Long-term morphological and power spectral studies of VHF amplitude scintillations recorded over Waltair (17.7°N, 83.3°E), India

This research reports on recently recorded 250 MHz amplitude scintillations at Waltair (17.7°N, 83.3°E), a low-latitude station in India, using the signals radiated from a geostationary satellite (FLEETSAT, 73°E) during a six-year period (2008 - 2013), which covers extremely low and higher solar activity years (2008 and 2013). The morphological features in terms of local time, month, and season during different geophysical conditions are presented. The scintillation patches (segregated based on their occurrence durations) have shown an increasing trend with the increasing sunspot activity. The scintillation patches with 30-min duration show increasing trends with increasing sunspot activity, and their occurrence frequencies also show increasing trends with increasing sunspot activity. The scintillation activity during disturbed epochs (Kp index lies between 3+ and 9) is found to be less compared to its quiet day counterparts. The plausible mechanisms for these observational results are discussed. In addition, power spectral characteristics, including Fresnel frequency, upper role of frequency and spectral slope of scintillations are calculated and the salient results are presented

Observations of Equatorial Kelvin Wave Modes in FORMOSAT-3/COSMIC GPS RO Temperature Profiles

In this study, we analyze FORMOSAT-3/COSMIC (F3/C) GPS radio occultation (RO) derived temperature components for the period September 2006 to February 2008. Results show the presence of slow Kelvin waves (wave period > 10 days) with higher zonal wavenumbers (either one or two) in the upper troposphere and lower stratosphere (UTLS). The vertical wavelengths of these waves are found to be in the range of 5 - 12 km. The predominant Kelvin waves observed in the temperature fluctuations are in the altitude range between 15 and 28 km and centered on the tropical tropopause. The downward phase progression of these waves suggests that the derived waves are propagating upward, with the source region located at lower altitudes possibly due to tropical convective heating. The zonal winds retrieved using radiosonde observations over Singapore (1¢XN, 104¢XE) during this period show a periodicity of ~24 - 26 months in the stratosphere, and quasi-biennial oscillation (QBO) characteristics with eastward zonal winds from March 2006 to May 2007 and westward winds from June 2007 to July 2008 respectively. Our results further show that the Kelvin wave characteristics are enhanced during the westward phase of QBO and diminish during the eastward phase, in line with the previous reported results. Furthermore, an examination of outgoing longwave radiation (OLR) data shows that deep convection activity is developed episodically over the Indonesian archipelago during the observation period, thereby indicating that the Kelvin wave events observed in temperature fluctuations are either driven by convective activity (convectively coupled waves) or by a broad spectrum of convective variability (free waves) over the Indonesian region

Daytime E-Region Irregularities During the 22 July 2009 Solar Eclipse over Chung-Li (24.9°N, 121.2°E), a Moderate Mid-Latitude Station

The 22 July 2009 solar eclipse with an obscuration of > 83% at Chung-Li (24.9¢XN, 121.2¢XE, Dip 35¢XN) in Taiwan during noon hours has provided a unique opportunity for us to examine its impact on E-region irregularities which were observed simultaneously by the 52 MHz coherent radar and a co-located ionosonde. Significant observations revealed that the daytime E-region strong backscatter echoes at multiple heights and a sudden intensification of the weak sporadic E-layer during the 22 July 2009 solar eclipse. These results follow the research findings of Patra et al. (2009). As the incident solar radiation suddenly blocked by intruding Moon during solar eclipse events that would generally create night-like ionospheric conditions, it is surmised that the E-region irregularities were indeed induced by the eclipse associated effects. The induced effects resulted in faster recombination of molecular ions, generation of gravity waves and electric fields that could have created a conducive environment to excite plasma irregularities through a gradient-drift instability mechanism. The vertical shears of radar Doppler velocity and the peak radar backscatter at the node of Doppler velocity shear, as resolved by the coherent scatter radar with interferometer technique, were possibly due to the upward propagating gravity waves and wave-induced polarization electric fields. The present observational results should not only be highly useful to ascertain plausible mechanisms responsible for nighttime E-region irregularities, but also provided evidence that a solar eclipse could generate E-region plasma irregularities over temperate mid-latitudes for the first time