[1] In this paper we study the off-electrojet low-latitude daytime E region plasma irregularities using first multi-instrument observations in India made during July 2004 by the MST radar from Gadanki (13.5°N, 79.2°E, magnetic latitude 6.4°N), Langmuir probe on board the RH-300 Mk II rocket, and ionosonde from Sriharikota (13.6°N, 80.2°E, magnetic latitude 6.4°N). Radar echoes were confined to altitudes below 105 km and were observed in the form of a descending echoing layer with the descent rate of 1 km/h. Virtual height of the E layer, as observed by ionosonde, shows identical descending behavior. A detailed analysis based on the radar and ionosonde observations shows that the radar echoes are related to the range spread in the ionogram. Rocket observations made on 23 July 2004 revealed weak plasma irregularities with scale sizes more than 100 m and no noticeable irregularity at shorter scales. The spectral slope of the irregularities observed by the rocket probe is found to be À4 for scales in between 1 km and 100 m. During the rocket launch, radar did not detect any echo conforming that the small-scale irregularities were not present. Examination of concurrent observations of neutral wind made by TIMED Doppler interferometry suggests that zonal wind plays a crucial role in forming electron density layers, which become unstable via the gradient drift instability with background electric field or/and zonal neutral wind generating low-latitude E region plasma irregularities.Citation: Patra, A. K., N. Venkateswara Rao, D. V. Phanikumar, H. Chandra, U. Das, H. S. S. Sinha, T. K. Pant, and S. Sripathi (2009), A study on the low-latitude daytime E region plasma irregularities using coordinated VHF radar, rocket-borne, and ionosonde observations,

Abstract.A campaign to study turbulence in the mesosphere, over low latitudes in India, using rocket-borne measurements and Indian MST radar, was conducted during July 2004. A rocket-borne Langmuir probe detected a spectrum of electron density irregularities, with scale sizes in the range of about 1 m to 1 km, in 67.5-78.0 km and 84-89 km altitude regions over a low latitude station Sriharikota (13.6 • N, 80.2 • E). A rocket-borne chaff experiment measured zonal and meridional winds about 30 min after the Langmuir probe flight. The MST radar located at Gadanki (13.5 • N, 79.2 • E), which is about 100 km west of Sriharikota, also detected the presence of a strong scattering layer in 73.5-77.5 km region from which radar echoes corresponding to 3 m irregularities were received. Based on the region of occurrence of irregularities, which was highly collisional, presence of significant shears in zonal and meridional components of wind measured by the chaff experiment, 10 min periodicity in zonal and meridional winds obtained by the MST radar and the nature of wave number spectra of the irregularities, it is suggested that the observed irregularities were produced through the neutral turbulence mechanism. The percentage amplitude of fluctuations across the entire scale size range showed that the strength of turbulence was stronger in the lower altitude regions and decreased with increasing altitude. It was also found that the amplitude of fluctuations was large in regions of steeper electron density gradients. MST radar observations showed that at smaller scales of turbulence such as 3 m, (a) the thickness of the turbulent layer was between 2 and 3 km and (b) and fine structures, with layer thicknesses of about a km or less were also embedded in these layers. Rocket also detected 3-m fluctuations, which were very strong (a few percent) in lower altitudes (67.5 to 71.0 km)Correspondence to: H. Chandra (hchandra@prl.res.in) and small but clearly well above the noise floor at higher altitudes. Rocket and radar results also point to the possibility of existence of thin layers of turbulence (<450 m). The turbulence parameters estimated from rocket-borne measurements of electron density fluctuations are consistent with those determined from MST radar observed Doppler spectra and the earlier works.

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[1] We carried out high-cadence (5 min) and high-spatial resolution (2°magnetic latitude) observations of daytime OI 630.0 nm airglow emission brightness from a low-latitude station to understand the behavior of neutral dynamics in the daytime. The results indicate that the wave periodicities of 12-20 min, and 2 h exist over a wide spatial range of around 8°-12°magnetic latitudes. The 20-80 min periodicities in the dayglow seem to appear more often in the measurements closer to the magnetic equator and not at latitudes farther away. Further, periodicities in that range are found to be frequent in the variations of the equatorial electrojet (EEJ) strength as well. We show that wave periodicities due to the neutral dynamics, at least until around 8°magnetic latitude, are influenced by those that affect the EEJ strength variation as well. Furthermore, the average daily OI 630.0 nm emission brightness over 3 months varied in consonance with that of the sunspot numbers indicating a strong solar influence on the magnitudes of dayglow emissions.Citation: Pallamraju, D., U. Das, and S. Chakrabarti (2010), Short-and long-timescale thermospheric variability as observed from OI 630.0 nm dayglow emissions from low latitudes,

Temperature data from Global Positioning System based Radio Occultation (GPS RO) soundings of the Formosa Satellite mission 3/Constellation Observing System for Meteorology, Ionosphere and Climate (FORMOSAT-3/COSMIC or F-3/C) micro satellites have been investigated in detail to study the Kelvin wave (KW) properties during September 2008 to February 2009 using the two-dimensional Fourier transform. It is observed that there was strong KW activity during November and December 2008; large wave amplitudes are observed from above the tropopause to 40 km – the data limit of F-3/C. KW of wavenumbers E1 and E2 with time periods 7.5 and 13 days, dominated during this period and the vertical wavelengths of these waves varied from 12 to 18 km. This event is very interesting as the QBO during this period was westerly in the lower stratosphere (up to ~ 26 km) and easterly above, whereas, climatological studies show that KW get attenuated during westerlies and their amplitudes maximise during easterlies and westerly shears. In the present study, however, the eastward propagating KW crossed the westerly lower stratosphere as the vertical extent of the westerly wind regime was less than the vertical wavelengths of the KW. The waves might have deposited eastward momentum in the upper stratosphere at 26–40 km, thereby reducing the magnitude of the easterly wind by as much as 10 m s⁻¹. The outgoing long wave radiation (OLR) is also investigated and it is found that these KW are produced due to deep convections in the lower atmosphere