Srivastava A.K.,Indian Institute of Tropical Meteorology |
Ram K.,University of Tokyo |
Pant P.,Aryabhatta Research Institute of Observational science |
Hegde P.,Space Physics Laboratory |
Joshi H.,Aryabhatta Research Institute of Observational science
Environmental Research Letters | Year: 2012
This letter presents the contribution of black carbon (BC) to the total aerosol optical depth (AOD) and subsequently to the direct radiative forcing (DRF) at Manora Peak in the Indian Himalayan foothills. Measurements of the chemical composition of aerosols, carried out from July 2006 to May 2007, together with concurrently measured BC mass concentrations were used in an aerosol optical model to deduce the radiatively important aerosol optical parameters for composite aerosols. On the other hand, BC mass concentrations alone were used in the optical model to deduce the optical parameters solely for BC aerosols. The derived aerosol optical parameters were used independently in a radiative transfer model to estimate the DRF separately for composite and BC aerosols. The average BC mass concentration was found to be 0.98 (±0.68)μgm3 during the entire observation period, which contributes <3% to the total aerosol mass and ∼ 17% to the total AOD at Manora Peak. The mean surface forcing was found to be 14.0 (±9.7) and 7.4 (±2.1)Wm2, respectively for composite and BC aerosols whereas mean atmospheric forcing was about +14 (±10) and +10 (±3)Wm 2 for these aerosols. These results suggest that BC aerosols exert relatively large surface heating (∼45% higher) as compared to composite aerosols and contribute ∼70% to the total atmospheric forcing at Manora Peak. Such a large warming effect of BC may affect the strength of Himalayan glaciers, monsoon circulation and precipitation over the Indian region. © 2012 IOP Publishing Ltd.
Singh A.K.,University of Lucknow |
Singh R.P.,Space Physics Laboratory |
Siingh D.,Indian Institute of Tropical Meteorology
Planetary and Space Science | Year: 2011
The plasmasphere sandwiched between the ionosphere and the outer magnetosphere is populated by up flow of ionospheric cold (∼1 eV) and dense plasma along geomagnetic field lines. Recent observations from various instruments onboard IMAGE and CLUSTER spacecrafts have made significant advances in our understanding of plasma density irregularities, plume formation, erosion and refilling of the plasmasphere, presence of thermal structures in the plasmasphere and existence of radiation belts. Still modeling work and more observational data are required for clear understanding of plasmapause formation, existence of various sizes and shapes of density structures inside the plasmasphere as well as on the surface of the plasmapause, plasmasphere filling and erosion processes; which are important in understanding the relation of the process proceeding in the Sun and solar wind to the processes observed in the Earths atmosphere and ionosphere. © 2011 Elsevier Ltd. All rights reserved.
Ram K.,Physical Research Laboratory |
Sarin M.M.,Physical Research Laboratory |
Hegde P.,Space Physics Laboratory
Atmospheric Chemistry and Physics | Year: 2010
A long-term study, conducted from February 2005 to July 2008, involving chemical composition and optical properties of ambient aerosols from a high-altitude site (Manora Peak: 29.4° N, 79.5° E, ∼1950ma.s.l.) in the central Himalaya is reported here. The total suspended particulate (TSP) mass concentration varied from 13 to 272 ìgm.3 over a span of 42 months. Aerosol optical depth (AOD) and TSP increase significantly during the summer (April- June) due to increase in the concentration of mineral dust associated with the long-range transport from desert regions (from the middle-East and Thar Desert in western India). The seasonal variability in the carbonaceous species (EC, OC) is also significantly pronounced, with lower concentrations during the summer and monsoon (July-August) and relatively high during the post-monsoon (September-November) and winter (December-March). On average, total carbonaceous aerosols (TCA) and water-soluble inorganic species (WSIS) contribute nearly 25 and 10% of the TSP mass, respectively. The WSOC/OC ratios range from 0.36 to 0.83 (average: 0.55±0.15), compared to lower ratios in the Indo- Gangetic Plain (range: 0.35-0.40), and provide evidence for the enhanced contribution from secondary organic aerosols. The mass fraction of absorbing EC ranged from less than a percent (during the summer) to as high as 7.6% (during the winter) and absorption coefficient (babs, at 678 nm) varied between 0.9 to 33.9Mm -1 (1Mm.1=10 -6 m -1). A significant linear relationship between babs and EC (μCm -3) yields a slope of 12.2 (±2.3) m 2 g -1, which is used as a measure of the mass absorption efficiency (σabs) of EC. © 2010 Author(s).
Xavier P.K.,University of Victoria |
John V.O.,University of Victoria |
Buehler S.A.,Lulea University of Technology |
Ajayamohan R.S.,UK Met Office |
Sijikumar S.,Space Physics Laboratory
Geophysical Research Letters | Year: 2010
Using a new data set we demonstrate the variability of upper troposphere humidity (UTH) associated with the Indian Summer Monsoon (ISM). The main advantage of the new data set is its all-sky representation which is essential to capture the full variability of humidity even in cloudy areas. We show that UTH undergoes significant variations during the active/break phases of the monsoon and discuss the mechanisms. The interannual variations of monsoon are also well reflected in the UTH. A preliminary investigation into the cause of the 2009 monsoon failure reveals anomalous subsidence and suppressed convection over the monsoon region due to anomalous warm conditions in the equatorial Pacific throughout the summer. The large scale drying of the upper troposphere may also have contributed to a negative feedback in suppressing convection. Copyright © 2010 by the American Geophysical Union.
Ambili K.M.,Space Physics Laboratory |
Choudhary R.K.,Space Physics Laboratory |
St.-Maurice J.-P.,University of Saskatchewan
Journal of Geophysical Research: Space Physics | Year: 2014
A sunrise undulation (SU) is observed by ionosondes when new ionization is produced at sunrise in the upper F region at the geomagnetic equator. It creates a very quick upward transition in the F region peak altitude (hmF2), which subsequently undergoes a sharp descent at a rate far in excess of any electrodynamic drift. The peak density also increases rapidly during the descent. However, the detection of the new plasma with ionosondes is possible only if plasma from the night before has undergone enough recombination, which, on average, can vary from one location to another and one season to the next. With this in mind, we have studied seasonal variations in the SU occurrence in 2010 at two widely separated geomagnetic equatorial stations in longitude, at Jicamarca in Peru and Trivandrum in India. Noticeable differences were found in the characteristics of undulation observed at the two locations. While full undulation (both ascend and descend in hmF2) was observed throughout the year at Trivandrum, only the descending part of undulation was visible at Jicamarca. Plasma density just before sunrise, on average, was 2 times larger at Jicamarca than at Trivandrum. The average hmF2, which peaks during night, was also higher at Jicamarca by as much as 100 km compared to Trivandrum. We traced the origin of these differences to the evolution of zonal electric field between sunset and local midnight at the two locations. The downward drift during this period was steeper at Trivandrum compared to Jicamarca, particularly during equinox. In addition, the strength of the downward drifts at Jicamarca decreased and even underwent a sign reversal prior to sunrise during equinox and winter months. In comparison, the downward motion at Trivandrum only became stronger during early morning hours. The contrast between the vertical drift at the two stations provides a very reasonable qualitative explanation for the differences in the characteristics of SU observed at the two stations. ©2014. American Geophysical Union. All Rights Reserved.