Relationship of the North Atlantic Oscillation and the total seasonal rainfall over Libya

1. Relationship of the North Atlantic Oscillation and the total seasonal rainfall over Libya Taher A. Sharif Department of Atmospheric science, University of AlFateh, Tripoli, Libya Taher.sharif@gmail.com

2. Outline • North Atlantic oscillation Overview • Correlation of NAO index with seasonal rainfall over Libya • Summary MedCLIVARWokshop Trieste Oct 2008

3. Definition of North Atlantic Oscillation • The North Atlantic Oscillation (NAO) establishes a link between the intensity of the Icelandic low pressure and Azores high pressure. • It is traditionally quantified by an index defined as the difference between normalized SLP anomalies in the Azores and Icelandic regions, respectively. MedCLIVARWokshop Trieste Oct 2008

4. NAO Index MedCLIVARWokshop Trieste Oct 2008

5. North Atlantic Variability Climate variability in the North Atlantic sector, comprise three primary interrelated phenomena: • Tropical Atlantic Variability (TAV) • North Atlantic Oscillation (NAO) • Atlantic Meridional Overturning Circulation (MOC) MedCLIVARWokshop Trieste Oct 2008

6. Other Important Actors • Arctic Oscillation (AO) • Blocking High (a persistent anomalous high pressure over Northern Europe) • Atlantic Ridge (Northward extension of Azores High pressure) MedCLIVARWokshop Trieste Oct 2008

7. Normal Sea-level pressure for January MedCLIVARWokshop Trieste Oct 2008

8. Normal sea-level pressure for July MedCLIVARWokshop Trieste Oct 2008

9. Sea Level Pressure NAO exhibits two main anomalies of pressure cores of opposite signs, Extending respectively from Iceland to Spitzberg and from center of the Atlantic to the Iberian peninsula. MedCLIVARWokshop Trieste Oct 2008

10. Sea Level Pressure MedCLIVARWokshop Trieste Oct 2008

11. Positive NAO • Deepening of the Icelandic Low (negative SLP anomalies over the Icelandic region throughout the Arctic). • Strengthening and eastward extension of the Azores High (positive SLP anomalies over the Azores region) MedCLIVARWokshop Trieste Oct 2008

12. Positive NAO MedCLIVARWokshop Trieste Oct 2008

13. Features Associated with Positive NAO • Stronger than average westerlies across middle latitudes in the Atlantic and western Europe. • Colder winter conditions dominate the northwest Atlantic. • Warmer weather over Europe. • Storm tracks are shifted to the north with wetter conditions from Iceland through Scandinavia. • Dryer conditions over south-western Europe and the Mediterranean Basin. MedCLIVARWokshop Trieste Oct 2008

14. Negative NAO • Weakening of the Icelandic Low ( positive SLP anomalies over the Icelandic region throughout the Arctic). • Weakening the Azores High (negative SLP anomalies over the Azores region). MedCLIVARWokshop Trieste Oct 2008

15. Negative NAO MedCLIVARWokshop Trieste Oct 2008

16. Features Associated with Negative NAO • Weaker than average westerlies across middle latitudes in the Atlantic and western Europe. • Warmer winter conditions dominate the northwest Atlantic. • cooler weather over Europe. • Storm tracks are shifted to the south with dryer conditions from Iceland through Scandinavia. • Wetter conditions over south-western Europe and the Mediterranean Basin. MedCLIVARWokshop Trieste Oct 2008

17. Standardized seasonal Mean (JFM) NAO index (1950-2008) MedCLIVARWokshop Trieste Oct 2008

18. Correlatin between NAO index and Seasonal Rainfallover Libya MedCLIVARWokshop Trieste Oct 2008

19. Correlation between monthly NAO index and October to November Total Rainfall for Tripoli MedCLIVARWokshop Trieste Oct 2008

20. Fig 1: The Correlation Between August NAO Index and October to February Rainfall MedCLIVARWokshop Trieste Oct 2008

21. Fig 2: The Correlation Between August NAO Index and November to February Rainfall MedCLIVARWokshop Trieste Oct 2008

22. Fig 3: The Correlation Between August NAO Index and December to February Rainfall MedCLIVARWokshop Trieste Oct 2008

23. Fig 4: The Correlation Between August NAO Index and January to February Rainfall MedCLIVARWokshop Trieste Oct 2008

24. On-going work Nowadays scientists are involved in a major research program focusing on Atlantic climate variability in the context of CLIVAR. The main objectives of the program are: • To describe and model coupled atmosphere-ocean-land interactions in the Atlantic sector, quantify there influence on the regional and global climate system, and determine their predictability. • To assemble quantitative historical and real time data sets that may be used to test, improve and initialize models of coupled Atlantic climate variability. • To investigate the sensitivity of the MOC to changes in the surface forcing and assess the likelihood of abrupt climate change. MedCLIVARWokshop Trieste Oct 2008

25. Summary • NAO is a very important synoptic feature in predicting climate over Europe and Mediterranean regions. • Rainfall over Libya is significantly correlated with NAO index. It increases when the NAO is in negative phase. • NAO variability seems to be a possible predictor for statistical prediction of climate over Europe and Mediterranean regions. • The Standing mean of Icelandic low, Azores high and Siberian high pressure are natural synoptic controller systems That should be preserved for any climate prediction modelling over Europe and Mediterranean. MedCLIVARWokshop Trieste Oct 2008

26. Thank you MedCLIVARWokshop Trieste Oct 2008