title: Linear acoustic waves in a nonisothermal atmosphere. II. photospheric resonator model of three-minute umbral oscillations

authors: Chae, Jongchul

subjects: Science & Technology

abstract: The velocity oscillations observed in the chromosphere of sunspot umbrae resemble a resonance in that their power spectra are sharply peaked around a period of about three minutes. In order to describe the resonance that leads to the observed 3-minute oscillations, we propose the photospheric resonator model of acoustic waves in the solar atmosphere. The acoustic waves are driven by the motion of a piston at the lower boundary, and propagate in a nonisothermal atmosphere that consists of the lower layer (photosphere), where temperature rapidly decreases with height, and the upper layer (chromosphere), where temperature slowly increases with height. We have obtained the following results: (1) The lower layer (photosphere) acts as a leaky resonator of acoustic waves. The bottom end is established by the piston, and the top end by the reflection at the interface between the two layers. (2) The temperature minimum region partially reflects and partially transmits acoustic waves of frequencies around the acoustic cutoff frequency at the temperature minimum. (3) The resonance occurs in the photospheric layer at one frequency around this cutoff frequency. (4) The waves escaping the photospheric layer appear as upwardpropagating waves in the chromosphere. The power spectrum of the velocity oscillation observed in the chromosphere can be fairly well reproduced by this model. The photospheric resonator model was compared with the chromospheric resonator model and the propagating wave model.

text: Linear acoustic waves in a nonisothermal atmosphere. II. photospheric resonator model of three-minute umbral oscillations The velocity oscillations observed in the chromosphere of sunspot umbrae resemble a resonance in that their power spectra are sharply peaked around a period of about three minutes. In order to describe the resonance that leads to the observed 3-minute oscillations, we propose the photospheric resonator model of acoustic waves in the solar atmosphere. The acoustic waves are driven by the motion of a piston at the lower boundary, and propagate in a nonisothermal atmosphere that consists of the lower layer (photosphere), where temperature rapidly decreases with height, and the upper layer (chromosphere), where temperature slowly increases with height. We have obtained the following results: (1) The lower layer (photosphere) acts as a leaky resonator of acoustic waves. The bottom end is established by the piston, and the top end by the reflection at the interface between the two layers. (2) The temperature minimum region partially reflects and partially transmits acoustic waves of frequencies around the acoustic cutoff frequency at the temperature minimum. (3) The resonance occurs in the photospheric layer at one frequency around this cutoff frequency. (4) The waves escaping the photospheric layer appear as upwardpropagating waves in the chromosphere. The power spectrum of the velocity oscillation observed in the chromosphere can be fairly well reproduced by this model. The photospheric resonator model was compared with the chromospheric resonator model and the propagating wave model.

year: 2019

title: The death of a Prophet: the end of Muhammad's life and the beginnings of Islam [Book Review]

authors: Drury, Abdullah

abstract: This article reviews the book “The death of a Prophet: the end of Muhammad's life and the beginnings of Islam”, by Stephen J. Shoemaker.

text: The death of a Prophet: the end of Muhammad's life and the beginnings of Islam [Book Review] This article reviews the book “The death of a Prophet: the end of Muhammad's life and the beginnings of Islam”, by Stephen J. Shoemaker.

year: 2013

title: Indigenizing outdoor play in New Zealand: A conversation analysis approach

authors: Bateman, Amanda

abstract: This chapter focuses on a single case analysis of one trip to a local bush reserve in New Zealand. The observations included in this chapter begin by exploring the way in which a promise to the Maori God Tane Mahuta is managed by the teachers and children at the beginning of the excursion. The promise made is part of the mundane, everyday activity engaged in by these children and teachers during their weekly visit to the bush reserve, where every child is required to recite a phrase that promises not to hurt the creatures, animals or plants of Tane Mahuta when they are playing in the forest. In the first of the video-recorded episodes, explicit reference to Tane Mahuta is initially oriented through one of the children reciting the promise, unprompted, at the beginning of the recording. The second observation reveals one of the teachers explaining to a child the rules of entering the forest: that you have to ask permission from Tane Mahuta before you enter. When a child does not want to say the promise, he is encouraged to do so collaboratively with the teacher before entering the forest. Only once the child has said the promise does he enter, demonstrating the importance of the verbal commitment and participation in the accountable action of promise-making by the participants prior to entering the forest.

text: Indigenizing outdoor play in New Zealand: A conversation analysis approach This chapter focuses on a single case analysis of one trip to a local bush reserve in New Zealand. The observations included in this chapter begin by exploring the way in which a promise to the Maori God Tane Mahuta is managed by the teachers and children at the beginning of the excursion. The promise made is part of the mundane, everyday activity engaged in by these children and teachers during their weekly visit to the bush reserve, where every child is required to recite a phrase that promises not to hurt the creatures, animals or plants of Tane Mahuta when they are playing in the forest. In the first of the video-recorded episodes, explicit reference to Tane Mahuta is initially oriented through one of the children reciting the promise, unprompted, at the beginning of the recording. The second observation reveals one of the teachers explaining to a child the rules of entering the forest: that you have to ask permission from Tane Mahuta before you enter. When a child does not want to say the promise, he is encouraged to do so collaboratively with the teacher before entering the forest. Only once the child has said the promise does he enter, demonstrating the importance of the verbal commitment and participation in the accountable action of promise-making by the participants prior to entering the forest.

year: 2017