Meridional wind on Venus was detected for the first time in both hemispheres
2017 March 15

15th March, 2017 – The first scientific evidence on Venus of a wind circulation between the equator and the poles, also named meridional wind, was gathered by an international team led by Pedro Machado, of the Instituto de Astrofísica e Ciências do Espaço (IA¹) and Faculdade de Ciências da Universidade de Lisboa (FCUL). This result was published² today in the scientific journal Icarus, a reference publication in the field of Solar System research.

Analysing the light from the sun reflected on the top of the clouds on Venus, Pedro Machado and his team identified, in both hemispheres, a wind component perpendicular to the equator, consistent with the characteristic atmospheric circulation of an Hadley cell³ and with an average velocity of 81 km/h.

Pedro Machado (IA e FCUL) says that “this detection is crucial to understand the transfer of energy between the equatorial region and the high latitudes, shedding light on a phenomenon that for decades has remained unexplained and which is the super-rotation⁴ of the Venus atmosphere.”

Presently, the scientific community is searching for a physical model capable of explaining this phenomenon of super-rotation. In this paper, the team is adding to this model through a study of the wind parallel to the equator, or zonal wind, and how it changes with time and with the latitude, together with the first results concerning the presence of a meridional wind. One of the next steps is to detect the branch of meridional wind at lower altitude along which the air returns to the equator.

Machado and his team have also designed the only method today which uses visible light to measure, from telescopes on Earth, the instantaneous speed of the wind in the atmosphere of another planet. It is based on the Doppler effect5 that the clouds, due to their motion, apply on the light of the Sun reflected on them.

Pedro Machado adds: “Several research groups attempted to measure the meridional wind on Venus. Attempts made until now based on observations from the ground were unsuccessful, while those using data from the Venus Express mission were limited to the southern hemisphere and produced results that were inconclusive”.

Data used in this study published today were gathered from simultaneous and coordinated observations of the atmosphere of Venus conducted with the Venus Express spacecraft, from the European Space Agency (ESA), and with the Canada-France-Hawaii Telescope (CFHT) using the high resolution spectrograph ESPaDOnS.

NOTES:

1. The Instituto de Astrofísica e Ciências do Espaço (Institute of Astrophysics and Space Sciences – IA) is the largest Portuguese research unit in space sciences and integrates researchers from the University of Lisbon and the University of Porto. The institute encompasses most of the field’s national scientific output and it was evaluated as Excellent in the last evaluation from the European Science Foundation (ESF). IA's activity is funded by national and international funds, including Fundação para a Ciência e a Tecnologia (UID/FIS/04434/2013), POPH/FSE and FEDER through COMPETE 2020.

2. The scientific paper “Venus cloud-tracked and doppler velocimetry winds from CFHT/ESPaDOnS and Venus Express/VIRTIS in April 2014”, by Pedro Machado, Thomas Widemann, Javier Peralta, Ruben Gonçalves, Jean-François Donati, and David Luz, was published today in the scientific journal Icarus, Volume 285 (DOI: 10.1016/j.icarus.2016.12.017).

3. An Hadley cell, identified for the first time in the Earth atmosphere by George Hadley in the 18th century, is an atmospheric circulation characterised by the rise of warm air in the equatorial regions and flowing towards the poles to medium latitudes, where the air goes down back to near the surface and returns to the equator.

4. The super-rotation of Venus atmosphere is a phenomenon in which, due to the winds parallel to the equator, or zonal winds, the atmosphere circles the planet in just little more than four Earth days, that is, 60 times faster than the rotation period of the solid globe, which is 243 Earth days.

5. The Doppler effect, for the case of electromagnetic radiation, is the increase or decrease of the characteristic wavelength of the radiation emitted or reflected by an object, and received by an observer, due to the motion of the object relative to the observer. From this effect it is possible to derive the relative velocity of the object.


Contacts:

Pedro Machado
machado@oal.ul.pt

Science Communication Group

Sérgio Pereira
spereira@iastro.pt


Ricardo Cardoso
Reis Ricardo.Reis@iastro.pt



João Retrê (Coordination, Lisbon)
jretre@iastro.pt


Daniel Folha (Coordination, Porto)
Daniel.Folha@iastro.pt