D A R G A N M . W . F R I E R S O N U N I V E R S I T Y O F W A S H I N G T O N , D E P A R T M E N T O F A T M O S P H E R I C S C I E N C E S L E C T U R E 1 : 3 / 2 8 / 1 1 GFD II: Balance Dynamics ATM S 542Atmospheric Motions  Fluid motion on the sphere! Water vapor global composite (U Wisc)Class Summary  Connecting GFD to the real atmosphere  Looking for ways to interpret atmospheric circulations  Understanding of why different classes of motions occurInstabilities  Exponential growth of perturbations Kelvin-Helmholtz InstabilityBaroclinic Instability  Responsible for midlatitude weather patterns  “Cyclogenesis” Slide courtesy of Greg Hakim• Center has lowest pressure winds are ~geostrophic • Warm air moves poleward and upward • Cold air moves equatorward and downward • “Warm front” & “cold front” • Clouds & precipitation • ~ “comma” shape. Cyclone Structure Slide courtesy of Greg Hakim7 • Intense vortex • Cold air: shallow cellular convection • Warm air: stratiform cloud • Sharp frontal boundaries Zoom in on cold front… Pacific Extratropical Cyclone Slide courtesy of Greg HakimScale collapse at cold front: “rope cloud”---narrow line convection. Slide courtesy of Greg Hakim FrontogenesisWhat is “balance dynamics” anyway?  And why is it important?  We’ll illustrate this with some history:  The first NWP experiment (Richardson, 1922)  The first successful NWP model (Charney, Fjortoft, & von Neumann, 1950) All info on this topic is from Peter Lynch: Check out his book “The Emergence of NWP”!Numerical Weather Prediction (NWP)  Improvements in weather prediction over the last 60 years are among the most impressive accomplishments of society Simmons & Hollingsworth ‘02 Northern Hem. 3 day forecast Southern Hem. 3 day forecast 5 day forecasts (NH & SH) 7 day forecasts (NH & SH) 1980 2002Lewis Fry Richardson  British mathematician, physicist, atmospheric scientist  Scientific career very influenced by his Quaker beliefs (pacifism)  Made the first numerical weather prediction in 1922 Also had a dream of the future of weather prediction…The Forecast Factory  Filled with employees (“computers”) doing calculations He estimated 64,000 “computers” (people) would be necessary to forecast over the globe Richardson’s dream in 1922 of a global forecasting systemRichardson’s Experiment SLP and surface temperature Used data from May 20, 1910Richardson’s Experiment 500 mbar heights and 500-400 mbar thickness Data taken when Halley’s Comet was passing through the atmosphere Tabulated values from these charts by hand!Richardson’s Calculations  Served as ambulance driver with the Friends’ Ambulance Unit in France during WWI  Transported injured soldiers, often under heavy fire  Took 1000 hours of work to perform the calculations  “My office was a heap of hay in a cold rest billet”  Calculation book was lost during the battle of Champagne  But recovered months later under a heap of coal  Eventually published in 1922Richardson’s resultsUW Rooftop data variabilityExtrapolating noisy rates of change Unbalanced motions which average to zero on top of a smoothly changing signal can really mess up forecasts! Balancing initial conditions is still a problem today! (big problem in data assimilation)Richardson’s forecastRichardson’s Forecast  Richardson himself realized that gravity waves (“imbalanced initial conditions”) were the problem  He suggested smoothing of initial conditions  And proposed 5 different methods for this  Unfortunately he couldn’t implement them due to computational expense  But we can reproduce the results using today’s computers…“Balancing” the initial conditionsThe First Successful NWP Experiment  Fast gravity waves were the problem:  Why not try predicting with a model that has no gravity waves?  John von Neumann, Jule Charney, Ragnar Fjortoft  Research proposal proposed three uses for NWP:  Weather prediction (duh)  Planning where to take observations  Weather modification!The First Computer!  ENIAC: The Electronic Numerical Integrator and ComputerThe First Computer!  ENIAC: The Electronic Numerical Integrator and