Cross-equatorial Rossby wave propagation in JJA climatological flow
23rd Annual CESM Workshop Climate Variability and Change working group session
Yanjie Li1, Jianping Li2, Sen Zhao3, Feifei Jin3, Jin Feng4
1. Institute of Atmospheric Physics, Chinese Academy of Sciences;
2. GCCES, Beijing Normal University;
3. University of Hawaii, Honolulu, USA4. Institute of Urban Meteorology, CMA, Beijing
06/19/2018, Boulder
Basic model: Mid-latitude β-plane
(Rossby 1939, 1945; Yeh 1949) (Longuit-Higgins 1964, 1965; Hoskins and Karoly 1981)
2
2
2 0cos cos cos
Mu vt x y a x
ψ ψϕ ϕ ϕ
∇∂ ∂ ∂ Ω ∂+ + + = ∂ ∂ ∂ ∂
Development of the Rossby wave propagation theory
Spherical coordinate
Dimension:
Basic state:Cited from http://class.atmos.ucla.edu/aos102/rossby.html
Lat-Varying Lon- and Lat-varyingRest Atmos
(Hoskins and Karoly 1981) (Webster and Holton 1982; Hoskins and Ambrizzi 1993)(Yeh 1949)
U(φ) U(λ, φ)
(Yeh 1949)
Cross-eq propagation in DJF through the tropical westerly window
Tropical westerly duct
Qy/U
(Li et al., 2015, follow HA93)
Stationary waves could cross the tropical easterly with zonal mean meridional wind Vincluded in the basic state (Schneider and Watterson 1984, Miu et al. 1990). However, fewstudies has considered this issue in JJA climatological flow, which is accompanied by strongmonsoonal cross-eq flow.
Including V provides possibility of crossing easterly
Lon- and Lat-varying Lon- and Lat-varying(Hoskins and Ambrizzi 1993)
U(λ,φ) U(λ,φ) ADD V(λ, φ)
Stationary wavenumber HA93
Stationary wavenumber with-V
mid-latitude
tropics
(Li et al., 2015)x
Y (k, l)
α γη
With V, Stationary waves can exist in tropical easterly
Exp1: Northerly
Meridional wavenumber solutions in ideal basic flows; With-V: red; Without-V (same as HK81): gray
Exp2: Southerly
(Li et al., 2015)
Setting of the ideal basic flows
At critical latitude U=0,
Tilt of constant phase line
Meridional group velocity
Northerly SoutherlyZonal wavenumber 1 Zonal wavenumber 3
Zonal wavenumber 3Zonal wavenumber 1
Exp2: Southerly
Exp1: Northerly
Specific tilt structure
Preferred tilting and direction for waves across easterly
Propagation direction along with the meridional background flow
Northerly
NE
SW
NW
SE
Southerly
Barotropic Model results
Northerly Southerly Without-V as HK81
Cross-EQ propagation under JJA climatological flow
Steered by the strongcross-eq flow
Wave ray trajectories resultsstarting from NH and SHtropics.
2
NH forcing
NH->SH
Limited in SH
Preferred spot:Asian-AustralianSummer monsoonregion
(Li et al., 2015)
SH forcing
Barotropic model resultsto NH and SH forcing.
Summary
• Stationary waves could propagate across the tropical easterlyunder the JJA flow;
• Preferred tilting structure and direction determined by V;
• Preferred spot: Asian-Australian Monsoon region;
• Cross-EQ stationary wave propagation could contribute to theinterhemispheric teleconnection related to the Asianmonsoon(Sakaguchi et al. 2016; Zhao et al., under review).
• Wave ray tracing method based on the theory in HN flowprovides a useful tool to identify the role of the wavepropagation in the teleconnection.
On-going works
• How will the cross-eq Rossby wave propagation change underthe climate change?
• Rossby wave behaviors in high-latitude, and its role in Arcticwarming effect on mid-latitude extreme events.
• Samples of the basic state in CESM simulations.
[email protected] for your attention
Related publication:
• Li Yanjie, Jian Ping Li, Fei-Fei Jin, Sen Zhao. 2015: Interhemispheric propagation of the stationary Rossby waves in the horizontally non-uniform basic flow. Journal of the Atmospheric Sciences. 72, 3233-3256, doi:10.1175/JAS-D-14-0239.1.
• Zhao Sen, Jianping Li, Yanjie Li. 2015: Dynamics of an interhemispheric teleconnection across the critical latitude through a southerly duct during boreal winter, J. Climate, 28, 7437-7456, doi:10.1175/JCLI-D-14-00425.1.
• Zhao Sen, Jianping Li, Yanjie Li, Fiefei Jin, Jiayu Zheng, 2018: Interhemispheric influence of the Indo-Pacific convection oscillation on Southern Hemisphere rainfall, Climate Dynamic, Under review.
• Koichi Sakaguchi, Jian Lu, L. Ruby Leung, Chun Zhao, Yanjie Li, Samson Hagos, 2016: Sources and Pathways of the Upscale Effects on the Southern Hemisphere Jet in MPAS-CAM4 Variable-Resolution Simulations. Journal of Advances in Modeling Earth Systems, 8, 1786-1805, doi: 10.1002/2016MS000743.
1Ray tracing and wave flux
IPCO
IOD MPCO
Applied to the SH connection with NH convective forcing
IPCO: the second dominant mode of convection over the Indo-Pacific region during JJA;Connected with EASM closely;Connected with Brazil and Australia rainfall significantly.
Data
(Zhao et al., 2018, CD, under review)
2 Applied to the upscale effects on the SH jet of MPAS-CAM4 variable-resolution simulations
Refinement in Asia Refinement in SA
upscale effects on theSH jet in MPAS-CAM4simulations
Basic flow from VRAsia Basic flow from UR120 Stationary wave relatedto the ASM precipitationcould propagate to theSH middle latitude, whichis an important pathwayfor this upscale effect.
Refinement in Asia can enhance wave sources and upper southerly flow.
Sakaguchi et al. 2016