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Abstract The quiet time ionospheric plasma bubbles that occur almost every day become a significant threat for radio frequency (RF) signal degradation that affects communication and navigation systems. We have analyzed multi‐instrument observations to determine the driving mechanism for quiet time bubbles and to answer the longstanding problem, what controls the longitudinal and seasonal dependence of ionospheric irregularity occurrence rate? While VHF scintillation and GNSS ROTI are used to characterize irregularity occurrence, the vertical drifts from JRO and IVM onboard C/NOFS, as well as gravity waves (GWs) amplitudes, extracted SABER temperature profiles, are utilized to identify the potential driving mechanism for the generation of small‐scale plasma density irregularities. We demonstrated that the postsunset vertical drift enhancement may not always be a requirement for the generation of equatorial plasma bubbles. The tropospheric GWs with a vertical wavelength (4 km < λv < 30 km) can also penetrate to higher altitudes and provide enough seeding to the bottom side ionosphere and elicit density irregularity. This paper, using a one‐to‐one comparison between GWs amplitudes and irregularity occurrence distributions, also demonstrated that the GWs seeding plays a critical role in modulating the longitudinal dependence of equatorial density irregularities. Thus, it is becoming increasingly clear that understanding the forcing from a lower thermosphere is critically essential for the modeling community to predict and forecast the day‐to‐day and longitudinal variabilities of ionospheric irregularities and scintillations.
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An Observed Trend Between Mid‐Latitudes Km‐Scale Irregularities and Medium‐Scale Traveling Ionospheric Disturbances
Abstract We describe observations of a trend between the level of km‐scale irregularity activity and the amplitudes of medium‐scale traveling ionospheric disturbances (MSTIDs) at mid‐latitudes using data from December 2019 through June 2021. These include measurements of both heigh‐specific and vertically integrated quantities. Region‐specific, bottom‐side measurements were made with the dynasonde system near Wallops Island (WI) and included phase structure function parameters related to km‐scale irregularities as well as height‐specific tilts/density gradients, which are especially sensitive to MSTIDs. A complementary data set was derived from the nearby Deployable Low‐band Ionosphere and Transient Experiment (DLITE) array in southern Maryland. The DLITE array was used to measure the vertically integrated irregularity index,CkL, via scintillometry of bright cosmic radio sources at 35 MHz. Transverse gradients in the line‐of‐sight total electron content (TEC) were also measured with DLITE using apparent shifts in the sources' sky positions. Relatively simple layer‐based models for the vertical distribution of km‐scale irregularities applied to dynasonde‐measured properties yielded results that correlated well with DLITE measurements ofCkL. Similarly, spectral analysis showed that fluctuation amplitudes of vertically integrated bottom‐side density gradients derived from dynasonde data were well correlated with DLITE TEC gradient measurements. A significant trend was found betweenCkLand TEC gradient MSTID amplitudes among DLITE‐based data as well as among the extrapolated dynasonde measurements. Additionally, within the bottom‐side F‐region, irregularity levels were found to be well correlated with fluctuation amplitudes for the tilt as measured with the WI dynasonde.
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- Award ID(s):
- 1643119
- PAR ID:
- 10444966
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Radio Science
- Volume:
- 57
- Issue:
- 5
- ISSN:
- 0048-6604
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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