Signatures of Thermospheric‐Exospheric Coupling of Hydrogen in Observed Seasonal Trends of H <i>α</i> Intensity

Gallant, M. A.; Mierkiewicz, E. J.; Nossal, S. M.; Qian, Liying; Burns, A. G.; Zacharias, Anissa; Roesler, F. L.

doi:10.1029/2018ja026426

Cited by 5 publications

(18 citation statements)

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“…Additional observations from this Pine Bluff annular‐summing Fabry‐Perot are shown in Mierkiewicz et al (). The Balmer α column emission intensities in Figure 4 of Mierkiewicz et al () contain observations from throughout the year, and, as shown in Gallant et al (), the intensity has a seasonal dependence, particularly at low shadow altitudes. To isolate effects other than seasonal and because sky conditions are typically best in winter, our focus for this reanalysis study is on winter observations.…”

Section: Resultsmentioning

confidence: 88%

“…The 1991 pre‐WHAM observations were taken in the zenith direction, and the corresponding shadow altitude for a solar depression of 45° was 2,783 km. This comparison at a midrange shadow altitude reduces uncertainty due to higher intensities observed at low shadow altitudes during dawn compared with intensities at the same shadow altitudes during dusk conditions (Gallant et al, ).…”

Section: Resultsmentioning

confidence: 99%

“…The transport of solar Lyman β radiation is a nonlinear process including excitation via multiple scattering of hydrogen atoms within the Earth's shadow. Forward modeling with a radiative transfer code can be used to more accurately compare observations with model simulations by using the simulated density profiles coupled with the radiative transfer code to calculate intensities that would be observed from the ground (Gallant et al, 2019;Nossal et al, 2012). For the Gallant et al (2019) and Nossal et al (2012) studies, the NRLMSISE-00 model (Picone et al, 2002) was used to generate both the hydrogen density profile and the background thermosphere.…”

Section: Discussionmentioning

confidence: 99%

“…Forward modeling with a radiative transfer code can be used to more accurately compare observations with model simulations by using the simulated density profiles coupled with the radiative transfer code to calculate intensities that would be observed from the ground (Gallant et al, ; Nossal et al, ). For the Gallant et al () and Nossal et al () studies, the NRLMSISE‐00 model (Picone et al, ) was used to generate both the hydrogen density profile and the background thermosphere. The profile was extended upward using the analytic exospheric model of Bishop ().…”

Section: Discussionmentioning

confidence: 99%

“…The data comparison presented here also includes observations taken by a higher-resolution Fabry-Perot using the annular-summing spectroscopy technique. This instrument was used to take observations from the Pine Bluff, WI observatory, some of which were taken during the same observing period as the WHAM Solar Cycle 23 observations and are included here (Gallant et al, 2019;Mierkiewicz et al, 2012). This Fabry-Perot was coupled to a pointing and tracking siderostat as well as to a CCD Camera.…”

Section: Higher-resolution Annular-summing Fabry-perot Interferometermentioning

confidence: 99%

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Geocoronal Hydrogen Emission Variation Over Two Solar Cycles

et al. 2019

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Ground-based hydrogen Balmer-α observations from Northern midlatitudes span multiple solar cycles, facilitating investigation of decadal scale variations, including natural variability in the hydrogen response to solar geophysical changes. Here we present a reanalysis of ground-based hydrogen emission observations from the early 1990s and their comparison with observations obtained in [2000][2001] in the context of the extended Northern Hemisphere midlatitude geocoronal hydrogen emission data set. This work suggests an increase in hydrogen emission intensity between the solar-maximum period of 1990-1991 (Solar Cycle 22) and the near-solar-maximum period of 2000-2001 (Solar Cycle 23), with the caveat that this is a limited data set and that there are calibration uncertainties discussed in this paper. Solar activity was higher during the earlier solar maximum period. Thus, the apparent increase in intensity is counter to previous observations from midlatitudes in which the observed intensity increases with higher solar activity. This increase was also not seen in comparison of intensities from three solar minima periods. Further, the apparent increase in intensity is also likely of larger magnitude than model simulations would predict due to increases in methane and carbon dioxide. We will discuss the reanalysis and recalibration of the 1990-1991 observations using current analysis approaches and the interpretation of these observations in the context of observations and modeling of hydrogen variation over different time scales. The detailed review of the calibration procedures has also provided insights to guide design of future observations. Plain Language Summary Atomic hydrogen is a key constituent of the thermosphere and exosphere, the uppermost region of the Earth's atmosphere. Hydrogen in this region is a by-product of molecules at lower altitudes that contain hydrogen such as water vapor and methane, two of the greenhouse gases most important to the energy balance of the Earth. The 11-year solar cycle is a major source of natural variability in the upper atmosphere. Here we present observations of geocoronal hydrogen emissions (~400 km and above) taken by ground-based Fabry-Perot instruments at Wisconsin and at the Kitt Peak, Observatory in Arizona. These observations span two solar cycles and suggest an increase in the geocoronal hydrogen emission intensity between the 1990-1991 solar maximum (Solar Cycle 22) and the 2000-2001 near-solar-maximum (Solar Cycle 23) periods, with the caveat that this is a limited data set and there are calibration uncertainties. Solar activity was higher during the earlier solar maximum period. The apparent increase in intensity is counter to previous observations from midlatitudes in which the observed intensity increases with higher solar activity. Further, the apparent increase in intensity is also likely of larger magnitude than model simulations would predict due to increases in methane and carbon dioxide.

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Section: Resultsmentioning

confidence: 88%

Section: Resultsmentioning

confidence: 99%