Climatologies of severe convective storms in Turkey, their environments, and their impacts

Severe convection is responsible for many hazardous events such as large hail, tornadoes, severe non-tornadic winds, heavy rainfalls and lightnings. These events cause loss of lives and damage to property in Turkey. Considering their effects on life and property and the global increasing trends of them, both short range probabilistic forecasting and nowcasting of these local storms are significant, however challenging issues. Defining the spatial and temporal distributions of these events is a prerequisite for understanding and predicting the environmental conditions that are favorable for them. In other words, knowledge on geographical, seasonal and daily distribution of severe convective storms is an essential need for improving abilities of forecast society. This thesis contributes the building of 'Storm Data of Turkey' as its first step. Convective storms are local scale events. Because of their small scales, conventional observational networks are not capable to catch all of them. Therefore, creating a storm database requires too much effort and collaborative working. Many parties, such as meteorological service observers, voluntary observer networks, and general public take part in reporting of these storms. Official records, newspapers and news agency archives, social media are good sources for collecting these reports. This dissertation presents report-based climatologies of severe convection related events, specifically severe hail and severe non-tornadic winds in Turkey. The severe hail climatology part of the reseach shows that severe hail (≥1.5 cm) is observed to be associated with a variety of thunderstorm types in Turkey and can occur in any season of the year. However, very large (≥4.5 cm) hail is usually associated with supercell storms. All parts of the country are vulnerable. The largest hailstones exceed 5 cm in diameter and approach 1 kg in mass. Severe hail in Turkey is most likely in May and June, especially in interior parts of the country. Severe hail is least likely in the winter, though when it occurs in winter, it is most likely along the southern and western coasts. The afternoon and early evening hours are the most favorable time of the day for severe hail. Seasonal and monthly distribution of severe nontornadic convective wind events shows that although the big portion of this events (51%) occur in summer they can occur in any time of year. They are most frequent in June, 33% of all events occurred in this month and 15% in September. According to the reports including storm duration information, only two of them were longer than six hours and most of them continued for 1 to 3 hours (42%). Second outcome of this research is on the impacts of severe convective storms on society. A dataset covering January 1930 to June 2014 on lightning related fatalities and injuries in Turkey is created. There were 745 incidents, resulting in 898 deaths, 150 serious injuries and 536 injuries during this period. The total number of fatalities was 31 in 2012, 26 people in 2013 and 25 people in 2014. With a Turkish population of around 73.7 million, the number of fatalities were 0.42 per million in 2012, 0.35 per million in 2013 and 0.34 per million in 2014 (January–June). The total number of human injuries was 36 in each of 2012 and 2013, and 62 in 2014. Considering the population, the rate of injuries was 0.49 per million in each of 2012 and 2013, and 0.84 per million in 2014 (January–June). Incidents were most frequent in late spring all around Turkey and were rare during winter. The majority of lightning incidents occurred during the afternoon, with fewer occurring at night. The number of incidents was higher over the highly populated western parts, especially in Istanbul and relatively lower in central and eastern Turkey. Geographical, annual and diurnal distributions of the incidents were comparable to thunderstorm and lightning observations, as well as with the report-based severe weather climatologies for Turkey. The risk of being struck by lightning was highest for the people participating outdoor activities such as farming and shepherding. The number of male victims was nearly twice the number of female victims. Almost all of the incidents occurred in rural areas. The number of victims under trees is a sign of the need for awareness campaigns. Report-based datasets are primary sources for severe convective storm climatologies. However, they have some disadvantages. Observations of hazardous, convection related local scale phenomena such as severe hail, tornadoes and damaging winds have a subjective nature. They are critically sensitive to some parameters such as population density differences, time of the day of occurrence and reporting issues (e.g., subjective estimation of wind speed by non-expert human observers and alike). Due to subjective nature of their observations, regional climatology, temporal variability and trends of these phenomena have been difficult to be defined properly (e.g., Diffenbaugh et al. 2008). Thus, climate change assessments have avoided from certain judgments about the effects of anthropogenic global warming on current and future variability of these phenomena (e.g., Intergovernmental Panel on Climate Change 2007). Usage of numerical models is an alternative method to get rid of mentioned disadvantages of report-based climatologies. Spatial analysis of environmental controls such as CAPE (convective available potential energy) and vertical wind shear on the global reanalysis data shows that there is a significant similarity between distribution of observed severe convective storms and these environmental controls (Brooks et al., 2003; Romero et al., 2007; Gensini and Ashley, 2011). In this thesis, an objective climatology of severe convective storm environments is established. Various environmental parameters associated with severe convective storms were calculated for a domain covering Europe, Middle East and North Africa for the 35-year period of 1979–2014 using ERA-interim data. Specifically, surface-based convective available potential energy (SBCAPE), mixed-layer (lowest 500m) convective available potential energy (MLCAPE), most unstable convective available potential energy (MUCAPE), surface-based convective inhibition energy (SBCIN), mixed-layer (lowest 500m) convective inhibition energy (MLCIN), most unstable convective inhibition energy (MUCIN), surface-based lifting condensation level (SBLCL), mixed-layer (lowest 500m) lifting condensation level (MLLCL), 0–6 km wind shear, 0–3 km wind shear, 0–1 km wind shear and mid-tropospheric (700–500-hPa) lapse rate (LR7050) were calculated. Previous research shows that, individual parameters did not discriminate well between severe and non-severe deep moist convection. Considering instability and shear together improves discrimination sharply (e.g., Davies and Johns 1993, Johns et al., 1993, Craven and Brooks 2004, Gensini and Ashley 2011). Therefore, proxy distribution of severe convective storms is enquired with the help of a parameter based on product of MLCAPE and deep layer shear. Results shows that the ITCZ, Mediterranean Sea, Red Sea and Arabian clearly exerts a dominating influence on the CAPE distribution patterns over the domain. Influence is not limited to directly over the seas but is noted over the coasts of these seas. Seasonal cycle of CAPE fields is very clearly defined with larger values during summer than in the winter for all over the domain. For the transition seasons, CAPE values are higher in autumn than spring over Mediterranean, Red and Arabian Seas and neighboring countries as expected. After peak summer insolation, these large water bodies remain warm for several weeks and perform as intense heat and moisture sources. This effect is slightly visible over southern parts of Black Sea and Caspian Sea due to lower insolation, related with their higher latitudes. With the strengthening of the jet stream during winter, the highest average 0–6 km wind shear values occur beneath the jet regions. Overlapping of ingredients seems most probable during spring over a zonal belt including southern Europe, northern Africa and Turkey. Another finding is large 0–1 km wind shear values over the Arabian Sea and Somalia from June to September, related to the Somalia low-level jet. This region is notable considering the extreme SBCAPE values available at that time of the year together with these large wind-shear values. Seasonal and geographical distributions of the environments over Turkey are compatible with report-based severe weather climatologies of Turkey. The long-term variations in severe convective storm environments are worthy of future study.