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Boltzmann plot determined from the OH(8-3) P-branch lines shown in the HiTIES spectrum from Fig. 2, taken on the 15 December 2015 at 01:40 UT with an integration time of 2 min. The solid black line is a linear fit to the P 1 lines (shown as blue circles); the inverse of the slope gives a rotational temperature of 193.9 K. Errors on the OH intensities I are obtained from the residuals of the spectral fit.
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We have developed a spectral fitting method to retrieve upper atmospheric parameters at multiple altitudes simultaneously during times of aurora, allowing us to measure neutral temperatures and column densities of water vapour. We use the method to separate airglow OH emissions from auroral O⁺ and N2 in observations between 725 and 740nm using the...
Contexts in source publication
Context 1
... of the initial rotational level, h is Planck's constant, c is the speed of light, and k is Boltzmann's constant. If we assume a Boltzmann distribution for the rotational level pop- ulation, the function is linear and the inverse of the slope of the fitted straight line is the neutral temperature. An exam- ple of a Boltzmann plot can be found in Fig. 3. In determin- ing the temperature, we make use of the strongest P-branch OH(8-3) lines recorded by HiTIES, the four P 1 lines: P 1 (2), P 1 (3), P 1 (4), and P 1 (5). These are shown in blue circles in Fig. 3; see also these lines labelled in the spectrum in Fig. 2. As LTE is not always assured, especially in the higher vibra- tional ...
Context 2
... and the inverse of the slope of the fitted straight line is the neutral temperature. An exam- ple of a Boltzmann plot can be found in Fig. 3. In determin- ing the temperature, we make use of the strongest P-branch OH(8-3) lines recorded by HiTIES, the four P 1 lines: P 1 (2), P 1 (3), P 1 (4), and P 1 (5). These are shown in blue circles in Fig. 3; see also these lines labelled in the spectrum in Fig. 2. As LTE is not always assured, especially in the higher vibra- tional states of OH ( Pendleton et al., 1993), we place con- straints on the variance between the linear fit and the P 1 and P 2 lines (the latter are the red circles in Fig. 3). A given tem- perature retrieval is ...
Context 3
... and P 1 (5). These are shown in blue circles in Fig. 3; see also these lines labelled in the spectrum in Fig. 2. As LTE is not always assured, especially in the higher vibra- tional states of OH ( Pendleton et al., 1993), we place con- straints on the variance between the linear fit and the P 1 and P 2 lines (the latter are the red circles in Fig. 3). A given tem- perature retrieval is rejected if the linear fit to P 1 line variance is greater than 0.05 or if the linear fit to P 2 line variance is over 0.3. For more information on this process, see Chadney et al. ...
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Citations
... The red line in Figure 5 shows the scaled-residual spectra measured by the H-α panel of the HiTIES instrument during the "open" event, integrated between 18:35:00 and 18:36:10 UT. As before, a fit for the spectra (excluding H-α) has been obtained using methods outlined in Chadney and Whiter (2018) and Price et al. (2019), which has then been taken away from the integrated spectra. Similarly to the "closed" event, H-α emission is present, at 6563 Å, but here the emission is much narrower in its wavelength extent. ...
This paper presents observations of polar cap arc substructure down to scale sizes of meters and temporal resolution of milliseconds. Two case studies containing polar cap arcs occurring over Svalbard are investigated. The first occurred on 4 February 2016 and is consistent with formation on closed field lines; the second occurred on 15 December 2015 and is consistent with formation on open field lines. These events were identified using global‐scale images from the Special Sensor Ultra‐violet Spectrographic Imager (SSUSI) instruments on board Defense Meteorological Satellite Program (DMSP) spacecraft. Intervals when the arcs passed through the small‐scale field of view of the Auroral Structure and Kinetics (ASK) instrument, located on Svalbard, were then found using all sky images from a camera also located on Svalbard. These observations give unprecedented insight into small‐scale polar cap arc structure. The energy and flux of the precipitating particles above these arcs are estimated using the ASK observations in conjunction with the Southampton Ionospheric model. These estimates are then compared to in situ DMSP particle measurements, as well as data from ground‐based instrumentation, to infer further information about their formation mechanisms. This paper finds that polar cap arcs formed on different magnetic field topologies exhibit different behavior at small‐scale sizes, consistent with their respective formation mechanisms.
... Other emissions such as from airglow (OH) and electron precipitation (N 2 (1PG)) are also present in this wavelength region. These emissions are modelled using methods outlined by Chadney and Whiter [2018] and Price et al. [2019] to obtain the spectra for the 'H-α' emission. Data from the 'H-α' panel is used in this thesis to determine the topology of the field lines on which polar cap aurora is formed by the presence (or lack) of precipitating protons (which are a sign of closed field lines). ...
... These estimates will be further investigated in Section 5.4 but for now we note that, due to the high values of the estimated energy and energy flux and the structure of the auroral forms seen in Fig. 5.4, this observation appears to be consistent with formation on closed field lines and is hence referred to as the 'closed' event for the remainder of this chapter. from OH, N 2 , N + and O + 2 emissions (but not H-alpha) have been fitted in this spectra using methods outlined in Chadney and Whiter [2018] and Price et al. [2019]. The overall fit, excluding the H-α emission at 6563Å, is shown in red. ...
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Context. Water vapor in the atmosphere undergoes quick spatial and temporal variations. This has a serious impact on ground-based astronomical observations from the visible band to the infrared band resulting from water vapor attenuation and emission.
Aims. We seek to show how the sky spectrum of an astronomical observation can be used to determine the amount of precipitable water vapor (PWV) along the line of sight toward the science target.
Methods. In this work, we discuss a method to retrieve the PWV from the OH(8-3) band airglow spectrum. We analyzed the influences of the pressure and temperature of the atmosphere and the different water vapor vertical distributions on the PWV retrieval method in detail. Meanwhile, the accuracy of the method was analyzed via Monte Carlo simulations. To further verify the method of PWV retrieval, we carried out cross comparisons between the PWV retrieved from OH airglow and PWV from the standard star spectra of UVES using equivalent widths of telluric absorption lines observed from 2000 to 2016 at Cerro Paranal in Chile.
Results. The Monte Carlo tests and the comparison between the two different methods prove the availability the PWV retrieval method from OH airglow. These results show that using OH airglow spectra in astronomical observations, PWVs along the same line of sight as the astronomical observations can be retrieved in real time.
Conclusions. We provide a quick and economical method for retrieving the water vapor along the same line of sight of astronomical observation in the real time. This is especially helpful to correcting the effect of water vapor on astronomical observations.
