===== Research Highlights =====

==== Comparison of Meridional Flows from GONG and SDO/HMI ====

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nocite=2015ApJ...805..133J
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[{{:wiki:science:gong_hmi.jpg?direct&300 |Inverted meridional circulation flows for GONG and HMI, as well as cuts through them.}}]

In this paper we took our travel-time measurements from earlier work and tried to infer the deep, large-scale flows inside the Sun. To get some sense of our results using GONG ground-based data, we compared our results to those obtained from space-based data in {[2013ApJ...774L..29Z]}.

We find some similarities between each group, notably a very unexpected shallow equatorward flow only 10% into the Sun. Such a feature had been expected to lie around 30% into the Sun. While the Stanford group finds some evidence of again a northward flow deeper down, our results do not indicate such a structure within the uncertainties.

While the similarities are encouraging, the paper shows that when taking into consideration mass conservation in the convection zone, both results have some important inconsistencies that require much more analysis and understanding. 




==== Deep Meridional Flow Measurements from GONG Data ====

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nocite=2014ApJ...784..145K
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[{{ :wiki:science:dtmaps.jpg?direct&300|Travel-time difference maps in the north-south direction (top), east-west direction (middle), and the difference between the two (bottom). }}]

This paper showed travel-time measurements of about 650 days of GONG data. Signatures of meridional flow in the deep convection zone are present, and preliminary evidence of a change of sign, indicating an equatorward flow for some large travel distances as seen in other recent work, is found. This is the first time this has been seen in GONG data. We only find reasonable results after correcting for center-to-limb systematics as in the {[2012ApJ...749L...5Z]} work, whereby we subtract off east-west measurements from the north-south ones (see figure on right).

While that paper used space-based SDO/HMI observations, we use ground-based GONG data. This suggests that some systematics are not instrument specific, but have real solar origins. The work of {[2012ApJ...760L...1B]} explores one possible source of systematic errors due to granulation flows. 


==== References ====

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