Investigation of negative cloud radiative forcing over the Indian subcontinent and adjacent oceans during the summer monsoon season

ACPDRadiative properties of clouds over the Indian subcontinent and nearby oceanic regions (0-25° N, 60-100° E) during the Asian summer monsoon season (June-September) are investigated using the Clouds and Earth's Radiant Energy System (CERES) Top of the Atmosphere (TOA) flux data. Using multi-year satellite data, the net cloud radiative forcing (NETCRF) at the TOA over the Indian region during the Asian monsoon season is examined. The seasonal mean NETCRF is found to be negative (with its magnitude exceeding ~ 30 W m−2) over (1) the northern Bay of Bengal (close to the Myanmar-Thailand coast), (2) the Western Ghats and (3) the coastal regions of Myanmar. Such strong negative NETCRF values observed over the Indian monsoon region contradicts the assumption that near cancellation between LWCRF and SWCRF is a generic property of all tropical convective regions. The seasonal mean cloud amount (high and upper middle) and corresponding cloud optical depth observed over the three regions show relatively large values compared to rest of the Indian monsoon region. Using satellite derived cloud data, a statistical cloud vertical model delineating the cloud cover and single scattering albedo was developed for the three negative NETCRF regions. The shortwave (SW), longwave (LW) and net cloud radiative forcing over the three negative NETCRF regions are calculated using the Rapid Radiative Transfer Model (RRTM) with cloud vertical model as input. The NETCRF estimated from CERES observations show good comparison with that computed using RRTM (within the uncertainty limit of CERES observations). Sensitivity tests are conducted using RRTM to identify the parameters that control the negative NETCRF observed over these regions during the summer monsoon season. Increase in atmospheric water vapor content during the summer monsoon season is found to influence the negative NETCRF values observed over the region

Empirical model for mean temperature for Indian zone and estimation of precipitable water vapor from ground based GPS measurements

Estimation of precipitable water (PW) in the atmosphere from ground-based Global Positioning System (GPS) essentially involves modeling the zenith hydrostatic delay (ZHD) in terms of surface Pressure (<I>P<sub>s</sub></I>) and subtracting it from the corresponding values of zenith tropospheric delay (ZTD) to estimate the zenith wet (non-hydrostatic) delay (ZWD). This further involves establishing an appropriate model connecting PW and ZWD, which in its simplest case assumed to be similar to that of ZHD. But when the temperature variations are large, for the accurate estimate of PW the variation of the proportionality constant connecting PW and ZWD is to be accounted. For this a water vapor weighted mean temperature (<I>T<sub>m</sub></I>) has been defined by many investigations, which has to be modeled on a regional basis. For estimating PW over the Indian region from GPS data, a region specific model for <I>T<sub>m</sub></I> in terms of surface temperature (<I>T<sub>s</sub></I>) is developed using the radiosonde measurements from eight India Meteorological Department (IMD) stations spread over the sub-continent within a latitude range of 8.5°–32.6° N. Following a similar procedure <I>T<sub>m</sub></I>-based models are also evolved for each of these stations and the features of these site-specific models are compared with those of the region-specific model. Applicability of the region-specific and site-specific <I>T<sub>m</sub></I>-based models in retrieving PW from GPS data recorded at the IGS sites Bangalore and Hyderabad, is tested by comparing the retrieved values of PW with those estimated from the altitude profile of water vapor measured using radiosonde. The values of ZWD estimated at 00:00 UTC and 12:00 UTC are used to test the validity of the models by estimating the PW using the models and comparing it with those obtained from radiosonde data. The region specific <I>T<sub>m</sub></I>-based model is found to be in par with if not better than a similar site-specific <I>T<sub>m</sub></I>-based model for the near equatorial station, Bangalore. A simple site-specific linear relation without accounting for the temperature effect through <I>T<sub>m</sub></I> is also found to be quite adequate for Bangalore. But for Hyderabad, a station located at slightly higher latitude, the deviation for the linear model is found to be larger than that of the <I>T<sub>m</sub></I>-based model. This indicates that even though a simple linear regression model is quite adequate for the near equatorial stations, where the temperature variations are relatively small, for estimating PW from GPS data at higher latitudes this model is inferior to the <I>T<sub>m</sub></I>-based model

MENCA experiment aboard India’s Mars Orbiter Mission

The Mars Exospheric Neutral Composition Analyser (MENCA) aboard the Indian Mars Orbiter Mission (MOM) is a quadrupole mass spectrometer-based experiment. Making use of the highly elliptical and low inclination (~150°) orbit of MOM, MENCA will conduct in situ measurements of the composition and radial distribution of the Martian neutral exosphere in the 1–300 amu mass range in the equatorial and low latitudes of Mars. The functionality of MENCA has been tested during the Earth-bound and heliocentric phases of MOM before its operation in the Martian orbit. This article describes the scientific objectives, instrument details, design and development, test and evaluation, and calibration of the MENCA instrument

MicroMotility: State of the art, recent accomplishments and perspectives on the mathematical modeling of bio-motility at microscopic scales

Mathematical modeling and quantitative study of biological motility (in particular, of motility at microscopic scales) is producing new biophysical insight and is offering opportunities for new discoveries at the level of both fundamental science and technology. These range from the explanation of how complex behavior at the level of a single organism emerges from body architecture, to the understanding of collective phenomena in groups of organisms and tissues, and of how these forms of swarm intelligence can be controlled and harnessed in engineering applications, to the elucidation of processes of fundamental biological relevance at the cellular and sub-cellular level. In this paper, some of the most exciting new developments in the fields of locomotion of unicellular organisms, of soft adhesive locomotion across scales, of the study of pore translocation properties of knotted DNA, of the development of synthetic active solid sheets, of the mechanics of the unjamming transition in dense cell collectives, of the mechanics of cell sheet folding in volvocalean algae, and of the self-propulsion of topological defects in active matter are discussed. For each of these topics, we provide a brief state of the art, an example of recent achievements, and some directions for future research

Interdependence of tropical cirrus properties and their variability

The mean properties of tropical cirrus, such as cloud top, cloud base, optic centre, cloud strength/optical depth, asymmetry factor and cloud depolarization, as well as their heterogeneities are examined using lidar observations over 281 nights from a tropical station Gadanki (13.5° N, 79.2° E) during the period 1998–2002. This study shows that as the cloud optical depth (τc) increases the cloud becomes more asymmetric in its scattering property. The amount of asymmetry is less than 2% for very low values of (τc and increases nonlinearly with an increase in (τc. The physical properties of these clouds also show significant variation with different time scales during the course of each night. On average, while the short-term variations in (τc are in opposite phase with those of the asymmetry factor (ξ) and volume depolarization ratio (δ), the long-term variation in (τc extending over a night are found to be in opposite phase with that of ξ and in-phase with that of δ. The short-term variations in δ and (τc were attributed to possible changes in the cloud particle orientation and the long period variations to cloud evolution process. The value of δ shows a pronounced variation along the vertical, with low values near the cloud top and cloud base and high values in the middle, which is attributed to the cloud dynamics

FTIR spectroscopic study of the interaction of CO<SUB>2</SUB> and CO<SUB>2</SUB> + H<SUB>2</SUB> over partially oxidized Ru/TiO<SUB>2</SUB> catalyst

At least three distinct linearly bound carbonyl species are identified in the adsorption of CO2 or CO2 + H2 over Ru---RuOx/TiO2 catalyst. The relative concentration and the growth of these species depend on metal oxidation state, presence of hydrogen, reaction temperature, and duration of exposure. The presence of preadsorbed or coadsorbed hydrogen promotes formation of x173-1 type species, the RuOx-(CO)adspecies develop only on prolonged exposure to a dose of CO2 or CO2 + H2. The oxygen or the hydrogen ligand bonded to ruthenium facilitates C---O bond scission. The widely reported lower temperature requirement for the CO2 methanation reaction as compared to that of CO is attributed to the high reactivity of nascent carbonyl species which give methane directly via "active" carbon formation. As shown earlier (Gupta et al., J. Catal. 137, 437 (1992)), the CO methanation requires multistep transformations, making the process energy intensive, particularly in the 300-450 K temperature range. The studies using 2H and 13C labeled adsorbates helped in the identification of oxygenated surface species having vibrational bands in the 1000-1800 cm-1 region. These species are regarded as inactive side products formed on the support and/or at the Ru-support interfaces