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)

(1) Departament Física/Universitat de les Illes Balears, Palma

(2) Delegació a Illes Balears/Agència Estatal de Meteorologia, Palmaagusti.jansa@gmail.com

REUNIÓN PREDIMED 2014A. 5-6 Junio 2014Sala Seminarios Física. 3r piso Mateu Orfila. UIB.

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

Climatic mediterraneity = Köppen’s Cs type = Temperate, not arid, seasonal, with dry season, during summer

Example: Palma - airport

Temperatures - Palma aeroport

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5,0

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G F M A M J J A S O N D

Pluges - Palma aeroport

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G F M A M J J A S O N D

Climatic mediterraneity: Mediterranean summer vs. subtropical anticylonic domain

The Mediterranean climate is characterised by alternating between mid-latitude and subtropical circulations

G500

Mediterranean summer is characterised by the subtropical anticyclonic domain (Hadley cell edge)

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.

1011

1012

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1016

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1020

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J F M A M J J A S O N D

MSLP

1440

1460

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J F M A M J J A S O N D

G850

5450

5500

5550

5600

5650

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J F M A M J J A S O N D

G500

Time evolution, from local point of view (over Palma, AEMET and NCEP reanalysis)

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

Surface temperature trends: May/June maximum

Temperatures mitjanes anuals Aeroport Palma(sèrie original, sense homogeneitzar)

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17,5

18

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1973-2009 1973-2012 Lineal (1973-2009) Lineal (1973-2012)

Tendències mensuals (ºC/any) Aeroport Palma 1973-2009(sèrie original, sense homogeneitzar)

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G F M A M J J A S O N D

Tendències anuals (ºC/dècada):1973-09: 0,541973-12: 0,49

Cu0 = Catalunya (excepte Ebre)Cu4 = GuadianaCu5 = GuadalquivirCu6 = SudCu7 = SeguraCu8 = Xúcar / ValènciaCu9 = EbreCuB = Illes BalearsPalma-Airport Temperature trend

Homogenised series 1973-1012

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J F M A M J J A S O N D

Trend TX

Pval TX

Trend TN

Pval TN

Trend TM

Palma-Airport Temp. trend

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JF MA MJ JA SO ND

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

G500 trend - NCEP - 1973-2012

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JF MA MJ JA SO ND

Correlacions entre temperatura en superfície a l'aeroport de Palma i geopotencial de 500 hPa sobre Balears

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GF MA MJ JA SO ND

Geopotencial 500 hPa a Balears (NCEP/NCAR)

5650

5670

5690

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5830

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Anual 1948-2012

MJ 1948-2012

Lineal (Anual 1948-2012)

Lineal (MJ 1948-2012)

Geopotencial 500 hPa a Balears (NCEP/NCAR)

5650

5670

5690

5710

5730

5750

5770

5790

5810

5830

1973

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Anual 1973-2009

MJ 1973-2009

Lineal (Anual 1973-2009)

Lineal (MJ 1973-2009)

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

Maig/juny: temperatura en superfície i geopotencial de 500 hPaSelecció d’anys singulars

Maig/juny: configuració mitjana a 500 hPa en anys singulars

5700 5700

5700

5700 5700 5700

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

Most influential structures

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

Discussion: Tropical region, Hadley cells and mediterraneity expansion

Poleward tropical expansion NH SH TotalOLR 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 polewardexpansion 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”

GF, MJ, JAModel HadGEM2 – Experiments-Històric 1951-2005-RCP45 2006-2100-RCP85 2006-2100

Indication of insufficiency of climatic models simulations

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