clivar-es (11-13 feb 2009) estudio del acoplamiento estratosfera- troposfera y su influencia en la...

CLIVAR-ES (11-13 Feb 2009)CLIVAR-ES (11-13 Feb 2009)

Estudio del acoplamiento estratosfera-Estudio del acoplamiento estratosfera-troposfera y su influencia en la variabilidad troposfera y su influencia en la variabilidad

climática de la región Euro-Atlánticaclimática de la región Euro-Atlántica

Study of the stratosphere-troposphere Study of the stratosphere-troposphere coupling and its influence on the climate coupling and its influence on the climate

variability of the Euro-Atlantic regionvariability of the Euro-Atlantic region

Departamento de Geofísica y Meteorología

Universidad Complutense de Madrid (UCM))

Seminario CLIVAR-ES Madrid, 11-13 Febrero 2009

Encarna Serrano, Álvaro de la Cámara, Blanca Ayarzagüena,

Marta Ábalos y Beatriz González


Outline of the talk Outline of the talk 1. Introduction

Strato-troposphere coupling & Euro-Atlantic climate variability Dept. Geophysics & Meteorology, UCM

2. Relevant results (REN2005-06600-CO2):

2.1. Stratosphere-troposphere system and winter precipitation over Europe (in collaboration with Prof. C.R. Mechoso, UCLA)

2.2. Stratospheric final warmings and tropospheric circulation over the Euro-Atlantic region

3. Conclusions


Strat-troposphere coupling & Euro-Atlantic climate variability Dept. Geophysics & Meteorology, UCM

1. Introduction and 1. Introduction and BackgroundsBackgrounds

In recent times,a growing interest in the improved understanding of the impact of stratospheric anomalies on the tropospheric variability is observed (Baldwin & Dunkerton 2001, .….)

Certain studies have shown that large stratospheric anomalies descend to lower levels and are followed by changes at surface (temperature, geopotential…). The authors used indices based on the polar vortex strength (Baldwin & Dunkerton 2001; Thompson et al. 2002)


Geopotential anomalies at 1000 hPa

(Northern Hemisphere)

[data: ERA40, 1.125ºx1.125º]

Anomalous rainfall (Europe)

[data: Univ. Delaware, 0.5ºx0.5º]

1st MCA mode(Maximum

Covariance Analysis)

Monthly data, DJF

Dec-57 Dec-60 Dec-63 Dec-66 Dec-69 Dec-72 Dec-75 Dec-78 Dec-81 Dec-84 Dec-87 Dec-90 Dec-93 Dec-96Feb-99-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

Datos mensuales (DEF)

Va

lore

s e

sta

nd

ariza

do

sS

tan

dar

diz

ed v

alu

es

DJF (1957-1999)

pcp_idx (sfc = 45 %)


2. 2. ResultsResults: Stratosphere-troposphere system : Stratosphere-troposphere system and winter precipitation over Europeand winter precipitation over Europe

We have analized the stratosphere-troposphere coupling in the winter rainfall over Europewinter rainfall over Europe using a precipitationprecipitation index index (pcp_idx) connected with North hemisphere geopotential anomalies (A. Cámara et al., EGS2007, WCRP2007, to be submitted J.Climate).

22 HIGH cases

23 LOW cases


• Negative anomalies over the Arctic, shifted towards the Atlantic basin.

• The positive Euroatlantic mid-latitude centre of action is splitted.

• Overall, a wavy structure.


Composites of geopotential anomaliesZ 500 hPa

HIGH vs. LOW pcp_idxHIGH vs. LOW pcp_idx

• Narrower extension of the Northern centre of action.

• More zonally-symmetric pattern.

H I GH

LOW

WINTER

22 cases

23 cases



Composites of anomaliesZ 500 hPa


H I GH

LOW

Precipitation (std values)

WINTER



Composites of anomaliesZ 500 hPa


H I GH

LOW

Z 50 hPa

polar vortex strengthened at upper levels

polar vortex something

weakened at upper levels

WINTER



Time-latitude plot of the stratospheric jetstratospheric jet (zonal-mean zonal wind at 10 hPa) prior to, during and after extreme cases of pcp_idx.

High-minus-Low composite of [u10] (m/s) (Shading: significant difference at α = 0.01, t-test)

The westerlies at high latitudes (60ºN-80ºN)

are statistically significantly strongerstronger not

only during highhigh episodes (central month of

the diagram), but also during a 20-days during a 20-days

period prior toperiod prior to the extreme pcp_idx episode.

It suggests that the intensity of the stratospheric jetstratospheric jet at 10 hPa could be used as predictor of the anomalous

monthly rainfall regime over Europe.

WINTERHIGH vs. LOW pcp_idxHIGH vs. LOW pcp_idx



WINTER

SVRNeutral

conditionsWVR SVR

Neutral conditions

WVR

lag 0 lag -1

High pcp_idx

21 1 0 14 8 0

Low pcp_idx

4 14 5 4 13 6

Distribution of winter months (DJF) according to the extreme value of pcp_idx and the strength of the stratospheric polar vortex.

Criterion of Castanheira & Graf (2003)

Strong polar vortex regime (SVRSVR): [u]65ºN, 50hPa > 20 m/s

Weak polar vortex regime (WVRWVR): [u]65ºN, 50hPa < 10 m/s

Neutral conditions: 10 m/s [u]65ºN, 50hPa 20 m/s


High High pcp_idx ↔ strong polar vortex

LowLow pcp_idx ↔ weak polar vortex X



High High pcp_idx ↔ strong polar vortex

LowLow pcp_idx ↔ weak polar vortex X

WINTERHIGH vs. LOW pcp_idxHIGH vs. LOW pcp_idx

High High pcp_idx: troposphere -stratosphere coupling LowLow pcp_idx : not a clear troposphere -stratosphere coupling

Differences between AO and NAO?

Composite of Z500

LOW pcp_idxHIGH pcp_idx

AO-like Composite of Z500

NAO-like


2.2. Stratospheric final warmings (SFWs) 2.2. Stratospheric final warmings (SFWs) and tropospheric circulation over Euro-and tropospheric circulation over Euro-

Atlantic regionAtlantic region


The SFWs occur once per year at springtimespringtime, and present a large interannual variability.a large interannual variability.

Our studies Our studies deal with the relationship between the relationship between the late or early late or early occurrenceoccurrence of the SFW and of the SFW and changes in the tropospheric circulationchanges in the tropospheric circulation in spring months over the in spring months over the Euro-Atlantic regionEuro-Atlantic region

(B. Ayarzagüena & E. Serrano, J. Climate, accepted)


2.2. Stratospheric final warmings (SFWs) 2.2. Stratospheric final warmings (SFWs) and tropospheric circulation over Euro-and tropospheric circulation over Euro-

Atlantic regionAtlantic region


Selection of Selection of TWO sets of yearsTWO sets of years from the study period (45yrs) in from the study period (45yrs) in basis of the date on which the SFW occurs:basis of the date on which the SFW occurs:

EARLYEARLY yearsyears and and LATELATE yearsyears (reflecting a (reflecting a early or late breakup of the polar vortexearly or late breakup of the polar vortex).).

3th Jun

27th Mar Mean date Mean date 1717thth April April

1 std

day of year

Data: daily zonal wind (1958-02, ERA40)

Criterion of Black et al.Criterion of Black et al. 2006 2006

[u50] at 70ºN[u50] at 70ºN

date of SFWs

10 “early years”10 “early years”

7 “late years”7 “late years”


Early vs. Late yearsEarly vs. Late years


Differences in the Differences in the stratospheric mean flowstratospheric mean flow (related to differences in the (related to differences in the stationary wave activitystationary wave activity)

Zonal-mean zonal wind

(m·s-1)

APRIL

• In ‘In ‘early yearsearly years’, the ’, the polar vortexpolar vortex has already has already disappeareddisappeared and the easterlies extend and the easterlies extend to lower levels and latitudes than the climatology (mean flow has changed from to lower levels and latitudes than the climatology (mean flow has changed from westerlies to easterlies) westerlies to easterlies) anomalous low upward propagation of waves. anomalous low upward propagation of waves.

SPRING

• In ‘In ‘late yearslate years’, the ’, the polar vortex still persistspolar vortex still persists and stronger mean flow than the and stronger mean flow than the climatology about 30ºN northwards climatology about 30ºN northwards more difficulties than normal for waves to propagate upwards up to 20 hPa and less than normal above that level

[u] > 0

[u] < 0

easterlieseasterlies




Differences in Differences in 500-hPa geopotential 500-hPa geopotential andand zonal wind zonal wind fieldsfields

Z500 anomalies

(gpm)

APRIL

• In ‘In ‘late yearslate years’: well-defined Atlantic tripole of Z500 anomalies (negative values over ’: well-defined Atlantic tripole of Z500 anomalies (negative values over high latitudes and subtropical Atlantic, positive values at west of the British Isles)high latitudes and subtropical Atlantic, positive values at west of the British Isles)

• In ‘In ‘early yearsearly years’: different pattern to ‘’: different pattern to ‘late yearslate years’ (← Z500-tripole centers are ’ (← Z500-tripole centers are weaker, shifted and deformed. weaker, shifted and deformed.

AO+-like AO--like

SPRING




Differences in Differences in 500-hPa geopotential 500-hPa geopotential andand zonal wind zonal wind fieldsfields

Z500 anomalies

(gpm)

APRIL

AO+-like AO--like

AO+ AO- Total

early yearsearly years 4 6 10

late yearslate years 6 1 7

10 7 17

SPRING

Fisher-Irwin test

Independence between AO phase & late/early year

(92% confidence level)




Differences in the Differences in the storm track activity storm track activity (at 500 hPa)(at 500 hPa)

Units: gpm

APRIL

• Statistically significant Statistically significant differencesdifferences, between ‘, between ‘early early andand late late years, bothyears, both in the in the entranceentrance (North America coast) (North America coast) and exitand exit (Scandinavia) (Scandinavia) regions of the storm tracksregions of the storm tracks in in

the Atlantic area. the Atlantic area.

SPRING




Differences in the Differences in the storm track activity storm track activity (at 500 hPa)(at 500 hPa)

Units: gpm

• In ‘In ‘early yearsearly years’: compared to climatology, a ’: compared to climatology, a southward shift of ST activitysouthward shift of ST activity in the in the east coast of North America, and east coast of North America, and weakness along the whole Atlantic stripweakness along the whole Atlantic strip

APRIL

• In ‘In ‘late yearslate years’, the ’, the oppositeopposite occurs ( occurs (maximummaximum of the ST activity of the ST activity northwards upnorthwards up respect to climatology; respect to climatology; values > 40 gpm reach Scandinavian Peninsula)values > 40 gpm reach Scandinavian Peninsula)

SPRING



New topics under current New topics under current study study (REN2008-

06295) Degree of connection between the strength of the strength of the stratospheric polar vortexstratospheric polar vortex and the arctic ozone contentarctic ozone content (end of winter and during spring)

Analysis of how well the UCLA global model reproduces the UCLA global model reproduces the stratospheric circulationstratospheric circulation (→ estudios de sensibilidad)



ConclusionsConclusions- We have defined a precipitation index (pcp_idx), that is a good descriptor of the stratosphere – European rainfall connection in winter months, in such a way that its high values capture the stratosphere-troposphere coupling, and with potential use in seasonal forecasting.

- The late or early occurrence of the yearly SFWlate or early occurrence of the yearly SFW (spring months) seems to have some impact on the troposphere over the Euro-Atlantic impact on the troposphere over the Euro-Atlantic regionregion, especially in April. The storm track activity in late yearslate years (early early yearsyears) is such that leads to a higherhigher (lowerlower) number of storms crossing North Europe.

clivar-es (11-13 feb 2009) estudio del acoplamiento estratosfera- troposfera y su influencia en la...

Documents

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ucm composites of anomalies

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europe winter rainfall