סמינר בחוג לגיאופיזיקה: The phenomenon of atmospheric heat waves and its unusual occurrence in Los Angeles on 27 September 2010
Prof. Michael Kaplan, Desert Research Institute (DIR), USA
Heat waves and other seemingly local phenomena in the atmosphere are caused by large scale circulation systems phasing with complex terrain. One such important large scale circulation system is associated with planetary wave breaking when a massive Rossby wave amplifies and breaks producing a narrow distended trough. When this occurs the surfaces of constant entropy in the troposphere descend to the surface, heat the local atmosphere, and interact with surface sensible heating over elevated terrain. In a similar manner a remarkable sequence of atmospheric dynamical/thermodynamical processes lead to the hottest day ever recorded in Los Angeles, California and environs. Not only was this the hottest day ever in L.A. and many other Southern California locations but it occurred before 1300 hours local time and in late September only kilometers from the Pacific Ocean. This extraordinary event was the end result of multi-scale interactions involving the polar and subtropical jet streaks, an extraordinary easterly wave very far poleward for so late in the warm season, and local migrating mountain-plains solenoid. Our presentation will focus on four key atmospheric processes: 1) a massive planetary wave break in the polar jet stream over western North America and its interaction with the heated North American western plateau, 2) the interaction of that break with a persistent subtropical jet streak along the southern Pacific Coast, 3) the resulting easterly wave genesis uncommonly far poleward for so late in the season, and 4) the interaction of all these systems with the Los Angeles basin topography and the development of a subsequent mesoscale migrating solenoid in the basin. Multi-scale observations and multi-scale numerical simulations will be shown and described in the presentation.
מארגן הסמינר: פרופ' איל חפץ