Upload
sabrina-hart
View
228
Download
4
Tags:
Embed Size (px)
Citation preview
Teleconnections and the MJO: intraseasonal and interannual
variability
Steven Feldstein
June 25, 2012 University of Hawaii
Climate Prediction Center
The dominant Northern Hemisphere teleconnection patterns
North Atlantic Oscillation Pacific/North American pattern
NORTH ATLANTIC OSCILLATION
University of Hamburg
Earliest NAO observations
Norse (Viking) settlers arrived in Greenland in CE 985. The Norse, who appeared to be very interested observers of the weather, also seemed to be aware of teleconnection patterns in the North Atlantic basin.
There was an anonymous Norwegian book (approx. CE 1230), entitled the `King's Mirror'. This book, in the form of a discussion between father and son, wrote that severe weather in Greenland coincides with warmer weather at distant locations, and vice versa.
• Danish missionary Hans Egede (1745) wrote:
“In Greenland, all winters are severe, yet they are not alike. The Danes have noticed that when the winter in Denmark was severe, as we perceive it, the winter in Greenland in its manner was mild, and conversely.”
Hans Egede map in “History of Greenland”
• Walker (1932) used correlation analysis to find the dominant teleconnection patterns, including the NAO.
SEASONAL ROTATED EOFS
DAILY ROTATED EOFS
seasonal NAO
daily NAO
seasonal PNA
daily PNA
Feldstein (2000)
Corr=0.98 Corr=0.97
NAO PNA
Period (years)
Pow
er
Period (years)
Pow
er
POWER SPECTRA
An AR(1) process
Power spectral density function
Feldstein (2000)
= 9.5 days = 7.7 days
DAILY NAO INDEX & FORECAST (since ~2002)
Climate Prediction Center
Implication for interannual variability?
Feldstein (2002)
Climate Noise: relationship between daily &interannual NAO variability
Feldstein (2002)
Most interannual NAO variability is from Climate Noise
Physical processes of the NAO
Projections
Streamfunction tendency equation
NAO
Feldstein (2003)
NAO AMPLITUDE
Nonlinear
Linear
High-frequency eddies
Low-frequency eddies
Divergence
Vorticity Advection
Linear Nonlinear+
NAO DRIVING MECHANISMS
Feldstein (2003)
Benedict et al. (2004)
Day 1
Day 4
Day 7
Day 10
MODEL SIMULATIONNAO -NAO +
Franzke et al. (2004)
Init
ial p
ertu
rbat
ion
Area of small potential vorticity gradient
Physical processes for the PNA
In contrast to the NAO, the PNA is dominated bylinear processes: stationary eddy advection.
• Both phases of the PNA are excited by tropical convection
Tropical convection excites a small amplitude Rossby wave train via linear dispersion
Synoptic-scale eddies (remote pos phase; local neg phase) amplify PNA
OLR anomalies associated with the PNA
300-hPa streamfunction anomalies associated with OLR
PAPNA PNA
PNA Life Cycle
Summary of Physical Processes
• Prominent Northern Hemisphere teleconnection patterns have a timescale of 7-10 days
•Interannual variability of most teleconnection patterns arises primarily from climate noise
• The NAO is comprised of the remnants of breaking synoptic-scale waves; nonlinear process
• The PNA wavetrain is excited by tropical convection and then amplified by breaking synoptic-scale waves; primarily a linear process
Tropical Convection Associated with Tropical Convection Associated with the Madden-Julian Oscillation (MJO)the Madden-Julian Oscillation (MJO)
Phase 1
Phase 2
Phase 3Phase 4
Phase 5
Phase 6
Phase 7
Phase 8
Time between Phases ~ 6 days
180 ۫° 60 ۫°W20 ۫°E
Dominant intraseaonal oscillation in the tropics
MJO cycle: 30-60 days
Shading OLR
Time between phases ~ 6 days
From Wheeler and Hendon (2004)
From Wheeler and Hendon (2004)
Does the MJO affect Arctic surface air temperature?
MJO Phase 1 (neg PNA) MJO Phase 5 (pos PNA)
Zonal-mean zonal wind and temperature
MJO Phase 1 (neg PNA) MJO Phase 5 (pos PNA)
Eliassen-Palm Fluxes associated with the MJO
MJO Phase 1 (Phase 5) associated with a reduced (increased) poleward heat and wave activity flux
Planetary-scale (k-1,3)
Synoptic-scale (k=4,8)
Summary of physical processes (projections onto 7-10 day SAT)
MJO Phase 5 (pos PNA)MJO Phase 1 (neg PNA)
Mean Meridional Circulation
Negative PNA Positive PNA
Multi-level primitive equation model calculation of MJO-induced Arctic SAT change (GFDL dynamical core)Use MJO-like steady heating profiles for MJO phases 1 and 5 (100 randomly selected ensemble members): Initial value problem
MJO
phase
1
MJO
phase
5
MJO-induced poleward tracer (H20) transportComposite evolution of anomalous tracer concentration
MJO
phase
1
MJO
phase
5
Tracer (H20) transported equatorward (poleward) duringMJO phase 1 (phase 5) (Perhaps can explain observed downward IRassociated with MJO)
Sensitivity of midlatitude response to initial conditions
Projections onto 7-13 day SAT
Response to MJO convection very sensitive tointial conditions
MJO Phase 1 (neg PNA) MJO Phase 5 (pos PNA)
Concluding remarks
• Most of the major teleconnection patterns have a time scale of less than 10 days
• Most of the interannual variability of the major teleconnection patterns arises from climate noise
• The NAO and arises from synoptic-scale wave breaking and the PNA as a Rossby wave train response to MJO convection followed by amplification by synoptic-scale wave breaking
•MJO impacts Arctic SAT through changes in the excitation of poleward Rossby wave propagation (poleward heat flux and eddy-induced adiabatic warming/cooling) : Poleward Rossby wave propagation is weakened (strengthened) in MJO phase 1 (phase 5) and is associated with less (more) localized tropical convection
•Downward IR (surface sensible and latent heat flux) enhances (weakens) the impact of the MJO on Arctic SAT
•Anomalous downward IR may be associated with changes in poleward moisture transport associated with MJO