Impact of the Mediterranean oscillation on total lightning activity

Abstract

For the first time, the relationship between total (cloud-to-ground and intracloud) lightning activity and the Mediterranean Oscillation (MO) is addressed in this work. Data from optical transient detector (OTD) and lightning imaging sensor (LIS) were used to calculate the total flash density, and the MO was described using the Mediterranean Oscillation index (MOi). The study intended to analyse the monthly values of the variables, for the 19-year period from October 1995 to February 2015 and for the region between 31.25 N and 46.25 N, and between 3.75 W and 38.75 E (the Mediterranean Sea and bordering land areas). Moreover, the study was carried out for the whole year and a comparative analysis was also conducted with the results obtained for the cold periods (October to March) and warm periods (April to September), both for the positive and negative phases of the MOi. The results revealed that the lightning activity in the annual and cold periods was clearly similar, and the maximum values tended to concentrate over southern Italy and the central part of the Mediterranean Sea, while in the warm period lightning was scattered over the whole study area. When analysing the data from the cold period for the positive phase, significant negative correlations were observed in the west and central area. On the contrary, for the warm period, the significant negative correlation values tend to be concentrated in the eastern limit of the studied territory. During the negative phase of the MOi, most of the studied area showed significant positive correlation values during the cold period, whereas only a small area with negative correlation tended to concentrate on the eastern boundary during the warm period. The results are explained in terms of the circulation dynamics and temperature changes recorded for the MO.