Ozone decline and its effect on night airglow intensity of Na 5893 A at Dumdum (22.5 N, 88.5 E) and Halley Bay (76 S, 27 W)
P K Jana1,* and S C Nandi2
1Department of Chemistry, Institute of Education (P.G) for Women, Chandernagore,
Hooghly 712 138, West Bengal, India.
2Serampore High School, Serampore, Hooghly 712 201, West Bengal, India.
*email: pkjingl@yahoo.co.in

Abstract: The paper presents the effect of O3 depletion on night airglow emission of Na 5893 A line at Dumdum (22.5 N, 88.5 E), India and Halley Bay (76 S, 27 W), a British Antarctic service station. Calculations based on chemical kinetics show that the airglow intensity of Na 5893 A line will also be affected due to the depletion of O3 concentration. The nature of yearly variation and seasonal variation of the intensity of Na 5893 A line for the above two stations are shown and compared. It is shown that the rate of decrease of intensity of Na 5893 A line is comparatively more at Halley Bay due to the dramatic decrease of Antarctic O3 concentration. A possible explanation for this dramatic decrease of Antarctic O3 concentration  is also mentioned.


A numerical study of sea breeze circulation observed at a tropical site Kalpakkam on the east coast of India, under different synoptic flow situations
C V Srinivas*, R Venkatesan, K M Somayaji and A Bagavath Singh
Radiological Safety Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, India.
*e-mail: cvsri@igcar.ernet.in

Abstract: A simulation study of the sea breeze circulation and thermal internal boundary layer (TIBL) characteristics has been carried out at the tropical site Kalpakkam on the east coast of India, for operational atmospheric dispersion prediction. The community based PSU/NCAR MM5 Mesoscale meteorological model is used for the study. Three cases on typical days in summer (24 May 2003), southwest (SW) monsoon (1 July 2001) winter season (2 February 2003) with different largescale  flow pattern are studied. The MM5 model is used with 3 nested domains with horizontal grid resolutions 18 km, 6 km and 2 km and 26 vertical levels. The model is integrated for 24 hours in the above cases with initial and boundary conditions taken from NCEP-FNL analyses data. Observations of 10 meteorological stations and coastal boundary layer experiments conducted at Kalpakkam are used for comparison and validation of the simulation. The characteristics of simulated sea breeze and TIBL at Kalpakkam are seen to vary in the above cases according to the prevailing large-scale winds and surface fluxes. The sea breeze circulation is seen to develop early with larger strength and inland propagation in the summer case under the influence of moderate synoptic wind and strong heating conditions than in the SW monsoon and winter cases. The horizontal and vertical extents of TIBL are found to be larger in the summer case than in other cases. Although model parameters agree in general with observations, all the fine features are not clearly captured and some slowness in model sea breeze development is also seen. The results indicate the need to improve i) the initial conditions by assimilation of available surface/upper air observations to reduce model bias and ii) surface net radiation parameterisation. The model could predict the essential features of the local circulation and further improvement is expected with better initial condition data and incorporation of more realistic surface data.

Marine boundary layer characteristics during a cyclonic storm over the Bay of Bengal
Savita B Morwal1, S G Nagar , V S N Murty2,* and P Seetaramayya1
1Indian Institute of Tropical Meteorology, Pune 411 008, India.
2National Institute of Oceanography, Goa 403 004, India.
*e-mail: morwal@tropmet.res.in

Abstract: During the period 12–16 June 1996 a tropical cyclonic storm formed over the southwest Bay of Bengal and moved in a north–northeasterly direction. The thermodynamic characteristics of this system are investigated by utilizing the surface and upper air observations collected onboard ORV Sagar Kanya over the Bay of Bengal region. The response of the cyclonic storm is clearly evident from the ship observations when the ship was within the distance of 600–800 km from the cyclonic storm. This study explores why (i) the whole atmosphere from surface to 500 hPa had become warm and moist during the cyclonic storm period as compared to before and after the formation of this system and (ii) the lower layer of the atmosphere had become stable during the formative stage of the cyclonic storm.


High resolution numerical weather prediction over the Indian subcontinent
T S V Vijaya Kumar1,2,* and T N Krishnamurti1
1Department of Meteorology, Florida State University,Tallahassee, Fl 32306-4520, USA.
2Present address: Environmental Modeling Center, National Centers for Environmental Prediction, Camp
Springs, Maryland, USA.
*e-mail: vijay.tallapragada@noaa.gov

Abstract: In this study, the Florida State University Global Spectral Model (FSUGSM), in association with a high-resolution nested regional spectral model (FSUNRSM), is used for short-range weather forecasts over the Indian domain. Three-day forecasts for each day of August 1998 were performed using different versions of the FSUGSM and FSUNRSM and were compared with the observed fields (analysis) obtained from the European Center for Medium Range Weather Forecasts (ECMWF). The impact of physical initialization (a procedure that assimilates observed rain rates into the model atmosphere through a set of reverse algorithms) on rainfall forecasts was examined in detail. A very high nowcasting skill for precipitation is obtained through the use of high-resolution physical initialization applied at the regional model level. Higher skills in wind and precipitat ion forecasts over the Indian summer monsoon region are achieved using this version of the regional model with physical initialization.

A relatively new concept, called the ‘multimodel/multianalysis superensemble’ is described in this paper and is applied for the wind and precipitation forecasts over the Indian subcontinent. Large improvement in forecast skills of wind at 850 hPa level over the Indian subcontinent is shown possible through the use of the multimodel superensemble. The multianalysis superensemble approach that uses the latest satellite data from the Tropical Rainfall Measuring Mission (TRMM) and the Defense Meteorological Satellite Program (DMSP) has shown significant improvement in the skills of precipitation forecasts over the Indian monsoon region.


Summer monsoon intraseasonal oscillation over eastern Arabian Sea – as revealed by TRMM microwave imager products
S H Rahman* and B Simon
Atmospheric Sciences Division, Meteorology and Oceanography Group, Space Applications Centre (ISRO),
Ahmedabad 380 015, Gujarat, India.
*e-mail: amar−bangla@yahoo.com

Abstract: The time evolution of atmospheric parameters on intraseasonal time scale in the eastern Arabian Sea (EAS) is studied during the summer monsoon seasons of 1998–2003 using Tropical Rainfall Measuring Mission Microwave Imager (TMI) data. This is done using the spectral and wavelet analysis. Analysis shows that over EAS, total precipitable water vapour (TWV) and sea surface wind speed (SWS) have a periodicity of 8–15 days, 15–30 days and 30–60 days during the monsoon season. Significant power is seen in the 8–15-day time scale in TWV during onset and retreat of the summer monsoon. Analysis indicates that the timings of the intensification of 8–15, 15–30, and 30–60 days oscillations have a profound effect on the evolution of the daily rainfall over west coast of India. The positive and negative phases of these oscillations are directly related to the active and dry spells of rainfall along the west coast of India. The spectral analysis shows interannual variation of TWV and SWS. Heavy rainfall events generally occur over the west coast of India when positive phases of both 30–60 days and 15–30 days modes of TWV and SWS are simultaneously present.


Spatial monsoon variability with respect to NAO and SO
S B Kakade*
and S S Dugam
Indian Institute of Tropical Meteorology, Pune 411 008, India.
*e-mail: kakade@tropmet.res.in

Abstract: In this paper, the simultaneous effect of North Atlantic Oscillation (NAO) and Southern Oscillation (SO) on monsoon rainfall over different homogeneous regions/subdivisions of India is studied.  The simultaneous effect of both NAO and SO on Indian summer monsoon rainfall (ISMR) is more important than their individual impact because both the oscillations exist simultaneously throughout the year. To represent the simultaneous impact of NAO and SO, an index called effective strength index (ESI) has been defined on the basis of monthly NAO and SO indices.
The variation in the tendency of ESI from January through April has been analyzed and reveals that when this tendency is decreasing, then the ESI value throughout the monsoon season (June– September) of the year remains negative and vice versa. This study further suggests that during the negative phase of ESI tendency, almost all subdivisions of India show above-normal rainfall and vice versa. The correlation analysis indicates that the ESI-tendency is showing an inverse and statistically significant relationship with rainfall over 14 subdivisions of India. Area wise, about 50% of the total area of India shows statistically significant association. Moreover, the ESI-tendency shows a significant relationship with rainfall over north west India, west central India, central north east India, peninsular India and India as a whole. Thus, ESI-tendency can be used as a precursor for the prediction of Indian summer monsoon rainfall on a smaller spatial scale.


Discriminating four tectonic settings: Five new geochemical diagrams for basic and ultrabasic
volcanic rocks based on log–ratio transformation of major-element data
Surendra P Verma1,*, Mirna Guevara1 and Salil Agrawal2
1Centro de Investigaci´on en Energ´ıa, Universidad Nacional Aut´onoma de M´exico, Priv. Xochicalco s/no.,
Col Centro, Apartado Postal 34, Temixco 62580, Mexico.
2Department of Geology, University of Rajasthan, Jaipur 302 004, India.
*e-mail: spv@cie.unam.mx

Abstract: We present five new discriminant function diagrams based on an extensive database representative of basic and ultrabasic rocks from four tectonic settings of island arc, continental rift, ocean-island, and mid-ocean ridge. These diagrams were obtained after loge-transformation of concentration ratios of major-elements – a technique recommended for a correct statistical treatment of compositional data. Higher % success rates (overall values from ~83 to 97%) were obtained for proposing these new diagrams as compared to those (~82 to 94%) obtained from the discriminant analysis of the raw major-element concentration data (i.e., without the loge-transformation and without taking ratios of the compositional data, but using exactly the same database to provide an unbiased comparison), suggesting that such a data transformation constitutes a statistically correct and recommended technique. The new diagrams also resulted in less mis-classification of basic and ultrabasic rocks from known tectonic settings than the diagrams obtained from the raw data. The use of these highly successful new discriminant function diagrams is illustrated using Miocene to Recent basic and ultrabasic rocks from three areas of Mexico with complex or controversial tectonic settings (Mexican Volcanic Belt, Los Tuxtlas volcanic field, and Eastern Alkaline Province), as well as older rocks from three areas (Deccan, Malani, and Bastar) of India. Additionally, the major-element data from two ‘known’ continental arc settings are used to show that they are similar to those from the island arc setting. Continental rift setting is inferred for all Mexican cases and for one cratonic area of India (Malani) and an IAB setting for the Bastar craton. The Deccan flood basalt province of India is used to warn against an indiscriminate use of those discrimination diagrams that do not explicitly include the likely setting of the area under evaluation. An Excel template is also provided for an easy application of these new diagrams for discriminating the four settings considered in this work.