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Why do 2-day waves propagate westward?

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Abstract

In observations, the 2-day waves, identified as the convectively coupled equatorial inertio-gravity (IG) waves, only propagate westward. To understand this feature, a simple theoretical model is presented for the convectively coupled equatorial waves (CCEWs). Under the assumption that the convective heating is proportional to the vertical velocity on the first baroclinic mode, the nonlinear governing equation for the meridional velocity of the CCEWs can be derived. The optimal method is used to obtain the dispersion relation from this nonlinear equation, and the results show that the deep convection can slow down the IG waves by decreasing the mean state static stability, but the key leading to the westward propagation of the IG waves is the full meridional variation of the sea surface temperature (SST). The warm SST trapped near the equator excites long westward propagating IG waves, whereas the warm SST trapped near the ITCZ centered at 10° N excites short westward propagating IG waves. This theoretical model provides a simple tool to study the CCEWs in understanding the tropical circulation.

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Acknowledgements

This work was supported by the National Basic Research Program of China (2011CB309704), Special Scientific Research Project for Public Interest (grant no.GYHY201006021), and the National Natural Science Foundation of China (grant nos. 40890155, 40775051, U0733002, 40906014, and 40976015).

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Authors and Affiliations

  1. International Pacific Research Center, University of Hawai’i at Manoa, Honolulu, HI, 96822, USA

    Fei Liu

  2. Key Laboratory of Regional Climate-Environment Research for Temperate East Asia, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100029, China

    Gang Huang

  3. State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Center for Monsoon System Research, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100083, China

    Gang Huang

  4. National Marine Environmental Forecasting Center, Beijing, 100081, China

    Licheng Feng

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  1. Fei Liu
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  2. Gang Huang
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  3. Licheng Feng
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Correspondence to Gang Huang.

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Liu, F., Huang, G. & Feng, L. Why do 2-day waves propagate westward?. Theor Appl Climatol 106, 443–448 (2011). https://doi.org/10.1007/s00704-011-0450-8

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  • DOI: https://doi.org/10.1007/s00704-011-0450-8

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