FIGURE 1. Saturn's equatorial oscillation.

a, This temperature map was retrieved using the hydrogen collision-induced continuum (600 cm^-1) between the 20 and 2 hPa pressure levels, and the v₄-band of methane (1,300 cm^-1) between the 3 and 0.003 hPa pressure levels (see Supplementary Information). The contours indicate temperature in Kelvin. The CIRS observed the planet's limb each 5° of latitude between 45° S and 45° N (here and in b, negative latitudes lie in the southern hemisphere). The ten detectors were aligned vertically, perpendicular to the planet's limb. Each detector independently probed a given altitude with a vertical resolution of 50–100 km. The temperatures presented in this figure were retrieved from 15.5-cm^-1spectra. Vertical profiles of atmospheric temperature were retrieved by means of a constrained inversion with strong low-pass filtering at each limb position. The number of independent longitudes sampled for a given latitude varies between two and four. At the equator the temperature near 10 hPa is 17 K colder than it is at 20° S and 20° N, whereas the equatorial temperature is 20 K warmer near 1 hPa; near 0.1 hPa the equator is again 20 K colder, and at 0.01 hPa the equatorial region is 10 K warmer than it is at adjacent latitudes. b, This map presents the thermal wind field obtained by upward integration of the thermal wind equation on cylinders (see Supplementary Information). The contours indicate measured wind speed minus wind speed at 20 hPa, in metres per second. The dashed parabola delineates the exclusion zone within which the winds cannot be calculated from the thermal wind equation, but are instead interpolated. The error in temperature due to instrument noise is 2 K, and this propagates to an error of 5/(sine of latitude) m s^-1 per scale height in the zonal winds.