Comparing Ship-Track Droplet Sizes Inferred from Terra and Aqua MODIS Data

Kabatas, B.; Menzel, W. Paul; Bilgili, Ata; Gumley, Liam E.

doi:10.1175/jamc-d-11-0232.1

Cited by 7 publications

(10 citation statements)

References 24 publications

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“…Kabatas et al . [] studied ship tracks from late morning to early afternoon using MODIS Terra and Aqua observations. Based on their analysis, the correlation between Terra and Aqua droplet size estimates for all plumes was 0.92, and plumes with droplet size <9 µm were found more likely to extend beyond 600 km.…”

Section: Methodsmentioning

confidence: 99%

Aerosol‐cloud interactions in ship tracks using Terra MODIS/MISR

et al. 2015

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Simultaneous ship track observations from Terra Moderate Resolution Imaging Spectroradiometer (MODIS) and Multiangle Imaging Spectroradiometer (MISR) have been compiled to investigate how ship-injected aerosols affect marine warm boundary layer clouds for different cloud types and environmental conditions. By taking advantage of the high spatial resolution multiangle observations available from MISR, we utilized the retrieved cloud albedo, cloud top height, and cloud motion vectors to examine cloud property responses in ship-polluted and nearby unpolluted clouds. The strength of the cloud albedo response to increased aerosol level is primarily dependent on cloud cell structure, dryness of the free troposphere, and boundary layer depth, corroborating a previous study by Chen et al. (2012) where A-Train satellite data were utilized. Under open cell cloud structure the cloud properties are more susceptible to aerosol perturbations as compared to closed cells. Aerosol plumes caused an increase in liquid water amount (+38%), cloud top height (+13%), and cloud albedo (+49%) for open cell clouds, whereas for closed cell clouds, little change in cloud properties was observed. Further capitalizing on MISR's unique capabilities, the MISR cross-track cloud speed was used to derive cloud top divergence. Statistically averaging the results from the identified plume segments to reduce random noise, we found evidence of cloud top divergence in the ship-polluted clouds, whereas the nearby unpolluted clouds showed cloud top convergence, providing observational evidence of a change in local mesoscale circulation associated with enhanced aerosols. Furthermore, open cell polluted clouds revealed stronger cloud top divergence as compared to closed cell clouds, consistent with different dynamical mechanisms driving their responses. These results suggest that detailed cloud responses, classified by cloud type and environmental conditions, must be accounted for in global climate modeling studies to reduce uncertainties in calculations of aerosol indirect forcing.

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Section: Methodsmentioning

confidence: 99%

Aerosol‐cloud interactions in ship tracks using Terra MODIS/MISR

et al. 2015

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“…Although a number of methods for identifying causal relationships have been proposed (e.g. Koren et al, 2010;Gryspeerdt et al, 2016;McCoy et al, 2020), "natural experiments" (Rosenzweig and Wolpin, 2000), where the aerosol is perturbed independently of meteorology (such as by ships or industry ;Conover, 1966;Toll et al, 2019) are the standard way of isolating the causal aerosol effect. As these studies are often performed at relatively short times after the aerosol perturbation, understanding the timescales of the response is essential to interpret these results.…”

Section: Introductionmentioning

confidence: 99%

Observing the timescales of aerosol–cloud interactions in snapshot satellite images

Gryspeerdt

Goren²,

Smith

2021

Atmos. Chem. Phys.

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Abstract. The response of cloud processes to an aerosol perturbation is one of the largest uncertainties in the anthropogenic forcing of the climate. It occurs at a variety of timescales, from the near-instantaneous Twomey effect to the longer timescales required for cloud adjustments. Understanding the temporal evolution of cloud properties following an aerosol perturbation is necessary to interpret the results of so-called “natural experiments” from a known aerosol source such as a ship or industrial site. This work uses reanalysis wind fields and ship emission information matched to observations of ship tracks to measure the timescales of cloud responses to aerosol in instantaneous (or“snapshot”) images taken by polar-orbiting satellites. As in previous studies, the local meteorological environment is shown to have a strong impact on the occurrence and properties of ship tracks, but there is a strong time dependence in their properties. The largest droplet number concentration (Nd) responses are found within 3 h of emission, while cloud adjustments continue to evolve over periods of 10 h or more. Cloud fraction is increased within the early life of ship tracks, with the formation of ship tracks in otherwise clear skies indicating that around 5 %–10 % of clear-sky cases in this region may be aerosol-limited. The liquid water path (LWP) enhancement and the Nd–LWP sensitivity are also time dependent and strong functions of the background cloud and meteorological state. The near-instant response of the LWP within ship tracks may be evidence of a bias in estimates of the LWP response to aerosol derived from natural experiments. These results highlight the importance of temporal development and the background cloud field for quantifying the aerosol impact on clouds, even in situations where the aerosol perturbation is clear.

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“…The MODIS images are still only a snapshot of the cloud field, such that the time axis determined from the ship and cloud motion is not a real time axis. The unperturbed clouds will also develop over the time period (Christensen et al, 2009;Kabatas et al, 2013), such that the "unperturbed" clouds here are not a true measure of the at the time of the aerosol perturbation, having evolved since then. The polluted clouds will also have evolved, not necessarily in the same manner.…”

Section: Future Improvementsmentioning

confidence: 99%

“…Exogeneous aerosol perturbations (such as those from ships) are emitted independently of meteorological factors. With a limited spatial extent, they have clearly identifiable polluted and control regions, allowing the impact of the aerosol on the cloud field to be inferred (Durkee et al, 2000a), vary along their length (Kabatas et al, 2013) and can be tracked over several days, providing evidence of a long-lasting aerosol perturbation to cloud properties (Goren and Rosenfeld, 2012).…”

Section: Introductionmentioning

confidence: 99%

“…Although shiptracks appear in satellite images as linear cloud formations, they have no ability to transmit information along their length. This means that they can be considered as a chain of independently perturbed clouds with a similar initial aerosol perturbation (Kabatas et al, 2013). By linking shiptracks identified in satellite images (e.g.…”

Section: Introductionmentioning

confidence: 99%

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Observing the timescales of aerosol-cloud interactions in snapshot satellite images

Gryspeerdt¹,

Goren²,

Smith³

2020

Preprint

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Abstract. The response of cloud processes to an aerosol perturbation is one of the largest uncertainties in the anthropogenic forcing of the climate. It occurs at a variety of timescales, from the near-instantaneous Twomey effect, to the longer timescales required for cloud adjustments. Understanding the temporal evolution of cloud properties following an aerosol perturbation is necessary to interpret the results of so-called "natural experiments" from a known aerosol source, such as a ship or industrial site. This work uses reanalysis windfields and ship emission information matched to observations of shiptracks to measure the timescales of cloud responses to aerosol in instantaneous (or "snapshot") images taken by polar-orbiting satellites. As found in previous studies, the local meteorological environment is shown to have a strong impact on the occurrence and properties of shiptracks, but there is a strong time dependence in their properties. The largest droplet number concentration (Nd) responses are found within three hours of emission, while cloud adjustments continue to evolve over periods of ten hours or more. Cloud fraction is increased within the early life of shiptracks, with the formation of shiptracks in otherwise clear skies indicating that around 5–10 % of clear-sky cases in this region may be aerosol-limited. The liquid water path (LWP) enhancement and the Nd-LWP sensitivity are also time dependent and strong functions of the background cloud and meteorological state. The near-instant response of the LWP within shiptracks may be evidence of a retrieval bias in previous estimates of the LWP response to aerosol derived from natural experiments. These results highlight the importance of temporal development and the background cloud field for quantifying the aerosol impact on clouds, even in situations where the aerosol perturbation is clear.

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Comparing Ship-Track Droplet Sizes Inferred from Terra and Aqua MODIS Data

Cited by 7 publications

References 24 publications

Aerosol‐cloud interactions in ship tracks using Terra MODIS/MISR

Aerosol‐cloud interactions in ship tracks using Terra MODIS/MISR

Observing the timescales of aerosol–cloud interactions in snapshot satellite images

Observing the timescales of aerosol-cloud interactions in snapshot satellite images

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