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Start date: 2020 × Subject: Lagrangian analysis ×

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Now showing 1 - 2 of 2
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    Particle hygroscopicity during atmospheric new particle formation events: Implications for the chemical species contributing to particle growth
    (Göttingen : Copernicus, 2013) Wu, Z.; Birmili, W.; Poulain, L.; Poulain, L.; Merkel, M.; Fahlbusch, B.; Van Pinxteren, D.; Herrmann, H.; Wiedensohler, A.
    This study examines the hygroscopicity of newly formed particles (diameters range 25-45 nm) during two atmospheric new particle formation (NPF) events in the German mid-level mountains during the Hill Cap Cloud Thuringia 2010 (HCCT-2010) field experiment. At the end of the NPF event involving clear particle growth, we measured an unusually high soluble particle fraction of 58.5% at 45 nm particle size. The particle growth rate contributed through sulfuric acid condensation only accounts for around 6.5% of the observed growth rate. Estimations showed that sulfuric acid condensation explained, however, only around 10% of that soluble particle fraction. Therefore, the formation of additional water-soluble matter appears imperative to explain the missing soluble fraction. Although direct evidence is missing, we consider water-soluble organics as candidates for this mechanism. For the case with clear growth process, the particle growth rate was determined by two alternative methods based on tracking the mode diameter of the nucleation mode. The mean particle growth rate obtained from the inter-site data comparison using Lagrangian consideration is 3.8 (± 2.6) nm h-1. During the same period, the growth rate calculated based on one site data is 5.0 nm h-1 using log-normal distribution function method. In light of the fact that considerable uncertainties could be involved in both methods, we consider both estimated growth rates consistent.
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    The Lagrangian structure of ozone mini-holes and potential vorticity anomalies in the Northern Hemisphere
    (Göttingen : Copernicus GmbH, 2002) James, P.M.; Peters, D.
    An ozone mini-hole is a synoptic-scale area of strongly reduced column total ozone, which undergoes a growth-decay cycle in association with baroclinic weather systems. The tracks of mini-hole events recorded during the TOMS observation period over the Northern Hemisphere provide a database for building anomaly fields of various meteorological parameters, following each mini-hole center in a Lagrangian sense. The resulting fields provide, for the first time, a complete mean Lagrangian picture of the three-dimensional structure of typical ozone mini-holes in the Northern Hemisphere. Mini-holes are shown to be associated with anomalous warm anticyclonic flow in the upper troposphere and cold cyclonic anomalies in the middle stratosphere. Ascending air columns occur upstream and descent downstream of the mini-hole centers. Band-pass filtering is used to reveal the transient synoptic nature of mini-holes embedded within larger scale circulation anomalies. Significant correlations between ozone and Ertel's potential vorticity on isentropes (IPV) both near the tropopause and in the middle stratosphere are shown and then utilized by reconstructing the Lagrangian analysis to follow local IPV anomalies instead of ozone minima. By using IPV as a proxy for ozone, the geopotential anomaly dipolar structure in the vertical characteristics of mini-holes is shown to result from a superposition of two largely independent dynamical components, stratospheric and tropospheric, typically operating on different time scales. Hence, ozone mini-holes may be viewed primarily as phenomena of coincidence.