Is the Indian Summer Present in Romania?

Abstract

The first part of the study refers to the occurrence of the Indian summer events in Romania, over the 1961-2019 period. The second part analyses the Indian summer event recorded in Romania in October 2019. The datasets used for the first part were daily maximum and minimum temperatures recorded in the past 59 years at 23 climatological weather stations, divided into 6 regions. Regarding the methodology, first step was to determine the annual and seasonal occurrence of the first frost for each weather station, and then the presence of the warm spells (WSs), based on the percentile threshold method. So, we could determine WSs with different types of intensity (using the 90th, 95th, 98th percentile), and durations. For the Indian summer event recorded between 12 and 28 October 2019, daily maximum temperatures from 157 weather stations were compared to absolute maximum temperatures over the period 1961-2018. Synoptic conditions were determined using weather charts at sea level pressure, geopotential height and temperature of 925, 850, 700 and 500 hPa. The main finding is: Indian summer events are frequent in the Carpathians and in the Northern, Central and the Western regions of Romania, especially in November, followed by October; no matter the intensity, short duration events have high number of cases, and severe and extremely severe events were registered in the past 20 years; the Indian summer event from October 2019 was influenced by synoptic and local conditions, as well. Overall the Indian summer is not present in Romania every year, but it is more frequent and intense in the last 20 years.

Keywords

• indian summer
• warm spell
• percentile
• regions
• romania