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The atmospheric circulation patterns during dry periods in Lithuania

Rimkus E., Kažys J., Valiukas D., Stankunavičius G.

Oceanologia

2014

No. 56 (2)

223--239

This paper reveals the atmospheric circulation patterns during dry periods in Lithuania.~The research covers the period from 1961 to 2010. Atmospheric circulation features were analysed using the Hess and Brezowski classification of macro-circulation forms, NAO and AO indices, a 500 hPa geopotential height field and the Tibaldi-Molteni blocking index. Different phases of the dry period (developing, persisting and attenuation) were evaluated individually. Also, the regional differences of dry period formation were investigated. In general dry periods are determined by a decrease in zonal and an increase in meridional circulation forms as well as the atmospheric blocking process over the Baltic region longitudinal belt 0-20 days prior to the start of the dry period. An especially strong shift from general circulation patterns are observed during the developing phase of a dry period. Drought persistence in the Baltic region is almost always predetermined by strong anticyclonic circulation. Most drought development stages are associated with negative NAO/AO phases.

Temporal variation of extreme precipitation events in Lithuania

Rimkus E., Kažys J., Bukantis A., Krotovas A.

Oceanologia

2011

No. 53 (1-TI)

259-277

Heavy precipitation events in Lithuania for the period 1961-2008 were analysed. The spatial distribution and dynamics of precipitation extremes were investigated. Positive tendencies and in some cases statistically significant trends were determined for the whole of Lithuania. Atmospheric circulation processes were derived using Hess & Brezowski's classification of macrocirculation forms. More than one third of heavy precipitation events (37%) were observed when the atmospheric circulation was zonal. The location of the central part of a cyclone (WZ weather condition subtype) over Lithuania is the most common synoptic situation (27%) during heavy precipitation events. Climatic projections according to outputs of the CCLM model are also presented in this research. The analysis shows that the recurrence of heavy precipitation events in the 21st century will increase significantly (by up to 22%) in Lithuania.