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University of Nevada, Reno (2017)

Mechanisms of Interactions between Aerosol Physics and Atmospheric Dynamics

Hosseinpour, Farnaz

Titre : Mechanisms of Interactions between Aerosol Physics and Atmospheric Dynamics

Auteur : Hosseinpour, Farnaz

Université de soutenance : University of Nevada, Reno

Grade : Doctor of Philosophy (PhD) 2017

This study gained novel insights into mechanistic interactions of dust and smoke particles with large-scale climate dynamics. This study revealed that the variability Saharan dust radiative properties is significantly linked to high-frequency atmospheric wave activity across the tropical Atlantic storm tracks, while the variability of smoke particles from the South African biomass burning is attributed by low-frequency oscillations of baroclinic instability of the region. We proposed that the impacts of Saharan Air Layer (SAL) on large-scale climate dynamics mainly occur through coupling of dust radiative forcing with eddy energetics of the African easterly jet-African easterly waves (AEJ-AEWs) systems. This study quantified the thermal/mechanical impacts of oceanic SAL on activity of the AEWs and the regional feedback of eddies onto the mean-circulations from a climatological point of view. We found that both upstream and downstream developments of eddy energy are affected by oceanic SAL radiative forcing. It is suggested that dust radiative forcing has the capability to affect the transient changes in baroclinic instability of the jet-wave system through eddy available potential energy, and contribute in exchange of kinetic energy between the AEWs and AEJ through baroclinic and barotropic conversions. This study discussed that Saharan dust radiative properties have both constructive and destructive effects on behaviors of the AEWs, which depend on structure of the waves at different time-scale : the eddy kinetic energy (EKE) of the 2—6-day ultrahigh-frequency waves are amplified in average 1-day after enhancing of dust radiative forcing, while the EKE of the 6—11-day intermediate-frequency waves weakens during dust storm events. In addition, over the western African monsoon (WAM) region and the entrance of the tropical Atlantic storm track, the 2—6-day filtered AEWs become more barotropic during oceanic SAL outbreaks. The anomalous changes in meridional and quadruple momentum fluxes of 2—6-day filtered AEWs, associated with enhanced dust in the oceanic SAL, tend to an easterly feedback onto the southern edge of the mean-AEJ. However, at the middle- to exit region of the southern storm track, the anomalous convergent momentum fluxes of 2—6-day AEWs, associated with dust outbreak, tends to increase the regional baroclinic instability through the 3 main local energy packets, which may initiate a higher chance of hurricane activity. Applying ensemble of large NASA satellite observations data sets, such as MODIS, SeaWiFS and TRMM as well as GOCART aerosol model and MERRA reanalysis indicates that the suggested results are consistent regardless of the selected data sets. Overall, we proposed that the regional radiative properties of aerosols and thermal/mechanical activity of wave-jet systems are dynamically coupled and it is not suggested to consider either as a response to one another.

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