A review of past work in the subject areas of latent heat release in EXTRATROPICAL CYCLONES, within the concept of the potential vorticity framework or "PV thinking" is presented. It is also aimed to assess to what extent the conventional baroclinic instability theory can be applied to EXTRATROPICAL CYCLONES involving intense latent heat release. The main results of the previous studies concerning the effect of latent heat release on EXTRATROPICAL CYCLONES dynamics can be divided into two categories, depending on whether the impact of the diabatically generated PV anomaly on the baroclinic dynamics was very weak or strong. In the weak cases, cyclogenesis is primarily driven by baroclinic dynamics, with latent heat release playing a secondary role. Latent heating influences the baroclinic dynamics as simply by superposing a positive PV anomaly near the cyclone center without significantly altering the PV structure elsewhere. On the other hand, a few studies reveal that latent heat release can enhance largely the cyclone intensity, particularly when the surface thermal gradients are weak and alter significantly the structure of upper-level PV and surface thermal anomalies. The low-level diabatically produced PV anomaly is able to substitute for the absent surface warm anomaly.

Major hurricanes occur in the Atlantic Ocean every year over a seasonal period known as the Atlantic hurricane season. There is evidence to suggest that the hurricanes can be affected by the North Atlantic Oscillation (NAO), a low-frequency phenomenon occurring in a large region over the North Atlantic. In turn, hurricanes can affect the North Atlantic storm track by transition to EXTRATROPICAL CYCLONES in the midlatitude regions. The objective here is to investigate the relationship between hurricanes and the North Atlantic storm track through NAO index. For this, the correlation coefficient between daily NAO index and 6-hourly “accumulated cyclone energy” (ACE) index related to the hurricanes are computed and analyzed for July to October 2017–2019. Then, in the dynamical study using JRA-55 data and from the energy point of view, the vertically-averaged “eddy kinetic energy” (EKE) and the main terms involved in its dynamical evolution are computed for the hurricane season. Also, by selecting one of the major hurricanes in September, which has different conditions in terms of being affected by the North Atlantic Storm track and entering the midlatitudes, the relationships between hurricanes and the North Atlantic storm track are further investigated. Results show that when hurricanes are active for only about a week, they are limited to the subtropical region and have a higher correlation coefficient (about 95%) with NAO. But when hurricanes are active for more than a week and involve an EXTRATROPICAL transition phase, they have a relatively lower correlation coefficient with NAO. Also, the long-term statistical study (1995–2019) shows that although the number of hurricanes in the positive phase of NAO is about 7% more than that in the negative phase, but the relative prevalence of the negative phase of NAO at the time of hurricane activity in the main development region is slightly higher than that of the positive phase. In addition, hurricanes in which all activity is in the positive phase of NAO stretch to the east coast of the United States and are reinforced there, while hurricanes that all of their activity coincide with the negative phase of the NAO, occur in the Sargasso Sea and the CapeVerde regions. Therefore, NAO phases affect hurricane track during EXTRATROPICAL transition. The monthly mean values of the vertically-averaged EKE and the main dynamical terms of its time evolution equation in September show that eddy activity is weak during summer in the hurricanes activity zone,however, in the east coast of the United States and Canada, there are significant changes in the dynamical terms. Also, in the EXTRATROPICAL transition, the dynamical terms determining EKE evolution at the entrance of the Atlantic storm track have large amounts in the Labrador Sea due to deep convection, which suggests a significant energy exchange with hurricanes in this area. Another result is that baroclinic conversion and divergence of ageostrophic geopotential flux are the most important terms determining EKE evolution. Also, geographical location of the hurricanes during transition has a significant effect on the changes of EKE. If hurricanes are intensified in the east coasts of North America and Canada and occur at the same time in the positive phase of NAO, they could play a very important role in strengthening the North Atlantic storm track.

Separation efficiency of CYCLONES is affected by various parameters such as pressure drop, particle size, structural dimensions and operational conditions. This paper compare the separation efficiency of Abadan refinery FCCU’s CYCLONES with results of standard designing cyclone models. Initially standard cyclone designing models of Muschelnautz, Lapple and Barth were discussed, and then experimental data of Abadan refinery were compared with the results of the models. Comparison results confirmed that Muschelnautz model has been more accurate than the other studied models in evaluation the CYCLONES’ pressure drop and efficiency.

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.

In this study, for spatial-temporal analyzing of CYCLONES in 1376, the spatial range of 30 to 80 degrees of east longitude and 0 to 80 degrees of north latitude and geo potential data with 2/ 5* 2 / 5 degrees of networking in arc levels of 1000, 925, 850, 700, 600 and 500 Hpa have been used. These data are extracted for six hours (00, 06, 12, 18 Zulu) database (NCEP / NCAR). So that, the first geo potential databases were created in MATLAB software, then GRADS changed the data to maps and, SURFER combined maps and the final analysis has been done. Temporal analysis in Iran indicated that the most of CYCLONES frequency is related to the level of 500 Hpa with 27 / 2 percent and the lowest frequency with 11 percent is for the level of 850 Hpa. Winter with 31/5 percent has the most cyclone and, summer with 18/8percent has the lowest CYCLONES. Studies of spatial CYCLONES in Pakistan indicate the existence of low pressure in all seasons, which is developed at lower levels. In Iran strong spin cannot be found and cyclonic centers which affect Iran are mainly derived from different geographical areas and are not active inside the country.

Introduction The activity of synoptic CYCLONES plays an important role in determining the local climate and forming large-scale atmospheric circulation through the vertical and horizontal exchange of heat, humidity and momentum, coupled with interaction with large scale circulation centers. The CYCLONES are generally transmitter of the bad weather conditions and also represent the initial mechanism of transmitter moisture and heat to the pole. Systematic changes in geographical location or in the intensity / frequency of cyclone activities will make significant disparities among other regional climate impacts. The effects of mountainous obstacles on synoptic systems, especially the cyclone systems, are recognized. The mountain range is one of the factors that in addition to disrupting the uniformity of the earth face, it also disrupts the climatic uniformity. The purpose of this study is to determine the influence of thermodynamics of Zagros Mountain on the changes in CYCLONES entering the country from the west. Materials and methods For this purpose, the daily precipitation data were obtained from 13 stations of the Meteorological Organization in west Iran. Also geopotential data were extracted from the NCEP / NCAR databases with spatial resolution of 2. 5 × 2. 5 degrees and ERA-Interim data from ECMWF databases with spatial resolution of 0. 125 × 0. 125 degrees, their framework is 0 to 80 degrees east and 0 to 60 degrees north. Using the Factor Analysis method, April 14th-18th, 2003 was selected as the best pattern. After selecting the sample day, sea level pressure maps and geopotential heights of different levels were prepared and analyzed. Results and discussion The results of the analysis of these maps showed that the cyclone reaching the Zagros Mountains are dynamically strengthened from the day it formed until it arrived in Iraq. When they approach the Zagros, the vorticity and its omega are reduced, but crossing Zagros, a positive vorticity increase happens. These types of CYCLONES call Zagros CYCLONES. The relationship between the amplified cyclone with the divergence region of the middle and middle levels were observed at all stages. The Zagros roughness, like a wall, initially weakens the cyclone reached Iran and makes them bipolar. However, the passage of the CYCLONES from the mountain make the thermodynamic conditions of the descending air in the lee mountain range. The condition makes them revival. As the air reaches the roughness, a weak core remains in the Zagros range, and another nucleus is formed by passing through the mountains in the central regions of the country, and is reinforced in the next hours. Finally, the cyclone is amplified and leaves its moisture completely on Iran. These CYCLONES can be called Zagros second CYCLONES. Conclusion Mountain barriers are considered as the factors destroying the homogeneity of the local climate. Sometimes they act in the planet scale like the Rocky Mountains. Iran has a heterogeneous environment in term of geomorphology and climatology. One of the most outstanding effects of roughness on the climate is the change in the structure of systems passing through these barriers. Zagros Mountains is one of the main mountain ranges of Iran, with an almost northwest-southeast direction and with a maximum height of about 4, 400 meters at Zardkuh Peak. It has a significant impact on immigrant systems to the country. A study on the cyclone on April 14th, 2003 showed that this cyclone was formed on the April 12th on the northwest Europe, moving towards the Mediterranean Sea. Its trough arrives in the country on the April 14th and it reaches the slopes of Zagros on the 16th. As it is approaching Zagros, changes in pressure in the back and the lee of Zagros are increasing. Vorticity and divergences are completely different in two parts. In the Zagros, during a few days when the cyclone pass across the range, there is a negative vorticity. The vertical velocity also demonstrates subsidence in Zagros altitudinal areas. The results vividly prove that the cyclone gets weakened in collision with the mountain, and its movement gets slow, but it does not disappear. It is re-reinforced on the Zagros lee in the central part of the regions, and continued its route to outside the borders of the country.

The aim of this research is to analyze the climatology of the Northern Hemisphere EXTRATROPICAL storm tracks in different seasons using the ERA5 data for the period 1979-2023. To do this, we applied the Lagrangian feature tracking method on the relative vorticity and the positive meridional wind at 850 hPa to identify storm tracks. A positive meridional wind extrema indicates the poleward advection of warm air in the east of a cyclone center, while a negative value points to an equatorward advection of cold air in the west of a cyclone center. Therefore, tracking the positive meridional wind extrema can be applied to identify the storm-driven intrusion of warm air into the Arctic, which can accelerate the Arctic sea-ice melting. It should be noted that in identification and analysis of storm tracks based on the feature tracking method, it is important to choose an appropriate meteorological field. For instance, if we apply mean sea level pressure (MSLP) to track storm tracks, the western parts of the Mediterranean storm track can be detected, while it is not possible to detect the eastern parts. Also, tracking the positive meridional wind extrema is more useful, compared to tracking the relative vertical vorticity at 850 hPa pressure level and MSLP fields, to investigate the impact of EXTRATROPICAL storm tracks on the Arctic sea ice, because this field is associated with the poleward advection of warm air. In this study, in addition to the track density and mean intensity of storms, we investigated the genesis and lysis densities. Also, we discussed the main entrance pathways of EXTRATROPICAL storms into the Arctic.Our results show that storm tracks are the strongest in winter and the weakest in summer. The west of the North Atlantic and North Pacific oceans are active oceanic basins for the genesis of storms. The center of the North Pacific is also a secondary genesis region for oceanic storms, particularly in winter. There is a maximum of the genesis density in the east of the Rocky Mountains, and also in the Tibetan Plateau. In the former case, most storms reach a lysis maxima on the east coast of North America and west of Greenland. In the latter case, some storms reach a lysis maxima on the east coast of Asia and some of them enter the North Pacific and penetrate into the Bering Sea. In some regions, storm tracks are connected with each other. For example, the Atlantic storm track can feed the storm track in North Russia, while the storm track in North Russia can feed the Northeast Asian storm track. We identified noticeable stretching of the Atlantic storm track from the west of the North Atlantic to the Arctic, through the Greenland and Norwegian seas, which indicates the storm-driven intrusion of warm and moist air from the North Atlantic into the Arctic. Tracking the positive meridional wind extrema reveals a significantly higher lysis density in the Bering Sea compared to tracking the vertical relative vorticity extrema. Hence, storms that penetrate as far as the Bering Sea/Strait can bring heat and moisture from the North Pacific into the Arctic. This storm-driven intrusion of warm and moist air can cause a local melting of sea ice in the Arctic or slow down the sea-ice production, especially in winter.

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.