Fine-Scale Turbulence, Cloud Microphysics, and Radiative Cooling Rate Measurements in the Entrainment Interface Layer of Marine Stratocumulus

• Applicants: Dr. Holger Siebert; Professor Dr. Manfred Wendisch
• Subject Area: Atmospheric Science
• Term: from 2015 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 275522730

• Final Report Year: 2020

Final Report Abstract

During this project, high-resolution helicopter-borne measurements of aerosol, cloud, turbulence, and radiation properties were collected during 16 flights around Graciosa/Azores to sample the marine boundary layer (MBL) and the free troposphere (FT) during the one-month period of the ACORES campaign. Small-scale entrainment processes under cloudy and cloudless conditions with respect to the boundary layer and aerosol stratification were investigated. The helicopterborne observations suggest, in combination with concurrent ground-based measurements, that MBL and FT are disconnected in terms of aerosol properties. The MBL is dominated by bimodal size distributions, while in the FT monomodal size distributions are dominant. New particle formation has been observed in the FT and directly above Stratocumulus (Sc). To which extent this particle production will influence the aerosol budget, will be part of further analysis. The number of available CCN is in accordance with the shape of the aerosol size distribution. Particles larger than 80 nm served as CCN at a supersaturation 0.2 % at all sites. This means that the accumulation mode aerosol particles inhibited the typical hygroscopicity of marine aerosol particles. The observed cases of new particle formation do not influence the number of CCN at typical Sc supersaturation, as they did not grow into the relevant size range within the observation period. The close collocation of the in-situ cloud turbulence and microphysical observations performed by ACTOS with the remote-sensing observations of radiation and brightness temperature collected by SMART-HELIOS turned out to be of major importance to verify remote sensing retrievals. In addition, the interpretation of the high-resolution in-situ observations along the flight path requires the combination with the ‘birds-eye view’ of the cloud field provided by SMART-HELIOS. For the fast transition between cloud and cloudless conditions as observed during ACORES, this key advantage cannot be realized by a single research aircraft. Preliminary analysis indicates that spatial inhomogeneity of brightness temperature varies on scales of less than 100 m significantly. These findings are supported by observed high spatial variability of the turbulent cloud-top structure on similar horizontal scales. Within the same Sc-layer regions with extreme local temperature gradients of up to 4 Km^-1 were found followed by much smoother vertical gradients of temperature and wind speed in the direct vicinity. Due to the comparably limited operational area of the helicopter, all airborne observations are located in the vicinity of the ENA site with its comprehensive set of remote-sensing devices. In particular, the ACTOS and SMART-HELIOS observations to the North of Graciosa cover the same cloud layers as seen 556 by the remote-sensing station, which allows for statistical comparison of cloud and turbulence properties with high fidelity. Energy dissipation rates derived in-situ and remotely around cloud top agree remarkably well in terms of their mean values although exhibiting different variability due different averaging. Finally, the utility of the data is further amplified by its coordination with the Aerosol and Cloud Experiments in the Eastern North Atlantic (ACE-ENA), for which the first project part (IOP1) overlapped in time. The in-situ measurements from the ARM Gulfstream G1 aircraft located on Terceira Island, and which also flewin the vicinity of Graciosa,will provide additional opportunities for inter-comparison and for combining complementary measurements.

Publications

• 2017: Measurements of solar and terrestrial heating and cooling rate profiles in Arctic and sub-tropic stratocumulus. 19th EGU General Assembly, EGU2017 , proceedings from the conference held 23-28 April, 2017 in Vienna, Austria., p.14684
  Gottschalk, M., F. Lauermann, A. Ehrlich, H. Siebert, and M. Wendisch
  
• (2018)., 2018b: Airborne investigation of the vertical layering and transport processes of aerosol particles in the marine boundary layer and the free troposphere over the atlantic ocean. 10th International Aerosol Conference (IAC 2018), St. Louis, MO, USA, 2-7 September 2018
  Wehner, B., S. Henning, F. Lauermann, J. Lückerath, K.-E. Szodry, G. Roberts, and H. Siebert
  
• 2018: Fine-scale structure of the marine stratocumulus cloud top over the azores. 15th Conference on Cloud Physics, Vancouver, Canada, 8-13 July 2018
  Szodry, K.-E., J. Fugal, S. Henning, F. Lauermann, S. Malinowski, J. Nowak, R. A. Shaw, H. Siebert, F. Stratmann, B. Wehner, and M. Wendisch
  
• 2018: Free tropospheric aerosol characteristics over the north eastern atlantic ocean and its relationship to the marine boundary layer. 10th International Aerosol Conference (IAC 2018), St. Louis, MO, USA, 2-7 September 2018
  Wehner, B., K. Chevalier, S. Henning, K. Weinhold, O. Welz, C. Mazzoleni, P. Fialho, S. Shum, S. Viviani, and G. Roberts
  
• 2019: Details of mixing events at the top of marine stratocumulus observed during ACORES2017. EGU General Assembly 2019
  Nowak, J., K.-E. Szodry, H. Siebert, and S. Malinowski
  
• 2019: Increased particle concentrations on top of marine stratocumulus clouds over the northeast atlantic ocean. European Aerosol Conference (EAC), Gothenburg, Sweden, 25-30 August 2019
  Wehner, B., J. Lückerath, K.-E. Szodry, S. Henning, F. Lauermann, and H. Siebert
  
• 2019: Vertical aerosol particle exchange in the marine boundary layer estimated from helicopter-borne measurements in the azores region. European Aerosol Conference (EAC), Gothenburg, Sweden, 25-30 August 2019
  Lückerath, J., A. Held, and B. Wehner
  
• 2019: Vertical distribution of cloud condensation nuclei in marine air masses over the northern atlantic (acores campaign). European Aerosol Conference (EAC), Gothenburg, Sweden, 25-30 August 2019
  Henning, S., B. Wehner, G. Roberts, K. Chevalier, J. Lückerath, F. Lauermann, K.-E. Szodry, K. Weinhold, C. Mazzoleni, P. Fialho, S. Schum, and H. Siebert
  
• 2020: Observations of aerosol, cloud, turbulence, and radiation properties at the top of the marine boundary layer over the Eastern North Atlantic Ocean: The ACORES campaign. Bull. Amer. Meteor. Soc., 1–59
  Siebert, H., K. E. Szodry, U. Egerer, B. Wehner, K. C. S. Henning, J. Lückerath, O. Welz, K. Weinhold, F. Lauermann, M. Gottschalk, A. Ehrlich, M. Wendisch, P. Fialho, S. Viviani, G. Roberts, S. Schum, R. A. Shaw, C. Mazzoleni, J. Nowak, S. Malinowski, K. Karpinska, W. Kumala, and D. Czyżewska