General circulation of the solar atmosphere from observational evidence
- 28 Downloads
One of the main results of the rotating cylinder experiments ofFultz andHide is that the general flow regime in them is essentially determined by the ratio of the angular velocity of the fluid motions (relative to the cylinder) to that of the cylinder itself. Extending these results to the atmosphere of the sun, leads to the hypothesis that the layer in which spots are imbedded should exhibit a non-axially symmetric pattern, of theRossby type.
The fluid motions, characteristic of such a general circulation pattern, are mainly along spherical surfaces, and have a wavelike (eddy) appearance similar to the planetary waves in the upper troposphere of the terrestrial atmosphere. These eddies transport momentum along these spherical surfaces from regions of relatively lower angular velocity to regions of higher velocity. Tracers (e.g., sunspots) imbedded is such a flow would show a correlation between their proper motions in latitude and longitude, such that spots moving equatorward will tend to have larger longitudinal motions (toward the west limb), and vice versa.
Analysis of ten years (1935 to 1944) of Greenwich spot data shows a consistent, and (statistically) very significant correlation of spot group proper motions, in the proper sense. These results provide strong support for the existence of large-scale waves which are some modest fraction of the solar circumference, but larger than the sunspot groups. Moreover, these waves transport angular momentum (up the gradient of angular velocity) toward the equatorial regions from higher latitudes across at least the entire sunspot zone. It is not known, however, whether these eddies are the primary (or only) source of momentum to maintain the ‘equatorial acceleration’ of the sun. However, if this source were shut off, and all other processes continued unabated, this layer of the sun between latitudes ±20° would reach solid rotation in about 51/2 rotations.
Because this eddy transport of momentum is counter to the gradient of angular velocity, there is an implied transformation of the kinetic energy of the eddies into the kinetic energy of the mean east-west flow. Of possibly even more interest, however, might be the possibility of transfers of kinetic energy between eddies of all different scale sizes extending down the entire spectrum to include sunspot groups and the spots themselves. Moreover, some eddy size(s) in this layer is likely to be primarily responsible for a conversion of potential to kinetic energy.
A result of subsidiary interest is the systematically higher value of solar rotation (at all latitudes) derivable from this data, which includes all spots which survive for at least two days. In contrast to the work of previous authors who used only long-lived spots, the result obtained when many small spots are used, indicates perhaps a variation of the rotation rate with height in the solar atmosphere.
The results provide no evidence to indicate the existence of significant meridional circulations (latitudinal driffs).
KeywordsAngular Velocity Solar Atmosphere Proper Motion Planetary Wave Meridional Circulation
Unable to display preview. Download preview PDF.
- C. de Jager,Structure and Dynamics of the Solar Atmosphere, Encyclopedia of Physics, Vol. 52, Astrophysics III: The Solar System (1959), 80.Google Scholar
- D. Fultz, R. R. Long, G. V. Owens, W. Bohan, R. Kaylor andJ. Weil,Studies of Thermal Convection in a Rotating Cylinder with some Implications for Large-Scale Atmospheric Motions, Meteorological Monographs, Amer. Met. Soc.4, 21 (1959), 104.Google Scholar
- L. Goldberg,Introduction, The Sun, edited by G. P. Kuiper, Univ. of Chicago Press (1953), p. 1.Google Scholar
- R. Hide,An Experimental Study of Thermal Convection in a Rotating Liquid, Phil. Trans. Roy. Soc. [A],250 (1958), 441.Google Scholar
- P. G. Hoel,Introduction to Mathematical Statistics (J. Wiley, London 1947), 258 pp.Google Scholar
- K. O. Kiepenheuer,Solar Activity, The Sun, edited by G. P. Kuiper, Univ. of Chicago Press (1953), 322.Google Scholar
- H.-L. Kuo,Energy-Releasing Processes and Stability of Thermally Driven Motions in a Rotating Fluid, J. Meteor.13 (1956), 82.Google Scholar
- E. N. Lorenz,Simplified Dynamic Equations Applied to the Rotating-Basic Experiments, J. Atm. Sci.19 (1962), 39.Google Scholar
- H. W. Newton,The Sun's Rotation Period Derived from Recurrent Sunspots, 1924–1933, M.N.R.A.S.95 (1934), 60.Google Scholar
- H. W. Newton andM. L. Nunn,The Sun's Rotation Derived from Sunspots and Additional Results, 1934–1944, M.N.R.A.S.111 (1951), 413.Google Scholar
- H. H. Plaskett,Limb Darkening and Solar Rotation, M.N.R.A.S.123 (1962), 541.Google Scholar
- Royal Obervatory, Greenwich,Determination of the Solar Rotation from Long-lived Spots, M.N.R.A.S.85 (1925), 548.Google Scholar
- V. P. Starr,An Essay on the General Circulation of the Earth's Atmosphere, J. Meteor.5 (1948), 39.Google Scholar
- V. P. Starr,Galactic Dynamics in the Light of Meteorological Theory, Geof. pura e appl., Vol. 56 (1963/III), 163.Google Scholar
- V. P. Starr andR. M. White,A Hemispherical Study of the Atmospheric Angular-momentum Balance, Quart. J. Roy. Met. Soc.77 (1951), 215.Google Scholar
- V. P. Starr andR. M. White,Two Years of Momentum Flux Data for 31°N, Tellus4 (1952), 332.Google Scholar
- V. P. Starr andR. R. Long,The Flux of Angular Momentum in Rotating Model Experiments, Geophys. Res. Paper No. 24, Air Force Cambridge Res. Lab. (1953), 103.Google Scholar
- J. Tuominen,Die systematische Strombewegung der Sonnenflecken in heliographischer Breite, Z. Ap.21 (1941), 96.Google Scholar
- J. Tuominen,On the Dependence of the Systematic Drift of Sunspots in Heliographic Latitude on Phase in the 22-year Cycle of the Sun, Z. Ap.30 (1952), 261.Google Scholar
- J. Tuominen,The Latitude Drift of Sunspot Groups, Z. Ap.37 (1955), 145.Google Scholar
- F. Webster,The Effect of Meanders on the Kinetic Energy Balance of the Gulf Stream, Tellus13 (1961), 392.Google Scholar