Space Physics Laboratory
Space Physics Laboratory
Manju G.,Space Physics Laboratory |
Aswathy R.P.,Space Physics Laboratory
Journal of Atmospheric and Solar-Terrestrial Physics | Year: 2017
An analysis of Gravity wave induced travelling ionospheric disturbances (GW-TIDs) in the thermosphere during high and low solar epochs is undertaken using ionosonde data at Trivandrum (8.50N, 770E). Wavelet analysis is performed on the temporal variations of foF2 and the amplitudes of waves present in two period bands of (0.5–1.5) h and (2–4) h are extracted. The real height profiles are generated at 15 min internal for the whole day (for sample days) during high and low solar activity years. The study reveals that the GW-TID activity is significantly greater for solar minimum compared to solar maximum for the period 8.5–17.5 h. Diurnally the GW-TID activity in the (2–4) h period band peaks in the post sunset hours for both high and low solar epochs. For the 0.5–1.5 h period band, the diurnal maximum in GW-TID is occurring in the post sunset hours for high solar epoch while it occurs in the morning hours around 10 h LT for low solar epoch. Seasonally the day time GW-TID activity maximizes (minimizes) for winter (vernal equinox). The post sunset time GW-TID maximizes (minimizes) either for summer/winter (vernal equinox). The other interesting observation is the anti correlation of GW-TID in upper thermosphere with solar activity for day time and the correlation of the same with solar activity in the post sunset hours. The present results for daytime are in agreement with the equatorial daytime GW-TID behaviour reported from CHAMP satellite observations. The GW-TID activity during post sunset time for equatorial region upper thermosphere has not been reported so far. © 2017 Elsevier Ltd
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.
Choudhary R.K.,Space Physics Laboratory |
St.-Maurice J.-P.,Space Physics Laboratory |
St.-Maurice J.-P.,University of Saskatchewan |
Ambili K.M.,Space Physics Laboratory |
And 2 more authors.
Journal of Geophysical Research: Space Physics | Year: 2011
The January 15, 2010, solar annular eclipse crossed the magnetic equator in the middle of the day over India, in a region instrumented with several magnetometers, Total Electron Content stations using GPS data, and an ionosonde located very near the center of the eclipse. With the help of a one-dimensional model appropriate for the region of interest we show that the ionosonde data was consistent with a lower F region plasma that was moving upwards with only modest velocities in the morning hours and moving resolutely downwards in the afternoon hours. This motion agreed well with the local magnetometer data which revealed a weakened electrojet taking place in the morning hours while a full-blown counter-electrojet was present in the afternoon hours. We show that the unusual solar eclipse-induced electrodynamics resulted in a reduction in the Total Electron Content depletion not just at the magnetic equator but also, more markedly, in the Equatorial Ionization Anomaly (EIA) zone, a further 10 degrees to the north. This latter point clearly shows that the eclipse led to a cut-off in the supply of plasma provided through the equatorial fountain, by altering a fundamental aspect of the equatorial electrodynamics. Copyright 2011 by the American Geophysical Union.
Ravindrababu S.,Jawaharlal Nehru Technological University |
Ratnam M.V.,National Atmospheric Research Laboratory |
Sunilkumar S.V.,Space Physics Laboratory |
Parameswaran K.,Space Physics Laboratory |
Journal of Atmospheric and Solar-Terrestrial Physics | Year: 2014
The structure and variability of tropical tropopause over Gadanki (13.5°N, 79.2°E) are delineated using data obtained from Indian MST radar operated in the vertical mode as a part of intense Tropical Tropopause Dynamics (TTD) campaigns conducted under the CAWSES India Phase II (Theme 3) program. Radar measurements for 72. h in each month from December 2010 to September 2013 have been considered. The identified tropopause altitude with radar (RTH) is compared with the cold point (CPH) and lapse rate tropopause altitudes (LRH) obtained from simultaneous radiosonde data at three hourly intervals during these campaigns. Most of the time, a very good agreement between the RTH and CPH and/or LRH from radiosonde measurements is observed. The mean difference between RTH and CPH and RTH and LRH is found to be 0.1±1. km and 0.5±1. km, respectively. The smaller differences between RTH and CPH noticed in the present work when compared to other mid- and polar latitudes might be due to the well defined tropopause structure in the tropical latitudes. As the radar provides reliable data on the tropopause, its long-term variability is investigated using the data from 2007 to 2012 available from the MST radar. © 2014 Elsevier Ltd.
Naseema Beegum S.,National Physical Laboratory India |
Krishna Moorthy K.,Space Physics Laboratory |
Gogoi M.M.,Space Physics Laboratory |
Suresh Babu S.,Space Physics Laboratory |
Pandey S.K.,ISTRAC Ground Station
Annales Geophysicae | Year: 2012
Long-term measurements of spectral aerosol optical depth (AOD) using multi-wavelength solar radiometer (MWR) for a period of seven years (from 2002 to 2008) from the island location, Port Blair (11.63°N, 92.7°E, PBR) in the Bay of Bengal (BoB), along with the concurrent measurements of the size distribution of near-surface aerosols, have been analyzed to delineate the climatological features of aerosols over eastern BoB. In order to identity the contribution of different aerosol types from distinct sources, concentration weighted trajectory (CWT) analysis has been employed. Climatologically, AODs increase from January to reach peak value of ∼0.4 (at 500 nm) in March, followed by a weak decrease towards May. Over this general pattern, significant modulations of intra-seasonal time scales, caused by the changes in the relative strength of distinctively different sources, are noticed. The derivative (α') of the Angstrom wavelength exponent ± in the wavelength domain, along with CWT analysis, are used to delineate the different important aerosol types that influence this remote island. Corresponding changes in the aerosol size distributions are inferred from the numerical inversion of the spectral AODs as well from (surface) measurements. The analyses revealed that advection plays a major role in modifying the aerosol properties over the remote island location, the potential sources contributing to the accumulation mode (coarse mode) aerosols over eastern BoB being the East Asia and South China regions (Indian mainland and the oceanic regions). © 2012 Author(s). CC Attribution 3.0 License.
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).
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.
Suresh Raju C.,Space Physics Laboratory |
Renju R.,Space Physics Laboratory |
Antony T.,Space Physics Laboratory |
Mathew N.,Space Physics Laboratory |
Krishna Moorthy K.,Space Physics Laboratory
IEEE Geoscience and Remote Sensing Letters | Year: 2013
This letter discusses the background thermodynamic conditions of a convective cloud during the occurrence of a waterspout. This study is conducted using a very unique experimental observation of a ground-based multifrequency microwave radiometer which was set to scan the atmosphere in seven elevation angles. The spatio-temporal variations of the cloud microphysical parameters during the evolution of a multicell convective cumulus system are studied. Humidity and temperature anomalies deduced from the radiometric observation could clearly explain the convective processes like the formation of an intense updraft of moist air, convective heating due to large latent heat energy release, and cooling of the lower atmosphere below 2-km altitude by the downdrafting dry air. The measurements from collocated IR radiometer, surface met sensors, and calculated CAPE showed the formation of an intense convection in a humid warm atmosphere over a shallow warm ocean (conducive to formation of a waterspout). Studies on the evolution of cloud parameters during the life cycle of convective precipitation are of great interest in weather forecasting. © 2012 IEEE.
Ambili K.M.,Space Physics Laboratory |
Ambili K.M.,University of Saskatchewan |
St.-Maurice J.-P.,University of Saskatchewan |
Choudhary R.K.,Space Physics Laboratory
Geophysical Research Letters | Year: 2012
This paper shows that, contrary to previous explanations, the apparent undulating motion of the equatorial F region peak at sunrise is produced by photochemistry rather than dynamics. Our study is based on an investigation of the behavior of the early morning ionosphere observed by a Digital Ionosonde at Trivandrum, India. The phenomenon is rooted in the production of new plasma at the upper F region altitudes soon after sunrise. As the peak photoproduction rate moves down in altitude and increases in magnitude the newly formed plasma follows a similar trend. Once the density becomes large enough to be detected by an ionosonde, a jump is observed in the F region peak altitude. The jump is followed by a quick downward motion of the increasingly strong F peak. Chemistry causes the downward motion of the F peak to end near 250km. Electrodynamics is not responsible for the sunrise undulation, but plays an indirect role in the detection of the sunrise effect by simultaneously lowering during the night the peak height and decreasing the density. When detectable, the remnant plasma introduces a lower peak height that facilitates the observation of the initial increase in peak height, while the lower background density allows the relatively small initial density increase from photoionization to be observed. © 2012. American Geophysical Union. All Rights Reserved.