Auflistung nach Autor:in "Colbeck, Ian"

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Condensation nuclei (CN) and ultrafine CN in the free troposphere to 12 km. A case study over the Jungfraujoch High‐Alpine research station
(Wiley, 15.09.1999) Nyeki, Stephan; Kalberer, Markus; Lugauer, Matthias; Weingartner, Ernest; Petzold, Andreas; Schröder, Franz; Colbeck, Ian; Baltensperger, Urs
Condensation nuclei (CN) were measured in the free troposphere (FT) above the Jungfraujoch (JFJ) high-alpine research station (3454 m; Switzerland) from 4.5 to 12 km asl in a case study on July 30, 1997. Vertical profiles of CN concentration for d ≥ 5 nm (N≥5), d ≥ 15 nm (N≥15 15) were measured, and indicated that ultrafine CN (UCN; 5 ≤ d ≤ 15 nm; N5-15) exhibited a distinct increase with altitude. Some evidence for near-constant values of d(logCN)/dz within discrete layers was found, which generally coincided with different airmasses as delineated by changes in the lapse rate dθ/dz at ∼ 5.5, 6.4, 9.0 and 10.6 km asl. In addition, CN concentration was mapped over a 40 × 75 km horizontal domain at 8.0 km asl centered above the JFJ. A pronounced variation in N≥5,N≥15 and specific humidity, but not in UCN, exhibited quasi-stationary 2-D features and was attributed to the chance encounter of a mountain wave. The case study provides further evidence that the upper FT may be a source of new particles.
01A - Beitrag in wissenschaftlicher Zeitschrift
Convective boundary layer evolution to 4 km asl over High‐alpine terrain. Airborne lidar observations in the Alps
(Wiley, 01.03.2000) Nyeki, Stephan; Kalberer, Markus; Colbeck, Ian; De Wekker, Stephan; Furger, Markus; Gäggeler, Heinz W.; Koßmann, Meinolf; Lugauer, Matthias; Steyn, Douw; Weingartner, Ernest; Wirth, Martin; Baltensperger, Urs
Mountain ranges have important influences on the structure and composition of the convective boundary layer (CBL) and free troposphere (FT). Evolution of the summer CBL, measured over the European Alps using airborne lidar, was clearly observed to attain a near-uniform height up to 4.2 km asl by early afternoon. A climatology of in-situ high-alpine aerosol measurements suggests that such substantial growth, corresponding to ∼ 0.3 of the mid-latitude tropopause height, often occurs during summer months. Subsequent nocturnal collapse of the CBL was estimated to result in the venting of ∼ 0.8 ± 0.3 (SO4 4) Gg/day into a FT residual layer, leeward of the Alps.
01A - Beitrag in wissenschaftlicher Zeitschrift
The background aerosol size distribution in the free troposphere. An analysis of the annual cycle at a high‐alpine site
(Wiley, 01.12.1998) Nyeki, Stephan; Li, F.; Weingartner, Ernest; Streit, Niklaus; Colbeck, Ian; Gäggeler, Heinz W.; Baltensperger, Urs
Measurements during free tropospheric (FT) and planetary boundary layer (PBL) conditions were conducted over an annual cycle at the Jungfraujoch high-Alpine research station (3454 m), Switzerland, in order to establish diurnal and seasonal cycles of the background continental aerosol over central Europe. Using a condensation nucleus counter (TSI 3025) and an optical particle counter (PMS Las-X) from June 1996 to May 1997, the following were determined: (1) accumulation mode lognormal parameters and (2) number concentrations for the nucleation (diameter d < 0.1 μm), accumulation (0.1 ≤ d ≤ 1.0 μm), and part of the coarse (1.0 < d ≤ 7.5 μm, designated “coarse”) modes. Lognormal parameters were found to be similar for FT and PBL conditions, and exhibited a weak seasonality in geometric median diameter dGN =0.13 and 0.10 μm, and standard deviation σG = 1.73 and 1.64 for summer and winter, respectively. Aerosol number concentrations in each mode exhibited a more pronounced seasonality, with FT concentrations being lower than those for PBL. Summer and winter FT median concentrations for the nucleation, accumulation, and “coarse” modes were 405 and 195 cmˉ³, 114 and 26 cmˉ³, and 0.052 and 0.014 cmˉ³, respectively. These results provide tentative support of other long-term observations that the FT background aerosol mode appears to vary mainly in concentration rather than accumulation mode shape. Further analysis indicated that only the total concentration in each mode varied with weather type and a classification between that of a remote continental and polar aerosol model was found for the Jungfraujoch.
01A - Beitrag in wissenschaftlicher Zeitschrift
The Jungfraujoch high‐alpine research station (3454 m) as a background clean continental site for the measurement of aerosol parameters
(Wiley, 01.03.1998) Nyeki, Stephan; Baltensperger, Urs; Colbeck, Ian; Jost, Dieter T.; Weingartner, Ernest; Gäggeler, Heinz W.
The first annual data set of climatically important aerosol parameters, measured at the Jungfraujoch (JFJ) high-alpine research station (3454 m, Switzerland) from an ongoing field campaign since July 1995, is presented. Analysis of diurnal variations in continuous measurements of the total and backward hemispheric scattering coefficients (σSP, σBSP), the absorption coefficient (σAP, from aethalometer data), condensation nuclei (CN) concentration, and epiphaniometer signal (related to surface area (S) concentration) established the diurnal period 0300 – 0900 as being representative of the free tropospheric background aerosol. The annual data set was then edited to omit (1) the period 0900–0300 (i.e., 18 hours), taken to represent possible planetary boundary layer influenced conditions and (2) in-cloud conditions using a cloud liquid-water monitor. The seasonal aerosol cycle exhibited a July maximum and a December minimum in most aerosol parameters. Typical monthly median values for the free troposphere exhibit the following seasonal maxima and minima, respectively: σSP (550 nm) ∼ 16.1 and 0.43 × 10ˉ⁶/m, σBSP (550 nm) ∼ 2.10 and 0.09 × 10ˉ⁶/m, σAP (550 nm) ∼ 10.4 and 0.76 × 10ˉ⁷/m (≈ 104 and 7.6 ng mˉ³ black carbon), CN concentration ∼ 670 and 280 cmˉ³, and epiphaniometer signal ∼ 9.26 and 0.67 counts/s (S concentration ≈24.1 and 1.7 μm2 cmˉ³). Aerosol parameters were found to be comparable in magnitude to other NOAA baseline and regional stations and suggest that a clean continental designation for the JFJ site is applicable, when removing the planetary boundary layer influenced period.
01A - Beitrag in wissenschaftlicher Zeitschrift