MEA 443 Fall 2008 Course Outline and Review Sheet

Within this course overview/outline, I have indicated what is expected of you. In using this document as a study guide to assist in your preparation for the final exam, note that there is no guarantee that all exam topics are represented here. However, I have made my best effort to clarify expectations, and if you know the material indicated below then you should do very well on the exam.

I. Review A. Basics 1.) Scales of Motion 2.) Coordinate Systems 3.) Basic Variables and Notation 4.) Governing Equations B. Geopotential, Thickness, and the Thermal Wind 1.) Geopotential 2.) Hypsometric Equation 3.) Thermal Wind Relation 4.) Applications C. Vorticity and the Vorticity Equation 1.) Definitions 2.) “Types” of Vorticity 3.) The Vorticity Equation 4.) Applications: Rossby Waves, Cyclones, and Fronts

Questions (Weeks 1 and 2) • The midlatitude westerly jet stream is narrow, and centered at an altitude of roughly 10 km. Explain this observation using physical principles, and in your own words. What is the link between fronts, jets, and temperature gradients? • Be able to use thermal wind arguments to explain wind or temperature patterns in jet streams. • Know how to do a scale analysis for a given equation or meteorological quantity, such as vorticity, divergence, or the frontogenetical function. • Given some data (e.g., a map analysis), be able to compute vorticity, and determine if a feature is a trough or ridge. • Know the basic meteorological variables quantities and their physical meaning (e.g., Geopotential, Geopotential height, potential temperature, etc.) • Why is the wind subgeostrophic in a trough and supergeostrophic in a ridge? • Know the terms in the vorticity equation and what they represent, physically. • What are Rossby waves and why do they propagate westward relative to the background flow? What factors dictate Rossby wave phase speed? • Given the appropriate information (horizontal maps or soundings), be able to identify regions of cold and warm advection. From appropriate horizontal maps, be able to identify positive and negative vorticity advection.

II. Synoptic-Scale Dynamics A. Quasigeostrophic theory (Carlson Ch. 4, Bluestein V.I., Ch. 5) 1. Overview and purpose of QG 2. The QG approximations 3. The QG system of equations 4. The QG omega and height-tendency equations 5. QG omega equation 6. Interpretation of QG omega 7. The cancellation problem and the q-vector approach 8. The QG height-tendency equation 9. Physical interpretation of the QG height-tendency equation 10. Addition of diabatic processes to QG system 11. QGPV and the height-tendency equation

Expectations: • Know the approximations that went into the QG theory. To what types of weather system does it apply, and when is it not relevant? • What is the physical interpretation of the QG omega? How does this relate to thermal wind, geostrophic, and hydrostatic balance? • What is a typical value for vertical velocity on the synoptic scale? • Know how to interpret terms in the QG omega, height tendency, vorticity equations. How does one go about deriving a vorticity equation? • What are the differences between the “full” and QG vorticity equations? • Be able to correctly apply QG reasoning in a forecast situation. Understand the significance of q-vector convergence, differential PVA, WA, CA, etc. • Be able to compute q-vectors given idealized or observed data. • Be able to explain the evolution of troughs and ridges based on height-tendency equation concepts. • What are the advantages of q vectors relative to the “traditional” QG omega equation terms? • Know how to recognize QG frontogenesis, given q-vectors and isotherms.

B. Cyclones and Cyclogenesis (Carlson Ch. 10, Bluestein V.II., Ch. 1) 1. Introduction and Climatology 2. Frontal Evolution and the Cyclone Life Cycle 3. Cyclogenesis 4. Jet/Trough dynamics and surface cyclogenesis a.) Petterssen type A and B cyclogenesis b.) Upper trough structure and evolution c.) Sutcliffe-Petterssen “self development” concept d.) QG energetics 5. Nonlinear Processes and Explosive cyclogenesis a.) Surface processes and feedbacks b.) Definition of “explosive” cyclones c.) Presidents’ Day cyclone example

Expectations: • Know (geographically) where cyclones tend to form and why they tend to form there. • Why do cyclones frequently form along fronts? What equation explains this? • Know Petterssen “type A” vs. “type B” cyclogenesis; what is the role of the upper trough in cyclone development? • What is “self development”? Given some data, could you recognize it? • What process ultimately limits the cyclone self development process? • Know the energetics of cyclones. What are the energy sources? How does trough tilt factor in? Given some data, determine the sign of the energy conversion. • Given some data, be able to assess the factors that determine the expected evolution of an upper level trough and/or accompanying surface cyclone. • In what sense is explosive cyclogenesis a non-linear process? What physical processes are important to cyclogenesis? • Where do explosively deepening cyclones tend to form? Why are these regions favored?

III. Regional Synoptic Meteorology A. Cold-air damming (Handout material, Bluestein V.II., pp. 359-362) 1.) Introduction to Cold-Air Damming (CAD) 2.) CAD physics a. Force balance in CAD b. Theoretical parameters and CAD structure c. Thermal advection and CAD d. Diabatic processes e. Upper-level processes 3.) CAD classification and impact a. NWS CAD sub-types b. Sensible weather impacts 4.) CAD Erosion and model prediction 5.) CAD, cyclogenesis, and p-type

Expectations: • Given a sea-level pressure analysis with surface observations, how can you tell if CAD is underway? • What is the physical mechanism of CAD? What is responsible for the pressure distribution? Be able to figure out where ridging and troughing would develop, given a hypothetical situation with isobars and an orographic barrier. • Know the Froude number, the Rossby radius of deformation, and the force balance expected during CAD. • Given some data, be able to classify a CAD event using the NWS scheme. • Understand the role of diabatic processes in CAD. • Know the typical model problems relating to CAD • What are the mechanisms that lead to the erosion of CAD? Physically, how does CAD erosion occur? • How does the CAD climatology relate to winter weather climatology? B. Winter Precipitation Processes and Forecasting 1.) General considerations and climatology 2.) Physical processes a.) Factors affecting the thermal profile b.) Model representation of winter weather physics c.) Case study comparison 3.) Lake-effect snowstorms 4.) Precipitation-type forecasting techniques Expectations: • What is “partial thickness”? How, theoretically, does thickness help us with precipitation-type forecasting? • Given a temperature profile or thickness information, be able to form a prediction of expected precipitation-type at the surface, based on either the partial thickness nomogram or sounding interpretation. • What are the mechanisms responsible for lake-effect snow? • What diabatic processes can alter precipitation type at the surface? What are the limitations of numerical models in accounting for these biases? • Given a real data set, be able to make a precipitation type and amount prediction, based on techniques used in class and your knowledge of meteorological processes. • Understand the basic impacts of freezing, melting, thermal advection, adiabatic ascent, and other mechanisms that can impact surface precipitation type.

C. Isentropic Analysis (Carlson Ch. 12) 1. Basics 2. Interpretation of Isentropic Charts a.) Montgomery streamfunction and geostrophic flow b.) Constructing an isentropic map c.) Representation of vertical motion on an isentropic surface d.) The “Frozen wave approximation” e.) Interpretation of system-relative airflow in the isentropic framework 3. Applications Expectations: • Know the basic premise behind isentropic analysis. Understand why it is advantageous to use potential temperature as a vertical coordinate, and know what complications can arise from this. • Why do we call lines of constant potential temperature “isentropes”? • Be able to tell the difference between profiles of T and θ, and locate upper fronts, jets, and the tropopause on a cross-sectional plot. • Given an isentropic map, you should be able to identify regions of isentropic uplift or subsidence. • Why does isentropic moisture transport provide a more accurate picture of moisture advection than isobaric methods? • What is “storm-relative isentropic flow”, and why is it useful? • Be familiar with the “conveyor belt” paradigm, and be able to identify the main airstreams in a midlatitude system. IV. Fronts and Jets A. Fronts and Frontogenesis (Carlson Ch. 13, 14) 1. Frontogenesis a.) General frontal properties b.) Review of kinematic frontogenesis mechanisms c.) QG frontogenesis d.) Transverse circulations: The Sawyer-Eliassen Equation e.) Frontal collapse and frontal dynamics 2. Types of fronts a.) Cold frontal structures b.) Warm fronts c.) Occluded fronts d.) The coastal front 3. Upper Fronts and Jets

Expectations: • Know the basic frontal properties. Given data, be able to locate and analyze a front. • Why are fronts frequently accompanied by clouds and precipitation? • Know the basic mechanisms of frontogenesis. • Specifically, why are fronts favored along the southeast coast of the U.S. and Texas? Know the mechanisms of coastal frontogenesis. How does it relate to CAD? • What is the difference between “kinematic” and “dynamic” frontogenesis? • What is “frontal collapse”? • What are “katafronts” and “anafronts”? • How do the dynamics of upper fronts differ from surface fronts? • What is potential vorticity? How does it relate to upper fronts? • Know the straight-jet model, and understand why the associated circulations exist. What is meant by “thermally direct” and “thermally indirect”? Where do each of these circulations occur? • When is the straight-jet model not applicable? How is it modified for strongly curved flow? Or strong thermal advection? • What is the link between frontal circulations and QG forcing? • What is the difference between a primary and secondary circulation?

V. Atmospheric Modeling (Numerical Weather Prediction, NWP) A. Background, Overview of Operational NWP 1. Historical background of NWP 2. Premise and an example 3. Finite differencing of equations 4. A simple program 5. Overview B. Details: 1. Numerics: Vertical coords, hydrostatic and non-hydrostatic 2. Grid point versus spectral models 3. Data assimilation, initialization, and boundary conditions 4. Sources of model error 5. Ensemble prediction C. Operational model characteristics D. Model Output Statistics (MOS)

Expectations: • Know the basic approach to weather forecasting. For example, if surface, upper-air, and satellite data are provided, in addition to numerical forecast output, I expect that you would be able to make and defend a forecast. • Know how numerical forecast models work. What types of observation go into the model analyses? Is the model analysis really an observational analysis? • What is the CFL condition? Why does it matter in operational modeling and weather prediction? • For the NAM and GFS, know the type of model (spectral or gridpoint), the approximate vertical and horizontal grid spacing, and the vertical coordinate. • Know what the term “parameterization” means. What is it? Why is it necessary? How can it limit the accuracy of NWP? • Know the main limitations of NWP- what are the main sources of error? • Why are there two different “kinds” of precipitation in numerical models? • Be able to provide a basic explanation of how a CP scheme works. • What happens when a model is run at high resolution without a CP scheme? • What are some ways that CP schemes can influence a weather forecast? What can forecasters do to tell if the CP scheme is important to the forecast? If they find that it is, how does this change the way they interpret the information? • Know what ensemble forecasting is, and what information it provides beyond what a deterministic forecast can provide. • What is “data assimilation”, and how does it relate to the numerical forecast process? • What is MOS? What information does it include, and what is the basis for MOS forecasts? What are the limitations of MOS?