Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.a51k..02k&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #A51K-02
Physics
3314 Convective Processes, 3329 Mesoscale Meteorology, 3364 Synoptic-Scale Meteorology, 3374 Tropical Meteorology
Scientific paper
This contribution will discuss some observational aspects of the organization of equatorial rainfall systems. It is well-known that convective disturbances in the tropics occur over a very broad spectrum of scales, ranging from individual cumulus 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. The envelopes of these waves are in turn are comprised of a broad spectrum of mesoscale features, which are predominantly westward propagating. While it is certainly evident that the larger envelopes must be creating a favorable environment for the higher frequency activity within them, the precise mechanisms for this modulation are still a subject of debate, as is the inverse role of the mesoscale disturbances in the upscale transfer of energy. Interestingly, a census of a large number of individual MJOs shows that they are 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. A majority of the westward propagating features move much 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.
Kiladis George N.
Tulich Stefan
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