Morphology and seasonal characteristics of low latitude E-region quasiperiodic echoes studied using large database of Gadanki radar observations

摘要

In this paper we study the morphology, seasonal features, and statistics of low latitude quasiperiodic (QP) echoes using an unprecedented data set of 147 nights of observations spanning over all seasons made using the Gadanki radar. The QP echoes have periods 2–20 min and occur on more than 50% nights. They are often found embedded in descending echoing layers whose characteristics resemble to those of tidal winds. Their occurrence shows strong seasonal dependence with 48% of the time in summer, 26–32% in equinox, and 14% in winter. The QP echoes have a tendency to appear first during 21–00 LT, which could last for 2–8 h, leading to their maximum occurrence rate during postmidnight hours. Height-time occurrences of radar echoes and QP structures both show common descending behavior, which agree extremely well with the observed descending behavior of the Es layers. We also find that the seasonal variations of QP echo occurrence are in very close agreement with that of the Es activity, tidal activity in the same height region, and also gravity wave activity in the mesosphere. Interestingly, the occurrence statistics are much more than their midlatitude counterpart; and time of first appearance, time of maximum occurrence, and duration of QP echoes all strongly contrast the midlatitude features. These observations have been discussed in detail in the light of current understanding of QP echoes.