Temporal structure of thermal inversions in Łeba (Poland)

Abstract

This study presents the detailed characteristics of thermal inversions based on a 10-year aerological measurement series (2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014) conducted in Łeba (Poland). The analyses included surface-based inversions (SBIs) and elevated inversions (ELIs) in the atmospheric layer up to 3000 m. In the case of SBIs, this layer extended directly from the ground level to an altitude above which the air temperature decreases with altitude, whereas for ELIs, which have a base above ground level, only the lowermost inversion layer was taken into consideration. The results of the monthly and seasonal variations in the selected parameters for air temperature inversions (thickness-ΔZ, strength-ΔT, base-Z B ) were analysed separately at night-time (00 UTC) and daytime (12 UTC). The thermal structure of the boundary layer up to 3000 m was primarily determined by ELIs, which occurred at a frequency of approximately 70% at both times during the 24-h period. The SBIs showed a pronounced temporal structure that occurred every second night throughout the year and from April to September, with a frequency similar to that of the ELI (approximately 60%). The worst vertical air exchange conditions, which resulted from the simultaneous occurrence of SBIs and ELIs, were found in 30% of nights from April to October. Elevated inversions generally formed in a layer from approximately 820 to 1200 m, which was the lowermost ELI in winter and the highest ELI in summer; however, in all seasons, the lowest base height was characteristic of daytime inversions. Both surface-based and elevated inversion layers were distinguished by comparable thicknesses, particularly for those occurring at night-time (generally within the range of 150-200 m). From November to March, greater thicknesses were identified in ELIs with lower occurrences, whereas SBIs were identified in the remaining months of the year.

Temporal and spatial variability of elevated inversions over Europe based on ERA‐Interim reanalysis

“…() and Czarnecka et al . () indicated similar temporal variations in the inversion depth and strength as well as EI base height. Also, Joly and Richard () concluded that their results obtained on the basis of the observational data for the Jura Mountains are consistent with those obtained in our previous studies on SBI parameters (Palarz et al ., ).…”

“…On the macro‐scale, the variations identified for EI frequency are generally not accompanied by changes in other EI parameters. This does not preclude, however, the validity of the trends observed on a more local scale (Stryhal et al ., ; Czarnecka et al ., ). For example, Stryhal et al .…”

“…Although most of the low‐level temperature inversions form in the layer up to 800 hPa, considering the previous studies carried out by among others Wetzel and Brümmer () and Czarnecka et al . (), we decided to restrict the four analysis of the low‐level EI to those temperature inversions whose bases lay up to 3,000 m AGL, which for low altitudes is comparable with the pressure level of 700 hPa. Since our research indicated that fewer than 2.5% of the temperature inversions have bases located between 2,000 and 3,000 m AGL, we assume that the results obtained can be also compared with the findings of Stryhal et al .…”

“…Note that EI parameters were calculated solely for the lower‐most inversion layer, what is consistent with the previous studies carried out by among others Czarnecka et al . ().…”

“…(), for Hamburg by Brümmer and Schultze (), for Łeba by Czarnecka et al . (), for Prague by Stryhal et al . (), and for Moscow by Lokoshchenko ().…”