EGU2020-18767, updated on 12 Jun 2020
https://doi.org/10.5194/egusphere-egu2020-18767
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Atmospheric electric field in the Atlantic marine boundary layer: first results from the SAIL project

Susana Barbosa1, Mauricio Camilo2, Carlos Almeida1, José Almeida1, Guilherme Amaral1, Karen Aplin3, Nuno Dias1, António Ferreira1, Giles Harrison4, Armando Heilmann5, Luis Lima1, Alfredo Martins1, Igor Silva1, Diana Viegas1, and Eduardo Silva1
Susana Barbosa et al.
  • 1INESC TEC, Porto, Portugal
  • 2Marinha, CINAV (Centro de Investigação Naval), Portugal
  • 3University of Bristol, Bristol UK
  • 4University of Reading, Department of Meteorology, Reading, UK
  • 5Universidade Federal do Paraná, Curitiba, Brasil

The study of the electrical properties of the atmospheric marine boundary layer is important as the effect of natural radioactivity in driving near surface ionisation is significantly reduced over the ocean, and the concentration of aerosols is also typically lower than over continental areas, allowing a clearer examination of space-atmosphere interactions. Furthermore, cloud cover over the ocean is dominated by low-level clouds and most of the atmospheric charge lies near the earth surface, at low altitude cloud tops.

The relevance of electric field observations in the marine boundary layer is enhanced by the the fact that the electrical conductivity of the ocean air is clearly linked to global atmospheric pollution and aerosol content. The increase in aerosol pollution since the original observations made in the early 20th century by the survey ship Carnegie is a pressing and timely motivation for modern measurements of the atmospheric electric field in the marine boundary layer. Project SAIL (Space-Atmosphere-Ocean Interactions in the marine boundary Layer) addresses this challenge by means of an unique monitoring campaign on board the ship-rigged sailing ship NRP Sagres during its 2020 circumnavigation expedition.

The Portuguese Navy ship NRP Sagres departed from Lisbon on January 5th in a journey around the globe that will take 371 days. Two identical field mill sensors (CS110, Campbell Scientific) are installed on the mizzen mast, one at a height of 22 m, and the other at a height of 5 meters. A visibility sensor (SWS050, Biral) was also set-up on the same mast in order to have measurements of the extinction coefficient of the atmosphere and assess fair-weather conditions. Further observations include gamma radiation measured with a NaI(Tl) scintillator from 475 keV to 3 MeV, cosmic radiation up to 17 MeV, and atmospheric ionisation from a cluster ion counter (Airel). The 1 Hz measurements of the atmospheric electric field and from all the other sensors are linked to the same rigorous temporal reference frame and precise positioning through kinematic GNSS observations.

Here the first results of the SAIL project will be presented, focusing on fair-weather electric field over the Atlantic. The observations obtained in the first three sections of the circumnavigation journey, including Lisbon (Portugal) - Tenerife (Spain), from 5 to 10 January, Tenerife - Praia (Cape Verde) from 13 to 19 January, and across the Atlantic from Cape Verde to Rio de Janeiro (Brasil), from January 22nd to February 14th, will be presented and discussed.

How to cite: Barbosa, S., Camilo, M., Almeida, C., Almeida, J., Amaral, G., Aplin, K., Dias, N., Ferreira, A., Harrison, G., Heilmann, A., Lima, L., Martins, A., Silva, I., Viegas, D., and Silva, E.: Atmospheric electric field in the Atlantic marine boundary layer: first results from the SAIL project, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18767, https://doi.org/10.5194/egusphere-egu2020-18767, 2020

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Presentation version 1 – uploaded on 05 May 2020
  • CC1: Comment on EGU2020-18767, Kenneth Cummins, 07 May 2020

    Very interesting study. I am quite interested in your findings (as they emerge), to compare with measurements made on NOAA offshore buoys near Florida, using Campbell field mills. One comment -- you will need to determine an enhancement factor for your Campbell sensors in their operational locations on the ship.    

    • AC1: Reply to CC1, Susana Barbosa, 08 May 2020

      Thanks! We'll make the data available and hopefuly we'll have much more results soon... 

      I find the calibration of the field mills the trickiest thing...  it's OK for the temporal variability - the pattern is similar in the two field mills we have (most of the time), but the absolute value is another story... I've made measurements on-shore first with the pier empty, then with the ship docked to the pier, and finally on the ship itself, but still  its the aspect I'm less confident with...