Advances in Science and Research www.adv-sci-res.net 1992-0628 1992-0636 2 7th EMS Annual Meeting and 8th European Conference on Applications of Meteorology 2007 2008 10.5194/asr-2-139-2008 http://www.adv-sci-res.net/2/139/2008/ http://www.adv-sci-res.net/2/139/2008/asr-2-139-2008.html http://www.adv-sci-res.net/2/139/2008/asr-2-139-2008.pdf 139 143 2008-07-18 Mesoscale heat waves induced by orography I. Gladich I. Gallai D. B. Giaiotti Gp. Mordacchini A. Palazzo F. Stel fulvio.stel@arpa.fvg.it ARPA CRMA – Regional Center for Environmental Modelling, via Cairoli 14, 33057 Palmanova, Italy ICTP – the "Abdus Salam" International Centre for Theoretical Physics, Miramare, Trieste, Italy CNMCA – Centro Nazionale di Meteorologia e Climatologia Aeronautica, Pratica di Mare, 00040 Rome, Italy This work is devoted to the analysis of an unusual and sudden thermal fluctuation that interested portions of Friuli Venezia Giulia (Italy) during the night of 27 July 1983. The whole 1983 summer was extremely warm in Europe and in particular on the Italian peninsula, from the Alps down to Sicily. Nevertheless, the day of 27 July 1983 in Friuli Venezia Giulia deserves special attention because the observed maximum temperatures did not occur during day-time but during night-time (from 23:00 up to 24:00 LT, 21:00–22:00 UTC). Peaks of 34.8°C and values of relative humidity of the order of 28% were registered by the official network of weather stations. This event interested mainly the central-eastern part of the plain of Friuli Venezia Giulia, a few kilometers far from the Slovenian border and relieves. The thermal anomalies lasted up to an hour, then temperatures decreased toward values more usual for the climate of the month. The study of this event is carried out with the aid of the AR-WRF numerical atmospheric model, initialized through the ECMWF analysis. The numerical simulations highlight the important role played by orography, jointly with the peculiar thermal structure of the atmosphere, for the enhancing of the internal wave pattern over that area. According to the sensitivity studies realized, the amplification of the internal wave pattern might represent a possible explanation for that meteorological enigma. Bernstein, B. C. and Johnson, R. H.: A dual-doppler radar 5 10 B study of an OK PRE-STORM heat burst event, Mon. Weather Rev., 122, 259–273, 1994. Dudhia, J.: Numerical study of convection observed during the winter monsoon experiment using a mesoscale two-dimensional model, J. Atmos. Sci., 46, 3077–3107, 1989. Frich, A., Alexander, L. V., Della-Marta, P., Gleason, B., Haylock, M., Klein Tank, A. M. G., and Peterson, T.: Observed coherent changes in climatic extremes during the second half of the twentieth century, Climate Res., 19, 193–212, 2002. Froude, G. and Simmonds, J.: Phenomenal temperature oscillations in Aden, Meteor. Mag., 94, 185–187, 1965. Giaiotti, D. B., Steinacker, R., and Stel, F.: Atmospheric Convection: Research and Operational Forecasting Aspects, Springer, Wien, NewYork, Udine, 2007. Gladich, I.: Study of non hydrostatic effects in the interaction between flow and orography, Thesis dissertation, University of Trieste, 2005 (in Italian). Gossard, E. E. and Hooke, W. H.: Waves in the Atmosphere, Elsevier Scientifc Publishing Company, 1975. Hong, S.-Y., Noh, Y., and Dudhia, J.: A new vertical diffusion package with an explicit treatment of entrainment processes, Mon. Weather Rev., 134, 2318–2341, 2006. Huschke R. E.: Glossary of meteorology, American Meteorological Society, Boston, 1989. Johnson B. C.: The heat burst of 29 May 1976, Mon. Weather Rev., 111, 1776–1792, 1983. Lane J. D.: Climatological analysis of heatbursts in Oklahoma, Proceedings of the 21st AMS Conference on Severe Local Storms, abstract no P2.9, 2002. Meehl, G. A. and Tebaldi, C.: More Intense, More Frequent, and Longer Lasting Heat Waves in the 21st Century, Science, 305, 994–997, 2004. Mlawer, E. J., Taubman, S. J., Brown, P. D., Iacono, M. J., and Clough, S. A.: Radiative transfer for inhomogeneous atmospheres: RRTM, a validated correlated-k model for the longwave, J. Geophys. Res., 102D, 16 663–16 682, 1997. Robinson, P. J.: On the Definition of Heat Waves, J. App. Meteorol., 40, 762–775, 2001. Seibert P.: South Foehn Studies Since the ALPEX Experiment, Meteorol. Atmos. Phys., 43, 91–103, 1990. Yoshino, M. M.: Local wind Bora, University of Tokio Press, Tokio, 1976.