Cloud and Aerosol Distributions From SAGE III/ISS Observations

Schoeberl, M. R.; Jensen, Eric R.; Wang, Tao; Taha, Ghassan; Ueyama, Rei; Wang, Yi; DeLand, Matthew T.; Dessler, A. E.

doi:10.1029/2021jd035550

Cited by 4 publications

(1 citation statement)

References 73 publications

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“…For both seasons equatorward of the upward heating bulge, air descends rapidly into the opposite hemisphere. The descending circulation branch is coincident with a reduction in both cloud fraction and aerosol concentration as seen in Stratospheric Aerosol and Gas Experiment (SAGE) III data (M. Schoeberl et al., 2021).…”

Section: Climatology Of the Upper Troposphere And Lower Stratospherementioning

confidence: 63%

A Lagrangian View of Seasonal Stratosphere‐Troposphere Exchange

2022

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Stratosphere-troposphere exchange (STE) is the key process regulating the flow of ozone-depleting trace gases, water vapor and other constituents into and out of the stratosphere. The overall circulation responsible for this exchange was first deduced by Brewer (1949), and it consists of upwelling in the tropics and downwelling at extratropical latitudes. This circulation is now referred to as the Brewer-Dobson circulation (BDC). Holton et al. (1995) provides a modern dynamical perspective on STE. Basically, planetary wave-breaking in the extratropical lower stratosphere drives a fluid-dynamical pump that draws air upward in the tropics and drives air downward at the pole (Haynes et al., 1991). The upward moving tropical air is forced out of radiative equilibrium, and thus the air is radiatively heated producing a net diabatic heating in the tropical upper troposphere and lower stratosphere (UTLS). Stratospheric planetary-wave breaking is most intense during winter in the Northern Hemisphere. As a result, the BDC is stronger during boreal winter and the tropical tropopause temperatures are colder than during austral winter (Yulaeva et al., 1994). Holton et al. (1995 noted that the global mass exchange rate is thus determined by the fluid-pump and not by overshooting convection or extra-tropical tropopause folding as had been previously argued.With the broad details of BDC mechanics in hand, more recent efforts have focused on the dynamics of the very lowest part of the stratosphere and the upper tropical troposphere. The BDC appears to consist of two branches: a deep branch that is forced by planetary-scale wave breaking in the mid-stratosphere (Gettelman et al., 2011;

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Section: Climatology Of the Upper Troposphere And Lower Stratospherementioning

confidence: 63%

A Lagrangian View of Seasonal Stratosphere‐Troposphere Exchange

2022

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Three-wavelength approach for aerosol-cloud discrimination in the SAGE III/ISS aerosol extinction dataset

et al. 2023

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The tropical upper troposphere and lower stratosphere (UTLS) region is dominated by aerosols and clouds affecting Earth’s radiation budget and climate. Thus, satellites’ continuous monitoring and identification of these layers is crucial for quantifying their radiative impact. However, distinguishing between aerosols and clouds is challenging, especially under the perturbed UTLS conditions during post-volcanic eruptions and wildfire events. Aerosol-cloud discrimination is primarily based on their disparate wavelength-dependent scattering and absorption properties. In this study, we use aerosol extinction observations in the tropical (15°N-15°S) UTLS from June 2017 to February 2021, available from the latest generation of the Stratospheric Aerosol and Gas Experiment (SAGE) instrument-SAGE III onboard the International Space Station (ISS) to study aerosols and clouds. During this period, the SAGE III/ISS provided better coverage over the tropics at additional wavelength channels (relative to previous SAGE missions) and witnessed several volcanic and wildfire events that perturbed the tropical UTLS. We explore the advantage of having an extinction coefficient at an additional wavelength channel (1550 nm) from the SAGE III/ISS in aerosol-cloud discrimination using a method based on thresholds of two extinction coefficient ratios, R1 (520 nm/1020 nm) and R2 (1020 nm/1550 nm). This method was proposed earlier by Kent et al. [Appl. Opt. 36, 8639 (1997)APOPAI0003-693510.1364/AO.36.008639] for the SAGE III-Meteor-3M but was never tested for the tropical region under volcanically perturbed conditions. We call this method the Extinction Color Ratio (ECR) method. The ECR method is applied to the SAGE III/ISS aerosol extinction data to obtain cloud-filtered aerosol extinction coefficients, cloud-top altitude, and seasonal cloud occurrence frequency during the entire study period. Cloud-filtered aerosol extinction coefficient obtained using the ECR method revealed the presence of enhanced aerosols in the UTLS following volcanic eruptions and wildfire events consistent with the Ozone Mapping and Profiler Suite (OMPS) and space-borne lidar-Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP). The cloud-top altitude obtained from the SAGE III/ISS is within 1 km of the nearly co-located observations from OMPS and CALIOP. In general, the seasonal mean cloud-top altitude from the SAGE III/ISS events peaks during the December, January, and February months, with sunset events showing higher cloud tops than the sunrise events, indicating the seasonal and diurnal variation of the tropical convection. The seasonal altitude distribution of cloud occurrence frequency obtained from the SAGE III/ISS also agrees well with CALIOP observations within 10%. We show that the ECR method is a simple approach that relies on thresholds independent of the sampling period, providing cloud-filtered aerosol extinction coefficients uniformly for climate studies irrespective of the UTLS conditions. However, since the predecessor of SAGE III did not include a 1550 nm channel, the usefulness of this approach is limited to short-term climate studies after 2017.

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Retrieving instantaneous extinction of aerosol undetected by the CALIPSO layer detection algorithm

et al. 2022

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Abstract. Aerosols significantly affect the Earth–atmosphere energy balance and climate change by acting as cloud condensation nuclei. Specifically, the susceptibility of cloud and precipitation to aerosols is stronger when aerosols are faint but tends to be saturated in polluted conditions. However, previous methodologies generally miss these faint aerosols based on instantaneous observations because they are too optically thin to be detected and are therefore usually unretrieved. This result in a large underestimation when quantifying aerosol climate impacts. Here, we focus on retrieving and verifying the instantaneous extinction of undetected faint aerosol by the CALIPSO layer detection algorithm on a global scale. Using the observations during the Stratospheric Aerosol and Gas Experiment III on the International Space Station (SAGE III/ISS) as constraints, the lidar ratios of undetected faint aerosol are estimated with a global median of 42.2 and 24.5 sr at the stratosphere and the troposphere, respectively. The retrieved extinction of undetected aerosol during night-time shows good agreement with the independent 12-month SAGE III/ISS product on a 1∘ average. The corresponding correlation coefficient and averaged normalized root-mean-square error are 0.66 % and 100.6 %, respectively. The minimum retrieved extinction coefficients can be extended to 10−3 and 10−4 km−1 with an uncertainty of 35 % and 125 % during night-time, respectively. The CALIPSO retrieval during daytime has a positive bias and relatively low agreement with SAGE III/ISS due to the low signal-to-noise ratio caused by sunlight. This study has great potential for improving the understanding of aerosol variations and the quantification of aerosol impacts on global climate change.

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Cloud and Aerosol Distributions From SAGE III/ISS Observations

Cited by 4 publications

References 73 publications

A Lagrangian View of Seasonal Stratosphere‐Troposphere Exchange

A Lagrangian View of Seasonal Stratosphere‐Troposphere Exchange

Three-wavelength approach for aerosol-cloud discrimination in the SAGE III/ISS aerosol extinction dataset

Retrieving instantaneous extinction of aerosol undetected by the CALIPSO layer detection algorithm

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