Abstract:
t We present analysis of more than 2000 lightning-generated whistlers recorded at a low-latitude
station, located at Allahabad (geographic latitude, 25.40°N; geographic longitude, 81.93°E; L = 1.081), India,
during December 2010 to November 2011. The main focus of this work is on the correlation between
observed low-latitude whistlers and lightning activity detected by the World-Wide Lightning Location
Network near the conjugate point (geography 9.87°S, 83.59°E) of Allahabad. Whistler occurrence is higher in
the postmidnight period as compared to the premidnight period. Whistlers were observed in the daytime
only on 2 days that too before 8:30 LT (morning). Seasonally, occurrence is maximum during winter months,
which is due to more lightning activity in the conjugate region and favorable ionospheric conditions. About
63% of whistlers were correlated with lightning strokes in the vicinity of the conjugate point within spatial
extent of 1000 km (conjugate area). Most (about 53%) whistlers were found to be associated with lightning
strokes that were offset to the southeast of the conjugate point. The results indicate that an energy range of
7.5–17.5 kJ of lightning strokes generate most of whistlers at this station. The L shell calculations show that
propagation paths of the observed whistlers were embedded in the topside ionosphere. Based on these results
we suggest a possibility of ducted mode of propagation even for such very low latitude whistlers.
