Evaluation of MODIS and Himawari‐8 Low Clouds Retrievals Over the Southern Ocean With In Situ Measurements From the SOCRATES Campaign

Kang, Litai; Marchand, Roger; Smith, William L.

doi:10.1029/2020ea001397

Cited by 20 publications

(24 citation statements)

References 88 publications

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“…Cloud observations occur in more altitude bins to the south, either a manifestation of the more frequent occurrence of multi‐layered clouds in the southern SO or the more frequent sampling in that region during SOCRATES. Most N d samples range between 60 and 100 or more mg −1 (similar in cm −3 , Figure ) which is consistent with satellite derived N d climatologically (Bodas‐Salcedo et al., 2019; Grosvenor et al., 2018; I. L. McCoy et al., 2020) and instantaneously (Kang et al., 2021) sampled in this region and season.…”

Section: Resultssupporting

confidence: 83%

Influences of Recent Particle Formation on Southern Ocean Aerosol Variability and Low Cloud Properties

et al. 2021

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The Southern Ocean (SO) is our closest present-day (PD) analog to the pre-industrial (PI) state due to its pristine aerosol (Hamilton et al., 2014). It is also frequently cloudy, providing ample opportunity for aerosol-cloud interactions (ACI) to take place. Understanding the climate response to changes in anthropogenic aerosol (i.e., PI to PD states) will help to reduce the uncertainty in global climate model climate sensitivity and improve climate predictions (Andreae et al., 2005;Forster, 2016). Aerosol-cloud interactions are the main contributor to uncertainty in total radiative forcing (Bellouin et al., 2020). Poor understanding of PI aerosol state is a leading driver of this uncertainty (Carslaw et al., 2013), making observations in pristine

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Section: Resultssupporting

confidence: 83%

Influences of Recent Particle Formation on Southern Ocean Aerosol Variability and Low Cloud Properties

et al. 2021

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“…This issue has been partially addressed here by examining the dependence on satellite scattering angle, which is generally assumed to provide information regarding cloud shadowing for the forward-scattering view ( < 90) and enhanced illumination for the backscattering directions ( > 90). Under this simple framework, it is generally interpreted that high values of reflectance at the backscattering direction are associated with an overestimation of τ and underestimation of r e , and vice versa for the forward-scattering direction where shadowing occurs (Kato et al, 2006). Indeed, MODIS observations over Brazil have shown differences between forward and backscattering angles up to 6 µm for r e for cumulus clouds (Vant-Hull et al, 2007).…”

Section: Discussionmentioning

confidence: 99%

“…While Witte et al (2018) pointed to the importance of counting on in situ observations that fully capture the droplet size distribution, our study relies on two independent airborne datasets, lending confidence in the satellite assessment. While accounting for precipitation in the in situ observation would decrease the MODIS r e bias by 0.41 µm, the remaining discrepancy is possibly explained by a combination of viewing geometry and 3D radiative transfer effects (Kato et al, 2006). While independent aircraft datasets corroborated the results for satellite r e , assessment of τ was based only on comparisons with the RSP τ , with no direct estimates of liquid water path (LWP).…”

Section: Discussionmentioning

confidence: 99%

“…Despite closer agreement between GOES-13 and MODIS r e for high MODIS VZA, systematically larger GOES-13 r e than MODIS points to other factors in explaining the systematic biases for GOES-13. While some aspects of the viewing geometry and illumination effects on MODIS r e and τ have been explored to some degree in a number of studies (e.g., Marshak et al, 2006;Kato et al, 2006;Horvath et al, 2014), it remains largely unknown to what extent previous analyses are ap- plicable to geostationary sensor geometry. We have previously shown the sensitivity of the MODIS-GOES difference to VZA, consistent with the effect of pixel coarsening, and the non-linearity of the reflectance-r e and reflectance-τ relationship dependent on VZA (Liang and DiGirolamo, 2013).…”

Section: Goes-13 and Modis Intercomparisonmentioning

confidence: 99%

“…Passive-based cloud algorithms typically rely on a visible channel for retrieving cloud optical depth (the vertically integrated cloud extinction coefficient) and an absorbing nearinfrared channel for estimating cloud effective radius (r e , the ratio of the third to the second moment of the droplet size distribution), which, in turn, can be utilized for indirectly estimating liquid water path. Numerous studies have documented factors that can possibly bias the passive satellite cloud retrievals based on bi-spectral algorithms, including among others subpixel variability, clear-sky contamination, solar and viewing angles effects, and three-dimensional radiative effects (e.g., Marshak et al, 2006;Kato et al, 2006;Zhang et al, 2012). Despite these sources of uncertainty, comparisons between in situ aircraft data and MODIS retrievals for marine stratocumulus clouds have shown excellent correlations for effective radius, optical depth, and liquid water path in the eastern Pacific and northeast Atlantic (Painemal and Zuidema, 2011;Painemal et al, 2012;Noble and Hudson, 2015;Zhang et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

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Evaluation of satellite retrievals of liquid clouds from the GOES-13 imager and MODIS over the midlatitude North Atlantic during the NAAMES campaign

et al. 2021

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Abstract. Satellite retrievals of cloud droplet effective radius (re) and optical depth (τ) from the Thirteenth Geostationary Operational Environmental Satellite (GOES-13) and the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard Aqua and Terra, based on the Clouds and the Earth's Radiant Energy System (CERES) project algorithms, are evaluated with airborne data collected over the midlatitude boundary layer during the North Atlantic Aerosols and Marine Ecosystems Study (NAAMES). The airborne dataset comprises in situ re from the Cloud Droplet Probe (CDP) and remotely sensed re and τ from the airborne Research Scanning Polarimeter (RSP). GOES-13 and MODIS (Aqua and Terra) re values are systematically greater than those from the CDP and RSP by at least 4.8 (GOES-13) and 1.7 µm (MODIS) despite relatively high linear correlation coefficients (r=0.52–0.68). In contrast, the satellite τ underestimates its RSP counterpart by −3.0, with r=0.76–0.77. Overall, MODIS yields better agreement with airborne data than GOES-13, with biases consistent with those reported for subtropical stratocumulus clouds. While the negative bias in satellite τ is mostly due to the retrievals having been collected in highly heterogeneous cloud scenes, the causes for the positive bias in satellite re, especially for GOES-13, are more complex. Although the high viewing zenith angle (∼65∘) and coarser pixel resolution for GOES-13 could explain a re bias of at least 0.7 µm, the higher GOES-13 re bias relative to that from MODIS is likely rooted in other factors. In this regard, a near-monotonic increase was also observed in GOES-13 re up to 1.0 µm with the satellite scattering angle (Θ) over the angular range 116–165∘; that is, re increases toward the backscattering direction. Understanding the variations of re with Θ will require the combined use of theoretical computations along with intercomparisons of satellite retrievals derived from sensors with dissimilar viewing geometry.

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Influences of Recent Particle Formation on Southern Ocean Aerosol Variability and Low Cloud Properties

McCoy

Bretherton

Wood

et al. 2021

Preprint

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Controls on pristine aerosol over the Southern Ocean (SO) are critical for constraining the strength of global aerosol indirect forcing. Observations of summertime SO clouds and aerosols in synoptically varied conditions during the 2018 SOCRATES aircraft campaign reveal novel mechanisms influencing pristine aerosol-cloud interactions. The SO free troposphere (3-6 km) is characterized by widespread, frequent new particle formation events contributing to much larger concentrations ([?] 1000 mg-1) of condensation nuclei (diameters > 0.01 μm) than in typical sub-tropical regions. Synoptic-scale uplift in warm conveyor belts and sub-polar vortices lifts marine biogenic sulfur-containing gases to free-tropospheric environments favorable for generating Aitken-mode aerosol particles (0.01-0.1 μm). Free-tropospheric Aitken particles subside into the boundary layer, where they grow in size to dominate the sulfur-based cloud condensation nuclei (CCN) driving SO cloud droplet number concentrations (Nd ˜60-100 cm-3). Evidence is presented for a hypothesized Aitken-buffering mechanism which maintains persistently high summertime SO Nd against precipitation removal through CCN replenishment from activation and growth of boundary layer Aitken particles. Nudged hindcasts from the Community Atmosphere Model (CAM6) are found to underpredict Aitken and accumulation mode aerosols and Nd, impacting summertime cloud brightness and aerosol-cloud interactions and indicating incomplete representations of aerosol mechanisms associated with ocean biology.

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Evaluation of MODIS and Himawari‐8 Low Clouds Retrievals Over the Southern Ocean With In Situ Measurements From the SOCRATES Campaign

Cited by 20 publications

References 88 publications

Influences of Recent Particle Formation on Southern Ocean Aerosol Variability and Low Cloud Properties

Influences of Recent Particle Formation on Southern Ocean Aerosol Variability and Low Cloud Properties

Evaluation of satellite retrievals of liquid clouds from the GOES-13 imager and MODIS over the midlatitude North Atlantic during the NAAMES campaign

Influences of Recent Particle Formation on Southern Ocean Aerosol Variability and Low Cloud Properties

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