# Geography 622.01: Boundary Layer Climatology

## Instructor: John Arnfield

## Course Scope and Objectives

The primary purpose of this course is to describe, analyse and, to a limited extent, simulate near-surface climates and climatic processes. “Near-surface” in this context implies the environmental layer from about a kilometre or so in the atmosphere (but with emphasis on the first few tens of meters) to a few meters in the substrate. The term “climate” refers to spatio-temporal patterns of air movement, temperature, humidity and other atmospheric concentrations, while “climatic processes” is to be interpreted to mean the exchange of momentum, heat, water vapour and other entities which are both governed by and control the patterns of the climatic elements.

From a horizontal scale point of view, this course is mainly restricted to atmospheric features in the conventional micro- and local scale categories (from about 10 mm to 50 km). Such phenomena normally possess characteristic time scales from about 1 second to about one day. Emphasis will be upon the climatic aspects of these phenomena; that is, generalizations over time periods much longer than their characteristic time scale. However, no attempt to exclude shorter-term (meteorological) analysis of these topics will be made, especially where this is necessary for a deeper understanding of the climates.

Additional objectives of the course are as follows.

- to encourage the student to think analytically about climatological and meteorological problems,
- to encourage the student to feel comfortable representing physical systems in mathematical symbols to aid analysis,
- to encourage the student to think about climatological/meteorological phenomena in terms of exchange processes of energy, mass and momentum, rather than in terms of simple structural variables like temperature, wind speed and humidity,
- to encourage the student to adopt a scientific approach to the explanation of climatological and meteorological phenomena,
- to encourage the student to think and write economically, precisely and logically about the subject matter of the course, and
- to encourage the student to see the relevance of surface, subsurface and boundary-layer phenomena to climatological and meteorological phenomena at larger time and space scales.

## Classes

Geography 622.01 meets for three 80 minute classes per week.

## Prerequisites

**Climatology and meteorology**. It will be assumed in lectures and in the exercises that students have a competent knowledge of the prerequisite courses in climatology/meteorology (Geography 520 or Atmospheric Sciences 230). Specific knowledge from these courses will be required in the following areas: (a) the global radiation budget and its components, (b) the gas laws, (c) atmospheric stability, (d) humidity variables, and (e) atmospheric dynamics. Other areas of these courses may be relevant in understanding examples offered in support of lecture material.

**Mathematics**. Prerequisite mathematics is required to the level of Mathematics 152. The methods of differential and integral calculus will be employed in lectures, and facility with this material will be required in the exercises and in the examinations.

**Physics**. Prerequisite physics is required to the level of Physics 132. Occasionally, students may require a concept or variable value or technique from the physics prerequisite to understand lecture material or to complete exercises. More significantly, they will require the perspective learned in the physics prerequisite courses to help with the exercises, especially in setting up a “word problem” in a mathematical form for solution.

## Reference Material

The course text is Oke, T.R., 1987, *Boundary Layer Climates*.

In addition, lecture notes will be available for many sections of the course.

## Course Components

**Lectures**. Lectures will be used to discuss basic physical principles in boundary layer climatology. The majority of the theory and analysis required for the understanding of the material covered in this course will be introduced in lectures. Much of this material is not available from any other source or is available in a form which is less convenient for this course. In addition, the level of treatment in the lectures is more rigorous than that adopted by the textbook.

**Textbook**. The text covers some aspects of basic theory (Part I) but is mainly devoted to specific applications of those principles to particular natural atmospheric environments and to anthropogenically-modified atmospheric environments (Parts II and III, respectively). As indicated above, the text deals with course topics less rigorously than is the case in the lecture sequence. Its function is to provide more descriptive information on microclimates to complement the more analytical approach adopted in lectures.

**Exercises**. Exercises will be assigned regularly to test the student’s ability to derive and manipulate equations and to use meteorological tables, charts, formulae and published data sources to perform calculations relating to the subject matter of the course. During the quarter, 15 exercises will be assigned. Students have one week to complete each exercise but they will be assigned much more frequently than that. The score for the exercise portion of the course grade will be the mean of the 9 best scores.

## Evaluation

The course grade will depend upon the student’s performance in two midterm exams (each worth 16%), a final examination (worth 32%), and the exercises (worth 36%).

## Course Outline

**The nature of boundary layer climatology.**- Basic definitions and concepts.
- Boundary layer climatology and radiation.
- PBL structure and the surface energy budget.
- Structure and process in climatology.
- Boundary layer climatology and boundary layer meteorology.
- Some related subject areas.
- The significance of boundary layer climatology.

**The physics of electromagnetic radiation.**- Basic terminology and concepts.
- Absorption and emission by gases.
- Blackbody radiation.
- Radiation from real bodies.
- Radiative transfer.
- Scattering of radiation.
- Reflection of radiation.

**Longwave and shortwave radiation.****Solar geometry and extraterrestrial solar radiation.**- Solar geometry.
- Solar radiation outside the atmosphere.

**Solar radiation at the earth’s surface.**- General characteristics of solar radiation at the surface.
- Modelling solar irradiance at the ground.
- Solar radiation on slopes.

**Longwave radiation at the earth’s surface.**- General characteristics.
- Estimating the counter radiation.
- Terrestrial radiation on slopes.

**The net radiation of the earth’s surface.**- Definition of net radiation.
- Importance of net radiation.
- Examples of radiation budgets.
- The surface albedo.
- The surface emissivity.

**The surface energy budget.**- The nature of the surface energy budget.
- Energy budget examples.

**Wind and turbulence in the lower atmosphere.**- Turbulence in the lower atmosphere.
- The vertical shearing stress in the lower atmosphere.
- The wind profile in the surface boundary layer.

**The turbulent fluxes of heat and water vapour in the lower atmosphere.**- Turbulent fluctuations of temperature and humidity.
- Eddy correlation evaluation of the eddy fluxes.
- Flux-gradient relations for heat and water vapour.
- Profile methods of eddy flux evaluation.

**Natural evaporation from the earth’s surface.**- Introduction.
- Some preliminaries.
- Derivation of the generalized combination model.
- The aerodynamic resistance.
- Potential evaporation.
- Equilibrium evaporation.
- Vegetated surfaces – the “big leaf” model.
- Water budget approaches to evaporation.

**Some microclimatological aspects of plant environment.**- Microclimates of plant canopies.
- Meteorological approaches to plant canopy photosynthesis.

**The microclimate of soils.**- Heat and moisture transfer in soils.
- Soil temperature and moisture content profiles.
- One-dimensional treatment of heat flux and temperature change.
- A formal analysis of heat fluxes and temperature evolution in soils.

Updated: 18/09/2018