Perpendicular and off-perpendicular to B observations of 150-km echoes: evidence of meridional modulation and structure

Abstract

Although discovered more than 40 years ago [Balsley, 1964], there is still no physical mechanism that explains the occurrence of coherent echoes from altitudes around 150 kms (the so called 150-km echoes). East-West oblique beam [Fawcett, 1999] as well as wide beam imaging observations at Jicamarca, indicates that temporal variability of 150-km echoes (the pearls in the necklace) is not due to structuring and/or modulation in the zonal direction. These results point to a meridional modulation [E. Kudeki, personal communication]. Recently Chau [2004] reported the observations of echoes from off-perpendicular to B angles, implying that the aspect sensitivity (i.e., the North-South angular brightness) is not a narrow Gaussian as originally thought…