Imaging radar observations and theory of type I and type II quasi‐periodic echoes

[1] Midlatitude E region plasma irregularities have been investigated using the Middle and Upper Atmosphere (MU) radar in Shigaraki, Japan, and the Clemson 30 MHz radar in South Carolina, USA. A new in-beam imaging technique has been incorporated in the data analysis. Radar images reveal that the coherent backscatter associated with quasi-periodic (QP) echoes mainly arrives from spatially localized, elongated scattering regions and that striations in radar range-time-intensity (RTI) maps are the signatures of the migrations of these regions through the sparsely filled illuminated volume. The scattering regions in question appear to maintain altitude as they drift. Refraction and finite aspect angle sensitivity permit field-aligned irregularities in the regions to be detected by radars over a broad range of zenith angles. Circulation observed within the scattering regions is consistent with simulations of polarized E region plasma clouds described in a companion paper, as is the occasional appearance of type I echoes. Several long, continuous bands of scatterers are also evident in the radar images.

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

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

[3]  L. Smith,et al.  Incoherent scatter radar observations of irregular structure in mid‐latitude sporadic E layers , 1978 .

[4]  R. Tsunoda.  On polarized frontal structures, type‐1 and quasi‐periodic echoes in midlatitude sporadic E , 1998 .

[5]  David L. Hysell,et al.  Effects of large horizontal winds on the equatorial electrojet , 2002 .

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

[7]  David L. Hysell,et al.  Imaging coherent backscatter radar observations of topside equatorial spread F , 1997 .

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

[9]  L. Smith,et al.  Sporadic-E layers and unstable wind shears , 1980 .

[10]  M. Yamamoto,et al.  A possible mechanism for echo striation generation of radar backscatter from midlatitude sporadic E , 2000 .

[11]  D. Hysell,et al.  The 30‐MHz radar interferometer studies of midlatitude E region irregularities , 2000 .

[12]  M. Larsen,et al.  A shear instability seeding mechanism for quasiperiodic radar echoes , 2000 .

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

[14]  R. Pfaff,et al.  Large amplitude quasi-periodic fluctuations associated with a mid-latitude sporadic E layer , 1995 .

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

[16]  T. Maruyama.  Observations of quasi‐periodic scintillations and their possible relation to the dynamics of Es plasma blobs , 1991 .

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

[18]  Takeshi Sakanoi,et al.  Traveling ionospheric disturbances detected in the FRONT Campaign , 2001 .

[19]  J. Skilling,et al.  Maximum entropy image reconstruction: general algorithm , 1984 .

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

[21]  K. Schlegel,et al.  Large polarization electric fields associated with midlatitude sporadic E , 1998 .

[22]  R. Tsunoda,et al.  Coupled electrodynamics in the nighttime midlatitude ionosphere , 2001 .

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

[24]  J. G. Ables,et al.  Maximum Entropy Spectral Analysis , 1974 .

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

[26]  Miguel F. Larsen,et al.  Winds and shears in the mesosphere and lower thermosphere: Results from four decades of chemical release wind measurements , 2002 .

[27]  E. Kudeki,et al.  Radar interferometric imaging of field‐aligned plasma irregularities in the equatorial electrojet , 1991 .

[28]  Donald T. Farley,et al.  Aspect sensitivity of equatorial electrojet irregularities and theoretical implications , 1989 .

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

[30]  G. G. Bowman.  Quasi-periodic scintillations at mid-latitudes and their possible association with ionospheric sporadic-E structures , 1989 .

[31]  Donald T. Farley,et al.  Radar interferometry: A new technique for studying plasma turbulence in the ionosphere , 1981 .

[32]  Susan K. Avery,et al.  Empirical wind model for the upper, middle and lower atmosphere , 1996 .

[33]  R. Woodman.  Coherent radar imaging: Signal processing and statistical properties , 1997 .

[34]  E. Jaynes.  On the rationale of maximum-entropy methods , 1982, Proceedings of the IEEE.

[35]  Ronald F. Woodman,et al.  An empirical model of quiet-day ionospheric electric fields at middle and low latitudes , 1980 .

[36]  R. Sudan,et al.  Unified theory of Type I and Type II irregularities in the equatorial electrojet , 1983 .

[37]  Shoichiro Fukao,et al.  High resolution mapping of TEC perturbations with the GSI GPS Network over Japan , 1998 .