Proceedings of the Kanyakumari Academy of Arts and Sciences Physics O 7 TOTAL COLUMNAR OZONE CONTENT OVER NAGERCOIL DATA SMOOTHING AND ANALYSIS

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1 Proceedings of the Kanyakumari Academy of Arts and Sciences Physics O 7 TOTAL COLUMNAR OZONE CONTENT OVER NAGERCOIL DATA SMOOTHING AND ANALYSIS K.ELAMPARI *, T.CHITHAMBARATHANU, R.KRISHNA SHARMA Department of Physics, S.T. Hindu College, Nagercoil ABSTRACT This study reports observations of the total columnar ozone (TCO) over Nagercoil (8 11' N, 77 29' E) for the period from December 2004 to July The TCO data is obtained from the Ozone Monitoring Instrument (OMI) on the Aura spacecraft of NASA. The total number of data set used is 2 11 (=2048). The data set is smoothed using Fast Fourier Transform (FFT) and is compared with observed ones. The mean value of ozone concentration from the observed data is DU, its standard deviation is 13.24DU and its range is 77DU. The FFT smoothed data set is used in the seasonal analysis of TCO. High variability of the TCO is registered in the year The monthly mean values of TCO marked a clear seasonal variation with a maximum around June or July (~288 DU) and a minimum around December or January (~242 DU). It is found that the total average TCO of this region is 261±10.61 DU. TCO for this region shows a slight downward trend. Keywords: Total Columnar Ozone (TCO), OMI, FFT Corresponding Author: K.Elampari, elampari@rediffmail.com Introduction Ozone (O3) is one of the most extensively measured trace gases in the atmosphere and is the key trace constituent that participates in the chemistry and radiation of the earth s middle atmosphere (Meena GS & Jadhav D B). A decrease in stratospheric ozone will result in an increase in ultraviolet B radiation, which will have negative impacts on human health. Total ozone refers to the total amount of ozone contained in a vertical column in the atmosphere above the ground extending (87%) and in the Troposphere (10%) has a measurable effect on the total ozone column. The conceptual "ozone layer" is not some delicate, static and fragile wrapping about the outer atmosphere but rather a dynamic and highly volatile component, both created and destroyed by solar radiation. The amount of ozone in the Troposphere and lower Stratosphere in general depends on both dynamics and chemistry. The dynamical influences include wave driving of the stratospheric circulation from the earth s surface to the upper edge of the atmosphere. The integral of the ozone profile from the ground to the top of the atmosphere is the total columnar ozone (TCO) and it varies with season and altitude (WMO, 2008). The amount of ozone in the upper stratosphere (above 40kms) is about 3% of the total ozone. Thus the variations occurring above 40 kms have little measurable effect on the total ozone column. The variation of ozone in the lower Stratosphere where its density is maximum and Tropopause folds. The chemistry part includes the photochemical production and destruction of O3 (Nandita & Iyer,2005). The standard way to express total ozone levels (the amount of ozone in a vertical column) in the atmosphere is by using Dobson units (DU). The mean total ozone amount in the atmosphere is about 299 DU when average over the globe. It varies geographically and seasonally and is a minimum, slightly less than 260DU at equatorial latitudes and increases pole ward

2 Proceedings of the Kanyakumari Academy of Arts and Sciences Physics O 8 in both hemispheres to a maximum of about 400DU at sub polar latitudes (Anna Mani, 1993). Over the years, variations of total ozone are found to be influenced by many parameters ; solar UV flux changes, quasibiennial oscillation(qbo), El Ninosouthern oscillation (ENSO) and atmospheric increases in CH4, N2O and CFCs (Kuang-Jung & Ling Yung, 1999). Ozone creation and destruction both cause variation in ozone levels. Ozone creation is dependent on the supply of solar UV radiation. Any variations of this supply could result in variations in ozone (Hosseinian & Gough, 2000). In this study, we investigate the characteristics of the TCO over Nagercoil (8 11' N, 77 29' E), India for the period from December 2004 to July The climate of this region is divided into four seasons. The winter season extends from January to February followed by Summer from March to May, Southwest monsoon from June to September and North East Monsoon from October to December. DATA The TCO over entire globe is continuously measured by the Ozone Monitoring Instrument (OMI) on the Aura spacecraft of NASA. Aura is part of the Earth Science Projects Division, a program dedicated to monitoring the complex interactions that affect the globe using NASA satellites and data systems. OMI continues the TOMS record for total ozone and other atmospheric parameters related to ozone chemistry and climate. The TCO for the period from December 2004 to July 2010 is obtained from OMI. Data Smoothing Using Fourier Transforms. In statistics, to smooth a time series data set is to create an approximating function that attempts to capture important patterns in the data, while leaving out noise or other finescale structures/rapid phenomena. The use of Fourier analysis allows the detection of variations from daily through seasonal and inter annual time scales (Elson et al.., 1994). A time series data h(t) can be converted to frequency spectrum H(f) by means of Fourier Transform. Selected parts of the frequency spectrum H(f) can easily be subjected to piecewise mathematical manipulations (attenuated or completely removed). These manipulations result into a modified or "filtered" spectrum HΜ(f). By applying inverse Fourier transform HΜ(f) the modified signal or "filtered" signal hμ(t) can be obtained. Therefore, signal smoothing can be easily performed with removing completely the frequency components from a certain frequency and up, while the useful (information bearing) low frequency components are retained. The Fourier transform creates a vector of complex numbers consisting of real and imaginary parts. The real part of the complex number provides information about the amplitudes and frequencies in terms of cosine functions and the imaginary part provides the same information in terms of sine functions (Peter Bloomfield, 2000). In this work, FFT is used to separate the seasonal components of TCO from the dayto-day variations. Analysis of TCO Figure 1 is the plot of the daily TCO values obtained for the study region from the OMI. The mean ozone concentration value from the observed data is DU, its standard deviation is 13.24DU and its range is 77DU. For FFT smoothed data, mean, standard deviation and range are DU, DU and DU respectively. The FFT smoothed TCO data is then used in the subsequent analysis and is represented in figure 2. It shows a clear seasonal variation that is repeated consistently year after year. The maxima, minima, mean and rate of change of TCO are tabulated in table 1. The monthly mean TCO values for the entire study period are

3 Dec-04 Mar-05 May-05 Aug-05 Nov-05 Feb-06 May-06 Aug-06 Nov-06 Feb-07 May-07 Aug-07 Nov-07 Feb-08 May-08 Aug-08 Nov-08 Feb-09 May-09 Aug-09 Nov-09 Feb-10 May-10 TCO (DU) Proceedings of the Kanyakumari Academy of Arts and Sciences Physics O 9 plotted against months and is shown in figure 3. The ozone concentration is found to increase in summer followed by winter. The primary cause of large increase in the values of ozone in summer is due to the high solar flux during the season. Since the lower stratospheric ozone is effectively shielded from UV radiation during southwest monsoon, the level of ozone is almost constant in June, July and August. It decreases during north east monsoon and reaches a minimum in December-January. It is because the atmospheric circulation is such that it transports ozone from low latitudes to poles. Thereafter it gradually increases throughout the summer and reaches a peak. This trend is consistently observed in all the years from 2005 to 2010 (as shown in Fig.1). Kulkarni et al., (1959) have observed similar results for the nearby station Kodaikanal. Studies reveal that wind transport of ozone is principally responsible for the seasonal variations of latitude dependent ozone patterns.the distribution of the ozone at different locations in the Indian subcontinent results in an earlier peak ozone concentration at higher latitudes compared to lower latitudes. It may be due to the reverse Hadley cell circulation and this circulation is such that it transports ozone during winter from low latitudes to poles. This transport is responsible for summer maxima at higher latitudes and is less rapid during summer, and the maxima gradually decays and moves to lower latitudes (Nandita & Iyer, 2005). Singh, Sarkar & Singh (2002) have reported an increasing trend in columnar ozone for the period for Kodaikanal and Delhi, which matches with the observations for Rajkot as reported by Nandita & Iyer (2005). But in this current observation, a slight downward trend in the TCO is observed. TCO (DU) Fig 1. Total Columnar Ozone for the period from 2005 to 2010 Days Fig 2. Fourier filtered TCO content Table 1. Monthly Maximum, Minimum, Mean and Rate of Change of TCO for the period Month Maximum Minimum Mean ± DEC Days y = x Rate of change (DU/Month) JAN ± FEB ± MAR ± APR ± MAY ± JUN ± JUL ± AUG ± SEP ± OCT ± NOV ± ±

4 JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC TCO ( DU) Proceedings of the Kanyakumari Academy of Arts and Sciences Physics O Months Fig 3. Monthly mean TCO The following is the summary of the characteristics of TCO in the study region. High variability of the TCO content is registered for The monthly mean values of TCO marked seasonal variation with a maximum around June or July (~288 DU) and a minimum around December or January (~242 DU).The total average ozone value is 261±10.61 DU. From table 1, it is clear that the rate of increase of TCO is the largest in Summer (6.66 DU/Month), the smallest in South west monsoon (0.39 DU/Month). The rate of decrease in the TCO is pronounced during North East monsoon (8.9 DU/Month). Acknowledgement The TCO data used in this study is obtained from TOMS- OMI online data Anna Mani (1993), Ozone in the Tropics, Current Science,VOL.64, no.5,10 March1993. Elson L S, Gloria L Manney, Lucien Froidevaux, Joe Waters W (1994), Large-Scale Variations in Ozone from the First Two Years of UARS MLS Data. J. Atmos. Sci., 51, Hosseinian R and Gough A (2000), Total Column Ozone Variability Over Toronto, Ontario, Canada, The Great Lakes Geographer, Vol. 7, No Kuang-Jung Hsu and Yuk Ling Yung (1999), Ozone trend over Taiwan from TOMS data, TAO, Vol.10, No Kulkarni, R N, Angreji P D, Ramanathan K R, (1959),Comparison of ozone amounts measured at Delhi (28 1/2 ) Srinagar (34 ) and Tateno (36 ) in , Atmospheric References system, developed and maintained by the NASA. The authors are grateful to Aura Validation Data Center (NASA) for providing OMI data. Conclusion In this study, the amount of TCO is found to be higher in even years than that of odd years. This may be due to the periodic quasi-biennial oscillation (QBO) of the equatorial zonal wind in the tropical stratosphere with a mean period of 28 to 29 months. Year 2006 records a maximum value of TCO. A well defined seasonal maxima and minima occurred. Seasonal maxima varied between June and July, and minima between December and January. The variations in the TCO would be caused by chemical and dynamic destruction processes related to the temperatures and photochemical reactions due to solar radiation. For the entire study period, a slight downward trend is observed in the TCO but not below 220 DU, a condition of ozone hole. Ozone, Proceedings of the Symposium held July, 1969 in Oxford. Meena G S, Jadhav D B, (2007), Study of diurnal and seasonal variation of atmospheric NO2,O3 H2O and O4 at Pune, India, Atmosfera 20(3), Nandita D Ganguly and Iyer K N (2005), Study of variations in Columnar Ozone Concentration at Rajkot, J. Ind. Geophys. Union, Vol.9, No.3, pp Peter Bloomfield, 2000, Fourier Analysis of Time Series. An Introduction, John Wiley & Sons,Inc. WMO, WMO Guide to Meteorological Instruments and Methods of observation WMO-No. 8 (2008).

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6 Proceedings of the Kanyakumari Academy of Arts and Sciences Physics O 12 Personal References Meena G S, Jadhav D B, (2007), Study of diurnal and seasonal variation of atmospheric NO2,O3 H2O and O4 at Pune, India, Atmosfera 20(3), (Book E,P52) Nandita D.Ganguly and K.N.Iyer (2005), Study of variations in Columnar Ozone Concentration at Rajkot, J. Ind. Geophys. Union, Vol.9, No.3, pp (Fn: 4nandita.pdf) Anna Mani (1993), Ozone in the Tropics,Current Science,VOL.64,no.5,10 March1993 ( File: pdf) Kuang-Jung Hsu and Yuk Ling Yung (1999), Ozone trend over Taiwan from TOMS data,, TAO, Vol.10, No (File: N121Hsu_1999.pdf) Hosseinian R and Gough A (2000), Total Column Ozone Variability Over Toronto, Ontario, Canada, The Great Lakes Geographer, Vol. 7, No (FN: HosseinianGough.pdf)

7 Proceedings of the Kanyakumari Academy of Arts and Sciences Physics O 13 Peter Bloomfield, 2000, Fourier Analysis of Time Seris. An Introduction, John Wiley & Sons,Inc. 2. Book E, page Riley, K.F., M.P. Hobson and S.J. Benice, Mathematical Methods for Physics and Engineering.,Cambridge University Press, U.K. WMO GUIDE TO METEOROLOGICAL INSTRUMENTS AND METHODS OF OBSERVATION WMO-No. 8 (2008), WMO (6 August 2008) a. Switzerland Kulkarni, R N, Angreji P D, Ramanathan K R, (1959),Comparison of Ozone Amounts Measured at Delhi (28 1/2 ) Srinagar (34 ) and Tateno (36 ) in , Atmospheric Ozone, Proceedings of the Symposium held July, 1969 in Oxford. Elson L S, Gloria L Manney, Lucien Froidevaux, Joe Waters W (1994), Large-Scale Variations in Ozone from the First Two Years of UARS MLS Data. J. Atmos. Sci., 51,

8 Proceedings of the Kanyakumari Academy of Arts and Sciences Physics O 14 File: pdf Day-to-day