Details

Autor(en) / Beteiligte

• Tabataba-Vakili, F.
• Rogers, J.H.
• Eichstädt, G.
• Orton, G.S.
• Hansen, C.J.
• Momary, T.W.
• Sinclair, J.A.
• Giles, R.S.
• Caplinger, M.A.
• Ravine, M.A.
• Bolton, S.J.

Titel

Long-term tracking of circumpolar cyclones on Jupiter from polar observations with JunoCam

Ist Teil von

• Icarus (New York, N.Y. 1962), 2020-01, Vol.335, p.113405, Article 113405

Ort / Verlag

Elsevier Inc

Erscheinungsjahr

2020

Quelle

Elsevier ScienceDirect Journals

Beschreibungen/Notizen

• We use observations from the JunoCam instrument on the Juno spacecraft to map the polar regions of Jupiter between 2016 and 2018. These polar maps track the long-term evolution of the pentagonal and octagonal structures of circumpolar cyclones (CPCs). The south-polar pentagonal and north-polar octagonal arrangements of the CPCs have remained largely stable over the last 2 years of observation. The morphologies of individual cyclones also remain largely stable for 1–2 years, although some changes are observed, so that the location of each CPC is uniquely identifiable. At both north and south poles, individual cyclones move around the center to a limited extent, and there is a gap of variable width between one pair of south polar CPCs. Measurements at consecutive closest approaches (perijoves, 53 days apart) show small movements of individual cyclones both eastward and westward. However, the south-polar CPCs have a long-term systematic westward drift rate of 1.5 ± 0.2° per orbit or 0.040 ± 0.005 m/s, whereas north polar CPCs do not show a consistent drift in longitude. Around the perimeter of the southern pentagon, we detect no rapid jet in short-term animations, and we provide evidence that anticyclonic white ovals may have a range of longitudinal drifts between −44 and +15° per orbit (+1.8 to −0.7 m/s). Measurement of the angular velocities within the cyclones shows increasing angular velocity with decreasing radius, except in the inner bright cloud deck of one class of northern CPCs, which are inferred to have smaller or even negative angular velocities very near the center. Tangential wind velocities within the cyclones range up to 100 m/s (and even >100 m/s in the southern polar cyclone) and are maximal between radii of ~900–1600 km. Overall, we find that the behavior of the polar cyclones constellations compares well to vortex crystal theory, even though the theory does not include anticyclonic vorticity. •We present polar images taken by the JunoCam instrument on Juno.•We track the long-term positions and morphologies of the circumpolar cyclones found around the poles of Jupiter's atmosphere.•Results indicate a slow monotonic westward drift rate in for the southern pentagon, and a slow, more variable drift for the northern octagon.•Measurements of internal cyclone velocity show that once a maximum tangential wind speed is reached, wind speeds decline with increasing radius.•A comparison with vortex-crystal theory matches well even though the theory does not include anticyclonic vorticity.