Atomic nitrogen and oxygen ions in the daytime high‐latitude F region

We combined a simple plasma convection model with an ionospheric-atmospheric composition model in order to study the plasma density features associated with strong convection in the winter high-latitude F region. Our numerical study produced time-dependent, three-dimensional, ion density distributions for the ions NO +, O 2 +, N2 + , 0 + , N +, and He +. We covered the highlatitude ionosphere above 42° N magnetic latitude and at altitudes between 160 and 800 km for a time period of one complete day. From our study, we found the following: (1) For strong convection, the electron density exhibits a significant variation with altitude, latitude, longitude, and universal time. A similar result was obtained in our previous study dealing with a weak convection model. (2) For strong convection, ionospheric features, such as the main trough, the aurorally produced ionization peaks, the polar hole, and the tongue of ionization, are evident but they are modified in comparison with those found for slow convection. (3) For strong convection, the tongue of ionization is much more pronounced than for weak convection. (4) The polar hole that is associated with quiet geomagnetic activity conditions does not form when the plasma convection is strong. (5) For strong convection, a new polar hole appears in the polar cap at certain universal times. This new polar hole is associated with large downward, electrodynamic plasma drifts. (6) For strong convection, the main or mid-latitude electron density trough is not as deep as that found for a weak convection model. However, it is still strongly UT dependent. (7) The ionospheric parameters N mF2' hmFt, and the topside plasma density scale height exhibit an appreciable variation over the polar region at a given UT.

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Plasma density features associated with strong convection in the winter high‐latitude F region

Sojka¹,

Raitt²,

Schunk³

1981

“…Hence, even with lower solar fluxes in winter (increased solar zenith angle), a significantly enhanced He+ density is expected in the winter hemisphere [Raitt et al, 1978;Ottley and Schunk, 1980]. Below 400 km, the atmosphere conditions favor enhanced 0+ densities lD winter, which is the winter anomaly where N mF2 is greater in winter than in summer (see, for example, Schunk and Raitt, [1980]). This occurs because the production of 0+ is greater owing to the higher winter [0] densities, and the 0+ loss rate is lower owing to the smaller winter [Nil and [Oil densities.…”

Section: Neutralatmospherementioning

confidence: 99%

“…He++ N 2 -N++ N + He He++ N 2 -N 2 ++ He He++02-0++0+ He where the photoionization frequencies and chemical coefficients are given in the reviews by Torr and TOIP [1982] and Schunk and Nagy [1980].…”

Section: He+hv-he++ementioning

confidence: 99%

Large‐scale counterstreaming of H⁺ and He⁺ along plasmaspheric flux tubes

Richards¹,

Schunk²,

Sojka³

1983

An interhemispheric plasma transport model has been used to study the flow characteristics of H + , He + , and 0 + along closed geomagnetic field lines for solstice conditions at noon local time. The calculations were carried out for the flux tube that passes through Millstone Hill. Both symmetric and asymmetric neutral winds in the conjugate ionospheres were considered. Initially, the flux tube content was partially depleted, and the subsequent refilling was studied until a steady state flow was established between the winter and summer hemispheres. The main conclusion to be drawn from this study is that H + -He + counterstreaming can be expected along a large segment of a plasmaspheric flux tube at solstice. For both symmetric and asymmetric wind patterns, the He + flow is from the winter to the summer ionosphere not only in the steady state, but during flux tube refilling owing to the winter helium bulge and the depletion of N 2 • For symmetric poleward neutral winds in both hemispheres, H + and 0 + flow up from the conjugate ionospheres during flux tube refilling, which leads to large-scale H +-He + counterstreaming in the summer hemisphere. In the steady state, both H + and He + flow from the winter to the summer ionosphere and no light-ion counterstreaming occurs. When the neutral wind in the summer hemisphere is set to zero, which acts to reduce the F region 'winter anomaly,' H +-He + counterstreaming occurs in the summer hemisphere during refilling and along the entire flux tube in the steady state. The H + and He + counterstreaming velocities obtained are too small to excite plasma instabilities, but large enough to be measured.

“…The ionosphericatmospheric composition model takes account of solar EUV radiation, energetic particle precipitation, diffusion, thermospheric winds, electrodynamic drifts, energydependent chemical reactions, and magnetic storm induced neutral composition changes [ef. Schunk and Raitt, 1980]. For boundary conditions on the ion densities, we equated local production and loss rates at the lower boundary (140 km) and we assumed no flux of ions across our upper boundary (800 km).…”

mentioning

confidence: 99%

Seasonal variations of the high‐latitude F region for strong convection

Sojka

Schunk²,

Raitt

1982

We combined a plasma convection model with an ionospheric-atmospheric composition model in order to study the seasonal variations of the high-latitude F region for strong convection. Our numerical study produced time-dependent, three-dimensional, ion density distributions for the ions NO+, 0/, N/, 0+, N+, and He+. We covered the high-latitude ionosphere above 42°N magnetic latitude and at altitudes between 160 and 800 km for a time period of one complete day. From our study we found the following: (1) For strong convection, the high-latitude ionosphere exhibits a significant UT variation both during winter and summer. (2) In general, the electron density is lower in winter than in summer. However, at certain universal times the electron density in the dayside polar cap is larger in winter than in summer owing to the effect of the midlatitude 'winter anomaly' in combination with strong antisunward convection. (3) In both summer and winter, the major region of low electron density is associated with the main or midlatitude trough. The trough is deeper and its local time extent is much greater in winter than in summer. (4) Typically, the electron density exhibits a much larger variation with altitude in winter than in summer. (5) The ion composition and molecular/atomic ion transition altitude are highly UT dependent in both summer and winter. (6) The ion composition also displays a significant seasonal variation. However, at a given location the seasonal variation can be opposite at different universal times. (7) High-speed convection cells should display a marked seasonal variation, with a much larger concentration of molecular ions near the F region peak in summer than in winter.