Dynamics of the polar off-limb regions

D. BanerjeeD. BanerjeeIndian Institute of AstrophysicsIndian Institute of Astrophysics

E.O’Shea E.O’Shea & J.G. Doyle& J.G. Doyle

((Armagh ObservatoryArmagh Observatory))

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MotivationCoronal Holes (CH) Coronal Holes (CH) Source region of the Source region of the

Fast Solar WindFast Solar Wind

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Spectroscopic observations:

4(Doyle, Teriaca, Banerjee, 1999)

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Observational log: Coronal Diagnostic spectrometer (CDS/SoHO)Coronal Diagnostic spectrometer (CDS/SoHO) Long temporal series sequence for 11 TR and coronal Long temporal series sequence for 11 TR and coronal

lines formed between 2.5 x 10lines formed between 2.5 x 105 5 to 2.5 x 10 to 2.5 x 106 6 K.K. We will present only results from coronal lines Mg x We will present only results from coronal lines Mg x

609,625 609,625 Å Å Slit width 4 x 240 arc secSlit width 4 x 240 arc sec Exposure time 60 secExposure time 60 sec

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Using measurements of Mg x 609 & 624 lines, we seek to find evidence of line width decrease far-off limb –Can they be due to wave dissipation??

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Variatiation of Dopler width with radial distance

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Coronal hole diagnostics upto 8 solar radii

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Concluding remarks:

A Comparison shows that the decrease in line widths happens around the same heights where the dominant excitation changes from collisional to radiative.

This should further correspond to sudden drop in electron Density.

The reported decrease in line widths in coronal ions at largeThe reported decrease in line widths in coronal ions at largeAltitudes off-limb may not simply related to wave dissipation!!Altitudes off-limb may not simply related to wave dissipation!!

Above 1150 arc sec, the ratio of the two Mg X lines reducesTo values that we might expect for a radiatively dominantExcitation mode

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Let us turn our attention to something else:Namely, dynamic events close to the limb

Location of the limb

Dynamic activity at the limbMacrospicule??

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Space-time (X-T) plots of the radiant flux for the s26438 dataset

We suggest that the decrease in flux is evidence of a localized evacuation of plasma

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S26406 dataset, px18

The combination of evidence of evacuated and blue-shifted

Plasma indicates presence of dyanamic event...

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What is a blinker?

Sudden enhancement is flux observed in transition region linesObserved with CDS (Harrison 1997)

Preferentially occuring near network boundaries above regions of strong unipolar magnetic field

Blinkers may be on-disk signature of spicule??

Explosive events and blinkers are separate phenomenon

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Summary:

Evacuation event, linked to the reconnection process are Observed as dramatic reduction in intensity flux in OV and Mg X lines.

Following the recipe for identifying for blinkers, as outlinedBy Brkovic et al (2001), we can say blinkers are present off-limb

Blinkers are occuring above regions of dynamic activity, That produces evacuation events and quasi-periodic oscillations

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Summary

We suggest that the blinkers are signatures of macro-spiculesPresent at the temperature of the OV line

Signatures of up-flow of plasma in spicule like event, resulting in brightenings and blue-shifts followed by falling back of this plasma under gravity, resulting in correspondingRed-shift

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Blinker

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Explosive Event: