Hongrui Wang

Scaling Behavior of Structure Functions of the Longitudinal Magnetic Field in Active Regions on the Sun

In the framework of a refined Kolmogorov hypothesis, the scaling behavior of the Bz-component of the photospheric magnetic field is analyzed and compared with flaring activity in solar active regions. We use Solar and Heliospheric Observatory Michelson Doppler Imager, Huairou (China), and Big Bear measurements of the Bz-component in the photosphere for nine active regions. We show that there is no universal behavior in the scaling of the Bz-structure functions for different active regions. Our previous study has shown that scaling for a given active region is caused by intermittency in the field, (B)(), describing the magnetic energy dissipation. When intermittency is weak, the Bz field behaves as a passive scalar in the turbulent flow, and the energy dissipation is largely determined by the dissipation of kinetic energy in the active regions with low flare productivity. However, when the field (B)() is highly intermittent, the structure functions behave as transverse structure functions of a fully developed turbulent vector field, and the scaling of the energy dissipation is mostly determined by the dissipation of the magnetic energy (active regions with strong flaring productivity). Based on this recent result, we find that the dissipation spectrum of the Bz-component is strongly related to the level of flare productivity in a solar active region. When the flare productivity is high, the corresponding spectrum is less steep. We also find that during the evolution of NOAA Active Region 9393, the Bz dissipation spectrum becomes less steep as the active regions flare activity increases. Our results suggest that the reorganization of the magnetic field at small scales is also relevant to flaring: the relative fraction of small-scale fluctuations of magnetic energy dissipation increases as an active region becomes prone to producing strong flares. Since these small-scale changes seem to begin long before the start of a solar flare, we suggest that the relation between scaling exponents, calculated by using only measurements of the Bz-component, and flare productivity of an active region can be used to monitor and forecast flare activity.

SIGNATURE OF AN AVALANCHE IN SOLAR FLARES AS MEASURED BY PHOTOSPHERIC MAGNETIC FIELDS

We analyzed time variations of turbulent parameters of the photospheric magnetic field of four active regions obtained during the course of major solar flares using longitudinal magnetograms from the Big Bear Solar Observatory and from SOHO/MDI full-disk measurements. Analysis of the data indicated that, before each flare, the degree of intermittency of the magnetic field had been increasing for 6-33 minutes and reached a maximum value approximately 3-14 minutes before the peak of the hard X-ray emission for each event. This result seems to suggest the existence in an active region of a turbulent phase prior to a solar flare. We also found that the maximum of the correlation length of the magnetic energy dissipation field tends to follow (or to occur nearly simultaneously) with the peak of the hard X-ray emission. The data suggest that the peak in the correlation length might be a trace of an avalanche of coronal reconnection events. We discuss the results in the framework of the concept of self-organized criticality.

Magnetic Power Spectra Derived from Ground and Space Measurements of the Solar Magnetic Fields

We study magnetic power spectra of active and quiet regions by using Big Bear Solar Observatory and SOHO/MDI measurements of longitudinal magnetic fields. The MDI power spectra were corrected with Gaussian Modulation Transfer Function. We obtained reliable magnetic power spectra in the high wave numbers range, up to k=4.6xa0Mm−1, which corresponds to a spatial scale l=1.4xa0Mm. We find that the occurrence of the spectral discontinuity at high wave numbers, k≥3xa0Mm−1, largely depends on the spatial resolution of the data and it appears at progressively higher wave numbers as the resolution of the data improves. The spectral discontinuity in the raw spectra is located at wave numbers about 3 times smaller than wave numbers, corresponding to the resolution of the data, and about 1.5–2.0 times smaller in the case of the noise- and-resolution corrected spectra. The magnetic power spectra for active and quiet regions are different: active-region power spectra are described as ∼k−1.7, while in a quiet region the spectrum behaves as ∼k−1.3. We suggest that the difference can be due to small-scale dynamo action in the quiet-Sun photosphere. Our estimations show that the dynamo can generate more than 6% of the observed magnetic power.

Timing parameter optimization for comparison experiments of TSIM

The optimization problem of an absolute radiometers timing parameters is investigated for comparison experiments of Total Solar Irradiance Monitor (TSIM). Comparison experiments were performed to establish the TSIMs contact with other space radiometers for measuring total solar irradiance (TSI). Since the comparison experiments had to be performed on a tight schedule under the impact of weather conditions, the measurement parameters for the comparison experiments were selected carefully using optimized solutions of timing parameters. The optimized solutions were identified by a genetic algorithm (GA) based on a thermal model of an absolute radiometer. The thermal model includes terms of heat radiation, air conduction, etc. Fitness value function and constraints of GA are constructed using the thermal model. The experimental results indicate that the selected measurement parameters are sufficient to implement accurate calibration of TSI, providing more opportunities for solar observation.

Total solar irradiance monitors, space instruments for measuring total solar irradiance on FY-3 satellites

Total Solar Irradiance (TSI) has been recorded daily by Total Solar Irradiance Monitors (TSIM) with overlapping measurements on FY-3 (Feng Yun-3) series satellites since 2008. Instrument descriptions, operation in space and flight performance of three TSIMs are presented in this paper. TSI is measured by electrical substitution radiometers integrated in TSIM, with traceability to SI. TSIM/FY-3A and TSIM/FY-3B share nearly the same design. Since TSIM/FY-3A and TSIM/FY-3B have no pointing system, the Sun is only observed when the Sunlight sweeps TSIM’s field-of-view and TSI measurements are influenced inevitably by solar pointing errors. TSIM/FY-3C, a radiometer package was constructed with a pointing system for solar tracking in order to achieve accurate solar pointing. TSIM/FY-3C was sent into orbit in September 2013 onboard FY-3C satellite. Daily TSI measurements have been performed by TSIM/FY-3C with autonomous accurate solar tracking for 1 year. TSIM/FY-3C is in a good instrument health according to its on-orbit data.