310/1749-9 ICTP-COST-CAWSES-INAF-INFN International Advanced School on Space Weather 2-19 May 2006 Introduction to Middle Atmospheric Dynamics Kevin Peardon HAMILTON Professor and Chair Department of Meteorology, and International Pacific Research Center (IPRC) University of Hawai`i at Manoa Honolulu, HI 96822 USA These lecture notes are intended only for distribution to participants
Introduction to Middle Atmospheric Dynamics Kevin Hamilton International Pacific Research Center, and Department of Meteorology University of Hawaii at Manoa
Zonal Mean and Eddy Components " Overall the strongest gradients in circulation are north-south rather than east-west So we describe circulation as zonal-mean (average around latitude circles) plus eddy (deviations form zonal-mean) components Zonal-mean circulation consists of generally strong zonal flow and much weaker overturning circulation in the meridional plane (mean meridional circulation, MMC)
Zonal Mean and Eddy Components " Overall the strongest gradients in circulation are north-south rather than east-west " So we describe circulation as zonal-mean (average around latitude circles) plus eddy (deviations form zonal-mean) components Zonal-mean circulation consists of generally strong zonal flow and much weaker overturning circulation in the meridional plane (mean meridional circulation, MMC)
Zonal Mean and Eddy Components " Overall the strongest gradients in circulation are north-south rather than east-west " So we describe circulation as zonal-mean (average around latitude circles) plus eddy (deviations form zonal-mean) components " Zonal-mean circulation consists of generally strong zonal flow and much weaker overturning circulation in the meridional plane (mean meridional circulation, MMC)
Dominant Balances Determining the MMC Write nonlinear advection in terms of eddy flux convergences Look for steady state Consider only dominant terms for extratropical region
"Transformed-Eulerian" Equations " Define a transformed MMC that is "forced" (mostly) by the diabatic heating " Effects of eddy fluxes on the zonal mean takes the form of an "Eliassen-Palm (EP) flux divergence " TE MMC is close to Lagrangian MMC
Tropical Middle Atmosphere Quasi-biennial Oscillation Semiannual Oscillation Tropical Effects on Extratropics
Tropical Mean Flow Dynamics Near the equator the eddy forcing of zonalmean momentum (EP flux divergence) is not balanced by Coriolis torques, but directly forces mean flow accelerations Sustained, but self-limiting eddy driven mean flow forcing comes from upwardpropagating gravity waves (and related equatorial-planetary waves)
Tropical Mean Flow Dynamics " Near the equator the eddy forcing of zonalmean momentum (EP flux divergence) is not balanced by Coriolis torques, but directly forces mean flow accelerations Sustained, but self-limiting eddy driven mean flow forcing comes from upwardpropagating gravity waves (and related equatorial-planetary waves)
Tropical Mean Flow Dynamics " Near the equator the eddy forcing of zonalmean momentum (EP flux divergence) is not balanced by Coriolis torques, but directly forces mean flow accelerations " Sustained, but self-limiting eddy driven mean flow forcing comes from upwardpropagating gravity waves (and related equatorial-planetary waves)