Monday, 12 January 2009: 11:30 AM
Mesoscale organization of equatorial waves
Room 129A (Phoenix Convention Center)
This contribution will discuss some observational aspects of the organization of equatorial rainfall systems in support of the Year of Tropical Convection (YOTC). It is well-known that convective disturbances in the tropics occur over a very broad spectrum of scales, ranging from individual cells to planetary scale features such as the Madden-Julian Oscillation (MJO). It is also observed that the larger scale features are composed of smaller scale equatorial waves, so that for example the "envelope" of the MJO is often comprised of eastward propagating Kelvin, and westward inertio-gravity waves. These in turn are comprised of a broad spectrum of mesoscale features, which are predominantly westward propagating. A majority of these features move too quickly (greater than 20 m/s) to be explained solely by advection. A space-time spectrum of high resolution satellite cloudiness data shows an overall dominance of westward over eastward power, especially at higher zonal wavenumbers and frequencies. In particular, a spectral peak extends from the previously well-documented large scale westward inertio-gravity peak into the westward portion of the mesoscale region, with a dispersion relationship representative of pure gravity waves. These westward gravity waves are strongly modulated by the diurnal cycle, especially over the continents. Understanding the precise role of these scale interactions is likely a crucial step towards the improved simulation of equatorial disturbances in models. Interestingly, different MJOs will be shown to be comprised of a wide variety of smaller scale disturbance types from case to case, suggesting that parameterization of their upscale impacts of might be feasible.