CO₂ Thermal Infrared Signature Following a Sprite Event in the Mesosphere

Abstract

Sprites are a potential thermal infrared radiation source in the stratosphere and mesosphere through molecular vibrational excitation. We developed a plasma‐chemical model to compute the vibrational kinetics induced by a sprite streamer in the 40‐ to 70‐km altitude range until several tens of seconds after the visible flash is over. Then, we computed the consecutive time‐dependent thermal infrared spectra that could be observed from the stratosphere (from a balloon platform), high troposphere (from an aircraft), and low troposphere (aircraft or altitude observatory) using a nonlocal thermodynamic equilibrium radiative transfer model. Our simulations predict a strong production of CO2 in the (001) vibrational level which lasts at least 40 s before falling to background concentrations. This leads to enhanced emissions in the long‐wavelength infrared, around 1,000 cm−1, and midwavelength infrared, around 2,300 cm−1. The maximum sprite infrared signatures (sprite spectra minus background spectra) reach several 10−7 W/sr/cm2/cm−1 after propagation through the mesosphere and stratosphere, to an observer located at 20–40 km of altitude. This maximum signal is about 1 order of magnitude lower if propagated until the troposphere. From the two spectral bands, the 1,000‐cm−1 one could be detected more easily than the 2,300‐cm−1 one, which is more affected by atmospheric absorption (CO2 self‐trapping at all altitudes and H2O mostly in the troposphere). With a sufficiently sensitive instrumentation, mounted in an open stratospheric balloon platform for example, the 1,000‐cm−1 band could be detected from 20–40 km of altitude.

Maximum Sprite Streamer Luminosity Near the Stratopause

“…For example, the tendrils in the streamer zone are on occasion optically very bright (e.g., Soula et al, , Figure 5a, F41, Mlynarczyk et al, , Figure 3, F7G). These sprite streamer luminosities near the stratopause are important because they reflect the emissions from vibrational states of N 2 and CO 2 from the near to far infrared part of the spectrum (e.g., Bucsela et al, ; Gordillo‐Vazquez et al, ; Kanmae et al, ; Picard et al, ; Parra‐Rojas et al, ; Romand et al, , and references therein). In particular, it is predicted that intermediate (50 ms) and long (100 ms) duration current flows associated with lightning discharges inside thunderclouds assist to sustain the vibrational states of CO 2 (Parra‐Rojas et al, ).…”

Comparison of Lightning Channel Luminosity Versus Time Profiles in the Infrared and Visible Ranges

“…According to Romand et al. (2018), who studied detectability of IR emission associated with sprites, CO 2 emission in the 3–5 μm range is significantly affected by atmospheric absorption (CO 2 self‐trapping and H 2 O), but it could potentially have contributed to the emission recorded by our IR camera.…”

AS-CRI: A New Metric of FTIR-Based Apparent Spectral-Contrast Radiant Intensity for Remote Thermal Signature Analysis

“…Such radiance measurements are of great utility in infrared signatures. The IR signature is important to various areas, including Earth science [2], environment [3], weather [4], and military [5]. Remote measurements of Earth's temperature are useful for an analysis of the global warming problem.…”

“…This model can provide a high-resolution spectrum using a Michelson interferometer from the shortwave to midwave band [26]. The spectral resolution is user-selectable up to 0.25 [cm −1 ]; the noise equivalent spectral radiance (NESR) was 7 [nW/(cm 2 • sr • cm −1 )]; the radiometric accuracy is approximately 2 K. Such high sensitivity and accuracy is possible because the high-sensitivity sensor is combined with automatic high-efficiency calibration sources (hot black body, 95 • ; cold black body, 25 • ). An automatic weather station (AWS) recorded the environmental weather information per 10 s. The controlled field experiment was conducted three times (11:00, 14:00, and 16:00) a day between January to August in 2018.…”

“…The red lines indicate the OPD IDs used inFigure 9a.Figure 9cshows the results of spectrum extraction by applying the FFT to the interferogram(Figure 9b). The unit of the y-axis inFigure 9cis just the spectral intensity in arbitrary units.Figure 9dshows the wavenumber [cm −1 ]-calibrated spectrum using the Nyquist sampling theorem and HeNe laser with λ = 632.8 nm.Figure 9epresents the finally estimated spectral radiance [W/(m2 • sr • cm −1 )] at the same pixel calibrated using the hot/cold blackbody and Planck's law. The TELOPS FTIR system provides the spectral radiance in wavenumber units ([W/(m 2 sr cm −1 )]).…”