The intra-seasonal variation of the blocking index over the European domain during the analysed dry periods gave a clear sign of blocking over the Baltic region longitudinal belt 0–20 days before the dry period started. Also, these blocking patterns

were identified as being the strongest between dry periods attributed to other clusters (Figure 4b). The most extreme drought in the summer of 1992 had the strongest blocking signal, which was related to the more extended blocked circulation to the west, while other droughts were related only to regional, short-lived blocking episodes. Moreover, blocking tended to recur during the drought development phases of the three severe droughts analysed: 1994, 1996 and 2002 Dasatinib (Figure 5). If the first two composites correspond to weak AO circulation (a positive geopotential anomaly over the European Arctic), selleck chemical then the third one resembles a more intense zonal circulation over subpolar latitudes and is similar to a north-shifted NAO-like pattern. Actually, the periods involved in this cluster represent the most unstable development: transient synoptic scale waves cross the north-eastern Atlantic and northern Europe, while other cyclonic systems develop over southern Europe and the Mediterranean. So drought development

is initiated by transient ridges crossing Great Britain, southern Scandinavia and the Baltic Sea, while frontal activity

is shifted northwards from this track (Figure 4c). Composite analysis of the 500 hPa height anomalies for the dry periods shows a very diverse picture: from the weak gradient in the upper high pressure field to the weak cyclonic circulation over the southern Baltic region. The composite field of the persisting phase of the four longest dry episodes in Lithuania shows a very distinctive dipole pattern at the Interleukin-2 receptor 500 hPa level with a positive anomaly centre located over Scandinavia, and a negative centre (negative anomaly belt) over western Europe, the Mediterranean and the Balkans (Figure 6). This points to the generation of anticyclones over Scandinavia, which give rise to the persistent rainfall deficiency in Lithuania. Also, this pattern resembles the summer Scandinavian blocking high (Cassou et al. 2005) and the positive phase of the Scandinavia teleconnection pattern (Bueh & Nakamura 2007), which is less prominent in summer than in other seasons. An analysis of the Hess and Brezowski macro-circulation forms shows that dry periods are determined by a decrease in zonal and an increase in meridional circulation form patterns in Lithuania. This corresponds to other findings (Jaagus, 2006, Avotniece et al., 2010 and Kažys et al., 2011) in the eastern Baltic region.