A study of the shape of topside electron density profile derived from incoherent scatter radar measurements over Arecibo and Millstone Hill

Abstract

[1] The shape of the topside electron density (Ne) profile is studied using incoherent scatter radar (ISR) measurements. On the basis of more than 90,000 and 84,000 Ne profiles measured over Arecibo (18.4°N, 66.7°W, dip 49.7°) and Millstone Hill (42.6°N, 71.5°W, dip 71.6°), respectively, shape factors have been derived by fitting the ISR observed profile using a Chapman-type layer with a height-independent scale height. The results reveal that the shape factor shows a general departure from the typically used values of 0.5 (Chapman a layer) except during the night and also undergoes appreciable variation with local time, season, solar activity, and latitude. Over Arecibo, the averaged shape factor is characterized by a daytime maximum of $0.55-0.75, a nearly constant nighttime value close to 0.5, and a marked morning decline; over Millstone Hill, the shape factor shows pronounced seasonal variations, and the diurnal variation in summer is opposite to that in other seasons. Over both stations, the shape factor exhibits a high correlation with the F 2 layer peak electron density (N m F 2 ), and it has strong solar cycle dependence during the late morning hours. It indicates that the temperature structure of the topside ionosphere can explain much of the variation of the shape factor when the plasma density is low, especially during nighttime. During daytime hours, the topside shape factor is thought to be associated with ion-neutral drag during periods of large plasma density.Citation: Luan, X., L. Liu, W. Wan, J. Lei, S.-R. Zhang, J. M. Holt, and M. P. Sulzer (2006), A study of the shape of topside electron density profile derived from incoherent scatter radar measurements over Arecibo and Millstone Hill, Radio Sci., 41, RS4006,

The dependence of plasma density in the topside ionosphere on the solar activity level

“…Moreover, the shape of the topside plasma density profiles or the scale height may also vary with solar activity (Chuo, 2007;Kutiev et al, 2006;Kutiev and Marinov, 2007;Liu et al, 2007a;Luan et al, 2006;Stankov and Jakowski, 2006). With measurements from incoherent scatter radar, digisonde, topside sounder, and radio occultation techniques, the plasma scale heights around the F peak and the topside ionosphere are found to become larger at higher solar activity (Kutiev et al, 2006;Lei et al, 2005;Liu et al, 2006aLiu et al, , 2007aStankov and Jakowski, 2006), which will also increase plasma density at the DMSP altitude as a key role by further decreasing the reduced height z in Eq.…”

Variations of topside ionospheric scale heights over Millstone Hill during the 30-day incoherent scatter radar experiment

“…In combining this investigation with that of Luan et al (2006), evidence exists that both contributions from the temperature structure and diffusion processes can greatly control the shape of the electron density profile and the ratio VSH/H p in the topside ionosphere over Millstone Hill. Following the theoretical prediction, the values of VSH/H p tend to decrease as (dT p /dh)/T p becomes larger.…”

“…However, results at both Arecibo and Millstone Hill illustrate that the altitude gradients of plasma temperatures (dT p /dh) are significant in the topside temperature profiles during some local time intervals. Furthermore, besides the contributions from the topside temperature structure, the diffusion process (W D =0) can also greatly influence the shape of the topside profiles over Arecibo and Millstone Hill (Luan et al, 2006). Thus, as shown in Fig.…”

“…The ionospheric scale height, as a measure of the shape of electron density (N e ) profiles or the altitude dependence of electron density, is one of the key ionospheric parameters, due to its intrinsic connection to the ionospheric dynamics, plasma temperature and compositions (Luan et al, 2006;Stankov and Jakowski, 2006b). Several definitions of the ionospheric scale heights exist (Liu et al, 2007).…”

An analysis of the scale heights in the lower topside ionosphere based on the Arecibo incoherent scatter radar measurements

“…It is evident that the scale height is an inherent parameter in these ionospheric profile functions [ Stankov et al , 2003; Belehaki et al , 2006]. The scale height is one of the important ionospheric characteristics, due to both a measure of the shape of the electron density profile and its intrinsic connection to the ionospheric dynamics, plasma thermal structure and compositions [ Luan et al , 2006; Stankov and Jakowski , 2006b; Webb et al , 2006]. By studying the behavior of the ionospheric scale heights, we may be capable of answering many open questions in the ionospheric physics, particularly those related to the ionosphere composition and dynamics [e.g., Liu et al , 2004; Luan et al , 2006].…”