The Economic Recession: Early Impacts on Health Care Safety Net Providers

Examines how the recession and state and local budget cuts affected safety-net clinics' capacity to meet demand in five communities, the extent to which federal stimulus funds mitigated the impact, strategies for sustainability, and implications

Flow Field Evolution of a Decaying Sunspot

We study the evolution of the flows and horizontal proper motions in and around a decaying follower sunspot based on time sequences of two-dimensional spectroscopic observations in the visible and white light imaging data obtained over six days from June~7 to~12, 2005. During this time period the sunspot decayed gradually to a pore. The spectroscopic observations were obtained with the Fabry-P\'{e}rot based Visible-Light Imaging Magnetograph (VIM) in conjunction with the high-order adaptive optics (AO) system operated at the 65 cm vacuum reflector of the Big Bear Solar Observatory (BBSO). We apply local correlation tracking (LCT) to the speckle reconstructed time sequences of white-light images around 600 nm to infer horizontal proper motions while the Doppler shifts of the scanned \FeI line at 630.15 nm are used to calculate line-of-sight (LOS) velocities with sub-arcsecond resolution. We find that the dividing line between radial inward and outward proper motions in the inner and outer penumbra, respectively, survives the decay phase. In particular the moat flow is still detectable after the penumbra disappeared. Based on our observations three major processes removed flux from the sunspot: (a) fragmentation of the umbra, (b) flux cancelation of moving magnetic features (MMFs; of the same polarity as the sunspot) that encounter the leading opposite polarity network and plages areas, and (c) flux transport by MMFs (of the same polarity as the sunspot) to the surrounding network and plage regions that have the same polarity as the sunspot.Comment: 9 pages, 7 figures, The Astrophysical Journal, accepted September, 200

Mesogranulation and Supergranulation in the Sun

Simultaneous satellite and ground-based observations of supergranular velocities in the Sun were made using the University of Colorado UV Spectrometer on OSO 8 and the Sacramento Peak Observatory diode array instrument. We compare our observations of the steady Doppler velocities seen toward the limb and at disk center in several spectral lines that span 1400 km in their heights of formation. Our observations indicate that supergranular flows are able to penetrate at least 11 density scale heights in the atmosphere. Seen at radius vector 0.8, the dynamic range of these motions increases from about 800 m/s in the photosphere to about 3000 m/s in the middle chromosphere. At disk center, regions of downflow tend to correlate with the bright Ca II network, those of upflow with the darker areas. The dynamic range of these vertical motions is only about 200 m/s in the photosphere but increases in the middle chromosphere to a value comparable with that seen at radius vector 0.8. Thus a distinct change appears to occur in the flow structure: whereas the horizontal component of the velocity predominates in the low photosphere, suggesting strong braking of the vertical momentum there, the motions higher in the atmosphere are more isotropic. These observations imply that supergranular velocities should be evident in the transition region. In addition to supergranular scale flows, our observations at disk center show a 7000 km scale of motion, which may be convective in origin. We call this mesogranulation. Mesogranules are most apparent in the MgI 5173A spectral line formed in the lower chromosphere. In the low photosphere, they are masked to some extent by the large signals from granulation and five-minute oscillations. Our SiII 1817A observations of the middle chromospheric motions indicate that a 7000 km scale of motion is also present there. If the scale of granulation is related to the depth of the HI ionization zone, and that of supergranulation to the Hell zone, then the mesogranules may represent the scale of motion driven in the Hel ionization zone. The decrease of the kinetic energy flux with height in the atmosphere suggests that major dissipation is occurring in these flows

Spatial distribution and statistical properties of small-scale convective vortex-like motions in a quiet Sun region

High-resolution observations of a quiet Sun internetwork region taken with the Solar 1-m Swedish Telescope in La Palma are analyzed. We determine the location of small-scale vortex motions in the solar photospheric region by computing the horizontal proper motions of small-scale structures on time series of images. These plasma convectively-driven swirl motions are associated to: (1) downdrafts (that have been commonly explained as corresponding to sites where the plasma is cooled down and hence returned to the interior below the visible photospheric level), and (2) horizontal velocity vectors converging into a central point. The sink cores are proved to be the final destination of passive floats tracing plasma flows towards the center of each vortex. We establish the occurrence of these events to be 1.4 x 10^(-3) and 1.6 x 10^(-3) vortices Mm^(-2) min^(-1) respectively for two time series analyzed here.Comment: 8 pages, 6 figures. Accepted for publication in Monthly Notices of the Royal Astronomical Societ

Horizontal supergranule-scale motions inferred from TRACE ultraviolet observations of the chromosphere

We study horizontal supergranule-scale motions revealed by TRACE observation of the chromospheric emission, and investigate the coupling between the chromosphere and the underlying photosphere. A highly efficient feature-tracking technique called balltracking has been applied for the first time to the image sequences obtained by TRACE (Transition Region and Coronal Explorer) in the passband of white light and the three ultraviolet passbands centered at 1700 {\AA}, 1600 {\AA}, and 1550 {\AA}. The resulting velocity fields have been spatially smoothed and temporally averaged in order to reveal horizontal supergranule-scale motions that may exist at the emission heights of these passbands. We find indeed a high correlation between the horizontal velocities derived in the white-light and ultraviolet passbands. The horizontal velocities derived from the chromospheric and photospheric emission are comparable in magnitude. The horizontal motions derived in the UV passbands might indicate the existence of a supergranule-scale magnetoconvection in the chromosphere, which may shed new light on the study of mass and energy supply to the corona and solar wind at the height of the chromosphere. However, it is also possible that the apparent motions reflect the chromospheric brightness evolution as produced by acoustic shocks which might be modulated by the photospheric granular motions in their excitation process, or advected partly by the supergranule-scale flow towards the network while propagating upward from the photosphere. To reach a firm conclusion, it is necessary to investigate the role of granular motions in the excitation of shocks through numerical modeling, and future high-cadence chromospheric magnetograms must be scrutinized.Comment: 5 figures, accepted by Astronomy & Astrophysic

Magnetohydrostatic atmospheres

We show that the atmospheric and magnetic height variations are coupled in general MHS equilibria with gravity when isolated thin non-force-free flux tubes are present. In gas-dominated environments, as in stellar photospheres, flux tubes must expand rapidly with height to maintain pressure balance with the cool surroundings. But in magnetically dominated environments, as in stellar coronae, the large-scale background magnetic field determines the average spreading of embedded flux tubes, and rigidly held flux tubes {\it require} a specific surrounding atmosphere with a unique temperature profile for equilibrium. The solar static equilibrium atmosphere exhibits correct transition-region properties and the accepted base coronal temperature for the sun's main magnetic spherical harmonic. Steady flows contribute to the overall pressure, so equilibria with accelerated wind outflows are possible as well. Flux tubes reflect a mathematical degeneracy in the form of non-force-free fields, which leads to coupling in general equilibrium conditions. The equilibrium state characterizes the system average in usual circumstances and dynamics tend to maintain the MHS atmosphere. Outflows are produced everywhere external to rigidly held flux tubes that refill a depleted or cool atmosphere to the equilibrium gas profile, heating the gas compressively.Comment: 12 pages, 5 figures, accepted by A&

On mesogranulation, network formation and supergranulation

We present arguments which show that in all likelihood mesogranulation is not a true scale of solar convection but the combination of the effects of both highly energetic granules, which give birth to strong positive divergences (SPDs) among which we find exploders, and averaging effects of data processing. The important role played by SPDs in horizontal velocity fields appears in the spectra of these fields where the scale $\sim$4 Mm is most energetic; we illustrate the effect of averaging with a one-dimensional toy model which shows how two independent non-moving (but evolving) structures can be transformed into a single moving structure when time and space resolution are degraded. The role of SPDs in the formation of the photospheric network is shown by computing the advection of floating corks by the granular flow. The coincidence of the network bright points distribution and that of the corks is remarkable. We conclude with the possibility that supergranulation is not a proper scale of convection but the result of a large-scale instability of the granular flow, which manifests itself through a correlation of the flows generated by SPDs.Comment: 10 pages, 11 figures, to appear in Astronomy and Astrophysic