A review of the theories concerning the equatorial F2 region ionosphere

Goldberg, R. A.

doi:10.1109/proc.1969.7164

Cited by 9 publications

(5 citation statements)

References 45 publications

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“…Such distributions have been derived by a number of authors [17l- [20]. It should also be mentioned that diffusive equilibrium along magnetic field lines appears to be consistent with the major features of the "geomagnetic anomaly" in the topside ionosphere [21].…”

Section: Proceedings Of the Ieee June 1969supporting

confidence: 61%

Diffusive equilibrium in the topside ionosphere

Bauer

1969

Proc. IEEE

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Diffusive equilibrium is an idealized concept, representing a limiting case of the continuity equation for charged particles in the ionosphere. Since plasma diffusion can proceed rather rapidly above the F, peak-the plasma density distribution in the topside ionosphere can, in general, be approximated by a diffusive equilibrium distribution. The density scale height of this distribution depends on the mean ionic mass (i.e., ion composition), and the electron and ion temperatures and their gradients. While diffusive equilibrium is reasonably representative of the distribution of plasma density (and therefore of the major ions), the distribution of the minor ions in the topside ionosphere may still be affected strongly by chemical and transport processes. Because of the magnetic field control of plasma diffusion, equilibrium conditions apply along magnetic field lines. At latitudes where the magnetic dip is fairly high (/>Bo'), diffusive equilibrium applies directly t o vertical density profiles. At high latitudes (beyond the "trough"), where the local plasma density can be very low, an almost "collisionless" regime prevails, leading t o an "ion-exosphere" distribution, which decays with altitude much faster than a diffusive equilibrium distribution. Although diffusive equilibrium may not always be strictly applicable, the concept provides a readily available analytical model for the general features of the topside ionosphere.

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Section: Proceedings Of the Ieee June 1969supporting

confidence: 61%

Diffusive equilibrium in the topside ionosphere

Bauer

1969

Proc. IEEE

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“…Because the E region electron density is mainly governed by the solar zenith angle and the spatial distribution of the F region electron density is highly dependent on the magnetic field lines, it is straightforward to infer that the magnetic control property of the retrieval error in the simulated E region electron density is resulted from the spatial structure of F region electron density during the GPS RO retrieval process. Theoretical and experimental results both show that the equatorial anomaly in F region starts to develop at around 9 A.M., reaches maximum at around 14 P.M. and vanishes after 20 P.M. [ Goldberg , ; Stening , ]. If the COSMIC‐retrieved E region electron density is indeed contaminated by the retrieval error caused by the F region electron density structure, one might expect that temporal variations in the PE and RMSE of the COSMIC‐retrieved N m E should be in harmony with those of the equatorial anomaly in F region.…”

Section: Discussionmentioning

confidence: 99%

Improvement of GPS radio occultation retrieval error of E region electron density: COSMIC measurement and IRI model simulation

Chu

2015

JGR Space Physics

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In this article, we use the International Reference Ionosphere (IRI) model to simulate temporal and spatial distributions of global E region electron densities retrieved by the FORMOSAT-3/COSMIC satellites by means of GPS radio occultation (RO) technique. Despite regional discrepancies in the magnitudes of the E region electron density, the IRI model simulations can, on the whole, describe the COSMIC measurements in quality and quantity. On the basis of global ionosonde network and the IRI model, the retrieval errors of the global COSMIC-measured E region peak electron density (N m E) from July 2006 to July 2011 are examined and simulated. The COSMIC measurement and the IRI model simulation both reveal that the magnitudes of the percentage error (PE) and root mean-square-error (RMSE) of the relative RO retrieval errors of the N m E values are dependent on local time (LT) and geomagnetic latitude, with minimum in the early morning and at high latitudes and maximum in the afternoon and at middle latitudes. In addition, the seasonal variation of PE and RMSE values seems to be latitude dependent. After removing the IRI model-simulated GPS RO retrieval errors from the original COSMIC measurements, the average values of the annual and monthly mean percentage errors of the RO retrieval errors of the COSMIC-measured E region electron density are, respectively, substantially reduced by a factor of about 2.95 and 3.35, and the corresponding root-mean-square errors show averaged decreases of 15.6% and 15.4%, respectively. It is found that, with this process, the largest reduction in the PE and RMSE of the COSMIC-measured N m E occurs at the equatorial anomaly latitudes 10°N-30°N in the afternoon from 14 to 18 LT, with a factor of 25 and 2, respectively. Statistics show that the residual errors that remained in the corrected COSMIC-measured N m E vary in a range of À20% to 38%, which are comparable to or larger than the percentage errors of the IRI-predicted N m E fluctuating in a range of À6.5% to 20%.

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“…Nevertheless, salient winter and semiannual anomalies are both found in N m E peaks and F region anomaly crests, which show maximum in equinox, minimum in summer, and medium in winter seasons. We also note that the loci of the electron density crests of the F region EIA tend to tilt toward and extend to midlatitude with decreasing altitude, and the angles between the slant EIA loci and the local geomagnetic field lines generally increase with decreasing height [ Goldberg , 1969]. Theoretical investigations have suggested that the plasma drift perpendicular to the magnetic field line, which is driven by neutral wind through neutral‐ion collision and/or E × B effect, is very likely the cause of the tilt of the F region EIA crests [ Bramley and Peart , 1965; Balan and Bailey , 1995].…”

Section: Discussionmentioning

confidence: 99%

“…Equatorial ionization anomaly (EIA) has been investigated by scientists using different means for more than a half century [ Mitra , 1946; Goldberg , 1969; Walker and Strickland , 1981; Yeh et al , 2001; H. F. Tsai et al , 2001; Liu et al , 2007]. It has long been well known that the F region equatorial anomaly crests are situated on both sides of the geomagnetic equator in latitude regions ± 15°–20°, and an electron density trough is located over the geomagnetic equator [ Bramley and Peart , 1965; Goldberg , 1969; Kelley , 1989]. This feature is generally believed to be the result of a fountain mechanism that lifts the ionizations in the equatorial region up to topside ionosphere through E × B drift effect, which is driven by the east‐directed electric field E originated in E region through the dynamo effect.…”

Section: Introductionmentioning

confidence: 99%

“…In light of the presences of gravity, ion‐neutral collision, and plasma pressure gradient forces, the ionizations are diffused downward approximately along tilted geomagnetic field lines and eventually are accumulated in the lower F region to form two off‐equator density crests that characterize the equatorial anomaly. Although it has long been suspected that the structure of the equatorial anomaly might extend from F region down to E region [ Goldberg , 1969], very limited experiments were conducted in the past to examine the probable link of the equatorial anomaly between the F and E regions. For example, with ground‐based ionosonde measurements, Croom et al [1959] reported that the quasi‐equatorial anomaly structure can be found at levels as low as 160 km.…”

Section: Introductionmentioning

confidence: 99%

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A new aspect of ionospheric E region electron density morphology

Chu

2009

J. Geophys. Res.

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[1] From global measurements of ionospheric electron density profiles made by the FORMOSAT-3/COSMIC satellites, the morphology of E region electron density is investigated. Seasonal, latitudinal, and diurnal variations in daytime E region electron density are well described by the Chapman theory, and the E layer peak electron density N m Eanditspeakheighth m Earegovernedbythesolarzenithanglecinaccordancewithrelations relations N m E /(cosc) p and h m E /ln(secc), respectively. However, it is revealed that there are three geomagnetic latitude regions where striking enhancements of the E region electron density occur. One of them is located at the geomagnetic equator with relatively narrow latitude extent of about 6°-10°, and the other two with much wider latitude extent of about 10°-20°appear on both sides of the geomagnetic equator in latitude regions ±20°-30°, respectively. The locations of these E region density enhancements are asymmetrical about the geomagnetic equator in solstice seasons, and they have a salient tendency to shift toward (away from) the summer (winter) hemisphere. The off-equator E region electron density enhancements are closely connected with the bottomside of the F region equatorial anomaly crests, where the component of the electron density parallel to the magnetic field line is maximum. It appears that the off-equator E region electron density enhancements are very likely the footprints of the F region equatorial anomaly crests. The morphologies of the exponent n and coefficient K in the power law relation between c and f o E (E region critical frequency) are also examined. There is a tendency for the n and K values to be larger in local winter than in local summer seasons in the latitudinal regions the same as the off-equator electron density enhancements. In addition, it is found that a minor peak in the K values is nearly continuously present in all seasons over the geomagnetic equator. A comparison shows significant discrepancies in the E region electron density morphologies between COSMIC measurement and IRI model prediction. Furthermore, compelling evidence is provided to show the presences of longitudinal wave number 3 and 4 structures of the electron density in the height region 100-200 km, which are in coincident with the longitudinal structures of equatorial electrojet. It is believed that these longitudinal 3-and 4-peak structures are very likely associated with nonmigrating diurnal tides propagating eastward in ionospheric E region.

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A review of the theories concerning the equatorial F2 region ionosphere

Cited by 9 publications

References 45 publications

Diffusive equilibrium in the topside ionosphere

Diffusive equilibrium in the topside ionosphere

Improvement of GPS radio occultation retrieval error of E region electron density: COSMIC measurement and IRI model simulation

A new aspect of ionospheric E region electron density morphology

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