The splitting of the frequencies of the global resonant acoustic modes of the Sun by large-scale Ñows and rotation permits study of the variation of angular velocity ) with both radius and latitude within the turbulent convection zone and the deeper radiative interior. The nearly uninterrupted Doppler imaging observations, provided by the Solar Oscillations Investigation (SOI) using the Michelson Doppler Imager (MDI) on the Solar and Heliospheric Observatory (SOHO) spacecraft positioned at the Lagrangian point in continuous sunlight, yield oscillation power spectra with very high signal-to-L 1 noise ratios that allow frequency splittings to be determined with exceptional accuracy. This paper reports on joint helioseismic analyses of solar rotation in the convection zone and in the outer part of the radiative core. Inversions have been obtained for a medium-l mode set (involving modes of angular degree l extending to about 250) obtained from the Ðrst 144 day interval of SOI-MDI observations in 1996. Drawing inferences about the solar internal rotation from the splitting data is a subtle process. By applying more than one inversion technique to the data, we get some indication of what are the more robust and less robust features of our inversion solutions. Here we have used seven di †erent inversion methods. To test the reliability and sensitivity of these methods, we have performed a set of controlled experiments utilizing artiÐcial data. This gives us some conÐdence in the inferences we can draw from the real solar data. The inversions of SOI-MDI data have conÐrmed that the decrease of ) with latitude seen at the surface extends with little radial variation through much of the convection zone, at the base of which is an adjustment layer, called the tachocline, leading to nearly uniform rotation deeper in the radiative interior. A prominent rotational shearing layer in which ) increases just below the surface is discernible at low to mid latitudes. Using the new data, we have also been able to study the solar rotation closer to the poles than has been achieved in previous investigations. The data have revealed that the angular velocity is distinctly lower at high latitudes than the values previously extrapolated from measurements at lower latitudes based on surface Doppler observations and helioseismology. Furthermore, we have found some evidence near latitudes of 75¡ of a submerged polar jet which is rotating more rapidly than its immediate surroundings. Superposed on the relatively smooth latitudinal variation in ) are alternating zonal bands of slightly faster and slower rotation, each extending some 10¡ to 15¡ in latitude. These relatively weak banded Ñows have been followed by inversion to a depth of about 5% of the solar radius and appear to coincide with the evolving pattern of "" torsional oscillations ÏÏ reported from earlier surface Doppler studies.

It is a long-standing puzzle that the Sun's photosphere--its visible surface--rotates differentially, with the equatorial regions rotating faster than the poles. It has been suggested that waves analogous to terrestrial Rossby waves, and known as r-mode oscillations, could explain the Sun's differential rotation: Rossby waves are seen in the oceans as large-scale (hundreds of kilometres) variations of sea-surface height (5-cm-high waves), which propagate slowly either east or west (they could take tens of years to cross the Pacific Ocean). Calculations show that the solar r-mode oscillations have properties that should be strongly constrained by differential rotation. Here we report the detection of 100-m-high 'hills' in the photosphere, spaced uniformly over the Sun's surface with a spacing of (8.7 +/- 0.6) x 10(4) km. If convection under the photosphere is organized by the r-modes, the observed corrugated photosphere is a probable surface manifestation of these solar oscillations.

During the Spacelab 2 mission the Plasma Diagnostics Package (PDP) performed a fly‐around of the shuttle at distances of up to 300 meters while an electron beam was being ejected from the shuttle. We discuss a magnetic conjunction of the shuttle and the PDP while the electron gun was operating in a steady (DC) mode. During this conjunction, the PDP detected a clear funnel‐shaped emission that is believed to be caused by whistler‐mode emission from the beam. Ray‐path calculations show that the shape of the funnel can be accounted for by whistler‐mode waves propagating near the resonance cone. Because the beam and waves are propagating in the same direction, the radiation must be produced by a Landau, ω/k∥ = vb, interaction with the beam. Other types of waves generated by the beam are also described.

No abstract

The precise shape of the Sun has not been convincingly determined, despite half a century of modern photoelectric observations. The expected deviation of the solar-limb shape from a perfect circle is very small, but such asphericity is sensitive to the Sun's otherwise invisible interior conditions, as well as the solar atmosphere. We use evidence from a long-running experiment based in space to show that, when analyzed with sufficiently high spatial resolution, the Sun's oblate shape is distinctly constant and almost completely unaffected by the solar-cycle variability seen on its surface. The solar oblateness is significantly lower than theoretical expectations by an amount that could be explained by a slower differential rotation in the outer few percent of the Sun.