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• 1. [Article] Atmospheric sulfur cycling in the southeastern Pacific – longitudinal distribution, vertical profile, and diel variability observed during VOCALS-REx

  Dimethylsulfide (DMS) emitted from the ocean is a biogenic precursor gas for sulfur dioxide (SO₂) and non-sea-salt sulfate aerosols (SO₄²⁻). During the VAMOS-Ocean-Cloud-Atmosphere-Land Study Regional ...

  Citation × Citation Citation Abstract Copy Title: Atmospheric sulfur cycling in the southeastern Pacific – longitudinal distribution, vertical profile, and diel variability observed during VOCALS-REx Author: Shank, L. M., Hawkins, L. N., Zagorac, N., Blomquist, B. W., Bates, T. S., Coffman, D. J., Yang, M., Brewer, W. A., Huebert, B. J., Zuidema, P. D., Howell, S. G., Quinn, P. K., Benedict, K. B., Bandy, A. R., Covert, D. S., Tucker, S. C., McNaughton, C. S., Clarke, A. D., de Szoeke, Simon P., Collett, J. L., Russell, L. M. Dimethylsulfide (DMS) emitted from the ocean is a biogenic precursor gas for sulfur dioxide (SO₂) and non-sea-salt sulfate aerosols (SO₄²⁻). During the VAMOS-Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) in 2008, multiple instrumented platforms were deployed in the Southeastern Pacific (SEP) off the coast of Chile and Peru to study the linkage between aerosols and stratocumulus clouds. We present here observations from the NOAA Ship Ronald H. Brown and the NSF/NCAR C-130 aircraft along ~20° S from the coast (70° W) to a remote marine atmosphere (85° W). While SO₄²⁻ and SO₂ concentrations were distinctly elevated above background levels in the coastal marine boundary layer (MBL) due to anthropogenic influence (~800 and 80 pptv, respectively), their concentrations rapidly decreased west of 78° W (~100 and 25 pptv). In the remote region, entrainment from the free troposphere (FT) increased MBL SO₂ burden at a rate of 0.05 ± 0.02 μmoles m⁻² day⁻¹ and diluted MBL SO₄² burden at a rate of 0.5 ± 0.3 μmoles m⁻² day⁻¹, while the sea-to-air DMS flux (3.8 ± 0.4 μmoles m⁻² day⁻¹) remained the predominant source of sulfur mass to the MBL. In-cloud oxidation was found to be the most important mechanism for SO₂ removal and in situ SO₄²⁻ production. Surface SO₄²⁻ concentration in the remote MBL displayed pronounced diel variability, increasing rapidly in the first few hours after sunset and decaying for the rest of the day. We theorize that the increase in SO₄²⁻ was due to nighttime recoupling of the MBL that mixed down cloud-processed air, while decoupling and sporadic precipitation scavenging were responsible for the daytime decline in SO₄²⁻. Title: Atmospheric sulfur cycling in the southeastern Pacific – longitudinal distribution, vertical profile, and diel variability observed during VOCALS-REx Author: Shank, L. M., Hawkins, L. N., Zagorac, N., Blomquist, B. W., Bates, T. S., Coffman, D. J., Yang, M., Brewer, W. A., Huebert, B. J., Zuidema, P. D., Howell, S. G., Quinn, P. K., Benedict, K. B., Bandy, A. R., Covert, D. S., Tucker, S. C., McNaughton, C. S., Clarke, A. D., de Szoeke, Simon P., Collett, J. L., Russell, L. M. Dimethylsulfide (DMS) emitted from the ocean is a biogenic precursor gas for sulfur dioxide (SO₂) and non-sea-salt sulfate aerosols (SO₄²⁻). During the VAMOS-Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) in 2008, multiple instrumented platforms were deployed in the Southeastern Pacific (SEP) off the coast of Chile and Peru to study the linkage between aerosols and stratocumulus clouds. We present here observations from the NOAA Ship Ronald H. Brown and the NSF/NCAR C-130 aircraft along ~20° S from the coast (70° W) to a remote marine atmosphere (85° W). While SO₄²⁻ and SO₂ concentrations were distinctly elevated above background levels in the coastal marine boundary layer (MBL) due to anthropogenic influence (~800 and 80 pptv, respectively), their concentrations rapidly decreased west of 78° W (~100 and 25 pptv). In the remote region, entrainment from the free troposphere (FT) increased MBL SO₂ burden at a rate of 0.05 ± 0.02 μmoles m⁻² day⁻¹ and diluted MBL SO₄² burden at a rate of 0.5 ± 0.3 μmoles m⁻² day⁻¹, while the sea-to-air DMS flux (3.8 ± 0.4 μmoles m⁻² day⁻¹) remained the predominant source of sulfur mass to the MBL. In-cloud oxidation was found to be the most important mechanism for SO₂ removal and in situ SO₄²⁻ production. Surface SO₄²⁻ concentration in the remote MBL displayed pronounced diel variability, increasing rapidly in the first few hours after sunset and decaying for the rest of the day. We theorize that the increase in SO₄²⁻ was due to nighttime recoupling of the MBL that mixed down cloud-processed air, while decoupling and sporadic precipitation scavenging were responsible for the daytime decline in SO₄²⁻. Close

• 2. [Article] The VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx): goals, platforms, and field operations

  The VAMOS¹ Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) was an international field program designed to make observations of poorly understood but critical components of the coupled ...

  Citation × Citation Citation Abstract Copy Title: The VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx): goals, platforms, and field operations Author: Mechoso, C. R., Brioude, J., Abel, S. J., Brewer, A., Springston, S. R., Williams, S., Weller, R. A., Bates, T. S., Garreaud, R., Covert, D. S., Grados, C., Huebert, B., Wood, R., Russell, L. M., Chaigneau, A., Bretherton, C. S., Brown, W. O. J., Daum, P., Klenner, L. Gallardo, Bower, K. N., Fairall, C., Allen, G., Fochesatto, J., Yuter, S. E., Krejci, R., Albrecht, B. A., Vaughan, G., Straneo, F., Toniazzo, T., de Szoeke, Simon P., Coe, H., Palikonda, R., Minnis, P., Chand, D. The VAMOS¹ Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) was an international field program designed to make observations of poorly understood but critical components of the coupled climate system of the southeast Pacific. This region is characterized by strong coastal upwelling, the coolest SSTs in the tropical belt, and is home to the largest subtropical stratocumulus deck on Earth. The field intensive phase of VOCALS-REx took place during October and November 2008 and constitutes a critical part of a broader CLIVAR program (VOCALS) designed to develop and promote scientific activities leading to improved understanding, model simulations, and predictions of the southeastern Pacific (SEP) coupled ocean-atmosphere-land system, on diurnal to interannual timescales. The other major components of VOCALS are a modeling program with a model hierarchy ranging from the local to global scales, and a suite of extended observations from regular research cruises, instrumented moorings, and satellites. The two central themes of VOCALS-REx focus upon (a) links between aerosols, clouds and precipitation and their impacts on marine stratocumulus radiative properties, and (b) physical and chemical couplings between the upper ocean and the lower atmosphere, including the role that mesoscale ocean eddies play. A set of hypotheses designed to be tested with the combined field, monitoring and modeling work in VOCALS is presented here. A further goal of VOCALS-REx is to provide datasets for the evaluation and improvement of large-scale numerical models. VOCALS-REx involved five research aircraft, two ships and two surface sites in northern Chile. We describe the instrument payloads and key mission strategies for these platforms and give a summary of the missions conducted. Title: The VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx): goals, platforms, and field operations Author: Mechoso, C. R., Brioude, J., Abel, S. J., Brewer, A., Springston, S. R., Williams, S., Weller, R. A., Bates, T. S., Garreaud, R., Covert, D. S., Grados, C., Huebert, B., Wood, R., Russell, L. M., Chaigneau, A., Bretherton, C. S., Brown, W. O. J., Daum, P., Klenner, L. Gallardo, Bower, K. N., Fairall, C., Allen, G., Fochesatto, J., Yuter, S. E., Krejci, R., Albrecht, B. A., Vaughan, G., Straneo, F., Toniazzo, T., de Szoeke, Simon P., Coe, H., Palikonda, R., Minnis, P., Chand, D. The VAMOS¹ Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) was an international field program designed to make observations of poorly understood but critical components of the coupled climate system of the southeast Pacific. This region is characterized by strong coastal upwelling, the coolest SSTs in the tropical belt, and is home to the largest subtropical stratocumulus deck on Earth. The field intensive phase of VOCALS-REx took place during October and November 2008 and constitutes a critical part of a broader CLIVAR program (VOCALS) designed to develop and promote scientific activities leading to improved understanding, model simulations, and predictions of the southeastern Pacific (SEP) coupled ocean-atmosphere-land system, on diurnal to interannual timescales. The other major components of VOCALS are a modeling program with a model hierarchy ranging from the local to global scales, and a suite of extended observations from regular research cruises, instrumented moorings, and satellites. The two central themes of VOCALS-REx focus upon (a) links between aerosols, clouds and precipitation and their impacts on marine stratocumulus radiative properties, and (b) physical and chemical couplings between the upper ocean and the lower atmosphere, including the role that mesoscale ocean eddies play. A set of hypotheses designed to be tested with the combined field, monitoring and modeling work in VOCALS is presented here. A further goal of VOCALS-REx is to provide datasets for the evaluation and improvement of large-scale numerical models. VOCALS-REx involved five research aircraft, two ships and two surface sites in northern Chile. We describe the instrument payloads and key mission strategies for these platforms and give a summary of the missions conducted. Close