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

Sun, Xiaoyu; Palm, Mathias; Notholt, Justus; Müller, Katrin

doi:10.5194/acp-2022-653

Cited by 2 publications

(1 citation statement)

References 24 publications

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“…In the UTLS, the Brewer-Dobson circulation and its interplay with the uprising branch of the Hadley circulation take over control. As the ITCZ acts as a boundary for interhemispheric transport (Sun et al, 2023), its position north of Palau from July until October inhibits transport of potentially polluted Northern Hemispheric air masses to the region, which further promotes the seasonal mid-tropospheric O 3 minimum and is further explored in back trajectory analysis by Müller et al (2023).…”

Section: Discussionmentioning

confidence: 99%

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

Müller,

Tradowsky,

von der Gathen

et al. 2023

Preprint

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Abstract. The Tropical West Pacific is recognized as an important region for stratosphere-troposphere exchange, but has been a measurement gap in the global ozone sounding network. The Palau Atmospheric Observatory (PAO) was established to study the atmospheric composition above the remote Tropical West Pacific with a comprehensive instrumental setup. Since 2016, two laboratory containers in Palau host an Fourier-transform infrared spectrometer, a lidar (micro lidar until 2016, cloud and aerosol lidar from 2018), a Pandora 2S photometer and laboratory space for weather balloon soundings with ozone-, water-vapor-, aerosol- and radiosondes. In this analysis, we focus on the continuous, fortnightly ozone sounding program with Electrochemical Concentration Cell (ECC) ozone sondes. The aim of this study is to introduce the PAO and its research potential, present the first observation of the typical seasonal cycle of tropospheric ozone in the Tropical West Pacific based on a multiannual record of in situ observations, and investigate major drivers of variability and seasonal variation from 01/2016 until 12/2021 related to the large scale atmospheric circulation. We present the PAO ozone (O3) volume mixing ratios (VMR) and relative humidity (RH) time series complemented by other observations. The site is exposed to year-round high convective activity reflected in dominating low O3 VMR and high RH. In 2016, the impact of the strong El Niño is evident as a particularly dry, ozone-rich episode. The main modulator of annual tropospheric O3 variability is identified as the movement of the Intertropical Convergence Zone (ITCZ), with lowest O3 VMR in the free troposphere during the ITCZ position north of Palau. An analysis of the relation of O3 and RH for the PAO and selected sites from the Southern Hemispheric ADditional OZonesondes (SHADOZ) network reveals three different regimes. Palau’s O3/RH distribution resembles the one in Fiji, Java and American Samoa, but is unique in its seasonality and its comparably narrow Gaussian distribution around low O3 VMR and the evenly distributed RH. A previously found bimodal distribution of O3 VMR and RH could not be seen in the Palau record. Due to its unique remote location, Palau is an ideal atmospheric background site to detect changes in air dynamics imprinted on the chemical composition of the tropospheric column. The efforts to establish, run and maintain the PAO have succeeded to fill an observational gap in the remote Tropical West Pacific and give good prospects for ongoing operations. The ECC sonde record will be integrated into the SHADOZ database in the near future.

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Section: Discussionmentioning

confidence: 99%

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

Müller,

Tradowsky,

von der 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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Determination of the chemical equator from GEOS-Chem model simulation: a focus on the Tropical Western Pacific region

Cited by 2 publications

References 24 publications

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

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

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

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