Interactions between convection and the Saharan Air Layer in the tropical Atlantic Ocean are quantified using a novel compositing technique that leverages geostationary cloud observations to add temporal context to the polar orbiting CloudSat and the Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellites allowing aerosol optical depth (AOD) changes to be tracked throughout a typical convective storm life cycle. Four years of CALIPSO observations suggests that approximately 20% of the dust mass in every 10° longitude band between 10°W and 80°W is deposited into the ocean. Combining a new convective identification algorithm based on hourly geostationary cloud products with
- NSF-PAR ID:
- 10129213
- Date Published:
- Journal Name:
- Atmospheric Chemistry and Physics
- Volume:
- 19
- Issue:
- 3
- ISSN:
- 1680-7324
- Page Range / eLocation ID:
- 1587 to 1603
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract A O D dustprofiles along the CALIPSO track reveals that wet scavenging by convection is responsible for a significant fraction of this deposition across the Atlantic. Composites of 4 years of convective systems reveal that, on average, convection accounts for 15% ± 7% of the dust deposition in each longitude band relative to preconvective amounts, implying that dry deposition and scavenging by nonconvective events are responsible for the remaining 85% of dust removal. In addition, dust layers are detrained at upper levels of the atmosphere between 8 and 12 km by convective storms across the Atlantic. The dust budget analysis presented here indicates that convection lofts 1.5% ± 0.6% of dust aerosol mass to altitudes greater than 6 km. This may have significant implications for cloud formation downstream of convection since lofted dust particles can act as effective ice nucleating particles, altering cloud microphysical and radiative properties, latent heating, and precipitation rates. -
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Atmospheric aerosols are key contributors to cloud condensation nuclei (CCN) and ice nucleating particle (INP) formation, which can offset positive radiative forcing. Aerosol particles can undergo many cycles of droplet activation and subsequent drying before their removal from the atmosphere through dry or wet deposition. Cloud-aerosol-precipitation interactions are affected by cloud droplet or ice crystal formation, which is related to the physicochemical properties of aerosol particles. Isoprene-derived secondary organic aerosol (iSOA) is an abundant component aerosol and has been previously found in INPs and cloud water residues, and it includes both soluble and insoluble residues in its particle matrix. Currently, most of our understanding of iSOA is derived from studying the soluble residues, but there has been a measurement gap for characterizing the insoluble residues. These measurements are needed as previous research has suggested that insoluble components could be important with respect to CCN and INP formation. Herein, a unique approach is utilized to collect the insoluble residues of SOA in ~3 μm droplets collected from a Spot Sampler from Aerosol Devices, Inc. iSOA is generated by reactive uptake of IEPOX onto acidic seed particles (ammonium sulfate + sulfuric acid) in a humidified atmospheric chamber under dark conditions. Droplets are impacted directly on a substrate or in a liquid medium to study the roles of insoluble residues from both single-particle and bulk perspectives. A suite of microspectroscopy techniques, including Raman and optical photothermal infrared (O-PTIR) spectroscopy, are used to probe the chemical composition of the residues. Atomic force microscopy – photothermal infrared (AFM-PTIR) spectroscopy and Nanoparticle Tracking Analysis (NTA) are used to measure the size distributions of the residues. These insights may help understand the properties of residues from cloud droplet evaporation and subsequent cloud-aerosol-precipitation interactions in the atmosphere.more » « less
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Abstract A gravity wave (GW) model that includes influences of temperature variations and large‐scale advection on polar mesospheric cloud (PMC) brightness having variable dependence on particle radius is developed. This Complex Geometry Compressible Atmosphere Model for PMCs (CGCAM‐PMC) is described and applied here for three‐dimensional (3‐D) GW packets undergoing self‐acceleration (SA) dynamics, breaking, momentum deposition, and secondary GW (SGW) generation below and at PMC altitudes. Results reveal that GW packets exhibiting strong SA and instability dynamics can induce significant PMC advection and large‐scale transport, and cause partial or total PMC sublimation. Responses modeled include PMC signatures of GW propagation and SA dynamics, “voids” having diameters of ∼500–1,200 km, and “fronts” with horizontal extents of ∼400–800 km. A number of these features closely resemble PMC imaging by the Cloud Imaging and Particle Size (CIPS) instrument aboard the Aeronomy of Ice in the Mesosphere (AIM) satellite. Specifically, initial CGCAM‐PMC results closely approximate various CIPS images of large voids surrounded by smaller void(s) for which dynamical explanations have not been offered to date. In these cases, the GW and instabilities dynamics of the initial GW packet are responsible for formation of the large void. The smaller void(s) at the trailing edge of a large void is (are) linked to the lower‐ or higher‐altitude SGW generation and primary mean‐flow forcing. We expect an important benefit of such modeling to be the ability to infer local forcing of the mesosphere and lower thermosphere (MLT) over significant depths when CGCAM‐PMC modeling is able to reasonably replicate PMC responses.
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/acp-19-1587-2019
