Improved analysis of plasmasphere motion using the VLA radio interferometer

Hoogeveen, G. W.; Jacobson, A. R.

doi:10.1007/s005850050437

Cited by 13 publications

(27 citation statements)

References 9 publications

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“…For instance, co-rotation within the plasmasphere will yield an observed speed for such irregularities of 150 m s À1 for heights of about 2000 km. For these observations, this corresponds to a McIlwain L-parameter of about 2.1, which is typical for the irregularities previously discovered with the VLA [Hoogeveen and Jacobson, 1997]. These disturbances will be discussed further in section 5.…”

Section: Multisource 3-d Spectrasupporting

confidence: 62%

Climatology of midlatitude ionospheric disturbances from the Very Large Array Low‐frequency Sky Survey

2012

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[1] The results of a climatological study of ionospheric disturbances derived from observations of cosmic sources from the Very Large Array (VLA) Low-frequency Sky Survey (VLSS) are presented. We have used the ionospheric corrections applied to the 74 MHz interferometric data within the VLSS imaging process to obtain fluctuation spectra for the total electron content (TEC) gradient on spatial scales from a few to hundreds of kilometers and temporal scales from less than one minute to nearly an hour. The observations sample nearly all times of day and all seasons. They also span latitudes and longitudes from 28 N to 40 N and 95 W to 114 W, respectively. We have binned and averaged the fluctuation spectra according to time of day, season, and geomagnetic (K p index) and solar (F10.7) activity. These spectra provide a detailed, multiscale account of seasonal and intraday variations in ionospheric activity with wavelike structures detected at wavelengths between about 35 and 250 km. In some cases, trends between spectral power and K p index and/or F10.7 are also apparent. In addition, the VLSS observations allow for measurements of the turbulent power spectrum down to periods of 40 s (scales of $0.4 km at the height of the E-region). While the level of turbulent activity does not appear to have a strong dependence on either K p index or F10.7, it does appear to be more pronounced during the winter daytime, summer nighttime, and near dusk during the spring.

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Section: Multisource 3-d Spectrasupporting

confidence: 62%

Climatology of midlatitude ionospheric disturbances from the Very Large Array Low‐frequency Sky Survey

2012

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“…These properties imply that they are likely located within the plasmasphere and are the same magnetic eastward directed (MED) disturbances discovered by Jacobson and Erickson [1992b] with the VLA. These were described in more detail by Hoogeveen and Jacobson [1997] as relatively long plasmaspheric irregularities stretched along field lines. After 03:00, westward and southwest directed waves begin to dominate the DFT-based azimuth spectra.…”

Section: Spectral Analysis 221 Self-calibration Datamentioning

confidence: 99%

“…Seminal investigations by Jacobson and Erickson [1992a] and Jacobson and Erickson [1992b] used 330 MHz observations with the VLA to identify and explore several wave-like phenomena identified within the data. Follow-up work done by Hoogeveen and Jacobson [1997] showed that a new class of waves found by Jacobson and Erickson [1992a] were located within the plasmasphere. They were shown to essentially be density fluctuations formed perpendicular to magnetic field lines at McIlwain L-parameters between about 1.8 and 4 which co-rotated with the plasmasphere with a moderate amount of (mostly) westward convection.…”

Section: Introductionmentioning

confidence: 99%

“…[5] Here, we detail a new interferometer-based approach that builds upon this previous work of Jacobson and Erickson [1992a], Hoogeveen and Jacobson [1997], and Helmboldt et al [2012b] by using a $5 hour 74 MHz observation of a very bright VHF source as well as several moderately bright sources spread over a 15 area on the sky (or, about 80 km at an altitude of 300 km). This new technique allows for a more thorough evaluation of the environment of fluctuations on medium to large scales than can be obtained with observations of a single source.…”

Section: Introductionmentioning

confidence: 99%

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Very large array observations of disturbed ion flow from the plasmasphere to the nighttime ionosphere

Helmboldt¹,

Intema²

2012

Radio Science

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[1] We present the results of a multiscale analysis of TEC fluctuations using a roughly five-hour observation of the bright radio source Virgo A with the Very Large Array (VLA) at 74 MHz in its B configuration. Our analysis combines data sensitive to fine-scale structure ($10 km and <0.001 TECU in amplitude) along the line of sight to Virgo A as well as larger structures (hundreds of km) observed using several ($30) moderately bright sources in the field of view. The observations span a time period from midnight to dawn local time during 1 March 2001. Several groups of magnetic eastward directed (MED), wavelike disturbances were identified and determined to be located within the plasmasphere (2.1 < L < 2.9). We have also detected evidence of non-wavelike structures associated with these disturbances which are propagating roughly toward magnetic north. These likely represent a non-uniform density flow from the plasmasphere toward the nighttime ionosphere. AE and K p indices and GPS TEC data indicate that during the observations, there were low levels of geomagnetic activity accompanied by somewhat localized depletions in ionospheric density. Thus, the observed plasmaspheric disturbance may be part of a flow triggered by these ionospheric depletions, likely associated with forcing from the lower atmosphere which is typically more prominent during quiet geomagnetic conditions. In addition, we have also observed several roughly westward directed and southeast directed waves located within the ionosphere. They are coincident in time with the plasmaspheric disturbances and may be related to the deposition of material onto the nighttime ionosphere.Citation: Helmboldt, J. F., and H. T. Intema (2012), Very large array observations of disturbed ion flow from the plasmasphere to the nighttime ionosphere, Radio Sci., 47, RS0K03,

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“…The plasma was inferred to reside between 2000-and 10,000-km altitude on magnetic L shells of L = 2 -3. Hoogeveen and Jacobson [1997] subsequently demonstrated that the plasma was not actually ''frozen on'' the field lines but was often convected westward or eastward across the field lines. They argued that the restricted range of L shells observed was a limitation of the instrumentation and observations rather than the physics of the plasmasphere.…”

Section: Introductionmentioning

confidence: 99%

Simultaneous radio interferometer and optical observations of ionospheric structure at the Very Large Array

et al. 2009

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[1] Radio astronomers are searching the cosmos for new scientific discoveries at increasingly lower radio frequencies and with larger antenna arrays, but their observations of the sky are blurred by the dynamic ionosphere. At the same time, ionospheric scientists are seeking to understand, at increasingly higher spatial and temporal resolutions, the dynamics that drive the ionosphere and its effects on technological systems. Advancements in radio astronomy at the Very Large Array (VLA) are leading to advancements in ionospheric physics and vice versa. We review some of the ionospheric observations made by the VLA at low frequency. Results from a 2003 summer campaign at the VLA are discussed, during which an all-sky optical camera was used to monitor ionospheric structure during VLA 74-MHz operations. The camera and additional off-site sensors, including ionosondes and incoherent scatter radar, were used to identify the dominant, summer nighttime ionospheric phenomena contributing to VLA signal distortion. Knowledge of the specific phenomena, including their spatial and temporal characteristics, can be used to improve low-frequency, astronomical imaging. Similarly, the VLA observations can be used to investigate ionospheric phenomena in great detail, leading to an improved understanding of ionospheric physics. Key to these findings is the identification of specific ionospheric phenomena using support sensors. Implications for the development of the Long Wavelength Array are discussed.

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Improved analysis of plasmasphere motion using the VLA radio interferometer

Cited by 13 publications

References 9 publications

Climatology of midlatitude ionospheric disturbances from the Very Large Array Low‐frequency Sky Survey

Climatology of midlatitude ionospheric disturbances from the Very Large Array Low‐frequency Sky Survey

Very large array observations of disturbed ion flow from the plasmasphere to the nighttime ionosphere

Simultaneous radio interferometer and optical observations of ionospheric structure at the Very Large Array

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