Recent progress in studying equatorial and low-latitude irregularities with Equatorial Atmosphere Radar
T. Yokoyama1, M. Yamamoto2, Y. Otsuka3, A. K. Patra4, S.-Y. Su5, S. Fukao2, and D. L. Hysell1
- Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, USA
- Research Institute for Sustainable Humanosphere, Kyoto University, Uji, Japan
- Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya, Japan
- National Atmospheric Research Laboratory, Tirupati, India
- Institute of Space Science, National Central University, Chung-Li, Taiwan
The 47-MHz Equatorial Atmosphere Radar (EAR) in West Sumatra, Indonesia (0.20ºS, 100.32ºE, -10.14º dip latitude) has the unique capability of rapid beam scanning on a pulse-to-pulse basis. EAR can take a snapshot of backscatter echoes with zonal and altitude distances of several hundred kilometers within a few minutes. Since the first operation of EAR in 2001, many important aspects, for example, onset, growth and spatial distribution of equatorial spread F, have been revealed with EAR and presented in the last ISEA meeting. We will focus on the following subjects studied in recent years. (1) Weak irregularities are observed in the valley region (120-160km altitudes) in the post-sunset period. These echoes have similar horizontal structure to that of F-region plumes and propagate eastward with the same velocity. (2) Plasma blobs detected by ROCSAT-1 in the northern hemisphere coincided with the resurgence of radar plumes. The zonal structure and upward drift velocity of the blobs correspond to those of the plumes on the common magnetic flux tube. These two results suggest strong electrodynamical coupling between E and F regions, and northern and southern hemispheres. (3) While the occurrence of post-sunset spread F decreases in the low solar activity period, post-midnight irregularities have been frequently observed with EAR. The characteristics of these echoes are similar to the midlatitude spread F observed with MU radar rather than equatorial spread F. They propagate westward with a structure aligned from northeast to southwest. (4) Daytime 150-km echoes are detected with EAR. The major characteristics are common to those observed in the equatorial regions. On the other hand, the echo intensity in the east-west plane is not uniform but has strong asymmetry that is opposite to equatorial observations. Because the EAR location is in transition between equatorial and midlatitude region, the EAR is an important tool to study latitudinal coupling as well as vertical coupling.