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.

lyj@mail.iap.ac.cnThanks 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