Shin-Yi Su

Brightening of 630.0 nm equatorial spread‐F airglow depletions

[1] Observations from the Boston University all-sky imaging system at Arecibo, Puerto Rico (18.3°N, 66.7°W, 28°N mag), show an unusual behavior of nighttime 630.0-nm airglow depletions. Associated with equatorial spread-F (ESF), these structures move eastward before reversing their motion and become airglow enhancements. Few other cases have been found, all during December solstices. For the case study presented here, data from the Arecibo incoherent scatter radar and the Republic of China Scientific Satellite (ROCSAT-1) provide supporting information. The radar shows that around local midnight the background zonal and meridional plasma motions reverse to westward and southward, respectively. ROCSAT-1 shows enhanced ion density, i.e., a low-latitude plasma blob, above the bright feature recorded by the all-sky imager, indicating a possible connection between both phenomena. Drifts parallel to the magnetic field are observed only in the region where the enhancement occurs. One possible interpretation of this change in the brightness of the depleted structure involves the influence of northward meridional winds and a reversal in the zonal drift motion, most likely caused by a zonal wind reversal.

Wavelet analysis on transient behavior of wind fluctuations observed by MST radar

Wind fluctuations observed by the MST radar technique often show complicated temporal behavior. Waves with different periods may occur at different times. Conventional fast Fourier transform (FFT) analysis will not be able to follow the temporal evolution of the wave spectrum. Multiscale, multiresolution wavelet analysis proposed in this paper is quite useful to study this transient behavior of the waves. A complex Gabor wavelet with a few cycles of monochromatic waves is chosen as the wavelet base, and this choice leads to successful results for gravity-wave like wind disturbances observed by MST radar in the troposphere. Possible interpretations in terms of nonlinear wave-wave or wave-mean flow interactions are proposed.

An upward moving thin layer in the equatorial F region observed by a digisonde

[i] This study presents an observation of a thin layer motion in the equatorial F region for the first time. The thin layer is detected by the Jicamarca Digisonde from 1000 to 1230 LT (1500 to 1730 UT) on 14 October 1996. We apply the inversion and fitting processes to derive the parameters (peak density, peak height, scale heights) of a thin layer. Results show that the thin layer has a constant total content of 2.48 × 10 6 el/cm 2 that might be formed by the long-lived metallic ions. From 1000 to 1200 LT, the layer is lifted upward from 164.6 to 275.9 km height with a velocity of 15.5 m/s, where the topside and bottomside scale heights are 2.8-5.0 and 1.2-2.4 km, respectively. In addition to the characteristics of the thin layer, this observation further provides evidence for the vertical transport of metallic ions in the equatorial F region.