NOPR Collection: Special Issue on middle atmospheric dynamics and coupling in the tropics (Guest Editors: S K Dhaka & S Gurubaran)

COSMIC Satellite observations on seasonal variation of pressure at cold point tropopause and its relation with tropical easterly jet over tropical region

2013-11-05T16:42:04Z

Title: COSMIC Satellite observations on seasonal variation of pressure at cold point tropopause and its relation with tropical easterly jet over tropical region Authors: Kumar, V; Dhaka, S K; Jain, A; Chaudhary, A; Bhatnagar, R; Gupta, A; Panwar, V; Singh, N; Reddy, K K Abstract: 92.60.hf; 92.60.hv; 93.30.Vs; 84.40.Ua Page(s): 292-297

Hourly radiosonde observation of humidity and temperature and high resolution vertical wind using the Equatorial Atmosphere Radar during convection over Koto Tabang, Indonesia in CPEA-II campaign

2013-11-01T16:45:10Z

Title: Hourly radiosonde observation of humidity and temperature and high resolution vertical wind using the Equatorial Atmosphere Radar during convection over Koto Tabang, Indonesia in CPEA-II campaign Authors: Bhatnagar, R; Panwar, V; Shibagaki, Y; Hashiguchi, H; Fukao, S; Kozu, T; Takahashi, M; Dhaka, S K Abstract: Distinct wave perturbations for ~ 2-3 hours were observed during Coupling Processes in Equatorial Atmosphere-II in temperature and vertical wind in the tropopause region (~17-19 km) using hourly radiosonde launchings and high resolution Equatorial Atmosphere Radar observations, respectively over Koto Tabang (100.32°E, 0.20°S) during active convective events. Perturbations in temperature and humidity were found to be strongly anti-correlated in the upper troposphere and lower stratosphere region. Observations suggest that convective storm had increased humidity by a factor of 3-5 in the middle and upper troposphere (water vapour mixing ratio were also increased over convective period); gravity waves were generated near and above tropopause, which were not detected during no-convection period. Hourly temperature observations, which have covered complete life cycle of two convective storms of 7-8 hours, showed a significant enhancement in water vapour mixing ratio up to ~15-16 km height that corresponds to a level of strong wind shear existing below tropopause. There is a significant decrease in temperature around this level of strong wind shear. Page(s): 277-291

Airglow measurements of wave damping at upper mesospheric altitudes over a low latitude station in India

2013-11-02T16:43:28Z

Title: Airglow measurements of wave damping at upper mesospheric altitudes over a low latitude station in India Authors: Taori, A; Kamalakar, V Abstract: In this paper, nighttime mesospheric OH and O₂ temperature variability over Gadanki, a low latitude station in the Indian sector during February 2010 have been studied. It has been noted that mesospheric wave amplitudes show large variability from one night to the other. Occasionally, the mesospheric waves show larger amplitudes in O₂ data compared to the amplitudes of similar period waves in OH data indicating the amplification in wave amplitudes. For the waves noted simultaneously at OH and O₂ data, the damping factors have been calculated. The analysis reveals a highly dynamic upper mesosphere with some of the waves showing upward propagation (damping factor < 1), some reaching to their saturation levels (damping factor ~1) and few waves getting strongly damped (damping factor >1). Page(s): 371-379

VHF radar observations of mesospheric echoes and their relationship with thermal structure over Gadanki (13.5°N, 79.2°E)

2013-11-03T16:43:56Z

Title: VHF radar observations of mesospheric echoes and their relationship with thermal structure over Gadanki (13.5°N, 79.2°E) Authors: Sridharan, S; Suresh, M; Ramesh, K Abstract: There have been several reports on the comparison of daytime mesospheric echoes and their relationship with nighttime thermal structure. In the present work, a few cases are presented in which mesospheric echoes, observed with the MST radar at Gadanki (13.5°N, 79.2°E) during January-February 2011, are compared with temperature information obtained by Sounding of Atmosphere by Broadband Emission Radiometry (SABER) instrument onboard Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics (TIMED) satellite, when there is an overpass near Gadanki close to the time when the echoes are observed. It is found that the mesospheric echoes occur at heights where temperature is minimum or tends to be minimum as compared to the temperature at adjacent heights. The temperature lapse rate decreases below and increases above the height of maximum echoes. This relationship is consistently observed in all the cases considered in the present work. It appears that echoes arise due to change in the refractive index associated with electron density fluctuations caused probably by wave breaking and subsequent turbulence, which could be inferred from the minimum temperature (dynamical cooling) at the height of wave breaking. Page(s): 364-370