© crown copyright met office the stratosphere and seasonal to decadal prediction adam scaife, sarah...

© Crown copyright Met Office

The stratosphere and Seasonal to Decadal

Prediction

Adam Scaife, Sarah Ineson, Jeff Knight and Andrew Marshall

January 2009


Intraseasonal to Seasonal

• Early studies suggested an NAO/AO response to imposed stratospheric changes in GCMs

• Observations show downward propagation of wind anomalies from the upper stratosphere

• Some studies show additional predictability from the stratosphere on monthly to seasonal timescales


Dynamical forecastDynamical forecast + 70hPa stat fcast

Christiansen 2005

Downward propagating winds

Baldwin and Dunkerton 2001

See also:

Kodera et al 1990, Boville 1984

Surface wind at 60N


Winter 2005/6

• Extreme stratospheric warming

• Downward propagation

• Surface cooling and extreme snowfall


Winter 2005/6 ensembles

Tropospheric models (HadAM/HadGAM)• 50/25 members• HadISST as a boundary condition

Tropospheric Model + stratospheric perturbation• 25 members• HadISST as lower boundary condition• Perturbed stratosphere from 1st Jan

Zonal wind at 50hPa

Adam Scaife

Control PerturbedObserved

Scaife and Knight, QJRMS, 2008


Standard

model

Extended

model

39.3km

84.1km

HadGEM2-A 15-member

ensemble hindcasts

(1 Dec – 30 Apr)

15 winters, 1962-2005

Extended and Standard Models


Predictability of stratospheric warmings

Improved seasonal prediction of European winter cold spells:

StandardExtended

0.6 | 0.30.6 | 0.40.7 | 0.30.7 | 0.20.4 | 0.1Peak easterly magnitude(fraction of observed)

12 | 89 | 612 | 1215 | 1013 | 5Maximum lead time for capture (days)

EventMean

26 Feb1999

15 Dec1998

7 Dec1987

24 Feb1984

Zonal wind(10hPa,60N)

(Ext | Stand)

Marshall and Scaife, submitted


Atmospheric blocking

Climate models and weather forecasts underestimate blocking frequency after >5 days

Strat-trop model reproduces maximum blocking frequency in both Pacific and Atlantic sectors

Is ultra-high horizontal resolution essential?

Climate model blocking frequencies (D’Andrea et al. 1997, Tibaldi and Molteni 1990)


Interannual to Decadal

• It is not only the ocean which contains a long memory. Stratospheric processes have a long memory too! For example the QBO has a period of 2-3 yrs and is predictable for 1-2 cycles.

• Key elements of interannual to decadal variability are strongly influenced by stratospheric processes.

• Some key recent examples…..


Remote El Nino effects

Model El Nino anomaly (50hPa geopotential height) Observations (Hamilton, 1993)

Ineson and Scaife, Nature Geoscience, (2009)


Remote El Nino Effects

Zonal Wind Temperature



Remote El Nino Effects

Jan-Feb PMSL Jan-Feb T2m



Remote El Nino effects

50hPa gph

Standard

PMSL

Extended


Quasi-Biennial Oscillation

50mb geopotential height anomalies (m): QBOE-QBOW composites

Negative phase of the AO, as observed(statistically significant)

Analysis Model

Marshall and Scaife (2009), submitted


Quasi-Biennial Oscillation - surface

Surface temperature anomalies (K): QBOE-QBOW composites

Cooling over northern Europe, as observed

Analysis Model

AO response captured in early stages of winter seasonal hindcasts

Better representation of the QBO could lead to improved forecasts at seasonal-to-multiannual timescales

Marshall and Scaife (2009), submitted


Quasi-Biennial Oscillation in models

QBOW: 1963/64, 1982/83, 1992/93 and 1998/99

QBOE: 1962/63, 1974/75, 1983/84, 1989/90, 1991/92, 1995/96 and 1997/98

Standard model drifts to easterly bias (c.f. Hamilton and Boer 2008)

Extended model simulates realistic QBO (Scaife et al., 2000)

=> Interannual predictability for extratropics in winter

QBO anomaly, 30hPa

DEC JAN FEB MAR APR

0

10

20

- 20

- 10


Decadal climate: Antarctica

Ozone depletion led to increased Antarctic winds from the stratosphere to the surface.

Observations and models agree on the impact: cooling over pole surrounded by warming

Ozone recovery expected by ~2060 so this signal will reverse

Potential for decadal prediction skill?

Change per 30 yrs, Thompson and Solomon (2002)


Decadal climate: NAO trends

“Tropospheric models” do not easily capture the observed NAO trend.

Note 1960s to 1990s change


Decadal NAO trends

Change in NAO index

Observations have a large increase in NAO

Control run has very little increase in NAO(includes GHG, aerosols, observed SST etc)

NAOU50hPa

Both NAO and stratospheric wind increase

Decrease in recent years

Similar multiannual variability

1960 2000


Decadal NAO trends

Change in NAO index Change in surface pressure

Impose a body force in the model stratosphere (c.f. Norton 2003)

=> Increase in stratospheric wind from 1960s to 1990s

=> Increase in NAO similar to observed value


Decadal Surface Climate trends

Model Temperature Observed Temperature

European T trends 1960s-1990s

HadAM3 ctl 0.15K/decade

HadAM3 expt 0.59K/decade

Observations 0.53K/decadeModel Precipitation Observed Precipitation

Scaife et al. GRL, 2005


• Stratospheric dynamics are important for seasonal to decadal surface variability

• Several sources of predictability/variability:

• Sudden Warmings -> persistent anomalies 30-60d

• ENSO -> extratropics -> stratosphere -> NAO

• Volcanoes -> stratosphere -> extratropics -> NAO

• QBO -> extratropics -> NAO

• Decadal climate variability involves the stratosphere

• Low lid models do not represent these processes

• Necessary to achieve good skill for the extratropics


SPARC – Stratospheric Processes And their role in Climate

1 - Climate-Chemistry Interactions

• How will stratospheric ozone and other constituents evolve?

• How will changes in stratospheric composition affect climate?

• What are the links between changes in stratospheric ozone, UV radiation and tropospheric chemistry?

2 - Detection, Attribution, and Prediction of Stratospheric Change

• What are the past changes and variations in the stratosphere? o

• How well can we explain past changes in terms of natural and anthropogenic effects?

• How do we expect the stratosphere to evolve in the future, and what confidence do we have in those predictions?

3 - Stratosphere-Troposphere Dynamical Coupling

• What is the role of dynamical and radiative coupling with the stratosphere in extended-range tropospheric weather forecasting and determining long-term trends in tropospheric climate?

• By what mechanisms do the stratosphere and troposphere act as a coupled system?


SPARC Activities

• Gravity Waves

• Data Assimilation

• CCM Validation

• Laboratory Studies joint with IGAC

• SOLAR Influence for SPARC (SOLARIS)

• SPARC Dynamical Variability Activity

• DynVar Top

• DynVar intraseasonal

• DynVar climate change

• DynVar ideal

• ALL LONG SIMULATIONS – not initialised

• UTLS/SPARC Tropopause Initiative


Possible WGSIP/SPARC interaction and stratospheric experiments

• Hi Top – Low Top Hindcasts?

• Parallel to WGSIP-CHFP

• Extended models

• Same initial ocean data? Just initialising extra atmosphere?

• Interannual predictability from the QBO?

• Extended model or a simple parametrization (available)

• Easy experiment – cheap. Requires a few years of E and W QBO with a reasonable number of members. Could lead directly to forecast improvements.

© crown copyright met office the stratosphere and seasonal to decadal prediction adam scaife, sarah...

Documents