Tidal and gravity waves study from the airglow measurements at Kolhapur (India)
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Medium Frequency Radar, Indian Institute of Geomagnetism, Shivaji University Campus, Kolhapur 416 004, India. 2 Indian Institute of Tropical Meteorology, Pune 411 008, India. 3 Department of Physics, Banaras Hindu University, Varanasi 221 005, India. 4 Geophysical Services, Makarpura Road, ONGC, Vadodara 390 009, India. 5 Department of Physics, University of Lucknow, Lucknow 226 007, India. ∗ Corresponding author. e-mail: rupesh ghodpage@rediffmail.com
Simultaneous photometric measurements of the OI 557.7 nm and OH (7, 2) band from a low latitude station, Kolhapur (16.8◦ N, 74.2◦ E) during the period 2004–2007 are analyzed to study the dominant waves present in the 80–100 km altitude region of the atmosphere. The nocturnal intensity variations of different airglow emissions are observed using scanning temperature controlled filter photometers. Waves having period lying between 2 and 12 hours have been recorded. Some of these waves having subharmonic tidal oscillation periods 4, 6, 8 and 12 hours propagate upward with velocity lying in the range 1.6–11.3 m/s and the vertical wave length lying between 28.6 and 163 kms. The other waves may be the upward propagating gravity waves or waves resulting from the interaction of inter-mode tidal oscillations, interaction of tidal waves with planetary waves and gravity waves. Some times, the second harmonic wave has higher vertical velocity than the corresponding fundamental wave. Application of these waves in studying the thermal structure of the region is discussed.
1. Introduction Atmospheric tides, planetary waves and gravity waves play significant role in dynamic features of the Mesosphere and Lower Thermosphere (MLT) region by transporting energy and momentum horizontally and vertically upward and also providing dynamical linkage between the lower atmosphere and the MLT region. Atmospheric tides are the global response of the atmosphere to the periodic forcing of solar heating; propagate westward following the motion of the Sun (Chapman and Lindzen 1970) with periodicities equal to the
solar day and its sub-harmonics (i.e., 24, 12, 8, 6, 4, 3, 2 hr, etc). Tides are classified as migrating and non-migrating. The non-migrating tides lead to strong longitudinal variations in amplitude and phase of diurnal tide, whereas the migrating tides contain diurnal, semidiurnal, terdiurnal and other harmonics. The diurnal (24 hr period) tide is mainly excited by the direct absorption of the sunlight by water vapour in the troposphere and the stratosphere, whereas the semidiurnal tide (12 hr periods) is caused by ozone heating in the upper stratosphere and the lower mesosphere. Studies of the diurnal and the semidiurnal tides and its
Keywords. Tidal and gravity wave; airglow emission; mesosphere and lower thermosphere (MLT); planetary waves. J. Earth Syst. Sci. 121, No. 6, December 2012, pp. 1511–1525 c Indian Academy of Sciences
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influences in the mesospheric region at various geographical locations have been made using lidar (Taylor et al. 1999; Liu et
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