The Origin of Jupiter's Great Red Spot (2406.13222v1)

Abstract: Jupiter's Grat Red Spot (GRS) is the largest and longest-lived vortex of all solar system planets but its lifetime is debated and its formation mechanism remains hidden. G. D. Cassini discovered in 1665 the presence of a dark oval at the GRS latitude, known as the "Permanent Spot" (PS) that was observed until 1713. We show from historical observations of its size evolution and motions that PS is unlikely to correspond to the current GRS, that was first observed in 1831. New numerical simulations rule out that the GRS formed by the merging of vortices or by a superstorm, but most likely formed from a flow disturbance between the two opposed Jovian zonal jets north and south of it. If so, the aearly GRS should have had a low tangential velocity so that its rotation velocity has increased over time as it shrunk.

• The paper demonstrates that disturbances in Jupiter’s zonal flows are the most plausible mechanism for the formation of the Great Red Spot.
• It integrates historical data from the 17th century with numerical simulations using SW and EPIC models to analyze the vortex’s evolution.
• The study highlights a consistent shrinkage in the GRS's dimensions over time, suggesting potential future instability in the planet’s atmosphere.

Analyzing the Genesis and Evolution of Jupiter's Great Red Spot

The paper investigates the enigmatic origin and evolution of Jupiter's Great Red Spot (GRS), leveraging a combination of historical observations and contemporary numerical simulations. By analyzing the GRS—the largest and long-lasting vortex within our solar system—this paper offers significant insights into planetary dynamics and atmospheric phenomena.

Historical Context and Observations

The authors meticulously analyze historical records dating back to the 17th century to ascertain whether the feature observed by G. D. Cassini, referred to as the "Permanent Spot" (PS), is synonymous with the GRS first definitively sighted in 1831. Their analysis indicates that the PS and the GRS are distinct entities, with the former not persisting through the observational records after 1713. This is inferred through thorough investigations of recorded sizes, motions, and morphological parameters, asserting the GRS's independent genesis around the 19th century.

Measurements of the GRS's dimensions reveal a consistent shrinkage trend: the zonal (east-west) length, meridional (north-south) width, and eccentricity have all diminished since comprehensive observations began in 1879. The shrinkage rate has accelerated in recent years, leading to speculation about the GRS's future stability or potential dissolution. The measured dynamics of the surrounding Hollow add further depth to the understanding of the GRS's morphological evolution.

Numerical Simulation Approaches

The paper's significant contribution lies in its numerical simulation efforts, evaluating three potential formation mechanisms: super-storm generation, vortex mergers, and disturbances in Jupiter's zonal flows. The investigative methodology relies heavily on Shallow Water (SW) models and EPIC models, both computational frameworks adept at simulating atmospheric dynamics under Jovian conditions.

• Super-storm Hypothesis: This approach explores whether a massive convective system resembling those observed on Saturn, such as the Great White Spot, could have catalyzed the GRS's formation. Simulations, however, indicate that such generated vortices do not match the GRS's initial dimensions or dynamics, rendering this hypothesis less viable.
• Vortex Merger Theory: The potential for anticyclones merging to create a larger structure such as the GRS is examined. Historically evidenced in other Jupiter vortices, this formation mechanism is computationally possible yet unlikely, given that observation records do not document the necessary precursors for such large-scale mergers.
• Disturbance in Zonal Flows: This proposed genesis mechanism involves disturbances between opposing zonal jet streams, effectively generating an elongated cell that shrinks and stabilizes into the GRS. This model fits the observed historical data of the GRS appearing as an elongated ellipsis and changing into a more compact form, aligning with changes in peripheral velocity over time.

Implications and Future Directions

The findings assert that the GRS's formation was more plausibly initiated by a disruption in zonal flows, progressing into its observed formation through the persistence of atmospheric dynamics unique to Jupiter. Such insight into the stability, longevity, and potential future of the GRS could illuminate our comprehension of fluid dynamics in large planetary atmospheres.

These simulations advance our understanding of anticyclonic phenomena, adding context to both Jovian atmospheric processes specifically and to fluid dynamics in rotating planetary atmospheres broadly. Future developments could further refine these models to account for deeper dynamics using data from missions like Juno, possibly predicting future changes in scale and energy of the GRS with broader implications for understanding exoplanetary atmospheres exhibiting analogous features.