The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
I V Ptashnik - One of the best experts on this subject based on the ideXlab platform.
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water vapour foreign Continuum absorption in near infrared windows from laboratory measurements
Philosophical Transactions of the Royal Society A, 2012Co-Authors: I V Ptashnik, Robert Mcpheat, Keith P Shine, K.m. Smith, Gary R WilliamsAbstract:For a long time, it has been believed that atmospheric absorption of radiation within wavelength regions of relatively high infrared transmittance (so-called ‘windows’) was dominated by the water vapour self-Continuum, that is, spectrally smooth absorption caused by H2O−H2O pair interaction. Absorption due to the foreign Continuum (i.e. caused mostly by H2O−N2 bimolecular absorption in the Earth's atmosphere) was considered to be negligible in the windows. We report new retrievals of the water vapour foreign Continuum from high-resolution laboratory measurements at temperatures between 350 and 430 K in four near-infrared windows between 1.1 and 5 μm (9000–2000 cm−1). Our results indicate that the foreign Continuum in these windows has a very weak temperature dependence and is typically between one and two orders of magnitude stronger than that given in representations of the Continuum currently used in many climate and weather prediction models. This indicates that absorption owing to the foreign Continuum may be comparable to the self-Continuum under atmospheric conditions in the investigated windows. The calculated global-average clear-sky atmospheric absorption of solar radiation is increased by approximately 0.46 W m−2 (or 0.6% of the total clear-sky absorption) by using these new measurements when compared with calculations applying the widely used MTCKD (Mlawer–Tobin–Clough–Kneizys–Davies) foreign-Continuum model.
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water vapor self Continuum absorption in near infrared windows derived from laboratory measurements
Journal of Geophysical Research, 2011Co-Authors: I V Ptashnik, Robert Mcpheat, Keith P Shine, K.m. Smith, Gary R WilliamsAbstract:In most near-infrared atmospheric windows, absorption of solar radiation is dominated by the water vapor self-Continuum and yet there is a paucity of measurements in these windows. We report new laboratory measurements of the self-Continuum absorption at temperatures between 293 and 472 K and pressures from 0.015 to 5 atm in four near-infrared windows between 1 and 4 m (10000-2500 cm-1); the measurements are made over a wider range of wavenumber, temperatures and pressures than any previous measurements. They show that the self-Continuum in these windows is typically one order of magnitude stronger than given in representations of the Continuum widely used in climate and weather prediction models. These results are also not consistent with current theories attributing the self Continuum within windows to the far-wings of strong spectral lines in the nearby water vapor absorption bands; we suggest that they are more consistent with water dimers being the major contributor to the Continuum. The calculated global-average clear-sky atmospheric absorption of solar radiation is increased by 0.75 W/m2 (which is about 1% of the total clear-sky absorption) by using these new measurements as compared to calculations with the MT_CKD-2.5 self-Continuum model.
Lucia Kleint - One of the best experts on this subject based on the ideXlab platform.
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hydrogen balmer Continuum in solar flares detected by the interface region imaging spectrograph iris
The Astrophysical Journal, 2014Co-Authors: P Heinzel, Lucia KleintAbstract:We present a novel observation of the white light flare (WLF) Continuum, which was significantly enhanced during the X1 flare on 2014 March 29 (SOL2014-03-29T17:48). Data from the Interface Region Imaging Spectrograph (IRIS) in its near-UV channel show that at the peak of the Continuum enhancement, the contrast at the quasi-Continuum window above 2813 A reached 100%-200% and can be even larger closer to Mg II lines. This is fully consistent with the hydrogen recombination Balmer-Continuum emission, which follows an impulsive thermal and non-thermal ionization caused by the precipitation of electron beams through the chromosphere. However, a less probable photospheric Continuum enhancement cannot be excluded. The light curves of the Balmer Continuum have an impulsive character with a gradual fading, similar to those detected recently in the optical region on the Solar Optical Telescope on board Hinode. This observation represents a first Balmer-Continuum detection from space far beyond the Balmer limit (3646 A), eliminating seeing effects known to complicate the WLF detection. Moreover, we use a spectral window so far unexplored for flare studies, which provides the potential to study the Balmer Continuum, as well as many metallic lines appearing in emission during flares. Combined with future ground-based observations of the Continuum near the Balmer limit, we will be able to disentangle various scenarios of the WLF origin. IRIS observations also provide a critical quantitative measure of the energy radiated in the Balmer Continuum, which constrains various models of the energy transport and deposit during flares.
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hydrogen balmer Continuum in solar flares detected by the interface region imaging spectrograph iris
arXiv: Solar and Stellar Astrophysics, 2014Co-Authors: P Heinzel, Lucia KleintAbstract:We present a novel observation of the white-light flare (WLF) Continuum, which was significantly enhanced during the X1 flare on March 29, 2014 (SOL2014-03-29T17:48). Data from the Interface Region Imaging Spectrograph (IRIS) in its NUV channel show that at the peak of the Continuum enhancement, the contrast at the quasi-Continuum window above 2813 \AA\ reached 100 - 200 % and can be even larger closer to the Mg II lines. This is fully consistent with the hydrogen recombination Balmer Continuum emission, which follows an impulsive thermal and non-thermal ionization caused by the precipitation of electron beams through the chromosphere. However, a less probable photospheric Continuum enhancement cannot be excluded. The light curves of the Balmer Continuum have an impulsive character with a gradual fading, similar to those detected recently in the optical region on Hinode/SOT. This observation represents a first Balmer-Continuum detection from space far beyond the Balmer limit (3646 \AA), eliminating seeing effects known to complicate the WLF detection. Moreover, we use a spectral window so far unexplored for flare studies, which provides the potential to study the Balmer Continuum, as well as many metallic lines appearing in emission during flares. Combined with future ground-based observations of the Continuum near the Balmer limit, we will be able to disentangle between various scenarios of the WLF origin. IRIS observations also provide a critical quantitative measure of the energy radiated in the Balmer Continuum, which constrains various models of the energy transport and deposition during flares.
Gary R Williams - One of the best experts on this subject based on the ideXlab platform.
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water vapour foreign Continuum absorption in near infrared windows from laboratory measurements
Philosophical Transactions of the Royal Society A, 2012Co-Authors: I V Ptashnik, Robert Mcpheat, Keith P Shine, K.m. Smith, Gary R WilliamsAbstract:For a long time, it has been believed that atmospheric absorption of radiation within wavelength regions of relatively high infrared transmittance (so-called ‘windows’) was dominated by the water vapour self-Continuum, that is, spectrally smooth absorption caused by H2O−H2O pair interaction. Absorption due to the foreign Continuum (i.e. caused mostly by H2O−N2 bimolecular absorption in the Earth's atmosphere) was considered to be negligible in the windows. We report new retrievals of the water vapour foreign Continuum from high-resolution laboratory measurements at temperatures between 350 and 430 K in four near-infrared windows between 1.1 and 5 μm (9000–2000 cm−1). Our results indicate that the foreign Continuum in these windows has a very weak temperature dependence and is typically between one and two orders of magnitude stronger than that given in representations of the Continuum currently used in many climate and weather prediction models. This indicates that absorption owing to the foreign Continuum may be comparable to the self-Continuum under atmospheric conditions in the investigated windows. The calculated global-average clear-sky atmospheric absorption of solar radiation is increased by approximately 0.46 W m−2 (or 0.6% of the total clear-sky absorption) by using these new measurements when compared with calculations applying the widely used MTCKD (Mlawer–Tobin–Clough–Kneizys–Davies) foreign-Continuum model.
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water vapor self Continuum absorption in near infrared windows derived from laboratory measurements
Journal of Geophysical Research, 2011Co-Authors: I V Ptashnik, Robert Mcpheat, Keith P Shine, K.m. Smith, Gary R WilliamsAbstract:In most near-infrared atmospheric windows, absorption of solar radiation is dominated by the water vapor self-Continuum and yet there is a paucity of measurements in these windows. We report new laboratory measurements of the self-Continuum absorption at temperatures between 293 and 472 K and pressures from 0.015 to 5 atm in four near-infrared windows between 1 and 4 m (10000-2500 cm-1); the measurements are made over a wider range of wavenumber, temperatures and pressures than any previous measurements. They show that the self-Continuum in these windows is typically one order of magnitude stronger than given in representations of the Continuum widely used in climate and weather prediction models. These results are also not consistent with current theories attributing the self Continuum within windows to the far-wings of strong spectral lines in the nearby water vapor absorption bands; we suggest that they are more consistent with water dimers being the major contributor to the Continuum. The calculated global-average clear-sky atmospheric absorption of solar radiation is increased by 0.75 W/m2 (which is about 1% of the total clear-sky absorption) by using these new measurements as compared to calculations with the MT_CKD-2.5 self-Continuum model.
P Heinzel - One of the best experts on this subject based on the ideXlab platform.
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hydrogen balmer Continuum in solar flares detected by the interface region imaging spectrograph iris
The Astrophysical Journal, 2014Co-Authors: P Heinzel, Lucia KleintAbstract:We present a novel observation of the white light flare (WLF) Continuum, which was significantly enhanced during the X1 flare on 2014 March 29 (SOL2014-03-29T17:48). Data from the Interface Region Imaging Spectrograph (IRIS) in its near-UV channel show that at the peak of the Continuum enhancement, the contrast at the quasi-Continuum window above 2813 A reached 100%-200% and can be even larger closer to Mg II lines. This is fully consistent with the hydrogen recombination Balmer-Continuum emission, which follows an impulsive thermal and non-thermal ionization caused by the precipitation of electron beams through the chromosphere. However, a less probable photospheric Continuum enhancement cannot be excluded. The light curves of the Balmer Continuum have an impulsive character with a gradual fading, similar to those detected recently in the optical region on the Solar Optical Telescope on board Hinode. This observation represents a first Balmer-Continuum detection from space far beyond the Balmer limit (3646 A), eliminating seeing effects known to complicate the WLF detection. Moreover, we use a spectral window so far unexplored for flare studies, which provides the potential to study the Balmer Continuum, as well as many metallic lines appearing in emission during flares. Combined with future ground-based observations of the Continuum near the Balmer limit, we will be able to disentangle various scenarios of the WLF origin. IRIS observations also provide a critical quantitative measure of the energy radiated in the Balmer Continuum, which constrains various models of the energy transport and deposit during flares.
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hydrogen balmer Continuum in solar flares detected by the interface region imaging spectrograph iris
arXiv: Solar and Stellar Astrophysics, 2014Co-Authors: P Heinzel, Lucia KleintAbstract:We present a novel observation of the white-light flare (WLF) Continuum, which was significantly enhanced during the X1 flare on March 29, 2014 (SOL2014-03-29T17:48). Data from the Interface Region Imaging Spectrograph (IRIS) in its NUV channel show that at the peak of the Continuum enhancement, the contrast at the quasi-Continuum window above 2813 \AA\ reached 100 - 200 % and can be even larger closer to the Mg II lines. This is fully consistent with the hydrogen recombination Balmer Continuum emission, which follows an impulsive thermal and non-thermal ionization caused by the precipitation of electron beams through the chromosphere. However, a less probable photospheric Continuum enhancement cannot be excluded. The light curves of the Balmer Continuum have an impulsive character with a gradual fading, similar to those detected recently in the optical region on Hinode/SOT. This observation represents a first Balmer-Continuum detection from space far beyond the Balmer limit (3646 \AA), eliminating seeing effects known to complicate the WLF detection. Moreover, we use a spectral window so far unexplored for flare studies, which provides the potential to study the Balmer Continuum, as well as many metallic lines appearing in emission during flares. Combined with future ground-based observations of the Continuum near the Balmer limit, we will be able to disentangle between various scenarios of the WLF origin. IRIS observations also provide a critical quantitative measure of the energy radiated in the Balmer Continuum, which constrains various models of the energy transport and deposition during flares.
K.m. Smith - One of the best experts on this subject based on the ideXlab platform.
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water vapour foreign Continuum absorption in near infrared windows from laboratory measurements
Philosophical Transactions of the Royal Society A, 2012Co-Authors: I V Ptashnik, Robert Mcpheat, Keith P Shine, K.m. Smith, Gary R WilliamsAbstract:For a long time, it has been believed that atmospheric absorption of radiation within wavelength regions of relatively high infrared transmittance (so-called ‘windows’) was dominated by the water vapour self-Continuum, that is, spectrally smooth absorption caused by H2O−H2O pair interaction. Absorption due to the foreign Continuum (i.e. caused mostly by H2O−N2 bimolecular absorption in the Earth's atmosphere) was considered to be negligible in the windows. We report new retrievals of the water vapour foreign Continuum from high-resolution laboratory measurements at temperatures between 350 and 430 K in four near-infrared windows between 1.1 and 5 μm (9000–2000 cm−1). Our results indicate that the foreign Continuum in these windows has a very weak temperature dependence and is typically between one and two orders of magnitude stronger than that given in representations of the Continuum currently used in many climate and weather prediction models. This indicates that absorption owing to the foreign Continuum may be comparable to the self-Continuum under atmospheric conditions in the investigated windows. The calculated global-average clear-sky atmospheric absorption of solar radiation is increased by approximately 0.46 W m−2 (or 0.6% of the total clear-sky absorption) by using these new measurements when compared with calculations applying the widely used MTCKD (Mlawer–Tobin–Clough–Kneizys–Davies) foreign-Continuum model.
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water vapor self Continuum absorption in near infrared windows derived from laboratory measurements
Journal of Geophysical Research, 2011Co-Authors: I V Ptashnik, Robert Mcpheat, Keith P Shine, K.m. Smith, Gary R WilliamsAbstract:In most near-infrared atmospheric windows, absorption of solar radiation is dominated by the water vapor self-Continuum and yet there is a paucity of measurements in these windows. We report new laboratory measurements of the self-Continuum absorption at temperatures between 293 and 472 K and pressures from 0.015 to 5 atm in four near-infrared windows between 1 and 4 m (10000-2500 cm-1); the measurements are made over a wider range of wavenumber, temperatures and pressures than any previous measurements. They show that the self-Continuum in these windows is typically one order of magnitude stronger than given in representations of the Continuum widely used in climate and weather prediction models. These results are also not consistent with current theories attributing the self Continuum within windows to the far-wings of strong spectral lines in the nearby water vapor absorption bands; we suggest that they are more consistent with water dimers being the major contributor to the Continuum. The calculated global-average clear-sky atmospheric absorption of solar radiation is increased by 0.75 W/m2 (which is about 1% of the total clear-sky absorption) by using these new measurements as compared to calculations with the MT_CKD-2.5 self-Continuum model.
