Climatology
Mohsen Armesh; Mahmood khosravi; Mohammad Saligheh
Volume 22, Issue 65 , November 2018, , Pages 45-62
Abstract
This study aimed to evaluate the variability of summer precipitation in the South East of Iran was selected stations and the precipitation associated was investigated with IOD index. For this purpose was used weekly precipitation data from June to September stations of Zahedan, Kerman, Bandar Abbas, ...
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This study aimed to evaluate the variability of summer precipitation in the South East of Iran was selected stations and the precipitation associated was investigated with IOD index. For this purpose was used weekly precipitation data from June to September stations of Zahedan, Kerman, Bandar Abbas, Iranshahr and Bam and weekly IOD index data. The method of this study is the correlation coefficient and discrete wavelet analysis. The results showed that in the positive phase of the IOD Index, warm air and humid of West Africa, sucked by low pressure the Persian Gulf and Pakistan and conditions creates convection in southeast of Iran, while IOD negative phase, in addition to shiftting the intertropical Convergence Zone, low pressure Persian Gulf and Pakistan are gone and West Indian Ocean for cooling than normal, stable atmosphere reigns. Summer precipitation correlation analysis between Bandar Abbas and Iranshahr with IOD index showed the strongest association. After the precipitation signal analysis of the stations showed of the Zahedan station on Level 4 and 3, respectively, at 99 and 95% was related to IOD index. The following series Kerman and Bam precipitation did not show any relationship with IOD index. Data analysis by the discrete wavelet transform showed that the most important cycle repeating 11-year occurred in the IOD index. Zahedan and Iranshahr showed periodic cycles relatively similarly. In Kerman was appeared 7-year cycle dominant and in Bandar Abbas and Bam the 11-year cycle. The process of reducing the number of weeks along with summer precipitation in the form of stations is contrary to the IOD index. But the increased intensity of precipitation stations is directly related to this index. Also Bandar Abbas, Iranshahr and Zahedan have more balanced precipitation cycles, but summer precipitation anomalies are intense in Kerman and Bam.
Climatology
Mohamad Saligeh; mohammadhosain naserzadeh; ali ghaffari
Volume 22, Issue 64 , September 2018, , Pages 129-147
Abstract
The mechanisms of climbing rainfall in different areas follow different patterns. Identification of those patterns can increase the environmental planning .The stability indicators which are known as instability indicators are relations through which we can study the amount of instability ...
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The mechanisms of climbing rainfall in different areas follow different patterns. Identification of those patterns can increase the environmental planning .The stability indicators which are known as instability indicators are relations through which we can study the amount of instability of convection of the atmosphere in any area for studying and predicting falls. These indicators are used for convection activities and basically are studied by thermodynamics diagrams and Radio sounds data. The main aim of this paper is studying the chronological features of precipitations over 5 mm .and determining convection precipitation parts of Tabriz spring station based on higher layers of atmosphere . the Tabriz station precipitation data were received from the weather organization cartulary regarding the 35 – year statistic periods and precipitation data for over 5 mm .were chosen while the time frequency was studied . After choosing the samples, the skew – T diagrams of precipitation days inadittion to the instability indicators such as (LI -TT – SI – KI – PW - CAPE)were analyzed . The processing of these data in seasonal scale indicate a frequent happening of those instabilities. The maximum occur once of the precipitations for the April with 131 frequency cases and minimum of this precipitator is in June with 35 cases were observed .The results of drawing skew – t diagrams and measuring the instability indicators show that the role of convection factor is important in spring precipitations because the convection factor is only the main factor not only the amount of convection is critical but also the needed instability for rain is provided. In general, after studying 263 rain samples in spring , it turned out that the convection factor has the most important role in rain occurrence in May and June and the hazards of flood threaten the area .
Mahmood Khosravi; Mohammad Salighe; Behrooz Sabaghi
Volume 16, Issue 37 , November 2011, , Pages 59-81
Abstract
The sea surface temperature (SST) variations play a very important role in the creation and maintenance of climatological and oceanographic processes such as heavy precipitation and subsequent floods, large-scale sea level fluctuations and tropical cyclones.
In this paper the effects of Oman sea surface ...
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The sea surface temperature (SST) variations play a very important role in the creation and maintenance of climatological and oceanographic processes such as heavy precipitation and subsequent floods, large-scale sea level fluctuations and tropical cyclones.
In this paper the effects of Oman sea surface temperature (SST) on the autumn and winter precipitation of its northern coast, were investigated.
The SST data was obtained from NCEP archives based on 4 points averaging nodes in Oman sea surface using GRADS software. Also the climatic data of 3 stations of Iranian coast (Chahbehar, Jask and Bandar Abas) were used.
The warm (Rw), cold (Rc) and normal (Rb) periods of Oman SST were explained and the median of precipitations in each periods is calculated. The Rw\Rb, Rc\Rb and Rc\Rw ratios were used for evaluating the effects of these conditions on the precipitations anomalies on the coast.
The results shown that the spring warm (cold) SST conditions in Oman sea can decrease (increase) precipitation in the selected stations of regions. Also the winter and autumn precipitation on northern coasts is remarkable, being synchronous to positive anomalies of summer SST.
For considering the mechanism of the effect of Oman sea surface temperature on coastal precipitation, the stream lines, relative humidity and Omega maps were prepared and used. The results showed that the SST effects on stream lines and relative humidity on sea surface are the major mechanisms of precipitation anomalies. Generally during higher precipitation periods, the streamlines over the sea are navigate a longer route and therefore the moisture contents of rainfall systems and ascending currents are suitable for precipitation.
