Determination of atmospheric circulation patterns causing high temperatures in the South-East of France between June and September: case of the Côte d'Azur.

This article examines whether the atmospheric fields selected after correlation tests with observed temperature data can reproduce, through classification, the types of atmospheric circulations observed during the summer on the Côte d'Azur, especially those associated with heat waves. The robustness of this classification of the reanalysis fields needs to be verified by comparing it with a classification based on observed temperatures, specifically targeting synoptic classes that favor very hot days. These data were also used for historical analyzes in order to observe their evolution in the study area. Finally, using observations (temperature, specific and relative humidity) measured by the Nice Airport station, the aim was to identify trends for 73 years (1949–2021). The reanalysis variables (temperature and specific humidity at 850 hPa, geopotential height at 500 hPa and meridional component V at 850 hPa) retained via correlations realized with the observed temperatures proved effective in their representations of the atmospheric conditions in place during the summertime. It seems that over the temporal range considered, the number of days within the synoptic class relating to heat waves is increasing, and those in the synoptic class relating to temperatures evaluated as low for the season are decreasing. After producing climatic means (1950–2021) from which ten-year means were then deduced, it can be observed that the anomaly compared to the climatic mean for the temperature at 850 hPa, and the geopotential at 500 hPa is intensified over the last two decades (2000–2009 and 2010–2019). The specific humidity at 850 hPa remains stable, the percentage of relative humidity experiences a drop compared to the climatic average and this is observed from the 1980–1989 decade, continuing its slight decrease over the following ten-year means. Concerning the evolution for the Nice-Airport station, the temperature has increased significantly and it seems that this increase is accentuated at night, the specific humidity is stagnant, while the relative humidity is significantly decreasing. [ABSTRACT FROM AUTHOR]