TY - JOUR

T1 - Dual-mode E-region plasma wave observations from Millstone Hill.

AU - del Pozo, C. F.

AU - Foster, J. C.

AU - St Maurice, J. P.

PY - 1993

Y1 - 1993

N2 - The unique capabilities of the Massachusetts Institute of Technology Millstone Hill Radar facility allow for high-sensitivity, dual-mode probing of the unstable auroral ionosphere. From almost simultaneous observations of the E and F regions, we have determined both the local electric field and the spectral properties of the plasma wave backscatter. We present observations and analysis of the unstable auroral E region during local afternoon to early morning hours (respectively, the eastward and the westward electrojet conditions) and identify modified two-stream (Farley-Buneman) waves as well as two kinds of waves associated with the turbulence created by such waves. One of these types has properties similar to those of type II waves reported in the literature, whereas the second type has a broader spectrum, is detected in all directions, and appears to be new. From our observations, onset of turbulence corresponds to an electric field threshold of the order of 20 mV/m. We have detected the presence of an azimuthal asymmetry in both the threshold field and the observed phase velocities with systematically greater values which we attribute to the presence of a 50 m/s E-W neutral wind at E region heights. The maximum observed volume reflectivity for type I waves ranges exceeded 10−11 m−1 (60 dB above the stable thermal fluctuations) and that of the secondaries was of the order of 20 dB smaller.

AB - The unique capabilities of the Massachusetts Institute of Technology Millstone Hill Radar facility allow for high-sensitivity, dual-mode probing of the unstable auroral ionosphere. From almost simultaneous observations of the E and F regions, we have determined both the local electric field and the spectral properties of the plasma wave backscatter. We present observations and analysis of the unstable auroral E region during local afternoon to early morning hours (respectively, the eastward and the westward electrojet conditions) and identify modified two-stream (Farley-Buneman) waves as well as two kinds of waves associated with the turbulence created by such waves. One of these types has properties similar to those of type II waves reported in the literature, whereas the second type has a broader spectrum, is detected in all directions, and appears to be new. From our observations, onset of turbulence corresponds to an electric field threshold of the order of 20 mV/m. We have detected the presence of an azimuthal asymmetry in both the threshold field and the observed phase velocities with systematically greater values which we attribute to the presence of a 50 m/s E-W neutral wind at E region heights. The maximum observed volume reflectivity for type I waves ranges exceeded 10−11 m−1 (60 dB above the stable thermal fluctuations) and that of the secondaries was of the order of 20 dB smaller.

M3 - Journal article

VL - 98

SP - 6013

EP - 6032

JO - Journal of Geophysical Research

JF - Journal of Geophysical Research

SN - 0148-0227

IS - A4

ER -