Các nghiên cứu hiện tại trong vật lý được chia ra làm một số ngành riêng biệt, nhằm mục đích tìm hiểu các khía cạnh khác nhau của thế giới vật chất. Vật lý chất rắn được cho là ngành lớn nhất, quan tâm tới tính chất của phần lớn các vật chất, như chất rắn và chất lỏng trong thế giới thường ngày của chúng ta, dựa trên các đặc tính và tương tác giữa các nguyên tử. | 5 Wave-Vortex Interactions 179 ity. By definition this strengthens the analogy between passive advection and wave refraction which then leads to more stretching of k and to even more reduced fig reinforcing the This process and the attendant wave-vortex interactions were studied under the name wave capture in 17 . The key question is How does the mean flow react to the exponentially growing amount of pseudomomentum P that is contained in a wavepacket The answer to this question follows reasonably easily once we have written down the impulse plus pseudomomentum conservation law for threedimensional stratified flow. Impulse Plus Pseudomomentum for Stratified Flow This is discussed in detail in 17 so we only summarize the result. Basically it is possible to write down a useful impulse for the horizontal mean flow in the Boussinesq system provided the mean stratification surfaces remain almost flat in the chosen coordinate system. Specifically we assume that VH uH 0 and wL 0 and also that the mean stratification surfaces L constant are horizontal planes to sufficient approximation. There is an exact GLM PV law pqL V L V X uL - p DLqL 0 if DL p pV uL 0 but with the above assumption we have the simpler qL z V X uL - p VH X uLH - Ph . We can now define the total horizontal mean flow impulse and pseudomomentum by IH ị y -x 0 qL dxdydz and PH ị pH dxdydz and we then find the conservation law d IH P H _ f r L ------ FH dxdydz. dt-------------------------------------------J 14 The slowdown of the wavepacket is reminiscent of the well-known shear-induced critical layers which inhibit vertical propagation past a certain critical line. Still the details are quite different . here the wavenumber grows exponentially in time whereas in the classical critical layer scenario it grows linearly in time. 180 O. Buhler Us . x 0 x xA x xd Fig. A wavepacket indicated by the wave crests and arrow for the net pseudomomentum is squeezed by .
