Synoptic Conditions Generating Heat Waves and Warm Spells in Romania

Lucian Sfîcă,Iulian Iordache,Antoniu-Flavius Ciupertea,Adina-Eliza Croitoru

doi:10.3390/atmos8030050

Lucian Sfîcă, Iulian Iordache + Show 2 more

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https://doi.org/10.3390/atmos8030050

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Abstract

Heat waves and warm spells are extreme meteorological events that generate a significant number of casualties in temperate regions, as well as outside of temperate regions. For the purpose of this paper, heat waves and warm spells were identified based on daily maximum temperatures recorded at 27 weather stations located in Romania over a 55-year period (1961–2015). The intensity threshold was the 90th percentile, and the length of an event was of minimum three consecutive days. We analyzed 111 heat wave and warm spell events totaling 423 days. The classification of synoptic conditions was based on daily reanalysis at three geopotential levels and on the online version of a backward trajectories model. The main findings are that there are two major types of genetic conditions. These were identified as: (i) radiative heat waves and warm spells (type A) generated by warming the air mass due to high amounts of radiation which was found dominant in warm season; and (ii) advective heat waves and warm spells (type B) generated mainly by warm air mass advection which prevails in winter and transition seasons. These major types consist of two and three sub-types, respectively. The results could become a useful tool for weather forecasters in order to better predict the occurrence of heat waves and warm spells.

Highlights

Extreme high temperatures and related events such as heat waves (HWs) and warm spells (WSs) have been largely documented to show that they have increased in magnitude and frequency over the last few decades in most regions of the planet [1,2,3,4,5,6,7,8,9,10,11,12,13]
The synoptic conditions for HWs/WSs occurrence in Romania resulting from our analysis, can be divided into two major types: (i) Radiative–advective HWs/WSs, for which radiative forcing plays the leading role in the occurrence of high temperature
We bring a large scale perspective to the HWs/WSs occurrence conditions in Romania, but these results can be useful for some neighboring regions

Summary

Introduction

Extreme high temperatures and related events such as heat waves (HWs) and warm spells (WSs) have been largely documented to show that they have increased in magnitude and frequency over the last few decades in most regions of the planet [1,2,3,4,5,6,7,8,9,10,11,12,13]. When a relative threshold is used to define extreme high temperature events over the year, HWs term is employed for summer, late spring, and early winter events (May–September), while WS term is frequently used for winter, late autumn, and early spring events (October–April). They have become a very important issue as they imply a significant threat to life and property in times of accelerated population growth and climate change [14]. The August 2003 HW alone is considered as the worst natural disaster in Europe of the last 50 years, with an estimated death toll exceeding 30,000 people [14,27], followed by other similar events such as in July 2007 with great impact on Southeastern Europe and in July 2010 bringing a historical HW in Eastern Europe [28]

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