English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

The south-north travel-time differences are measured by applyingtime-distance helioseismology to the MDI and HMI medium-degree Dopplergramscovering May 1996-April 2017. Our data analysis corrects for several sources ofsystematic effects: P-angle error, surface magnetic field effects, andcenter-to-limb variations. An interpretation of the travel-time measurements isobtained using a forward-modeling approach in the ray approximation. Thetravel-time differences are similar in the southern hemisphere for cycles 23and 24. However, they differ in the northern hemisphere between cycles 23 and24. Except for cycle 24's northern hemisphere, the measurements favor asingle-cell meridional circulation model where the poleward flows persist downto $\sim$0.8 $R_\odot$, accompanied by local inflows toward the activity beltsin the near-surface layers. Cycle 24's northern hemisphere is anomalous:travel-time differences are significantly smaller when travel distances aregreater than 20$^\circ$. This asymmetry between northern and southernhemispheres during cycle 24 was not present in previous measurements (e.g.,Rajaguru & Antia 2015), which assumed a different P-angle error correctionwhere south-north travel-time differences are shifted to zero at the equatorfor all travel distances. In our measurements, the travel-time differences atthe equator are zero for travel distances less than $\sim$30$^\circ$, but theydo not vanish for larger travel distances. This equatorial offset for largetravel distances need not be interpreted as a deep cross-equator flow; it couldbe due to the presence of asymmetrical local flows at the surface near the endpoints of the acoustic ray paths.

astronomy and astrophysics

Solar meridional circulation from twenty-one years of SOHO/MDI and  SDO/HMI observations: Helioseismic travel times and forward modeling in the  ray approximation