Measurements of the Sun's High Latitude Meridional Circulation
| Autor: | David H. Hathaway, Katie Kosak, Lisa Rightmire-Upton |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 2012 |
| Předmět: |
010504 meteorology & atmospheric sciences
FOS: Physical sciences Rotation 01 natural sciences Latitude symbols.namesake 0103 physical sciences Differential rotation Astrophysics::Solar and Stellar Astrophysics Clockwise 010303 astronomy & astrophysics Solar and Stellar Astrophysics (astro-ph.SR) Physics::Atmospheric and Oceanic Physics 0105 earth and related environmental sciences Physics Astronomy and Astrophysics Geodesy Astrophysics - Solar and Stellar Astrophysics 13. Climate action Space and Planetary Science Meridional flow Physics::Space Physics symbols Solar rotation Polar Doppler effect |
| Popis: | The meridional circulation at high latitudes is crucial to the build-up and reversal of the Sun's polar magnetic fields. Here we characterize the axisymmetric flows by applying a magnetic feature cross-correlation procedure to high resolution magnetograms obtained by the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). We focus on Carrington Rotations 2096-2107 (April 2010 to March 2011) - the overlap interval between HMI and the Michelson Doppler Investigation (MDI). HMI magnetograms averaged over 720 seconds are first mapped into heliographic coordinates. Strips from these maps are then cross-correlated to determine the distances in latitude and longitude that the magnetic element pattern has moved, thus providing meridional flow and differential rotation velocities for each rotation of the Sun. Flow velocities were averaged for the overlap interval and compared to results obtained from MDI data. This comparison indicates that these HMI images are rotated counter-clockwise by 0.075 degrees with respect to the Sun's rotation axis. The profiles indicate that HMI data can be used to reliably measure these axisymmetric flow velocities to at least within 5 degrees of the poles. Unlike the noisier MDI measurements, no evidence of a meridional flow counter-cell is seen in either hemisphere with the HMI measurements: poleward flow continues all the way to the poles. Slight North-South asymmetries are observed in the meridional flow. These asymmetries should contribute to the observed asymmetries in the polar fields and the timing of their reversals. 6 pages, 3 color figures, accepted for publication in The Astrophysical Journal Letter |
| Databáze: | OpenAIRE |
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