Session 3 - Subsurface motions and flows

Conveners: Dean Pesnell (GSFC), Rebecca Centeno (HAO/NCAR)
Tuesday 30/10, 11:00 - 12:00
Tuesday 30/10, 16:30 - 18:15

A principal goal of the HMI investigation is to better characterize flows in the solar interior. Solar dynamics are a critical component of solar activity on both global scales and local scales. Of particular interest is the very difficult problem of finding the return flow (or flows) of meridional circulation. Other interesting areas of current research involve solar differential rotation, especially at high latitudes, and differences between the current solar cycle and previous ones; the characterization of the spectrum of velocities with depth; the characterization of local flow structures; and the calibration and improvement of far-side imaging techniques.

Plenary speaker: Vincent Böning (MPS)

Talks

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Tuesday October 30, 11:00 - 12:00

11:00	HMI Summary	Scherrer, P	Invited Oral
	Phil Scherrer
	Stanford University
11:30	Solar interior flows: Recent results and current challenges	Böning, V	Invited Oral
	Vincent Böning[1]
	[1] Max Planck Institute for Solar System Research
	Helioseismology has had great success in determining the solar interior rotation profile, its dependence on the solar cycle and its temporal variation. After reviewing these results, I will turn to two less understood phenomena in the solar interior, namely meridional circulation and the nature of convective flows in the deep interior. I will argue that both of these phenomena can be brought to a similar understanding. Helioseismic inversions for the deep solar meridional flow have not yet come to a consistent picture, for which there are several possible reasons. A number of systematic effects have been shown to be present in the data. Among those is a spurious center-to-limb effect. Although progress has been made to characterize this effect, its origin is not yet understood. Furthermore, it was shown that inferences of the meridional flow are ambiguous in the lower half of the convection zone for two years of data. In addition, several results suggest a time dependence of the deep meridional flow. An even larger discrepancy exists in measurements of the spectrum of convective velocities at depth. Here, I will present a new approach to reexamine one of the conflicting studies that is based on a more accurate model for the observations. Finally, I will close with a short review of a few interesting recent results, among which are the detection of equatorial Rossby waves and a study of wave-like properties of supergranulation. Both of these results imply that helioseismology agrees with surface observations such as correlation tracking. These are good news for tackling the challenges ahead.

Tuesday October 30, 16:30 - 18:15

16:30	Statistical constraints on active region emergence from the surface motion of the polarities	Schunker, H	Oral
	Hannah Schunker[1], Aaron Birch[1], Robert Cameron[1], Doug Braun[2], Laurent Gizon[1,3]
	[1] Max Planck Institute for Solar System Research, [2] NorthWest Research Associates, [3] Georg-August-Universitaet Goettingen, Institut fuer Astrophysik
	We measured the motion of the two main opposite polarities in 154 emerging active regions using line-of-sight magnetograms from SDO/HMI. Our results reveal two phases of the emergence process defined by the rate of change of the separation speed as the polarities move apart. Phase one begins when the opposite polarity pairs first appear at the surface, with an east-west alignment and an increasing separation speed of 1.6 +/- 0.4 km/s. Phase two begins when the separation speed starts to decrease, about 0.1 days after emergence, and ends about 2.5 days after emergence when the polarities have stopped separating. This is consistent with the picture of Chen, Rempel, & Fan (2017): during phase one, the peak of a flux tube breaks through the surface and then, during phase two, the magnetic field lines are straightened by magnetic tension to eventually lie directly above their subsurface footpoints. The scatter in the location of the polarities is consistent with the length and time scales of supergranulation, supporting the idea that convection buffets the polarities as they separate. On average, the polarities emerge with an east-west orientation with the tilt angle developing over time independent of flux, in contrast to predictions from thin flux tube theory.
16:45	Revisiting helioseismic constraints on subsurface convection	Birch, A	Oral
	Aaron Birch[1],Tom Duvall[1],Laurent Gizon[1,2],Shravan Hanasoge[3],Bradley Hindman[4], Kaori Nagashima[1], Katepalli Sreenivasan[5]
	[1] Max-Planck-Institut für Sonnensystemforschung, [2] Georg-August-Universität Göttingen, [3] Tata Institute of Fundamental Research, [4] University of Colorado Boulder,[5] Department of Physics, Courant Institute of Mathematical Sciences, and Department of Mechanical and Aerospace Engineering, New York University
	There is disagreement by orders of magnitude between different helioseismic measurements of the the amplitude of subsurface convective flows. In addition, there are enormous differences between some measurements and simulations of subsurface convection. Further observational and theoretical work on the topic of solar subsurface convection is crucial. Motivated by the need to establish a clear baseline for future work, we present a uniform view of the existing results by expressing upper limits and flow estimates as root-mean-square velocity per multiplet for all cases. The disagreements between the upper limit of Hanasoge, Duvall, and Sreenivasan (2012), the ASH simulations of Miesch et al. (2008), and the helioseismic analysis of Greer et al. (2015) remain, but are reduced in amplitude. Reconciling the helioseismic measurements may involve reconsidering the assumptions about the vertical correlations of the flow field and the methods for separating signal and noise.
17:00	Temporal evolution of solar meridional flow in the deep interior during 2010-2018	Chen, R	Oral
	Ruizhu Chen[1,2], Junwei Zhao[2]
	[1]Physics Department, Stanford University, [2] Hansen Experimental Physics Laboratory, Stanford University
	Meridional flow plays an important role in solar dynamo, which drives solar cycles of magnetic field variations, and it is curious whether the meridional flow itself also shows temporal variations during difference phases of a solar cycle. Here we employ a comprehensive time-distance measurement scheme and derive the solar meridional flow using 8 years of SDO/HMI Doppler-velocity data, and explore the temporal evolution of the meridional-flow profile. Our comprehensive measurement scheme utilizes acoustic travel-time shifts measured along all radial directions of the solar disk for all travel distances. By solving a set of linear equations, we disentangle the systematic center-to-limb effect and meridional-flow-induced travel-time shifts from the measurements, and then invert the flow-induced travel-time shifts for the meridional flow. Our 8-year-averaged meridional-flow profile shows a 3-layer structure: an equatorward flow is sandwiched between two poleward flow zones above and beneath it. Moreover, the 3-layer flow pattern is more significant when solar activity level is low, while the flow structure is more complicated during the active phase of the solar cycle, indicating that the meridional flow variation is correlated with the solar cycle variation.
17:15	Twenty-one-year helioseismic measurement of solar meridional circulation from SOHO/MDI and SDO/HMI: Anomalous northern hemisphere during cycle 24	Liang, Z	Oral
	Zhi-Chao Liang[1], Laurent Gizon[123], Aaron C. Birch[1], Thomas L. Duvall, Jr.[1], S. P. Rajaguru[4]
	[1]Max-Planck-Institut f\"ur Sonnensystemforschung, [2]Institut f\"ur Astrophysik, Georg-August-Universit\"at G\"ottingen, [3]Center for Space Science, New York University Abu Dhabi, [4]Indian Institute of Astrophysics
	We apply time-distance helioseismology to MDI and HMI medium-degree Dopplergrams covering May 1996--April 2017, i.e., 12-yr of cycle 23 and 9-yr of cycle 24. Our data analysis takes several systematic effects into account, including the P-angle error, surface magnetic field effects, and the center-to-limb variations. For comparison, forward-modeled travel-time differences are computed in the ray approximation for representative meridional flow models. The measured travel-time differences are similar in the southern hemisphere for cycles 23 and 24. However, they differ in the northern hemisphere between cycles 23 and 24. Except for cycle 24's northern hemisphere, the measurements favor a single-cell meridional circulation model where the poleward flows persist down to about 0.8 solar radii, accompanied by local inflows toward the activity belts in the near-surface layers. Cycle 24's northern hemisphere is found to be anomalous: travel-time differences are significantly smaller when travel distances are greater than 20 deg. This asymmetry between northern and southern hemispheres during cycle 24 was not present in previous measurements (e.g., Rajaguru & Antia 2015), which assumed a different P-angle error correction where south-north travel-time differences are shifted to zero at the equator for all travel distances. In our measurements, the travel-time differences at the equator are zero for travel distances less than about 30 deg, but they do not vanish for larger travel distances. Rather than a P-angle error, this equatorial offset for large travel distances might be caused by the asymmetrical near-surface flows around the end points of the acoustic ray paths.
17:30	HMI Full-disk Vector Magnetograms: Products and Issues	Liu, Y	Oral
	Yang Liu, HMI team
	Stanford University
	HMI vector magnetic field over the Sun's disk is derived from the measured Stokes parameters (I, Q, U, V) using a Milne-Eddington based inversion model. The 180 degree azimuth ambiguity is resolved using the Minimum Energy algorithm for pixels in active regions and for strong-field pixels (the field is greater than about 150 G) in quiet Sun regions. Three other methods are used for the rest of the pixels: the potential-field method, the radial-acute angle method, and the random method. HMI vector magnetic field synoptic charts are one of the data products produced from the full-disk vector magnetograms. We evaluate the three methods for weak-field pixels, and demonstrate that the random method is the best for synoptic charts in term of low noise level and no additional artifacts being introduced to the charts. We show two issues in the full-disk vector magnetograms: noise distribution and change sign of field. It is shown that the nooise varies over the Sun's disk and this pattern is also dependent on the orbital velocity. The east-west component of magnetic field in the quiet Sun regions changes its sign when crossing the central meridian, though this sign change does not affect the vector field synoptic charts: the charts use observation at the central meridian. We place a discussion here on what causes this sign change and potential methods to solve this issue.
17:45	HMI Data Corrected for Scattered Light Compared to Hinode SOT-SP Data	Norton, A	Oral
	A.A. Norton[1], T.L. Duvall, Jr.[2], J. Schou[2], M.C.M Cheung[3], P.H. Scherrer[1], K.C. Chu[1], J. Sommers[1]
	[1] HEPL, Stanford University, [2] Max Planck Institute for Solar System Research, [3] Lockheed Martin Solar and Astrophysics Laboratory
	In March 2018, the Helioseismic Magnetic Imager (HMI) team began providing full-disk data to the public on a daily basis that were corrected for scattered light. In addition to the intensity and magnetogram data, the improved vector magnetic field maps are also provided. The process uses a Richardson-Lucy algorithm and a known PSF. The deconvolution results in a few percent decrease in umbral intensity corresponding to a ~200 K decrease in temperature, a doubling of the intensity contrast of granulation from 3.6 to 7.2%, an increase in total field strength values (not only line-of-sight B) in plage by ~1.4, faculae brightening and network darkening, and a partial correction for the convective blue-shift. The new data series can be found in JSOC with names similar to the original but with the qualifying term ‘_dcon’ or ‘_dconS’ appended (denoting whether the deconvolution was applied to the filtergrams or Stokes images). Comparisons to near-simultaneous Hinode SOT-SP data demonstrate that the correction brings the two instruments into much better agreement, including the inverted magnetic field parameters. We compare our results to similar efforts in the literature such as work by Diaz Baso and Asensio Ramos (2018) in which HMI intensity and magnetogram data was enhanced using neural networks and super-resolution.
18:00	Investigation of Acoustic Halos using Multi-Height SDO Observations	Tripathy, S	Oral
	S.C. Tripathy[1], Kiran Jain[1], S. Kholikov[1], O. Burtseva[1], F. Hill[1], P. Cally][2]
	[1]National Solar Observatory, Boulder, Co 80303 USA, [2] Monash University, Clayton, Victoria 3800, Australia
	The interpretation of acoustic waves surrounding active regions has been a challenging task since the influence of magnetic field on the incident waves is not fully understood. As a result, structure and dynamics of active regions beneath the surface show significant uncertainties. Recent numerical simulations and helioseismic measurements in active regions have demonstrated that the key to the understanding of these complex processes requires a synergy between models and helioseismic inferences from observations. In this context, using data from Helioseismic Magnetic Imager and Atmospheric Imaging Assembly instruments on board the Solar Dynamics Observatory, we characterize the spatio-temporal power distribution around active regions as a function of the height in the solar atmosphere. We find power enhancements (acoustic halos) occur above the acoustic cutoff frequency and extends up to 10 mHz in HMI Doppler and AIA 170 nm observations and are strong functions of magnetic field and their inclination angle. We also examine the relative phases and cross-coherence spectra and find different wave characteristics at different heights.

Posters

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e-Posters

On the depth dependence of solar equatorial Rossby waves	Proxauf, B
Bastian Proxauf[1,2], Laurent Gizon[1,2] , Björn Löptien[1], Aaron C. Birch [1], Jesper Schou[1], Richard S. Bogart[3]
[1]Max Planck Institute for Solar System Research, [2]University of Göttingen, [3]W. W. Hansen Experimental Physics Laboratory, Stanford University, USA
Here we use local helioseismology and local correlation tracking of granulation to infer horizontal flows on the solar surface and in the interior. From these flows, we compute maps of the radial vorticity at different depths in order to study Rossby waves. We show that the frequencies of these waves agree well with a simple theoretical dispersion relation. Also, we show that Rossby waves have significant amplitudes in the first 20 Mm below the surface and investigate the dependence of the Rossby waves on depth. We find an unexpected, presumably spurious dip in the wave power and a depth-independent phase and we conclude that further studies are needed.
First comprehensive calculation of the whole solar convection zone	Hotta, H
H. Hotta [1], H. Iijima [2], K. Kusano [2]
[1] Chiba university, [2] Nagoya university
The solar convection zone is filled with the turbulent convection zone in highly stratified plasma. The temporal and spatial scales vary significantly in the solar convection zone due to large density and temperature contrasts. The temporal and spatial scales of the thermal convection at the bottom of the convection zone are a month and the 200 Mm, while those are minutes and 1 Mm at the solar surface, respectively. Due to these significant changes, the numerical calculations for the deep convection zone and the solar surface are almost completely separated and direct comparisons between the deep convection zone and the photospheric observation are limited. The thermal convection is excited at the efficient cooling at very thin cooling layer around the surface and descends to the deep convection zone. It is inevitable to cover whole convection zone in a comprehensive calculation in order to understand the thermal convection itself. We, for the first time, succeed in carrying out such a comprehensive calculation covering the whole convection zone. We implement the realistic radiative transfer around the surface and our new version of the equation of state is applicable both to the deep convection zone and the solar surface. We now have a way to compare the deep convection calculation and the photospheric observation directly using our new calculations. We find that the influence of the solar surface is unexpectedly weak on the deep convection. We report the detailed analysis and future application of our calculation.
Rossby waves in the solar convection zone measured by deep-focus time-distance helioseismology	Duvall, T
T.L. Duvall Jr.[1], A.C. Birch[1], Z.-C. Liang[1], and L. Gizon[1][2]
[1] Max Planck Institute for Solar System Research, [2] Institut für Astrophysik, Georg-August-Universität Göttingen
Recent work by Loeptien et al. has shown spectral signatures of equatorial Rossby waves in the solar photosphere (via correlation tracking of granulation) and in the outer 20 Mm of the convection zone (via helioseismic ring diagrams). This result is potentially extremely important for understanding convection zone dynamics and as such should be studied by all available techniques. To this end we have searched for these Rossby waves using deep-focus time-distance helioseismology in 8 years of HMI medium resolution (medium l) Dopplergrams. We also see the signatures of equatorial Rossby waves for focus depths of 0 Mm (photosphere) down to 70 Mm below the surface. At 105 Mm (mid convection zone) and 210 Mm (bottom of convection zone) no such signatures are seen, although whether this is a s/n issue is not determined. We will hopefully be able to determine the radial eigenfunctions of the Rossby waves from this type of measurement.
Towards improved multi-ridge fitting method for ring-diagram analysis	Nagashima, K
Kaori Nagashima[1], Aaron C. Birch[1], Jesper Schou[1], Bradley Hindman[2], Laurent Gizon[1,3]
[1] Max-Planck-Institut für Sonnensystemforschung, [2] University of Colorado Boulder, [3] Georg-August-Universität Göttingen
Ring-diagram analysis is one of the important methods of local helioseismology for probing subsurface flows. In ring-diagram analysis the Doppler shifts of oscillation mode frequencies due to flows are measured by fitting a model function to the local oscillation power spectra. Here we propose alteration of the multi-ridge fitting method developed by Greer et al. (2014). It is well known that the solar oscillation power is chi-square distributed (with two degrees of freedom), and the fitting in the existing multi-ridge fitting is done with the maximum likelihood method based on this probability distribution function. However, the power is in practice remapped from Cartesian to polar coordinates and/or smoothed in azimuth of the wavevector. The smoothed power is approximately normally distributed. We demonstrate that the probability distribution function of the logarithm of the normally-distributed power is approximated by a normal distribution with a variance that is independent of the expectation value of the power. Therefore, we alter the fitting method using the logarithm of the power with a least-square method. In this presentation we report the bias and noise levels in the updated fitting results as well as the crosstalk between the parameters using a Monte Carlo simulation of the power spectra.
Statistical Analysis of Acoustic Wave Power and Flows around Solar Active Regions	Rabello soares, M
M. Cristina Rabello-Soares[1], Richard S. Bogart[2], Philip H. Scherrer[2]
[1]Universidade Federal de Minas Gerais, [2]Stanford University
We analyze the effect of a sunspot in its quiet surroundings applying a helioseismic technique on almost three years of Helioseismic and Magnetic Imager (HMI) observations obtained during solar cycle 24 to further study the sunspot structure below the solar surface. The attenuation of acoustic waves with frequencies lower than 4.2 mHz depends more strongly on the wave direction at a distance of 6°–7° from the sunspot center. The amplification of higher frequency waves is highest 6° away from the active region and is largely independent of the wave’s direction. We observe a mean clockwise flow around active regions, the angular speed of which decreases exponentially with distance and has a coefficient close to ‑0.7 degree‑1. The observed horizontal flow in the direction of the nearby active region agrees with a large-scale circulation around the sunspot in the shape of cylindrical shell. The center of the shell seems to be centered around 7° from the sunspot center, where we observe an inflow close to the surface down to ∼2 Mm, followed by an outflow at deeper layers until at least 7 Mm.

p-Posters

Subsurface Flows During Cycle 23 and 24	Komm, R
Rudolf Komm[1], Rachel Howe[2], Frank Hill[1]
[1]National Solar Observatory, Boulder, CO 80303, [2]University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
We study the solar-cycle variation of subsurface flows from the surface to a depth of 16 Mm. We have used ring-diagram analysis to analyze Dopplergrams obtained with the MDI Dynamics Program, the GONG, and the SDO/HMI instrument. We combine the zonal and meridional flows from the three data sources and we derive their temporal variation in a consistent manner for Solar Cycle 23 and 24. For Cycle 24, the flow patterns are precursors of the magnetic activity. The timing difference between the occurrence of the flow pattern and the magnetic one increases almost linearly with increasing latitude. For example, the fast zonal and meridional flow appear about 2.1 years and 2.5 years respectively before the magnetic pattern at 30 degree latitude in the northern hemisphere, while in the southern one the differences are 3.2 years and 2.6 years. The flow patterns of Cycle 25 are present and have reached 30 degree latitude. The amplitude differences of Cycle 25 are about 22% smaller than those of Cycle 24 but comparable to those of Cycle 23. In addition, we divide the data into subsets of low and high magnetic activity and study the variation of the quiet- and active-region flows during Solar Cycle 23 and 24.
The HMI Ring-Diagram Pipeline: Recent Developments and Future Prospects	Bogart, R
Richard Bogart[1],Charles Baldner[1],Sarbani Basu[2],Kiran Jain[3],Shea Hess Webber[1]
[1]Stanford University,[2]Yale University,[3]National Solar Observatory
The HMI ring-diagram pipeline produces tracked Doppler data cubes at three different size and time scales, their power spectra, two independent types of "mode" (ridge) fits to the spectra, and inversions of fit parameters measuring the mean near- and sub-surface flows. Ancillary products include measures of the mean magnetic activity associated with the tracked cubes, rotation averages of the power spectra at different Stonyhurst locations, and long-term averages of the input Dopplergrams. Active efforts are currently underway to improve many of these products. We review recent changes to the analysis procedures and products, discuss known problems, and describe modifications and updates in progress, under development, and/or contemplated for the near future.
The Minimum Energy Principle Applied to Parker's Coronal Braiding and Nanoflaring Scenario	Aschwanden, M
Markus Aschwanden [1] and A.A. van Ballegooijen [2]
[1] Lockheed Martin, Solar and Astrophysics Laboratory, [2] Harvard-Smithonian Center for Astrophysics
Parker's coronal braiding and nanoflaring scenario predicts the development of tangential discontinuities and highly misaligned magnetic field lines, as a consequence of random buffeting of their footpoints due to the action of sub-photospheric convection. The increased stressing of magnetic field lines is thought to become unstable above some critical misalignment angle and to result into local magnetic reconnection events, which is generally referred to as Parker's ``nanoflaring scenario''. In this study we show that the minimum (magnetic) energy principle leads to a bifurcation of force-free field solutions for helical twist angles at |phi(t)| = pi, which prevents the build-up of arbitrary large free energies and misalignment angles. The minimum energy principle predicts that neighbored magnetic field lines are almost parallel (with misalignment angles of Delta mu ~ 1.6-1.8 deg, and do not reach a critical misalignment angle prone to nanoflaring. Consequently, no nanoflares are expected in the divergence-free and force-free parts of the solar corona, while they are more likely to occur in the chromosphere and transition region.
Interactions of waves with solar convection	Schou, J
Jesper Schou
Max-Planck-Institut für Sonnensystemforschung
Some of the most significant problems in our understanding of solar and stellar oscillations are believed to be related to their interaction with the near surface convection. One such problem is the center to limb effect seen in many helioseismic measurements. Another the so-called surface term. Here I will briefly describe these problems and some preliminary results of trying to address them using large scale hydrocode simulations.
Impact of observational duty cycle on the measurement of local helioseismic mode parameters	Tripathy, S
Sushanta Tripathy[1], Richard Bogart [2], Kiran Jain[1]
[1]National Solar Observatory, Boulder, Co 80303 USA, [2] Stanford University, Sanford, CA 94305, USA
The effect of data gaps on the power spectra and the mode parameters can be explored by imposing a simulated observing window function on a continuous time series of predefined length as is used in standard ring diagram analysis. Here, we investigate the effect of these gaps in HMI data on board SDO through a Monte Carlo analysis. It may be noted that in case of HMI observations, the data gaps occur primarily due to the eclipses and calibrations and thus the distribution can be characterized by a two-element quasi-periodic population. From the Monte Carlo simulations, we examine (i) the presence or absence of the individual modes in the different fitting methods, (ii) systematic effects in frequencies and flow parameters, (iii) systematic effects in the inversions, and (iv) the extent to which these effects depend on the length of the analysis interval. As a base line, we use the absolutely continuous HMI data (no gaps) that are available for periods of up to a week but no more due to the weekly calibration of HMI and/or AIA data. The study uses data both from quiet and active periods.
A New Approach for Calculating Three-Dimensional Flow Sensitivity Kernels Using Global-Scale Wavefield Simulations	Zhao, J
Thomas Hartlep[1] & Junwei Zhao[2]
[1] Bay Area Environmental Research Institute, Moffett Field, California 94035, U.S.A. [2] W. W. Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305, U.S.A.
At present, a common method for inferring the Sun's interior meridional-circulation profile is to invert helioseismically measured travel-time shifts using so-called sensitivity kernels describing the sensitivity of the travel times to flows in the interior. Ray-approximation kernels, despite their shortcomings, have been used by many authors and provided tremendous insight into the solar interior. In the meantime, more realistic global-scale Born-approximation kernels have been developed by some authors. Here, we introduce another approach for calculating three-dimensional flow kernels. In this approach, we perform global-Sun wavefield simulations with small flow perturbations placed at some location inside the simulated Sun and measure the travel-time shifts they cause. A linear equations links the flow model, we prescribe, and the travel-time shifts, we measure, with the sensitivity kernel. By computing many such simulations, with perturbations at many different depths and locations relative to the wave source, this set of linear equations can be successfully solved numerically for the sensitivity kernels.
Near-Surface Flow Anomalies in Solar Cycle 24 As Determined By Ring-Diagram Analysis	Baldner, C
Charles Baldner [1], Sarbani Basu [2], Richard Bogart [1], Rachel Howe [3]
[1] Stanford University, [2] Yale University, [3] University of Birmingham
Small variations relative to long term mean flows in the near-surface layers of the Sun can be detected and characterized using local helioseismology. Some of these anomalies appear to be related to the progression of the solar cycle, others have significantly shorter timescales. In this work we exploit eight years of high resolution data from the Helioseismic and Magnetic Imager (HMI) on the Solar Dynamics Observatory (SDO) spacecraft covering the majority of solar cycle 24. We employ ring diagram analysis to measure flow anomalies throughout the shallowest 20Mm of the solar convection zone. We explore, in particular, the asymmetry in flows between the northern and southern hemispheres to search for signs of the onset of the solar cycle 25 torsional oscillation. We also further study persistent high latitude flow anomalies that have been previously detected.
A fragile detection of solar g-modes	Schunker, H
Hannah Schunker[1], Jesper Schou[1], Patrick Gaulme[1], Laurent Gizon [1,2]
[1] Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen [2] Georg-August-Universität Göttingen, Institut für Astrophysik, Friedrich-Hund-Platz 1, 37077 Göttingen
The most recent claimed detection of g-mode oscillations in the Sun using SOHO-GOLF observations has regenerated the field of helioseismology to probe the core of the Sun. I will show that the most recent claimed detection of g-modes is fragile, and highlight the parameters in the analysis method that are the most important for the detection. Moreover, I will show that the g-mode detection is extremely sensitive to the start time of the GOLF time series.