ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-10-8563-2010 Temperature variability and trends in the UT-LS over a subtropical site: Reunion (20.8° S, 55.5° E) Bègue N. 1 Bencherif H. 1 Sivakumar V. 2 3 Kirgis G. 1 Mze N. 1 Leclair de Bellevue J. 1 Laboratoire de l'Atmosphère et des Cyclones, UMR 8105 CNRS, Université de la Réunion, Reunion Island, France National Laser Centre (NLC), Council for Scientific and Industrial Research, Pretoria, South Africa Department of Geography, Geo-informatics and~Meteorology, University of Pretoria, Pretoria, South Africa 13 09 2010 10 17 8563 8574 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/10/8563/2010/acp-10-8563-2010.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/10/8563/2010/acp-10-8563-2010.pdf

This paper mainly focuses on the trends and variability of the UT-LS temperature using radiosonde observations carried out over 16 years (January 1993 to December 2008) from a southern subtropical site, Reunion (20.8° S, 55.5° E), using a linear-regression fitting model. Two kinds of tropopause definitions, namely, cold point tropopause (CPT) and lapse rate tropopause (LRT) are used. In order to characterize and quantify the relationship between regional oceanic forcing and temperature at UT-LS, we took into account the Indian Ocean Dipole (IOD) for the estimation of temperature trends. Results show that the main component is the Annual Cycle (AC), particularly at tropopause (CPT, LRT) and in the lower stratosphere (LS) where more than 26.0±2.4% of temperature variability can be explained by AC. The influence of IOD on the variability of the temperature is at highest ratio at CPT and LS, with respectively 12.3±7.3% and 13.1±5.9%. The correlations between IOD and temperature anomalies at UT-LS are barely significant, which are found to be in close agreement with the results obtained by Rosenlof et al. (2008) over the western tropical Pacific Ocean. The temperature trend in the LS reveals a cooling of about −0.90±0.40 K per decade. The cooling trend at LS is found to be in close agreement with the others studies. Trend estimates in the LS suggest that IOD forcing contributes to increasing cooling by about 0.16±0.05 K per decade. Past works have shown that the additional carbon dioxide increase has a minor effect in the LS, and suggested that other effects than ozone and carbon dioxide changes have to be considered, in order to explain the observed temperature changes in the LS. From this study, we can suggest that the SST changes can be considered also, in addition to effects due to ozone and carbon dioxide changes, in order to explain the observed temperature changes in the LS. As a consequence, our results support the assumption that the Indian Ocean may have a slight impact on temperature variability and on temperature change in the LS over Reunion.

 References Angell, J. K.: Variations and trends in tropospheric and stratospheric global temperatures, 1958–87, J. Climate, 1(12), 1296–1313, 1988. Baray, J.-L., Ancellet, G., Taupin, G., Bessafi, M., Baldy, S., and Keckhut, P.: Subtropical tropopause break as a possible stratospheric source of ozone in the tropical troposphere, J. Atmos. Sol.-Terr. Phys., 60, 27–36, 1998. Behera, K. S. and Yamagata, T: Influence of the Indian Ocean Dipole on the Southern Oscillation, J. Meteorol. Soc. Jpn., 81(1), 169–177, 2002. Bencherif, H., Portafaix, T., Baray, J. L., Morel, B., Baldy, S., Leveau, J., Moorgawa, A., Michaelis, M. M., Hauchecorne, A., Keckhut, P., and Diab, R.: LIDAR observations of lower stratosphericaerosols over South Africa linked to large scale transport across the southern subtropical barrier, J. Atmos. Sol.-Terr. Phys., 65, 707–715, 2003. Bencherif, H., Diab, R., Portafaix, T., Morel, B., Keckhut, P., and Moorgawa, A.: Temperature climatology and trend estimates in the UTLS region as observed over a southern subtropical site, Durban, South Africa, Atmos. Chem. Phys., 6, 5121–5128, 2006. Clain, G., Baray, J.-L., Delmas, R., Diab, R., Leclair de Bellevue, J., Keckhut, P., Posny, F., Metzger, J. M., and Cammas, J. P.: Tropospheric ozone climatology at two southern Hemisphere tropical/subtropical site, (Reunion Island and Irene, South Africa) from ozone sondes, LIDAR, and in situ aircraft measurements, Atmos. Chem. Phys., 9, 1723–1734, 2009. Finger, F. G., Nagatani, R. M., Gelman, M. E., Long, C. S., and Miller, A. J: Consistency between variations of ozone and temperature in the stratosphere, Geophys. Res. Lett., 22, 3477–3480, 1995. Gaffen, D. J: Historical changes in radiosonde instruments and practices, WMO/TD-No: 541, Instruments and Observing Methods Report 50, World Meteorological Organisation, 123 pp., 1993. Gaffen, D.J: A digitized metadata set of global upper-air station histories, NOAA Tech. Memo. ERL-ARL 211, Silver Spring, MD, 38 pp., 1996. Guirlet M., Keckhut, P., Godin, S., and Megie, G.: Description of the long-term ozone data series obtained from different instrumental techniques at a single location: the Observatoire de Haute-Provence (43.9° N, 5.7° E), Ann. Geophys., 18, 1325–1339, doi:10.5194/angeo-18-1325-2000, 2000. Hauchecorne, A., Chanin, M. L., and Keckhut, P.: Climatology and trends of the middle atmospheric temperature (33–37 km) as seen by Rayleigh lidar over the south of France, J. Geophys. Res., 96, 15297–15309, 1991. Holton, J. R., Haynes, P. H., McIntyre, M. E., Douglass, A. R., Rood, R. B., and Pfister, L.: Stratosphere-troposphere exchange, Rev. Geophys, 33, 403–439, 1995. Izumo, T., Valariad, J., Lengaigne, M., Boyer Montegut, C., Behera, K., Luo, J.-J., Cravatte, S., Masson, S., and Yamagata, T: Influence of the state of the Indian Ocean Dipole on the following year's El Niño, Nat. Geosci., 168–172, doi:10.1038/NGEO 760, 2010. Keckhut, P., Hauchecorne, A., and Chanin, M. L.: Midlatitude long-term variability of the middle atmosphere: Trends and cyclic and episodic changes, J. Geophys. Res, 100(D9), 18887–18897, 1995. Kerzenmacher, T. E., Keckhut, P., Hauchecorne, A., and Chanin, M.-L: Methodological uncertainties in multi-regression analyses of middle-atmospheric data series, J. Environ. Monit, 8, 682–690, 2006. Langematz, U., Kunze, K., Krüger, K. M., Labitze, K., and Roff, G. L: Thermal and dynamical changes of stratosphere since 1979 and their link to ozone and CO2 changes, J. Geophys. Res, 108(D1), 4027, doi:10.1029/2002JD002069, 2003. Logan, J. A: Trends in vertical distribution of ozone: An analysis of ozonesonde data, J. Geosphys. Res., 99(D12), 25553–25586, 1994 Li, T., Leblanc, T., and McDermid, I. S.: Interannual variations of middle atmospheric temperature as measured by the JPL lidar at Mauna Loa Observatory, Hawaii (19.5° N, 155.6° W), J. Geophys. Res., 113, D14109, doi:10.1029/2007JD009764, 2008. McCormick, P., Thomason, L. W., and Trepte, C. R.: Atmospheric effects of the Mt Pinatubo eruption, Nature, 373, 399–404, 1995. Morioka, K., Tomoki, T. and Yamagata, T: Climate variability in the southern Indian Ocean as revealed by self-organizing maps, Clim. Dynam., doi:10.1007/s00382-010-0843-x, 2010. Mote, P. W., Rosenlof, K. H., McIntyre, M. E., Carr, E. W., Gille, J. C., Holton, J. R., Kinnersley, J. S., Pumphrey, H. C., Russell III, J. M., and Waters, J. W.: An atmospheric tape recorder: the imprint of tropical tropopause temperatures on stratospheric water vapor, J. Geophys. Res., 101, 3989–4006, 1996. Naujokat, B.: An update of the observed quasi-biennale oscillation of the stratospheric wind over the tropic, J. Atmos. Sci., 43, 1873–1877, 1986 Oort, A. H. and Liu, H.: Upper-air temperature trends over the globe, 1958–1989, J. Clim., 6, 292–307, 1993. Pan, L. L, Randel, W. J., Gary, B. L., Mahoney, M. J.,, and Hinsta, E. J: Definitions and sharpness of the extratopical tropopause: A trace gas perspective, J. Geophys. Res., 109, D23103, doi.10.1029/2004JD004982, 2004. Parker, D. E.: On the detection of temperature changes induced by increasing atmospheric carbon dioxide, Q. J. Roy. Meteor. Soc., 111, 587–601, 1985. Parker, D. E. and Cox, D. I: Towards a consistent global climatological rawinsonde data-base, Int. J. Climatol., 15, 473–496, 1995. Parker, D. E., Gordan, M., Cullum, D. P. N., Sexton, D. M. H., Folland, C. K., and Rayner, N.: A new global gridded radiosonde temperature database and recent temperature trends, Geophys. Res. Lett., 24, 1499–1502, 1997. Pastel, M., Goutail, F., Pazmiño, A., Pommereau, J. P., and Held, G.: Proceedings of Reunion Island International symposium, 143-146, 2007. Pitari, G., Palermi, S. and Visconiti, G : Ozone response to a CO2 doubling: Results from a stratospheric circulation model with heterogeneous chemistry, J. Geophys. Res., 97(D5), 5953–5962, 1992. Politowitcz, P. A. and Hitchman, M. H : Exploring the effect of forcing quasi-biennal oscillations in a two model, J. Geophys. Res., 102, 16481–16497, 1997. Posny, F., Metzger, J. M., and Baray, J. L.: A successful change at la Reunion Island station (21° S, 55.5° E), SHADOZ Newsletter, No. 11, 2010. Ramaswamy, V., Chanin, M.-L., Angell, J., Barnett, J., Gaffen, D., Gelman, M., Keckhut, P., Koshelkov, Y., Labitzke, K., Lin, J.-J. R., O'Neill, A., Nash, J., Randel, W., Rood, R., Shine, K., Shiotani, M., and Swinbank, R.: Stratospheric temperature trends: observations and model simulations, Rev. Geophys., 39(1), 71–122, 2001. Randel, W. J. and Cobb, J. B.: Coherent variations of monthly mean column ozone and lower stratospheric temperature, J. Geophys. Res., 99(D3), 5433–5447, 1994. Randel, W. J., Wu, F., and Gaffen, D. J : Interannual variability of the tropical tropopause derived from radiosonde data and NCEP reanalyses, J. Geophys. Res., 105, 15509–15523, 2000. Randel, W. J., F. Wu, Oltmans, S. J., Rosenlof, K. H., and Nedoluha, G. E: Interannual changes of stratospheric Water vapour and correlations with tropical tropopause temperature, J. Atmos. Sci., 61, 2133–2148, 2004. Randel, W. J, Wu, F., Vomel, H., Nedoluha, G. E., and Forster, P : Decreases in stratospheric water vapour after 2001: Links to changes in the tropical tropopause and the Brewer-Dobson circulation, J. Geophys. Res., 111(D12), D12312, doi:10.1029/2005JD006744, 2006. Randel, W. J, Shine, K. S, Austin, J., Barnett, J., Claud, C., Gillett, N. P., Keckhut, P., Langematz, U., Lin, R., Long, C., Mears, C., Miller, A., Nash, J., Seidel, D. J, Thompson, D. W. J, Wu, F., Yoden, S.: An update of observed stratospheric temperature trends, J. Geosphys. Res., 114, D02107, doi:10.1029/2008JD010421, 2009. Reid, G. C. and Gage, K. S.: On the annual variation in height of the tropical tropopause, J. Atmos. Sci., 38, 1928–1938, 1981. Reid, G. C. and Gage, K. S: Inter-annual Variations in the height of the tropical tropopause, J. Geophys. Res., 90(D3), 5629–5635, 1985. Rosenlof, K. H., Kley, D., Russell III, J. M, Chiou, E. W, Johnson, D. G, Kelly, K. K., Michelsen, H. A., Nedohula, G. E., Remsberg, E. E., Toon, G. C., and McCormick, M. P.: Stratospheric water vapour increases over the past half century, Geosphys. Res. Lett., 28, 1195–1199, 2001. Rosenlof, K. H. and Reid, G. C.: Trends in the temperature and water vapor content of the tropical lower stratosphere: Sea surface connection, J. Geophys. Res., 113, D06107, doi:10.1029/2007JD009109, 2008. Saji, N. H., Goswami, B. N., Vinayachandran, P. N., and Yamagata, T.: A dipole mode in the tropical Indian Ocean, Nature, 401, 360–363, 1999. Seidel, D. J., Ross, R. J., and Angell, J. K.: Climatological characteristics of the tropical tropopause as revealed by radiosonde, J. Geophys. Res., 106, 7857–7878, 2001. Sivakumar, V., Baray, J. L., Baldy, S., and Bencherif, H.: Tropopause characteristics over a southern subtropical site, Reunion Island (21° S, 55° E): Using radiosonde-ozonesonde data, J. Geophys. Res., doi:10.1029/2005JD006430, 2006. Sivakumar, V, Portafaix, T., Bencherif, H., Godin-Beekmann, S. and Baldy, S: Stratospheric ozone climatology and variability over a southern subtropical site: Reunion Island (21° S; 55° E), Ann. Geophys., 25, 2321–2334, doi:10.5194/angeo-25-2321-2007, 2007. Sorensen, J. H. and Nielsen, N. W.: Intrusion of stratospheric ozone to the free troposphere through tropopause folds-A case study, Phys. Chem. Earth (B), 26, 801–806, 2001. Tiao, G. C., Daming, X., Pedrick, J. H., Xiaodong, Z., and Reinsel, G. C.: Effect of autocorrelation and temporal schemes on estimates of trend and spatial correlation, J. Geophys. Res., 95, 20507–20517, 1990. Thompson, A. M., Witte, J. C., McPeters, R. D., Oltmans, S. J., Schmidlin, F. J., Logan, J. A., Fujiwara, M., Kirchhoff, V. W. J. H., Posny, F., Coetzee, G. J. R., Hoegger, B., Kawakami, S., Ogawa, T., Johnson, B. J., Vömel, H., and Labow, G : Southern Hemisphere Additional Ozonesondes (SHADOZ) 1998–2000 tropical ozone climatology: 1.Comparison with Total Ozone Mapping Spectrometer (TOMS)and ground-based measurements, J. Geophys. Res., 108(D2), 8238, doi:10.1029/2001JD000967, 2003 Thompson, A. M., Witte, J. C., Oltmans, S. J., Schmidlin, F. J., Logan, J. A., Fujiwara, M., Kirchhoff, V. W. J. H., Posny, F., Coetzee, G. J. R., Hoegger, B., Kawakami, S., Ogawa, T., Fortuin, J. P. F., and Kelder, H. M.: South Hemisphere Additional Ozonesondes (SHADOZ) 1998–2000 tropical ozone climatology: 2.tropospheric variability and the zonal wave-one, J. Geophys. Res, 108(D2), 8241, doi:10.1029/2002JD002241, 2003. Thompson, A, Witte, J. C., Herman, G. J., Oltmans, S. J., Johnson, B. J., Volker W. J., Kirchoff, V. W. J. H., and Schmidlin, F. J.: Soutern Hemisphere Additionnal Ozonesonde (SHADOZ) 1998-2004 tropicale ozone climatology: 3. Instrumentation, station to station variability, and evaluation with simulated flight profiles, J. Geophys. Res., 112(D3), D03304,, doi:10.1029/2005JD007042, 2007. Weatherhead, E. C., Reinsel, G. C., Tiao, G. C., Meng, X., Choi, D., Cheang, W., Keller, T., DeLuis, J., Wuebbles, D. J., Kerr, J. B, Miller, A. J, Oltmans, S. J., and Frederick, J. E.: Factor affecting the detection of trends: Statistical considerations and application to environmental data, J.Geophys.Res., 103(D14), 17149–17161, 1998. WMO: A three dimensional science: Second session of the commission for aerology, WMO bull, IV, (4), 134–138, 1957. WMO: Scientific assessment of ozone depletion: 1994, Global Ozone Res. Monit. Proj., Rep. 37, 1995. WMO: Scientific assessment of ozone depletion: 2006, Global Ozone Res. Monit. Proj., Rep. 50, 2007. Yamagata, T., Behera, S. K., Luo, J. J, Masson, S., Jury, M. R., and Rao, S. A: Coupled Ocean-Atmosphere Variability in the Tropical Indian Ocean., American Geophysical Union Book Ocean-Atmosphere Interaction and Climate Variability, Washington DC, USA, 189–212, 2004.