Proceedings with Extended Abstracts (single PDF file) - Radio ...

To observe the E region FAI echoes, the antenna beam was positioned at 13 deg duemagnetic north from vertical so as to look transverse to the magnetic field in the meridianplane. The observation range was from 84 to 144 km to cover the interesting Low altitude QP(LQP) echoes and the normal QP echoes at higher altitudes. The range resolution is 600meters; time resolution is 15 seconds (2.5 s for single spectrum including processing time),Doppler velocity window of -354 to 354 m/s and resolution of 5.5 m/s. The spectral moments,providing information on the total signal power, weighted mean Doppler velocity and spectralwidth, are computed using the expressions given by Woodman [1985].Data presentationBy summarizing the main results of the early observation we find that: (1) QP echoesappeared during most of the nighttime from the altitudes between 102 and 116 km, (2) theLow-altitude QP (LQP) echoes occurred both during daytime and nighttime and are confinedto a slowly descending layer with a thickness of about 2-4 km in the height range of 90-100km, and (3) two to three layered structures of continuous nature existed during both daytimeand nighttime [Choudhary and Mahajan; 1999; Pan and Rao; 2002]To show the morphological characteristics of the field-aligned E layer irregularitiesover Gadanki, we present statistical results of the radar echoes obtained with a 15-day dataset gathered in 1998 and 1999. Both the daytime (09 to 18 LT) as well as the nighttime (18 to06 LT) observations has been implemented.Figure 1 and 2 show the percentage of occurrence of E region echoes during thedaytime and nighttime, respectively. The threshold value of the signal-to-noise ratio is –6 dBand the time-range resolution bin is 15 min x 1.2 km. As we can see from the Figure 1, mostof the daytime E-region echoes appear at the ranges below 100 km and there is no echodetected above the range of 110 km. Since those irregularities present the QP (which is theso-called LQP echoes) and the continuous features, we further separate them into twocategories. For the daytime LQP echoes, the percentage of occurrence is about 69 %. 63% ofthem occurred at the ranges between 98 and 100 km and 34% of them at 95 to 97 km ranges.The period of the daytime LQP echoes categorize at ~2 minutes (72%), at ~5 minutes (23%)and at 60 to 90 seconds (8%). The layered structures confined QP and continuous echoes arealmost horizontally distributed. By examining the Figure 1, we find that the occurrence of thenoontime (11 to 14LT) E-region echoes were less than the other periods.Figure 2 is the percentage of occurrence of E region echoes during the 18 to 08 LTperiod. We notice that there are two regions with significant occurrence percentage: onebelow 100kmFigure 1. The percentage of the daytime E-region echoes.Figure 2. The percentage of the nighttime E-region echoes.ranges that is similar to the daytime echoes and the other between 105 to 120 km ranges.Usually multi-layers exist at the upper region during the nighttime and get transformed intoQP echoes [Choudhary and Mahajan, 1999]. The characteristics of the QP echoes observed at115