cases, the frequency of the upward trends was more than that of downward ones. The spatial distribution of significant wind speed showed that the increase mostly occurred in eastern part. Clustering gave us the turning point around 1990. Clearly, when clusters were mapped, they indicated the same pattern as the Z value maps derived from Mann–Kendall test which meant that the outputs of the mentioned method confirmed the other one. As the wind speed trends in different stations likely to follow the previous evapotranspiration (ET₀) trend results in Iran, it confirms that wind speed was an effective parameter on ET₀, even though other parameters should be considered too.  相似文献   

Substructure and the cusp and fold relations     

Amir Babak Aazami  Priyamvada Natarajan 《Monthly notices of the Royal Astronomical Society》2006,372(4):1692-1698

Gravitational lensing of a background source by a foreground galaxy lens occasionally produces four images of the source. The cusp and the fold relations impose conditions on the ratios of magnifications of these four-image lenses. In this theoretical investigation, we explore the sensitivity of these relations to the presence of substructure in the lens. Starting with a smooth lens potential, we add varying amounts of substructure, while keeping the source position fixed, and find that the fold relation is a more robust indicator of substructure than the cusp relation for the images. This robustness is independent of the detailed spatial distribution of the substructure, as well as of the ellipticity of the lensing potential and the presence of external shear.  相似文献   

An investigation of trends in precipitation volume for the last three decades in different regions of Fars province, Iran   总被引：1，自引：1，他引：0  

Hossein Ahani  Mehrzad Kherad  Mohammad Reza Kousari  Mehdi Rezaeian-Zadeh  Mohammad Amin Karampour  Faezeh Ejraee  Saeedeh Kamali 《Theoretical and Applied Climatology》2012,109(3-4):361-382

Under condition of climate changes as global warming, monitoring and detecting trend of precipitation volume is essential and will be useful for agricultural sections. Considering the fact that there were not enough research related to precipitation volume, this study aimed to determine trends in precipitation volume, monthly and annually in different regions of Fars province for the last three decades (33?years period; 1978–2010). Fars province is located in arid and semi-arid regions of Iran, and it plays an important role in agricultural production. Inverse distance weighting interpolation method was used to provide precipitation data for all regions. To analyze the trends of precipitation volume, Mann–Kendall test, Sen’s slope estimator, and 10-year moving average low-pass filter (within time series) were used. The negative trends were identified by the Sen’s slope estimator as well as Mann–Kendall test. However, all the trends were insignificant at the surveyed confidence level (95%). With regards to the application of 10-year moving average low-pass filter, a considerable decreasing trend was observed after around year 1994. Since one of the most important restrictions in agricultural development of the Fars province is lack of sufficient water resources, any changes onward to lack of sufficient precipitation impose impressive pressure and stress on valuable resources and subsequently agricultural production.  相似文献   

Observed changes in relative humidity and dew point temperature in coastal regions of Iran   总被引：2，自引：0，他引：2  

P. Hosseinzadeh Talaee  A. A. Sabziparvar  Hossein Tabari 《Theoretical and Applied Climatology》2012,110(3):385-393

The analysis of trends in hydroclimatic parameters and assessment of their statistical significance have recently received a great concern to clarify whether or not there is an obvious climate change. In the current study, parametric linear regression and nonparametric Mann?CKendall tests were applied for detecting annual and seasonal trends in the relative humidity (RH) and dew point temperature (T _dew) time series at ten coastal weather stations in Iran during 1966?C2005. The serial structure of the data was considered, and the significant serial correlations were eliminated using the trend-free pre-whitening method. The results showed that annual RH increased by 1.03 and 0.28?%/decade at the northern and southern coastal regions of the country, respectively, while annual T _dew increased by 0.29 and 0.15°C per decade at the northern and southern regions, respectively. The significant trends were frequent in the T _dew series, but they were observed only at 2 out of the 50 RH series. The results showed that the difference between the results of the parametric and nonparametric tests was small, although the parametric test detected larger significant trends in the RH and T _dew time series. Furthermore, the differences between the results of the trend tests were not related to the normality of the statistical distribution.  相似文献   

Application of integrated geoelectrical methods in Khenadarreh (Arak,Iran) graphite deposit exploration     

Hamidreza Ramazi  Mohammad Reza Hossein Nejad  Aenollah Azizzadeh Firoozi 《Journal of the Geological Society of India》2009,74(2):260-266

This paper is devoted to application of SP, resistivity and mise-a-la-masse method in Khenadarreh (Arak, Iran) graphite deposit exploration. Mise-a-la-masse method is one of the main geophysical exploration methods used to investigate conductive bodies with outcrops on the surface or in exploratory pits. By integrating mise-a-la-masse results with other geoelectrical methods, such as self-potential and resistivity surveys, useful results can be acquired. Powerful survey design, data processing and interpretation methods can make geoelectrical surveying results more reliable. Here, we applied integrated geoelectrical methods to explore the Khenadarreh-bala graphite deposit in the Sarband region of the Markazi province, Iran. We present a new and simple method for processing and interpreting mise-a-la-masse data, which corrects for the effect of distance from the current electrode in the conductive body. After correction, the residual potential values corresponded with the SP results and the apparent resistivity pseudosections. The geophysical results were confirmed by drill holes in the study area.  相似文献   

Biostratigraphy and Sequence Stratigraphy of the Tarbur Formation (Maastrichtian) from Iranian Zagros Foreland Basin, Southwest of Iran     

Hossein GHANBARLOO  Amrollah SAFARI  Hossein VAZIRI-MOGHADDAM 《《地质学报》英文版》2022,96(1):147-166

Shallow carbonate deposits(Tarbur Formation)were formed in the Zagros foreland basin with dynamic tectonics during the Maastrichtian age.From the viewpoint of reconstruction of depositional conditions in these deposits,studies of biostratigraphy,microfacies,microtaphofacies,and sequence stratigraphy were performed in a single area at Tang-e Shabi Khoon,northwest of Zagros.Based on the identification of two assemblage zones consisting of benthic foraminifera in these strata,the formation was deposited during the middle to late Maastrichtian.The number of cycles in test size and type of coiling in Loftusia decreased from the study area toward the northwest of the Neotethys basin.The input of clastic sediments affected the distribution of Loftusia and rudists in the study area.Nine microfacies,six microtaphofacies,and one terrigenous facies(shale)were identified based on the sedimentary features.These deposits of the middle-late Maastrichtian were deposited on a homoclinal carbonate ramp.The platform can be divided into restricted and semi-restricted lagoon,shoal,and open marine environments.In the study area,the deposits of the Tarbur Formation were deposited during four third-order depositional sequences.Local fault activities affected the formation of depositional sequences in the study area.  相似文献   

‘Corrigendum to “Uniform and graded bed-load sediment transport in a degrading channel with non-equilibrium conditions” [International Journal of Sediment Research 35 (2020) 115–124/04-258]’     

Khabat Khosravi  Amir H.N. Chegini  James R. Cooper  Prasad Daggupati  Andrew Binns  Luca Mao 《国际泥沙研究》2021,36(1):163

  相似文献   

Numerical Modeling of Tropical Cyclone-Induced Storm Surge in the Gulf of Oman Using a Storm Surge–Wave–Tide Coupled Model     

Siahsarani  Amir  Karami Khaniki  Ali  Aliakbari Bidokhti  Abbas-Ali  Azadi  Majid 《Ocean Science Journal》2021,56(3):225-240

Ocean Science Journal - A storm surge is a complex phenomenon in which current, tide, and waves interact with each other. Even if the wind is the main force of driving the surge, waves and tide are...  相似文献   

Modeling and assessing the effects of land use changes on runoff generation with the CLUE-s and WetSpa models     

Mohammady  Majid  Moradi  Hamid Reza  Zeinivand  Hossein  Temme  A.J.A.M.  Yazdani  Mohammad Reza  Pourghasemi  Hamid Reza 《Theoretical and Applied Climatology》2018,133(1-2):459-471

Theoretical and Applied Climatology - Land use change is an important determinant of hydrological processes and is known to affect hydrological parameters such as runoff volume, flood frequency,...  相似文献