Characteristics of the tropical tropopause over different longitudes

The characteristics of the cold point tropopause (CPT), convective tropopause (COT) and tropical tropopause layer (TTL) in the tropical region at different longitudes are studied using radiosonde data at 5 stations in the tropical belt (±15°) and high resolution GPS radiosonde data from April 2006 to December 2008 at Gadanki (13.5°N, 79.2°E) also a tropical station. The CPT over Gadanki is found to be higher than over the rest of the stations. This aspect is further confirmed using COSMIC GPS RO observations. In the Northern Hemisphere (NH) winter, the CPT is coldest over stations in the Pacific region compared to the other stations while in the NH summer, it is coldest at Gadanki, a station in the Indian monsoon region. The range of seasonal variation of the CPT temperature is found to be quite small over Gadanki compared to the other stations whereas that of the CPT altitude is nearly the same.     

The masses of black holes in the nuclei of spirals

We use the innermost kinematics of spirals to investigate whether these galaxies could host the massive black hole remnants that once powered the quasi-stellar object (QSO) phenomenon. Hundreds of rotation curves of early- and late-type spirals are used to place upper limits on the central black hole (BH) masses. We find that (i) in late-type spirals, the central massive dark objects (MDOs) are about 10–100 times smaller than the MDOs detected in ellipticals, and (ii) in early-type spirals, the central bodies are likely to be in the same mass range as the elliptical MDOs. As a consequence, the contribution to the QSO/active galactic nuclei (AGN) phenomenon by the BH remnants eventually hosted in spirals is negligible: ρ _BH(Sb–Im)<6×10⁴ M_⊙ Mpc⁻³ . We find several hints that the MDO mass versus bulge mass relationship is significantly steeper in spirals than in ellipticals, although the very issue of the existence of such a relation for late Hubble type objects remains open. The upper limits on the masses of the BHs resident in late-type spirals are stringent: M _BH10⁶–10⁷ M_⊙, indicating that only low-luminosity activity could possibly have occurred in these objects .     

Influence of Different Stress Conditions on Behavior of Rockfill Materials

Rockfill material is the most readily available and the most flexible material for the construction of dams especially in the seismic prone regions. The material is obtained either by blasting available rock or is collected from the alluvial deposits of the river. During construction of the dam, the available rockfill material is compacted to required density layer by layer using various sophisticated compactors to achieve the required density and slope. Gradually the vertical load on the lower layers goes on increasing due to placement of subsequent layers of the materials to achieve the desired height. This may result in variation of grain size distribution of the lower layers due to the breakage of particles. This will certainly influence the shear parameters. Present studies have been carried out to find the influence of loading the rockfill materials under two different stress conditions i.e. multistage loading and single stage loading on the grain size distribution and its subsequent effect on its shear parameters. Consolidated drained triaxial shear tests have been conducted on the materials obtained by blasting available rock as well as on the materials collected from the alluvial deposits of the river which are generally used for construction of rockfill dams. Test data have been analyzed to study the breakage factor and corresponding shear parameters under both conditions.     

An index for tropical temperate troughs over southern Africa

Strong cases of the tropical temperate troughs (TTT) that are responsible for the most of the summer rainfall over subtropical southern Africa are analyzed. An index for identifying the TTT is introduced for the first time using anomalies of outgoing longwave radiation (OLR) and the wind. The TTT is associated with a ridge-trough-ridge wave-like structure in the lower troposphere over southern Africa and the adjoining Indian Ocean. Therefore, the index considers physical processes that occur over southern Africa, adjoining the Atlantic and Indian Oceans to depict the variability of the TTT events. Unusually strong TTT events are identified when the standard deviations of the TTT indices defined by the OLR and wind anomalies in the selected regions are above 1.5 and 0.5 respectively. After applying this criterion and filtering out consecutive events, 55 TTT events are identified during the study period of December–January–February seasons from 1980–1981 to 2009–2010. From the composite analyses of those 55 events, it is found that the TTTs evolve with suppressed (enhanced) convection over the southwest Indian Ocean adjacent to Madagascar (southern Africa). The suppressed convection is, in turn, found to be associated with the enhanced convection around Sumatra in the southeast tropical Indian Ocean. This may explain why more TTT events occur in La Niña years as compared to El Niño years. Time evolution of the canonical TTT event shows that it starts 3 days prior to the mature phase of the event, suggesting possible predictability. After reaching a matured state, the system moves east toward the Indian Ocean and decays within the subsequent couple of days. In addition, the intertropical convergence zone (ITCZ) structure changes over Southern Africa/Madagascar during the TTT event and remains similar to climatology over other regions. The results indicate that the continental part of the ITCZ intensifies prior to the TTT event and then spreads southward following the mid-latitude influence during and after the event.