Iran country because of great spreading with a view to geographical longitude and latitude‚ existence the contortion of unevenness configuration and locating in exposed of air masses attacking has special circumstances in terms of temporal. The overall structure influenced by latitude‚ altitude and air masses. So that with changing each of these factors the temperature will change. In other words the general condition of temperature is a function of latitude and altitude and other factors such as aquatic area and land forms has a role in creating temperature structure that is referred as local factors...

Forecasting temperature as one of the important climatic parameters plays a major role in climate change research. Therefore, in this study, the surface data of the average daily temperature of selected stations in the Caspian Sea (Anzali, Gorgan, Rasht, Babolsar and Ramsar) and the data of geopotential height of level of 500 hPa whose data were extracted from the website NCEP/DOE under the US National Oceanic and Atmospheric Organization in hours 00: 00, 03: 00, 06: 00, 09: 00, 12: 00, 15: 00, 18: 00, and 21: 00 in the Zulu. During the period from 01/01/1979 to 01/01/2011 AD, four observation days per day were extracted from the NCEP / DOE website for the whole of the northern hemisphere, and then the correlation between the average daily temperature and geopotential data of the 500 hPa equilibrium was calculated throughout the northern hemisphere. The results of the correlation showed that the US with 28, the northern China with 30, Africa with 53 and at last, Japan with 69 pixels have the most pixels. In general, in the northern hemisphere, there are 180 points whose correlation with the temperature of selected station is very high. Also, the forecasting model of stations shows that for each geopotential meter increase, the average daily temperatures of the stations of Anzali, Gorgan, Rasht, Babolsar, and Ramsar increases as 0.1, 1.1, 0.1, 0.1, and 0.1 respectively.

In this research the detection, frequency and quality of behavior of extratropical cyclones in different seasons of year within 1995-1996 are studied. To reach such a goal, data of geopotential height with six-hour temporal resolution and spatial resolution (2.5. 2.5) for different levels (500, 600, 700, 850, 925, 1000) were extracted from atmospheric databases and used (NCEP/NCER). Cyclones were identified by which two requirements were considered including 1- the places whose geopotential height is minimum in relation to the eight neighboring places, 2- regional geopotential height gradient in nine points present in at least 100m/1000km. The results show that in all levels, cyclones in winter and autumn have the highest frequency with very little difference. Frequency distribution in winter is more unified than other seasons and cyclonic areas intend to lower latitudes. One of the most evident features of this season is the presence of cyclonic areas in Mediterranean region. Spring is in the third level due to its cyclonic frequency. From frequency perspective summer cyclones have the least amount with the highest difference. Gang cyclone as the most evident features of other cyclones in 1000 and 925 HP levels are seen in spring and summer. Summer rainfalls and 120-day winds of Sistan in the southeast of Iran are related to the formation of such a system.

ABSTRACTAmong the cyclones that affect the sometimes-widespread rainfall in Iran are the merging systems of the Mediterranean and Red Seas. Therefore, it is very important to obtain the changes in the intensity of the geopotential height and the geopotential height shift of the Mediterranean-Red Sea convection patterns as one of the factors of the manifestations of these gyres, as well as the precipitation in some areas of Iran. To carry out this research, the data of geopotential height level of 1000 hectopascals related to the European Center for Medium-term Atmospheric Forecasting and ERA-Entrim version were used as a six-hour observation during the period of 1979-2018. To investigate the presence of jumps and fluctuations in the intensity of the Mediterranean-Red Sea cyclone centers during the statistical period, the Alexanderson index, known as the Standard Normal Homogeneity Test (SNHT) index, was used. A non-parametric chi-square statistic was exerted to verify and investigate the significance of the trend between geopotential height data and geopotential height tilt data. The parametric linear regression method was used to analyze and model the long-term trend. The findings of the present research indicate the increase of geopotential height in the place of the formation of the circulation centers of the Mediterranean Sea, as well as the decrease of the pressure gradient in the average annual values, which will probably lead to a decrease in instability and precipitation in the affected areas. The geopotential height shift data of the Mediterranean Sea had a significant jump in 1996, which divided the time series into two periods before and after the jump. The results indicate an upward trend in these two time periods, but the second period, with a gentler slope, has increased compared to the previous periodExtended AbstractIntroductionMediterranean Sea and Red Sea cyclones are a type of extratropical-tropical merge system that can influence precipitation over Iran. These combined Mediterranean-Red Sea cyclones form concurrently over the Mediterranean and Red Sea basins. They may sometimes merge as they track eastward, bringing precipitation to Iran (particularly southern and southwestern Iran). Changes in these merged cyclone systems are likely linked to shifts in Iran's precipitation climatology. Examining trends in the intensity of Mediterranean-Red Sea cyclones can thus provide insights into changes in Iran's precipitation patterns. This study investigates trends in the intensity of combined Mediterranean-Red Sea cyclonic systems and their relationship to precipitation over Iran. Cyclone intensity is assessed using geopotential height data at the 1000 hPa level over 40 years. Statistical tests, including chi-square and linear regression analysis, are applied to the geopotential height time series to detect significant trends. The focus is on examining changes in geopotential height slopes and trends that may indicate cyclone intensity changes. This research aims to improve understanding of how Mediterranean-Red Sea cyclones change and identify their impacts on Iran's precipitation climatology. The results can aid in tracking precipitation changes and projecting future climate scenarios for the region. The intensity trends may also provide broader insights into how climate change influences global cyclone behavior. Materials and methodsTo examine the changes in intensity of atmospheric systems and geopotential height, as well as the geopotential height shift of Mediterranean-Red Sea cyclones from 1979 to 2018, geopotential height data at the 1000 hPa level were utilized. The study area encompassed coordinates ranging from -10° E to 120° E and 0° N to 80° N, with a spatial resolution of 0.25° x 0.25°. This area consisted of 321 x 521 pixels, totaling 167,241 pixels. The Mediterranean and Red Sea cyclones, which are extratropical-tropical systems that occasionally merge and influence precipitation in Iran, were investigated. Statistical tests, such as chi-square and linear regression analysis, were conducted on the geopotential height time series for each pixel within the studied region to identify significant trends. The primary focus was analyzing changes in geopotential height slopes and trends, which could indicate cyclone intensity alterations. Results and DiscussionThis section presents the findings and discussion on the changes observed in monthly geopotential height intensity and geopotential height gradient of Mediterranean-Red Sea cyclones. In the Mediterranean Sea, an upward trend was observed in the geopotential height intensity, while a downward trend was observed in the geopotential height gradient. The increase in geopotential height over the circulation centers of the Mediterranean Sea and the decrease in pressure gradient are likely to result in reduced atmospheric instability and precipitation in the region. These results align with Darende's (2013) and Skleris et al. (2012) findings. Contrasting the Mediterranean Sea, the analysis of the Red Sea data revealed a downward trend in geopotential height and an upward trend in geopotential height intensity, indicating an increase in instability. This finding is consistent with the results of Asakereh and Khani (2021). No statistically significant trends were observed in the annual averages of geopotential height and geopotential height gradient in the Red Sea. However, the annual averages of both geopotential height and its gradient in the Mediterranean Sea exhibited a decreasing trend. A notable shift in the Mediterranean geopotential height occurred in 1996, dividing it into two distinct phases. Both phases showed an upward trend, albeit with a gentler slope in the second phase. The annual trend of geopotential height in the Mediterranean Sea revealed a decreasing pattern, which has been previously documented in studies by Alpert (1994, 2004).  ConclusionThese studies suggest that while this reduction in geopotential height has taken place, cyclone tracks have shifted towards northern latitudes, resulting in increased drought and decreased precipitation in regions influenced by these cyclones, including Iran. The studies also acknowledge that changes in high-pressure systems near the tropics and alterations in cyclone direction contribute to variations in dry seasons and reduced precipitation. Further investigation of long-term changes in the geopotential height of the Mediterranean Sea identified three distinct phases in the time series: 1988-1979, 2005-1989, and 2006-2018. The decreasing trend in Mediterranean Sea cyclones persists until the final years of the period, indicating a potential cause for the reduction in atmospheric instability. The Kolmogorov-Smirnov statistical test was employed to determine the appropriate statistical test (parametric or non-parametric) for comparing means and variances across different periods. The parametric tests (one-sample t-test) and the one-way variance test confirmed the normal distribution of the data. Furthermore, no statistically significant trends were observed when examining the geopotential height intensity and gradient of two-day continuities of Mediterranean-Red Sea cyclones. FundingThere is no funding support. Authors’ ContributionAll of the authors approved the content of the manuscript and agreed on all aspects of the work. Conflict of InterestAuthors declared no conflict of interest. AcknowledgmentsWe are grateful to all the scientific consultants of this paper.

Topographic masses above the geoid are considered as a major obstacle in geoid determination by using Global Gravitational Models (GGMs). GGMs provide the possibility of the Earth's potential field modeling as the expansion of the external-type series of spherical harmonics. Applying the external expansion to obtain disturbing potential on the geoid within the topographic masses will cause a bias called „ topographic bias‟ . This study deals with calculating geoidal height using Earth Gravitational Model 2008 (EGM08). In order to do so, two methods of Direct Analytical Continuation one and Rapp's Indirect one are utilized. The Analytical Continuation Approach is based on using EGM08 within the topographic masses and applying topographic bias. Alternatively, Rapp‟ s Approach is based on calculating height anomaly and its downward continuation on the geoid. The success of these two methods to geoid simulation on 490 GPS-Levelling stations in mountainous region of Colorado in the USA were evaluated. The results are an indicator of the fact that two methods are compatible with each other with centimetric accuracy compared to GPS-Levelling points. Also, it suggests an improvement in the relative and absolute accuracy of the geoidal height resulting from EGM08 about 60% in both methods. The numerical investigation revealed that taking advantage of height harmonic models instead of point actual height can bring a bias in the matter of a few centimeters on the geoid. Moreover, the absolute accuracy of Rapp's Approach is higher than Analytical Continuation Approach in geoid determination in comparison GPS-Levelling points.

Global geopotential models (GGMs) are mainly used in the remove-compute-restore (RCR) technique applied to gravity field modeling such as geoid determination and height datum unification. The increase in the number and quality of gravity data has led the developers of GGMs to produce models with higher resolution and accuracy. Basically, the long-wavelength coefficients of the gravity field are computed based on satellite data, while the medium- and short-wavelength coefficients are calculated based on terrestrial (land and sea) data. One of the main challenges regarding the evaluation of high-degree GGMs is to compute the associated Legendre functions of the first kind based on the usual recursive formulas. Since most computational softwares use the double-precision format by default, an important question is whether this level of precision is sufficient to numerically evaluate the associated Legendre functions of the first kind? To answer this question, the computation of the associated Legendre functions of the first kind in different degrees and latitudes is studied based on MATLAB software, which uses the double-precision format by default. From the numerical results, we find that the calculation of associated Legendre functions of the first kind up to degree of 2190 (the highest degree of existing GGMs), does not have sufficient accuracy at latitudes between 56°20׳ and 78°33׳, where the most critical state occurs at the latitude 60°. We also find that the accuracy of the calculation of associated Legendre functions at the latitude 60° (the most critical state) significantly decreases for the degrees higher than 2029. These results imply that the usual computational softwares based on the double-precision format are not suitable for calculating the associated Legendre functions in all degrees and latitudes. This is due to the fact that if we consider the associated Legendre functions of the first kind in the form of a matrix with the dimensions corresponding to the degree and order of the functions, as the degree increases, the numbers on the main diagonal approach to the number 10-308 and thus they are considered zero. In the recursive method, the entries below the main diagonal are calculated from the entries on the main diagonal. Since the entries below the main diagonal become very large as they move away from the main diameter, any error in computing the main diagonal entries leads to a large error in computing the entries below the main diagonal. In this paper, we also study the challenges of using the associated Legendre functions of the first kind in the production of gravity field functionals based on a GGM, utilizing MATLAB software. The results show that the gravity potential computation up to degree of 2190 suffers from very large computational errors at latitudes between 57°32׳ and 60°13׳. We observe that the safe degrees for the gravity potential computation in all latitudes are degrees less than 2065. The critical latitudes and degrees for the gravity calculation are somewhat different. The results indicate that the gravity computation up to degree of 2190 leads to very large errors at latitudes between 57°41׳ and 60°13׳. In addition, the maximum degree of expansion that grants sufficient accuracy for the calculation of gravity for all latitudes is estimated to be 2071. Therefore, since the usual computational software based on the double-precision format is not suitable for evaluating the current high-degree GGMs, in this research, a new proposal based on the use of the “long double-precision” format is presented and evaluated. Based on our evaluations, the use of the long double-precision format throughout the computational procedure provides sufficient accuracy to compute the gravity field functionals based on the current high-degree GGMs.

foehn pour warm and dry under certain conditions on the slopes of the mountains are caused by the wind. When the amplitude of the adiabatic air humidity climbs to the summit of the mountains, If you have enough moisture saturation and the formation of clouds or rain lost its moisture, dries With the passage of the mountain range behind the wind, will sink into the bottom of the valley or plain. The data used in this research include fires and meteorological data. Information on distribution time, place and the fire of the Department of Natural Resources Gilan, Mazandaran and Golestan period (1390-1384) collected data from weather elements such as temperature, humidity, wind and pressure for the three northern governorates and Semnan provinces, Tehran and Qazvin was obtained from the National Weather Service. The synoptic situation day to analyze the fire ground level pressure data, geopotential, air temperature, relative humidity, zonal and meridional wind components, sensible heat flux and instability index (omega) of the website of the National Centers for Environmental Prediction and the National Center for Atmospheric Research (NCEP / NCAR) was received. After weather conditions in the southern and northern slopes of the Alborz action synoptic maps of the three days prior to the event every forest fire GrADS software and using MODIS satellite images of the mountain clouds in time event was screened.This phenomenon (foehn) is not a local event, but the influence of the general circulation of the atmosphere and the system is moving west wind, And the ripples and the range of moisture conditions and rainfall, wind strength and weakness of will. Moving West to East West winds associated with this phenomenon.

Introduction Blocking is one of the most protruding flow patterns and has received attention during the last decades due to its effect on seasonal weather characteristics. The first qualitative conditions for the blocked atmospheric flow was introduced by Rex in 1950 telling the atmospheric jet becomes divided into two separated parts with a considerable connected mass transport, the flow to be meridional at the splitting point and downstream, and the state to continue for at least ten days with a zonal width of at least 45 degrees. The new ideas formulated by Rex became the basis for several blocking indices. Most of the indices detect typical atmospheric patterns. For shorter time series, particular criteria have been used, although, the majority of the analyses are in the 500 hPa geopotential height. In the face of the differences between the index classifications, they draw similar conclusions regarding the patterns of the Northern Hemisphere blocking climatology. However, the blocking frequency is the percentage of time steps an assured longitude. It can be as low as 5% or higher than 20%. The main aims for this wide range of frequencies in automatic recognition are modifications of the Rex criteria and the use of different parameters. Due to its simplicity, the index of Tibaldi and Molteni (TM-Index) has become a standard in automated blocking detection analyses. An important problem of the TM-Index is that it cannot effectively distinguish between blocking and cut-off low patterns, since both fulfill the TM-Index criteria. The adapted TM-Index MTM has a higher rejection rate for cut-off lows. Limits in the Rex conditions can be measured as implementations of independent filters which show synergetic effects if they are used in run...

To investigate the changes in atmospheric circulation in the Northern Hemisphere, geopotential height data from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) was analyzed from 1948 to 2020. A trend test was conducted on the geopotential height data to examine these changes. The results indicated significant alterations over the 70-year period in the polar regions, mid-latitudes, and other latitudes. In winter, particularly in December, a negative core of decreased geopotential height at the 10-hectopascal level was observed over the polar cap, reaching a minimum of-8 geopotential meters. Conversely, the North Pacific Ocean exhibited a maximum core of the geopotential height trend, exceeding 4. 5 geopotential meters. This pattern was also evident in January and February, with a decreasing trend noted in northern Europe and the Eurasian region. In spring, a downward trend in geopotential height was observed in the area affected by the polar vortex, extending towards northeastern Russia. The analysis revealed that the most significant changes in the polar hemisphere during the first 37 years occurred in November and December. In contrast, the most substantial decreases in the polar sphere during the subsequent 37 years were noted in November, December, and March. Changes in November and March were nearly identical across both periods, with the first 37 years showing an increase in the polar hemisphere and a peak geopotential height of 140 geopotential meters in November. In the latter 37 years, a decline in the polar sphere was evident.