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Indexed in Scopus Compendex and Geobase Elsevier, Chemical Abstract Services-USA, Geo-Ref Information Services-USA ISSN 0974-5904, Volume 05, No. 05

www.cafetinnova.org

October 2012, P.P. 1123-1128

Stable Isotope Systematics of Atmospheric Vapour at Hyderabad and Roorkee M. S. RAO1, GOPAL KRISHAN1, BHISHM KUMAR2, M. ANITHA3, B. KIRAN KUMAR3 and P. NAGABHUSHANAM3 1

National Institute of Hydrology, Roorkee-247667 (Uttarakhand) 2 Isotope Hydrology Section, IAEA, Vienna, Austria 3 CSIR-National Geophysical Research Institute, Hyderabad Email: drgopal.krishan@gmail.com

Abstract: Stable isotopes (δ18O and δD) of ground level atmospheric vapour (GLV) are used to identify long range spatial correlation in moisture variability between two geo-graphically and geo-climatically different places Roorkee in the foot hills of Siwaliks in the north western part of the Gangetic plains and Hyderabad in the Deccan Plateau of peninsular India. A very good isotopic correlation in atmospheric moisture and absolute humidity was observed during 2008-10 in southern and northern part of India due to common (Arabian Sea and Bay of Bengal) dominant moisture source to both the regions but their magnitude in the total moisture and time of onset and duration is different in both the regions. These components and their timings are also changing in the recent years. In southern India, these are appearing early while are getting delayed in northern India. The results on long range correlation in GLV help understanding monsoon dynamics and climate change. Keywords: Stable Isotopes; Atmospheric Vapour; Monsoon Dynamics; Arabian Sea; Bay of Bengal; IWIN Introduction: Atmospheric moisture is an important component in the water cycle. Its movement is controlled by source and sinks of moisture and atmospheric dynamics. It is brought into the region by the convergence of regional moisture advected into the area and is removed through process of transpiration and evaporation of surface water sources and soil moisture, which sometimes also influence the precipitation through a feedback loop and recycling of the moisture. Local moisture conditions change over the year depending upon the availability of the surface wetness, vegetation cover, landform and energy budget. Major flux of moisture on the Indian subcontinent comes through southwest monsoon (June to September), which transports large amount of moisture that arrives through Arabian Sea and Bay of Bengal branches (figure 1b). During other seasons the source of moisture is local/regional (figure 1a). About 70% of India’s food production and economy depends on southwest monsoon. The monsoon exhibit large variability in space and time and is attributed to parameters such as sea surface temperature, snow cover, soil moisture, global forcing etc. The space scale variability varies between as small as a rainfall region represented by rainfall recorded at a rain gauge station to the complete monsoon region. The time-scale varies from daily to

inter annual and to decades, centuries and even millennia.

Figure 1: Isotopic Data (δ18o), Water Vapour Data and Wind Trajectory (Source: Krishan et al, 2012a; www.Tropmet.Res.In/Ochamp/Extended_Abstracts/.../O C-000101.pdf) It is not possible to distinguish the sources of vapour through ground-based meteorological parameters (humidity, temperature etc.) or through chemical

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M. S. RAO, GOPAL KRISHAN, BHISHM KUMAR, M. ANITHA, B. KIRAN KUMAR and P. NAGABHUSHANAM analysis of water vapour, as whether originating from SW/NE monsoon, local vapour or due to Western Disturbance. However, as these vapours have differences in their relative isotopic composition (1H1H16O, 1H2H16O and 1H1H18O), therefore, isotopic composition of vapours can be used to distinguish and indentify their source [1] and timings of their arrival and departure at the site of observation [2]. Application of oxygen and hydrogen isotope ratios for tracing the hydrological cycle is based on simple principle that lighter isotopologues of H2O preferentially evaporate, whereas heavier isotopologues preferentially condense, resulting in characteristic isotopic composition in terms of abundance ratio of heavy to light isotopes (R = 18 O/16O or D/1H), expressed as δ in per mil (‰) units with reference to international standard [δ18Oor δD = (Rsample/Rstd – 1) x 1000]. Since vapours and rains have associated features, therefore,a proportionate change is expected in their isotopic composition whenever source of their origin changes. The advantage of monitoring vapour over rain is due to its all-time availability round the clock in almost everywhere. Department of Science and Technology, Government of India, initiated a National Programme on Isotope Fingerprinting of Waters in India in 2007. Under this programme, groundwater, surface water and atmospheric waters are being collected to get the first level nationwide isotopic data mapping of water

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resources of India [3, 4]. Under this, atmospheric moisture samples are being collected at Hyderabad, Andhra Pradesh (lat. 17022’, long. 78028’) and at Roorkee, Uttarakhand (lat. 29052’, long. 77053’). Geographically, these two locations are separated latitudinally (12.50) than longitudinally (0.580) and ,hence, were considered important in analyzing latitudinal vapour transport process especially with respect to process dependent phenomena, which can be monitored from their isotopic signatures. Identical procedure has been adopted for sample collection and isotopic analysis. The present study has been carried out to find out ground level vapour systematics at Roorkee and Hyderabad. Methodology: The condensed ground level air moisture samples for isotopic analyses are collected on daily basis by condensation method [5]. In this method, the air moisture sample is collected using the conical condensation device (figure 2). The conical condensation device comprises; (i) Aluminum cone; (ii) metallic stand for holding and vertically aligning the Aluminum cone at desired height; (iii) a lid with knob for covering the Aluminum cone; and (iv) a cylindrical wire-mesh cover for protecting the cone and the sample bottles.

Figure 2: Condensation Device for Collection of Air Moisture. The aluminum cone is aligned using the 8-screws provided for it, such that the tip of the cone is positioned just above the bottle and the droplets of the moisture condensed on the surface of the cone falls straight into

the bottle. A 5-ml sampling bottle is placed into the groove at the base of the stand and ensured that the bottle is open (stub and cap removed), completely inserted into the groove and not shaking freely. The ice

International Journal of Earth Sciences and Engineering ISSN 0974-5904, Vol. 05, No. 05, October 2012, pp. 1123-1128


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Stable Isotope Systematics of Atmospheric Vapour at Hyderabad and Roorkee

cubes are put into the cone up to the top, leaving little more space required for fixing the lid. The aluminum cone (filled with ice cubes and sealed by lid) in the stand is placed such that the axis of the aluminum cone is vertically aligned with the bottle placed in the groove. The position of the cone is adjusted such that the tip of the aluminum cone is centred at 0.5 cm above the mouth of the bottle. This will ensure that droplets of moisture condensing outside the aluminum cone can fall straight into the bottle and the falling droplets can be seen. Depending on prevalent relative humidity, it takes 30 minutes to 60 minutes for collecting 5 to 10 ml of liquid condensate. However, during the rainy season when relative humidity is very high, the sampling bottle is filled even within 30 minutes. After setting up the conical condensation device the date, time, temperature and relative humidity are recorded using thermohygrometer [5]. Stable isotopes (2H or D and 18O) in water have been analysed using GV-Isoprime Dual Inlet Isotope Ratio Mass Spectrometer. For δ D analysis, 400 µl of the water sample is equilibrated with H2 along with Pt catalyst at 40°C for 3 hrs. and the gas is introduced into the mass spectrometer. The δ 18O of the sample is measured by equilibrating 400 µl of water with CO2 gas at 40°C for 7 h and the equilibrated gas is introduced into the mass spectrometer. The measured values are reported as delta (δ) values [6]. The precision of measurement for δ 2H is ± 1‰ and that for δ 18O is ± 0.1‰. Results & Discussion: The time variation of isotopic composition of ground level atmospheric vapour (δD and δ18O) for the period from January, 2008 to December, 2010 observed at the stations Roorkee and Hyderabad is shown in the figure III. A very good correlation between the isotopic data of Roorkee and Hyderabad is found i.e. 72% for δ18O & 68% for δD. The time spectrum shows similar annual cyclic variation of isotopic composition of air moisture at both the stations with their troughs and crests appearing during July to September (which is monsoon period) and February to April, respectively. The overall variation in isotopic composition during an annual cycle is about 15‰ in δ18O and 60‰ in δD at Roorkee and approximately 10‰ in δ18O and 60‰ in δD at Hyderabad. It is unusual to get similar periodic isotopic pattern at both these stations that are geoclimatically well separated from each other. The sampling station Roorkee is located in the foot hills of Siwaliks in the north western part of the Gangetic plains whereas, Hyderabad is located in the Deccan Plateau of peninsular India which is well separated from Gangetic Plains by Vindhyans and hills of Satpura, Maikala, Gawaligarh, Ajantha etc. Therefore, it is unexpected to

get same moisture winds without any change in isotopic composition at Roorkee. Using the isotopic data on precipitation, Sengupta and Sarkar [7] inferred that monsoon vapours at Delhi contains about 20% vapours originating from Arabian Sea and the remaining from Bay of Bengal. Since Roorkee is located close to Delhi similar inference may also be attributed to Roorkee i.e, Roorkee receives moisture both from Bay of Bengal and Arabian Sea branch. The combination of Arabian Sea and Bay of Bengal moisture arriving at Roorkee is also apparent in the figure 1- b for the wind pattern of 4th August 2008. The sampling station Hyderabad is located between the Bay of Bengal and Arabian Sea coast and therefore it is also expected receives moisture from both of these surface water sources. Air mass isotopically gets lighter in its composition with the removal of heavy isotope fraction due to the rainout process along its wind track. With the progressive advancement inland and orographic heights the rain out process affects a continuous decrease in its heavy isotope fraction [8]. However, orographic and distance effect is partially nullified in the present case as Hyderabad is located at higher altitude (536 m above msl) than that at Roorkee (268 m above msl) but it is nearer to the sea coast (250 km from east coast and 540 km from west coast, respectively) than to Roorkee (1500 km from Bay of Bengal and 1150 km from Arabian Sea). As a combined effect of orography and inland distance from coast, the isotopic composition of vapour that reaches at Hyderabad after rain out at eastern and western ghats is almost equally depleted as that of the air mass that reaches at Roorkee after its rain out over Gangetic plain. It is also known that isotopic composition of rain at a given location also depends upon local temperature as it causes evaporation of falling rain drop. Further, the local humidity controls the dew point controlling the isotopic composition of condensing moisture. Since, temperature and relative humidity at Hyderabad and Roorkee during monsoon are in similar range they modulate the isotopic signal to a similar extent. Thus, due to common source of origin of air-moisture, similar amount of rain out amount and similar weather conditions during monsoon a similar variation in isotopes composition of air-mass is observed at these two places. On these predominant common features, local variability may be observed as minor variations in the two patterns. More important to the observation of similarity in isotopic signals at these two far off locations is that the isotopic data tracks the integrated history of moisture depletion and which may be used as a new tool in atmospheric dynamics. The previous research on isotopic measurement on rain water could not be used in monsoon and climate research as the rain based data is a non-continuous series and the

International Journal of Earth Sciences and Engineering ISSN 0974-5904, Vol. 05, No. 05, October 2012, pp. 1123-1128


M. S. RAO, GOPAL KRISHAN, BHISHM KUMAR, M. ANITHA, B. KIRAN KUMAR and P. NAGABHUSHANAM observations are event based whereas the air-moisture observations provides daily or even hourly data at any

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geographical location and which can be incorporated into a suitable model for weather & climate prediction.

Figure 3: Variation in Isotopic Composition (δ18O and δD) at Roorkee and Hyderabad (2008-10) One of the important differences between the two isotopic patterns is the observation of constantly depleting isotopic troughs at Roorkee from 2008 to 2010 which is not clearly seen in the isotopic pattern at Hyderabad. From pattern at 2010 it can be seen that at Hyderabad, depletion in isotopic composition stops after July and attained a value close to -20‰. But, at Roorkee this depletion continued till August and reached a value -25‰. In order to examine this aspect we compared absolute humidity (AH) and rainfall trends at these places (figure 4). The rainfall ranged from 0.31 to 660.3 mm at Roorkee (normal rainfall =1156.4 mm) with 92% occurring during SW monsoon (June to September) and at Hyderabad it ranged from 0.4 to 433 mm (normal rainfall = 828.5 mm) with 87% occurring during June to October. During monsoon period, the absolute humidity is also found to increase by approximately 42% at Roorkee and 28% at Hyderabad, as compared to the winter months (December-January).

Time variation spectrum of AH at Hyderabad and Roorkee shows almost similar features with a difference of baseline shift by 5g/m3 at Roorkee compared to that at Hyderabad. Comparison of figures 3 & 4 show that the periods of high AH at Roorkee and Hyderabad are related with the periods of depleted isotopic composition and this occurs between end of May to beginning of September, which covers entire monsoon from onset to withdrawal. Over the period from 2008 to 2010, although there is not much change in the integrated AH over a year, but, the peaks at Hyderabad appear to get shifted early (from 2008 to 2010) and at Roorkee the peak appears to get delayed during this period. For example; in 2008, AH in Hyderabad peaked during August and that at Roorkee during July whereas, in 2010, AH peaked in Hyderabad during July while that at Roorkee in August. It is probably due to late arrival of monsoon vapours at Roorkee than at Hyderabad (figure 5).

International Journal of Earth Sciences and Engineering ISSN 0974-5904, Vol. 05, No. 05, October 2012, pp. 1123-1128


Stable Isotope Systematics of Atmospheric Vapour at Hyderabad and Roorkee

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Figure 4: Variation in Absolute Humidity at Rookee and Hyderabad (2008-10)

Figure 5: Dates of (a) Monsoon Onset and (b) Withdrawal at Roorkee and Hyderabad (source: http://www.imd.gov.in/section/nhac/dynamic/Monsoon_frame.htm) The isotopic composition of vapour appeared to get depleted from 2008 to 2010 at Roorkee. These results clearly indicate changing climatic conditions from isotopic [9] and absolute humidity spectrum of recent years .Such a change supports the need to analyze atmospheric dynamics of India separately for southern and northern India. Conclusions: To summarize, isotopic correlation in atmospheric moisture and absolute humidity variation in southern and northern part of India shows multiple sources of origin of moisture. The origin of dominant sources of moisture is although common (Arabian Sea and Bay of Bengal) to both the regions but their magnitude in the total moisture and time of onset and duration is different

in both the regions. These components and their timings are also changing in the recent years. In southern India, these are appearing early while are getting delayed in northern India. Timings and quantitative estimates of these components may be examined through developing a national level network of stations. A detailed analysis using such network data may provide new insight into monsoon and climate dynamics. Acknowledgements: The work was carried out under the project “National Programme on Isotope Fingerprinting of Waters of India� and authors are thankful to DST-SERC (Funded by DST vide IR/54/ESF/05-2004 dated July17, 2007) for sponsoring the study. Dr M. Mohanty (DST) for his consistent and timely cooperation during the tenure of

International Journal of Earth Sciences and Engineering ISSN 0974-5904, Vol. 05, No. 05, October 2012, pp. 1123-1128


M. S. RAO, GOPAL KRISHAN, BHISHM KUMAR, M. ANITHA, B. KIRAN KUMAR and P. NAGABHUSHANAM this project. The comments and useful suggestions from the unknown reviewers are duly acknowledged. References: [1] Krishan, Gopal, Rao, M. S. and Kumar, Bhishm., 2012a. Identification of Sources of Atmospheric Vapour using Isotopic Signature of Air Moisture at Roorkee, Uttarakhand, India. Paper presented in an International conference on “Opportunities and Challenges in Monsoon Prediction in a Changing Climate" (OCHAMP-2012), Pune, India, 21-25 February 2012 at IITM, Pune. www.tropmet.res.in/ochamp/extended_abstracts/.../ OC-000101.pdf [2] Krishan, Gopal, Rao, M.S., Jaiswal, R.K. and Kumar, Bhishm. 2012c. Observation of monsoon dynamics between Roorkee and Sagar using isotopic techniques. Paper presented in a National Seminar on “Application of isotopes & radiation technology for societal benefits (AIRTS-2012)”, 21-23 June, 2012 at Bangalore University, India, 47. [3] Gupta, S. K. and Deshpande, R. D., 2005. The Need and Potential Applications of a Network for Monitoring of Isotopes in Waters of India, Current Science, 88, 107-118. [4] Deshpande, R.D. and Gupta, S.K., 2008, National programme on isotope fingerprinting of waters of

[5]

[6]

[7]

[8] [9]

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India (IWIN). In Glimpses of Geosciences Research in India, the Indian Report to IUGS Indian National Science Academy, Singhvi, A. K., Bhattacharya, A, Guha, S. (eds). Indian National Science Academy: New Delhi, 10–16. Krishan, Gopal, Rao, M. S. and Kumar, Bhishm, 2011. Instrumentation for measurement of isotopic composition of air moisture, Journal of Instrument Society of India, v. 41, 217-220. Coplen, T. B., 1996. New guidelines for reporting stable hydrogen, carbon, and oxygen isotope-ratio data, Geochim Cosmochim Acta, 60, 3359–3360. Sengupta, S. and Sarkar, A., 2006. Stable isotope evidence of dual (Arabian Sea and Bay of Bengal) vapour sources in monsoonal precipitation over north India: Earth and Planetary Science Letters, v. 250, p. 511–521. Clark, I.D. and Fritz, P., 1997. Environmental Isotopes in Hydrogeology: Boca Raton, Lewis, 328. Krishan, Gopal, Rao, M. S. and Kumar, Bhishm., 2012b. Study of climatological conditions using isotopic signature of air moisture at Roorkee, Uttarakhand, India. Paper presented in an International conference “India Water Week 2012Water Energy and Food Security: Call for Solutions" (IWW-2012), 10-14 April 2012 at New Delhi, India, 231-232. India water week. water. tallyfox.com/filefield-private/files/.../5516

International Journal of Earth Sciences and Engineering ISSN 0974-5904, Vol. 05, No. 05, October 2012, pp. 1123-1128

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