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Status of Ring-diagram Analysis of MOTH Data

Kiran Jain

Collaborators: F. Hill, C. Toner

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Outline

• Motivation• The MOTH data• Ring−diagram analysis

Problem with MOTH data and the possible solution

• Preliminary Results

Comparison with GONG • Summary and Future work

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Motivation

• Over last several decades, helioseismology has been a powerful tool to study the dynamics of the solar interior. However, relatively less efforts have been made to study the properties and the structure of the solar atmosphere.

• The seismology of solar atmosphere is also important to understand the excitation and damping mechanism of the acoustic waves- whether there are acoustic cavities in the solar atmosphere!

• With the efforts of groups from Hawai and Italy, unique data sets are now available to study the seismology of the solar atmosphere. The instrument used for these observations is known as MOTH.

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The MOTH data (Magneto-Optical filters at Two Heights)

• Simultaneous Observations (Red and Blue wings) of two spectral lines:

K 769.9 nm (Photosphere)

Na D2 589.0 nm (Chromosphere)

(These two lines are formed about 360 km apart in the solar atmosphere.)

• Observing runs during Austral summer at South Pole (Dec, 2002 - Jan, 2003)

• Image size : 512 x 512 pixel2

(low resolution as compared to GONG/MDI)

• Cadence : 10 sec

(high cadence as compared to GONG/MDI)

Data Products : Dopplergrams & Intensitygrams

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Analysis

To process MOTH images (for Jan 18-20, 2003) through standard ring-diagram pipeline,

Images were flipped.

The cadence was changed to 1 min (by adding 6 MOTH images).

total number of regions across the solar disk: 137

each region is 30º x 30º and was tracked for 1-day (1440 min).

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Flow maps - Problem with data

Severe washing machine effect -

Regions are not properly tracked.

K (Top)

Na (Right)

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Possible solution to the problem

Calculated angular-correlations between MOTH and MDI data - poor correlation coefficients.

K and Na images have different correlation with MDI.

Example :

Residual rotation for MOTH –K and MDI images

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After applying corrections to offset angle, and re-processing data

through ring-pipeline,

Flow map for

MOTH - K

Thus, washing machine effect disappears in MOTH-K analysis.

But, we did not see much improvement in MOTH-Na analysis: further efforts are going on.

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Preliminary Results (K-line) ( - diagram from fitted spectrum at the disk center)

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Change in frequency between two locations

Figure (Top Left) : Frequency difference between two locations on the equator (and Longitude 30º E & 30º W).

Figure (bottom right) : Frequency difference between two locations at 0º Longitude (and Latitude 30º N and 30º S).

Open questions: Why are we getting these frequency differences? Since these regions are located at a equal distance from the disk center, what could be the possible factors responsible for these difference?

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MOTH – K data

Various mode parameters as a function of frequency

at disk center

(different colors for different n-values)

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Comparison between MOTH and GONG

Observing height of GONG - Ni line is about 200 km above the base of the photosphere while height for MOTH - K line is about 420 km.

Since GONG images are 839 x 839 pixel2, we reduced the resolution of these images to 512 x 512 pixel2 to match with MOTH data.

new GONG images were processed through ring-pipeline with same patch area (30º x 30º) and were tracked for 1-day (1440 min).

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Change in frequency (ν) = νMOTH – νGONG

(at disk center)

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Change in frequency between two locations MOTH (blue) and GONG (red)

Figure (Top Left) : Frequency difference between two locations on the equator (and Longitude 30º E & 30º W).

Figure (bottom right) : Frequency difference between two locations at 0º Longitude (and Latitude 30º N and 30º S).

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Comparison between MOTH-K and GONG at the disk center

Blue : GONG Red : MOTH

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Horizontal and vertical flows GONG (blue) & MOTH (red)

Figure (Top Left) : UX and UY at Latitude 0º and Longitude 30º E.

Figure (bottom right) : UX and UY at Latitude 30º N and Longitude 0º.

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Summary and future work

The simultaneous observations at different heights show that

• There is a difference in mode frequencies

• The amplitude and background reduce with increasing observing height.

• We do not see any significant change in the line width at the disk center.

• Horizontal and vertical flows also show some difference but errors in the fitting are large!

There are differences in mode frequencies at same radial distances from the center. Why?

A detailed analysis is in progress to study various mode parameters at different locations on the solar disk as well as with varying observing heights.

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Many more things to do

Comparison of flows after inversion (with depth)

Similar analysis with intensity data and compare results with velocity data

Seismology of active regions with different observing heights

Another observing campaign is in progress with

• upgraded camera (1024 x 1024) • observations of four spectral lines – K, Na D2, Ca II and He I

With new data sets, we will carry out similar analysis to study mode characteristics in higher solar atmosphere.