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Volume 1, Issue 2 (7-2014)
Hot, humid weather causes to the sultry feel. Sultry condition is usually accompanied with loss of physical ability and human respiratory and it has an adverse effect on peoples who have circulatory or other heart problems and this feeling is more than others. Sultry feel is a feeling like any other sensitive reflections of mental state. And this state apparently can’t be measured by special instruments. With this description, there are a lot of efforts has been done to identify this phenomenon by meteorologists and climatologists. And a series of psychological climate tests show that we can examine the creation and incidence of this sense based on empirical studies as a scientific and objective attitude. Therefore, this study aims to classify the sultry days in the southern half of Iran based on sultry continuous hours. And the obtained results are presented as a form of zoning maps.
The studied zone in this research is selected stations in the southern half of the country located in the province of Sistan & Baluchestan, Kerman, Hormozgan, Fars, Bushehr and Khuzestan. This area is located between two latitude 25 and 35 north and length of 47 to 63 east degrees. To achieve this goal, hourly partial pressure of water vapor of 13 selected stations were obtained for a period of 15 years (1995-2009) from Meteorological agency. After obtaining data and creating the database, to separate sultry conditions from non-sultry conditions, threshold of partial pressure of water vapor of Scharlou which was equivalent to 8.18 Hpa were used.
Based on these data, the hours and days that the partial pressure of water vapor was equal or greater than 8.18 hpa will have sultry conditions and otherwise, they have non-sultry conditions. Then, based on this threshold, sultry days were divided into eight categories. The basis of this classification is that if in a particular day among eight branches of observation, one station, only in one observation record a pressure equal to or greater than 8.18 hpa was observed, it will be placed in first class and if only two observed records a value equal or greater than defined value, it will be placed in second catagory and finally, if all eight observations amounts equal to or greater than 8.18 had been recorded, it will be placed in eight class. After placing the sultry days in one of eight branches of classes, long-term averages of monthly, quarterly, quarterly and annual were calculated and mapped.
Based on defined thresholds, sultry days were separated from non-sultry days, then sultry days were extracted and it was placed in first to eighth classes. The results of this classification showed that on monthly scale, January has the fewest sultry days in twelve months of the year. In this month, only two stations of Chabahar and Bandar Abbas had the sultry days of eighth classes. It means that 24 hours, they were in sultry conditions. Other stations that have a sultry day in this month, often their sultry days are from first to fourth classes and it means that they had maximum 3 to 12 hours of sultry conditions during the day. Most sultry days can be seen in two June and July months. So, in these two months, all studied stations have at least one sultry day,Specially in three stations of Chabahar, Bandar Abbas and Bushehr. And all 61 days, they have sultry conditions. In terms of classification of sultry days, all 61 days of Chabarhar station are part of sultry days of eighth class. In two stations of Bandar Abbas and Bushehr, except few days that are from sixth and seventh classes, other days are from eightth class, other stations experienced one of the eightth classes of sultry days with different ratios. , and at the seasonal scale, winter has the lowest days of sultry and summer has the most days of sultry days. In term of classification of sultry days in seasonal scale, there are conditions as monthly scale. The interesting point in summer season is that sultry days on two stations of Zabul (35 days) and Iranshahr (51 days) are considered due to their Geographical locations. In Zabul station, the reason of these sultry days can be due to the neighborhood of this station with Hamoon Lake. But it should be mentioned about Iranshahr stationthat the reason of its sultry condition is entrance of monsoon low pressure and moisture transfer by the system on the south-east of Iran an especially Iranshahr. On an annual basis, it was also observed that always in south east of Iran (Especially Chabahar station), the number of sultry days is much more than south west of Iran, also occurring sultry days with eighth, seventh and sixth classes in this zone is so different from south-west of Iran. The reason of these differences in number of sultry days and sultry classes related to the latitude of south east of Iran which is lower that south west and in other words, we can say that climate of south East of Iran is more similar to tropical climate than subtropical climate.
Volume 6, Issue 2 (9-2019)
The application of Extreme value analysis method in heat wave hazard climatology; case study in Mid-Southern Iran
Abstract
Greenhouse warming poses the main cause of atmospheric hazards’ exacerbation and emergence in recent years. Earth planet has been witnessing frequent and severe natural hazards from the distant past; however, global warming has strongly influenced the occurrence of some atmospheric hazards, especially the ones induced by temperature and has increased the frequency and severity of those risks. Such extreme risks arising from temperature element and being affected by global warming could be referred to hot days and their frequency more than one day which undergo heat waves. Of the studies conducted worldwide in conjunction with the phenomenon of heat waves, the following can be pointed out; Schär (2015) has focused his studies on the Persian Gulf and the worst heat waves expected in this area. The recent work revealed an upper limit of stability which enables the adaptability of human body with heat stress and humidity. If people are exposed to a combination of temperature and humidity over long periods higher than this level, they will lead to hyperthermia and death, because heat dissipation from the body is physically impossible. Paul and al-Tahrir (2015) using a high-resolution regional climate model demonstrated that such a situation can occur much earlier. In Iran, in relation to heat waves, Ghavidel (2013) analyzed climatic risk of Khuzestan province in 2000 regarding super heat waves using the clustering approach. The obtained results unveiled the establishment of a low pressure at ground level and high pressure dominance at mid-altitudes up to 500 hp as well as the increase in atmosphere thickness having led to the ground overheating. Added to that, the source of heat entering into Khuzestan is advective and hot and dry air transport through Arabian Peninsula, Iraq and Africa. Ghavidel and Rezai (2014) addressed in a study to determine the temperature-related threshold and analyze the synoptic patterns of super heat temperatures in southeast region of Iran; the results of study approved that the only pattern effective on the occurrence of super heat days in Iran’s southeast is the establishment of the Grange’s heat low-pressure at ground level and subtropical Azores high elevation dominance at 500 hPa level. In this study, absolute statistical indicators, also recognized as above-threshold values approach, were used in order to identify, classify and heat waves synoptic analysis in the warm period of the year in the southern half of Iran. To use above-mentioned indicators, firstly daily maximum temperature statistics of studied stations with the highest periods were averaged every day once in June to September and once for the months of July and September. Using statistical indicators of long-term mean and standard deviation or base period, indicators would be defined for the classification of heat waves and days with peak extreme temperatures. In such classifications, usually long-term average or base period is multiplied by 1 to 3 to 4 times standard deviation and each time is account for the factor of each class.
To select the days for synoptic analysis, averaging was performed of all classified waves into four heat wave categories of low, intermediate, strong and super heat; accordingly based on the maximum blocks in each class of heat waves, days that had the highest temperature values were selected as the class representative for mapping and synoptic analysis.
This study dealt with investigating heat waves synoptic during the year’s warm period in the southern half of Iran. Studies showed that a variety of synoptic systems in the year’s warm period affect the study area. As well as, synoptic analyses concluded that in the southern half of Iran over the year’s warm period when occurring heat waves, low-pressure status dominates the ground level (caused by Gang’s low-pressure and local radiant mode); thus high-pressure status with closed curves is prevailing in atmosphere’s upper levels that gives rise to the divergence, air fall and Earth's surface heating. Studying the status of the atmosphere thickness in the days with the heat wave in the study area indicates its high altitude and thickness that this itself implies the existence of very hot air and susceptibility of the conditions for the occurrence of heat waves. In addition, wind maps at atmosphere’s different levels well illustrate the wind of very warm and hot air masses from the surrounding areas to the southern part of Iran; therefore it can be noted that aforementioned hot air masses mainly wind from places like different regions of the Arabian Peninsula, Iraq, North Africa and the low latitudes to the study area.
Keywords: Synoptic analysis, heat waves, maximum blocks, southern half of Iran.
Volume 7, Issue 1 (5-2020)
Farshad Pazhoh[1], PhD in Synoptic Climatology, Department of Natural Geography, Faculty of Geographical Sciences, University Kharazmi, Tehran, Iran
Every year, important parts of a large part of our country are affected by the climatic hazards of heavy precipitation and lots of damages are done to the country. If the generating circulation patterns of heavy precipitation waves will identify, its occurrence can be predicted from at least one or two days before the beginning of the sequence of patterns ending in floods (Alijani, 2006, 156). Occurrence of heavy precipitation, so that its amount is more than the soil penetration capacity, causes runoff and floods. Now, if these heavy precipitations occur in urban areas, it is associated with more dangers, because the permeability in urban areas is less than in out-of-town areas, and a significant amount of such precipitation in urban areas has turned into runoff and floods. Cause damages to places, buildings and urban facilities (Taheri Behbahani and Bozorgzadeh, 1996, 2).
Two sets of data were used to conduct this research. One is surface data and the other is high atmospheric data. For this purpose, in the first category, the related precipitation data of the cold season of 8 synoptic stations in the southern half of Iran (Table 2) in the period from December 1, 1970 to March 31, 2014 were obtained from the Meteorological Organization. To identify the occurrence of heavy precipitation leading to major floods in the study area, considering that heavy precipitation has covered more than 50% of stations and the precipitation of each station is more than 95% during the study period.
Considering the above two conditions, 61 heavy and pervasive precipitations were selected from the total precipitations above the percentile of 95% of the stations. In the second category, high atmospheric data obtained from the National Oceanic and Atmospheric Administration of the United States. The synoptic scale in order to tracking the troposphere synoptic patterns includes a longitude of 20 west degrees to 100 east degrees and a latitude of 0 to 80 north degrees. In the selected synoptic scale, 1790 cells are located; the distance between each cell is 2.5 by 2.5 arc degrees.
In order to identify the jet stream patterns, first the factor analysis method with Varimax rotation was applied on the geo potential height data of 500 hPa during the selected 61 days of heavy and pervasive precipitations and found that the first 12 factors explain more than 90% data’s diffraction. The first factor accounts for about 32% of geo potential height data diffraction (Table 4). In the next step, in order to reduce the data volume and identify the synoptic patterns, the cluster analysis method was performed on the scores of the first 12 factors by the integration method and 4 synoptic patterns affecting the arrangement of the winds were extracted. Then, for each of the identified patterns, a representative day that had the highest correlation with the desired pattern determined (Table 3) and appropriate maps for the representative days of the patterns were drawn and analysed.
The results showed that the merged jet stream patterns (subtropical-sub polar), tropical jet stream (ridge-trough), orbital subtropical jet stream and meridian subtropical jet stream were effective in the occurrence of heavy precipitation, which meridian subtropical jet patterns and merged have played the most important role. In the first pattern, the merged jet stream plays role in 16 days and 26.3% of the precipitation days. The merged jet streams core is generally located on the Red Sea, and the subtropical jet stream penetrates from North Africa, and after crossing the Red Sea and northern Saudi Arabia, the left half of the jet stream’s exit covers the whole of the southern and central half of the country. The sub polar jet stream in a northwest-southeast direction from central and the west of the Europe from the centre and west of Europe penetrate to the lower latitudes and from central and eastern part of the Mediterranean and at the entrance part of the left side merge with subtropical jet stream. In the merger pattern, the sub polar jet stream corresponding to the western half of the trough of the middle-level of troposphere plays the role of cold air Advection and transferring the western winds to the lower latitudes, and the subtropical jet stream, corresponds to the eastern half of the trough, play the role of the discharge and divergence of warm and southern humid air on the southern half of the country’s atmosphere. In the second pattern, the subtropical jet stream (ridge-trough structure) with 13 days and 21.3%, generally in Northeast Africa, the subtropical jet stream with a huge ridge structure in direction of northwest to south east extends to the centre of the Red Sea and Saudi Arabia and also the trough structure of jet stream stretches from north of Iraq to the centre of the Red Sea. This trough structure’s sinkhole of jet stream this subtropical sinkhole has caused the left half of the jet stream's outlet with meridian curvature cover the whole of the southern half and most of the country after crossing Saudi Arabia and the Persian Gulf. But in the third pattern of the orbital subtropical jet stream, which plays a role in 14 days and 23.4% of heavy and pervasive precipitation days, the jet stream core has the most stretching and range, mainly from the eastern Mediterranean and north of Saudi Arabia to the western half of Iran, and the jet stream structure is completely formed west to east with least meridian structure. The intensity and pervasiveness of precipitations in this pattern such as the second one is weaker than the other patter. However, in the fourth pattern, the meridian sub-tropical jet stream is present as the most frequent pattern with 18 days and 29% of the selected precipitations days. In this pattern the jet stream has a southwest to northeast direction and the jet stream's core, like the third pattern, generally extends from north of Saudi Arabia to centre of Iran and sometimes to northeast of Iran. The locating of this jet stream with a suitable curvature on the important water resources of the south of the country and corresponding to the north eastern half of the trough from north eastern of Africa to north eastern of Iran after the merged pattern, has caused the most pervasive and intensive precipitations days in the south of the country.
Keywords: Heavy and Pervasive precipitation, Cluster Analysis, Subtropical Jet stream, Low Pressure, Trough, Southern half of Iran
Volume 8, Issue 1 (5-2021)
Synoptic Patterns that Determine the Trajectory of Precipitation Systems of Sudanese Originntroduction
Introduction
Precipitation as an important climatic element has many irregularities and fluctuations. Iran, especially its southern half, has significant precipitation fluctuations. Several atmospheric systems are involved in the formation of precipitation in this region from of Iran. Sudanese system is one of the most important precipitation systems in Iran. This system, in different synoptic conditions, enters Iran from different input sources and passes through Iran in different ways.
The important and influential role of Sudan's low pressure on precipitation in Iran, especially in the southern part of the country, has been repeatedly demonstrated in numerous studies. But the formation and its expansion have received little attention. These reasons have led to the consideration of the position of Sudan's low-pressure synoptic expansion as an influential factor in the southern half of Iran precipitation. Therefore, the position of the expansion of this important climatic system has been investigated separately in the precipitation of the three regions south west, south middle and south east.
Materials and Methods
Two categories of data were used for this study. These data include daily precipitation data from the Iranian Meteorological Organization and the ERA interim gridded data include Sea Level Pressure (SLP) and the Geopotential Height of the 700 HP atmospheric level of the ECMWF. Second category data with horizontal resolution of 0.5 × 0.5° degrees during 1997-2017 statistical period were prepared.
To achieve the purpose of the study, the southern half of Iran was first divided into three regions: South-West, South-Mid and South-East. After extracting daily precipitation of the selected stations in all three geographic regions, a total of 142 precipitation systems was identified by applying the required criteria. From this number of precipitation systems, respectively, were obtained in the south west 107, south middle 19 and southeast 16, respectively. Then, the source of precipitation systems was extracted using the atmospheric lower level maps. Subsequently, the central core and zone of the first closed curve around the Sudanese low pressure were extracted separately for each group. The main axis of the Sudanese low-pressure trough are also drawn on all rainy day. Finally, the model or pattern of atmospheric circulation in the precipitation systems of the regions is presented separately.
Results and Discussion
The purpose of this study was to determine the position of the central core and the pattern of expansion of the first closed curve around the Sudanese system and the Sudanese system trough in precipitation in each of the three regions of the southern half of Iran. Since the arrangement of precipitation systems may vary in different months of the year, depending on the general atmosphere of the atmosphere, the position of the core, the pattern of expansion of the low-pressure trough and the trough of 700-hPa atmospheric level is analyzed separately each month.
In the synoptic pattern of systems, entering from the south west of Iran, the Arabian Subtropical High Pressure with the southwest-northeast direction is located in the eastern half of the Arabian Peninsula and west of the Oman Sea. In this pattern, the troughs are generally north-south. As a result, the rainfall intensity and intensity of precipitation systems, entering the south west of Iran are higher than the other two routes. The focal point of troughs this route is between 30 to 40° east (Eastern Mediterranean). In systems with South-Mid route, the Arabian Subtropical High Pressure has slightly shifted southward and found a northeast-southwest axis. In this pattern, the Mediterranean troughs are generally northeast-southwest. This pattern causes precipitation in the eastern half of the Iran. Or at least no precipitation in the northwest and west of the Iran.
The synoptic pattern of precipitation systems that enter Iran from the southeast is somewhat more complex. In this pattern, the Arabian Subtropical High Pressure has an unusual eastward shift. So that it is based in India. The troughs of this path showed two completely opposite patterns. In some systems, the troughs in the southwest-northeast direction with the orbital inclination, covers the whole of Saudi Arabia and southern Iran. On the contrary, in some systems the troughs stretch quite opposite to the first group, the northwest-southeast direction.
This asymmetry in the expansion of the troughs should be traced to the general topography of the Tibetan Plateau and the circulation pattern of caused by the presence of the Tibetan anticyclone. Basically Mediterranean troughs are disrupted in their usual eastward displacement after a longitude of 60 degrees. As you can see, the Sudanese low-pressure troughs for the South-East Route lack structural discipline and coordination.
Conclusion
The results of this study show that the location and pattern of expansion of the first closed curve around low pressure in different precipitation months and systems of the three zones do not differ significantly in location. Rather, it is the most important system in determining the direction of Sudanese systems, the Arabian Subtropical High Pressure and the pattern of expansion of the eastern Mediterranean trough. In the synoptic pattern of systems, entering from the south west of Iran, the Arabian Subtropical High Pressure with the southwest-northeast direction is located in the eastern half of the Arabian Peninsula and west of the Oman Sea. In this pattern, the troughs are generally north-south. In systems with South-Mid route, the Arabian Subtropical High Pressure has slightly shifted southward and found a northeast-southwest axis. In this pattern, the Mediterranean troughs are generally northeast-southwest. The synoptic pattern of precipitation systems that enter Iran from the southeast is somewhat more complex. In this pattern, the Arabian Subtropical High Pressure has an unusual eastward shift. So that it is based in India. The Sudanese low-pressure troughs for the South-East Route lack structural discipline and coordination. This asymmetry in the expansion of the troughs should be traced to the general topography of the Tibetan Plateau and the circulation pattern of caused by the presence of the Tibetan anticyclone.
Keywords: Synoptic Patterns, Sudanese Low Pressure system, Eastern Mediterranean Trough, Southern Half of Iran, Arabian Subtropical High Pressure.
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