Persistence Behavior of Heat and Momentum Fluxes in Surface-Atmosphere Exchange

The characterization of heat and momentum fluxes is of paramount importance for a plethora of applications, ranging from engineering to Earth sciences. In the geophysical context, these fluxes quantify the surface-atmosphere momentum and heat exchanges, which eventually drive the Earth's climate. Therefore, it is of paramount importance to develop a comprehensive understanding of the turbulent generation mechanisms of the heat and momentum fluxes, which eventually would lead to better parameterization schemes for weather and climate models. In spite of its fundamental appeal, it is not evident till date how the turbulent structures associated with velocity and temperature fluctuations interact to produce the emergent flux signatures. In this work, we investigate this issue by studying the switching patterns of intermittently occurring turbulent fluctuations from one state to another, a phenomenon called persistence.

Specifically, the concept of persistence has been found to have many diverse practical applications, ranging from non-equilibrium statistical mechanics to financial dynamics to distribution of time scales in turbulent flows and many more. By separating the flux transporting motions to four different quadrants, we discover that the persistence patterns for heat and momentum fluxes are widely different. Moreover, we uncover power-law scaling and length scales of turbulent motions that cause this behavior. Furthermore, by separating the phases and amplitudes of flux events, we explain the origin and differences between heat and momentum transfer efficiencies in atmospheric turbulence. Our findings provide new understanding on the connection between flow organization and flux generation mechanisms, two cornerstones of turbulence research.