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Aristotle University of Thessaloniki (AUTH) 2017

Study of dust aerosol – climate interactions using a regional climate model

Tsikerdekis, Athanasios of Dimitrios

Titre : Study of dust aerosol – climate interactions using a regional climate model

Μελέτη των αλληλεπιδράσεων σωματιδίων σκόνης - κλίματος με τη χρήση ενός κλιματικού μοντέλου περιοχής

Auteur : Tsikerdekis, Athanasios of Dimitrios

Etablissement de soutenance : Aristotle University of Thessaloniki (AUTH)

Grade : Doctor of Philosophy (PhD) 2017

Résumé
This PhD dissertation investigates various dust-climate intertwined processes using a regional climate model (RegCM4) that includes a detailed online dust production-transport-deposition scheme. The evaluation of the model is conducted using numerous ground-based gridded observational, satellite-derived and re-analysis datasets such as LIVAS, CRU, ERA-interim, CERES, TRMM and CMSAF. In the first one an encyclopedic description of dust related processes (emission, transport, deposition) is given followed by an analytical description of the online dust scheme of RegCM4. The second chapter describes the observational and modeling datasets used. In the third chapter the sensitivity of dust bin size discretization in the regional climate model RegCM4 for the period 2007-2014 over the Sahara and the Mediterranean is investigated. Two discretization methods of the dust size distribution are applied, keeping the total mass constant : 1) the default RegCM4 4-bin approach, where the size range of each bin is calculated using an equal, logarithmic separation of the total size range of dust, using the diameter of dust particles and 2) a newly implemented 12-bin approach with each bin defined according to an isogradient method where the size ranges are dependent on the dry deposition velocity of dust particles. The new dust binning approach increases the dust column burden by 4% and 3% for fine and coarse particles respectively, which increases DOD by 10% over the desert and the Mediterranean. In the fourth chapter the westward Trans-Atlantic transport of dust from the Sahara towards the South and Central America is simulated using the regional climate model RegCM4 for the period December 2006 to November 2014. According to RegCM4 the total dust deposition for the examined 8 year period is 4.3±0.4 Tg•yr-1, 154.5±10.7 Tg•yr-1 and 10.3±0.6 Tg•yr-1 for the Amazon basin, the Atlantic ocean and the Caribbean respectively. Dry deposition is the dominant deposition process in the Atlantic accounting for 88.9% of the total deposition in contrast to Caribbean where wet deposition accounts for 85.4%. In the Amazon basin dry deposition takes up to 67.4% of total deposition. In the fifth chapter the radiative direct and semi-direct effect of dust is explored using the regional climate model RegCM4 over the Mediterranean, Sahara and Sahel. The simulations cover a historical decade which spans from 1999-01-01 to 2009-11-30 and a future decade that ranges from 2089-01-01 to 2099-11-30. The future atmospheric climate changes are driven by the Representative Concentration Pathway 4.5 (RCP4.5). The results for the historical period show that the direct RE of dust dominates in comparison to the semi-direct RE in both winter and summer, although during summer the semi-direct effect in the longwave spectrum accounts for almost 50% of total radiative effect over some parts of the desert. In the future period the dust concentration are spatially similar to the historical period but enhanced over the desert (+8%). When dust is radiatively active in a future climate simulation it can decrease the summer daily maximum temperature by 0.3°C over Sahel and increase it locally in eastern Sahara and western Sahel up to 0.2°C.

Mots clés : Aerosol dust ; Dust-climate interactions ; Regional climate model ; Climate change ; Aerosol size distribution ; Aerosol effects on solar radiation

Présentation (National Archives PhD)

Page publiée le 14 décembre 2022