Measurement Report: The Palau Atmospheric Observatory and its Ozonesonde Record - Continuous Monitoring of Tropospheric Composition and Dynamics in the Tropical West Pacific

Müller, Katrin; Tradowsky, Jordis S.; von der Gathen, Peter; Ritter, Christoph; Patris, Sharon; Notholt, Justus; Rex, Markus

doi:10.5194/egusphere-2023-1023

Cited by 2 publications

(17 citation statements)

References 6 publications

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“…Most of the air reaching Palau has crossed the Pacific and has thus been cleaned of O 3 precursors from anthropogenic or other continental pollution. Palau has a hot, humid and wet climate all year, resulting in a continuously high convective activity (Gettelman and Forster, 2002;Müller et al, 2023). This persistent high convective activity creates a well-mixed profile of uniformly low O 3 VMR throughout the free troposphere, as illustrated in Fig.…”

Section: Tracers and Process Understandingmentioning

confidence: 98%

“…Balloon-borne measurements with ECC ozonesondes (Komhyr, 1969;Smit, 2014) are the most practical way to observe and continuously monitor O 3 in situ, especially at more remote sites (e.g., Thompson et al, 2019). The specific instrumentation (models SPC 6A and Vaisala RS92/41) and dataset are introduced and described in detail by Müller et al (2023), who provide additional meteorological and climatological context for the Palau time series. While carefully following the Standard Operating Procedures (SOP) as recommended by Smit (2014), the O 3 VMR are calculated using a pressure dependent background current correction (see Müller et al, 2023, for details).…”

Section: Sondesmentioning

confidence: 99%

“…As a consequence and in compliance with acknowledged El Niño Southern Oscillation (ENSO) indices (c.f. Müller et al, 2023), data before August 2016 was disregarded in some of the following statistical seasonal analysis and will be referred to as "excluding El Niño 2016". The 2019 El Niño episode, weaker in nature, is still included.…”

Section: Sondesmentioning

confidence: 99%

“…In this environment the HO x driven loss of O 3 is favored (see reaction R2) resulting in a lifetime of about 5 days for boundary layer O 3 (e.g., Liu et al, 1983;Kley et al, 1997). The low NO x environment is fostered by dominating easterly winds in the annual mean and entire tropospheric column (Müller et al, 2023). Most of the air reaching Palau has crossed the Pacific and has thus been cleaned of O 3 precursors from anthropogenic or other continental pollution.…”

Section: Tracers and Process Understandingmentioning

confidence: 99%

“…34°N, 134.47°E). The instrumental setup and meteorological conditions for the time series used in this study are introduced in more detail in a companion study by Müller et al (2023) (c.f. Müller, 2020.…”

Section: Introductionmentioning

confidence: 99%

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Air Mass Transport to the Tropical West Pacific Troposphere inferred from Ozone and Relative Humidity Balloon Observations above Palau

Müller

Wohltmann

Gathen

et al. 2023

Preprint

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Abstract. Due to the unique local air chemistry, the transport history of tropospheric air masses above the remote tropical West Pacific (TWP) is reflected by local ozone (O3) and relative humidity (RH) characteristics. In boreal winter, the TWP is the main global entry point for air masses into the stratosphere and therefore a key region of atmospheric chemistry and dynamics. However, a long-term in situ monitoring of tropospheric O3 to assess the variability of TWP air masses and the respective controlling processes has yet been missing. The aim of our study was to identify air masses with different origins and pathways to the TWP and their seasonality using the new Palau time series (2016–2019) of mostly fortnightly Electrochemical Concentration Cell ozone and radio soundings. Based on monthly statistics of O3 volume mixing ratios and RH we defined a free tropospheric locally-controlled background and analyzed anomalies for both tracers in the 5–10 km altitude range. We found that anomalously high O3 indicates a remote origin, while RH is controlled by a range of dynamical processes resulting in a bimodality in RH anomalies. The Palau time series confirms a year-round presence of low O3 background air masses and a seasonal mid-tropospheric cycle in O3 with a prominent anti-correlation between O3 volume mixing ratios and RH. We assumed five different types of air masses with differing tracer characteristics and origin which we validated by analyzing backward trajectories calculated with the transport module of the Lagrangian chemistry and transport model ATLAS. The main result is a clear separation of origin and pathways for the two most contrasting types of air masses, i.e. ozone-poor and humid versus ozone-rich and dry air. Both, potential vorticity and air mass origin analyses, reveal no indication for stratospheric influence for the ozone-rich dry air masses. Rather, we found indications for O3 production due to biomass burning or anthropogenic pollution at the origins of these air masses and drying due to clear sky subsidence during long-range transport. The seasonal occurrence is tied to the position of the Intertropical Convergence Zone which opens a pathway from potential source regions which are confirmed by the trajectory analysis. We conclude, that dominant ozone-poor and humid air masses are of local or Pacific convective origin and occur year-round, but dominate from August until October. Anomalously dry and ozone-rich air is generated in Tropical Asia and subsequently transported to the TWP via an anti-cyclonic route, mostly from February to April. The areas of origin suggest different sources of ground pollution as a cause for O3 production. We propose large-scale descent within the tropical troposphere and subsequent radiative cooling in connection with the Hadley circulation as responsible for the vertical displacement and dehydration.

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Section: Tracers and Process Understandingmentioning

confidence: 98%

Section: Sondesmentioning

confidence: 99%

Section: Sondesmentioning

confidence: 99%

Section: Tracers and Process Understandingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Air Mass Transport to the Tropical West Pacific Troposphere inferred from Ozone and Relative Humidity Balloon Observations above Palau

Müller

Wohltmann

Gathen

et al. 2023

Preprint

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Determination of the chemical equator from GEOS-Chem model simulation: a focus on the tropical western Pacific region

et al. 2023

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Abstract. The tropical western Pacific (TWP) plays an important role in global stratosphere–troposphere exchange and is an active region of the interhemispheric transport (IHT). Common indicators for transport between the hemispheres like the tropical rain belt are too broad or lack precision in the TWP. In this paper, we provide a method to determine the atmospheric chemical equator (CE), which is a boundary for air mass transport between the two hemispheres in the tropics. This method used the model output from an artificial passive tracer simulated by the chemical transport model GEOS-Chem in the troposphere. We investigated the movement of the CE in the tropics, which indicates the migration of atmospheric circulation systems and air mass origins. Our results show the CE on different timescales, suggesting that the different features of the IHT in different regions are highly related to the variation in the circulation systems. We compared the CE with the tropical wind fields, indicating that the region of IHT does not coincide with the convergence of the 10 m wind fields in the tropical land sectors and the TWP region. We compared the CE with the atmospheric composition such as satellite data of CH4 and model simulation of sulfur hexafluoride (SF6). The results show that the CE and north–south gradient of CH4 in the Indian Ocean in January are well consistent with each other, which indicates the CE has good potential to estimate the IHT inferred by observations. We discussed the vertical extent and the meridional extent of the IHT. We find that the vertical structure above 2 km has a slight northern tilt in the Northern Hemisphere (NH) winter season and a southern tilt in the NH summer, meaning the seasonality of the migration of the CE at the lower altitude is larger than that at the higher altitude. The meridional extent of the CE indicates a narrow transition zone where IHT happens throughout the year. We find that the meridional extent above South America is larger compared to other regions. The distribution of the land–sea contrast plays an important role in the meridional extent of IHT. We focus on the TWP region and further compared the tropical rain belt with the CE. There is a broad region of high precipitation occurring in the TWP region, and it is difficult to determine the IHT by the rain belt. In the NH winter, the CE is not consistent with the tropical rain belt in the TWP but is confined to the southern branch of the peak of the rain belt. For the other seasons, both indicators of IHT agree.

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Measurement Report: The Palau Atmospheric Observatory and its Ozonesonde Record - Continuous Monitoring of Tropospheric Composition and Dynamics in the Tropical West Pacific

Cited by 2 publications

References 6 publications

Air Mass Transport to the Tropical West Pacific Troposphere inferred from Ozone and Relative Humidity Balloon Observations above Palau

Air Mass Transport to the Tropical West Pacific Troposphere inferred from Ozone and Relative Humidity Balloon Observations above Palau

Determination of the chemical equator from GEOS-Chem model simulation: a focus on the tropical western Pacific region

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