http://nopr.niscair.res.in/handle/123456789/3209 Search the Channel search http://nopr.niscair.res.in/simple-search http://nopr.niscair.res.in/handle/123456789/3306 Title: Range rate variation studies of the low-altitude quasi-periodic radar echoes during SEEK-2 campaign <br/> <br/>Authors: Pan, C J; Brahmanandam, P S <br/> <br/>Abstract: The first experimental evidence on range rate reversal of lowaltitude quasi-periodic (LQP) echoes from nighttime midlatitude sporadic E region with systematic characteristics in their occurrences for the echoes observed during SEEK- 2 (Sporadic-E Experiment over Kyushu) campaign with 24.515 MHz frequency agile radar located at Tanegashima in southern Japan (30.75ºN, 130.03ºE, geomagnetic latitude 20.97ºN, dip angle 43.2ºN) is presented. Four reversal cases of LQP echoes are found during the observation period. The reversal times of these echoes from positive QP to negative QP are found between 2000 and 2400 hrs LT and negative QP to positive QP around 0200 hrs LT. Besides, Doppler velocities associated with these echoes show preferential directions meaning that they are consistent with the sign of range rate of QP echoes in most cases. As the backscatter echoes studied are confined to the collision dominated lower E region and semi-diurnal tide is most pronounced at latitude higher than 30º, large-period neutral winds such as tidal and planetary waves in addition to atmospheric gravity waves play a role in the generation and control of these backscatter echoes. <br/> <br/>Page(s): 50-56 Thu, 29 Jan 2009 22:58:59 GMT http://nopr.niscair.res.in/handle/123456789/3261 Title: Testing of Solar2000 EUV flux model in 900-1350 Å wavelength range using greenline dayglow emission <br/> <br/>Authors: Krishna, M V Sunil; Singh, Vir <br/> <br/>Abstract: The contribution of photodissociation of molecular oxygen to the total volume emission rate of greenline dayglow emission at 5577 Å is modelled in the present study. The Solar EUV radiation fluxes for modelling are obtained from the Solar2000 V 2.25 model. The modelling has been done in the altitude range 92-105 km, where photodissociation and three body recombination are main contributing processes to greenline dayglow emission. The present results are discussed in the light of Wind Imaging Interferometer (WINDII) observations of greenline dayglow emission in the altitude range 92-105 km. It is found that the Solar2000 V2.25 flux model gives better agreement with the WINDII observations especially in the range 92-96 km where earlier models predicted a very low emission rate. In the mesospheric emission peak region, present results are higher than the measurements and this discrepancy may possibly be attributed to higher values of solar fluxes for those spectral lines which are main sources of production of greenline dayglow emission. The present study suggests the re-examination of Solar2000 flux model at least for those spectral lines which are the main sources of greenline dayglow emission in mesospheric emission peak region. <br/> <br/>Page(s): 37-41 Thu, 29 Jan 2009 22:58:59 GMT http://nopr.niscair.res.in/handle/123456789/3254 Title: Mesospheric, lower thermospheric dynamics and external forcing effects: A review <br/> <br/>Authors: Kazimirovsky, E S; Vergasova, G V <br/> <br/>Abstract: A review is presented on some of the most important experimental results and models obtained by international scientific community during last decade for the mesospheric and lower thermospheric dynamics (mean winds, planetary waves, tides and internal gravity waves). In addition to climatological features, the external forcing – the coupling from below (stratosphere) and possible influence of solar and geomagnetic activity on the dynamical processes at this region are presented. <br/> <br/>Page(s): 7-36 Thu, 29 Jan 2009 22:58:59 GMT http://nopr.niscair.res.in/handle/123456789/3237 Title: Comparative analysis of the effect of ionospheric delay on user position accuracy using single and dual frequency GPS receivers over Indian region <br/> <br/>Authors: Shukla, Ashish K; Shinghal, Priya; Sivaraman, M R; Bandyopadhyay, K <br/> <br/>Abstract: The ionosphere acts as a prominent source of range errors for users of Global Positioning System (GPS) satellite signals requiring accurate position determination. Various models and mathematical formulations have been devised to calculate the absolute range error caused due to ionospheric delay. The present study aims at comparing two methods for calculating delay due to ionosphere: (i) using grid based model at L1 carrier frequency with bilinear interpolation technique; and (ii) using pseudo-range measurements at both L1 and L2 carrier frequency. For analyzing the effect of ionospheric delay on the seasonal behaviour of positional accuracy, a quantitative analysis has been done for all quiet days (Ap index < 50) in 2005 using GPS data for International GNSS Service (IGS) Bangalore (IISc) receiver in January, March and June. Various corrections such as satellite clock bias, transit time, ionospheric delay corrections, etc. are applied to pseudo-ranges to calculate the user coordinates. For single frequency (L1) receivers, ionospheric delay corrections have been applied using IGS total electron content data derived from grid based ionospheric model; and for the dual frequency receivers, pseudo-range measurements at L1 and L2 carrier frequencies have been used. It has been observed that there is an improvement of 1-4 m in the standard deviation of position errors when the ionospheric delay correction is applied using pseudo-range measurements at L1 and L2 frequencies (dual frequency receiver) as compared to L1 frequency only. It has also been observed that some residual errors still remain in the estimated user position even after using dual frequency receivers. <br/> <br/>Page(s): 57-61 Tue, 24 Feb 2009 04:38:51 GMT