3:30 PM - 5:00 PM
[AAS05-P07] Relationships between the phase speed and vertical structure in convectively coupled westerly inertial gravity waves
Keywords:Tropical meteorology, convectively coupled equatorial waves
Equatorial waves are atmospheric waves that are trapped in the equatorial region due to the larger variations of Colioli's parameter. The activities of cumulus convection are significantly modulated by the phase of the equatorial waves, and, in turn, the latent heat released by the cumulus convection affects the structure and phase velocity of the equatorial waves. The equatorial wave in which such kind of interactions play an essential role is called the “convectively coupled equatorial wave” (CCEW). There are many unexplored aspects of the basic mechanisms that couple waves and convection in CCEWs. Phase speed is one of them, and CCEWs are known to be quite slower than the phase speed of equatorial waves theoretically derived in the dry atmosphere framework. However, the reason for this remains unknown. In this paper, we investigate the relationship between the characteristics of the variation of atmospheric field data (temperature and vertical velocity) associated with precipitation and the phase speed of the "faster" and "slower" components of the phase speed of CCEWs to obtain clues on this challenge. In this poster, we especially focus on the westward inertial gravity wave (WIG), which is a type of CCEWs.
Based on time series of temperature and vertical velocity filtered into faster and slower components of WIG, we conducted composite analysis of them. As a result, compared to the faster component, the slow component has a larger tilt and the depth of variation of temperature and vertical velocity in the lower troposphere is shallower, and a 90-degree phase shift between the two. These features were suggestively manifested in the phase and cross spectrum between precipitation and vertical mode-decomposed vertical velocity, with the second mode leading (increasing tilt) at shallower equivalent depths (slower component), and the third mode (shallower structure) dominating relatively.
These relationships can be explained somewhat consistently from a comparison of temperature and vertical velocity variations and vertical modes in real space. In particular, the phase speeds of the faster and slower components of the WIG (n=1) were very close to the propagation speed of the second and third modes with deep and shallow structures in the lower layers, respectively. This suggests that the depth of the gravity wave structure in the lower atmosphere is important for the phase speed of the WIG (n=1). In the dry troposphere framework, the slow phase velocity is explained by the shallowness of the vertical structure, and the present results are consistent with such an interpretation.
Based on time series of temperature and vertical velocity filtered into faster and slower components of WIG, we conducted composite analysis of them. As a result, compared to the faster component, the slow component has a larger tilt and the depth of variation of temperature and vertical velocity in the lower troposphere is shallower, and a 90-degree phase shift between the two. These features were suggestively manifested in the phase and cross spectrum between precipitation and vertical mode-decomposed vertical velocity, with the second mode leading (increasing tilt) at shallower equivalent depths (slower component), and the third mode (shallower structure) dominating relatively.
These relationships can be explained somewhat consistently from a comparison of temperature and vertical velocity variations and vertical modes in real space. In particular, the phase speeds of the faster and slower components of the WIG (n=1) were very close to the propagation speed of the second and third modes with deep and shallow structures in the lower layers, respectively. This suggests that the depth of the gravity wave structure in the lower atmosphere is important for the phase speed of the WIG (n=1). In the dry troposphere framework, the slow phase velocity is explained by the shallowness of the vertical structure, and the present results are consistent with such an interpretation.