Auroral <i>E</i>-region electron density gradients measured

Abstract

Abstract. In the theory of E-region plasma instabilities, the ambient electric ®eld and electron density gradient are both included in the same dispersion relation as the key parameters that provide the energy for the generation and growth of electrostatic plasma waves. While there exist numerous measurements of ionospheric electric ®elds, there are very few measurements and limited knowledge about the ambient electron density gradients, rN e , in the E-region plasma. In this work, we took advantage of the EISCAT CP1 data base and studied statistically the vertical electron density gradient length, L z N e = dN e =dz , at auroral E-region heights during both eastward and westward electrojet conditions and di erent ambient electric ®eld levels. Overall, the prevailing electron density gradients, with L z ranging from 4 to 7 km, are found to be located below 100 km, but to move steadily up in altitude as the electric ®eld level increases. The steepest density gradients, with L z possibly less than 3 km, occur near 110 km mostly in the eastward electrojet during times of strong electric ®elds. The results and their implications are examined and discussed in the frame of the linear gradient drift instability theory. Finally, it would be interesting to test the implications of the present results with a vertical radar interferometer.

First Observations of E‐Region Near Range Echoes Partially Modulated by F‐Region Traveling Ionospheric Disturbances Observed by the Same SuperDARN HF Radar

“…Unsurprisingly, Haldoupis et al. (2000) found that L z takes on larger values at higher altitudes in the topside ionosphere, that is, from 10 km to greater than 25 km.…”

“…At high latitudes, the magnetic field is near‐vertical. In order to get the appropriate value of L x , the magnetic dip angle ( I ) must be taken into account (Haldoupis et al., 2000): $$${L}_{x}=\frac{{L}_{z}}{\cos (I)}$$$ …”

Numerical Study of Plasma Density Gradient Effects on Farley-Buneman Waves Traveling in the Equatorial E Region

“…Haldoupis et al (2005) in di cated that the past ob ser va tions of HF and VHF au rora ra dar (e.g., Hanuise el al. 1991;Haldoupis et al 2000;Lacroix and Moorcroft 2001) could not find GD ef fect on FB waves, but ne glected a point that the very strong po lar ized elec tric field might ex ist in au rora re gion. The past stud ies of ra dar ob ser va tions (e.g., St.-Maurice et al 1986;Ravindran and Reddy 1993;Nielsen et al 2002) also in di cated that the large elec tron drift ve loc ity de rived from strong elec tric field would heat plasma and cre ate larger phase ve loc ity.…”

“…It was also ap plied ex ten sively in nu mer ous stud ies such as the in ter preta tions of types 3 and 4 VHF au rora ech oes (e.g., see a review by Moorcroft 2002). In situ rocket mea sure ments (Haldoupis et al 2000(Haldoupis et al , 2005 of E-re gion elec tron den sity pro file had shown that the den sity gra di ents ex isted widely in any lat i tude E-re gion of 100 -110 km al ti tude, and that the scale lengths of the destabilized plasma den sity gra di ent orig i nated from spo radic E layer were smaller than 2 km. How ever, Haldoupis et al (2005) ar gued against a den sity gra di ent ef fect on short-scale FB waves, be cause they found no gra di ent drift ef fects on low er ing the FB in sta bil ity thresh old and the wave length de pend ence of phase ve loc ity by the ob ser va tion of two ra dar fre quen cies at 144 and 50 MHz.…”

Ionospheric scintillation over Antarctica during the storm of 5–6 April 2010

“…[24] Incoherent scatter radar measurements [Haldoupis et al, 2000;Yin et al, 2008;Mitchell et al, 1998] have previously shown that during strong precipitation events, enhancements in E region electron density can reach up to 4 Â 10 11 electrons per cubic meter over an extended altitude range. Projecting this electron density over, for example, an arbitrary 50 km vertical distance equates to $2.5 TECU.…”