摘要：Extreme weather and climate events have received increased attention in the last years due to
their impact on different aspects of human activity. The aim of the present paper is to bring to better
understanding of the causes of extreme precipitation occurrence in Bulgaria.
An extreme precipitation month is defined as a month registering precipitation totals lower or higher than
certain thresholds. Extremely wet months are defined as months with total precipitation amounts higher
than 90% percentiles of the gamma distribution in the reference period 1961-1990. As extremely dry
month, we consider the month with total precipitation lower than 10% of the gamma distribution. Spatial
changes in the occurrence of extreme precipitation are investigated by the application of the cluster
analysis.
The circulation patterns were analyzed with regard to sea level pressure. The relation between the
fluctuations of the extreme months and atmospheric circulation mechanism teleconnection is study by the
North Atlantic Oscillation Indices (NAOI), the Eastern Atlantic pattern (EA) and the Mediterranean
Oscillation Indices (MOI).
关键词：Extremely wet month; Extremely dry month; the North Atlantic Oscillation; the
Mediterranean Oscillation Indices
