Equatorial waves in two-dimensional turbulence on the sphere

Josef Schröttle1,6, D.L. Suhas2,3, Nili Harnik1, Yair Cohen4,7, Jai Sukhatme2,5
1) Department of Geophysics, School of Earth Sciences, Tel Aviv University, Israel
2) Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bangalore, India
3) Dapartment of Earth and Planetary Science, University of California, Berkeley, USA
4) California Institute of Technology and Jet Propulsion Laboratory, Pasadena, USA
5) Divecha Centre for Climate Change, Indian Institute of Science, Bangalore, India
6) Satellite data assimilation & Destination Earth Team, ECMWF, Bonn
7) Climate Simulation Research, NVIDIA, Santa Clara, CA
On any given day in the tropics, satellite observations reveal a rich variety of clouds, accompanied by a range of precipitation types and strengths – even tropical cyclones. Within this sporadic activity, a striking feature is the formation of localized deep convection centers, in which most of the rain occurs. Severe thunderstorms may occur on a daily basis. While individual convection centers are quite short lived and variable, observations spanning several days reveal an organized aggregation of moist convective activity. The cause & effect of this aggregation is still not understood in the scientific community. Spectral analyses of moist convection-related quantities like outgoing long wave radiation show significant power at discrete spatial scales up to ≈ 10 000 km embedded in a red-noise spectrum originating from a fully turbulent atmosphere. The observed maximum variability in brightness temperature corresponds to theoretical equatorial wave dispersion relations on the β-plane.
The tropical convection can be seen to also aggregate in large scales driven by features found in dry dynamics, like tropical Rossby, gravity, Kelvin waves, and the MJO - one prominent 60-90 day time scale planetary wave, which has a strong influence on weather in the tropics and outside (influencing seasonal prediction skill). The interaction and influence of moisture on these large scale patterns is still not understood at a basic level. In computer simulations, groups around the globe are beginning to include the role of moisture in simple shallow water flow to better understand the challenge it poses from a physical perspective, as it makes the physics irreversible. We present first results from an ensemble of simulations indicating possible multiple-equilibria in the tropical flow, once latent heat release passes a certain threshold.
The talk will be organized as department seminar in zoom with several opportunities to reflect & ask questions.