Understanding Tropical – Extratropical Interac5ons and the MJO David M. Straus Center for Ocean-Land-Atmosphere Studies (COLA) George Mason University Acknowledgments: Priyanka Yadav Dr. Erik Swenson COLA Advanced School on Tropical-Extratropical InteracKons on Intraseasonal Time Scales 1 2017
The Madden–Julian oscilla5on (MJO) is the largest element of the intraseasonal (30–90 day) variability in the tropical atmosphere, and was discovered by Roland Madden and Paul Julian in 1971. Large-scale coupling between atmospheric circulaKon and tropical deep convecKon. The MJO is a traveling envelope of enhanced and suppressed convecKon that propagates eastward at approximately 4 to 8 m/s. Advanced School on Tropical-Extratropical InteracKons on Intraseasonal Time Scales 2 2017
Yadav, P., and D. M. Straus, 2017: CirculaKon Response to Fast and Slow MJO Episodes., Mon. Wea. Rev., 145, 1577-1596. Advanced School on Tropical-Extratropical InteracKons on Intraseasonal Time Scales 3 2017
h^p:// www.cpc.ncep.noaa.gov/ products/intraseasonal/ vpot_tlon.shtml Advanced School on Tropical-Extratropical InteracKons on Intraseasonal Time Scales 4 2017
Lin, H., G. Brunet and J. Derome, 2008: Forecast skill of the Madden-Julian OscillaKon in Two Canadian Atmospheric Models. Mon. Wea. Rev., 136, 4130-4149. Advanced School on Tropical-Extratropical InteracKons on Intraseasonal Time Scales 5 2017
Phase 3 412 days 30° N Phase 3: ConvecKon in 0° Indian Ocean, equatorial westerlies at dateline 30° S Phase 4 339 days 30° N Madden-Julian Oscilla5on 0° (MJO) 30° S Latitude MJO Standard Phases Phase 5 311 days 30° N Pictures show stream func5on at 300 0° hPa and OLR (W/m 2 ) 30° S Phase 6 371 days 30° N Phase 6: ConvecKon in W. Pacific, equatorial easterlies at 0° dateline 30° S C assou, C., 2008: Intraseasonal Phase 7 403 days interacKon between the Madden– 30° N Julian OscillaKon and the North AtlanKc OscillaKon. Nature , 455 , Advanced School on Tropical-Extratropical 0° 523–527 InteracKons on Intraseasonal Time Scales 6 2017 30° S
Understanding the extra-tropical response to the MJO Ø Measures of the observed Response: Simple regression, or composites of upper level fields (Z200) based on different phases of • the MJO. Should Z200 lag the MJO heaKng, and by how much? Changes in probability of teleconnecKon pa^erns (NAO, AO) and/or circulaKon regimes. • Ø StaKonary Wave Theory: Use of staKonary wave models (and other simplified models) to determine the steady • state response to the diabaKc heaKng associated with each phase of the MJO. (Ignore transient nature of heaKng) Ø Response to Tropical Pulses of heaKng Ø Role of mid-laKtude instabiliKes in the extratropical MJO response: Barotropic instability and the Simmons-Wallace-Branstator modes • Baroclinic instability and the role of storm track shihs • Ø Response to the full cycle of MJO transient heaKng IntervenKon Experiments • Response to Fast vs. Slow MJO Episodes • Ø Current Work and Future DirecKons Advanced School on Tropical-Extratropical InteracKons on Intraseasonal Time Scales 7 2017
Understanding the extra-tropical response to the MJO Ø Measures of the observed Response: Simple regression, or composites of upper level fields (Z200) based on different phases of • the MJO. Should Z200 lag the MJO heaKng, and by how much? Changes in probability of teleconnecKon pa^erns (NAO, AO) and/or circulaKon regimes. • Ø StaKonary Wave Theory: Use of staKonary wave models (and other simplified models) to determine the steady • state response to the diabaKc heaKng associated with each phase of the MJO. (Ignore transient nature of heaKng) Ø Response to Tropical Pulses of heaKng Ø Role of mid-laKtude instabiliKes in the extratropical MJO response: Barotropic instability and the Simmons-Wallace-Branstator modes • Baroclinic instability and the role of storm track shihs • Ø Response to the full cycle of MJO transient heaKng IntervenKon Experiments • Response to Fast vs. Slow MJO Episodes • Ø Current Work and Future DirecKons Advanced School on Tropical-Extratropical InteracKons on Intraseasonal Time Scales 8 2017
Lagged composites of Z 500-hPa anomaly for MJO (a)–(c) phase 3 and (d)–(f) phase 7. Contour interval is 10 m. numbers in upper right corners are the projecKon of the composite anomalies onto the NAO Lin, H., G. Brunet and J. Derome, 2009: An Observed ConnecKon between the North AtlanKc OscillaKon and the Madden-Julian OscillaKon. J. Climate , 22 , 364–380. Advanced School on Tropical-Extratropical InteracKons on Intraseasonal Time Scales 9 2017
count the number of occurrences of each weather regime and Phase 1 239 days NAO - 30° N 0° NAO– 1,021 days (20%) 30° S Z 500 regimes Phase 2 339 days –50 –25 30° N –75 –100 0° 30° S Phase 3 412 days 30° N 0° NAO+ 1,485 days (30%) –25 30° S Phase 4 339 days 5 –50 2 30° N 0° 30° S Latitude 2 50 5 Phase 5 311 days NAO + 30° N 0° Atlantic ridge 1,146 days (23%) 30° S Phase 6 371 days 30° N 0° 30° S 50 5 2 Phase 7 403 days 30° N 0° Scandinavian blocking 1,339 days (27%) 30° S Phase 8 365 days 30° N 0° 30° S Cassou 2008 60° E 120° E 180° 120° W 60° W 0° Longitude Advanced School on Tropical-Extratropical InteracKons on Intraseasonal Time Scales 10 –32 –24 –16 –8 0 8 16 24 32 OLR (W m –2 ) 2017 Figure 2 | Dynamical and thermodynamical signatures of the eight phases –200 –100 0 100 200 Z500 (m) of the MJO. Wintertime composite of OLR (colour) and stream function
455 | 25 September 2008 Change of Occurrence of NAO+ / NAO- Associated with MJO Phases (Cassou, 2008) NAO– NAO+ Atlantic ridge Scandinavian blocking 30 Phase 1 0 –30 30 Phase 2 0 –30 30 Phase 3 0 –30 30 Occurrence (%) Phase 4 0 –30 30 Phase 5 0 –30 30 Phase 6 0 –30 30 Phase 7 0 –30 30 Phase 8 0 –30 0 2 4 6 8 10 12 14 0 2 4 6 8 10 12 14 0 2 4 6 8 10 12 14 0 2 4 6 8 10 12 14 Advanced School on Tropical-Extratropical Lag (days) InteracKons on Intraseasonal Time Scales The phase of the MJO influences the development of NAO life cycle two weeks later 11 2017 Lagged relationships between the eight phases of the MJO and suggestive of the MJO forcing. For white bars, either the change
Quasi-Sta5onary Wave Interpreta5on of Observed Response - Rossby wave source is created in the Indian and western Pacific Oceans as MJO convecKon propagates eastward through the Indian Ocean and into the western and central Pacific - StaKonary wave trains lead to the retracKon of the Pacific jet when the MJO- related convecKon is over the Indian Ocean and, hence, to changes in the associated fluxes of momentum – implicaKons for Rossby wave breaking? Quasigeostrophic index of refracKon relevant to the response – sensiKvity to - changes (or biases) in the “basic state” - The propagaKon of the MJO influence into the North AtlanKc region is less well understood, although the changes in storm tracks may play a role. Advanced School on Tropical-Extratropical InteracKons on Intraseasonal Time Scales 12 2017
! ! ∇⋅ ! ) = − D ζ − ! ∂ ζ ( ∂ t + J ( ψ , ζ + f ) = S = − v χ ζ v χ ⋅ ∇ ζ TradiKonal Source: Divergence x VorKcity VorKcity ~ f (Coriolis parameter) D used to specify tropical “heaKng” Addi5onal Source: Vor5city Advec5on by the Divergent flow Advanced School on Tropical-Extratropical InteracKons on Intraseasonal Time Scales 13 2017
Understanding the extra-tropical response to the MJO Ø Measures of the observed Response: Simple regression, or composites of upper level fields (Z200) based on different phases of • the MJO. Should Z200 lag the MJO heaKng, and by how much? Changes in probability of teleconnecKon pa^erns (NAO, AO) and/or circulaKon regimes. • Ø Sta5onary Wave Theory: Use of staKonary wave models (and other simplified models) to determine the steady • state response to the diabaKc heaKng associated with each phase of the MJO. (Ignore transient nature of heaKng) Ø Response to Tropical Pulses of heaKng Ø Role of mid-laKtude instabiliKes in the extratropical MJO response: Barotropic instability and the Simmons-Wallace-Branstator modes • Baroclinic instability and the role of storm track shihs • Ø Response to the full cycle of MJO transient heaKng IntervenKon Experiments • Response to Fast vs. Slow MJO Episodes • Ø Current Work and Future DirecKons Advanced School on Tropical-Extratropical InteracKons on Intraseasonal Time Scales 14 2017
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