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

Abstract

Tropospheric temperature inversions are thought to be an important feature of climate as well as a significant factor affecting air quality and low‐level cloud formation. The aim of this study is to investigate the temporal and spatial variability of the tropospheric temperature inversions, in particular so‐called elevated inversions, over Europe. The analysis is based on data gained from ERA‐Interim reanalysis for the period 1981–2015. The data consist of air temperature, and geopotential height from the entire vertical cross‐section of the troposphere, that is, from 1,000 to 100 hPa. The study examines the temporal (intra‐ and inter‐annual) variability of the temperature inversions based on their frequency, base height, depth, and strength. The analysis conducted revealed that the temperature inversions are a common phenomenon occurring in the lower troposphere. Their temporal and spatial variability is, however, determined by the inversion type. Surface‐based inversions (SBI) indicate a clear diurnal cycle, while the day–night variability of elevated inversions (EI) is far less pronounced. Two main regions of the most frequent EI occurrence may be distinguished. These are: (a) a marine area west of the Iberian Peninsula and (b) Eastern Europe. Both of them are located in areas which are under the influence of extensive high‐pressure systems—the permanent Azores High and semipermanent Siberian High, respectively. The development of EI should be therefore attributed to the large‐scale subsidence and adiabatic heating of air parcels. EI are also quite common over the other parts of the Atlantic Ocean, which is closely linked to the development of marine inversions. SBI tend to be stronger than EI—the mean seasonal inversion strength is usually substantially higher for SBI. In turn, EI reach higher values of the mean seasonal inversion depth as compared with SBI.

Low-tropospheric humidity inversions over Europe: spatiotemporal variability and relations to temperature inversions’ occurrence

“…On average, EHI develop at the highest altitude (Z B > 1,800 m AGL) in winter, spring, and autumn over extensive parts of the Atlantic Ocean, while at the lowest altitudes (Z B < 1,000 m AGL) in winter over Eastern Europe. Comparing to ETI, EHI tend to begin at higher altitudes (Palarz et al 2019), which is in line with previous studies carried out for the polar regions (Nygård et al 2013;Nygård et al 2014).…”

“…In the layer up to 5500 m AGL, in turn, a vast marine area located in the western part of the Mediterranean Sea and the eastern part of the Northeast Atlantic experiences the considerably higher frequency of EHI (FQ % > 50%) in summer, when the Azores High dominates the Atlantic Ocean reaching its greatest size and strength (not shown in this paper). This resembles broadly the spatiotemporal patterns of ETI described in our previous paper (Palarz et al 2019) and implies that the largescale subsidence and adiabatic heating of air parcels results not only in ETI development, but also enhances moisture condensation and consequently EHI formation.…”

“…The overarching aim of this study is, however, to access the mutual relations among HI and TI. This is closely related to the findings demonstrated in our previous work on the surface-based and elevated temperature inversions over Europe (Palarz et al 2018;Palarz et al 2019). The remainder of this paper is organized as follows: Section 2 gives a description of the data used and outlines the methods.…”

“…The humidity inversions were identified following the methodology applied in our previous studies on the low-tropospheric temperature inversions (Palarz et al 2018;Palarz et al 2019) enabling us to compare reliably the parameters of both inversion types. The definition of an inversion refers then to that reported in Kahl (1990), Wetzel and Brümmer (2011), Zhang et al (2011), and Gilson et al (2018.…”

“…Usually, above the pressure level of 400 hPa in winter and 300 hPa in summer, the amount of water vapour does not exceed 0.1 g kg −1 hence a reliable investigation of the humidity inversions may be limited there. Most of TI occurs, on the other hand, up to 700 hPa (Palarz et al 2019). Given the aim of this study, we decided therefore to restrict our analyses to inversions whose bases are located up to 3,000 m above ground level (AGL), which for low altitudes is comparable with the pressure level of 700 hPa.…”