Taher A. Sharif Department of Atmospheric science, University of AlFateh, Tripoli, Libya...
-
Upload
miguel-wells -
Category
Documents
-
view
216 -
download
1
Transcript of Taher A. Sharif Department of Atmospheric science, University of AlFateh, Tripoli, Libya...
Taher A. Sharif
Department of Atmospheric science, University of AlFateh, Tripoli, Libya
Outline
North Atlantic oscillation OverviewCorrelation of NAO index with
seasonal rainfall over LibyaSummary
2MedCLIVAR Wokshop Trieste Oct 2008
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.
3MedCLIVAR Wokshop Trieste Oct 2008
4MedCLIVAR Wokshop Trieste Oct 2008
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)
5MedCLIVAR Wokshop Trieste Oct 2008
Other Important Actors
Arctic Oscillation (AO)Blocking High (a persistent
anomalous high pressure over Northern Europe)
Atlantic Ridge (Northward extension of Azores High pressure)
6MedCLIVAR Wokshop Trieste Oct 2008
Normal Sea-level pressure for January
7MedCLIVAR Wokshop Trieste Oct 2008
Normal sea-level pressure for July
8MedCLIVAR Wokshop Trieste Oct 2008
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.
9MedCLIVAR Wokshop Trieste Oct 2008
Sea Level Pressure
Sea Level Pressure
10MedCLIVAR Wokshop Trieste Oct 2008
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)
11MedCLIVAR Wokshop Trieste Oct 2008
12MedCLIVAR Wokshop Trieste Oct 2008
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.
13MedCLIVAR Wokshop Trieste Oct 2008
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).
MedCLIVAR Wokshop Trieste Oct 2008 14
Negative NAO
15MedCLIVAR Wokshop Trieste Oct 2008
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.
Features Associated with Negative NAO
16MedCLIVAR Wokshop Trieste Oct 2008
17MedCLIVAR Wokshop Trieste Oct 2008
MedCLIVAR Wokshop Trieste Oct 2008 18
19MedCLIVAR Wokshop Trieste Oct 2008
Fig 1: The Correlation Between August NAO Index and October to February Rainfall
20MedCLIVAR Wokshop Trieste Oct 2008
Fig 2: The Correlation Between August NAO Index and November to February Rainfall
21MedCLIVAR Wokshop Trieste Oct 2008
Fig 3: The Correlation Between August NAO Index and December to February Rainfall
22MedCLIVAR Wokshop Trieste Oct 2008
Fig 4: The Correlation Between August NAO Index and January to February Rainfall
23MedCLIVAR Wokshop Trieste Oct 2008
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.
24MedCLIVAR Wokshop Trieste Oct 2008
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.
25MedCLIVAR Wokshop Trieste Oct 2008
MedCLIVAR Wokshop Trieste Oct 2008 26