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Diurnal asymmetry in slant column density of NO2, O3, H2O and O4 during CAIPEEX–IGOC over Mahabubnagar, a rural site in Southern Peninsular India
No full textIn order to study the column densities of atmospheric trace gases over a rural environment, zenith-sky scattered light observations have been carried out by employing a high-precision, portable UV-V-IR spectrometer (Ocean Optics Model HR2000) at Mahabubnagar (16°42′N, 77°58′E) during the Cloud Aerosol Interaction and Precipitation Enhancement Experiment–Integrated Ground Observational Campaign during October 1, 2011–November 11, 2011. The observed and calculated differential optical density spectra of NO2, O3, H2O and O4 are compared in the spectral range 462–498 nm and found good agreement within a percent deviation up to 1, 1, 0.5 and 0.8 %, respectively. Differential slant column densities (SCDdiff) of NO2, O3, H2O and O4 are retrieved to present the diurnal variation at morning and evening hours between 65° and 95° solar zenith angles (SZAs). The SCDdiff at morning and evening 90° SZA are observed to be 6.4 × 1016 and 9.4 × 1016 mol cm−2 for NO2; 1.03 × 1020 and 1.38 × 1020 mol cm−2 for O3; 1.7 × 1024 and 1.8 × 1024 mol cm−2 for H2O, 1.23 × 1044 and 1.57 × 1044 mol cm−2 for O4, respectively. The diurnal variations of NO2 in twilight period are observed to vary from 36 to 75 %, O3 from 23 to 40 %, H2O from 2 to 20 % and O4 from 23 to 53 % during the study period. The SCDs of NO2, O3 and O4 are observed to be higher in the evening twilight hours compared to the morning twilight hours, which may be due to higher temperature observed at evening as compared to morning between 65° and 95° SZAs
Study of equatorial plasma bubble during January to April 2012 over Kolhapur (India)
Get PDFOver 53 nights of all sky airglow imager data collected during January-April 2012 from the low latitude station Kolhapur (16.68°N, 74.26°E; 10.6°N dip latitude) have been analyzed to study the F-region dynamics through the imaging of OI 630 nm emission line. The observed night airglow data were supported by the ionosonde measurements from Tirunelveli (8.7°N, 77.8°E; 0.51°N dip latitude). Well defined magnetic field aligned depletions were observed during the observation period. Out of 53 nights, 40 nights exhibited the occurrence of north-south aligned equatorial plasma bubbles. These plasma bubbles were found moving towards east with drift speed in range between 70 to 200 m s-1. We have analyzed the zonal drift velocity variation and relation of bubble occurrence with the base height of the ionosphere together with the effects of the geomagnetic Ap and solar flux F10.7 cm index in its first appearance
Impact of ENSO on variability of AIRS retrieved CO2 over India
No full textThis study investigates the impact of ENSO on the CO2 variability over the Indian subcontinent for the period 2003–2011 based on the relationships between NINO indices derived from the sea surface temperature (SST) and AIRS-retrieved mid-tropospheric CO2 concentrations. The NINO4 region exhibits positive influence on the variability of CO2 almost during the entire year except for the post-monsoon/winter months (October through December; OND). Significant positive relationship (correlation coefficient r = +0.68) between NINO4 index and CO2 levels is observed for the month of June, while negative relationship (r = −0.73) for the month of October, and the negative relationship tends to continue till November with decreasing magnitudes (r = −0.41). The spatial distribution of mid-tropospheric CO2 concentrations during El Niño and La Niña periods also indicate large-scale impact over the Indian subcontinent with positive (negative) anomalies of about 1–2 ppm during El Niño (La Niña)
Marine Meteorological Atlas of Tropical Indian Ocean
Get PDFThis report discusses the preparation of climatology from the data which is from the ship observations obtained from the Indian Meteorological Department (IMD) and Naval Operations Data Processing and Analysis Centre (NODPAC). Processing of these datasets, extraction of surface meteorological variables and SST (Sea surface temperature), the quality control (QC) procedures followed are discussed. The individual records of International Comprehensive Ocean-Atmosphere Dataset (ICOADS) and those obtained from IMD are compared and the unique records from IMD data are extracted. The enhancement in ICOADS climatology after adding the unique records from IMD data and NODPAC is checked. ICOADS dataset has been found to be self robust, as there is no much significant improvement in the climatology even after adding new records . Frequency distribution of the ICOADS
dataset alone and after adding new records showed no much difference. Spatial correlation between ICOADS monthly climatology fields before and after adding the new records, is greater than 0.9 at all grid point
Algal species dynamics in North Arabian Sea using long term ocean colour satellite data
No full textNorth Arabian Sea experiences massive proliferation of variable algal species. The study presents variability of Noctiluca and its association with hydrographic parameters such as sea surface temperature (SST) and water column stability using ten years of satellite data. The area was categorized into three regions, North (23 to 26°N and 56 to 70°E), West (18 to 23°N and 56 to 62°E) and East (18 to 23°N and 62 to 74°E). The Noctiluca dominated area was extracted following approach of Dwivedi et. al. (2015) based on slope of Remote Sensing Reflectance (Rrs) between 488 to 443nm and 488 to 531nm. The data used in the present study depicted two distinct clusters based on regression between difference of Rrs(488) and Rrs(443) with Rrs(488) and Rrs(531). The major clusters representing Noctiluca falls within the range of 0.0004 to 0.0015 (Rrs488-Rrs443) and -0.0012 to -0.0004 (Rrs488-Rrs531). The occurrence of Noctiluca showed bi-modal distribution at an annual scale with the dominance in the northern region during winter monsoon (February- March). In western and eastern region higher frequency of Nuctiluca was during post monsoon having lag of one month from western (September) to eastern (October) region. The periodicity of Noctiluca, carried out using Fourier analysis, showed predominance at annual scale in Northern and semi-annual scale in Western and Eastern region. This indicates that the Noctiluca bloom in the northern region is primarily triggered by winter mixing whereas in western and eastern part of northern Arabian Sea it has combined effect of summer upwelling as well as winter mixing
Moisture dynamics of the northward and eastward propagating boreal summer intraseasonal oscillations: possible role of tropical Indo-west Pacific SST and circulation
No full textBoreal summer intraseasonal oscillation (BSISO) has complex spatial structure due to the co-existence of equatorial eastward and off-equatorial northward propagation in the equatorial Indian Ocean. As a result, equatorial Indian Ocean convection has simultaneous northward and eastward (NE), northward only (N-only) and eastward only (E-only) propagations. It is well established that the convection propagates in the direction of increasing moist static energy (MSE). The moisture and MSE budget analysis reveals that the horizontal advection of anomalous MSE contributes to positive MSE tendency, which is in agreement with the horizontal advection of column integrated moisture anomaly. Northward movement of warm SST and the anomalous moisture advected by zonal wind are the major initiative for the northward propagation of convection from the equatorial Indian Ocean in both NE and N-only category. At the same time warm SST anomaly in the equatorial west Pacific along with moisture advection caused by anomalous meridional wind is important for the equatorial eastward branch of NE propagation. As these anomalies in the west Pacific moves northward, equatorial Indian Ocean convection establishes over the equatorial west Pacific. The absence of these processes confines the BSISO in northward direction for N-only category. In the case of E-only movement, warm SST anomaly and moisture advection by zonal component of wind causes the eastward propagation of convection. Boundary layer moisture convergence always remains east of convection center in E-only propagation, while it coincides with convection centre in other two categories. Thus the present study concludes that the difference in underlying SST and atmospheric circulation in tropical Indo-west Pacific oceanic regions encourage the differential propagation of BSISO convection through moisture dynamics
Sub-seasonal behaviour of Asian summer monsoon under a changing climate: assessments using CMIP5 models
No full textNumerous global warming studies show the anticipated increase in mean precipitation with the rising levels of carbon dioxide concentration. However, apart from the changes in mean precipitation, the finer details of daily precipitation distribution, such as its intensity and frequency (so called daily rainfall extremes), need to be accounted for while determining the impacts of climate changes in future precipitation regimes. Here we examine the climate model projections from a large set of Coupled Model Inter-comparison Project 5 models, to assess these future aspects of rainfall distribution over Asian summer monsoon (ASM) region. Our assessment unravels a north–south rainfall dipole pattern, with increased rainfall over Indian subcontinent extending into the western Pacific region (north ASM region, NASM) and decreased rainfall over equatorial oceanic convergence zone over eastern Indian Ocean region (south ASM region, SASM). This robust future pattern is well conspicuous at both seasonal and sub-seasonal time scales. Subsequent analysis, using daily rainfall events defined using percentile thresholds, demonstrates that mean rainfall changes over NASM region are mainly associated with more intense and more frequent extreme rainfall events (i.e. above 95th percentile). The inference is that there are significant future changes in rainfall probability distributions and not only a uniform shift in the mean rainfall over the NASM region. Rainfall suppression over SASM seems to be associated with changes involving multiple rainfall events and shows a larger model spread, thus making its interpretation more complex compared to NASM. Moisture budget diagnostics generally show that the low-level moisture convergence, due to stronger increase of water vapour in the atmosphere, acts positively to future rainfall changes, especially for heaviest rainfall events. However, it seems that the dynamic component of moisture convergence, associated with vertical motion, shows a strong spatial and rainfall category dependency, sometimes offsetting the effect of the water vapour increase. Additionally, we found that the moisture convergence is mainly dominated by the climatological vertical motion acting on the humidity changes and the interplay between all these processes proves to play a pivotal role for regulating the intensities of various rainfall events in the two domains
Distribution of trace metals in surface seawater and zooplankton of the Bay of Bengal, off Rushikulya estuary, East Coast of India
No full textConcentrations of trace metals such as iron (Fe), copper (Cu), zinc (Zn), cobalt (Co), nickel (Ni), manganese (Mn), lead (Pb), cadmium (Cd), chromium (Cr), arsenic (As), vanadium (V), and selenium (Se) were determined in seawater and zooplankton from the surface waters off Rushikulya estuary, north-western Bay of Bengal. During the study period, the concentration of trace metals in seawater and zooplankton showed significant spatio-temporal variation. Cu and Co levels in seawater mostly remained non-detectable. Other elements were found at higher concentrations and exhibited marked variations. The rank order distribution of trace metals in terms of their average concentration in seawater was observed as Fe > Ni > Mn > Pb > As > Zn > Cr > V > Se > Cd while in zooplankton it was Fe > Mn > Cd > As > Pb > Ni > Cr > Zn > V > Se. The bioaccumulation factor (BAF) of Fe was highest followed by Zn and the lowest value was observed with Ni. Results of correlation analysis discerned positive affinity and good relationship among the majority of the trace metals, both in seawater and zooplankton suggesting their strong affinity and coexistence
An optical approach for synoptic monitoring of red Noctiluca scintillans bloom and its associates from space
Get PDFReddish discoloration of coastal waters along the east coast of India at latitude 19.3 was observed during April 2014. Phytoplankton analysis revealed presence of Red Noctiluca scintillans cells in the water samples. A technique of detecting green Noctiluca scintillans was developed earlier, which is based on the principle of recognition of spectral shapes remote sensing reflectance spectra for Aqua-MODIS bands. This was appropriately modified to detect red Noctiluca in the coastal waters of the bay of Bengal. Phytoplankton species images generated using the modified approach were validated using information on reported events of red and green Noctiluca in the coastal waters. In addition to this, the study reported here highlights two major developments. One is, the classified species image reveals co-existence of diatom, red and green Noctiluca in coastal waters of the east coast and the second, it has been demonstrated with satellite time-series images that red Noctiluca succeeds diato
Role of Indian Ocean SST variability on the recent global warming hiatus
No full textPrevious studies have shown a slowdown in the warming rate of the annual mean global surface temperature in the recent decade and it is referred to as the hiatus in global warming. Some recent studies have suggested that the hiatus in global warming is possibly due to strong cooling in the tropical Pacific. This study investigates the possible role of the Indian Ocean warming on the tropical Pacific cooling. Despite the continued rise in sea surface temperature (SST) over the tropical Indian Ocean, SST over the tropical Pacific has shown a cooling trend in the recent decade (2002 − 2012). It is well known fact that the Indian Ocean and the Pacific Ocean are strongly coupled to each other and the Indian Ocean basin wide warming is triggered by El Niño on interannual time scale. However, in the recent decade, this relationship is weakening. The recent Indian Ocean warming is triggering a Matsuno-Gill type response in the atmosphere by generating anomalous cyclonic circulations on either side of equator over the tropical Indian Ocean and anomalous easterlies along the tropical Pacific Ocean. These anomalous easterlies result in Ekman divergence in the equatorial Pacific and produce upwelling Kelvin waves, cools the tropical Pacific and therefore indirectly contributes to the hiatus in global warming