The spatio-temporal distribution of lightning over Israel and the neighboring area and its relation to regional synoptic systems

Abstract

Abstract. The spatio-temporal distribution of lightning flashes over Israel and the neighboring area and its relation to the regional synoptic systems has been studied, based on data obtained from the Israel Lightning Location System (ILLS) operated by the Israel Electric Corporation (IEC). The system detects cloud-to-ground lightning discharges in a range of ∼500 km around central Israel (32.5 • N, 35 • E). The study period was defined for annual activity from August through July, for 5 seasons in the period [2004][2005][2006][2007][2008][2009][2010].The spatial distribution of lightning flash density indicates the highest concentration over the Mediterranean Sea, attributed to the contribution of moisture as well as sensible and latent heat fluxes from the sea surface. Other centers of high density appear along the coastal plain, orographic barriers, especially in northern Israel, and downwind from the metropolitan area of Tel Aviv, Israel. The intra-annual distribution shows an absence of lightning during the summer months (JJA) due to the persistent subsidence over the region. The vast majority of lightning activity occurs during 7 months, October to April. Although over 65 % of the rainfall in Israel is obtained during the winter months (DJF), only 35 % of lightning flashes occur in these months. October is the richest month, with 40 % of total annual flashes. This is attributed both to tropical intrusions, i.e., Red Sea Troughs (RST), which are characterized by intense static instability and convection, and to Cyprus Lows (CLs) arriving from the west.Based on daily study of the spatial distribution of lightning, three patterns have been defined; "land", "maritime" and "hybrid". CLs cause high flash density over the Mediterranean Sea, whereas some of the RST days are typified by flashes over land. The pattern defined "hybrid" is a combination of the other 2 patterns. On CL days, only the maritime Correspondence to: S. Shalev (sigalit.shalev.1@gmail.com) pattern was noted, whereas in RST days all 3 patterns were found, including the maritime pattern. It is suggested that atmospheric processes associated with RST produce the land pattern. Hence, the occurrence of a maritime pattern in days identified as RST reflects an "apparent RST". The hybrid pattern was associated with an RST located east of Israel. This synoptic type produced the typical flash maximum over the land, but the upper-level trough together with the onshore winds it induced over the eastern coast of the Mediterranean resulted in lightning activity over the sea as well, similar to that of CLs.It is suggested that the spatial distribution patterns of lightning may better identify the synoptic system responsible, a CL, an "active RST" or an "apparent RST". The electrical activity thus serves as a "fingerprint" for the synoptic situation responsible for its generation.

Lightning flash multiplicity in eastern Mediterranean thunderstorms

“…The total area investigated in the present research covers Israel and its neighboring region and is ∼ 500 000 km 2 , of which 40 % are over the Mediterranean Sea. The spatio-temporal distribution of lightning over Israel and the neighboring area and a detailed description of the research methodology are described in Shalev et al (2011).…”

Lightning characteristics over the eastern coast of the Mediterranean during different synoptic systems

“…The low-level low is accompanied by an upper level trough that transports cold air into the region. According to Shalev et al (2011) who analyzed lightning activity over the region, more than 71 % of wintertime lightning flashes and 41 % of fall ones occur under this synoptic system. While transported over the Mediterranean, the cold continental air mass is destabilized and its moisture content increases due to the interaction with the warm sea.…”

“…Under such conditions, thunderclouds generally develop over the south and eastern part of the EM, exhibiting relatively high cloud bases, ∼ 2-3 km above sea level. These conditions occur mainly in fall months (October-November), and are associated with ∼ 43 % of the flashes at this time of the year (Shalev et al, 2011). In some cases the RST system extends towards the Mediterranean Sea and forms a close low over the sea, in a complex hybrid situation.…”

“…Altaratz et al (2003) and Shalev et al (2011) surveyed the climatology of ground lightning flashes over a period of several years using data from the national Israel Lightning Location System (ILLS). Altaratz et al (2003) investigated lightning characteristics over land versus over the sea, while Shalev et al (2011) discussed the link between the temporal-spatial properties of lightning strokes and the synoptic conditions. They proposed that spatial patterns of lightning strokes can be used as a proxy for the prevailing synoptic condition.…”

Sprite possibly produced by two distinct positive cloud-to-ground lightning flashes

“…The distance algorithm usually used for combining return strokes into one flash is 10 km (Rakov and Uman 2003;Van der Velde et al 2007). Some researchers also used 1 km (Shalev et al 2011). The two positive return strokes (labeled with CG1 and CG2 in Fig.…”