A role of neutral motions in formation of midlatitude E‐region field‐aligned irregularities

To explain observations of the E‐region 3.2‐m and 6.1‐m backscatter measured by the MU and FAR radars over Japan we propose that a source for generation of field‐aligned irregularities (FAI) is neutral gas motions operating over a wide altitude range. Due to an altitude dependence of ionospheric parameters these neutral motions may result in different dominating processes at different altitudes. On the basis of recent theories of neutral wind‐driven gradient drift and thermal instabilities [Kagan and Kelley, 1998; 1999] we show that thermal processes may both support the gradient drift instability and be responsible for sporadic‐E independent backscatter. In this scenario the time of FAI occurrence seems to follow a tidal mode behavior. The nighttime echo occurrence is most probably due to slower recombination.

[1]  Garcia,et al.  The structure of electromagnetic wave-induced 557.7-nm emission associated with a sporadic- E event over arecibo , 2000, Physical review letters.

[2]  M. Kelley,et al.  A thermal mechanism for generation of small‐scale irregularities in the ionospheric E region , 2000 .

[3]  J. Chau,et al.  Low‐latitude quasiperiodic echoes observed with the Piura VHF Radar in the E region , 1999 .

[4]  K. Schlegel,et al.  Evidence for planetary wave effects on midlatitude backscatter and sporadic E layer occurrence , 1999 .

[5]  M. Yamamoto,et al.  First observations of quasi‐periodic radar echoes from Stanford, California , 1999 .

[6]  D. Hysell,et al.  HF radar observations of quasiperiodic E layer echoes over North America , 1999 .

[7]  K. Mahajan,et al.  Tropical E region field aligned irregularities: Simultaneous observations of continuous and quasiperiodic echoes , 1999 .

[8]  M. Kelley,et al.  A wind‐driven gradient drift mechanism for mid‐latitude E‐region ionospheric irregularities , 1998 .

[9]  S. Fukao,et al.  DC electric field measurement in the SEEK Campaign , 1998 .

[10]  S. Fukao,et al.  Electric field measurements above and within a sporadic‐E layer , 1998 .

[11]  M. Larsen,et al.  The SEEK Chemical Release Experiment: Observed neutral wind profile in a region of sporadic E , 1998 .

[12]  M. Yamamoto,et al.  Height comparison of midlatitude E region field‐aligned irregularities and sporadic E Layer , 1998 .

[13]  M. Yamamoto,et al.  First 24.5‐MHz radar measurements of quasi‐periodic backscatter from field‐aligned irregularities in midlatitude sporadic E , 1998 .

[14]  H. Hayakawa,et al.  The SEEK (Sporadic‐E Experiment over Kyushu) Campaign , 1998 .

[15]  C. J. Pan,et al.  Quasi‐periodic echoes observed with the Chung‐Li VHF Radar during the SEEK Campaign , 1998 .

[16]  M. Yamamoto,et al.  Structures in sporadic‐E observed with an impedance probe during the SEEK Campaign: Comparisons with neutral‐wind and radar‐echo observations , 1998 .

[17]  M. Yamamoto,et al.  Middle and upper atmosphere radar observations of turbulence and movement of midlatitude sporadic E irregularities , 1995 .

[18]  M. Yamamoto,et al.  A morphological study on mid-latitude E-region field-aligned irregularities observed with the MU radar , 1992 .

[19]  Mamoru Yamamoto,et al.  Mid‐latitude E region field‐aligned irregularities observed with the MU radar , 1991 .

[20]  Mamoru Yamamoto,et al.  Gravity wave modulation of gradient drift instabilities in mid-latitude sporadic E irregularities , 1991 .

[21]  Susumu Kato,et al.  The MU radar with an active phased array system: 2. In‐house equipment , 1985 .

[22]  Susumu Kato,et al.  The MU radar with an active phased array system: 1. Antenna and power amplifiers , 1985 .

[23]  D. T. Farley,et al.  Vertical structure of the VHF backscattering region in the equatorial electrojet and the gradient drift instability , 1975 .

[24]  Mamoru Yamamoto,et al.  On the origin of quasi‐periodic radar backscatter from midlatitude sporadic E , 1994 .

[25]  M. Yamamoto,et al.  Spatial structure of the E region field-aligned irregularities revealed by the MU radar , 1994 .

[26]  S. Akasofu.  Magnetospheric Substorms: A Model , 1972 .