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Macro-physical, optical and radiative properties of tropical cirrus clouds and its temperature dependence at Gadanki (13.5° N, 79.2° E) observed by ground based lidar

2016-12-01T00:00:00Z

Title: Macro-physical, optical and radiative properties of tropical cirrus clouds and its temperature dependence at Gadanki (13.5° N, 79.2° E) observed by ground based lidar Authors: Dhaman, Reji K; Satyanarayana, M; Krishnakumar, V; Pillai, V P Mahadevan; Jayeshlal, G S; Raghunath, K; Ratnam, M Venkat Abstract: The macro-physical and optical properties of cirrus clouds and its temperature dependencies have been investigated at the National Atmospheric Research Laboratory (NARL; 13.5° N, 79.2° E), Gadanki, Andhra Pradesh, India; an inland tropical station during the period of observation January to December 2009 using a ground based pulsed monostatic lidar system data and radiosonde measurements. Based on the analysis of measurements the cirrus macrophysical properties such as occurrence height, mid cloud temperature, cloud geometrical thickness, and optical properties such as extinction coefficient, optical depth, depolarization ratio and lidar ratio have been determined. The variation of cirrus macrophysical and optical properties with mid cloud temperature have also been studied. The cirrus clouds mean height has been generally observed in the range of 9-17 km with a peak occurrence at 13-14 km. The cirrus mid cloud temperatures were in the range from -81 °C to -46 °C. The cirrus geometrical thickness ranges from 0.9-4.5 km and 56% of cirrus occurrences have thickness 1.0 -2.7 km. The monthly cirrus optical depth ranges from 0.01-0.47, but most (>80%) of the cirrus have values less than 0.1. The monthly mean cirrus extinction ranges from 2.8E-06 to 8E-05 and depolarization ratio and lidar ratio varies from 0.13 to 0.77 and 2 to 52 respectively. The temperature and thickness dependencies on cirrus optical properties have also been studied. A maximum cirrus geometrical thickness of 4.5 km is found at temperatures around – 46 °C with an indication that optical depth increases with increasing thickness and mid cloud temperature. The cloud radiative properties such as outgoing long-wave radiation (OLR) flux and cirrus IR forcing are studied. OLR flux during the cirrus occurrence days ranged from 348-456 W/m² with a low value in the monsoon period. The cirrus IR forcing varied from 3.13 – 110.54 W/m² and shows a peak at monsoon period. Page(s): 133-147

Global solar radiation characteristics at Dumdum (West Bengal)

2016-12-01T00:00:00Z

Title: Global solar radiation characteristics at Dumdum (West Bengal) Authors: Roy, Sukumar; Pal, Snigdha; Chakravarty, Nabajit Abstract: The data of the hourly global solar radiation (G) on a horizontal surface of Dumdum/ Gangetic West Bengal for the period 1980 to 2010 has been obtained. The diurnal extra terrestrial solar radiation for the station (22.39° N, 88.27° E) has been computed and then the clearness index has been calculated. The diurnal variations of the results have been studied. Also the daily total values and its monthly and seasonal averages as well as their frequency distribution in percentage have been computed and examined. The seasonal and climatic effects of the fluctuation of the results have been discussed. These effects have been particularly large during pre monsoon season (i.e. March to May); the period which experiences the thunderstorm activity the most in this area and this fact may be attributed as one of the cause for generation of the thunderstorm. The clearness index (G/G_o) shows that the incoming solar radiation is almost halved on reaching the earth. Also the comparative statistical as well as graphical study of average total global solar radiation with the average maximum temperature confirms once again the fact that the total global solar radiation is fairly related to average maximum temperature in correlation (0.77) as well as in wave form. Page(s): 148-153

Investigation on the source location of flares associated with type II radio bursts using multi-wavelength observations

2016-12-01T00:00:00Z

Title: Investigation on the source location of flares associated with type II radio bursts using multi-wavelength observations Authors: Selvarani, G; Suresh, K; Shanmugaraju, A Abstract: In this paper, a set of 145 type II bursts-associated solar flares observed during the period November1997 to December 2006 has been investigated. The radio bursts have been observed by Culgoora radio spectrograph and X-ray flares have been observed by GOES spacecraft. The main objectives are to study the distribution of locations of flares associated with type II bursts on the Sun and association of type II radio bursts with major solar flares and halo CMEs. Among the different latitudinal bins considered, more number of events occurred in the active latitude range 11-20° in both hemispheres. Shifting of dominance of type II-associated flare events from higher latitudes to equator has been seen from the butterfly diagram. Among the different longitudinal bins, more number of type IIs are found in the solar active longitudes around 50 degrees on both the eastern and western regions and in the range 10-20° west. That might be due to the favorable ambient/source conditions in the solar corona. In addition, the DH type II association with metric type IIs has been found to be nearly absent beyond the east longitude 50°. This east-west asymmetry in the low frequency type II bursts (DH type IIs) may be due to emission directivity of the low frequency radiations produced by CME-driven shocks. Page(s): 154-159

Investigation of ionospheric and geomagnetic response during 2011 Tohoku earthquake using ground based measurement

2016-09-01T00:00:00Z

Title: Investigation of ionospheric and geomagnetic response during 2011 Tohoku earthquake using ground based measurement Authors: Yaso, Norbaizura; Hasbi, Alina Marie; Abdullah, Mardina Abstract: This paper investigates co-seismic ionospheric disturbances (CID) during the M9.0, 11 March 2011 Tohoku earthquake. The investigation collects data from two sources which are GPS-TEC from GEONET data network and the geomagnetic field from MAGDAS data network. Three types of CID have been detected: direct acoustic wave (894m/s), secondary wave from the Rayleigh surface wave (2862 m/s), and gravity wave from a propagating Tsunami (226 m/s). The directivity of wave propagation has been found to be northward from the epicenter. Short period CID corresponding to direct acoustic waves have been firstly found about 7 min after the main shock and ended 38 min after the main shock with oscillation period varying from 2-7 min. The long period of CID corresponding to Tsunami waves firstly observed 20 min after the main shock, with 10 min of oscillation period and duration of 60 min. Geomagnetic field disturbances have been detected 10-11 min after the main shock with period of 4 min. These geomagnetic field disturbances have been associated with the short-period CID induced by the direct acoustic wave from the epicenter. The correlation between the ionospheric and geomagnetic disturbance shows a good agreement in wave characteristic. Page(s): 115-125