Three-dimensional isoneutral potential vorticity structure in the Indian Ocean

The three-dimensional isoneutral potential vorticity structure of the India n Ocean is examined using World Ocean Circulation Experiment and National O ceanic and Atmospheric Administration conductivity-temperature-depth data a nd historical bottle data. The distribution of the potential vorticity is s et by the Indian Ocean's source waters and their circulation inside the bas in. The lower thermocline has a high potential vorticity signal extending w estward from northwest of Australia and a low signal from the Subantarctic Mode Water in the south. The Antarctic Intermediate Water inflow creates pa tches of high potential vorticity at intermediate depths in the southern In dian Ocean, below which the field becomes dominated by planetary vorticity, indicating a weaker meridional circulation and weaker potential vorticity sources. Wind-driven gyre depths have lower potential vorticity gradients p rimarily due to same-source waters. Homogenization and western shadow zones are not observed. The P-effect dominates the effect of the Somali Current and the Red Sea Water on the potential vorticity distribution. Isopleths ti lt strongly away from latitude lines in the deep and abyssal waters as the Circumpolar Deep Water fills the basins in deep western boundary currents, indicating a strong meridional circulation north of the Antarctic Circumpol ar Current. The lower-gradient intermediate layer surrounded vertically by layers with higher meridional potential vorticity gradients in the subtropi cal Indian Ocean suggests that Rossby waves will travel similar to 1.3 time s faster than standard theory predicts. To the south, several pools of homo genized potential vorticity appear in the upper 2000 m of the Southern Ocea n where gyres previously have been identified. South of Australia the abyss al potential vorticity structure is set by a combination of the Antarctic C ircumpolar Current and the bathymetry.