An Intercomparison of VLF and Sounding Rocket Techniques for Measuring the Daytime <b><i>D</i></b> Region Ionosphere: Theoretical Implications

Siskind, David E.; Zawdie, K.; Sassi, Fabrizio; Drob, Douglas P.; Friedrich, Martin

doi:10.1029/2018ja025807

Cited by 11 publications

(36 citation statements)

References 59 publications

(88 reference statements)

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“…Siskind et al. (2018) finds this turnover altitude to be 68–70 km during daytime, however, this value is likely higher during the nighttime, and could well be higher for our sferic‐inferred ionospheres, which are both more general and include more information that single‐frequency VLF transmitter remote sensing. However, it should be noted that there are likely still significant uncertainties with both FIRI and our sferic‐inferred profiles.…”

Section: Resultsmentioning

confidence: 67%

“…As noted by Siskind et al. (2018), the sferic‐inferred ionosphere is probably more accurate at lower altitudes, and then above some level direct measurements from rockets, which partially underlay the FIRI model, become more accurate. Siskind et al.…”

Section: Resultsmentioning

confidence: 70%

“…As noted by Siskind et al (2018), the sferic-inferred ionosphere is probably more accurate at lower altitudes, and then above some level direct measurements from rockets, which partially underlay the FIRI model, become more accurate. Siskind et al (2018) finds this turnover altitude to be 68-70 km during daytime, however, this value is likely higher during the nighttime, and could well be higher for our sferic-inferred ionospheres, which are both more general and include more information that single-frequency VLF transmitter remote sensing. However, it should be noted that there are likely still significant uncertainties with both FIRI and our sferic-inferred profiles.…”

Section: Nighttime and Quiet Daymentioning

confidence: 80%

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A New Four‐Parameter D‐Region Ionospheric Model: Inferences From Lightning‐Emitted VLF Signals

McCormick

Cohen

2021

JGR Space Physics

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We present a new four‐parameter model of the D‐region (60–90 km) ionospheric electron density, useful in very low frequency (VLF, 3–30 kHz) remote sensing. VLF waves have a long history of use to indirectly infer D‐region conditions, as they reflect efficiently and thus are sensitive to small changes in the electron density. Most historical efforts use VLF observations along with a forward model of the D‐region and VLF propagation. The ionospheric assumptions in the forward model are altered until the output matches the observation. The most common D‐region model, known as the Wait‐Spies ionosphere, takes the electron density as exponentially increasing with altitude and specifies a height and steepness. This model was designed to capture the VLF propagation variations evident at a single frequency. The real D‐region is likely more complex. The limited number of D‐region rocket passes that have previously been compiled tend to show the existence of a “ledge” somewhere between 70 and 90 km. Broadband VLF signals emitted from lightning allows a more sophisticated parametrization. Using carefully averaged amplitudes and phases of VLF sferics, we formulate a more general four‐parameter D‐region model that includes a ledge discontinuity. Using lightning‐emitted VLF observations along with a theoretical model, we find that this model better describes the ionosphere during the daytime. During the ambient nighttime and during a solar flare the two‐parameter ionosphere may be sufficient, at least for the purposes of calculating broadband VLF propagation, since the ledge either weakens or moves outside the altitude range of VLF sensitivity.

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Section: Resultsmentioning

confidence: 67%

Section: Resultsmentioning

confidence: 70%

Section: Nighttime and Quiet Daymentioning

confidence: 80%

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A New Four‐Parameter D‐Region Ionospheric Model: Inferences From Lightning‐Emitted VLF Signals

McCormick

Cohen

2021

JGR Space Physics

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“…Comparisons between D region modeling and measured electron densities have also been made. Siskind et al (2018), reported that their modeled electron densities, at heights where these were relatively small, ∼100 cm −3 (at ∼60-70 km by day), tended to be smaller than the rocket wave measured electron densities but their modeled values agreed more closely with VLF-measured quiet-time electron densities.…”

Section: Electron Number Densitiesmentioning

confidence: 86%

Quiet Night Arctic Ionospheric D Region Characteristics

et al. 2021

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The lowest region of the Earth's ionosphere (containing free electrons) is the D region with its lower edge at heights generally around 70 km by day and 85 km by night. These heights are too low for satellite measurements (too much drag) and too high for aircraft or balloons. Rocket measurements (e.g., Friedrich & Torkar, 2001;Friedrich et al., 2018) have proved very useful but tend to be too transient and expensive to fully explore the significant diurnal, seasonal, and latitudinal variations around the Earth. Ground-based, high frequency radars (e.g., Singer et al., 2011) have also proved useful when available but are quite rare and are very limited in their geographical coverage. In contrast, very low frequency (VLF) radio waves, particularly from single-frequency, ground-based, man-made transmitters, have good geographical coverage and very good (often continuous) diurnal and seasonal coverage. These waves readily partially reflect from the lower edge of the D region with the resulting amplitude and phase changes being rather sensitive to its height and sharpness. The VLF waves also reflect very well from the Earth's surface, particularly the conducting oceans, enabling them to travel up to large distances (thousands of km) in the Earth-ionosphere waveguide bounded above by the D region.VLF radio subionospheric propagation has been used to refine our knowledge of the daytime D region by taking amplitude and phase measurements along radio paths both near (∼100 km from) the transmitter, where the direct ground wave signal dominates, and at greater distances (from ∼300 km up to several thousand km away) where the waves reflected from the D region dominate. The resulting phase and amplitude changes along the paths were then compared with calculations from VLF subionospheric modeling codes enabling the latitude-dependent characteristics (height and sharpness) of the daytime D region to be inferred, e.g., Thomson (2010) and Thomson et al. (2012Thomson et al. ( , 2014 at low latitudes, Thomson et al. ( , 2017 at midlatitudes, and Thomson et al. (2018) at high latitudes in the Arctic. The current study builds on these earlier studies to examine the nighttime Arctic D region.Diurnal VLF radio propagation recordings have been used to find the characteristics of the nighttime D region of the ionosphere at lower latitudes on a variety of long paths by comparing the observed changes in phase and amplitude between day and night with calculations from VLF propagation codes (Thomson & McRae, 2009;Thomson et al., 2007). For these comparisons the daytime results of Thomson (1993) and McRae and Thomson (2000) were used. In the present paper, we again use single-frequency, diurnal

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“…The low densities of the D region make local precision measurements with ionosondes and incoherent scatter radars difficult. In situ electron density observations are only available with rocket experiments and only sparse measurements of this type have been made (Siskind et al., 2018). On the other hand, remote sensing with ELF and VLF waves has a rich history since propagation of waves at these frequencies is sensitive to the D region electron density and long distance propagation in the Earth‐ionosphere waveguide allows for large geographic regions to be monitored (Gross & Cohen, 2020).…”

Section: Introductionmentioning

confidence: 99%

Quantification of Ionospheric Perturbations From Lightning Using Overlapping Paths of VLF Signal Propagation

2021

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The lowest region of the ionosphere, the D region (65-95 km altitude), plays an important role in magnetosphere-ionosphere coupling and strongly affects radio wave propagation for frequencies from less than 1 Hz up to 30 MHz. At sub-auroral and auroral latitudes the D region hosts natural electrojet currents that directly result from processes in the distant magnetosphere. Unlike the higher layers of the ionosphere, the D region is highly collisional so it is strongly perturbed by the precipitation of energetic particles from the magnetosphere, especially at nighttime. Perturbations from energetic particle precipitation can extend to middle and lower latitudes. Global and regional D region monitoring is therefore seen as a potential powerful space weather diagnostic. Atmospheric lightning is a source of strong electrostatic fields and a broad spectrum of intense radio wave radiation which can directly and indirectly perturb the D region anywhere on the globe (Inan et al., 2010). Although D region perturbations can occur at anytime, the nighttime D region is especially dynamic and challenging to specify since the dominant solar ionization process is absent.

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An Intercomparison of VLF and Sounding Rocket Techniques for Measuring the Daytime D Region Ionosphere: Theoretical Implications

Cited by 11 publications

References 59 publications

A New Four‐Parameter D‐Region Ionospheric Model: Inferences From Lightning‐Emitted VLF Signals

A New Four‐Parameter D‐Region Ionospheric Model: Inferences From Lightning‐Emitted VLF Signals

Quiet Night Arctic Ionospheric D Region Characteristics

Quantification of Ionospheric Perturbations From Lightning Using Overlapping Paths of VLF Signal Propagation

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