A case study on occurrence of an unusual structure in the sodium layer over Gadanki, India
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- A case study on occurrence of an unusual structure in the sodium layer over Gadanki, India
- Sarkhel, Sumanta
Mathews, John D.
Kerr, Robert B.
Mlynczak, Martin G.
Russell, James M. III
- Lidar observation; Sodium layer
- Issue Date
- Sarkhel, Sumanta., et al. 2015. A case study on occurrence of an unusual structure in the sodium layer over Gadanki, India. Sarkhel et al. Earth, Planets and Space, 67(19): 1-15.
- The height-time-concentration map of neutral sodium (Na) atoms measured by a Na lidar during the night of 18 to
19 March 2007 over Gadanki, India (13.5° N, 79.2° E) reveals an unusual structure in the Na layer for around 30 min
in the altitude range of 92 to 98 km which is similar to the usual ‘C’ type structures observed at other locations. In
order to understand the physical mechanism behind the generation of this unusual event, an investigation is carried
out combining the data from multiple instruments that include the meteor wind radar over Thiruvananthapuram,
India (8.5° N, 77° E) and the SABER instrument onboard the TIMED satellite. The temperature and wind profiles from the
data set provided by these instruments allow us to infer the Richardson number which is found to be noticeably less
than the canonical threshold of 0.25 above 92 km over Thiruvananthapuram suggesting the plausible generation of
Kelvin-Helmholtz (KH) billows over southwestern part of the Indian subcontinent. Based on the average wind speed and
direction over Thiruvananthapuram, it is proposed that the KH-billow structure was modified due to the background
wind and was advected with it in nearly ‘frozen-in’ condition (without significant decay) in the northeastward
direction reaching the Na lidar location (Gadanki). This case study, therefore, presents a scenario wherein the
initially deformed KH-billow structure survived for a few hours (instead of a few minutes or tens of minutes as
reported in earlier works) in an apparently ‘frozen-in’ condition under favorable background conditions. In this
communication, we suggest a hypothesis where this deformed KH-billow structure plays crucial role in creating
the abovementioned unusual structure observed in the Na layer over Gadanki.
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