Abstract
Abstract. This paper is the companion paper of Córdoba-Jabonero et al. (2021). It deals with the estimation of the long-wave (LW) and net dust direct radiative effect (DRE) during the dust episode that occurred between 23 and 30 June 2019 and was paired with a mega-heatwave. The analysis is performed at two European sites where polarized micro-pulse lidars ran continuously to retrieve the vertical distribution of the dust optical properties: Barcelona, Spain, 23–30 June, and Leipzig, Germany, 29–30 June. The radiative effect is computed with the GAME (global atmospheric model) radiative transfer model separately for the fine- and coarse-mode dust. The instantaneous and daily radiative effect and radiative efficiency (DREff) are provided for the fine-mode, coarse-mode and total dust at the surface, top of the atmosphere (TOA) and in the atmosphere. The fine-mode daily LW DRE is low (< 6 % of the short-wave (SW) component), which makes the coarse-mode LW DRE the main modulator of the total net dust DRE. The coarse-mode LW DRE starts exceeding (in absolute values) the SW component in the middle of the episode, which produces positive coarse-mode net DRE at both the surface and TOA. Such an unusual tendency is attributed to increasing coarse-mode size and surface temperature throughout the episode. This has the effect of reducing the SW cooling in Barcelona up to the point of reaching total net positive dust DRE (+0.9 W m−2) on one occasion at the surface and quasi-neutral (−0.6 W m−2) at TOA. When adding the LW component, the total dust SW radiative efficiency is reduced by a factor of 1.6 at both surface (on average over the episode the total dust net DREff is −54.1 W m−2 τ−1) and TOA (−37.3 W m−2 τ−1). A sensitivity study performed on the surface temperature and the air temperature in the dust layer, both linked to the heatwave and upon which the LW DRE strongly depends, shows that the heatwave contributed to reducing the dust net cooling effect at the surface and that it had nearly no effect at TOA. Its subsequent effect was thus to reduce the heating of the atmosphere produced by the dust particles.
Highlights
Without doubt, extreme air temperatures impact mortality (Basu and Samet, 2002), as well as mineral dust intrusions (Díaz et al, 2017)
The results are first discussed for the long-wave spectral range and for the whole spectral range in terms of dust direct radiative effect (Sect. 3.1.1) and in terms of radiative efficiency (Sect. 3.1.2), and a deeper analysis is performed at the BCN site (Sect. 3.2)
Instantaneous values are calculated from 05:00 to 19:00 UTC because GAME calculates short-wave and long-wave fluxes only during the hours of sunshine as it computes both components of the sun
Summary
Extreme air temperatures impact mortality (Basu and Samet, 2002), as well as mineral dust intrusions (Díaz et al, 2017). It deals with the estimation of the long-wave and net dust direct radiative effect during 23– 30 June 2019 This second part of the study is motivated by the high temperatures caused by the heatwave paired with the dust event. 3.2 presents a sensitivity study on the relationship between heatwave (by means of surface temperature and air temperature in the dust layer) and coarse-mode long-wave and total dust radiative effects. GAME outgoing (i.e., leaving the terrestrial atmosphere) long-wave radiation (OLR) was validated through comparison with CERES (Clouds and the Earth’s Radiant Energy System) OLR measurements in 11 cases of dust intrusion in Barcelona (Sicard et al, 2014a) Their results indicate a bias between simulated and measured OLR of −0.8 W m−2 and a root mean square error of 2.52 W m−2.
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