Large polarization electric fields associated with midlatitude sporadic E

Recent 50 MHz E region coherent backscatter observations and in situ rocket measurements established the existence of enhanced electric fields in the midlatitude ionosphere that can become at times sufficiently large to excite the Farley-Buneman instability. To understand the origin of these fields, we present a simple quantitative model that relates to a local polarization process acting inside spatially confined, nighttime sporadic E layers of dense ionization. By including the effects of field-aligned currents in the current continuity equation we estimate the necessary conditions on the relative horizontal E layer extent and the ratio of integrated Pedersen conductivities above and inside the layer for the generation of both zonal and meridional polarization fields. We show that the polarization process can account for the elevated electric fields of several millivolts per meter, which are implied often from backscatter Doppler measurements during unstable E region conditions at midlatitude. The polarization process can become much more effective for dense and strongly elongated Es layers under the action of an enhanced ambient electric field. In this case, large polarization fields that may be capable of exciting Farley-Buneman plasma waves can be sustained. The stringent requirements for strongly elongated sporadic E layers with sharp boundaries, low ionospheric Pedersen conductivities above the layer in relation to those inside, and relatively large ambient electric fields would explain why type 1 echoes are so rare in midlatitude E region backscatter.

[1]  D. T. Farley,et al.  Type-1 echoes from the mid-latitude E-Region ionosphere , 1997 .

[2]  C. Liu,et al.  The Observations of Sporadic E Irregularities in Equatorial Anomaly Crest Zone by Using Chung-Li VHF Radar , 1996 .

[3]  J. Delloue,et al.  Midlatitude E region coherent backscatter observed simultaneously at two HF radar frequencies , 1996 .

[4]  C. Haldoupis,et al.  High‐frequency Doppler radar observations of magnetic aspect sensitive irregularities in the midlatitude E region ionosphere , 1995 .

[5]  E. Chapin,et al.  Plasma wave excitation on meteor trails in the equatorial electrojet , 1994 .

[6]  K. Schlegel,et al.  Observation of the modified two‐stream plasma instability in the midlatitude E region ionosphere , 1994 .

[7]  K. Schlegel,et al.  A 50-MHz radio Doppler experiment for midlatitude E region coherent backscatter studies: System description and first results , 1993 .

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

[9]  Donald T. Farley,et al.  Radar Studies of Long-Wavelength Waves Associated With Mid-Latitude Sporadic E Layers , 1986 .

[10]  James C. G. Walker,et al.  Comparison of electrical conductivities in the E-AND F-regions of the nocturnal ionosphere , 1977 .

[11]  A. Gurevich,et al.  Electric fields in the Earth's magnetosphere and ionosphere , 1976 .

[12]  C. Kennel,et al.  Polarization of the auroral electrojet , 1972 .

[13]  D. T. Farley.  A plasma instability resulting in field‐aligned irregularities in the ionosphere , 1963 .

[14]  D. T. Farley.  A theory of electrostatic fields in the ionosphere at nonpolar geomagnetic latitudes , 1960 .

[15]  D. T. Farley,et al.  An explanation for type 1 radar echoes from the midlatitude E-region ionosphere , 1996 .

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

[17]  Michael C. Kelley,et al.  The Earth's Ionosphere : Plasma Physics and Electrodynamics , 1989 .