Meridional Flow/Solar Cycle
Presiding: F Hill, National Solar Observatory; Y Fan, High Altitude Observatory
SP32A-01 10:30h
2 Years of Meridional Circulation from GONG Ring Diagrams
Large Aperture Ring Diagram analysis has been used to search for meridional circulation variability using a 2-year GONG data series. This technique uses patches that are four times the size of the typically studied sections of 15 degrees in diameter, so we are able to recover information about lower l modes that penetrate deeper into the Sun. Although extending the working area allow us to reach further into the solar interior, there is a compromise between the size of the patch and the validity of the plane wave approximation used by the technique. In this particular study, we search for variability of the meridional flows as a function of depth for 25 consecutive Carrington rotations. We have studied patches of 30-degree diameter over the solar surface as they crossed the solar central meridian. The range of modes recovered with these larger regions goes down to l~100 and reach a maximum depth of approximately 0.96Rsun. A set of 15 overlapping sections, centered at latitudes 0,+/-7.5,+/-15,+/-22.5,+/-30.0,+/-37.5,+/-45.0 and +/-52.5, has been analyzed for 24 intervals of 1664 minutes covering each Carrington rotation from CR1985 to CR2009 (Jan-2002 to Dec-2003). Meridional circulation results from standard ring diagram analysis and this large-aperture technique are compared, as well as results obtained from two different instruments GONG and MDI. This work was supported in part by NASA grant NAG5-11703. SOHO is a project of international cooperation between ESA and NASA. This work utilizes data obtained by the Global Oscillation Network Group (GONG) Program, managed by the National Solar Observatory, which is operated by AURA, Inc. under a cooperative agreement with the National Science Foundation. The data were acquired by instruments operated by the Big Bear Solar Observatory, High Altitude Observatory, Learmonth Solar Observatory, Udaipur Solar Observatory, Instituto de Astrofisico de Canarias, and Cerro Tololo Interamerican Observatory.
SP32A-02 10:45h
Determining the Sun's Deep Meridional Flow Speed Using Active Latitude Drift Rates Since 1874
Dynamo models that incorporate a deep meridional return flow indicate that this flow regulates both the period and the amplitude of the sunspot cycle (Dikpati & Charbonneau 1999, ApJ, 518, 508 and Charbonneau & Dikpati 2000, ApJ, 543, 1027). We recently examined the equatorward drift of the active latitudes (as given by the centroid of the sunspot areas in each hemisphere) and found evidence supporting this view (Hathaway et al. 2003, ApJ, 589, 665 and Hathaway et al. 2004, ApJ, 602, 543). In those studies we fit the equatorward drift in each hemisphere for each sunspot cycle with a simple parabola - giving us a drift rate and its deceleration for each hemisphere/cycle. Here we analyze the same data (the Royal Greenwich Observatory/USAF/NOAA daily active region summaries) to determine the drift rates in each hemisphere on a yearly basis (rotation-by-rotation measurements smoothed to remove high frequencies) and fit them with a simple model for the meridional flow that provides the meridional flow speed as a function of latitude and time from 1874 to 2005. These flow speeds can be used to test dynamo models -- some of which have predictive capabilities.
SP32A-03 11:00h
Global, Local and Surface Measurements of Large-Scale Zonal Flows Near the Solar Surface
Migrating bands of weak zonal flow, associated with the activity bands in the solar cycle, have been observed at the solar surface for some time. More recently, these flows have been probed deep within the convection zone using global helioseismology, and examined in more detail close to the surface with the techniques of local helioseismology. We compare the results from global and local helioseismology using data from the Michelson Doppler Imager and the GONG network and also Doppler measurements from Mount Wilson, and find that the results are in reasonable agreement, with some explicable differences in detail. This was work was supported by the National Science Foundation and NASA.
SP32A-04 11:15h
Solar Torsional Oscillations and the Extended Solar Cycle
Torsional Oscillations were first observed on the surface of the sun as waves of small deviations from differential rotation, which propagate from the pole to the equator over solar-cycle time scales. More recently they have been inferred from observations of solar global oscillations to occur in the convection zone. Other solar phenomena, such as ephemeral regions and brightenings in the corona, have also been observed to propagate from near the poles to the equator over similar time scales. These other phenomena have been collectively referred to as the "Extended Solar Cycle". This paper will discuss the relationship between torsional oscillations as observed on the surface and in the convection zone and the "Extended Solar Cycle" as observed in the corona. R. C. Altrock was supported by the Air Force Office of Scientific Research.
http://nsosp.nso.edu/data/corona.html
SP32A-05 11:30h
SUNSPOT STATISTICAL PROPERTIES IN THE CYCLE 23 FROM THE SOLAR FEATURE CATALOGUE
The statistical analysis of sunspot area and magnetic field distributions in 1996-2004 are presented. The sunspot parameters are automatically extracted from the SOHO/NDI white light solar images (4 per day) and magnetograms (15 per day) and stored in the Solar Feature Catalogues (SFC). The number of sunspots is found to increase exponentially with the area decrease with a slightly increasing index from the solar minimum to its maximum. The N-S asymmetry in sunspot area distributions and its periodicity for different phases of the solar cycle and hemispheres is investigated with the period deduced. Longitudinal sunspot distributions also reveal a strong North-South asymmetry in the active longitude appearance and the relation to latitudinal distributions that depends on the phase of the solar cycle. The magnetic field distributions for the total and excess fluxes as a function of the sunspot heliospheric longitude and latitude are also presented for different phases of the solar cycle. These statistical properties of sunspots and their magnetic field are tested versus those predicted by the turbulent dynamo theory.
http://www.inf.brad.ac.uk/egso