Week
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Topic
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Learning Goals.
By the end of this module, you should be able to:
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1
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Mean BL characteristics. BLM Ch 1.
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- define the boundary layer (BL)
- identify BL components/layers
- sketch & describe BL evolution (depth, T, M, q or r, c) in fair and stormy weather
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explain why the BL is important
- explain and use Taylor's hypothesis
- calculate virtual potential temperature
- describe how turbulence and micrometeorology fit into the broad range of scales of meteorological motion.
- define and use all the key words (bold, italicized) in the "Intro to BLM" book chapter 1.
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2
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Statistical tools, TKE, eddy fluxes, Reynolds stress. BLM Ch 2.
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- show how to split dependent variables into mean and turbulent parts
- apply averaging rules
- explain and demonstrate the difference between linearizing vs. Reynolds averaging the governing eqs.
- calculate mean, variance, and standard deviation from a time series of meteorological data
- calculate covariance and correlation between pairs of meteorological variables
- translate between dynamic fluxes and kinematic fluxes
- relate certain statistics to physical processes:
velocity variances are components of TKE/mass; covariance with velocity
is like a kinematic flux.
- use small-eddy concepts to estimate turbulent fluxes likely within any mean vertical gradient
- use Einstein's summation notation
- discuss the difference between viscous stress and Reynold's stress.
- define and use the friction velocity u* and other scales for the surface layer.
- define and use all the key words (bold, italicized) in the "Intro to BLM" book Chapter 2.
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3
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Mean governing eqs for turbulent flow. BLM Ch 3.
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- describe the physics of each term in each governing equation.
- list the set of governing equations (i.e., the eqs. of motion)
- list and use the steps to find the Reynolds averaged equations for mean variables, variances, covariances, TKE.
- put mean and turbulent advection terms into flux form.
- describe and justify simplifying assumptions, such as
incompressible, Boussinesq, steady state, horizontally homogeneous,
negligible mean vertical velocity (subsidence), shallow motion,
hydrostatic, etc.
- describe and calculate the Reynolds number, and discuss how it relates to turbulence.
- compare the magnitudes of viscous stresses to Reynolds stresses (again)
- start with any new governing equation and do the operations
needed to find a forecast equation for the corresponding mean
variable.
- define and use all the key words (bold, italicized) in the "Intro to BLM" book chapter 3.
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4
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Forecast eqs for turbulent fluxes and variances. BLM ch 4.
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- define the buoyancy flux and the convective velocity scale
w* (i.e., the Deardorff velocity) and other mixed-layer scales.
- derive forecast eqs for turbulent departures (primed variables)
- derive forecast eqs for variances of variables
- derive forecast eqs for covariances of variables, such as fluxes.
- discuss the physical meaning and name of each term in those equations, and explain their behavior and magnitude.
- use small-eddy mixing approaches to estimate some of the terms.
- define and use all the key words (bold, italicized) in the "Intro to BLM" book chpater 4.
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5
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Turbulence kinetic energy (TKE) forecast eqs., and flow stability concepts. BLM Ch 5.
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- define the TKE and explain why it is important
- derive the TKE forecast equation from the eqs for velocity variances
- explain the name, physical meaning, and typical behavior/evolution of each term in the TKE forecast eq.
- relate terms in the TKE equation to: free and forced
convection, Richardson number, Obukhov length, and to dispersion
characteristis of smoke.
- describe the energy cascade in the inertial subrange and the key scaling variables that characterize it.
- define flow stability, and be able to determine static (nonlocal) and dynamic statibility and turbulence onset or decay.
- relate the different Richardson numbers (flux, gradient,
bulk) to each other, and how to use appropriate values of the critical
Richardson number.
- identify when/where turbulence is isotropic, homogeneous, stationary.
- relate the relative magnitudes of terms in the TKE eq to
behaviors that you can see or feel in the ABL (clouds, soaring
birds, gustiness you feel, displays on remote sensors)
- calculate dimensionless gradients of wind and temperature, and other scaling parameters.
- define and use all the key words (bold, italicized) in the "Intro to BLM" book chapter 5.
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6
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Turbulence closure. BLM Ch 6.
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- explain why there is a closure problem for turbulent flows
- explain and use the rules for creating valid parameterizations.
- compare the differences between local closures and nonlocal closures
- list the equations and unknowns for local closures of zero through 1.5-order.
- apply mixing length theory to estimate fluxes of any variable
- state the limitations and advantages of K-theory.
- use K-theory to estimate fluxes and future state of the atmosphere
- state the limitations and advantages of transilient turbulence theory closure.
- for nonlocal closure, be able to apply a transilient matrix to predict fluxes and the future state of the atmosphere.
- define and use all the key words (bold, italicized) in the "Intro to BLM" book chapter 6.
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7
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Tuesday: Boundary conditions & surface forcings. BLM Ch 7.
Thursday: Midterm Exam. (open books and notes and calculator)
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- explain how an effective surface flux compares to a turbulent flux.
- list the main components of the surface heat budget, and sketch their typical variation with time.
- relate drag & bulk-transfer relationships to the concept of fluxes across interfaces
- explain the different ways to partition surface forcings into sensible and latent-heat components.
- explain the time lag and amplitude reduction of temperature signals with increasing depth in the soil.
- define and use all the key words (bold, italicized) in the "Intro to BLM" book chapter 7.
The midterm exam covers all learning goals up through week 7.
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8
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Statistical tools for time series. BLM Ch 8.
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- compute and explain the value and limitations of autocorrelations and structure functions for turbulent flow.
- compute and interpret discrete Fourier transforms DFT
(forward and inverse), and discuss their value and limitations for
turbulence.
- explain the Nyquist frequency and how it affects spectra
calculations, and how to avoid aliasing when you sample continuous data.
- look at a time series and anticipate its spectrum, and be
able to look at a spectrum and be able to visualize the associated time
series.
- calculate and interpret energy spectra from the DFT.
- calculate and interpret cross spectra.
- explain the meaning of terms in the spectral representation of the TKE equation.
- define and use all the key words (bold, italicized) in the "Intro to BLM" book chapter 8.
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9
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Similarity theory. BLM Ch 9.
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- explain what is "similar" about similarity theory.
- perform Buckingham Pi analysis, and explain why it is useful.
- list key scaling variables for the surface layer, mixed layer, free convection, forced convection, etc.
- use similarity relationships while being wary of their limitations.
- derive and use the log wind profile, and explain how it varies with static stability.
- find values for the aerodynamic roughness length and friction velocity in the surface layer.
- utilize spectral similarity to explain the slope of energy
spectra in the inertial subrange, and use data in this subrange to
estimate TKE dissipation rate.
- define and use all the key words (bold, italicized) in the "Intro to BLM" book chapter 9.
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10
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Measurement and simulation techniques. BLM Ch 10.
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- list the components of a measurement system.
- list which sensors have fast-enough response to measure
turbulent characteristics of temperature, wind, humidity, and
pollutants.
- discuss the difference between in-situ and remote sensors, and describe their advantages and disadvantages.
- explain why large-eddy simulations (LES) are similar to
samples made in the real atmosphere, and explain the advantages and
disadvantages of LES.
- use the eddy-correlation method to calculate turbulent fluxes, variances and energies.
- use measurements of mean variables to estimate values of
turbulent quantities, and explain the advantages and limitations of
such an approach.
- define and use all the key words (bold, italicized) in the "Intro to BLM" book chapter 10.
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11
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Unstable mixed layer (daytime, convective). BLM Ch 11.
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- sketch and explain organized structures in the convective mixed layer (ML) and its surface layer.
- compare and contrast thermals and dust devils.
- predict the growth of the mixed layer during daytime, using either TKE or thermodynamic considerations.
- define the entrainment zone and the LCL zone, and how they relate with respect to boundary-layer cumulus clouds.
- explain the role of horizontal roll vortices and mesoscale cellular convection in organizing thermals and BL clouds.
- describe and solve for the dispersion of air pollutants in a convective ML.
- explain what entrainment is, what drives it, and how to calculate it.
- define and use all the key words (bold, italicized) in the "Intro to BLM" book chapter 11.
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12
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Stable boundary layer (nighttime). BLM Ch 12.
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- sketch typical vertical profiles and how the stable boundary layer (SBL) evolves.
- use idealized and bulk models to approximate SBL profiles
- list the physical processes that affect the SBL, and explain why the SBL is so difficulty to describe and measure.
- predict SBL depth and strength evolution
- explain the low-level jet and intertial oscillations: how they work, and how to model them.
- compare and contrast buoyancy waves and stably-stratified turbulence
- explain characteristics, evolution, and governing physics of drainage winds
- define and use all the key words (bold, italicized) in the "Intro to BLM" book chapter 12.
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13
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BL Clouds and geographic effects. BLM Ch 13 & 14.
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- explain the definitions and usage of cloud thermo variables
including static energies, CAPE, and lifting condensation level (LCL).
- use a conserved-variable diagram to estimate sources, entrainment, and mixing of air inside clouds.
- explain and use long- and short-wave radiation for cloud processes and evolution.
- discuss the different processes and characteristics of fair-weather cumulus clouds (Cu) vs. stratocumulus clouds (Sc).
- explain how evolution of the LCL zone and the entrainment control the formation, timing, and coverage of Cu.
- discuss processes, evolution, and decoupling in Sc layers.
- explain fog formation, dissipation, idealized processes that control the evolution.
- compare and contrast "geographically created" and "geographically modified" flows.
- list and explain the processes behind the geographic flows.
- explain and use the equations for internal boundary layers (IBLs) and TIBLs.
- define and use all the key words (bold, italicized) in the "Intro to BLM" book chapters 13 & 14.
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