Expansion of summer to spring in the Western Mediterranean

1. REUNIÓN PREDIMED 2014A. 5-6 Junio 2014 Sala Seminarios Física. 3r piso Mateu Orfila. UIB. Expansion of summer to spring in the Western Mediterranean Agustí Jansà (1), Víctor Homar (1), Romu Romero (1), José A. Guijarro (2), Climent Ramis (1) Departament Física/Universitat de les Illes Balears, Palma (2) Delegació a Illes Balears/Agència Estatal de Meteorologia, Palma agusti.jansa@gmail.com

2. Scheme of work: Climatic mediterraneity: Mediterranean summer vs. subtropical anticylonic domain Surface temperature trends: May/June maximum Local correlation between surface temperature and 500 hPa geopotential height: seasonal differences Regional structure of 500 hPa geopotential height trends: seasonality Particular study of May/June: detection and evolution of main patterns, contribution of them to surface temperature trend Discussion: Tropical region, Hadley cells and mediterraneity expansion Indication of insufficiency of climatic models simulations

3. Climatic mediterraneity: Mediterranean summer vs. subtropical anticylonic domain Climatic mediterraneity = Köppen’s Cs type = Temperate, not arid, seasonal, with dry season, during summer Example: Palma - airport

4. The Mediterranean climate is characterised by alternating between mid-latitude and subtropical circulations Mediterranean summer is characterised by the subtropical anticyclonic domain (Hadley cell edge) G500

5. Alternating between mid-latitude disturbances and subtropical anticyclone dominance is not evident at mean sea level, due to the hydrostatic effect of the warm/cold low level air masses.The upper levels offer an opportunity to visualise the alternating, its changes and its tendencies. Time evolution, from local point of view (over Palma, AEMET and NCEP reanalysis)

6. The 2D streamfunction could provide a better way to explore the time evolution of the Hadley cell extension and external edge position. Northern Hadley cell (NHC) Southern Hadley cell (SHC) When taking planetary zonal averages, the NHC tends to disappear during the northern hemisphere summer (effect of the monsoon circulation) Dimas & Wallace, 2003 We want to repeat the right figure, but for a zonal average only referred to Iberian/W-Mediterranean longitudes

7. Surface temperature trends: May/June maximum Tendències anuals (ºC/dècada): 1973-09: 0,54 1973-12: 0,49 Cu0 = Catalunya (excepte Ebre) Cu4 = Guadiana Cu5 = Guadalquivir Cu6 = Sud Cu7 = Segura Cu8 = Xúcar / València Cu9 = Ebre CuB = Illes Balears

8. Local correlation between surface temperature and 500 hPa geopotential height: seasonal differences

9. Tendències observades (m/dècada): Anual 1948-2012: 5,8 MJ 1948-2012: 6,5 Anual 1973-2012: 6,7 MJ 1973-2009: 13,9

10. Maig/juny: temperatura en superfície i geopotencial de 500 hPa • Selecció d’anys singulars

11. 5700 5700 5700 5700 5700 5700 • Maig/juny: configuració mitjana a 500 hPa en anys singulars

12. Regional structure of 500 hPa geopotential height trends: seasonality

18. Particular study of May/June: detection and evolution of main patterns, contribution of them to surface temperature trend

22. Most influential structures

23. Goodness of the MLR model (surface local temperature as regional PC scores function)

25. Discussion: Tropical region, Hadley cells and mediterraneity expansion Poleward tropical expansion NH SH Total OLR 2.70◦ − 0.78◦ 3.48◦ Precipitation 2.13◦ − 1.56◦ 3.69◦ SLP 0.67◦ − 0.54◦ 1.21◦ Simulated streamfunction 1.05◦ − 0.18◦ 1.23◦ Hu, Zhou, Liu, 2011 “simulated magnitudes of poleward expansion with SST forcing are all weaker than in reanalysis data.” “magnitudes from coupled GCM simulations are even weaker than those in atmospheric GCMs forced with SST alone”

26. Indication of insufficiency of climatic models simulations GF, MJ, JA Model HadGEM2 – Experiments -Històric 1951-2005 -RCP45 2006-2100 -RCP85 2006-2100 Dins de l’experiment històric, per al subperíode 1973-2005, només són significatives algunes tendències de HadGEM2:MJ JA SO 0,53 0,41 0,71