why was winter 2009/10 so cold?
DESCRIPTION
Why was Winter 2009/10 so cold?. Mike Blackburn National Centre for Atmospheric Science, University of Reading With input from Chris Bell, Thomas Toniazzo, Tim Woollings (NCAS; University of Reading); Brian Hoskins ( Grantham Institute, Imperial College) - PowerPoint PPT PresentationTRANSCRIPT
Why was Winter 2009/10 so cold?
Mike Blackburn
National Centre for Atmospheric Science, University of Reading
With input from
Chris Bell, Thomas Toniazzo, Tim Woollings (NCAS; University of Reading);
Brian Hoskins (Grantham Institute, Imperial College)
Thomas Jung, Laura Ferranti, Frederic Vitart (ECMWF)
Royal Meteorological Society, 5 February 2011
Summary of observed anomalies
• UK global
• Circulation patterns
NAO & blocking
• The phenomena
• Remote influences
Predictability – forecasts
Early winter 2010/11 – comparison
Attribution studies
Outline
Reading, 6 January 2010
Winter 20009/10 in the UK DJF averages
Reading: Tmax, Tmin DJF 0910
Temperature
• Mean 1.6°C
• 2.0°C below 1971-2000 average
Precipitation (%)
• Total 249mm
• 75% of average
Mike Stroud
European anomalies - DJF
NOAA Climate Prediction Center
Temperature Precipitation (% normal)
Surface air temperatureDecember 2009 January 2010 February 2010
DJF average
• Persistence
• Warm Arctic + sub-tropics
NOAA ESRL
Cold mid-latitudes, amid global warmth
NASA Goddard Institute for Space Studies – Hansen et al (2010)
Annual temperature anomalies relative to 1951-1980
Monthly comparison, 2010 vs. previous years
• DJF 2010 global average Ts second warmest on record to 2007
• Contribution from El Niño
“Global temperature is rising as fast in the past decade as in the prior two decades, despite year-to-year fluctuations associated with the El Niño-La Niña cycle of tropical ocean temperature”, Hansen et al (2010)
Westerly winds – DJF climatology
U 250hPa U 850hPa
NOAA ESRL
U 250hPa U 850hPa
NOAA ESRL
Westerly winds – DJF 2009/10
NOAA ESRL
Pressure – DJF 2009/10 anomalies
MSL PressureGeopotential height 500hPa
PMSL anomaly
NCEP reanalysis DJF 2009/10
Z500 anomaly
DJF average
Arctic Oscillation (AO)
North Atlantic Oscillation (NAO)
Z500
PMSLNOAA CPC
DJF average
Arctic Oscillation (AO)
North Atlantic Oscillation (NAO)
Z500
PMSL
NAO and AO time-series
NOAA CPC
DJF average
Arctic Oscillation (AO)
North Atlantic Oscillation (NAO)
Z500
PMSL
NAO and AO time-series
NOAA CPC; Colorado State University
Strongest AO- on record (>1900)
Iceland / Azores sea level pressure difference (NOAA ESRL)
NAO impacts in winter
Martin Visbeck, Columbia University
Positive phase Negative phase
NAO - example surface charts
UK Met Office
NAO Positive phase
2 February 2011
NAO Negative phase
5 January 2010
Upper troposphere height at 250hPaWeekly averages
NAO index
Greenland / Atlantic blocking is a strong NAO- flow regimeWoollings et al (2008, JAS; 2010, JCL)
ECMWF analyses
NOAA Climate Prediction Center(Tibaldi & Molteni blocking index)
NAO and blocking during winter 2009/10
NAO Index
Winter 2008/9Winter 2009/10
Giacomo Masato, University of Reading
Blocking frequency - percentage of days
(Pelly & Hoskins blocking index)
Blocking frequency anomalies
Early December onset of cold weather
ECMWF analyses
Animation for 04 – 11 Dec 2009:
http://www.met.reading.ac.uk/Data/CurrentWeather/archive/20091211/anims/Z250.large.gif
Animation for 11 – 18 Dec 2009:http://www.met.reading.ac.uk/Data/CurrentWeather/archive/20091218/anims/Z250.large.gif
NAO and blocking are natural variations of Atlantic weather
What factors influence them – alter the chance of high/low values?
Low extended range predictability (weeks, months)
complex interactions; multiple factors
Look at historical relationships with individual factors
What did these factors predict for DJF 2009/10?
Influences on NAO & Atlantic blocking
El Niño and La Niña
NOAA, Climate Prediction Center
Tropical convection generates Rossby waves that propagate into the extra-tropics, creating “teleconnections” with weather around the globe.
El Niño
NOAA ESRL
SST anomaly DJF 09/10
OLR anomaly DJF 09/10
NOAA Climate Diagnostics Bulletin
El Niño Teleconnections
PMSL DJF 09/10
PMSL response to moderate El Nino, Jan-Feb 1950-2000
Toniazzo & Scaife (2006)
Tropospheric teleconnections from a moderate El Niño
Project onto negative NAO
Expect response to be captured in seasonal forecasts
Dynamical DJF Forecast versus NCEP reanalysis
Z500
NCEP Reanalysis
Forecast for JFM
24
Z500 Anomalies: DJF 2009/10
Solar activity and Atlantic blocking
Woollings et al (2010)
Solar activity and Atlantic blocking
Woollings et al (2010)
Blocking frequency – composite anomalies (1958-2001)
Stratosphere – structure & variability
20°S80°S 60°S 40°S 20°N 40°N 60°N 80°N0°
20°S80°S 60°S 40°S 20°N 40°N 60°N 80°N0°
ERA-40 reanalysis
Tropopause ~10km (cold)
Stratopause ~50km (warm)
Polar vortex
Summer easterlies
Stratospheric variability:
Sudden Stratospheric Warmings (SSW)
Planetary waves
Quasi-Biennial Oscillation (QBO)
QBO waves
Latitude
Latitude
mean wind
Solar activity – mechanism 1
Kodera & Kuroda (2002)
At solar maximum:
Stratopause heating (UV+O3)
Alters planetary wave forcing
Weakens Brewer-Dobson circulation
Cools polar stratosphere, strengthens polar vortex
Downward influence on troposphere (Northern Annular Mode, NAM)
Potential interaction with tropical winds (QBO)(Gray et al (2001)
Solar activity – mechanism 2
Haigh et al (2005), Simpson et al (2009)
Idealised model response to lower stratospheric heating
Feedback between winds and weather systems in the storm-track
5K0K
Equatorial heating
Zonal wind climatology
Zonal wind response
Cold equatorial stratosphere in winter 2009/10 (solar-min + QBO?)
Temperature anomaly DJF 2009/10
Did we expect a disturbed stratospheric vortex in winter 2009/10?
DJF 09/10
QBO – equatorial winds
Modified mean state:
• Solar minimum (Labitzke & Van Loon 1988; Kodera and Kuroda 2002)
• QBO East (Holton & Tan 1980)
• Trend (stronger Brewer-Dobson circulation) (Charlton et al 2008; Bell et al 2010)
…all fit weaker than average polar vortex
Met Office analyses, University of Reading Labitzke and Kunze (2010, JGR)
QBO- east
30hP
a he
ight
, Nor
th P
ole
Did we expect a disturbed stratospheric vortex in winter 2009/10?
Increased planetary wave activity
• El Niño (Ineson and Scaife, 2009; Bell et al 2009)
• Blocking (Martius et al 2010)
• 25 of 27 SSWs in the period 1958-2001 were preceded by blocking
• SSW type is related to blocking location
Blocking frequency preceding stratospheric sudden warming (SSW) events, 1958-2001
Key features of stratospheric flow:• Minor warming – early December• Strong vortex until mid-January – major stratospheric sudden warming (SSW)• Weak, disturbed vortex late winter – persistent easterlies over polar cap
North Pole temperature at 10hPa Zonal wind at 60N 10hPa
Courtesy Andrew Charlton-Perez http://www.met.reading.ac.uk/research/stratclim/current/
Minor Major
Stratospheric vortex, DJF 2009/10
Pres
sure
Dec-01 Jan-01 Feb-01 Mar-01Dec-15 Jan-15 Feb-15
NAM index
Zonal mean zonal wind 60-90N
Pres
sure
Dec-01 Jan-01 Feb-01 Mar-01Dec-15 Jan-15 Feb-15
ECM
WF
oper
ation
al a
naly
sis
lower stratospheric split Strong mid-winter displacement SSW event
08-12-2009 01-02-2010
• Early December wave-2 simultaneous with blocking, confined to lower stratosphere
• Growth in vertical EP-flux is pre-blocking• Was it driven by PNA-type pattern (El Niño)?
• January blocking precedes SSW• Also strong PNA-like pattern, no NAO • Low EP flux (10hPa) in late winter due
to persistence of easterly anomalies in lower stratosphere
16 NOV 16 DEC 16 JAN 16 FEB 16 MAR 16 APR
EP-flux vector (10hPa, 60N)
16 NOV 16 DEC 16 JAN 16 FEB 16 MAR 16 APR
Vertical EP-flux (100hPa)
EQ
90N
Tropospheric precursors?
NOV 500hPa Z’
Japan Meteorological Agency; Freie Universtät Berlin
Eurasian snow cover in October
Cohen et al (2007, 2009)
AO -NAO -
Blocking
El NiñoEurasian snow cover (October)
Solar minimum QBO eastStratospheric
vortex
Tropical Atlantic
Planetary waves
PNA
Waves
NAM
latitude
height
Atlantic SST?
Attribution studies (1)
Cattiaux et al (2010)
• Use past relationship to predict magnitude of Winter 2010 anomaly
• European temperature
• Flow analogues
• Warm residual
• (1963 similar dynamics but colder)
Attribution studies (2)
Osborn (2011) in Weather
• Surface temperature
• Linear regression to estimate contribution of NAO-
• Residual shows European warmth
• Unexplained cold anomalies, USA, Siberia
Attribution studies (3)
NOAA Attribution Team (2010), ESRL
• US east coast snow
• Past snowstorms related to El Niño and NAO-
• Combine El Niño + NAO- regressions to account for temperature anomalies
Surface Air Temperature anomalies
Compare early Winter 2010/11
NOAA ESRL
Surface Air Temperature anomaly
December 2009 December 2010
• Remarkably similar temperature pattern
• Europe colder than 2009
• North Pacific & western USA differ
Compare early Winter 2010/11
NOAA CPC and ESRL
• Circulation change in mid-November across N.Hemisphere
• Strong NAO- again
• Pacific differs, short jet (La Niña)
• Differing factors: La Niña, QBO west
• Solar activity remains low
• Strong stratospheric vortex
250hPa wind speed
Persistent equatorward shift of jet stream
• Blocking, negative NAO
• Increased forecast skill – El Niño signal + persistence
Possible origins – factors working together?
….or chance, unpredictable?
• Attempts to attribute cold & snow anomalies
Further work
Forecast & hindcast diagnosis; anomalous forcing
Conclusions