3194 research outputs found
Sort by
Temporal asymmetry in aerosol optical characteristics:A case study at ahigh-altitude station, Hanle, in Ladakh region
No full textDiurnal features of aerosol optical depth (AOD) at a high-altitude station, Hanle (4500 m amsl) in the western Himalayas, were studied using direct/diffuse solar irradiance measurement from a Skyradiometer (Prede) during October 2007 to December 2010. The study reveals a diurnal asymmetry in the measured aerosol characteristics, with three types of diurnal variation in AOD. Among them, Types I and II are prominent during pre-monsoon, while Type III dominates during post-monsoon. Type I appears to be associated with new-particle formation process from gaseous precursors, in addition to the combination of anthropogenic and desert-dust aerosols, probably brought by the prevailing westerly/south-westerly winds during the pre-monsoon season. The diurnal feature of the Type II may be attributed by the transported desert-dust aerosols brought by the prevailing winds. Further, Type III may be associated with the aged background aerosols over the region, pertaining to a small contribution from gaseous precursors
Impact of climate change on the characteristics of Indian summer monsoon onset
Get PDFA high resolution regional climate modeling system, known as PRECIS (Providing REgional Climate for Impact Studies), developed by Hadley Centre for Climate Prediction and Research, UK, is applied for Indian subcontinent to assess the impact of climate change on the summer monsoon onset characteristics. The present day simulation (1961–1990) with PRECIS is evaluated for the characteristics of onset over Kerala, southernmost part of India, where the monsoon sets in over Indian landmass. The meteorological parameters like precipitation, outgoing long wave radiation (OLR), and low level winds are analysed to study the monsoon onset over Kerala. The model is able to capture the sudden and sharp increase of rainfall associated with the onset. The rapid built-up of convective activity over the southeastern Arabian Sea and Bay of Bengal is well represented by the model. PRECIS simulations, under scenarios of increasing greenhouse gas concentrations and sulphate aerosols, are analysed to study the likely changes in the onset characteristics in future, towards the end of present century (2071–2100). The analysis does not indicate significant difference in the mean onset dates in A2 and B2 scenarios. However, the variability of onset date is likely to be more towards the end of the 21st century especially in A2 scenario
Curious Case of Indian Ocean Warming
No full textRecent studies have pointed out an increased warming over the Indian Ocean warm pool (the central-eastern Indian Ocean characterized by sea surface temperatures greater than 28.0°C) during the past half-century, although the reasons behind this monotonous warming are still debated. The results here reveal a larger picture—namely, that the western tropical Indian Ocean has been warming for more than a century, at a rate faster than any other region of the tropical oceans, and turns out to be the largest contributor to the overall trend in the global mean sea surface temperature (SST). During 1901–2012, while the Indian Ocean warm pool went through an increase of 0.7°C, the western Indian Ocean experienced anomalous warming of 1.2°C in summer SSTs. The warming of the generally cool western Indian Ocean against the rest of the tropical warm pool region alters the zonal SST gradients, and has the potential to change the Asian monsoon circulation and rainfall, as well as alter the marine food webs in this biologically productive region. The current study using observations and global coupled ocean–atmosphere model simulations gives compelling evidence that, besides direct contribution from greenhouse warming, the long-term warming trend over the western Indian Ocean during summer is highly dependent on the asymmetry in the El Niño–Southern Oscillation (ENSO) teleconnection, and the positive SST skewness associated with ENSO during recent decades
Effect of growth rate and latewood content on basic density of wood from 120-to 154-Year-old natural-grown Teak (Tectona grandis L. f.)
Get PDFThe relationship between the radial variations of growth ring features and basic density were investigated in juvenile and mature wood for five 120-to150-year-old trees of Tectona grandis L. grown naturally in moist deciduous forest of Thane,Maharashtra. The study showed that the mean basic density of growth rings in juvenile wood was 0.665 (0.602-0.702) g cm-3 and 0.613 (0.562-0.665) g cm-3 in mature wood. The annual growth in juvenile period was high with a ring width mean of 4.03 mm and the latewood content represented 76.36 % of the annual growth, while in mature period was low with a ring width mean of 1.24 mm and the latewood content represented 59.41% of the annual growth. The patterns of radial variation of ring width, latewood content and basic density were more inherent in the juvenile wood than mature wood of all trees due to cambial ageing. The basic density of five individual trees showed an insignificant correlation between ring-width and
latewood content in juvenile wood, whereas a significant positive correlation was found in mature wood of most of individual trees. The mean ring width value of all trees showed a highly significant positive correlation with basic density in both types of wood but mean latewood content showed a non-significant or low significant correlatio
Impact of global warming on the energetics of lower tropospheric ultra-long waves and the Indian summer monsoon
Get PDFAnalyses of 60 years (1949–2008) of monthly energetics of the zonal waves derived from NCEP/NCAR
data indicate that ultra-long waves (waves 1 and 2) dominate the spectrum of lower tropospheric zonal
waves during monsoon season (June–September). Westerlies over the Indian subcontinent are a source
of energy to wave 1. Two oceanic anticyclones, one over Pacific and the other over Atlantic are sources
of energy to wave 2. These two waves are inversely correlated. Climatology of the energetics of ultralong
waves for the two epochs 1949–1978 (CLP1) and 1979–2008 (CLP2) of 30 years indicates that the
intensity of wave 1 has decreased by about 33% whereas the intensity of wave 2 has increased by about
27%. Northward transport of sensible heat during CLP1 changes to southward during CLP2. Larger
generation of zonal mean Available Potential Energy (APE) during CLP2 indicates more heating. A
larger conversion of kinetic energy (KE) of wave 1 into APE of wave 1 leads to weakening of wave 1
during CLP2. In case of wave 2, lower rate of conversion of KE to APE leads to stronger wave 2 during
CLP2
Observations of new particle formation at two distinct Indian subcontinental urban locations
No full textWhile the formation of new atmospheric aerosol particles and their subsequent growth have been observed under diverse environmental conditions globally, such observations are very scarce over Indian subcontinent. Here, we present the systematic analysis for new particle formation (NPF) from two distinct urban locations in India during April–May of two consecutive years. Particle size distributions were measured at Pune (18.53°N, 73.85°E) during 16 April–23 May, 2012 and at Kanpur (26.46°N, 80.32°E) during 16 April–23 May, 2013. The campaign mean total particle number concentration in the similar size range of 4–135 nm at Pune (12.2 × 103 cm−3) was higher than at Kanpur (7.9 × 103 cm−3), whereas the estimated total condensation sink (CS4–750) at Pune (16.2 × 10−3 s−1) was lower than at Kanpur (33.3 × 10−3 s−1). Despite lower particle number concentrations at Kanpur, larger particle sizes resulted in higher condensation sink than at Pune. The mean particle mode diameter at Kanpur was found larger by a factor of ∼1.8 than at Pune. NPF events were observed commonly at both sites, with lower frequency at Kanpur (14%) than that at Pune (26%). The derived particle growth rates, GR, and the formation rates of 5 nm particles, J5, ranged from 3.4 to 13.3 nm h−1 and 0.4 to 13.9 cm−3 s−1, respectively, which are generally comparable to typical values reported in previous studies. Generally, the particle growth rates were found higher at Kanpur, whereas the formation rates were higher at Pune. It appears that the presence of pre-existing large particles at Kanpur than at Pune suppressed formation rates and favored particle growth. Overall, NPF occurred at lower condensation sink, lower RH, higher solar radiation, and higher temperature
Influence of tropical cyclone "AILA" on atmospheric surface layer turbulence and fluxes at Ranchi during its landfall
No full textSurface layer turbulent fluxes and normalized wind spectra at Ranchi, India during the landfall of severe cyclonic storm ‘AILA’ are compared with the fair weather spectra. Spectral peaks are shifted to lower frequencies as AILA crosses the coast. Dominant eddy sizes after the landfall are observed to be much higher than those before the landfall especially for u component. Spectral energy during the passage of synoptic disturbance in the vicinity is lesser than that of Kaimal's spectrum owing to mismatch of empirical constant over tropics. Mean vertical velocity is positive (negative) before (after) the landfall, indicating dominance of updrafts (downdrafts)
Impact of seasonal rainfall variability on NDVI in the Tunga and Bhadra river basins, Karnataka, India
No full textRainfall is the major climatic factor that affects the growth and distribution of natural vegetation at a regional scale. The high space–time variability of rainfall in the Tunga and Bhadra river basins caused by the high-elevation Western Ghats mountains forces changes in the seasonal distribution of local vegetation. Understanding the relationship between vegetation greenness and rainfall is a key feature in managing the vegetation of the river basin. For this, we have analysed a 7-year (2005–2011) time series of the Moderate Resolution Imaging Spectroradiometer normalized difference vegetation index (NDVI) and Tropical Rainfall Measuring Mission 3B42 rainfall data. The results
show that rainfall exerts seasonal control on vegetation greenness. A significant negative correlation was observed for the monsoon season and a favourable positive association for the rest of the seasons. We found a maximum amount of vegetation greenness in the post-monsoon season (October–December). The availability of enough soil moisture from the southwest monsoon season along with suitable climatic conditions triggers an increased greenness amount during the post-monsoon months. We also investigated seasonal and monthly correlations of monsoon rainfall with the NDVI of its subsequent months. The results suggest that monsoon rainfall is a key factor that sustains the long-term greenness in the river basins