JOURNAL OF CLIMATE RESEARCH
Year:2012 | Volume:3 | Issue:9|Papers Count:8

Introduction: Main regions of citrus plantation are between 40 degrees northern and southern geographical latitudes. A considerable part of these regions are located at Mediterranean sub tropic (WMO, 1997). Citrus plantation has grown into a global industry for the last 70 years. Producing oil and citric acid is another reason for citrus plantation besides fresh fruit production. Temperature is the most important climatic element in citrus plantation. On the one hand, frosts to threaten yield and on the other hand, high Temperatures through extreme transpiration, make the fruit formation difficult. Optimum means daily temperature for citrus growth is from 23 to 30 degrees Celsius and growth is considerably reduced if the temperature is organization, 2004). Another effective process in the occurrence of heat waves at the southern strip is the air subsidence at a synoptically scale. Regarding the above mentioned studies, the most significant climatic restrictions that affect the yield quantity and quality in southern provinces are high temperature and air dryness.

Introduction: Climatic elements create the climate of a region Air felt temperature differs in different climates. For example, the temperature may be 20o Celsius in a clear day without clouds in March, in a sense of coolness to the temperature region, while the same temperature in summer and in other regional temperatures is considered a cold and uncomfortable. Severe wind blows at below zero temperatures can quickly withdraw heat from the body, to the extent that it may cause freezing of the skin. Wind Chill Temperature index (WCT) is very important and it can be used as a general guideline for deciding clothing requirements in cold weather conditions. North Khorasan Province, is considered as one of the country's Agriculture and Tourism poles But, this region has consistently experienced severe cold weather over the years. Recent studies show that extremely cold weather has sometimes disrupted the lives of the people living in this region. Due to the region's natural resources, mining, tourism, and increasing population, it seems necessary to implement a project the on better utilization in this. This plan will succeed if the mechanism and the role of the major climate systems affecting the climate of this region are correctly identified. Therefore, this study aims to identify major synoptic patterns which create severe cold weather of North Khorasan Province and its arrival to the area, to identify and predict these patterns, and to be alert enough to prevent and reduce the potential damages.

Introduction: Precipitation has always been under investigation as the most important climatic element from both temporal and spatial perspectives. One of the methods that contribute to the review of the course of precipitation in the past and present is the 'time series trend analysis'. So far, numerous statistical methods have been provided for the time series trend analysis, which can be categorized into two parametric and nonparametric methods. The nonparametric methods are based on the differences between observation data; these methods are independent from statistical distribution and are more appropriate for the series with more skewness and kurtosis. Therefore, the objective of this study is to investigate the precipitation time series trend over Iran in seasonal and annual scales using the Sen’s slope estimator nonparametric method.

Introduction: Drought is one of the most harmful environmental phenomena which has a devastating impact on agriculture, environment, economy and society. Drought happens during a period of water deficit in a region due to low precipitation, high evapotranspiration, high groundwater derivation or a mixture of the mentioned factors.Observations from space, especially from the NOAA polar-orbiting satellites, provide a synoptic view, permanent data archive, extra visual information, cost effectiveness, and a regular, repetitive view of nearly all of the earth’s surfaces (Johnson et al. 1993). Hence, remotely sensed data from NOAA’s AVHRR has been commonly used for national to global-scale drought monitoring activities since the 1980s and application of satellite based drought indices of vegetation health (TCI, VCI, VHI ) in drought identifying, analyzing, evaluating and monitoring has been studied world widely (Kogan 1997, Vogt et al. 1998, Seiler et al. 2000, Singh et al. 2003, Kogan et al. 2004, Bhuiyan 2008, Rahimzadeh Bajgiran et al. 2008).

Introduction: The northern branch of the Hadley cell forms the anticyclone centers over the subtropical regions around the world. One of these centers is the Middle East anticyclone that plays a main role in the weather of the region. This center has an annual spatial oscillation in the north-south direction. In summertime, it goes to the high latitudes and makes the weather of the Middle East very dry and hot and in winter; it comes back to the lower latitudes and lets the mid-latitude cyclones go across the northern Middle East and Iran. The main winter precipitation of Iran is closely related to these cyclones.Occurrence of any anomaly in the natural spatial variability changes the meteorological regimes over the region. Since ENSO is one of the global oscillations that can affect the weather in some parts of the world, this study aims to examine the likely effect of ENSO on the oscillation mentioned above.

Introduction: The El Nino and La Nina each favor a different location for the dips and bulges of the polar jet stream. They also affect the strength of the subtropical jet stream. In this way, they influence the weather in middle latitudes. The influence is greatest in the winter months when the coupling of the tropical and mid-latitude patterns is the best. In most El Nino winters, the warming of the air due to strong convection over warm water over the eastern and central Tropical Pacific helps energies the polar and subtropical jet streams to the north. A strong low pressure develops over the Aleutians. The polar jet stream curves to the north into northwestern North America, while the subtropical jet stream ripples across northern Mexico or the southern United States. During La Nina winters, on the other hand, the polar jet stream is strong and the subtropical jet stream weaker in the vicinity of North America (D’Aleo & Grube, 2002).The effect of ENSO on precipitation and temperature has been studied in detail by a number of Iranian researchers (Khosh Akhlagh, 1998; Azizi, 2000; Ghayor and Asakereh, 2001; Nazem al-Sadat and Ghassemi, 2003; Masoudian 2005, Khorshid Doost and Ghavidel Rahimi, 2006; Yar Ahmadi and Azizi 2007; Hagh Negahdar et al.; 2007). Most of these researches have attributed the increase and decrease of autumn rainfall to El Nino and La Nina respectively. Although it seems that seasonal distribution of rainfall during different ENSO phases does not follow any particular pattern, different patterns can be seen in each of the two compared phases. Givi et al (2009) indicated the positive and negative anomalies of precipitation in each El Nino and La Nina year. Not enough studies have been done on different phases of ENSO that affect the climate of Iran. This study aims to provide a more comprehensive analysis of changes in the 200Hpa jet stream in relation to various ENSO phases (for September, October, November and December).

Introduction: The Increase in greenhouse gases in recent decades has caused an increasing in the earth's temperature. As recent scenarios of the state board of climate change have predicted global average temperature increase to 0.76 ° C in the last century x up to 6.4°C until 2100 are expected (IPCC, 2001) This phenomenon is called "climate change". Climate change can be very effective on water resources system. In this sense, climate change is considered as one of the major challenges human beings face in future decades.In this study, using the atmospheric general circulation model (GCM) (General Circulation Model) under the scenario of greenhouse gases (SRES), changes in rainfall and temperature in the period 2010-2039 for stations of Ahvaz, Dezful and Khorramabad as selected stations of great Karun basin are simulated. The required data including average monthly temperature and total rainfall in mentioned time period are obtained from two models of HadCM3 & CSIRO and models of Atmospheric general circulation model scenario of a A2 & B1 and can be used from proportional method of basic and future periods. The results suggest an increase in temperature and a decrease in precipitation in the mentioned time period (2010-2039).