short-period waves in the solar atmosphere

Astron. Nachr./AN 324, No. 4, 356 (2003) / DOI 10.1002/asna.200310126 Short-period waves in the solar atmosphere M. WUNNENBERG, A. ANDJI ´ C and F. KNEER Universit¨ ats-Sternwarte G¨ ottingen, Geismarlandstr. 11, D-37083 G¨ ottingen, Germany Received 30 October 2002; accepted 7 January 2003; published online 20 May 2003 1. Introduction The heating of the lower and middle chromosphere may be caused by the following process: Turbulent flow fields in the convection zone generate upward propagating acoustic waves, which form shocks at about 500 km and dissipate their energy. As these waves have short periods (< 100 s) and oc- cur on small scales, we need high spatial and temporal resolution for detecting them. 2. Observations and data processing The data for this contribution were taken in August 2000 at solar disk center with the “G¨ ottingen” two-dimensional spec- trometer, which is based on two Fabry-Perot interferometers. By scanning through the Fe I 5434 ˚ A line a time series of 41.25 min with a cadence of 25 s was taken. The line center of this non-magnetic line is formed at about 600 km. Broadband and narrow-band images were taken simultane- ously in order to allow later reconstruction as described in Krieg et al. (1999). Bisectors were calculated at every point in the field of view (27 ×13 ) and then intensity and velocity maps at different bisector heights could be determined. Images of the time series, which belong to the same atmospheric height, were correlated and destretched to give 3D- data-boxes (x, y, t). Fig. 1. Time slices of broadband images (left) and line center velocities (right). Correspondence to: [email protected] Fig. 1 shows time slices from these boxes, one for the in- tensities of broadband images, where the evolution of gran- ules can be seen and another for the velocities near line center, obtained from the narrow-band images. For each point (x i ,y i ) of the 3D-boxes (i.e. one row in the time slice) a wavelet analysis with Morlet wavelets was per- formed with a code developed by Torrence & Compo (1998). The wavelet power spectra for periods between one and two minutes were calculated. 3. Results and outlook In Fig. 2 temporal velocity fluctuations, measured near line center, at one point in the field of view are presented together with the wavelet power spectrum. 0 10 20 30 40 -1.0 -0.5 0.0 0.5 1.0 velocity [km/s] 0 10 20 30 40 time [min] 1.0 1.2 1.4 1.6 1.8 period [min] Fig. 2. Velocity fluctuations (upper panel) and appertaining wavelet power spectrum in the 1–2 min range (lower panel). Thus, we are able to show the existence of short-period waves in the solar atmosphere. More and detailed information can be found in Wunnenberg et al. (2002). With the new GREGOR telescope better spatial and temporal resolution will be obtained and then we would be able to detect short-period waves with periods at about 20 s. References Krieg, J., Wunnenberg, M., Kneer, F., Koschinsky, M., Ritter, C.: 1999, A&A 343, 983 Torrence, C., Compo, G.P.: 1998, Bull. Amer. Meteor. Soc. 79, 61 (wavelet software is available at URL: http://paos.colorado.edu/research/wavelets) Wunnenberg, M., Kneer, F., Hirzberger, J.: 2002, A&A 395, L51 c 2003 WILEY-VCHVerlag GmbH & Co. KGaA, Weinheim 0004-6337/03/0406-0356 $ 17.50+.50/0

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Astron. Nachr./AN 324, No. 4, 356 (2003) / DOI 10.1002/asna.200310126

Short-period waves in the solar atmosphere

M. WUNNENBERG, A. ANDJIC and F. KNEER

Universitats-Sternwarte Gottingen, Geismarlandstr. 11, D-37083 Gottingen, Germany

Received 30 October 2002; accepted 7 January 2003; published online 20 May 2003

1. Introduction

The heating of the lower and middle chromosphere may becaused by the following process: Turbulent flow fields inthe convection zone generate upward propagating acousticwaves, which form shocks at about 500 km and dissipate theirenergy. As these waves have short periods (< 100 s) and oc-cur on small scales, we need high spatial and temporal reso-lution for detecting them.

2. Observations and data processing

The data for this contribution were taken in August 2000 atsolar disk center with the “Gottingen” two-dimensional spec-trometer, which is based on two Fabry-Perot interferometers.By scanning through the Fe I 5434 A line a time series of41.25 min with a cadence of 25 s was taken. The line centerof this non-magnetic line is formed at about 600 km.Broadband and narrow-band images were taken simultane-ously in order to allow later reconstruction as described inKrieg et al. (1999). Bisectors were calculated at every pointin the field of view (27′′×13′′) and then intensity and veloc-ity maps at different bisector heights could be determined.Images of the time series, which belong to the same atmo-spheric height, were correlated and destretched to give 3D-data-boxes (x, y, t).

Fig. 1. Time slices of broadband images (left) and line center veloc-ities (right).

Correspondence to: [email protected]

Fig. 1 shows time slices from these boxes, one for the in-tensities of broadband images, where the evolution of gran-ules can be seen and another for the velocities near line cen-ter, obtained from the narrow-band images.For each point (xi, yi) of the 3D-boxes (i.e. one row in thetime slice) a wavelet analysis with Morlet wavelets was per-formed with a code developed by Torrence & Compo (1998).The wavelet power spectra for periods between one and twominutes were calculated.

3. Results and outlook

In Fig. 2 temporal velocity fluctuations, measured near linecenter, at one point in the field of view are presented togetherwith the wavelet power spectrum.

0 10 20 30 40-1.0

-0.5

0.0

0.5

1.0

velo

city

[km

/s]

0 10 20 30 40time [min]

1.0

1.2

1.4

1.6

1.8

perio

d [m

in]

Fig. 2. Velocity fluctuations (upper panel) and appertaining waveletpower spectrum in the 1–2 min range (lower panel).

Thus, we are able to show the existence of short-periodwaves in the solar atmosphere.More and detailed information can be found in Wunnenberget al. (2002).With the new GREGOR telescope better spatial and tempo-ral resolution will be obtained and then we would be able todetect short-period waves with periods at about 20 s.

References

Krieg, J., Wunnenberg, M., Kneer, F., Koschinsky, M., Ritter, C.:1999, A&A 343, 983

Torrence, C., Compo, G.P.: 1998, Bull. Amer. Meteor. Soc. 79, 61(wavelet software is available at URL:http://paos.colorado.edu/research/wavelets)

Wunnenberg, M., Kneer, F., Hirzberger, J.: 2002, A&A 395, L51

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