Initial results from SKiYMET meteor radar at Thumba (8.5°N, 77°E): 2. Gravity wave observations in the MLT region

Abstract

[1] In the present communication, allSKy interferometric METeor (SKiYMET) radar observations of gravity wave activity in the mesosphere lower thermosphere (MLT) region over Thumba (8.5°N, 77°E) are presented. The present meteor radar system provides hourly zonal and meridional winds in the MLT region, which can be readily used for studying the tides, planetary waves, gravity waves of periods 2-6 hours, and other long period oscillations in this region. However, these hourly winds are not sufficient for studying short period gravity waves having periods less than an hour, which demand high temporal resolution measurements. Even though the winds are estimated on an hourly basis, information such as zenith angle, azimuth angle, and radial velocity of each detected meteor are archived. Using these details of the meteor, an algorithm is developed to obtain the 15-min temporal resolution wind data. The output of the algorithm is compared with hourly wind data, and it showed a good agreement during the high meteor shower periods. Most of the times high meteor counts are observed during late night and early morning hours (local) over this latitude. Continuous wind measurements during the high meteor shower periods are used for studying the gravity wave activity in the MLT region. As the wave activity is intermittent and nonstationary, wavelet analysis has been used for delineating the wave features. The results showed the upward propagating intermittent gravity waves with periods 1-2 and 4-5 hours. The new aspect of the present communication is the usage of meteor radar for gravity wave studies for the first time over this latitude and studying their seasonal variability.

TIMED/SABER observations of global gravity wave climatology and their interannual variability from stratosphere to mesosphere lower thermosphere

“…Several observational techniques widely employed for the study of gravity waves right from early years have been the Rocket soundings (e.g., Eckermann et al 1994), Aircraft/Balloon measurements (Nastrom and Fritts 1992), Wind profilers, Radars (Tsuda et al 1989;Riggin et al 1997;Kumar 2006Kumar , 2007aKumar et al 2007), Lidars (Wilson et al 1991a, b;Beatty et al 1992;Deepa et al 2006;Antonita et al 2007Antonita et al , 2008a, Radiosondes (Wang and Geller 2003;Tsuda et al 2004), and satellite observations in more recent times (Wu and Waters 1997;Namboothiri et al 2008;Preusse et al 2009). When most of these ground based observational techniques have limitations of spatial coverage, satellite observations enable global study and spatial characterization of gravity waves.…”

Gravity waves in the mesopause region observed by meteor radar: 1. A simple measurement technique

“…However, few studies have used meteorwind radar because of the limitations on their spatial and temporal resolution. Those studies that have been made using meteor radar have used either a generalisation of the dual-beam method applied to meteor radial velocities to measure gravity-wave variances and momentum fluxes (e.g., Hocking, 2005;Antonita et al, 2008;Clemesha and Batista, 2007), or restricted themselves to studies of large-scale gravity waves (e.g., Xiong et al, 2003;Manson et al, 2004;Kumar et al, 2007), or subdivided the meteor collecting volume of the radar into adjacent cells (e.g., Yamamoto et al, 1986;Oleynikov et al, 2005). This paper presents a simple new technique for studying highfrequency gravity waves using meteor radar.…”

Meteor radar observations of short-term variability of quasi 2 day waves and their interaction with tides and planetary waves in the mesosphere–lower thermosphere region over Thumba (8.5°N, 77°E)

“…Except this peak, the seasonal variations show maximum activity during summer and winter with an additional peak during October. The equatorial and gravity wave activity over low latitudes shows equinoctial maximum in contrast to the quasi 2 day wave activity [ Hirota , 1984; Kumar et al , 2007b]. Earlier observations from midlatitudes reported that the quasi 2 day wave is a summer time phenomenon [ Muller and Nelson , 1978; Manson and Meek , 1986; Merzlyakov et al , 2004; Limpasuvan et al , 2005].…”