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African and Indian Ocean teleconnections with Middle East climate

African and Indian Ocean teleconnections with Middle East climate. Questions for WLC: Is climate variability in the Arabian Sea and Africa associated with Middle East climate variability (particularly rainfall)? What mechanisms or causal links are there?

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African and Indian Ocean teleconnections with Middle East climate

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  1. African and Indian Ocean teleconnections with Middle East climate • Questions for WLC: • Is climate variability in the Arabian Sea and Africa associated with Middle East climate variability (particularly rainfall)? • What mechanisms or causal links are there? • How might this affect our choice of regional model domain? • Outline • A bit about WLC and WLC meteorology • Background on Middle East rainfall seasonal cycle • Case study of a rainy event in early November 1994 - mainly review of a paper by Krichak and Alpert • Other rainy Novembers (composites)

  2. EUPHRATES VALLEY Mesopotamian Civilisation 6500 BC JORDAN VALLEY Origin of agriculture, 10,000 BC First towns, 8500 BC NILE VALLEY Egyptian Civilisation, 3500 BC Water, Life and Civilisation • Overall Aim: To assess the impact of changes in the hydrological climate on past, present and future societies in the semi-arid regions of the Middle East and North Africa, with a case study of the Jordan Valley • Goals: • Increase our understanding of past water availability and the consequent major changes in human settlement from 20,000 BC to 2100 AD • Improve our ability to simulate present day hydrology in semi-arid regions of the MENA and to evaluate its impact on human activity • Make predictions of future changes in water availability for the MENA region and hence the constraints under which social and economic development, particular agriculture must occur

  3. A satellite image showing weather systems in the MENA region Tracks of weather systems entering the Jordan Valley from the Mediterranean WLC climate modelling: overall aims • To improve our understanding of the climate variability in the MENA region • To produce climate scenarios for past, present and future as inputs to the other projects April 2004

  4. 44km 22km The regional models. Black lines show show the whole model area whereas the grey lines show the model interior that lies inside the “blending” region. • Things to consider: • Boundary points • Orography • “Information flow” (cyclones) W=>E • Not too big – too much data/too slow!

  5. Middle East climate variability 1: Seasonal cycle • Most rainfall occurs as cyclones move eastwards across the Mediterranean in the boreal autumn and winter (see animation October - December 2005) • Large interannual variability relative to mean • Some hint in the animation that convection in the Red Sea may enhance events

  6. Middle East climate variability 2: Large-scale teleconnections Precipitation • Most obvious teleconnection is high rainfall associated with low rain/high pressure over Europe. In these conditions the Mediterranean storm track is “diverted” towards the ME • Also consistent teleconnection with Africa

  7. Case study of November 1-5 1994 (based on Krichak and Alpert (1998)) Rainfall time series for a station in Israel for November 1994 “Torrential cloudbursts, reported to be the worst experienced in 80 years at some locations, caused severe, widespread flooding and landslides in southeast France, Corsica and northwestern Italy during the four-day period in early November 1994” Obasi (1997)

  8. 1st Nov 6th Nov Development of SLP anomalies • Red Sea trough develops from Day 4 • High over Europe and low over the Middle East pattern most evident on Days 4 and 5

  9. Development of 850mb wind anomalies • Strong southerly flow into the Middle East at the beginning of the event • EM cyclone develops later on

  10. LTM Mean Anomaly Summary • Enhanced upper tropospheric westerlies • Enhanced southerly flow and EM cyclone • Higher relative humidity in the Arabian Sea • Perturbed stream function (more Arabian Sea influence) - later on in event only (5th November shown) • Deeper Red Sea trough (previous slide) 200mb wind 850mb wind Stream function Relative humidity (850mb)

  11. Backwards trajectories of low level wind greater than 7m/s 1-2 November 2-3 November 3-4 November 5-6 November • Initially moisture into the ME comes from Arabian Sea • Later on during the simulation, the EM cyclone develops

  12. 1-2 November 2-3 November 3-4 November 5-6 November Backwards trajectories of upper level wind greater than 40m/s • Prior to the development of the RST - there is a strong STJ • Previous work has shown this to be favorable for the RST development • This weakens then redevelops further to the south (less favorable for RST)

  13. Experiment design Lower RH in box shown. Compare with control (cntl-expt) One ensemble member 96 hour run Results Enhanced STJ and RST Higher humidity in Eastern Med Stronger EM cyclone Experiments with perturbed humidity 1 - cntl - expt

  14. Summary of November 1-5 event • Main conclusions • Development of the EM cyclone on November 2nd took place as a result of intensive propagation of the air masses from the Arabian Sea into the Red Sea region • Advection of moist air to the Red Sea took place before November 1st (Arabian Sea expts - not shown here) • African and Arabian Sea tropical convection supported intensification of the upper tropospheric jet stream over the Red Sea and stimulated the development of the RST circulation Sequence of events Advection of large amounts of moist air to equatorial Africa stimulates convective activity in the region STJ intensifies over the Red Sea This stimulates development of the Red Sea cyclone Development of the RST causes modification of the moisture advection with moisture advected northward into the Red Sea During/after the EM cyclogenesis the STJ and RST weaken and advection ofhte moist air masses are again directed towards tropical Africa

  15. Comparison with other rainy Novembers Comp of rainy Novs LTM Nov 1994 Streamfunction • More Arabian Sea influence in all rainy years • Increased RH in Arabian Sea • Enhanced RST in all years (not shown) RH mean RH anomaly

  16. Future work / implications for WLC modelling plans • Consider further case studies/ensembles of AGCM runs to confirm these results - in my opinion they are inconclusive as they stand • Modified RCM domain to include more of Arabian Sea - redo the expts • Note that global and regional results have similar problems with the seasonal cycle so this may be a “second order” effect for the seasonal cycle • However - this seems important for development of extreme events and therefore for impacts assessments • For this and other reasons we are now considering a greater emphasis on high resolution AGCM modelling with statistical downscaling to scales needed by hydrologists (~10-50km)

  17. Case study of November 1-5 1994 (based on Krichak and Alpert (1998)) Relative humidity

  18. Case study of November 1-5 1994 (based on Krichak and Alpert (1998)) • SLP in control integration • RST deepening captured to some degree

  19. Case study of November 1-5 1994 (based on Krichak and Alpert (1998)) • 850 hPa streamlines • Gradual incursion of stream lines from Arabian Sea into Middle East region captured well

  20. Precip anomaly for ME precip gt 1 s.d. Precip anomaly for ME precip lt -1 s.d.

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