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• 11. [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

• 12. [Article] Observations of Stratocumulus Clouds and Their Effect on the Eastern Pacific Surface Heat Budget along 20 degrees S

  This is the publisher’s final pdf. The published article is copyrighted by the American Meteorological Society and can be found at: http://www.ametsoc.org/pubs/journals/jcli/. To the best of our knowledge, ...

  Citation × Citation Citation Abstract Copy Title: Observations of Stratocumulus Clouds and Their Effect on the Eastern Pacific Surface Heat Budget along 20 degrees S Author: Yuter, Sandra, Mechem, David, Burleyson, Casey D., Fairall, Chris W., de Szoeke, Simon P., Zuidema, Paquita This is the publisher’s final pdf. The published article is copyrighted by the American Meteorological Society and can be found at: http://www.ametsoc.org/pubs/journals/jcli/. To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. Title: Observations of Stratocumulus Clouds and Their Effect on the Eastern Pacific Surface Heat Budget along 20 degrees S Author: Yuter, Sandra, Mechem, David, Burleyson, Casey D., Fairall, Chris W., de Szoeke, Simon P., Zuidema, Paquita This is the publisher’s final pdf. The published article is copyrighted by the American Meteorological Society and can be found at: http://www.ametsoc.org/pubs/journals/jcli/. To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. Close

• 13. [Article] Variability in the Southerly Flow into the Eastern Pacific ITCZ

  During boreal summer and fall, there is a strong southerly boundary layer flow across the equator into the east Pacific intertropical convergence zone (ITCZ). The modulation of this flow on synoptic to ...

  Citation × Citation Citation Abstract Copy Title: Variability in the Southerly Flow into the Eastern Pacific ITCZ Author: de Szoeke, Simon P., Bretherton, Christopher S. During boreal summer and fall, there is a strong southerly boundary layer flow across the equator into the east Pacific intertropical convergence zone (ITCZ). The modulation of this flow on synoptic to seasonal time scales is studied using an index of meridional pressure difference between the equator and the ITCZ along 95°W. Two complementary datasets from the East Pacific Investigation of Climate (EPIC) are used to study eastern Pacific variability. Daily measurements of sea level pressure (SLP) from Tropical Atmosphere Ocean (TOA) array buoys from May to November 2001 provide temporal coverage, and eight flights by a C-130 aircraft during September to October 2001 document the associated modulation of lower tropospheric vertical structure. The principal mode of variability of the perturbation SLP along 95°W from 1°S to 12°N, derived by principal component analysis from either the eight flights (PC1C-130) or from daily TAO buoy observations (PC1), explains 77% of the meridional pressure gradient variability. The pressure anomalies at 1.6 km are similar to those at the surface. The time series of the first mode of the TAO observations shows that most of the variance is in the 2–7-day range. Low pressure at 12°N is associated with southerly and westerly surface wind anomalies, and enhanced precipitation in the ITCZ. The depth of ITCZ convection is more strongly correlated to meridional wind above the planetary boundary layer (PBL) than to meridional wind within the PBL. There is little correlation of PBL meridional flow across the equator with ITCZ convection. Regression of PC1C-130 against the 95°W cross sections observed by dropwinsondes released during the eight C-130 flights shows correlations of westerlies to positive PC1C-130 (low pressure at 12°N). Between the equator and 4°N, statistically significant northerlies just above the PBL at 1–2-km height and southerlies at 4 km are correlated with negative PC1C-130, having high SLP at 12°N, an anomalously weak meridional SLP gradient, and suppressed convection in the ITCZ. PC1 is bandpass filtered and correlated with reanalysis fields to identify the structures that modulate meridional pressure gradients along 95°W. Most of the variability at periods less than 15 days is related to easterly waves. Seasonal trends in PC1 during May–October 2001 reflect the seasonal evolution of the sea and land surface temperatures. After the seasonal trend is removed, a geostrophic westerly jet at 12°N—probably related to the Madden–Julian oscillation—dominates PC1 variability on time scales longer than 15 days Title: Variability in the Southerly Flow into the Eastern Pacific ITCZ Author: de Szoeke, Simon P., Bretherton, Christopher S. During boreal summer and fall, there is a strong southerly boundary layer flow across the equator into the east Pacific intertropical convergence zone (ITCZ). The modulation of this flow on synoptic to seasonal time scales is studied using an index of meridional pressure difference between the equator and the ITCZ along 95°W. Two complementary datasets from the East Pacific Investigation of Climate (EPIC) are used to study eastern Pacific variability. Daily measurements of sea level pressure (SLP) from Tropical Atmosphere Ocean (TOA) array buoys from May to November 2001 provide temporal coverage, and eight flights by a C-130 aircraft during September to October 2001 document the associated modulation of lower tropospheric vertical structure. The principal mode of variability of the perturbation SLP along 95°W from 1°S to 12°N, derived by principal component analysis from either the eight flights (PC1C-130) or from daily TAO buoy observations (PC1), explains 77% of the meridional pressure gradient variability. The pressure anomalies at 1.6 km are similar to those at the surface. The time series of the first mode of the TAO observations shows that most of the variance is in the 2–7-day range. Low pressure at 12°N is associated with southerly and westerly surface wind anomalies, and enhanced precipitation in the ITCZ. The depth of ITCZ convection is more strongly correlated to meridional wind above the planetary boundary layer (PBL) than to meridional wind within the PBL. There is little correlation of PBL meridional flow across the equator with ITCZ convection. Regression of PC1C-130 against the 95°W cross sections observed by dropwinsondes released during the eight C-130 flights shows correlations of westerlies to positive PC1C-130 (low pressure at 12°N). Between the equator and 4°N, statistically significant northerlies just above the PBL at 1–2-km height and southerlies at 4 km are correlated with negative PC1C-130, having high SLP at 12°N, an anomalously weak meridional SLP gradient, and suppressed convection in the ITCZ. PC1 is bandpass filtered and correlated with reanalysis fields to identify the structures that modulate meridional pressure gradients along 95°W. Most of the variability at periods less than 15 days is related to easterly waves. Seasonal trends in PC1 during May–October 2001 reflect the seasonal evolution of the sea and land surface temperatures. After the seasonal trend is removed, a geostrophic westerly jet at 12°N—probably related to the Madden–Julian oscillation—dominates PC1 variability on time scales longer than 15 days Close

• 14. [Article] Mechanisms of convective cloud organization by cold pools over tropical warm ocean during the AMIE/DYNAMO field campaign

  To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by the author(s) ...

  Citation × Citation Citation Abstract Copy Title: Mechanisms of convective cloud organization by cold pools over tropical warm ocean during the AMIE/DYNAMO field campaign Author: Feng, Zhe, Hagos, Samson, de Szoeke, Simon P., Rowe, Angela K., Burleyson, Casey D., Martini, Matus N. To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by John Wiley & Sons, Ltd. on behalf of American Geophysical Union. The published article can be found at: http://sites.agu.org/ Title: Mechanisms of convective cloud organization by cold pools over tropical warm ocean during the AMIE/DYNAMO field campaign Author: Feng, Zhe, Hagos, Samson, de Szoeke, Simon P., Rowe, Angela K., Burleyson, Casey D., Martini, Matus N. To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by John Wiley & Sons, Ltd. on behalf of American Geophysical Union. The published article can be found at: http://sites.agu.org/ Close

• 15. [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