A chaotic long-lived vortex at the southern pole of Venus

Journal name:
Nature Geoscience
Volume:
6,
Pages:
254–257
Year published:
DOI:
doi:10.1038/ngeo1764
Received
Accepted
Published online

Polar vortices are common in the atmospheres of rapidly rotating planets1, 2, 3, 4. On Earth and Mars, vortices are generated by surface temperature gradients and their strength is modulated by the seasonal insolation cycle1, 2, 3. Slowly rotating Venus lacks pronounced seasonal forcing, but vortices are known to occur at both poles, in an atmosphere that rotates faster than the planet itself5, 6, 7, 8. Here we report observations of cloud motions at altitudes of 42 and 63km above Venus’s south pole using infrared images from the VIRTIS instrument onboard the Venus Express spacecraft. We find that the south polar vortex is a long-lived but unpredictable feature. Within the two cloud layers sampled, the centres of rotation of the vortex are rarely aligned vertically and both wander erratically around the pole with velocities of up to 16ms−1. At the two horizontal levels, the observed cloud morphologies do not correlate with the vorticity of the wind field and change continuously, and vertical and meridional wind shears are also highly variable. We conclude that Venus’s south polar vortex is a continuously evolving structure that is at least 20km high, extending through a quasi-convective turbulent region.

At a glance

Figures

  1. Polar projections of vortex morphology as observed at infrared wavelengths and zonal wind velocities.
    Figure 1: Polar projections of vortex morphology as observed at infrared wavelengths and zonal wind velocities.

    a, Upper (top panels) and lower (bottom panels) cloud levels on orbit 310. be, Upper cloud level on orbits 251 (b), 355 (c), 394 (d) and 475 (e). Latitude circles (dotted lines) appear every 5°. The white points show the rotation centre derived from the wind field. The largest vectors in each panel are 50ms−1 (a, upper cloud) and 46ms−1 (a, lower cloud), 37ms−1 (b), 40ms−1 (c), 38ms−1 (d) and 61ms−1 (e). Typical measurement errors are 4ms−1.

  2. Local relative vorticity maps and streamlines.
    Figure 2: Local relative vorticity maps and streamlines.

    a, Upper (top) and lower (bottom) cloud levels on orbit 310. be, Upper cloud level on orbits 251 (b), 355 (c), 394 (d) and 475 (e). Vorticities (10−5s−1) are colour coded and streamlines appear as continuous lines. Circles of constant latitude (dashed lines) are plotted at 5 degree intervals from Venus’s south pole. The centre of rotation (white points) is derived from the wind field and differs from the morphological centre (maroon points). Most of the vorticity maps resemble b, with no remarkable maxima. Vorticity errors are of the order of 2.5×10−5s−1.

  3. Vorticity map of the upper cloud layer on orbit 475 superimposed over vortex morphology (as seen in Fig. 1e).
    Figure 3: Vorticity map of the upper cloud layer on orbit 475 superimposed over vortex morphology (as seen in Fig. 1e).

    Circles of constant latitude (dashed lines) occur at 5 degree intervals. Vorticity values are colour-coded in units of 10−5s−1 and vorticity isolines (dotted contours, labels reflect vorticity values) and two centres of rotation as derived from the wind field (white points) are shown. High thermal emission features generally occur around regions of peak cyclonic vorticity and can be centred in regions of near-null vorticity. Vorticity errors are of the order of 2.5×10−5s−1.

  4. Vortex/'s erratic wandering.
    Figure 4: Vortex’s erratic wandering.

    Polar projection of the vortex centre of rotation for the lower (red) and the upper (blue) cloud layers in terms of latitude (concentric circles) and local time (radii, in hours). Numbers correspond to particular orbits. A measurement of the vortex centre was obtained in all of the analysed orbits, but only three short sequences and the trajectories run by the vortex centre during these sequences are shown here. These positions are accurate within 1° for the upper cloud and 4° for the lower cloud.

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Affiliations

  1. Departamento Física Aplicada I, Escuela Técnica Superior de Ingeniería, Universidad del País Vasco (UPV/EHU), Alda. Urquijo s/n, 48013 Bilbao, Spain

    • I. Garate-Lopez,
    • R. Hueso &
    • A. Sánchez-Lavega
  2. Unidad Asociada Grupo Ciencias Planetarias UPV/EHU-IAA(CSIC), 48013 Bilbao, Spain

    • R. Hueso &
    • A. Sánchez-Lavega
  3. Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astronomí, 18008 Granada, Spain

    • J. Peralta
  4. Observatório Astronómico de Lisboa (CAAUL), Tapada da Ajuda, 1349-018 Lisboa, Portugal

    • J. Peralta
  5. IASF/INAF, 100 Via del Fosso del Cavaliere, 00133 Rome, Italy

    • G. Piccioni
  6. LESIA/Observatoire de Paris, CNRS UPMC, Univ. Paris-Diderot, 5, Place Jules Janssen, 92195 Meudon, France

    • P. Drossart

Contributions

I.G-L. performed the image selection and wind measurements. R.H. designed the measurement software. A.S-L. coordinated this research and with J.P. made theoretical interpretations. P.D. and G.P. have coordinated the observations as Principal Investigators of VIRTIS. All the authors discussed the results and commented on the manuscript.

Competing financial interests

The authors declare no competing financial interests.

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