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Analysis of the Mediterranean Precipitation Associated with the North Atlantic Oscillation (NAO) Index via Hilbert-Huang Transformation. Hasan TATLI Department of Geography Çanakkale Onsekiz Mart University, Turkey. BALWOIS 2006. Problem Statement. --Teleconnection --

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Analysis of the Mediterranean Precipitation Associated with the North Atlantic Oscillation (NAO) Index via Hilbert-Huang Transformation

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Analysis of the Mediterranean Precipitation Associated with the North Atlantic Oscillation (NAO) Index via Hilbert-Huang Transformation

Hasan TATLI

Department of Geography

Çanakkale Onsekiz Mart University, Turkey

BALWOIS 2006


Problem Statement

--Teleconnection --

weather changes at one location

might be related to

weather changes at other remote locations

“happening at the same time”

BALWOIS 2006


  • --Teleconnection – Why?

  • effects on major regimes of precipitation andtemperature

    i) El-Nino-Southern Oscillation (ENSO

    ii) North Atlantic Oscillation

    iii) Southern Europe-North Atlantic

    iv) Arctic Oscillation

    v) Pacific Transition Pattern

    vi) others

  • have roles in resulting

  • a set of vitaleconomic, societal and environmental possessions

  • (“happening at the same time”)

BALWOIS 2006


The positive NAO index phase

  • The positive NAO index phase shows a stronger than usual subtropical high pressure center and a deep than normal Icelandic low.

  • The increased pressure difference results in more and stronger winter storms crossing the Atlantic Ocean on a more northerly track.

  • This results in warm and wet winters in Europe and in cold and dry winters in northern Canada and Greenland.

  • The eastern US experiences mild and wet winter conditions.

BALWOIS 2006


The negative NAO index phase

  • The negative NAO index phase shows a weak subtropical high and weak Icelandic low.

  • The reduced pressure gradient results in fewer and weaker winter storms crossing on a more west-east pathway.

  • They bring moist air into the Mediterranean and cold weather to northern Europe.

  • The US east cost experiences more cold air outbreaks and hence snowy winter conditions.

  • Greenland, however, will have milder winter temperatures.

BALWOIS 2006


BALWOIS 2006

Impacts of the NAO


Aim of the study:Without deseasoned NAOI, to extract whether it has roles in resulting the precipitation over Mediterrenean basin by simple statistical of cross-correlation analysis

Question:Can we reduce a high dimensional system into its simple subsystems?

Answer:Yes, but for practical purposes

Question: How?

Answer:By employing Hilbert-Huang Approach.


BALWOIS 2006

Suggested Method

Hilbert-Huang Transformation

Restriction:Requires band-limited signals


Data: Monthly series

Precipitation data is selected from the NCEP-NCAR reanalysis

(Kalnay et al., 1996; Kistler et al., 2001)

NAOI is selected according to Hurrell (1995), Jones et al. (1997)and Rogers (1997) during the period of 1950-2004.


BALWOIS 2006

Analysis Step


BALWOIS 2006

Analysis Step (Cont.)

Probability mass function of NAO Index


BALWOIS 2006

Analysis Step (Cont.)

Auto-Correlation function of NAO Index


BALWOIS 2006

Analysis Step (Cont.)

How many coordinates?


BALWOIS 2006

Suggested Method (Total NAO)


BALWOIS 2006

Suggested Method (Cont.)

Probability mass function of Total NAO Index


BALWOIS 2006

Suggested Method (Cont.)


BALWOIS 2006

Suggested Method (Cont.)

Too low coordinates? Yes, no?


BALWOIS 2006

Hilbert-Huang Transformation(Cont.)


BALWOIS 2006

Hilbert-Huang Transformation(Cont.)


BALWOIS 2006

Hilbert-Huang Transformation(Cont.)

Cross_correlation between Total_NAO and Precp.


BALWOIS 2006

Conclusions

Traditional Argues

  • The North Atlantic Oscillation is the largest mode of climate variability in the Atlantic Sector and possibly in the whole northern hemisphere.

  • Its impacts reach from the upper atmosphere to the bottom of the ocean and reach from America over to Europe and far into Asia.

  • The dynamics of the NAO are not fully understood and in particular its sensitivity to ocean, land or changes in the sea-ice conditions need more study.

  • Some scientist argue that the NAO is strongly coupled to the stratosphere and will be significantly influenced by "global warming".

  • Other scientist see evidence for coupling with the North Atlantic Ocean.

  • It has also been suggested that tropical ocean temperatures can influence the phase of the NAO.

  • It is unlikely that we will ever be able to predict the NAO with the same accuracy as we do for ENSO today.


BALWOIS 2006

Conclusions (Cont.)

the temporal behavior the NAO is investigated by taking its integration through the time, and decomposed by the EMD method of Huang (1998).

Is it able to add?

 The results of the proposed approach show that a noisy, non-stationary and non-linear high-order complex processmight be decomposed into its simple, but understandable sub-structures

Open Point!

  • What about the lengths of the records?


BALWOIS 2006

Thanks…!

Hasan TATLI


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