Michelson Doppler Imager Data Research Articles

Effects of flares on solar high-degree helioseismic acoustic mode amplitudes

ABSTRACT Several attempts have been made to observe whether solar flares excite acoustic modes since Charles Wolff suggested this possibility almost 50 yr ago. We look for the impact of flares on the amplitude of solar acoustic modes and other effects that are also affecting the mode amplitude. Solar acoustic mode amplitudes are known to be sensitive to magnetic fields. As flares usually occur in the presence of strong magnetic fields and most likely are the by-product of magnetic reconnection, we show how the magnetic field in and around the flaring region affects the mode amplitude. The mode amplitudes were obtained using ring-diagram analysis, which was first applied to a single event, the largest flare in the space age (the ‘Halloween Flare’, SOL2003-10-28T11:00), using MDI (Michelson Doppler Imager) data. Then, using HMI (Helioseismic and Magnetic Imager) data, the analysis was applied to the regions corresponding to the flares observed during the high-activity phase of cycle 24 and that fall into two groups. These two groups consist of small (10–60 erg cm−2 s−1) and large (>1200 erg cm−2 s−1) peak-flux flares, based on the Heliophysics Event Knowledgebase (HEK). The first set is used as a comparison to the results of the strong flares in the second set. After applying several corrections in order to take into account several sources of bias, we did not find any amplification in the inferred mode amplitude due to flaring activity larger than a 10 per cent uncertainty.

Inference of Solar Rotation from Perturbations of Acoustic Mode Eigenfunctions

Abstract Today’s picture of the internal solar rotation rate profile results essentially from helioseismic analyses of frequency splittings of resonant acoustic waves. Here we present another, complementary estimation of the internal solar rotation rate using the perturbation of the shape of the acoustic waves. For this purpose, we extend a global helioseismic approach developed previously for the investigation of the meridional flow to work on the components of the differential rotation. We discuss the effect of rotation on mode eigenfunctions and the observables based thereon. Based on a numerical study using a simulated rotation rate profile, we tailor an inversion approach and also consider the case of the presence of an additional meridional flow. This inversion approach is then applied to data from the Michelson Doppler Imager (MDI) on board the Solar Heliospheric Observatory and the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory. In the end, rotation rate profiles estimated from eigenfunction perturbation and frequency splittings are compared. The rotation rate profiles from the two different approaches are qualitatively in good agreement, especially for the MDI data. Significant differences are obtained at high latitudes >50° and near the subsurface. The result from HMI data shows larger discrepancies between the different methods. We find that the two global helioseismic approaches provide complementary methods for measuring the solar rotation. Comparing the results from different methods may help to reveal systematic influences that affect analyses based on eigenfunction perturbations, like meridional flow measurements.

Global-Mode Analysis of Full-Disk Data from the Michelson Doppler Imager and the Helioseismic and Magnetic Imager

Building upon our previous work, in which we analyzed smoothed and subsampled velocity data from the Michelson Doppler Imager (MDI), we extend our analysis to unsmoothed, full-resolution MDI data. We also present results from the Helioseismic and Magnetic Imager (HMI), in both full resolution and processed to be a proxy for the low-resolution MDI data. We find that the systematic errors that we saw previously, namely peaks in both the high-latitude rotation rate and the normalized residuals of odd a\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$a$\\end{document}-coefficients, are almost entirely absent in the two full-resolution analyses. Furthermore, we find that both systematic errors seem to depend almost entirely on how the input images are apodized, rather than on resolution or smoothing. Using the full-resolution HMI data, we confirm our previous findings regarding the effect of using asymmetric profiles on mode parameters, and also find that they occasionally result in more stable fits. We also confirm our previous findings regarding discrepancies between 360-day and 72-day analyses. We further investigate a six-month period previously seen in f\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$f$\\end{document}-mode frequency shifts using the low-resolution datasets, this time accounting for solar-cycle dependence using magnetic-field data. Both HMI and MDI saw prominent six-month signals in the frequency shifts, but we were surprised to discover that the strongest signal at that frequency occurred in the mode coverage for the low-resolution proxy. Finally, a comparison of mode parameters from HMI and MDI shows that the frequencies and a\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$a$\\end{document}-coefficients agree closely, encouraging the concatenation of the two datasets.

Solar-cycle variation of the rotational shear near the solar surface

Helioseismology has revealed that the angular velocity of the Sun increases with depth in the outermost 35 Mm of the Sun. Recently, we have shown that the logarithmic radial gradient ($\rm d\ln\Omega/\rm d\ln r $) in the upper 10~Mm is close to $-1$ from the equator to $60^\circ$ latitude.We aim to measure the temporal variation of the rotational shear over solar cycle 23 and the rising phase of cycle 24 (1996-2015). We used f mode frequency splitting data spanning 1996 to 2011 from the Michelson Doppler Imager (MDI) and 2010 to 2015 from the Helioseismic Magnetic Imager (HMI). In a first for such studies, the f mode frequency splitting data were obtained from 360-day time series. We used the same method as in our previous work for measuring $\rm d\ln\Omega/d\ln r $ from the equator to $80^\circ$ latitude in the outer 13~Mm of the Sun. Then, we calculated the variation of the gradient at annual cadence relative to the average over 1996 to 2015. We found the rotational shear at low latitudes ($0^\circ$ to $30^\circ$) to vary in-phase with the solar activity, varying by $\sim \pm 10$\% over the period 1996 to 2015. At high latitudes ($60^\circ$ to $80^\circ$), we found rotational shear to vary in anti-phase with the solar activity. By comparing the radial gradient obtained from the splittings of the 360-day and the corresponding 72-day time series of HMI and MDI data, we suggest that the splittings obtained from the 72-day HMI time series suffer from systematic errors. We provide a quantitative measurement of the temporal variation of the outer part of the near surface shear layer which may provide useful constraints on dynamo models and differential rotation theory.

BREAKOUT RECONNECTION OBSERVED BY THE TESIS EUV TELESCOPE

ABSTRACT We present experimental evidence of the coronal mass ejection (CME) breakout reconnection, observed by the TESIS EUV telescope. The telescope could observe solar corona up to 2 R ⊙ from the Sun center in the Fe 171 Å line. Starting from 2009 April 8, TESIS observed an active region (AR) that had a quadrupolar structure with an X-point 0.5 R ⊙ above photosphere. A magnetic field reconstructed from the Michelson Doppler Imager data also has a multipolar structure with an X-point above the AR. At 21:45 UT on April 9, the loops near the X-point started to move away from each other with a velocity of ≈7 km s−1. At 01:15 UT on April 10, a bright stripe appeared between the loops, and the flux in the GOES 0.5–4 Å channel increased. We interpret the loops’ sideways motion and the bright stripe as evidence of the breakout reconnection. At 01:45 UT, the loops below the X-point started to slowly move up. At 15:10 UT, the CME started to accelerate impulsively, while at the same time a flare arcade formed below the CME. After 15:50 UT, the CME moved with constant velocity. The CME evolution precisely followed the breakout model scenario.

The radial gradient of the near-surface shear layer of the Sun

Helioseismology has provided unprecedented information about the internal rotation of the Sun. One of the important achievements was the discovery of two radial shear layers: one near the bottom of the convection zone (the tachocline) and one near the surface. These shear layers may be important ingredients for explaining the magnetic cycle of the Sun. We measure the logarithmic radial gradient of the rotation rate ($\rm d\ln\Omega/\rm d\ln r$) near the surface of the Sun using 15 years of f mode rotational frequency splittings from the Michelson Doppler Imager (MDI) and four years of data from the Helioseismic and Magnetic Imager (HMI). We model the angular velocity of the Sun in the upper $\sim 10$ Mm as changing linearly with depth and use a multiplicative optimally localized averaging inversion to infer the gradient of the rotation rate as a function of latitude. Both the MDI and HMI data show that $\rm d\ln\Omega/\rm d\ln r$ is close to $-1$ from the equator to 60$^{\circ}$ latitude and stays negative up to 75$^{\circ}$ latitude. However, the value of the gradient is different for MDI and HMI for latitudes above $60^{\circ}$. Additionally, there is a significant difference between the value of $d\ln\Omega/d\ln r$ using an older and recently reprocessed MDI data for latitudes above $30^\circ$. We could reliably infer the value of $\rm d\ln\Omega/\rm d\ln r$ up to 60$^{\circ}$, but not above this latitude, which will hopefully constrain theories of the near-surface shear layer and dynamo. Furthermore, the recently reprocessed MDI splitting data are more reliable than the older versions which contained clear systematic errors in the high degree f modes.

Time-Series Analysis of Supergranule Characteristics at Solar Minimum

Sixty days of Doppler images from the Solar and Heliospheric Observatory (SOHO) / Michelson Doppler Imager (MDI) investigation during the 1996 and 2008 solar minima have been analyzed to show that certain supergranule characteristics (size, size range, and horizontal velocity) exhibit fluctuations of three to five days. Cross-correlating parameters showed a good, positive correlation between supergranulation size and size range, and a moderate, negative correlation between size range and velocity. The size and velocity do exhibit a moderate, negative correlation, but with a small time lag (less than 12 hours). Supergranule sizes during five days of co-temporal data from MDI and the Solar Dynamics Observatory (SDO) / Helioseismic Magnetic Imager (HMI) exhibit similar fluctuations with a high level of correlation between them. This verifies the solar origin of the fluctuations, which cannot be caused by instrumental artifacts according to these observations. Similar fluctuations are also observed in data simulations that model the evolution of the MDI Doppler pattern over a 60-day period. Correlations between the supergranule size and size range time-series derived from the simulated data are similar to those seen in MDI data. A simple toy-model using cumulative, uncorrelated exponential growth and decay patterns at random emergence times produces a time-series similar to the data simulations. The qualitative similarities between the simulated and the observed time-series suggest that the fluctuations arise from stochastic processes occurring within the solar convection zone. This behavior, propagating to surface manifestations of supergranulation, may assist our understanding of magnetic-field-line advection, evolution, and interaction.

Analysis of Supergranule Sizes and Velocities Using Solar Dynamics Observatory (SDO)/Helioseismic Magnetic Imager (HMI) and Solar and Heliospheric Observatory (SOHO)/Michelson Doppler Imager (MDI) Dopplergrams

Co-temporal Doppler images from Solar and Heliospheric Observatory (SOHO)/Michelson Doppler Imager (MDI) and Solar Dynamics Observatory (SDO)/Helioseismic Magnetic Imager (HMI) have been analyzed to extract quantitative information about global properties of the spatial and temporal characteristics of solar supergranulation. Preliminary comparisons show that supergranules appear to be smaller and have stronger horizontal velocity flows within HMI data than was measured with MDI. There appears to be no difference in their evolutionary timescales. Supergranule sizes and velocities were analyzed over a ten-day time period at a 15-minute cadence. While the averages of the time-series retain the aforementioned differences, fluctuations of these parameters first observed in MDI data were seen in both MDI and HMI time-series, exhibiting a strong cross-correlation. This verifies that these fluctuations are not instrumental, but are solar in origin. The observed discrepancies between the averaged values from the two sets of data are a consequence of instrument resolution. The lower spatial resolution of MDI results in larger observed structures with lower velocities than is seen in HMI. While these results offer a further constraint on the physical nature of supergranules, they also provide a level of calibration between the two instruments.

SOLAR CYCLE VARIATION OF SOUND SPEED INSIDE THE SUN

Empirical radial profiles of the changes in sound speed inside the Sun between solar minimum and solar maximum have been extracted from Michelson Doppler Imager data by Baldner & Basu and Rabello-Soares. Here, we compare these results with the theoretical radial profiles predicted by a model of magnetic inhibition of convective onset: In the model, the degree of magnetic inhibition is characterized by a parameter δ, which is essentially the ratio of magnetic pressure to gas pressure. We find that the theoretical profiles overlap significantly with the empirical results in the outer half of the convection zone. But differences in the deeper layers indicate that the model needs to be modified there. The main result that emerges in the present comparison is that the value of δ must be larger near the surface than at great depth. A secondary result is that, in the course of the solar cycle, the magnetic field magnitude at the base of the convection zone may be out of phase with the field near the surface.

Comparison of Line-of-Sight Magnetograms Taken by the Solar Dynamics Observatory/Helioseismic and Magnetic Imager and Solar and Heliospheric Observatory/Michelson Doppler Imager

We compare line-of-sight magnetograms from the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) and the Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory (SOHO). The line-of-sight magnetic signal inferred from the calibrated MDI data is greater than that derived from the HMI data by a factor of 1.40. This factor varies somewhat with center-to-limb distance. An upper bound to the random noise for the 1′′ resolution HMI 720-second magnetograms is 6.3 Mx cm−2, and 10.2 Mx cm−2 for the 45-second magnetograms. Virtually no p-mode leakage is seen in the HMI magnetograms, but it is significant in the MDI magnetograms. 12-hour and 24-hour periodicities are detected in strong fields in the HMI magnetograms. The newly calibrated MDI full-disk magnetograms have been corrected for the zero-point offset and underestimation of the flux density. The noise is 26.4 Mx cm−2 for the MDI one-minute full-disk magnetograms and 16.2 Mx cm−2 for the five-minute full-disk magnetograms observed with four-arcsecond resolution. The variation of the noise over the Sun’s disk found in MDI magnetograms is likely due to the different optical distortions in the left- and right-circular analyzers, which allows the granulation and p-mode to leak in as noise. Saturation sometimes seen in sunspot umbrae in MDI magnetograms is caused by the low intensity and the limitation of the onboard computation. The noise in the HMI and MDI line-of-sight magnetic-field synoptic charts appears to be fairly uniform over the entire map. The noise is 2.3 Mx cm−2 for HMI charts and 5.0 Mx cm−2 for MDI charts. No evident periodicity is found in the HMI synoptic charts.

First Global Rotation Inversions of HMI Data

We present the first 2-dimensional global rotational inversions of medium-degree p-mode data from the Helioseismic and Magnetic Imager, and compare the results with inversions of Michelson Doppler Imager data for the same time period. The inferred rotation profiles show good agreement between the two instruments.

INTERMITTENCY AND MULTIFRACTALITY SPECTRA OF THE MAGNETIC FIELD IN SOLAR ACTIVE REGIONS

We present results of a study of intermittency and multifractality of magnetic structures in solar active regions (ARs). Line-of-sight magnetograms for 214 ARs of different flare productivity observed at the center of the solar disk from January 1997 until December 2006 are utilized. Data from the Michelson Doppler Imager (MDI) instrument on-board the {\it Solar and Heliospheric Observatory} (SOHO) operating in the high resolution mode, the Big Bear Solar Observatory digital magnetograph and {\it Hinode} SOT/SP instrument were used. Intermittency spectra were derived via high-order structure functions and flatness functions. The flatness function exponent is a measure of the degree of intermittency. We found that the flatness function exponent at scales below approximately 10 Mm is correlated to the flare productivity (the correlation coefficient is - 0.63). {\it Hinode} data show that the intermittency regime is extended toward the small scales (below 2 Mm) as compared to the MDI data. The spectra of multifractality, derived from the structure functions and flatness functions, are found to be more broad for ARs of highest flare productivity as compared to that of low flare productivity. The magnetic structure of high-flaring ARs consists of a voluminous set of monofractals, and this set is much richer than that for low-flaring ARs. The results indicate relevance of the multifractal organization of the photospheric magnetic fields to the flaring activity. Strong intermittency observed in complex and high-flaring ARs is a hint that we observe a photospheric imprint of enhanced sub-photospheric dynamics.

On the success rate of the farside seismic imaging of active regions

[1] Seismic maps of the nonvisible side of the Sun (farside) have been used for almost a decade to follow large active regions before they rotate to face the Earth. Preliminary efforts to quantify the success rate of the technique (seismic holography) have been published with Michelson Doppler Imager (MDI) data. In this paper we present a thorough statistical analysis of 3 complete years of farside seismic maps (2003–2005) calculated using both Global Oscillation Network Group (GONG) data and a combined set of GONG and MDI data. A comparison with NOAA data of the frontside of the Sun during the same period shows that seismic maps detect about 40% of the total active regions that appear at the east limb of the Sun with a confidence level higher than 60%. The relationship found during this work between the seismic signature and the confidence level allows us to automatically highlight candidates in the farside seismic maps and to assign them the corresponding probability of appearance on the frontside.

A Cross-Comparison of Cotemporal Magnetograms Obtained with MDI/SOHO and SP/Hinode

We compared a set of cotemporal magnetograms of active regions obtained with the Michelson Doppler Imager (MDI) aboard SOHO and the Spectro-Polarimeter (SP) of the Solar Optical Telescope (SOT) on board Hinode. The comparison shows that even with the recent calibration of level-1.8 data, the magnetic flux density derived from the MDI data is still lower than that obtained with SP. The average ratio between current version 2008 MDI level-1.8 data and SP magnetograms is 0.71, and is 0.82 for version 2007 MDI level-1.8 data. The comparison also shows that the most recent version 2008 calibration of MDI level-1.8 data has successfully removed the center-to-limb variation, while version 2007 level-1.8 data did not, as estimated by Ulrich et al. (Solar Phys.255, 53, 2009).

RATES OF PHOTOSPHERIC MAGNETIC FLUX CANCELLATION MEASURED WITH HINODE

Photospheric magnetic flux cancellation on the Sun is generally believed to be caused by magnetic reconnection occurring in the low solar atmosphere. Individual canceling magnetic features are observationally characterized by the rate of flux cancellation. The specific cancellation rate, defined as the rate of flux cancellation divided by the interface length, gives an accurate estimate of the electric field in the reconnecting current sheet. We have determined the specific cancellation rate using the magnetograms taken by the Solar Optical Telescope (SOT) aboard the Hinode satellite. The specific rates determined with SOT turned out to be systematically higher than those based on the data taken by the Michelson Doppler Imager (MDI) aboard the Solar and Heliospheric Observatory. The median value of the specific cancellation rate was found to be 8 × 106 G cm s-1—a value four times that obtained from the MDI data. This big difference is mainly due to a higher angular resolution and better sensitivity of the SOT, resulting in magnetic fluxes up to five times larger than those obtained from the MDI. The higher rates of flux cancellation correspond to either faster inflows or stronger magnetic fields of the reconnection inflow region, which may have important consequences for the physics of photospheric magnetic reconnection.

The solar wind disappearance event of 11 May 1999: source region evolution

Context. A recent, detailed study of the well-known “ solar wind disappearance event ” of 11 May 1999 traced its origin to a coronal hole (CH) lying adjacent to a large active region (AR), AR8525 in Carrington rotation 1949. The AR was located at central meridian on 05 May 1999 when the flows responsible for this event began. We examine the evolution of the AR-CH complex during 5-6 May 1999 to study the changes that apparently played a key role in causing this disappearance event. Aims. To study the evolution of the solar source region of the disappearance event of 11 May 1999. Methods. Using images from the Soft X-ray Telescope (SXT), the Extreme-ultraviolet Imaging Telescope (EIT) and the Michelson Doppler Imager (MDI) to examine the evolution of the CH and AR complex at the source region of the disappearance event. Results. We find a dynamic evolution taking place in the CH-AR boundary at the source region of the disappearance event of 11 May 1999. This evolution, which is found to reduce the area of the CH, is accompanied by the formation of new loops in EUV images that are spatially-and-temporally correlated with emerging flux regions as seen in MDI data. Conclusions. In the period leading up to the disappearance event of 11 May 1999, our observations, during quiet solar conditions and in the absence of CMEs, provide the first clear evidence for Sun-Earth connection originating from an evolving AR-CH region located at central meridian. With the exception of corotating interacting regions (CIR), these observations provide the first link between the Sun and space weather effects at 1 AU, arising from non-explosive solar events.

Divergence and Vorticity of Solar Subsurface Flows Derived from Ring‐Diagram Analysis of MDI and GONG Data

We measure the relation between divergence and vorticity of subsurface horizontal flows as a function of unsigned surface magnetic flux. Observations from the Michelson Doppler Imager (MDI) Dynamics Program and Global Oscillation Network Group (GONG) have been analyzed with a standard ring-diagram technique to measure subsurface horizontal flows from the surface to a depth of about 16 Mm. We study residual horizontal flows after subtracting large-scale trends (low-order polynomial fits in latitude) from the measured velocities. On average, quiet regions are characterized by weakly divergent horizontal flows and small anticyclonic vorticity (clockwise in the northern hemisphere), while locations of high activity show convergent horizontal flows combined with cyclonic vorticity (counterclockwise in the northern hemisphere). Divergence and vorticity of horizontal flows are anticorrelated (correlated) in the northern (southern) hemisphere. This is especially noticeable at greater depth, where the relation between divergence and vorticity of horizontal flows is nearly linear. These trends show a slight reversal at the highest levels of magnetic flux; the vorticity amplitude decreases at the highest flux levels, while the divergence changes sign at depths greater than about 10 Mm. The product of divergence and vorticity of the horizontal flows, a proxy of the vertical contribution to the kinetic helicity density, is on average negative (positive) in the northern (southern) hemisphere. The helicity proxy values are greater at locations of high magnetic activity than at quiet locations.

Flares, Magnetic Fields, and Subsurface Vorticity: A Survey of GONG and MDI Data

We search for a relation between flows below active regions and flare events occurring in those active regions. For this purpose, we determine the subsurface flows from high-resolution Global Oscillation Network Group (GONG) and Michelson Doppler Imager (MDI) Dynamics Program data using the ring-diagram technique. We then calculate the vorticity of the flows associated with active regions and compare it with a proxy of the total X-ray flare intensity of these regions using data from the Geostationary Operation Environmental Satellite (GOES). We have analyzed 408 active regions with X-ray flare activity from GONG and 159 active regions from MDI data. Both data sets lead to similar results. The maximum unsigned zonal and meridional vorticity components of active regions are correlated with the total flare intensity; this behavior is most apparent at values greater than 3.2 × 10-5 W m-2. These vorticity components show a linear relation with the logarithm of the flare intensity that is dependent on the maximum unsigned magnetic flux; vorticity values are proportional to the product of total flare intensity and maximum unsigned magnetic flux for flux values greater than about 36 G. Active regions with strong flare intensity show a dipolar pattern in the zonal and meridional vorticity component that reverses at depths between ~2 and 5 Mm. A measure of this pattern shows the same kind of relation with total flare intensity as the vorticity components. The vertical vorticity component shows no clear relation to flare activity.

Magnetic Fields from SOHO MDI Converted to the Mount Wilson 150 Foot Solar Tower Scale

In order to permit the construction of long-duration time series dependent on the Sun's magnetic field, this paper presents a detailed cross-correlation between sets of simultaneous magnetograms from the Mount Wilson Observatory (MWO) and the Michelson Doppler Imager (MDI) aboard the SOHO spacecraft. The MWO 150 foot (45.72 m) solar tower telescope magnetogram data are for the Fe I 525.0 nm and Ni I 676.8 nm lines, and the MDI data are level 1.8 magnetograms also for the Ni I 676.8 nm spectral line. In these comparisons, we apply a saturation correction factor to the MWO 525.0 nm fields prior to the derivation of the MDI scale factor. Data from 1997 March to 2002 August are used for this work. We have found that the ratio of MWO Fe I 525.0 nm magnetograms over MDI magnetograms is about 1.7, and it is a function of the center-to-limb angle. Moreover, there are differences between the west-side and the east-side ratios, and these differences may come from the angle dependence of the Michelson filters in the MDI instrument. The MDI tuning changes, on the other hand, are not associated with significant jumps in the derived scale factor ratio. The average scale factors should be adequate for the construction of MDI images closely comparable to those of the saturation-corrected long-duration MWO 525.0 nm sequence.

Solar Subsurface Fluid Dynamics Descriptors Derived from Global Oscillation Network Group and Michelson Doppler Imager Data

We analyze Global Oscillation Network Group (GONG) and Michelson Doppler Imager (MDI) observations obtained during Carrington rotation 1988 (2002 March 30-April 26) with a ring-diagram technique in order to measure the zonal and meridional flow components in the upper solar convection zone. We derive daily flow maps over a range of depths up to 16 Mm on a spatial grid of 75 in latitude and longitude covering ±60° in latitude and central meridian distance and combine them to make synoptic flow maps. We begin exploring the dynamics of the near-surface layers and the interaction between flows and magnetic flux by deriving fluid dynamics descriptors such as divergence and vorticity from these flow maps. Using these descriptors, we derive the vertical velocity component and the kinetic helicity density. For this particular Carrington rotation, we find that the vertical velocity component is anticorrelated with the unsigned magnetic flux. Strong downflows are more likely associated with locations of strong magnetic activity. The vertical vorticity is positive in the northern hemisphere and negative in the southern hemisphere. At locations of magnetic activity, we find an excess vorticity of the same sign as that introduced by differential rotation. The vertical gradient of the zonal flow is mainly negative except within 2 Mm of the surface at latitudes poleward of about 20°. The zonal-flow gradient appears to be related to the unsigned magnetic flux in the sense that locations of strong activity are also locations of large negative gradients. The vertical gradient of the meridional flow changes sign near about 7 Mm, marking a clear distinction between near-surface and deeper layers. GONG and MDI data show very similar results. Differences occur mainly at high latitudes, especially in the northern hemisphere, where MDI data show a counter cell in the meridional flow that is not present in the corresponding GONG data.