Origin of extreme summers in Europe: the Indo-Pacific connection
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Origin of extreme summers in Europe: the Indo-Pacific connection Swadhin Behera • Jayanthi V. Ratnam Yukio Masumoto • Toshio Yamagata
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Received: 18 April 2012 / Accepted: 6 September 2012 / Published online: 25 September 2012 Ó Springer-Verlag 2012
Abstract Extreme summers of Europe are usually affected by blocking highs that shift between Western and Eastern Europe to cause regional variations in the surface temperature anomalies. Generally, the blocking high induces a regional temperature dipole with poles of warm and cold anomalies on two sides of Europe. The extreme summers of Western Europe, when the Eastern Europe is colder than normal, are usually associated with the teleconnections arising from positive Indian Ocean Dipole (IOD) events. In contrast, analogous warm events in Eastern Europe are usually associated with La Nin˜a. The western Pacific conditions that prevail during the turnaround phase of El Nin˜o to La Nin˜a are found to be responsible for developing the extreme Eastern Europe events. The role of North Atlantic Oscillation (NAO) is not blatant for the Eastern Europe summers though it has a weaker influence on Western Europe summers for which IOD plays a dominant role: The seasonal July–August correlation for Western Europe temperature with IOD index is higher than that with the NAO index. The teleconnections for both types of extremes are associated with a Rossby wavetrain that travel around the globe to reach the Europe. This circumglobal teleconnection is largely
S. Behera J. V. Ratnam Y. Masumoto Research Institute for Global Change, JAMSTEC, Yokohama, Japan S. Behera J. V. Ratnam T. Yamagata Application Laboratory, JAMSTEC, Yokohama, Japan S. Behera (&) 3173-25 Showa-machi, Kanazawa-ku, Yokohama, Kanagawa 236-0001, Japan e-mail: [email protected]
determined by the location of the tropospheric heat source. For Western Europe warm events, major contributions come from the atmospheric convections/diabatic heating over northwest India and southern Pakistan. For the Eastern Europe events, the convections over northwest Pacific, south of Japan, are found to project the signals on to the mid-latitude wave-guide. These patterns of teleconnection are so robust that those can be seen on daily to seasonal time-scales of atmospheric anomalies. The wavetrains are found to set-in a couple of weeks prior to the development of blocking highs and extreme hot conditions over Europe. Keywords Europe dipole Extreme summers Indian Ocean dipole La Nina
1 Introduction Europe has experienced unprecedented heat waves during several recent summers. From sweltering 2003 to the smoky 2010, many parts of Europe have seen some of the worst human and ecosystem losses on record. The 2003 event alone was responsible for about 40,000 heat wave related human deaths across Europe as attributed in several news-media reports. Though the fatality was not as severe, the heat waves of 2010 summer caused large-scale environmental damages in Eastern Europe. Some of the reports suggest that more than 600 wildfire
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