| The Propagation of Disturbances Excited by Low-Frequency Oscillations in the Tropics |
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| 作者姓名： | Lu Peisheng |
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| 作者单位： | LASG，Institute of Atmospheric Physics，Chinese Academy of Sciences，Beijing 100080 |
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| 摘 要： | The propagation of disturbances excited by low-frequency oscillations in the tropics is investigated by applying the theory of wave packet dynamics. For simplicity, a linearized barotropic model is adopted and the zonal circulation is taken as basic current. Suppose that the disturbances or waves are superimposed on jet-like westerly basic cur-rent and excited by the forcing in the tropics. We have (1) only the eastward propagating (m>0, n>0 and σ>0) low-frequency disturbances and the stationary (σ = 0) waves can propagate into the middle and high latitudes in the Northern Hemisphere; the others, such as the westward propagating low-frequency wave (m>0, n<0, σ<0) and the high-frequency waves, are restricted only in the vicinity of source region; (2) a stationary wave (σ = 0) reaches a given latitude even more quickly than some low-frequency ones (σ>0) due to the fact that the group velocity of stationary wave is larger; (3) there is a whole wave train excited by the forcing in the tropics and extended into the middle and high latitudes, if the amplitude of the source is independent on time, especially, the low-frequency wave (σ > 0) is of travelling type propagating along the ray; (4) if the source lasts only for an interval of time, namely, its amplitude also has the character of low-frequency oscillation, the excited wave train is not always a whole one, but is restricted in the vicinity of source region in the beginning, extended from the source region to the middle and high latitudes in its saturated stage, after that it gradually becomes weaker and weaker and is detectable only in some area at high latitude, and eventually disappears. Undoubtedly, case (4) is closer to the reality, even though case (3) gives a more impressive wavy pattern.
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| 收稿时间： | 5 January 1993 |
The propagation of disturbances excited by low-frequency oscillations in the tropics |
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| Lu Peisheng.The Propagation of Disturbances Excited by Low-Frequency Oscillations in the Tropics[J].Advances in Atmospheric Sciences,1993,10(3):287-295. |
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| Authors: | Lu Peisheng |
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| Institution: | LASG, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100080 |
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| Abstract: | The propagation of disturbances excited by low-frequency oscillations in the tropics is investigated by applying the theory
of wave packet dynamics. For simplicity, a linearized barotropic model is adopted and the zonal circulation is taken as basic
current. Suppose that the disturbances or waves are superimposed on jet-like westerly basic current and excited by the forcing
in the tropics. We have (1) only the eastward propagating (m>0,n>0 and σ>0) low-frequency disturbances and the stationary (σ = 0) waves can propagate into the middle and high latitudes in
the Northern Hemisphere; the others, such as the westward propagating low-frequency wave (m>0,n<0, σ<0) and the high-frequency waves, are restricted only in the vicinity of source region; (2) a stationary wave (σ = 0)
reaches a given latitude even more quickly than some low-frequency ones (σ>0) due to the fact that the group velocity of stationary
wave is larger; (3) there is a whole wave train excited by the forcing in the tropics and extended into the middle and high
latitudes, if the amplitude of the source is independent on time, especially, the low-frequency wave (σ>0) is of travelling
type propagating along the ray; (4) if the source lasts only for an interval of time, namely, its amplitude also has the character
of low-frequency oscillation, the excited wave train is not always a whole one, but is restricted in the vicinity of source
region in the beginning, extended from the source region to the middle and high latitudes in its saturated stage, after that
it gradually becomes weaker and weaker and is detectable only in some area at high latitude, and eventually disappears. Undoubtedly,
case (4) is closer to the reality, even though case (3) gives a more impressive wavy pattern. |
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| Keywords: | Wave packet Low-frequency oscillation Quasi-stationary source Non-stationary source |
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