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White, S. M.; Kundu, M. R.

doi:10.1023/a:1004975528106

Cited by 92 publications

(50 citation statements)

References 19 publications

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“…If we exclude transients such as flares, which are dominated by non-thermal emissions, then the main contributions are incoherent thermal free-free and gyroresonance emissions (Kundu 1965;White & Kundu 1997). The former prevail in cool dense plasmas, including the quiet Sun, but are also emitted by coronal loops, faculae, etc.…”

Section: What Distinguishes F30 From F107?mentioning

confidence: 99%

The 30 cm radio flux as a solar proxy for thermosphere density modelling

Wit

Bruinsma²

2017

J. Space Weather Space Clim.

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The 10.7 cm radio flux (F10.7) is widely used as a proxy for solar UV forcing of the upper atmosphere. However, radio emissions at other centimetric wavelengths have been routinely monitored since the 1950 s, thereby offering prospects for building proxies that may be better tailored to space weather needs. Here we advocate the 30 cm flux (F30) as a proxy that is more sensitive than F10.7 to longer wavelengths in the UV and show that it improves the response of the thermospheric density to solar forcing, as modelled with DTM (Drag Temperature Model). In particular, the model bias drops on average by 0-20% when replacing F10.7 by F30; it is also more stable (the standard deviation of the bias is 15-40% smaller) and the density variation at the the solar rotation period is reproduced with a 35-50% smaller error. We compare F30 to other solar proxies and discuss its assets and limitations.

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Section: What Distinguishes F30 From F107?mentioning

confidence: 99%

The 30 cm radio flux as a solar proxy for thermosphere density modelling

Wit

Bruinsma²

2017

J. Space Weather Space Clim.

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“…At this frequency bright gyroresonance emission is often present, if at all, only in the sense of circular polarization that corresponds to the gyration motion of electrons about the electric field (the magnetoionic "extraordinary" mode), because the other polarization (the "ordinary" mode) requires a lower harmonic to produce significant opacity and therefore requires a higher magnetic field strength (2700 G for the 2nd harmonic) that is usually not present in the corona (e.g., see White & Kundu 1997). Figure 11 shows two examples of VLA observations of sunspots at 15 GHz in the ordinary-mode polarization (in both cases bright gyroresonance sources are seen over the umbra in the opposite polarization).…”

Section: Umbrae At Centimeter Wavelengthsmentioning

confidence: 99%

The chromosphere above sunspots at millimeter wavelengths

Loukitcheva

Solanki

White

2014

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Aims. The aim of this paper is to demonstrate that millimeter wave data can be used to distinguish between various atmospheric models of sunspots, whose temperature structure in the upper photosphere and chromosphere has been the source of some controversy. Methods. We use observations of the temperature contrast (relative to the quiet Sun) above a sunspot umbra at 3.5 mm obtained with the Berkeley-Illinois-Maryland Array (BIMA), complemented by submm observations from Lindsey & Kopp (1995) and 2 cm observations with the Very Large Array. These are compared with the umbral contrast calculated from various atmospheric models of sunspots. Results. Current mm and submm observational data suggest that the brightness observed at these wavelengths is low compared to the most widely used sunspot models. These data impose strong constraints on the temperature and density stratifications of the sunspot umbral atmosphere, in particular on the location and depth of the temperature minimum and the location of the transition region. Conclusions. A successful model that is in agreement with millimeter umbral brightness should have an extended and deep temperature minimum (below 3000 K). Better spatial resolution as well as better wavelength coverage are needed for a more complete determination of the chromospheric temperature stratification above sunspot umbrae.

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“…The magnetic field in the upper solar atmosphere can be determined, for example, through extrapolations from the photosphere (Seehafer & Staude 1979;Falconer et al 1997;Yan & Sakurai 1997;Schrijver et al 1999;Régnier et al 2002) or from cyclotron radiation recorded at radio wavelengths in sufficiently strong fields (White & Kundu 1997). The first technique is, despite many advances, still uncertain in several decisive details and requires improved measurements in the upper atmosphere to test and calibrate it.…”

Section: Introductionmentioning

confidence: 99%

Retrieval of the full magnetic vector with the He I multiplet at 1083 nm

Lagg

Woch

Krupp

et al. 2004

A&A

159

203

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Abstract.A technique is presented to invert Stokes profiles of the He I 1083 nm multiplet lines in order to obtain the full magnetic vector and the line-of-sight velocity. The technique makes use of spectropolarimetry connected with the Zeeman effect supplemented by a simple Hanle effect based diagnostic when appropriate. It takes into account effects like line saturation, magnetooptical effects, etc. and is coupled with a genetic algorithm, which ensures that the global minimum in a goodness of fit hypersurface is found. Tests using both artificial and real data demonstrated the robustness of the method. As an illustration maps of deduced parameters of an emerging flux region are shown and briefly discussed.

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Untitled

Cited by 92 publications

References 19 publications

The 30 cm radio flux as a solar proxy for thermosphere density modelling

The 30 cm radio flux as a solar proxy for thermosphere density modelling

The chromosphere above sunspots at millimeter wavelengths

Retrieval of the full magnetic vector with the He I multiplet at 1083 nm

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