We perform azimuth time tracking of multiple thunderstorm centers on the globe, which are sources of extremely low frequency (ELF) electromagnetic waves propagating in the spherical Earth‐ionosphere cavity. For observations made in September 2023 we identify azimuths of numerous global emission centers using our data sampled at 3 kHz at the Hylaty station in Poland. We confirm significant and relatively regular thunderstorm azimuth variation during the solar terminator passage over the observation site. The magnitude and duration of the azimuth deviations depend on the observed azimuths but are also varying between successive days and changing detailed thunderstorm activity patterns. The measured maximum positive (preferentially at the sunrise time) and negative (preferentially at the sunset time) azimuth deviations reach even above 20 for waves propagating close to the terminator. We discovered also particular composite deviation structures, with the negative azimuth deviation directly preceding a larger positive one, sometimes occurring near the morning terminator passage 100 km above the surface. It is possibly the first detection of the ELF equivalent of the “greyline” transmission known in the HF radio propagation. At azimuths distant from the terminator one can observe decreasing of the regular deviation magnitude and occasionally lower magnitude deviations with opposite sign. The variations between successive days are expected to result from varying thunderstorm activity on Earth as well variability of ionospheric parameters, in particular of ionization gradients and nonuniformities occurring along the terminator. We postulate that the observed deviations result from a signal refraction at the varying ionospheric gradients.
The moving solar terminator (ST) generates atmospheric disturbances, broadly termed solar terminator waves (STWs). Despite theoretically recurring daily, STWs remain poorly understood, partially due to measurement challenges near the ST. Analyzing Michelson Interferometer for Global High‐resolution Thermospheric Imaging (MIGHTI) data from NASA's Ionospheric Connection Explorer (ICON) observatory, we present observations of STW signatures in thermospheric neutral winds, including the first reported meridional wind signatures. Seasonal analysis reveals STWs are most prominent during solstices, when they intersect the ST about ∼20° latitude from the equator in the winter hemisphere and have phase fronts inclined at a ∼40° angle to the ST. We also provide the first observed STW altitude profiles, revealing large vertical wavelengths above 200 km. Comparing these observations to four different models suggests the STWs likely originate directly or indirectly from waves from below 97 km. STWs may play an under‐recognized role in the daily variability of the thermosphere‐ionosphere system, warranting further study.
more » « less- Award ID(s):
- 1832988
- PAR ID:
- 10553735
- Publisher / Repository:
- Journal of Geophysical Research: Space Physics
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Space Physics
- Volume:
- 129
- Issue:
- 2
- ISSN:
- 2169-9380
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
Abstract -
Abstract We present the first global images of the daytime ionosphere equatorial arcs as manifested in the 83.4‐nm airglow. These images were collected by the Limb‐Imaging Ionospheric and Thermospheric Extreme‐Ultraviolet Spectrograph that commenced operations on the International Space Station in early 2017. We compare these to simultaneous images of the ionospheric radiative recombination airglow at 135.6 nm measured between 250‐ and 350‐km tangent altitudes, where the emission is generated primarily by radiative recombination of ionospheric plasma. We find that these signatures of the dense crests of the Equatorial Ionization Anomaly, their symmetry, and daily variability at 1300–1600 LT over 1–6 April 2017 do not show any strong periodicity during this time. These results are also important to the joint interpretation of these two correlated extreme and far ultraviolet emission features measured under solar minimum conditions and the evaluation of absorption and radiative transfer effects that affect these emissions differently.
-
Abstract The ultraviolet‐imaging spectrograph that comprises Global‐scale Observations of the Limb and Disk (GOLD) mission in geostationary orbit at 47.5°W longitude has taken full disk images at high cadence throughout the deep solar minimum period of 2019–2020. Synoptic (i.e., concurrent and spatially unified and resolved) observations of thermospheric temperature and composition at ∼150 km altitude are made for the first time, allowing GOLD to disambiguate temporal and spatial variations. Here we analyze the daytime effective temperature and column integrated O and N2density ratio (ΣO/N2) data simultaneously observed by GOLD over 120°W–20°E longitude and 60°S–60°N latitude from 13 October 2019 to 12 October 2020. Daily zonal mean values are calculated for each latitude and compared with NRLMSIS 2.0 and simulations from the Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM‐X). On average, the GOLD observations show higher temperatures than Mass Spectrometer Incoherent Scatter radar (MSIS) and WACCM‐X by ∼20–60 K (5%–10%) and 80–120 K (12%–18%), respectively. The ΣO/N2ratios observed by GOLD are larger than the MSIS results by ∼0.4 (40%) but smaller than the WACCM‐X simulations by ∼0.3 (30%). The observed and modeled results are correlated at most latitudes (
r = 0.4–0.8), and GOLD, MSIS, and WACCM‐X all display a similar seasonal variation and change with latitude. WACCM‐X simulates a larger annual variation in ΣO/N2, suggesting that the thermospheric circulation is overestimated and atmospheric waves and turbulence transport are not properly represented in the model. -
A new method is proposed for deriving extremely low frequency (ELF) wave arrival azimuths using the wide range of signal amplitudes, contrary to previously applied high amplitude impulses only. The method is applied to observations from our new magnetic sensor in the Hylaty station with an 18 bit dynamic range and a 3 kHz sampling frequency. We analyzed a day of 15 January 2022, to test the procedure against the ability to extract ELF signals generated during the Hunga Tonga volcano eruption. With complementary filtering of power line 50 Hz signatures, precise azimuth information can be extracted for waves from a multitude of thunderstorms on Earth varying during the day at different azimuths. A phenomenon of successive regular variation—decay or activation—of thunderstorms activity with varying azimuth is observed, possibly due to passing over the solar (day/night) terminator, and signatures of azimuth direction change during this passage can be noted. We also show that the erupting Hunga Tonga volcano associated impulses dispersed due to a long propagation path are clearly revealed in the azimuth distribution with analysis using parameters fitted to measure slowly varying signals, but not for fast varying impulses. We show that the Hunga Tonga related signals arrive from the azimuth ≈10° smaller than the geographic great circle path. The discrepancy is believed to be due to propagation through the polar region and in the vicinity of the solar terminator.more » « less
-
Growing evidence indicates that a selected group of global-scale waves from the lower atmosphere constitute a significant source of ionosphere-thermosphere (IT, 100–600 km) variability. Due to the geometry of the magnetic field lines, this IT coupling occurs mainly at low latitudes (
30°) and is driven by waves originating in the tropical troposphere such as the diurnal eastward propagating tide with zonal wave number s = −3 (DE3) and the quasi-3-day ultra-fast Kelvin wave with s = −1 (UFKW1). In this work, over 2 years of simultaneous in situ ion densities from Ion Velocity Meters (IVMs) onboard the Ionospheric Connection Explorer (ICON) near 590 km and the Scintillation Observations and Response of the Ionosphere to Electrodynamics (SORTIE) CubeSat near 420 km, along with remotely-sensed lower (ca. 105 km) and middle (ca. 220 km) thermospheric horizontal winds from ICON’s Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) are employed to demonstrate a rich spectrum of waves coupling these IT regions. Strong DE3 and UFKW1 topside ionospheric variations are traced to lower thermospheric zonal winds, while large diurnal s = 2 (DW2) and zonally symmetric (D0) variations are traced to middle thermospheric winds generatedin situ . Analyses of diurnal tides from the Climatological Tidal Model of the Thermosphere (CTMT) reveal general agreement near 105 km, with larger discrepancies near 220 km due toin situ tidal generation not captured by CTMT. This study highlights the utility of simultaneous satellite measurements for studies of IT coupling via global-scale waves.