SH13A-1502
Investigation of geomagnetic and solar activity over time span 1960-2001
The solar-terrestrial relationship has been widely studied by means of space weather indices and various solar wind parameters. In this study we perform such an investigation over four decades (1960--2001) on the global scale, and for the first time on the regional scale as well. The variations regarded as the remaining external field signal (thereafter RES) and present in the European observatory annual means of the Northward, X, magnetic component is used as an indicator of the regional geomagnetic activity and are investigated regarding different processes occurring on the Sun. In order to understand how various geomagnetic activity indices respond to the interplanetary disturbances during different periods of the solar cycle, the annual means of the solar activity index, F10.7, and geomagnetic Ap and Dst indices, are studied. The indices are inherently complex since they include contributions from different solar phenomena. By studying the cross-correlations we aim to distinguish between different generation mechanisms. The relationships between the solar parameter F10.7 and RES, Dst, Ap, characterized by high cross-correlation coefficients, suggest the possibility to evaluate the behaviour of these geomagnetic parameters on short timescale. We found finite time lags among the investigated parameters. Our study suggests a one year delay of both RES and Dst after F10.7. The Ap is clearly delayed for about two years with respect to F10.7 and about one year with respect to Dst and RES. This indicate that the Ap responds to the solar activity in a different manner than Dst and RES, which are dominated by the coronal mass ejections activity. On the other hand, it seems that Ap is more sensitive to the high--speed streams (HSS) and Alfvenic waves present in HSS. The existence of time lags gives us the possibility to forecast different parameters. Importantly, the proposed forecasting procedure offers the possibility to reconstruct the F10.7 from the inferred geomagnetic activity for the epochs prior to solar activity monitoring. This study contributes to understanding some physical processes on the Sun that cause the perturbations in the near-Earth interplanetary space and consequently in the Earth's magnetic field. Moreover such investigations may provide a better insight into the time evolution of the open and closed solar magnetic field, and into long term changes in the solar activity with related physical processes.
SH13A-1503
The Solar Rotation Rate Profile from 1915 to 1985
The Mount Wilson solar photographic archive digitization project makes available
to the scientific community in digital form a selection of the solar images in
the archives of the Carnegie Observatories.
This archive contains over 150,000 images of the Sun which were acquired over
a time span in excess of 100 years. The images include broad-band images called
White Light Directs, ionized CaK line spectroheliograms and Hydrogen
Balmer alpha spectroheliograms.
This project will digitize essentially all of the CaK and broad-band direct images
out of the archive with 12 bits of significant precision and up to 3000 by 3000
spatial pixels.
This project has already completed the digitization of essentially all of the CaK and
about 50% of the broad-band direct images
out of the archive with 12 bits of significant precision and up to 3000 by 3000
spatial pixels.
Solar images have been extracted and identified
with original logbook parameters of observation time and scan format,
and they are available from the project web site at www.astro.ucla.edu/~ulrich/MW_SPADP.
The rate of solar rotation over the whole solar surface can be
determined as a function of time using the day-to day motions of features on
these CaK images. We present here preliminary results for the period 1915 to 1975.
The pattern of rotation rate is determined by cross-correlating
observations taken on successive days for 11 separate latitude
zones spanning the solar disk between +/- 50 degrees in latitude.
We found that the average rotation rate of the Sun during the 20th century was higher
during periods of minimum activity than it was during periods of maximum activity.
The difference in the rotation rate at the equator can be estimated at about 0.01
microrad/s. We also found that the orthogonalized rotation coefficients
calculated from the northern and southern hemispheres separately
show an asymmetry between the two hemispheres, with the
northern hemisphere rotating slightly faster than the southern hemisphere.
http://www.astro.ucla.edu/~ulrich/MW_SPADP
SH13A-1504
Spectral Irradiance Variations and Magnetic Field Changes During Solar Cycle 23.
Both total irradiance and the Mg core-to-wing ratio was high at the maximum of weak solar cycle 23. However, photometric observations from the San Fernando Observatory show that both the number and size of active regions (spots and faculae) were low at the maximum of solar cycle 23 which points to the importance of the role of weak magnetic fields in irradiance variations. The purpose of this paper is to use new SOLIS spectromagnetograph observations in conjunction with a newly developed image analysis technique to compare irradiance time series as function of wavelengths with various surface magnetic features. One major goal is to compare features derived from the SOLIS images using the new technique with well-established features from SFO. Another important goal is to determine the contribution of active regions/weak fields to irradiance variations at various wavelengths, using the SOHO/VIRGO and SORCE/SIM data. A third goal is to determine the extent of irradiance variations not explained by magnetic structures. To do this, we use a new analysis technique to evaluate SOLIS spectromagnetograph observations.
SH13A-1505
New Method of Solar Maximum Prediction With Application to the Next Solar Cycle
The correct prediction of the maximum of sunspot numbers for the next solar cycle is of great importance for ionospheric and magnetospheric modeling and for planning of new spacecraft missions. Predictions made so far by other researchers for cycle 24 cover the range from 60 -70 sunspots to 170 -180 sunspots for the year of the next solar maximum. We present a new method of prediction and compare our results with those of other methods for previous cycles. Our prediction for cycle 24 will be discussed in the context of other predictions.
SH13A-1506
Using Data Assimilation Methods for Modeling and Predicting Solar Activity Cycles
Modern data assimilation methods allow us to adapt a model to observations by estimating the true state of a system and taking into account uncertainties in the data and the model. The Ensemble Kalman Filter (EnKF) method provides an effective data assimilation for models of nonlinear dynamics. It is based on analysis of an ensemble of model solutions. We implement the EnKF method for modeling the 11-year sunspot number variations. Using this approach we propose a new physics-based method for predicting for the strength of the solar sunspot cycles. For the initial modeling of the sunspot number we use a dynamo model of Kleeorin and Ruzmaikin dynamo model in a low-mode approximation. The model includes the Parker's dynamo equations and an equation for conservation of the magnetic helicity. Also, we accept Bracewell's suggestion to relate the toroidal magnetic field, B, to the sunspot number, W,in the form of a three-halfs law: W ~ B3/2. We investigate non-linear solutions of the dynamo model and find periodic and chaotic solutions for the convection zone parameters, which represent basic properties of the solar cycles, such as the mean profile of solar cycle and the relationship between the cycle amplitude and the growth and decay times. By applying the EnKF method to the non-linear periodic solutions we reproduce the annual variations of the sunspot number and investigate the predictive capabilities. For testing we calculate forecasts for the 10 previous cycles and find a reasonable agreement with the observations. The calculations of the forecast of the upcoming solar cycle 24 indicate that this cycle will be weaker than the previous one, with the maximum sunspot number of about 80. This investigation shows that data assimilation methods may be useful for evaluating solar dynamo models and for forecasting solar activity.
SH13A-1507
Automated detection of oscillations in extreme ultraviolet imaging data
The corona is now known to support many different types of oscillation. Initial detection of these oscillations currently relied on manual labor. With the advent of much higher cadence EUV (extreme ultraviolet) data at better spatial resolution, sifting through the data manually to look for oscillatory material becomes an onerous task. Further, different observers tend to see different behavior in the data. To overcome these problems, we introduce a Bayesian probability-based automated method to detect areas in EUV images that support oscillations. The method is fast and can handle time series data with even or uneven cadences. Interestingly, the Bayesian approach allows us to generate a probability that a given frequency is present without the need for an estimate of the noise in the data. We also generate simple and intuitive "quality measures" for each detected oscillation. This will allow users to select the "best" examples in a given dataset automatically. The method is demonstrated on existing datasets (EIT, TRACE, STEREO). Its application to Solar Dynamics Observatory data is also discussed. We also discuss some of the problems in detecting oscillations in the presence of a significant background trend which can pollute the frequency spectrum.
SH13A-1508
Study of Solar He II 30.4 nm Pulsations
Pulsations of solar He II 30.4 nm, the dominant contributor of the solar Extreme Ultraviolet (EUV) flux, have been studied using Solar and Heliospheric Observatory (SOHO) based Charge, Element and Isotope Analysis System/Solar EUV Monitor (CELIAS/SEM) 26-34 nm EUV data. We computed solar He II 30.4 nm pulsation parameters (amplitudes and frequencies) of more than 100 pulsations observed between 2001 and 2007 using the least squares method. The solar cycle dependence of these pulsations has been studied and will be presented. Possible physical mechanisms powering these pulsations will be discussed.
SH13A-1509
Using Prominence Mass Inferences in Different Coronal Lines to Obtain the He/H Abundance
In a previous study we developed a new technique for deriving prominence mass by observing how much coronal radiation in the Fe XII (19.5 nm) spectral line is absorbed by prominence material. In the present work we apply this method, which allows us to consider the effects of both foreground and background radiation in our calculations, to a sample of prominences absorbing in a coronal line that ionizes both H and He (lambda < 50.4 nm), and a line that ionizes only H (50.4 nm < lambda < 91.1 nm). This approach, first suggested by Kucera et al. (1998), permits the determination of the abundance ratio of neutral helium and hydrogen in the prominence. This ratio should depend on how the prominence is formed, on its current thermodynamic state, and on its dynamical evolution. Thus, it may provide useful insights into the formation and evolution of prominences.
SH13A-1510
The Microflare Height Distribution
We present an in-depth statistical survey of flare heights of all X-ray microflares as observed by RHESSI
between March 2002 and March 2007, a total of >25,000 events, an order of magnitude larger then
previous studies. The microflares were found using a new flare-finding algorithm designed to search the 6--
12~keV count-rate when RHESSI's full sensitivity was available in order to find the smallest events. The
flare centroid position are found at the peak time and as a function of energy (3-6, 6-12, 12-25 keV). Flares
are found to occur only in active regions, not in the "quiet" Sun. Flare heights are found using two
independent methods including that of Matsushita (1992). The distribution of flares at the limb are fitted with
a Monte Carlo simulations and the flare height deduced. We find that the 6-12 keV flare heights are
consistent with a flare height of ~3 arcseconds above the photosphere with small separation between the
thermal and nonthermal sources. The Matsushita method confirm these values.
http://sprg.ssl.berkeley.edu/~schriste/?p=49
SH13A-1511
RHESSI/GOES Xray Solar Flare Multitemperature plus Power law Spectra
We present spectral fits for RHESSI and GOES solar flare data that include both a Differential Emission Measure for thermal emission and a power law fit for nonthermal emission. This improvement over the traditional isothermal approximation for thermal flare emission is intended to help to resolve the ambiguity in the range where the thermal and nonthermal components may have similar photon fluxes. This "crossover" range can be anywhere from 10 to 30 keV for medium to large solar flares. It is also expected that the low energy cutoff of the nonthermal electron spectrum lurks in this enery range, or below, but is obscured by thermal emission. In this work we apply the process (initially presented at the 2007 SPD/AAS meeting for two solar flares and simulated data) to a large sample of GOES X and M class flares. For each flare we attempt to establish limits for the low energy cutoff of the nonthermal spectrum and the energy in nonthermal electrons. This research is supported by NASA contract NAS5-98033 and NASA grant NNX08AJ18G.
SH13A-1512
Temporal and Spatial Evolution of Localized UV and Hard X-ray Emission in Solar Flares
Localized ultraviolet and hard X-ray emission sources provide observational diagnostics of flare-accelerated particles and energy deposition within the chromosphere. The evolution of these emission sources in space and intensity provide insight into the evolving magnetic structure and energy release dynamics of the flaring region. Initial studies of UV and hard X-ray emission indicated a strong co-temporal relationship between the two emission suggesting a common energetic origin often attributed to accelerated particle production resulting from magnetic reconnection in the corona. While confirming the overall temporal correlation, recent spatially-resolved observations have determined that localized correlated UV and HXR sources can occur in spatially distinct locations emphasizing the importance of a complex evolving magnetic topology in governing the spatial emission distributions observed. We present here an analysis of M and X class flares observed in TRACE 1600 Å images and RHESSI 25-100 keV X-rays at high cadence. While observations of the initial impulses show strong co-spatial emission in both wavelengths; however, as the flare evolves, we find significant spatial separations between the temporally correlated emission sources requiring that a time varying complex magnetic structure must be present to transport particles and produce the varied spatial distributions. In addition, we find, for 6 events showing multiple impulses in their X-ray time profiles, that each X-ray impulse corresponds to a distinct distribution of X-ray emission emission sources suggesting that each impulse may correspond to additional magnetic reconnection events is distinct locations within the corona. Finally, we find UV sources which deviate from the expected hard X-ray temporal correlation and instead appear more strongly associated with lower energy thermal X-ray emission indicating thermal processes or the thermal particle acceleration must contribute significantly in the flare energy release process.
SH13A-1513
First IPS Radio Sources Detected By MEXART
We present a first study of strong radio sources that are known to exhibit interplanetary scintillations (IPS)
detected by the Mexican Array Radio Telescope (MEXART). These observations were made using one
quarter of the total antenna (16 rows of 64 dipoles each) and a Butler Matrix (BM) of 16X16 ports. The BM
displays 16 beams at different declinations (from -48 to +88 degrees). We report the directionality and
efficiency of the beams. These first observations of radio IPS sources and the calibration of the BM is the first
step to initiate MEXART IPS maps in the near future.
http://www.mexart.unam.mx
SH13A-1514
Non-force Free Coronal Extrapolation Based on the Principle of Minimum Dissipation Rate
The Principle of Minimum (energy) Dissipation Rate (MDR) originates from irreversible thermodynamics. In analogy to the Principle of Minimum Energy, it also follows a variational approach, but is more suitable for a complex and externally driven system like the solar corona. And in contrast, while the former yields a force- free magnetic field, the MDR gives a more general non-force free magnetic field with flow. The solution to the equation describing non-force free magnetic field resulted from MDR can be expressed as a superposition of two linear force-free fields with distinct α parameters, and one potential field (α≡0). Subsequently, the plasma states can also be derived, following standard MHD theory, given necessary boundary conditions. We present recent progress on applying the MDR theory to non-force free extrapolation of solar active region from vector magnetograms as bottom boundary data. We illustrate the approach of complete characterization of 3D magnetic field and plasma states by using numerical simulation data, and discuss its advantages and limitations.
SH13A-1515
Energy Buildup in a Quadrupolar Corona
We consider the buildup of magnetic energy in a force-free model corona with quadrupolar boundary conditions at the coronal base. Our broad goal is to explore the energetics of the corona prior to coronal mass ejections. Specifically, we compare the maximum possible energy with that of a fully open field with the same boundary conditions; Aly and Sturrock have conjectured that the latter is the upper bound on the energy of force-free fields without detached flux. As found earlier for dipolar and other bipolar boundary conditions, it appears possible in the quadrupolar case to develop solutions with detached flux ropes, whose energy exceeds the open-field energy. Calculation of the open-field energy proves more difficult in the quadrupolar case, where the configuration of current sheets is not obvious from symmetry, and we present a method for finding this energy.
SH13A-1516
Are Double Coronal X-ray Sources in Solar Flares Two Magnetic Flux Ropes in Merging?
Double coronal hard and soft X-ray sources in an M1.4 flare have recently been reported by Liu et al. (2008). Non-thermal emissions in the high energy band are observed in the inner region of each source, and thermal emissions in the low energy band are observed in the outer region. The upper source moves downward and the lower source moves upward. Eventually the two sources merge and form a single source. We propose that this observation can be explained by merging of two flux ropes as shown in Choe and Cheng (2000). In a reconnecting current sheet of a flare, a new flux rope can be generated in the lower corona while a pre-born flux rope is ascending in the higher corona. Since the two flux ropes carry axial currents of the same direction, they naturally attract each other. As coronal flux ropes tend to move upward by nature due to the huge inductance of the photosphere, the downward motion of the upper flux rope is mild while the upward acceleration of the lower flux rope is outstanding. In the system of two merging flux ropes, currents are concentrated not only in the current sheet between the two flux ropes, but also in the center of each flux rope. Thus the highest energy X-ray emission comes from the former region and the next highest emissions are from the latter regions. The outer parts of the flux ropes are filled with lower energy plasmas emitting thermal X-ray radiation. We will discuss what coronal conditions favor such formation and merging of two flux ropes.
SH13A-1517
The role of AR topology on excitation, trapping and damping of individual loop oscillations
We investigate the role of magnetic field topology on individual dense loop oscillation by the means of 3D MHD numerical simulations of two models of idealized active regions (AR's). The first model of AR is initialized as a straight cylinder surrounded by the fieldlines of the same length and orientation. The second model consists of a force-free dipole magnetic configuration and contains a loop with a higher density than its surroundings. Dipole fieldlines have position dependent length and orientation. We study different ways of excitation of transverse loop oscillations by an external pulse and by a nearly eigenmode excitation implemented inside the loop. We find that perturbation acting directly on a single loop excites oscillations both in cylindrical and dipole loop. However, the leakage of the wave energy is larger in a curved loop compared to straight loop. External excitation of the whole AR is efficient in the excitation of oscillation in the straight cylindrical AR, but results in less efficient excitation in the case of dipole AR loop. We claim that excitation of collective motion of straight fieldlines having the same wave-periods and planes of the oscillations requires much less energy than excitation of dipole fieldlines having position-dependent orientation and wave-periods and being excited individually, not having a collective mode of oscillation. We conclude that coherent motion of straight fieldlines is one of the factors that decreases the energy leakage from an oscillating loop, while individual motions of dipole fieldlines require more energy from the source to produce the loop oscillations, and also lead to higher damping rate compared to the straight field case.
SH13A-1518
Active Region Flux Dispersal
The ultimate fate of the magnetic flux introduced into the solar photosphere by active region (AR) emergence is unknown, but some process(es) must remove it from the photosphere: over each 11-year sunspot cycle, about 3000 ARs emerge, many introducing on the order of 1021 Mx of flux into the photosphere, and most (if not all) of this flux disappears over the cycle. Does AR flux submerge, a process that might underlie observed "flux cancellation" events? Does diffusion destroy AR flux in-place? Is photospheric flux from ARs somehow removed by ejection into the heliosphere? We expect some of these processes to affect the evolution of the spatial distribution of magnetic flux in individual ARs. Accordingly, we investigate the evolution of AR flux in MDI full-disk magnetograms of several active regions from 1996-1998 that reappear on the disk (which is relatively empty at this phase of the cycle) at least once. In addition, we characterize changes in the distribution functions of flux concentrations within each active region from one appearance to the next. Log- normal distributions, indicative of fragmentation and merging, have been found in snapshots of ARs fields, but the evolution of these distributions within individual ARs has yet to be characterized. This work is supported by the NSF, under grant ATM-051438.
SH13A-1519
The application of Gaussian Mixture and Histogram-based Bayesian methods to NSO/Kitt Peak VT data.
We applied Gaussian Mixture and Histogram-based Bayesian methods to recognize several solar features using Kitt Peak Vacuum Telescope (VT) observations from 1992-2003. We used 5D observations in the 868.8 nm line including LoS magnetic field, continuum intensity, radial velocity, line depth, and EqW. We applied the analysis for recognition of active regions, magnetic network, and sunspots, for the purpose of automatic recognition of solar activity, and linking solar activity to irradiance changes. The success of such a feature recognition process strongly depends on separation and sensitivity of observable and derivative parameters for different features. For some features it works very well for two kind of data, but in some other cases the probability of correct recognition of a feature is low without the adding complementary data. We discuss the advantages and limitations of these statistical methods, review the importance and possibility of using the complementary data, and compare our results with other methods which derive feature areas. This methodological review will help to create the strategy for new SDO/HMI analysis.