1/6/2024 0 Comments Cross dj le 1.5.2![]() Below, and will denote the zonal wave numbers, respectively, of free synoptic waves and quasistationary planetary-scale Rossby waves mentioned above. The quasistationary component of midlatitude free synoptic-scale waves with normally is weak, with the magnitude of the meridional velocity less than (1.5–2) m/s ( 26, 27). Generally the large-scale midlatitude atmospheric circulation is characterized by ( i) traveling free synoptic-scale Rossby waves with zonal wave numbers propagating predominantly in the longitudinal direction with the phase speed m/s, and ( ii) quasistationary planetary-scale Rossby waves with, frequency, and various zonal wave numbers as a response of atmospheric circulation to quasistationary (e.g., climatological mean) spatially inhomogeneous diabatic sources/sinks and orography ( 16– 28). The global observations attest that these extremes, such as the Russian heat wave in 2010 and the record heat wave in the United States in 2011, persisted over nearly the whole summer- which is not inherent in ordinary blockings with a characteristic e-folding time of about 5–7 d-and were in fact of hemispheric scale: a stable anomalous atmospheric circulation pattern enveloped the whole NH ( 4, 9- 14). In the meantime, several other unusually strong regional summer extremes already have occurred in recent years that make it questionable that only a purely stochastic mechanism of extremes is at work ( 8). ![]() For example, a return period of 100 y was estimated by Luterbacher et al. However, even when the warming trend found in the data is fully taken into account, and if an increase in SD of 50% is assumed, the extreme temperatures and duration of the summer 2003 heat wave still would be highly unlikely. We note that a shift and widening of the probability distribution due to global warming almost certainly will lead to a marked increase in the frequency of extreme warm-season events ( 5– 7). Schär and colleagues (2004) ( 3) proposed that the observed climatic warming trend ( i) shifted the probability distribution of summer temperatures toward warmer values and ( ii) widened this probability distribution so that extreme values become much more likely, possibly as the result of a positive feedback between temperature and soil dryness. Anomalous heat reigned for much of the summer over a large part of Europe, reaching the highest temperature anomalies in Switzerland, northwestern France, and southern Germany. Its remarkable feature was a persistent “blocked” circulation pattern over Europe ( 1– 4). The summer of 2003 was highly exceptional in the Northern Hemisphere (NH) ( 1– 4).
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |