STRUCTURES IN SPORADIC-E OBSERVED WITH AN IMPEDANCE PROBE DURING THE SEEK CAMPAIGN - COMPARISONS WITH NEUTRAL-WIND AND RADAR-ECHO OBSERVATIONS

In order to clarify the origin of the so-called quasi periodic echoes (QPE) that have been often detected by radar observations in the prese nce of sporadic-E (E-s) layers in the night-time midlatitude ionospher e, two sounding rockets wen launched during the SEEK (Sporadic-E Exper iment over Kyushu) campaign. Each rocket carried a swept-frequency imp edance probe to measure the E-region electron-density (N-e) profile. U sing the four N-e profiles obtained during the two rocket flights toge ther with a neutral-wind profile obtained from a trimethyl aluminum (T MA) chemical release experiment on one of the rockets and QPE obtained with a ground-based radar, we consider the role of wind shear in the formation of the observed E-s layers, and the question of whether QPE are associated with E-s layers that are modulated in altitude. The N-e profiles of E-s structures that were obtained in the presence of QPE were characterized by the highly concentrated thin layers. The formati on of such a thin layer by a neutral-wind shear process was confirmed in comparison with the TMA measurements. The peak N-e values of the E- s layers ranged from 2.2 to 9.3x10(4) el/cm(3) near 100-km altitude. T hese primary E-s layers were accompanied by significant secondary stru ctures that were located about 12 to 20 km above the main E-s layers a nd had peak N-e that ranged from 5.2x10(3) to 1.3x10(4) el/cm(3). The average altitude profiles of QPE approximately covered the range where the E-s-layer peaks appeared. Our principal finding is that the obser ved E-s structures tended to resemble horizontally stratified layers r ather than structures with deep altitude modulation like previous QPE model, although the rocket measurements were separated from those by r adar by 90 to 145 km.