Origin of Tropospheric Air Masses in the Tropical West Pacific and related transport processes inferred from balloon-borne Ozone and Water Vapour observations from Palau


Contact
katrin.mueller [ at ] awi.de

Abstract

Motivated by previous measurements of very low tropospheric ozone concentrations in the Tropical West Pacific (TWP) and the implied low oxidizing capacity of this key region for transport into the stratosphere in boreal winter (e.g. Rex et al. 2014), we set up an atmospheric research station in Palau (7°N 134°E) as part of the StratoClim campaign. Our analysis of regular balloon-borne tropospheric ozone observations at Palau from 01/2016-12/2019 gives unprecedented insights into transport processes and air mass origin in the TWP. We confirm the year-round dominance of a low ozone background in the mid-troposphere. Layers of enhanced ozone are often anti-correlated with water vapor and occur frequently. Moreover, the occurrence of respective layers shows a strong seasonality. Dry and ozone-rich air masses between 5 and 10 km altitude were observed in 71 % of the profiles from February until April compared to 25 % from August until October. By defining monthly atmospheric background profiles for ozone and relative humidity based on observed statistics, we found that the deviations from this background reveal a bimodal distribution of RH anomalies. A previously proposed universal bimodal structure of free tropospheric ozone in the TWP could not be verified (Pan et al. 2015). Back trajectory calculations (ATLAS) confirm that throughout the year the mid-tropospheric background is controlled by local convective processes and the origin of air masses is thus close to or East of Palau in the Pacific Ocean. Dry and ozone-rich air originates in tropical Asia and reaches Palau in anticyclonic conditions over an area stretching from India to the Philippines. This supports the controversial hypothesis of several studies which attribute ozone enhancement against the ozone-poor background to remote pollution events on the ground such as biomass burning (e.g. Andersen et al. 2016). A potential vorticity analysis revealed no stratospheric influence and we thus propose large-scale descent within the tropical troposphere as responsible for dehydration of air masses on their way to Palau.



Item Type
Conference (Poster)
Authors
Divisions
Primary Division
Programs
Primary Topic
Helmholtz Cross Cutting Activity (2021-2027)
N/A
Publication Status
Published
Event Details
EGU General Assembly, 01 Apr 2021 - 01 Apr 2021, online.
Eprint ID
54569
DOI 10.5194/egusphere-egu21-10199

Cite as
Müller, K. , Wohltmann, I. , von der Gathen, P. , Lehmann, R. and Rex, M. (2021): Origin of Tropospheric Air Masses in the Tropical West Pacific and related transport processes inferred from balloon-borne Ozone and Water Vapour observations from Palau , EGU General Assembly, online, April 2021 - April 2021 . doi: 10.5194/egusphere-egu21-10199


Download
[thumbnail of 2021_EGU_KM.pdf]
Preview
PDF
2021_EGU_KM.pdf

Download (6MB) | Preview

Share
Add to AnyAdd to TwitterAdd to FacebookAdd to LinkedinAdd to PinterestAdd to Email


Citation

Geographical region

Research Platforms
N/A

Campaigns
N/A


Actions
Edit Item Edit Item