Scientific Interests in OVSA Expanded Array

Haimin Wang

Physics of Elementary Bursts

Multi-wavelength Observations:Microwave imaging spectroscopyRHESSI demodulated light curves0.1”, 100ms resolution flare observations

from NST, IBIS, Yunnan 1-m telescope (it has small time overlap with OVSA, but similar science can be done with Chinese FASR)

Trajectories of the brightest pixels in flare kernels K2 (left) and K1 (right).

The time lapse is marked by the color table. The solid (dotted) contours indicate the positive (negative) longitudinal magnetic field.

Comparison of Halpha -1.3 Å intensity (thin lines) and hard X-ray flux (thick lines) for three flare kernels during the time interval 18:03:59 18:04:06 UT. For the Halpha emission, both the raw data and a 10-point smoothed curve are plotted.

Comparison of Halpha -1.3 Å intensity (thin lines) and hard X-ray

flux (thick lines) for three flare kernels during the time interval 18:04:22 18:04:29 UT. For the H emission, both the raw data and a 10-point smoothed curve are plotted.

Power spectra of the fast variations of the Halpha -1.3 Å

emission at the three

flare kernels 18:04:22 to 18:04:29 UT

HXR and Radio Observations of the 2011-Feb-15 Flare

The flare:

NOAA 11158 (S21O W21O)

Occurred at 01:44 UT, peaked around 01:55 UT

GOES class: X2.2

Energetic: White-Light Flare Up to 100 keV HXR No Gamma-ray emission Clear Sunquake (RHESSI NUDGET#148 by Hudson & FletcherHudson & Fletcher)

Green Continuum 5550 ÅBefore flare

Red Continuum 6684 Å01:51:03 UT

Unaltered image Contract-reversed

difference image

White-Light (From HINODE/SOT)

Flare ribbon (dark feature)

Overview of HXR (4 sec) and SXR time profiles

HXR (RHESSI)

Demodulated HXR light curves

More peaks than the low cadence light curves in previous slide

HXR (RHESSI)

01:48:28 --- 01:49:08 35 ~ 80 keV = 6.18

01:50:44 --- 01:51:36 30 ~ 80 keV = 6.13

01:52:36 --- 01:53:08 30 ~ 80 keV = 5.72

01:53:28 --- 01:54:00 30 ~ 50 keV

50 ~ 100 keV

= 5.24

= 4.53

01:54:56 --- 01:55:36 30 ~ 80 keV

45 ~ 100 keV

= 4.64

= 4.12

01:54:56 --- 01:55:36 30 ~ 40 keV = 7.84

HXR (RHESSI)

SHS variation

A peak at ~ 01:50:10 is NOT selected,Because the change of attenuator.

RADIO (KSRBL)

Radio light curve cadence ~ 2.2 sec

HXR vs. RADIO

01:54:56 --- 01:55:36 45 ~ 100 keV = 4.12HXR

RADIO

For electron flux, δx = + 1 = 5.12 (Silva et al. 2000)

α = 1.29δr = 1.11* α + 1.36 = 2.79(Silva et al. 2000)

δx - δr = 2.33,

Still within the upper limit of 2.7 as in Silva et al. 2000

3-D magnetic field extrapolation

• LFF

• NLFF (Large FOV of HMI and Seeing Free)

• Chromospheric Field Tracing

• STEREO Observations

--Microwave Diagnosis

Nonpotentiality of Chromospheric Fibrils

Objective:

We assume that chromospheric fibrils are magnetic field-aligned. By comparing the orientation of the fibrils with the azimuth of the embedding chromospheric magnetic field extrapolated from a potential field model, the shear angle, a measure of nonpotentiality, along the fibrils is readily deduced. Following this approach, we make a quantitative assessment of the nonpotentiality of fibrils in the active region NOAA 11092.

Data Sets: NOAA 11092, 2010 Aug. 2

H(656.3 nm)

Chromospheric LOS magnetogram(854.2 nm)

Instrument the Interferometric BIdimensional Spectrometer (IBIS)/DST

The Vector SpectroMagnetograph (VSM) /SOLIS

Resolution ~0.1”/pixel ~1”/pixel

Time 15:00 15:43 UT averaged 15:15 UT

Left: H image;

Right: LOS magnetogram, overlaid with the potential transverse field.

FOV: 254”264”

Method: Segmentation and Modeling of Chromospheric Fibrils

1: the original image after Gaussian smoothing; 2: the difference image between the original image and the smoothed image; 3: the segmented pieces of fibrils after the image thresholding; 4: the segmented pieces are grouped with the union-find algorithm and small groups are removed from the image; 5: the second-degree-polynomial modeling of fibrils (red curves); 6: the orientation of fibrils.

Left: The chromospheric azimuth field derived from the potential field model, overlaid with the chromospheric fibrils segmented from the H observations;Right: The chromospheric transverse field vectors derived from the potential field model, overlaid with the chromospheric fibrils segmented from the H observations.

Results: Chromospheric Fibrils vs. Chromospheric Potential Transverse Field

Results: Magnetic Shear along Fibrils

Left: the spatial distribution of the magnetic shear angle ;Right: the histogram of the magnetic shear angle .

Microwave Imaging Spectroscopy vs. NLFF Field Extrapolation

Objective:

Microwave observations provides unique and quantitative information on coronal magnetic fields, and are complementary to the morphological validation of nonlinear force-free (NLFF) field modeling. We will perform imaging spectroscopy in combination with the principle of gyroresonance to map out magnetic field strength at the base of corona above active regions. The coronal magnetic field obtained using microwave measurements will be compared with that obtained using NLFF field extrapolation to quantitatively examine the discrepancies.

Data Sets: NOAA 10930

Photospheric vector magneogram: the Spectro-Polarimeter (SP)/SOT/HinodeMicrowave: OVSA

Hudson, Fisher and Welsch (2008) and Fisher et al. (2010): Fields turn to more horizontal after a flare

Change of Lorentz Force:δfz=(BzδBz-BxδBx-ByδBy)/4π

Shuo: Estimation of the strength of Bt using weak field approximation.

Summary: Scientific Questions

• 1. Elementary Bursts

• 2. 3-D magnetic structure

Advanced NLFF Extrapolation

Chromospheric Field observation

STEREO reconstruction

• 3. Magnetic field restructuring after flares may be observable by EOVSA