Historical and Contemporary Trends in the Size, Drift, and Color of Jupiter's Great Red Spot

Observations of Jupiter’s Great Red Spot (GRS) span more than 150 years. This allows for careful measurements of its size and drift rate. High spatial resolution spacecraft data also allow tracking of its spectral characteristics and internal dynamics and structure. The GRS continues to shrink in longitudinal length at an approximately linear rate of 0.°194 yr^-1 and in latitudinal width at 0.°048 yr^-1. Its westward drift rate (relative to System III W. longitude) has increased from ∼0.°26/day in the 1980s to ∼0.°36/day currently. Since 2014, the GRS’s short wavelength (<650 nm) reflectance has continued to decrease, while it has become brighter at 890 nm, indicating a change in clouds/haze at high altitudes. In addition, its north-south color asymmetry has decreased, and the dark core has become smaller. Internal velocities have increased on its east and west edges, and decreased on the north and south, resulting in decreased relative vorticity and circulation. The GRS’s color changes from 2014 to 2017 may be explained by changes in stretching vorticity or divergence acting to balance the decrease in relative vorticity.