Berkeley Fluids Seminar
University of California, Berkeley
Bring your lunch and enjoy learning about fluids!
Monday, April 16, 2018
12:00-13:00, 3110 Etcheverry Hall
Prof. Philip Marcus (UC Berkeley)
Abstract: The current Juno spacecraft mission to Jupiter provides us with a wealth of new data to which we can apply geophysical fluid dynamics to better understand the Jovian atmosphere’s global circulation and dynamics. We discuss a range of observations (some very new and some old) and show how they were predicted or can now be explained by theory, or how they disagree with theory. In the latter case, it may point to weaknesses in our fundamental understanding in the Jovian atmosphere, but it may also point to weaknesses in the interpretation of the raw Juno measurements, which in some instances require a great deal of processing and unproved assumptions about the atmosphere. We consider some of the basic tools of geophysical fluids such as the Thermal Wind Equation (TWE), which provides the relationship between horizontal gradients of the temperature and vertical wind shear. This textbook equation is not valid at or near the equator, but here we derive an extension of it that is valid and which allows us to deduce wind shears, vertical plumes, and global circulations in the Jovian tropics and compare the theoretical results to Juno observations. We also examine the unexpected longevity of Jupiter’s Great Red Spot (first seen by Hook 1664, if, indeed, the Spot that he observed is the same one we see today). Vortices in the ocean and atmosphere dissipate energy via various mechanisms, including wave emission, turbulence, viscous loss, and thermal radiation. However, many Jovian vortices are observed to live much longer than the time scales of these dissipation processes. Here, we model these processes as either Rayleigh drag or Newtonian cooling with time scale and use simulations of the 3D equations to model observations. Our results show that vortices in fact do NOT decay at the imposed Rayleigh or Newton time scales; they decay much slower, sometimes by factors of 100. The slow decay is due to secondary meridional circulation crated by the primary vortices, which converts potential energy to the kinetic energy and slows down the decay. For very long-lived vortices, such as the Great Red Spot, our results imply that much weak forcing, compared to what originally thought, is needed to maintain the vortices indefinitely. The vertical structure of our long-lived, theoretically modeled and numerically computed Red Spot disagrees, in part, with Juno findings. We show how at least assumption (which we believe to be incorrect) used in interpreting the raw Juno data can lead to the disagreement.