Observation of Thermospheric Gravity Waves in the Southern Hemisphere With GOLD

Abstract

The middle thermosphere from~150 to 250 km is characterized by rapid increase in temperature with altitude and rapid ionization. The entire thermosphere is believed to be home to atmospheric waves that propagate through it, originating both in the atmospheric layers below and in the thermosphere itself. Within the middle thermosphere, direct observations of such waves are extremely sparse. The Global-scale Observations of the Limb and Disk (GOLD) far-ultraviolet imaging spectrometer is able to observe the middle thermosphere from geostationary orbit. During October 2018, a special observational campaign was performed, designed to identify atmospheric waves. Signatures in the 135.6-nm O airglow were seen that move northward with time, away from the southern polar region. These are consistent with a large-scale atmospheric gravity wave. These results are the first time 135.6-nm airglow has been used to track such a wave and highlight the ability of GOLD to observe such waves, even when at a modest amplitude, and track their motion.Plain Language Summary The upper region of the Earth's atmosphere, stretching from around 90-500 km above the surface, is known as the thermosphere. In this region, the temperature generally increases with altitude, but the strongest increase is in a region known as the middle thermosphere. The main source of heating in this region is absorption of ultraviolet light from the Sun, which also produces charged particles in this region, known as the ionosphere. Oscillations are observed in almost all the properties of the atmosphere at these altitudes, which are believed to result from waves within the atmosphere. In the middle thermosphere, there are very few direct observations of such waves. Global-scale Observations of the Limb and Disk (GOLD) is a new instrument that can observe the middle thermosphere by measuring emissions from the atmosphere call airglow. During a day in October 2018, GOLD observed what appear to be fluctuations in this airglow associated with such waves. The properties are determined, both from the GOLD observations and a theoretical model.

First Comparison of Traveling Atmospheric Disturbances Observed in the Middle Thermosphere by Global‐Scale Observations of the Limb and Disk to Traveling Ionospheric Disturbances Seen in Ground‐Based Total Electron Content Observations

“…During October 17-19, 2019, Channel B of the GOLD instrument was used to perform a special mode campaign, designed to identify the impacts of atmospheric waves on the middle thermosphere and their relation to similar fluctuations in the ionosphere. This basic experimental setup follows that described in England et al (2020), but with several important changes. The prior campaign demonstrated that GOLD is able to detect wave-like signatures in the airglow when it changes from regular operations in which it scans the Earth's disk, and instead stares at one location (one near vertical line as shown in Figure 1) for several hours.…”

“…The L1b processing includes geometric corrections for the detector and optics, filtering of the counts based on the detector pulse heights, a correction based on the detector deadtime (maximum count rate) and data are binned on a regular wavelength scale. England et al (2020) also used the Level 1b data, which provide the observed signal with the corrections described above at the highest available temporal and spatial cadence (spatial resolution of 48-km zonal by 17-km meridional at nadir and 2-min temporal cadence). From that prior study, it is evident that the perturbations to the airglow are relatively small in amplitude (below 1%) and are able to be seen in the L1b data that we will use here.…”

Daily Variability in the Terrestrial UV Airglow

“…A 20 km separation is approximately the scale height of N 2 and half the scale height of OI, so it is possible to consider that some process affecting the LBH layer may change with altitude and affect the 135.6-nm layer in a more pronounced manner. Examples of this kind of process are upward propagating gravity and acoustic waves that have been modeled and observed in the thermosphere [42,43], and recently observed in Earth's 135.6-nm emissions by GOLD [44].…”

Initial Observations by the GOLD Mission

“…A small portion of the observations use "special" modes which utilize the flexibility and independence of the channels to perform observations in which the instrument's operation is tailored to the objectives. Examples include the partial-disk scans conducted during the July 2019 eclipse (Aryal et al, 2019) and those made in search of gravity wave signatures in the lower-middle thermosphere that were reported by England et al (2020).…”

“…Journal of Geophysical Research: Space Physics special modes. An example of data collected using a special mode of operation to improve the SNR for a specific objective is the gravity waves observations reported by England et al (2020). Analyses of the current observations have also prompted the use of a modified version of the nightside scans used for observing each evening for early morning observations of the disk.…”