[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

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Abstract. GPS radio occultations by Formosa Satellite mission-3/Constellation Observing System for Meteorology, Ionosphere, and Climate (FORMOSAT-3/COSMIC) provide bending angle profiles, which are further processed to give profiles of temperature and water vapour in the lower atmosphere and electron density in the upper atmosphere. The level 2 "atmPrf" (atmospheric profile) product of version 2010.2640 gives temperature from surface to 0.2 hPa (∼ 60 km). This is a dry temperature data product that does not include relative humidity in the inversion process and hence is reliable at altitudes < 100 hPa and erroneous at lower altitudes. In the current study we compare the COS-MIC "atmPrf" data from December 2010 to November 2011 with other satellite (SABER/TIMED and MLS/Aura) temperatures from 50 to 0.2 hPa, COSMIC "wetPrf" data and reanalysis (NCEP, ERA-Interim and UKMO) outputs at 100, 10, 1 and 0.5 hPa pressure levels. The satellite comparisons show that below 1 hPa the observed median differences are most likely produced due to the biases in the retrievals of SABER and MLS. "atmPrf" and "wetPrf" temperatures compare extremely well in the common altitudes with differences being absolute zero between 200 and 10 hPa. When compared to reanalysis outputs, COSMIC seasonal means match NCEP and ECMWF seasonal mean temperatures very well, especially at 100 and 10 hPa. We conclude from this study that with the COSMIC dry temperature retrievals obtained from radio occultations of GPS, there is a 20 km extension of reliable data in the middle atmosphere. "atmPrf" data are of good quality and provide reliable and unprecedentedly large number of profiles at greater temporal and spatial resolutions for further studies and investigations of the middle atmosphere up to 1 hPa, i.e., approximately up to the stratopause at around 50 km.

A sixteen year long dataset of mesospheric OI 557.7 nm green line nightglow emission rate, measured over Kiso (35.79 • N, 137.63• E), Japan using ground-based photometers is spectrally investigated using the HilbertHuang Transform (HHT). The spectrograms reveal the presence of semi-annual, annual and quasi-biennial oscillations in consonance with the results obtained from wavelet analysis in an earlier study. In addition, due to the use of the HHT, we have been able to investigate the very low frequency solar cycle variation in the emission rate. It is found that there is a signi cant solar cycle effect on the oxygen green line emission rate. The mean amplitude of variation is approximately 20% and it is also found that it is maximum at midnight. A correlation study between the means of the emission rate and the solar radio ux at 10.7 cm also shows that the effect of solar activity on the oxygen green line emission rate is maximum at midnight.