Influence of lower stratosphere/upper troposphere transport events on surface ozone at the Everest-Pyramid GAW Station (Nepal): first year of analysis

Authors: Cristofanelli, P.1; Bonasoni, P.1; Bonafe, U.1; Calzolari, F.1; Duchi, R.1; Marinoni, A.1; Roccato, F.1; Vuillermoz, E.2; Sprenger, M.3

Source: International Journal of Remote Sensing, Volume 30, Numbers 15-16, 2009 , pp. 4083-4097(15)

Publisher: Taylor and Francis Ltd

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Abstract:

In this work, we present the first systematic identification of episodes of air mass transport from the lower stratosphere/upper troposphere (LS/UT) in the middle troposphere of the southern Himalayas. For this purpose, we developed an algorithm to detect LS/UT transport events on a daily basis at the Everest-Pyramid GAW station (EV-PYR, 5079 m a.s.l., Nepal). In particular, in situ surface ozone and atmospheric pressure variations as well as total ozone values from OMI satellite measurements have been analysed. Further insight is gained from three-dimensional backward trajectories and potential vorticity calculated with the LAGRANTO model. According to the algorithm outputs, 9.0% of the considered data set (365 days from March 2006 to February 2007) was influenced by this class of phenomena with a maximum of frequency during dry and pre-monsoon seasons. During 25 days of LS/UT transport events for which any influence of anthropogenic pollution was excluded, the daily ozone mixing ratio increased by 9.3% compared to the seasonal values. This indicates that under favourable conditions, downward air mass transport from the LS/UT can play a considerable role in determining the concentrations of surface ozone in the southern Himalayas.

Document Type: Research article

DOI: 10.1080/01431160902821940

Affiliations: 1: National Research Council, Institute of Atmosphere and Climate Sciences (ISAC), Italy 2: EV-K2-CNR Committee, Bergamo, Italy 3: ETH, Swiss Federal Institute of Technology, Zurich, Switzerland

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