The speed varies from around 1 km/s at the border between the umbra and the penumbra to a maximum of around double this in the middle of the penumbra and falls off to zero at the outer edge of the penumbra. Evershed first detected this phenomenon in January 1909, whilst working at the Kodaikanal Solar Observatory in India,[3] when he found that the spectral lines of sunspots showed doppler shift.
Afterwards, measurements of the spectral emission lines emitted in the ultraviolet wavelengths have shown a systematic red-shift. The Evershed effect is common to every spectral line formed at a temperature below 105 K; this fact would imply a constant downflow from the transition region towards the chromosphere. The observed velocity is about 5 km/s. Of course, this is impossible, since if it were true, the corona would disappear in a short time instead of being suspended over the Sun at temperatures of million degrees over distances much larger than a solar radius.
Many theories have been proposed to explain this redshift in line profiles of the transition region, but the problem is still unsolved, since a coherent theory should take into account all the physical observations: UV line profiles are redshifted on average, but they show back and forth velocity oscillations at the same time.
In synthesis, the proposed mechanisms are:
siphon flows in coronal loops driven by a pressure difference,[4]
different cross-sections of the coronal loops footpoints,[5]
^Evershed, J. (1909). "Radial movement in sun-spots". Monthly Notices of the Royal Astronomical Society. 69 (5): 454–458. Bibcode:1909MNRAS..69..454E. doi:10.1093/mnras/69.5.454.
^Subramanian, T.S. (1999). . Frontline. 16 (13). Archived from the original on 17 July 2012. Retrieved 27 April 2013.
^Meyer, F.; Schmidt, H.U. (1968). "Magnetisch ausgerichtete Strömungen zwischen Sonnenflecken". Z. Angew. Math. Mech. (in German). 48: 218. Bibcode:1968ZaMM...48..218M.
^Mariska, j.T.; Boris, J.P. (1983). "Dynamics and spectroscopy of asymmetrically heated coronal loops". The Astrophysical Journal. 267: 409. Bibcode:1983ApJ...267..409M. doi:10.1086/160879.
^Athay, R.G. (1984). "The origin of spicules and heating of the lower transition region". The Astrophysical Journal. 287: 412. Bibcode:1984ApJ...287..412A. doi:10.1086/162700.
^Kjeldseth-Moe; Brynildsen, N.; Brekke, P.; Engvold, O.; et al. (1988). "Gas flows in the transition region above sunspots". The Astrophysical Journal. 334: 1066. Bibcode:1988ApJ...334.1066K. doi:10.1086/166899.
^Hansteen, Viggo (1993). "A new interpretation of the redshift observed in optically thin transition region lines". The Astrophysical Journal. 402: 741. Bibcode:1993ApJ...402..741H. doi:10.1086/172174.
^Reale, F.; Serio, S.; Peres, G. (1996). "Radiatively-driven downdrafts and redshifts in transition region lines. I. Reference model". Astronomy and Astrophysics. 316: 215. Bibcode:1996A&A...316..215R.
^. Department of Posts, Government of India. Archived from the original on 12 August 2013. Retrieved 2 August 2013.
This spectroscopy-related article is a stub. You can help Wikipedia by expanding it.
evershed, effect, named, after, british, astronomer, john, evershed, radial, flow, across, photospheric, surface, penumbra, sunspots, from, inner, border, with, umbra, towards, outer, edge, speed, varies, from, around, border, between, umbra, penumbra, maximum. The Evershed effect named after the British astronomer John Evershed 1 is the radial flow of gas across the photospheric surface of the penumbra of sunspots from the inner border with the umbra towards the outer edge 2 The speed varies from around 1 km s at the border between the umbra and the penumbra to a maximum of around double this in the middle of the penumbra and falls off to zero at the outer edge of the penumbra Evershed first detected this phenomenon in January 1909 whilst working at the Kodaikanal Solar Observatory in India 3 when he found that the spectral lines of sunspots showed doppler shift Afterwards measurements of the spectral emission lines emitted in the ultraviolet wavelengths have shown a systematic red shift The Evershed effect is common to every spectral line formed at a temperature below 105 K this fact would imply a constant downflow from the transition region towards the chromosphere The observed velocity is about 5 km s Of course this is impossible since if it were true the corona would disappear in a short time instead of being suspended over the Sun at temperatures of million degrees over distances much larger than a solar radius Many theories have been proposed to explain this redshift in line profiles of the transition region but the problem is still unsolved since a coherent theory should take into account all the physical observations UV line profiles are redshifted on average but they show back and forth velocity oscillations at the same time In synthesis the proposed mechanisms are siphon flows in coronal loops driven by a pressure difference 4 different cross sections of the coronal loops footpoints 5 the return of spicules 6 multiple flows 7 nanoflares 8 and thermal instabilities during chromospheric condensation 9 The effect was commemorated in a postage stamp issued in India on 2 December 2008 10 See also Edit Solar System portal Astronomy portal Physics portal Space portalSpectroscopy Plasma physicsReferences Edit Stratton F J M 1957 John Evershed 1864 1956 Biographical Memoirs of Fellows of the Royal Society 3 40 51 doi 10 1098 rsbm 1957 0004 JSTOR 769351 Evershed J 1909 Radial movement in sun spots Monthly Notices of the Royal Astronomical Society 69 5 454 458 Bibcode 1909MNRAS 69 454E doi 10 1093 mnras 69 5 454 Subramanian T S 1999 Centenary of a solar observatory Frontline 16 13 Archived from the original on 17 July 2012 Retrieved 27 April 2013 Meyer F Schmidt H U 1968 Magnetisch ausgerichtete Stromungen zwischen Sonnenflecken Z Angew Math Mech in German 48 218 Bibcode 1968ZaMM 48 218M Mariska j T Boris J P 1983 Dynamics and spectroscopy of asymmetrically heated coronal loops The Astrophysical Journal 267 409 Bibcode 1983ApJ 267 409M doi 10 1086 160879 Athay R G 1984 The origin of spicules and heating of the lower transition region The Astrophysical Journal 287 412 Bibcode 1984ApJ 287 412A doi 10 1086 162700 Kjeldseth Moe Brynildsen N Brekke P Engvold O et al 1988 Gas flows in the transition region above sunspots The Astrophysical Journal 334 1066 Bibcode 1988ApJ 334 1066K doi 10 1086 166899 Hansteen Viggo 1993 A new interpretation of the redshift observed in optically thin transition region lines The Astrophysical Journal 402 741 Bibcode 1993ApJ 402 741H doi 10 1086 172174 Reale F Serio S Peres G 1996 Radiatively driven downdrafts and redshifts in transition region lines I Reference model Astronomy and Astrophysics 316 215 Bibcode 1996A amp A 316 215R Stamps 2008 Department of Posts Government of India Archived from the original on 12 August 2013 Retrieved 2 August 2013 This spectroscopy related article is a stub You can help Wikipedia by expanding it vte Retrieved from https en wikipedia org w index php title Evershed effect amp oldid 1170102172, wikipedia, wiki, book, books, library,
