The Atmospheric Boundary Layer

Meteorology 556 – The Atmospheric Boundary Layer

Lectures 9:05-10:20am Tu/Th, 103 Elec. Eng. West

Class web page: 

Course description: The atmospheric boundary layer is the layer of the atmosphere that is in frequent contact with the surface of the earth. It is the layer where life exists, and which mediates exchanges of energy, momentum, and chemicals between the earth’s surface and the atmosphere. The scales of motion in the atmospheric boundary layer, because of the presence of the earth’s surface, are small compared to the rest of the atmosphere. The dynamics, therefore, differ from those found in the “free” atmosphere.

This course describes the physical properties of the layer of the earth’s atmosphere that is in frequent contact with the earth’s surface, the atmospheric boundary layer. The course includes a descriptive overview of this layer using observations, then presents the governing equations and common simplifications used to describe the boundary layer. Conservation of mass, energy, and momentum, are covered. A core principle is the decomposition of the governing equations into a mean state and turbulent components, and the challenges introduced by this decomposition. The concepts of eddy diffusivity and closure methods are motivated by this challenge.

These principles and governing equations are used to understand the typical evolution of the atmospheric boundary layer as a function of time of day. Convective and stable boundary layer conditions are contrasted. The contrasting conditions are linked to changes in the exchange of energy, momentum and water vapor at the earth’s surface. The fundamentals of plume dispersion are described and tested. A simple numerical model of the atmospheric boundary layer is discussed and applied to atmospheric data.

Stability conditions in the atmosphere are further explored using the equation for turbulent kinetic energy. Parameters describing the turbulence state of the surface layer and boundary layer, including the Obukhov length, friction velocity, convective velocity scale, and Richardson number, are discussed and applied to typical boundary layer conditions and observations. Similarity theory is discussed as a means of describing turbulent properties of the atmospheric boundary layer as a function of stability conditions. Monin-Obukhov similarity theory for the surface layer is applied to atmospheric observations. Additional common atmospheric boundary layer states are described, including cloud topped boundary layers, marine boundary layers, and boundary layers in heterogeneous terrain.

Observational, measurement and numerical methods are presented and used in class assignments.

Objectives:  After successfully completing this course, a student will be able to.

  • recognize and describe the characteristics of the atmospheric boundary layer (ABL) and how it varies with time and in different environments;

  • readily apply the basic equations describing the ABL, and demonstrate understanding of the assumptions and conditions that make those equations applicable;

  • apply the equations governing the ABL to explain ABL phenomena quantitatively;

  • engage in non-quantitative, intuitive reasoning to formulate hypotheses concerning ABL phenomena;

  • apply some of the current methods used in the study of the ABL;

  • read, synthesize, and report on research literature in the field;

  • pose, perform, and report on research questions in boundary layer meteorology. 


Kenneth Davis, Professor of Atmospheric and Climate Science, Department of Meteorology and Atmospheric Science

512 Walker Building, 814-863-8601,

Office hours: 1-2pm or 4-5pm Tu; 11am-12pm Th.  You are free to stop by my office outside of office hours, but to guarantee that I will be available, call or email in advance.  I will sometimes miss these hours due to travel or meetings that are scheduled for me.  In these cases, I’ll give you as much warning as possible and find alternative hours.  I respond to email. Tu hours will shift between afternoon hours.  I’ll keep you updated. 

Important prior knowledge: Thermodynamics (e.g. Meteorology 431 or the equivalent), fluid mechanics applied to atmospheric flows (e.g. Meteorology 421, 521 or the equivalent), and comfort with quantitative data analyses.  The course is intended for graduate students in Meteorology and Atmospheric Science.  Graduate students from related fields with a sound knowledge of thermodynamics and fluid mechanics are welcome. Undergraduates in Meteorology seeking a more challenging treatment of materials covered in Meteorology 454 are also welcome. 

Class Expectations and Norms:

  • Students are encouraged to participate actively in class. If at all possible let me know in advance when you cannot attend.  If you miss a class, you are welcome to schedule time for an update on the materials covered.
  • Classes will most often be lecture format but fairly interactive.
  • Questions and discussions are always encouraged, in class and outside of class.
  • Due dates can be flexible if you have a good reason and give advance notice, but avoid this if at all possible to keep on track and keep the class together.
  • Assignments must be done individually. Any shared work on research projects must be approved in advance.  Collaborative discussion outside of class is allowed.
  • Students in this class are expected to write up their problem sets individually, to work the exams on their own, and to write their papers in their own words using proper citations.  Class members may work on the problem sets in groups, but then each student must write up the answers separately.  Students are not to copy problem or exam answers from another person's paper and present them as their own; students may not plagiarize text from papers or websites written by others.  Students who present other people's work as their own will receive at least a 0 on the assignment and may well receive an F or XF in the course.  Please see:Earth and Mineral Sciences Academic Integrity Policy, which this course adopts. To learn more, see Penn State's "Plagiarism Tutorial for Students." 

Materials: Most reading and some homework problems will be taken from An Introduction to Boundary Layer Meteorology by Roland Stull.  This text is strongly recommended. I may also use and refer to texts by Garratt, The atmospheric boundary layer, Wyngaard, Turbulence in the Atmosphere, and Panofsky and Dutton, Atmospheric Turbulence. 

Assistance with Textbooks: Penn State honors and values the socioeconomic diversity of our students. If you require assistance with the costs of textbooks for this course, contact the Office of Student and Family Services (120 Boucke Building, 863-4926, For additional need related to socioeconomic status please visit

Assignments and their intended purpose:

  1. Reading will be assigned and is best done in advance of the relevant lectures. Do not worry if you don't understand everything the first time you read it. Instead, try to do the reading prior to lecture even if you have to skip over some material that doesn't make much sense to you.  Ask questions in class or during office hours.
  2. Problem sets will focus on the core understanding that is being taught. I will design lectures around the problem sets, and the problem sets around the essential course units. Problem sets will be graded, though perhaps not in their entirety.
  3. Problem set solutions will be asked of a subset of students for each assignment. You must have these solutions approved by me prior to submitting them. They will be posted after the problem sets are turned in to aid preparation for the final exam.
  4. The final Exam will be comprehensive, will be open book and notes (yours only), and will be meant to reinforce your understanding of the materials covered in lecture and in the homework assignments.
  5. Literature reviews will enable you to explore, synthesize and report on a set of ABL research literature of your interest. The topic and scope must be approved in advance.
  6. Research projects will enable you to formulate, conduct and report on a simple scientific question in boundary layer meteorology. Topics must be approved in advance. 

Grading:  If grades run high, grades will be assigned on an absolute basis: 90% and above = A, 80-89 = B, etc.  I reserve the right to make this grading scale easier.  If assignments and exams prove more difficult than the scale above, I will curve the grades.  I will endeavor to give everyone a good feel for the course grading fairly early in the semester.  The overall course grade will be weighted approximately as follows:

  • Problem sets 35% (5-6 assignments, 7-6% each)
  • Exams 15% (one exam)
  • Research projects / literature reviews 50% (3-4 assigned, 16.7-12.5% each)

The weighting might change as the semester develops.  If so, you will be warned promptly, and the change will reflect where most of your work is being devoted. 

Schedule with due dates, and list of class topics:

See additional documentation. 

Course Copyright

All course materials students receive or to which students have online access are protected by copyright laws. Students may use course materials and make copies for their own use as needed, but unauthorized distribution and/or uploading of materials without the instructor’s express permission is strictly prohibited. University Policy AD 40, the University Policy Recording of Classroom Activities and Note Taking Services addresses this issue. For example, uploading completed labs, homework, or other assignments to any study site constitutes a violation of this policy. Students who engage in the unauthorized distribution of copyrighted materials may be held in violation of the University’s Code of Conduct, and/or liable under Federal and State laws.

For example, uploading completed labs, homework, or other assignments to any study site constitutes a violation of this policy. 

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In order to receive consideration for reasonable accommodations, you must contact the appropriate disability services office at the campus where you are officially enrolled, participate in an intake interview, and provide documentation If the documentation supports your request for reasonable accommodations, your campus’s disability services office ( will provide you with an accommodation letter. Please share this letter with your instructors and discuss the accommodations with them as early in your courses as possible. You must follow this process for every semester that you request accommodations. 


This course abides by the Penn State Attendance Policy E-11, and Conflict Exam Policy 44-35 Please also see Illness Verification Policy, and Religious Observance Policy Students who miss class for legitimate reasons will be given a reasonable opportunity to make up missed work, including exams and quizzes.  Students are not required to secure the signature of medical personnel in the case of illness or injury and should use their best judgment on whether they are well enough to attend class or not; the University Health Center will not provide medical verification for minor illnesses or injuries. Other legitimate reasons for missing class include religious observance, military service, family emergencies, regularly scheduled university-approved curricular or extracurricular activities, and post-graduate, career-related interviews when there is no opportunity for students to re-schedule these opportunities (such as employment and graduate school final interviews).  Students who encounter serious family, health, or personal situations that result in extended absences should contact the Office of the Assistant Vice President for Student Affairs (AVPSA) and Student Care and Advocacy for help:  Whenever possible, students participating in University-approved activities should submit to the instructor a Class Absence Form:, at least one week prior to the activity. 

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Deferred Grades

If you are prevented from completing this course within the prescribed amount of time for reasons that are beyond your control, it is possible to have the grade deferred with the concurrence of the instructor, following Penn State Deferred Grade Policy 48-40 ( To seek a deferred grade, you must submit a written request (by e-mail or U.S. post) to the instructor describing the reason(s) for the request. Non-emergency permission for filing a deferred grade must be requested before the beginning of the final examination period.  It is up to the instructor to determine whether or not you will be permitted to receive a deferred grade.  If permission is granted, you will work with the instructor to establish a communication plan and a clear schedule for completion. If for any reason, the coursework for the deferred grade is not complete by the assigned time, a grade of "F" will be automatically entered on your transcript. 

Military Personnel

Veterans and currently serving military personnel and/or spouses with unique circumstances (e.g., upcoming deployments, drill/duty requirements, disabilities, VA appointments, etc.) are welcome and encouraged to communicate these, in advance if possible, to the instructor in the case that special arrangements need to be made. 


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Mandated Reporting Statement

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List of topics.  Meteorology 556, The Atmospheric Boundary Layer. 

1) Basic characteristics of the boundary layer – 3 hours
Definition of the atmospheric boundary layer.
Vertical structure of the atmospheric boundary layer
Virtual potential temperature and ABL thermodynamic stability
The atmospheric boundary layer (ABL) diurnal cycle.
Taylor’s hypothesis 

2) Statistical properties of boundary layer turbulence – 3 hours
Variances, covariances, correlations, time lags, and distributions of boundary layer turbulence in stable and unstable conditions.
The spectrum of atmospheric turbulence
Turbulence decomposition and Reynolds averaging.
Turbulent fluxes and stresses
Limits in our ability to numerically simulate the ABL.  

3) Surface fluxes – 6 hours
Diel cycle of momentum, heat, and moisture fluxes, radiative fluxes.
The surface energy balance and the Bowen ratio.
Surface flux relationships including bulk aerodynamic flux estimates
The Penman-Monteith equation.
The influence of plants and soil on the surface energy balance. 

4) Governing equations applied to the ABL – 4.5 hours
Simplifications of the governing equations for the ABL.
Flux formulation in the governing equations.
The closure problem and covariance terms in the governing equations.
Eddy diffusivity and mixing lengths.
First order closure.
Higher order closure approaches. 

5) Applications of simplified governing equations for the ABL – 4.5 hours
Vertical structure of the boundary layer.
Mean variables and fluxes.
Flux divergences and ABL property time rates of change.
Entrainment fluxes.
Dispersion of scalars and dispersion modeling: The Gaussian plume model

8) ABL modeling – part I – 1.5 hours
Quantification of entrainment fluxes.
Mixed layer model. 

6) Dynamic stability, TKE – 6 hours
Flux and variance equations.
Turbulent kinetic energy budget.
Richardson number and Obukhov Length.
Stability regimes.
Atmospheric spectra, separation of scales, the inertial subrange. 

7) Similarity theory – 4.5 hours
Surface layer similarity.
Monin-Obukhov scaling.
Link back to eddy diffusivity.
Log wind profile.
Displacement height and roughness length.
Mixed layer similarity, other similarity regimes 

8) ABL modeling – part II – 1.5 hours
Ekman spiral.
TKE model.
Large eddy simulation. 

9) Convective and stable boundary layers – 3 hours (covered throughout – revisit to tie parts together)
Diurnal cycle of surface winds, temperature, moisture.
Temporal evolution of ABL depth, entrainment. 

10) Clouds and the ABL – 3 hours
Cumulus-topped boundary layers
Stratocumulus-topped boundary layers. 

11) Organized flows – 4.5 hours
Sea-breeze, low-level jets, drainage flow, inertial oscillation.
Mountain breezes, gravity waves, roll instability.
Flow over complex terrain