Sun-stirred Kraken Mare: Circulation in Titan’s seas induced by solar heating and methane precipitation

• Solar heating can cause gyres in Titan’s seas if they are transparent to sunlight.
• Solar heating barely causes currents if the seas are turbid.
• Non-uniform rainfall can cause meridional overturning.
• Gyres are more ubiquitous than meridional overturning in Titan’s seas.

Density-driven circulation in Titan’s seas forced by solar heating and methane evaporation/precipitation is simulated by an ocean circulation model. If the sea is transparent to sunlight, solar heating can induce anti-clockwise gyres near the sea surface and clockwise gyres near the sea bottom. The gyres are in geostrophic balance between the radially symmetric pressure gradient force and Coriolis force. If instead the sea is turbid and most sunlight is absorbed near the sea surface, the sea gets stratified in warm seasons and the circulation remains weak. Precipitation causes compositional stratification of the sea to an extent that the sea surface temperature can be lower than the sea interior temperature without causing a convective overturning. Non-uniform precipitation can also generate a latitudinal gradient in the methane mole fraction and density, which drives a meridional overturning with equatorward currents near the sea surface and poleward currents near the sea bottom. However, gyres are more ubiquitous than meridional overturning.