Nocturnal temperature inversions with warm layer at low atmospheric levels:

significant thermal contrasts in the Segura river basin district (2011-2020)

Abstract

The southeast of the Iberian Peninsula (Spain) is characterized by a significant recurrence of nocturnal temperature inversion processes (ITN), mainly due to the large number of clear days throughout the year. The Segura River Basin District (DHS) has an altitude difference of 2100m in 150km with alternating valley areas and orographically complex and rugged areas. This gives rise to marked night-time thermal contrasts, whose vertical thermal differences are 13.0ºC between cold air pools (CAP) and uneven surfaces. Thermal contrasts are analysed through 58 meteorological observatories in the 50 mornings with the highest intensity of thermal inversion in the last years of observation (2011-2020). Furthermore, the characteristics and triggering causes of such processes are analysed through the analysis of variables influencing the distribution of minimum temperatures (wind, relative humidity, ...). In addition, a high-resolution satellite analysis technique is presented, through the elaboration of thermographies (distribution of surface temperatures) by means of the ASTER sensor, which complement, from the spatial point of view, the distribution of minimum temperatures in the early mornings of ITN in some sectors of the study area. Among the most conclusive results, notable thermal differences stand out during stable early mornings (mean differences of 7.1ºC and absolute differences of 13ºC between observatories located at valley bottoms (CAP) and those located at higher altitudes, in orographically rugged areas), recorded under masses warm and dry air at a geopotential level of 850hPa.