CLIVAR-ES (11-13 Feb 2009) Estudio del acoplamiento estratosfera- troposfera y su influencia en la variabilidad climática de la región Euro-Atlántica Study of the stratosphere-troposphere coupling and its influence on the climate variability of the Euro-Atlantic region Departamento de Geofísica y Meteorología Universidad Complutense de Madrid (UCM)) Seminario CLIVAR-ES Madrid, Febrero 2009 Encarna Serrano, Álvaro de la Cámara, Blanca Ayarzagüena, Marta Ábalos y Beatriz González

CLIVAR-ES (11-13 Feb 2009) Outline of the talk 1.Introduction Strato-troposphere coupling & Euro-Atlantic climate variability Dept. Geophysics & Meteorology, UCM 2. Relevant results ( REN 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

CLIVAR-ES (11-13 Feb 2009) Strat-troposphere coupling & Euro-Atlantic climate variability Dept. Geophysics & Meteorology, UCM 1. Introduction and Backgrounds  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)

CLIVAR-ES (11-13 Feb 2009) Geopotential anomalies at 1000 hPa (Northern Hemisphere) [data: ERA40, 1.125ºx1.125º] Anomalous rainfall (Europe) [data: Univ. Delaware, 0.5ºx0.5º] 1 st MCA mode (Maximum Covariance Analysis) Monthly data, DJF Standardized values DJF ( ) pcp_idx (sfc = 45 %) Strat-troposphere coupling & Euro-Atlantic climate variability Dept. Geophysics & Meteorology, UCM 2. Results: Stratosphere-troposphere system and winter precipitation over Europe winter rainfall over Europeprecipitation index  We have analized the stratosphere-troposphere coupling in the winter rainfall over Europe using a precipitation 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

CLIVAR-ES (11-13 Feb 2009) Negative anomalies over the Arctic, shifted towards the Atlantic basin. The positive Euroatlantic mid-latitude centre of action is splitted. Overall, a wavy structure. Strat-troposphere coupling & Euro-Atlantic climate variability Dept. Geophysics & Meteorology, UCM Composites of geopotential anomalies Z 500 hPa HIGH vs. LOW pcp_idx Narrower extension of the Northern centre of action. More zonally-symmetric pattern. HIGHHIGH LOWLOW WINTER 22 cases 23 cases

CLIVAR-ES (11-13 Feb 2009) Strat-troposphere coupling & Euro-Atlantic climate variability Dept. Geophysics & Meteorology, UCM Composites of anomalies Z 500 hPa HIGH vs. LOW pcp_idx HIGHHIGH LOWLOW Precipitation (std values) WINTER

CLIVAR-ES (11-13 Feb 2009) Strat-troposphere coupling & Euro-Atlantic climate variability Dept. Geophysics & Meteorology, UCM Composites of anomalies Z 500 hPa HIGH vs. LOW pcp_idx HIGHHIGH LOWLOW Z 50 hPa polar vortex strengthened at upper levels polar vortex something weakened at upper levels WINTER

CLIVAR-ES (11-13 Feb 2009) Strat-troposphere coupling & Euro-Atlantic climate variability Dept. Geophysics & Meteorology, UCM stratospheric jet Time-latitude plot of the stratospheric 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) stronger high during a 20-days period prior to The westerlies at high latitudes (60ºN-80ºN) are statistically significantly stronger not only during high episodes (central month of the diagram), but also during a 20-days period prior to the extreme pcp_idx episode. stratospheric jet It suggests that the intensity of the stratospheric jet at 10 hPa could be used as predictor of the anomalous monthly rainfall regime over Europe. WINTER HIGH vs. LOW pcp_idx

CLIVAR-ES (11-13 Feb 2009) Strat-troposphere coupling & Euro-Atlantic climate variability Dept. Geophysics & Meteorology, UCM WINTER SVR Neutral conditions WVRSVR Neutral conditions WVR lag 0lag -1 High pcp_idx Low pcp_idx 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) SVR Strong polar vortex regime (SVR): [u] 65ºN, 50hPa > 20 m/s WVR Weak polar vortex regime (WVR): [u] 65ºN, 50hPa < 10 m/s Neutral conditions: 10 m/s  [u] 65ºN, 50hPa  20 m/s HIGH vs. LOW pcp_idx High High pcp_idx ↔ strong polar vortex Low Low pcp_idx ↔ weak polar vortex X

CLIVAR-ES (11-13 Feb 2009) Strat-troposphere coupling & Euro-Atlantic climate variability Dept. Geophysics & Meteorology, UCM High High pcp_idx ↔ strong polar vortex Low Low pcp_idx ↔ weak polar vortex X WINTER HIGH vs. LOW pcp_idx High High pcp_idx: troposphere -stratosphere coupling Low Low pcp_idx : not a clear troposphere -stratosphere coupling Differences between AO and NAO? Composite of Z500 LOW pcp_idx HIGH pcp_idx  AO-like Composite of Z500  N AO-like

CLIVAR-ES (11-13 Feb 2009) 2.2. Stratospheric final warmings (SFWs) and tropospheric circulation over Euro-Atlantic region Strat-troposphere coupling & Euro-Atlantic climate variability Dept. Geophysics & Meteorology, UCM springtime a large interannual variability.  The SFWs occur once per year at springtime, and present a large interannual variability.  Our studies relationship between the late or early occurrence of the SFW and changes in the tropospheric circulation in spring months over the Euro-Atlantic region  Our studies deal with the relationship between the late or early occurrence of the SFW and changes in the tropospheric circulation in spring months over the Euro-Atlantic region (B. Ayarzagüena & E. Serrano, J. Climate, accepted)

CLIVAR-ES (11-13 Feb 2009) 2.2. Stratospheric final warmings (SFWs) and tropospheric circulation over Euro-Atlantic region Strat-troposphere coupling & Euro-Atlantic climate variability Dept. Geophysics & Meteorology, UCM Selection of TWO sets of years from the study period (45yrs) in basis of the date on which the SFW occurs: EARLY years and LATE years (reflecting a early or late breakup of the polar vortex). EARLY years and LATE years (reflecting a early or late breakup of the polar vortex). 3 th Jun 27 th Mar Mean date 17 th April 1 std day of year Data: daily zonal wind ( , ERA40) Criterion of Black et al [u50] at 70ºN date of SFWs 10 “early years” 7 “late years”

CLIVAR-ES (11-13 Feb 2009) Early vs. Late years Strat-troposphere coupling & Euro-Atlantic climate variability Dept. Geophysics & Meteorology, UCM  Differences in the stratospheric mean flow (related to differences in the stationary wave activity  Differences in the stratospheric mean flow (related to differences in the stationary wave activity) Zonal-mean zonal wind (m·s -1 ) APRIL In ‘early years’, the polar vortex has already disappeared and the easterlies extend to lower levels and latitudes than the climatology (mean flow has changed from westerlies to easterlies)  anomalous low upward propagation of waves.In ‘early years’, the polar vortex has already disappeared and the easterlies extend to lower levels and latitudes than the climatology (mean flow has changed from westerlies to easterlies)  anomalous low upward propagation of waves. SPRING In ‘late years’, the polar vortex still persists and stronger mean flow than the climatology about 30ºN northwards In ‘late years’, the polar vortex still persists and stronger mean flow than the 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 easterlies

CLIVAR-ES (11-13 Feb 2009) Early vs. Late years Strat-troposphere coupling & Euro-Atlantic climate variability Dept. Geophysics & Meteorology, UCM  Differences in 500-hPa geopotential and zonal wind fields Z500 anomalies (gpm) APRIL In ‘late years’: well-defined Atlantic tripole of Z500 anomalies (negative values over high latitudes and subtropical Atlantic, positive values at west of the British Isles)In ‘late years’: well-defined Atlantic tripole of Z500 anomalies (negative values over high latitudes and subtropical Atlantic, positive values at west of the British Isles) In ‘early years’: different pattern to ‘late years’ (← Z500-tripole centers are weaker, shifted and deformed.In ‘early years’: different pattern to ‘late years’ (← Z500-tripole centers are weaker, shifted and deformed. AO + -like  AO - -like SPRING

CLIVAR-ES (11-13 Feb 2009) Early vs. Late years Strat-troposphere coupling & Euro-Atlantic climate variability Dept. Geophysics & Meteorology, UCM  Differences in 500-hPa geopotential and zonal wind fields Z500 anomalies (gpm) APRIL AO + -like  AO - -like AO + AO - Total early years 4610 late years SPRING Fisher-Irwin test Independence between AO phase & late/early year (92% confidence level)

CLIVAR-ES (11-13 Feb 2009) Early vs. Late years Strat-troposphere coupling & Euro-Atlantic climate variability Dept. Geophysics & Meteorology, UCM  Differences in the storm track activity (at 500 hPa) Units: gpm APRIL Statistically significant differences, between ‘early and late years, both in the entrance (North America coast) and exit (Scandinavia) regions of the storm tracks in the Atlantic area. Statistically significant differences, between ‘early and late years, both in the entrance (North America coast) and exit (Scandinavia) regions of the storm tracks in the Atlantic area. SPRING

CLIVAR-ES (11-13 Feb 2009) Early vs. Late years Strat-troposphere coupling & Euro-Atlantic climate variability Dept. Geophysics & Meteorology, UCM  Differences in the storm track activity (at 500 hPa) Units: gpm In ‘early years’: compared to climatology, a southward shift of ST activity in the east coast of North America, and weakness along the whole Atlantic stripIn ‘early years’: compared to climatology, a southward shift of ST activity in the east coast of North America, and weakness along the whole Atlantic strip APRIL In ‘late years’, the opposite occurs (maximum of the ST activity northwards up respect to climatology; values > 40 gpm reach Scandinavian Peninsula)In ‘late years’, the opposite occurs (maximum of the ST activity northwards up respect to climatology; values > 40 gpm reach Scandinavian Peninsula) SPRING

CLIVAR-ES (11-13 Feb 2009) Strato-troposphere coupling & Euro-Atlantic climate variability Dept. Geophysics & Meteorology, UCM New topics under current study ( REN ) strength of the stratospheric polar vortexarctic ozone content  Degree of connection between the strength of the stratospheric polar vortex and the arctic ozone content (end of winter and during spring) UCLA global model reproduces the stratospheric circulation  Analysis of how well the UCLA global model reproduces the stratospheric circulation (→ estudios de sensibilidad)

CLIVAR-ES (11-13 Feb 2009) Strato-troposphere coupling & Euro-Atlantic climate variability Dept. Geophysics & Meteorology, UCMConclusions - 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. late or early occurrence of the yearly SFW impact on the troposphere over the Euro-Atlantic regionlate yearsearly yearshigherlower - The late or early occurrence of the yearly SFW (spring months) seems to have some impact on the troposphere over the Euro-Atlantic region, especially in April. The storm track activity in late years (early years) is such that leads to a higher (lower) number of storms crossing North Europe.