Far ultraviolet observations of Earth's dayglow from the National Aeronautics and Space Administration (NASA) Global‐scale Observations of the Limb and Disk (GOLD) mission presents an unparalleled opportunity for upper atmosphere radiance data assimilation. Assimilation of the Lyman‐Birge‐Hopfield (LBH) band emissions can be formulated in a similar fashion to lower atmosphere radiance data assimilation approaches. To provide a proof‐of‐concept for such an approach, this paper presents assimilation experiments of simulated LBH emission data using an ensemble filter measurement update step implemented with National Oceanic and Atmospheric Administration (NOAA)'s Whole Atmosphere Model (WAM) and National Center for Atmospheric Research (NCAR)'s Global Airglow (GLOW) model. Primary findings from observing system simulation experiments (OSSEs), wherein “truth” atmospheric conditions simulated by NCAR's Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM) are used to generate synthetic GOLD data, are as follows: (1) Assimilation of GOLD LBH disk emission data can reduce the bias in model temperature specification (ensemble mean) by 60% under both geomagnetically quiet conditions and disturbed conditions. (2) The reduction in model uncertainty (ensemble spread) as a result of assimilation is about 20% in the lower thermosphere and 30% in the upper thermosphere for both conditions. These OSSEs demonstrate the potential for far ultraviolet radiance data assimilation to dramatically reduce the model biases in thermospheric temperature specification and to extend the utility of GOLD observations by helping to resolve the altitude‐dependent global‐scale response of the thermosphere to geomagnetic storms.
- PAR ID:
- 10312088
- Date Published:
- Journal Name:
- Atmospheric Measurement Techniques
- Volume:
- 14
- Issue:
- 11
- ISSN:
- 1867-8548
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract A total solar eclipse occurred in the Southern Hemisphere on 2 July 2019 from approximately 17 to 22 UT. Its effect in the thermosphere over South America was imaged from geostationary orbit by NASA's Global‐scale Observation of Limb and Disk (GOLD) instrument. GOLD observed a large brightness reduction (>80% around totality) in OI 135.6 nm and N2LBH band emissions compared to baseline measurements made 2 days prior. In addition, a significant enhancement (with respect to the baseline) in the ΣO/N2column density ratio (~80%) was observed within the eclipse's totality. This enhancement suggests that the eclipse induced compositional changes in the thermosphere. After the eclipse passed, a slight enhancement in ΣO/N2column density ratio (~7%) was also seen around the totality path when compared to measurements before the eclipse. These observations are the first synoptic imaging measurements of an eclipse's thermospheric effects with the potential to drastically improve and test our understanding of how the thermosphere responds to rapid, localized changes in solar short wavelength radiation.
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Abstract Current and previous thermospheric remote sensing missions use N2Lyman‐Birge‐Hopfield (LBH) band dayglow emission measurements to retrieve line‐of‐sight thermospheric composition and temperature. The precision of thermospheric composition and temperature retrieved from observations depends on the uncertainty in the relative LBH vibrational populations. In the laboratory, electron impact induced LBH emission measurements have shown that the relative vibrational populations change with gas pressure. However, it is not fully understood how these populations change for dayglow observations where the emissions that contribute to the observations vary with solar illumination and line‐of‐sight geometry. We quantify the relative vibrational populations as a function of solar zenith angle (SZA) and tangent altitude using Global‐scale Observations of Limb and Disk mission's LBH dayglow observations. We find that, while some lower vibrational levels show potential enhancement with increasing pressure (decreasing altitude), in general, they do not change significantly with SZA or tangent altitude for dayglow observations. The vibrational populations can thus be assumed as fixed parameters when retrieving neutral disk temperatures from remotely sensed LBH dayglow observations.
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null (Ed.)We have measured in the laboratory the far ultraviolet (FUV: 125.0–170.0 nm) cascade-induced spectrum of the Lyman-Birge-Hopfield (LBH) band system (a 1Πg → X 1Σg+) of N2 excited by 30–200 eV electrons. The cascading transition begins with two processes: radiative and collision-induced electronic transitions (CIETs) involving two states (a′ 1Σu− and w 1Δu → a 1Πg), which are followed by a cascade induced transition a 1Πg → X 1Σg+. Direct excitation to the a-state produces a confined LBH spectral glow pattern around an electron beam. We have spatially resolved the electron induced glow pattern from an electron beam colliding with N2 at radial distances of 0–400 mm at three gas pressures. This imaging measurement is the first to isolate spectral measurements in the laboratory of single-scattering electron-impact-induced-fluorescence from two LBH emission processes: direct excitation, which is strongest in emission near the electron beam axis; and cascading-induced, which is dominant far from the electron beam axis. The vibrational populations for vibrational levels from v′=0–2 of the a 1Πg state are enhanced by CIETs, and the emission cross sections of the LBH band system for direct and cascading-induced excitation are provided at 40, 100, and 200 eVmore » « less
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/amt-14-6917-2021
