Teleconnections physical processes and applications Steven Feldstein December

Teleconnections: physical processes and applications Steven Feldstein December 5, 2008 Mc. Gill University

The dominant Northern Hemisphere teleconnection patterns North Atlantic Oscillation Pacific/North American pattern Climate Prediction Center

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 seasonal NAO seasonal PNA Corr=0. 98 daily NAO Corr=0. 97 DAILY ROTATED EOFS daily PNA Feldstein (2000)

POWER SPECTRA = 9. 5 days Period (years) PNA Power NAO = 7. 7 days Period (years) An AR(1) process Power spectral density function Feldstein (2000)

DAILY NAO INDEX & FORECAST (since ~2002) Climate Prediction Center

Implication for interannual variability? Feldstein (2002)

Feldstein (2002) Climate Noise: relationship between daily & interannual NAO variability Most interannual NAO variability is from Climate Noise

Physical processes of the NAO Streamfunction tendency equation Projections NAO Feldstein (2003)

NAO DRIVING MECHANISMS Linear + Nonlinear NAO AMPLITUDE Nonlinear Linear High-frequency eddies Vorticity Advection Low-frequency eddies Divergence Feldstein (2003)

Day 1 Day 4 Day 7 Day 10 Benedict et al. (2004)

Initial perturbation NAO + MODEL SIMULATION NAO - Area of small potential vorticity gradient Franzke et al. (2004)

Are the previous solutions robust? NAO + (35 model runs) low-lat initial perturbation NAO - (35 model runs) high-lat initial perturbation mid-lat initial perturbation Franzke et al. (2004)

Regimes vs. Continuum Are teleconnection patterns characterized by 1. a small number of recurrent regimes (NAO, PNA, etc. ): enhanced predictability or 2. a continuum of patterns (NAO- and PNA-like patterns): reduced predictability Franzke and Feldstein (2005)

Regimes vs. Continuum • Define teleconnections as a sequence of one-point regression patterns • Teleconnections become non-orthogonal BASIS FUNCTIONS : teleconnection patterns (e. g. , NAO, PNA spatial patterns) : amplitude time series (e. g. , NAO, PNA indices) Franzke and Feldstein (2005)

NAO PNA Joint Probability Density Functions WP EA Teleconnections form a continuum Franzke and Feldstein (2005)

Summary of Physical Processes • Prominent Northern Hemisphere teleconnection patterns have a timescale of 7 -10 days • Interannual variability of most teleconnection patterns arises from climate noise, not necessarily from SST and/or sea ice • The NAO is comprised of the remnants of breaking synoptic-scale waves; nonlinear process • The PNA is primarily a linear dynamical process

APPLICATION: Middle Eastern precipitation l Is Middle East precipitation associated with the variability of a particular teleconnection pattern?

Middle Eastern precipitation Data and methodology l Data: daily precipitation data averaged over 12 sites in Israel. (Ziv et al. 2006, Quart. J. Roy. Meteorl. Soc. ) l Calculate composite 300 -h. Pa geopotential height field for dates with extreme precipitation l Daily SL (Southern Levant) index obtained by projecting the daily 300 -h. Pa geopotential height field onto composite pattern Feldstein and Dayan (2008)

Middle Eastern precipitation Composite 300 -h. Pa geopotential height field: Southern Levant (SL) pattern H L Feldstein and Dayan (2008)

300 -h. Pa geopotential evolution - Middle Eastern precipitation -6 days 0 days +5 days -4 days +2 days +7 days -2 days +4 days +9 days Feldstein and Dayan (2008)

Wave Packet & Middle East precip l Wave packet first observed in the northeast Pacific. The packet travels 3/4 of the distance around the earth before decaying over the northwest Pacific l Wave packet amplifies as it passes over western Europe and the Middle East. This coincides with enhanced precipitation over the Israel. l The wave packets have an eastward group velocity with a near zero phase velocity. l Are these wave packets related to the circumglobal teleconnection pattern (Branstator 2002)?

Circumglobal Teleconnection Pattern EOF 1 Wave packets associated with SL precip wet dry Time-averaged V 300 over persistent event (lag -6 to lag +9 days) Correlation with EOF 1 =0. 83 Correlation with EOF 1 =-0. 72

Wave packet evolution & potential vorticity gradient -6 days 0 days +5 days -4 days +2 days +7 days -2 days +4 days +9 days Feldstein and Dayan (2008)

Some Implications • The circumglobal wave packet may be a fundamental pattern of variability. • The circumglobal wave packet can influence interannual Middle East precipitation through climate noise. • Global warming --> poleward movement of extratropical wave guide (rising of tropopause) --> circumglobal wave packets move north of the Middle East --> disappearance of Jordan and Euphrates Rivers (Kitoh et al. 2008) • Forecasting: circumglobal wave packets used for 7 -day forecast of rain-gauge level precipitation with a hidden Markov model (Samuels, Lall, and Feldstein 2008) (water resources planning)

Precipitation change: ave(2080 -2099) - ave(1980 -1999) IPCC 2007

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 arises from nonlinear processes (wave breaking), while the PNA arises from linear processes • The circumglobal wave packet excites Middle East precipitation • Global warming: poleward movement of extratropical wave guide --> circumglobal wave packets bypass the Middle East.

Middle East Precipitation • Precipitation occurs when a circumglobal wave packet passes over western Europe & the Middle East • The wave packet is initiated over the northeast Pacific, travels eastward, until it decays over the northwest Pacific; group velocity: about 25 degrees longitude/day phase velocity: close to zero • Interannual variability of Middle East precip (droughts and floods) is associated with the winter-mean phase of wave packet. • Much of the interannual Middle East precip variability is due to climate noise • The circumglobal teleconnection pattern can be understood as a time average of the circumglobal wave packet confined to subtropical & extratropical wave guides (jets): a fundamental pattern • Global warming: poleward movement of extratropical wave guide (rising of tropopause) circumglobal wave packets bypass the Middle East.

EA/WR streamfunction tendency equation RHS of streamfunction tend. equation Relative vorticity advection LHS of streamfunction tend. equation Planetary vorticity advection Vorticity advection + nonlinear eddy fluxes Vorticity advection Nonlinear eddy fluxes Divergence

Circumglobal Teleconnection Pattern (Branstator 2002) from NCAR Community Climate Model From -remote ENSO response -global change experiments

7 -day Precipitation forecast using nonhomogeneous hidden Markov model external parameter: circumglobal wave packet Samuels, Lall, Feldstein (2008)