Influence of sea salt aerosols on the development of Mediterranean tropical-like cyclones

Medicanes are mesoscale tropical-like cyclones that develop in the Mediterranean basin and represent a great hazard for the coastal population. The skill to accurately simulate them is of utmost importance to prevent economical and personal damage. Medicanes are fueled by the latent heat released in the condensation process associated with convective activity, which is regulated by the presence and activation of cloud condensation nuclei, mainly originating from sea salt aerosols (SSAs) for marine environments. Henceforth, the purpose of this contribution is twofold: assessing the effects of an interactive calculation of SSA on the strengthening and persistence of medicanes, and providing insight into the casuistry and sensitivities around their simulation processes. To this end, a set of simulations have been conducted with a chemistry–meteorology coupled model considering prescribed aerosol (PA) and interactive aerosol (IA) concentrations. The results indicate that IA produces longer-lasting and more intense medicanes. Further, the role of the initialization time and nudging strategies for medicane simulations has been explored. Overall, the results suggest that (1) the application of spectral nudging dampens the effects of IA, (2) the initialization time introduces a strong variability in the storm dynamics, and (3) wind–SSA feedback is crucial and should be considered when studying medicanes.

Bark Effects on Stemflow Chemistry in a Japanese Temperate Forest I. The Role of Bark Surface Morphology

Stemflow can be an important pathway for the drainage of precipitation and related solutes through tree canopies to forest soils. As stemflow must drain along bark surfaces, the effects of bark structure on stemflow chemical composition is merited. This study examines the relationship between stemflow chemistry and bark surface structure for six species of varying bark morphology (four deciduous broadleaf trees and two evergreen coniferous trees) at a montane and an urban site in Japan. Stemflow from smooth-barked species contained greater concentrations of solutes that appear to be rinsed from the stem surface (i.e., sea salt aerosols); while, rougher-barked tree species contained greater or less concentrations of solutes that appear to be leached (e.g., Ca2+) or taken-up (e.g., inorganic N) by the bark, respectively. Site-specific atmospheric environments also influenced thee bark-stemflow chemistry relationships—where the greater elemental deposition in the urban plot generally resulted in greater stemflow chemistry than observed in the lower-deposition montane plot. Our results therefore suggest that the dynamics of dry deposition wash-off by stemflow, and the exchange of dissolved solutes between stemflow and the bark surface, are influenced by the surface structure of the bark and the site’s atmospheric environment. Therefore, the interactions between bark surface structure and its surrounding atmospheric environment are important factors in the stemflow-related elemental cycling between the tree and precipitation.

Influence of sea salt aerosols on the development of Mediterranean tropical-like cyclones

Medicanes are mesoscale tropical-like cyclones that develop in the Mediterranean basin and represent a great hazard for the coastal population. The skill to accurately simulate them is of utmost importance to prevent economical and personal damages. Medicanes are fuelled by the latent heat released in the condensation process associated to convective activity, which is regulated by the presence and activation of cloud condensation nuclei, originated mainly from sea salt aerosols (SSA) for marine environments. Henceforth, the purpose of this contribution is twofold: assessing the effects of an interactive calculation of SSA on the strengthening and persistence of medicanes; and providing insight on the casuistry and sensitivities around their simulation processes. To this end, a set of simulations has been conducted with a chemistry/meteorology coupled model considering prescribed aerosols (PA) and interactive aerosol concentrations (IA). The results indicate that IA produces longer-lasting and more intense medicanes. Further, the role of the initialization time and nudging strategies for medicane simulations has been explored. Overall, the results suggest that (1) the application of spectral nudging dampens the effects of IA; (2) the initialization time introduces a strong variability on the storm dynamics; and (3) wind-SSA feedback is crucial and should be considered when studying medicanes.

Impact of the particle mixing state on the hygroscopicity of internally mixed sodium chloride-ammonium sulfate single droplets: A theoretical and experimental study

Sodium chloride (NaCl) is the main constituent of sea-salt aerosols. During atmospheric transport, sea-salt aerosols can interact with gases and other particles including secondary aerosols containing ammonium sulfate ((NH4)2SO4). This...