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- ItemObservation of a Self-Limiting, Shear-Induced Turbulent Inversion Layer Above Marine Stratocumulus(Dordrecht [u.a.] : Springer, 2012) Katzwinkel, J.; Siebert, H.; Shaw, R.A.High-resolution measurements of thermodynamic, microphysical, and turbulence properties inside a turbulent inversion layer above a marine stratocumulus cloud layer are presented. The measurements are performed with the helicopter-towed measurement payload Airborne Cloud Turbulence Observation System (ACTOS), which allows for sampling with low true air speeds and steep profiles through cloud top. Vertical profiles show that the turbulent inversion layer consists of clear air above the cloud top, with nearly linear profiles of potential temperature, horizontal wind speed, absolute humidity, and concentration of interstitial aerosol. The layer is turbulent, with an energy dissipation rate nearly the same as that in the lower cloud, suggesting that the two are actively coupled, but with significant anisotropic turbulence at the large scales within the turbulent inversion layer. The turbulent inversion layer is traversed six times and the layer thickness is observed to vary between 37 and 85 m, whereas the potential temperature and horizontal wind speed differences at the top and bottom of the layer remain essentially constant. The Richardson number therefore increases with increasing layer thickness, from approximately 0. 2 to 0. 7, suggesting that the layer develops to the point where shear production of turbulence is sufficiently weak to be balanced by buoyancy suppression. This picture is consistent with prior numerical simulations of the evolution of turbulence in localized stratified shear layers. It is observed that the large eddy scale is suppressed by buoyancy and is on the order of the Ozmidov scale, much less than the thickness of the turbulent inversion layer, such that direct mixing between the cloud top and the free troposphere is inhibited, and the entrainment velocity tends to decrease with increasing turbulent inversion-layer thickness. Qualitatively, the turbulent inversion layer likely grows through nibbling rather than engulfment.
- ItemChemical composition of cloud water in the puerto rican tropical trade wind cumuli(Dordrecht : Springer, 2009) Gioda, A.; Mayol-Bracero, O.L.; Morales-García, F.; Collett, J.; Decesari, S.; Emblico, L.; Facchini, M.C.; Morales-De Jesús, R.J.; Mertes, S.; Borrmann, S.; Walter, S.; Schneider, J.As part of the Rain In Cumulus over the Ocean Experiment (RICO) and the Puerto Rico Aerosol and Cloud Study (PRACS), cloud water was collected at East Peak (EP) in Puerto Rico. The main objective of this study was to determine the concentrations of water-soluble species (Cl-, NO3 -, SO4 2-, NH4 +, Ca 2+, H+, Mg2+, K+, and Na +) in water samples taken from clouds influenced by tropical trade winds. The most abundant inorganic species were Na+ (average 465 μeq l-1) and Cl- (434 μeq l-1), followed by Mg2+ (105 μeq l-1), SO4 2- (61 μeq l-1), and NO3 - (25 μeq l -1). High concentrations of nss-SO4 2 (28 μeq l-1), NO3 - (86 μeq l-1), and H+ (14.5 μeq l-1) were measured with a shift in air masses origin from the North Atlantic to North American continent, which reflected a strong anthropogenic influence on cloud chemistry at EP. Long-range transport of particles and acid gases seems to be the factor responsible for fluctuations in concentrations and pH of cloud water at East Peak. When under trade wind influences the liquid phase concentrations of all inorganic substances were similar to those found in clouds in other clean maritime environments. © 2008 Springer Science+Business Media B.V.