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Natural gas is known as a widely used energy source in residential, business and industrial areas. During the transportation of natural gas by pipelines, accidents occur due to various reasons, which can also lead to gas output. These accidents are events that have the potential to pose important risks in terms of life and property safety, particularly in urban areas and surrounding of pipeline routings. In this study, accident scenarios were generated based on a natural gas distribution pipeline fire that occurred in Istanbul (NW Türkiye) on 28 April 2020 and the impact areas of the jet fire were calculated using the ALOHA program. The effects of source release factors (i.e., pipe length and diameter) and atmospheric conditions (i.e., wind speed, cloud cover, air temperature and relative humidity) on the thermal radiation threat distances associated with jet fire were calculated for the current and worst scenarios. As a result, it was found that pipe length and diameter have a significant effect on threat distances. In addition to the role of the synoptic circulation mechanism on the jet fire for the selected episodic event (position of low/high pressure centers), local atmospheric conditions also have an effect on the threat distance. From the modeling analysis, significant impact of wind speed, air temperature and relative humidity values on the threat distances were found. In the worst scenario, if there were strong northeasterly winds reaching 30.9 m per hour at the time of the jet fire, the threat distances would have been 21 m (red), 28 m (orange) and 42 m (yellow). This case shows that if a natural gas jet fire occurs under the influence of strong northeasterly winds (passing over the Black Sea without encountering any topographic obstacles), poisonous gas will be transported to long distances in a short time and will negatively affect social life and economy. [ABSTRACT FROM AUTHOR]

The aim of this work is to study precipitation chemistry in the cross-border region between Turkey and Bulgaria, situated on the south-eastern part of the Balkan Peninsula. A total of 115 wet deposition samples were collected and analysed for pH values and major ions (Na+, Mg2+, Ca2+, K+, NH4+, Cl−, NO3−, and SO42−) throughout the summer and autumn seasons of 2014. The enrichment factor analysis and non-sea salt estimates were conducted to determine the possible sources of ions in the wet deposition for the sampling period. The trajectories of the cyclones affecting the area during the study period were also analysed by separating them in different groups. The minimum, average and maximum pH values for the first group of cyclones (CG1) are 4.30, 6.04, 7.40, and 4.00, 6.14, 7.43 for the second group cyclones (CG2), respectively. The non-sea salt fractions of the K+ ion were found to be 0.94 in CG1 and 0.90 in CG2. Also, the Mg2+ ion in CG1 and CG2 is 44% and 60% of the sea salt source. [ABSTRACT FROM AUTHOR]

In this study, a climatological analysis of daily new snow cover data from 93 meteorological stations (10-2,400 m above sea level) over Turkey during the winter (December-March) period of 1967-2006 is presented. Series of snow cover depth (SCD) (≥1 cm) and number of snowy days (SDs) were analysed to determine the variability and statistically significant trends in the snow climatology. The results showed an inverse relation between SDs and SCD over the central (CAR) and eastern (EAR) Anatolian regions. While positive trends in SDs were observed in the CAR (77% of all stations), the new SCD decreased in time. On the other hand, the intensity of the daily snowfall over the EAR increased due to decreasing (increasing) SD (SCD) trends in the region, especially between the 500 and 1,000 m layer. It was found that higher SCDs occur in the EAR during winter with positive patterns in the east Atlantic/western Russia. The daily mean sea level pressure composite maps of high SCD (>5 cm) show that strong northeasterly flows enable the penetration of cold polar air to the EAR due to the interaction between the Siberian high-pressure centre over Europe and the low-pressure centre over the Caspian Sea. These results help further understanding of the regional variation of the snowfall pattern in Turkey and its response to global climatic change. [ABSTRACT FROM AUTHOR]

This paper investigates the precipitation types and background physical mechanisms of extreme precipitation events (EPEs) over western Turkey during the period 2006–2015. The EPEs are described as the precipitation values above the 90th percentile obtained from the hourly precipitation dataset, which has high spatial resolution. Precipitation types associated with EPEs are identified by using radar outputs and the Lamb weather type (LWT) approach. It is found that EPEs occurred more frequently in the Marmara and Aegean regions during autumn and winter months. In Marmara, mainly 21 %, 17 %, and 15 % of total autumn EPEs show convective, cyclonic, and sea-effect precipitation characteristics, respectively. While convective EPEs are seen more commonly in the southern portions, cyclonic and sea-effect-originated EPEs mainly affect the southwest and northeastern parts of Marmara. Among these three precipitation types, convective mechanisms generally produce more intense daily precipitation (66.1 mm on average) in the Marmara Region under the proper synoptic conditions (high-pressure center over the Balkan Peninsula and low-pressure center over the eastern Mediterranean). Based on the hourly observations, convective types of extreme precipitation (EP) show two peak values during afternoon and evening times of the day and are linked to diurnal heating. In terms of the Aegean Region, cyclone-originated EP, which includes 65 % of the total winter EPEs, is more common in the whole territory and reaches its peak value during the early hours of the day. [ABSTRACT FROM AUTHOR]

During the afternoon hours of July 27, 2017, an extreme hailstorm struck the most populated city of Turkey, Istanbul. This rapidly growing supercell which produces large hail led to numerous injuries and damaged automobiles, houses, aircrafts, crops, and infrastructure of the city. As a result of the movement of the cut-off cyclone from Middle East to western Turkey, warm air advection penetrated over Marmara, and the land surface temperature of Istanbul reached 34 °C (5 °C above the mean). The transport of significant amount of moisture, which was caused by excessive heating of Marmara Sea surface temperatures (24.9 °C), to the low levels of the atmosphere by strong southwesterly winds enabled the increase of low-level moisture convergence. Both abnormal temperature differences between land and 500-hPa level (41.5 °C) and excessive wind shear values (20.3 m/s) between surface and 6 km above ground level (AGL) increased the thermal instability and updraft conditions of the baroclinic atmosphere. This condition resulted in thunderstorms, stormy and gale wind gusts (31.9 m/s 15:20 UTC), extreme lightning activity (totally 2696 cloud-to-ground and 5791 intracloud), large hailstones between 3-6 cm diameter and high hourly precipitation amounts (38.7, 36.2, 29.8, and 27.2 mm in Sisli, Kadikoy, Uskudar, and Fatih regions, respectively, between 14:00 and 15:00 UTC) in the urban settlements of the city. The stability indices, Showalter, K, Total of totals, SWEAT, and CAPE also showed the high probability of severe thunderstorm occurrence over Istanbul. Based on a comparison among these five indices, the SWEAT index is most appropriate to represent the atmospheric conditions over the city owing to low-level moisture, warm air advection, and low and mid-level wind speed terms in its equation. [ABSTRACT FROM AUTHOR]

This paper investigates the climatology, precipitation types and background physical mechanisms of extreme precipitations events (EPEs) over western Turkey during the period 2006-2015. The EPEs are described as the precipitation values above the 90th percentile obtained from the hourly precipitation dataset having high spatial resolution. Precipitation types associated with EPEs are identified by using radar outputs and Lamb Weather Type (LWT) approach. It is found that EPEs occurred more frequently in the Marmara and Aegean regions during autumn and winter months. In Marmara, mainly 21 %, 17 % and 15 % of total autumn EPEs are observed as convective (E circulation types (CTs)), cyclonic (C), and sea-effect (NE) extreme precipitations (EPs), in order. While convective EPEs are generally more active in the southern portions having rugged topography, cyclonic and sea effect EPs are more effective in the southwest and northeastern parts of Marmara. Among these three precipitation types, convective CTs produce more intense daily precipitation in the Marmara region with daily average value of 66.1 mm. Based on the hourly observations, convective types of EP which developed by the interaction between high pressure center over Balkan Peninsula and low pressure center over eastern Mediterranean, show two peak values during afternoon and evening times of the day and are linked to diurnal heating. In terms of Aegean region, cyclonic originated EPs, which include 65 % of the total winter EPEs, are more common in the whole territory and reach to its peak value during the first hours of the day. [ABSTRACT FROM AUTHOR]

High levels of atmospheric pollutants have been frequently measured in Turkey during the last decade. Specifically, the occurrence of these high particulate matter concentrations is often related to either local-scale conditions or regional-scale transport. In order to better understand the atmospheric factors that trigger poor air quality, further research investigating the relationship between air pollution and meteorological variables or atmospheric circulation patterns is needed. In this study, the influence of synoptic-scale weather types on PM10 levels over the Aegean region of Turkey is investigated for the period 2008–2015. First of all, hourly PM10 concentrations of 13 air quality stations are respectively converted to daily, seasonal, and regional averages. The seasonal variability of PM10 values in the region indicates that high particulate matter concentrations are registered in winter, fall, spring, and summer months with mean values at 90.6 (± 38.3 standard deviation), 66.9 (± 28.3), 61.6 (± 23.4), and 54.1 (± 12.8) μg m−3, respectively. In regard to the synoptic-scale approach, eight directional and two vorticity types of the Lamb weather type (LWT) method are used in the analysis. Based on the results, poor air quality conditions are observed in all seasons during active southeasterly (SE, interaction between a low pressure over Italy and a high pressure over the Caspian Sea) circulation types (CTs). In winter, mainly easterly (E), SE, southerly (S), and anticyclonic (A) weather patterns result in above normal PM10 concentrations. In addition to these four CTs, southwesterly (SW) types also cause higher PM10 values in the spring season. During summer, SE, SW, westerly (W), and cyclonic (C) CTs are associated with above-normal PM10 values. During fall, obvious higher PM10 concentrations are found during SE, S, and A types. [ABSTRACT FROM AUTHOR]