Publications

Export 2 results:
Sort by: Author Title Type [ Year  (Desc)]
2018
Calmer, R, Roberts GC, Preissler J, Sanchez KJ, Derrien S, O'Dowd C.  2018.  Vertical wind velocity measurements using a five-hole probe with remotely piloted aircraft to study aerosol-cloud interactions. Atmospheric Measurement Techniques. 11:2583-2599.   10.5194/amt-11-2583-2018   AbstractWebsite

The importance of vertical wind velocities (in particular positive vertical wind velocities or updrafts) in atmospheric science has motivated the need to deploy multi-hole probes developed for manned aircraft in small remotely piloted aircraft (RPA). In atmospheric research, lightweight RPAs ( < 2.5 kg) are now able to accurately measure atmospheric wind vectors, even in a cloud, which provides essential observing tools for understanding aerosol-cloud interactions. The European project BACCHUS (impact of Biogenic versus Anthropogenic emissions on Clouds and Climate: towards a Holistic UnderStanding) focuses on these specific interactions. In particular, vertical wind velocity at cloud base is a key parameter for studying aerosol-cloud interactions. To measure the three components of wind, a RPA is equipped with a five-hole probe, pressure sensors, and an inertial navigation system (INS). The five-hole probe is calibrated on a multi-axis platform, and the probe-INS system is validated in a wind tunnel. Once mounted on a RPA, power spectral density (PSD) functions and turbulent kinetic energy (TKE) derived from the five-hole probe are compared with sonic anemometers on a meteorological mast. During a BACCHUS field campaign at Mace Head Atmospheric Research Station (Ireland), a fleet of RPAs was deployed to profile the atmosphere and complement ground-based and satellite observations of physical and chemical properties of aerosols, clouds, and meteorological state parameters. The five-hole probe was flown on straight-and-level legs to measure vertical wind velocities within clouds. The vertical velocity measurements from the RPA are validated with vertical velocities derived from a ground-based cloud radar by showing that both measurements yield model-simulated cloud droplet number concentrations within 10 %. The updraft velocity distributions illustrate distinct relationships between vertical cloud fields in different meteorological conditions.

2008
Furutani, H, Dall'osto M, Roberts GC, Prather KA.  2008.  Assessment of the relative importance of atmospheric aging on CCN activity derived from field observations. Atmospheric Environment. 42:3130-3142.   10.1016/j.atmosenv.2007.09.024   AbstractWebsite

The effect of atmospheric aging on the cloud condensation nuclei (CCN) activity of atmospheric aerosols was studied by comparing different air masses with different degrees of aging along the southern coast of California over the Pacific Ocean during a research cruise on the R/V Roger Revelle from 2-19 November 2004. Activation diameters (D(act)) were calculated using the measured CCN concentrations, condensation nuclei (CN) concentrations, and particle size distributions. Measurements of single particle size and chemistry, as well as black carbon (BC) concentrations with an aethalometer, were made to provide further insight into aerosol chemistry. A gradient of aerosol concentrations was encountered: along the coast of California, the highest BC and CN concentrations (1000-6000 ng m(-3) and 2000-15,000 cm(-3)) were measured which decreased as the ship moved away from shore to much lower values (<100 ng m(-3), similar to 300 cm(-3)). In all regions, external mixtures of organic carbon, elemental carbon, sea salt, and dust aerosols frequently associated with nitrate and sulfate were observed. A correlation plot between the CCN/CN ratio and D(act) exhibits a clear linear correlation, showing a distinct relationship between the extent of anthropogenic aging and CCN activity with the most highly aged air masses showing the highest CCN activity and smallest D(act). These results show changes in aerosol chemistry due to atmospheric aging that play an important role in determining the CCN activity of atmospheric aerosols. The present study demonstrates that variations in aerosol chemistry must be taken into account in models to adequately account for the physicochemical properties of atmospheric aerosols and their CCN activity. (C) 2007 Published by Elsevier Ltd.