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Unit 4.1 - Energy Budgets

Jim Washburne (University of Arizona)

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Summary

The purpose of this unit is to explore, compare, contrast, and calculate energy fluxes from different CZO field sites to better appreciate the critical differences in the driving radiative forces affecting each site. This module will help students complete their semester-long project by introducing them to critical baseline data collection and databases related to energy budgets.

The primary data set for this activity is the CZO tower network of a dozen met/flux towers spanning six different biomes/sites. Each site has a slightly different data format but it is easily manipulated in a spreadsheet. The lesson is divided into the following engaging activities:

  • Background lecture: Introduction to water and energy fluxes and balances
  • Database access and graphing activity: Students will learn what data exists in the CZO database and how to load and manipulate it using Excel.
  • Discovery activity: Students in small groups will compare monthly bar graphs of energy fluxes drawn from six Ameriflux sites and address questions concerning linkages with other variables and processes affecting energy partitioning.
  • Reference ET Activity: Students will learn about the Penman-Monteith formulation of evaporation and calculate this from common meteorological data and compare with field measurements of evapotranspiration. The class will discuss these results as time allows.

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Learning Goals

This unit guides students to analyze water and energy flux data collected in different biomes to better understand the measurements, processes, and regional exchanges of water and energy. This relates to the grand challenges of understanding basic climate and boundary layer dynamics and Earth's energy budget and radiative forcing. This module also relates to the geoscience literacy themes of energy sources driving Earth processes and Earth system changes that occur at multiple scales and the interconnections between the water and energy cycles. Two of the primary learning goals are to better understand how the conservation of mass and energy result in the water and energy budget equation and to be able to explore and extract data from the CZO flux database.

Students will:

  • Use water and energy cycle diagrams to discuss how water and energy are partitioned at the watershed scale.
  • Learn about the instrumentation used to collect water and energy flux data.
  • Examine radiative forcings collected from various CZO sites to compare various climatic and site-specific influences.
  • Explore and visualize energy flux data from the CZO database.
  • Calculate a measure of Effective Energy and Mass Transfer (EEMT) related to the potential for Critical Zone evolution.
  • Use CZO micro meteorological data to calculate reference evaporation at a site of their choice.

Context for Use

This week-long unit for advanced undergraduates/graduates explores Critical Zone energy flux data and models during two 75 minute class periods. This module, "Land-Atmosphere Exchanges," is part of the InTeGrate interdisciplinary course called "Introduction to Critical Zone Science." The physical basis will be introduced quickly, followed by prevailing theories or analytical perspectives so that at least half of each class period can be spent examining and analyzing CZO data sets.

Description and Teaching Materials

Introduction

There are two tracks an instructor can follow through these materials: the standard approach covers the basic ideas in a fairly qualitative manner. An advanced approach will require more time and is more quantitative.

Unit 4.1 - Day 1 (75 minutes total)

Day 1 - Lesson Plan Overview

  • Assign background reading to students at the end of the previous class.
  • There are two tracks an instructor can follow through these materials: the standard approach covers the basic ideas in a fairly qualitative manner. An advanced approach will require more time and is more quantitative.

Day 1 - Instructions and Materials

Introduction to Water/Energy Cycles and Budgets Lecture (35 min) - The purpose of these slides are to introduce the basic water/energy budget equations and begin to think about what factors affect water/energy partitioning. The basic measurement technique for each component is illustrated. There are 24 slides.

  • Standard Lecture: Introduction to Water and Energy Budgets & Fluxes (24 slides, ~35 min)
    • Student Lecture Notes: Intro to Water/Energy Budgets & Fluxes - Printable (6/pg) Student Note Set (Acrobat (PDF) 754kB Feb23 17)
    • Instructor Lecture Slides: Intro to Water/Energy Budgets & Fluxes Instructor Slide Set (PowerPoint 2007 (.pptx) 2.6MB Feb25 17)

Activity 4.1 - Energy Flux Graphing Activity

Exploring CZO Met/Flux Field Sites & Database (15 min) - These slides introduce the students to the original six Critical Zone Observatories so they have an idea of the physiographic setting. The handout summarizes the basic structure and content of the CZO data archive. The two major shortcomings of the CZO data set, at this point in time, are a lack of consistency in formatting and measured parameters.

  • Supporting Slides: Exploring the CZO Met/Flux database (Post-lecture, groups) (33 slides, ~15 min)
    • Student Lecture Notes: CZO Field Sites and Data- Printable (6/pg) Student Note Set (Acrobat (PDF) 991kB Oct14 13)
    • Instructor Lecture Slides: CZO Field Sites & Database Instructor Slide Set (PowerPoint 2007 (.pptx) 4.3MB Dec23 16)
  • Supporting Handout:

Working with the CZO Met/Flux Database: Energy Flux Graphing Activity 
(see Teaching notes and tipsfor more info)
The ultimate goal is to get the students actually working with typically archived energy flux data, first by graphing it and then by using it to calculate something called reference evaporation. In-class: Start exploring the CZO Met/Flux database and examine metadata that will be crucial to understanding the data record (see related questions on worksheet).

Step 1 - In-class exploration of database and metadata - Have the students start exploring the CZO database by examining the metadata that is critical to understanding the data record. Choose one of the following activities. The basic difference is the size and complexity of the associated data files. The basic goal of this activity is to explore and work with real data from the CZOs.

  • Support: Alternative In-class metadata handout (PowerPoint 2007 (.pptx) 348kB Dec23 16).
  • Practical Matters - Accessing the CZO Met/Flux database (demonstration for students, ~10 min)
  • Basic Activity: Download the Daily data set (57 kB):
  • Advanced Activity: Download the 30 minute time-interval data set (1,955 kB):
  • Save this data to your hard drive (typically under "downloads" on a PC).
  • Open this file (called "WU_2010_Lower_Prov_Met_daily.csv" or "Tower_Vcm_2010_gapfilled.csv") in Excel. It should automatically parse the comma delimited fields into separate columns. If not, the "Text Import Wizard" will help you do this.

Step 2 - Introduction to Homework graphing assignment - Note that most of the interesting parameters have already been plotted using Matlab (Table 4.1.1) at the annual scale. These have been pre-averaged to show only daily and weekly values. The Excel graphs will look significantly different so students should not worry that their plots do not look exactly like these.

Homework Instructions - Produce two sets of labeled graphs demonstrating that you can visualize this data set using Excel or Matlab. Create two versions (by editing the x-axis), one set showing the full annual cycle and one set focused in on a 10 day period (ie. DOY 170-180). Note: one way to do this requires you to know that Excel indexes its days from 1/1/1900=1 so 1/1/2010=365.25*110=Roundup(40177.5)+1=40179.

  • Homework (review assignment by illustrating expectations using the following Example graphs, ~5 min)
    • (Basic): Find a daily average data set; OR (Advanced): Use a 30 min data set. 
      Look for a different data set and make 2 plots with at least 2 variables/plot of meteorological variables (such as TA or VPD) and energy flux variables such as (Rn, H or LE) verses Calendar or Julian date. Once you have the basic plot, make sure you make it readable (titles, etc).
  • Set 1: Annual period - at least 2 meteorologic parameters and 2 energy parameters.
  • Set 2: Ten-day period - at least 2 meteorologic parameters and 2 energy parameters.
  • Example plots: 
  • Prepared data Files - Note: if you are having trouble downloading from the CZO data archive, try using the following two files:
  • Questions (5 min)

Lesson Plan: Unit 4.1 - Day 2 (75 minutes total)

Day 2 - Lesson Plan Overview

  • Discovery Activity: Examining Annual Energy Flux Graphs (30 min) - The purpose of this exercise is for the students to compare and contrast energy data from six met/flux measurement sites to discover and think about the causal or physical relationships among these variables.
    • Introduction & Setup ( 3 min) - One way to introduce this activity is to say: "The purpose of this exercise is for you to compare and contrast data from six met/flux measurement sites to discover and think about the causal or physical relationships among these variables. Note that not all these sites have the same kind of vegetation (what differences might you expect between grassland, evergreen and deciduous covers?). This is real data so expect a certain amount of ambiguity. What you need to do over the next 10-15 minutes is to get in small groups, read the handout and answer the discussion questions as a group. Be prepared to share observations and discuss your answers with the rest of the class later. Your primary task is to think about and look for factors that might control the magnitude of the various energy fluxes. Focus primarily upon relationships between the parameters for a single site; although you might also see consistent patterns from one site to another. The bottom-line question we will be addressing throughout this unit is "What controls the annual shape of the energy flux curve?"
    • You might want to quickly shuffle through the set of graphs on a classroom display to briefly describe the layout of the graphs, although most of this information is described on page two of the worksheet.
    • Break the class into groups of two to four students. Hand out a set of six energy flux graphs to each group.
    • Small group exploration (15 min)
    • Class discussion (10 min) - The worksheet key (see Assessments) highlights some of the relationships your students might observe but there will undoubtedly be others. There is also a set of annotated graphs below that highlight some of the relationships between energy and carbon fluxes. Some students might misinterpret a relationship between some variables. Try to point out some complicating factors or suggest they think about the problem more physically, which might resolve the misunderstanding. This discussion could obviously be extended if you have the time.

The following activity was found to be very challenging for many users. Part of the reason may be unfamiliarity with using moderately complex formulas; but the greatest problem was just running out of time. The activity is fairly well supported - if you have the time to prepare the students in class and they have finished the previous homework. Two alternative pathways here if you want to skip the more advanced material is to skip talking about Effective Energy and Mass Transport (EEMT) and just demonstrate the results of calculation ET or you can spend more time on the previous day's lesson or reviewing the students' homework in class.

Optional: Introduce the Concept of EEMT. This requires more quantitative skills.

  • Exploring Reference ET - Lecture Introduction (15 min)
  • Working with the CZO Met/Flux Database: Calculating Reference ET Activity (25 min) -
    • In-class: complete the first part of this worksheet, particularly to make sure students can do the unit conversions.

Day 2 - Instructions and Materials

  • Pre-class reading assignment:
  • Review issues and student homework associated with Activity 4.1. (~5 min)

Activity 4.2 - Examining Annual Energy Balance Graphs 

Activity 4.3 - Calculating Reference ET (Advanced, Optional)

  • The following topics are most appropriate for advanced classes and graduates but can serve as interesting lecture material for other students.
  • Introduction to Effective Energy and Mass Transport (EEMT) (9 slides, ~20 min)
    • Student Lecture Notes: Introduction to EEMT Equation - Printable (6/pg) Student Note Set (Acrobat (PDF) 333kB Feb23 17)
    • Instructor Lecture Slides: Introduction to EEMT Equation Instructor Slide Set (PowerPoint 2007 (.pptx) 703kB Feb25 17)
  • Working with the CZO Met/Flux database - Calculating Reference ET (10 slides, ~20 min)
    • Student Lecture Notes: Calculating Reference ET, Printable (6/pg) Student Note Set (Acrobat (PDF) 266kB Feb23 17)
    • Instructor Lecture Slides: Calculating Reference ET Instructor Slide Set (PowerPoint 2007 (.pptx) 864kB Feb25 17)

In-class: complete the first part of this worksheet, particularly to make sure students can do the unit conversions.

CZO Flux Tower Graphs
BC: Boulder Creek Betasso (Acrobat (PDF) 42kB Jul6 13)
JBC: Jemez Basin Catalina Mts VCmc (Acrobat (PDF) 45kB Jul6 13), VCpp (Acrobat (PDF) 45kB Jul6 13)
SSN: Southern Sierra Nevada p301 (Acrobat (PDF) 45kB Jul6 13), sjer (Acrobat (PDF) 45kB Jul6 13), shorthair (Acrobat (PDF) 45kB Jul6 13)
SSH: Susquehanna-Shale Hills SH2009 (Acrobat (PDF) 32kB Jul6 13), SH2010 (Acrobat (PDF) 78kB Jul6 13)
CRB: Christina River Basin swrc (Acrobat (PDF) 41kB Jul6 13)
LUQ: Luqillo, PR Bisley (Acrobat (PDF) 41kB Jul6 13)
CZO Water/Energy Fluxes using Matlab Full set of 10 (Acrobat (PDF) 420kB Sep21 13)

Citation: CZO Tower Data. Various Investigators. Logistical support and/or data were provided by the NSF-supported Critical Zone Observatory.

Teaching Notes and Tips

Day 1 Activity: Working with the CZO Met/Flux Database: Energy Flux Graphing Activity (25 min)

Many students seem to have trouble working with large data sets (more trouble on Macs; Less on PC's) so be ready to provide help as needed. A shorter "getting started" data set is provided for those who are not ready for the size and complexity of the online data archive.

  • Step 1 (20 min) - In-class exploration of fundamental concepts and metadata - Have the students start exploring the CZO database by examining the metadata that is critical to understanding the data record.
    • ATTENTION - this will require computer browser connectivity for each group. If you don't have computer access, you will have to print this file out and distribute 1 set/group. Note: the data columns have been numbered for convenience.
  • Step 2 (5 min) - Introduction to Homework graphing assignment - Note that most of the interesting parameters have been plotted using Matlab (Table 4.1.1) at the annual scale. These have been pre-averaged to show only daily and weekly values. The Excel graphs will look significantly different so students should not worry that their plots do not look exactly like these.

Assessment

Students get credit for In class participation (~ 10 pts).

Activity 1 - Students explore and visualize energy fluxes from the CZO database. Questions 1-10 in the worksheet are designed to get students thinking more quantitatively about energy flux units and some of the factors that affect them. Filling out the table of data set variable names may seem tedious, but there is no better way to start becoming conversant with these variables. The students will produce four graphs of the CZO data set.

  • Energy Flux Graphing (15 pts)
  • Graphs should be evaluated using the Graph Grading Rubric (Microsoft Word 2007 (.docx) 17kB Dec23 16). (15 pts)

Activity 2 - Groups look at monthly averaged met/flux data to make some simple observations and speculate about driving factors affecting the partitioning of energy at the watershed scale. Five discussion questions help them focus on important issues and serve as a useful formative evaluation of small group understanding. The answers provided here are exemplary. There is no single right answer.

  • Energy Flux Discovery (15 pts)

Activity 4 - Oftentimes, scientists will calculate secondary factors from primary measurements. The activity gives the students practice at building a more complex secondary equation into their Excel spreadsheet. Referring to the Appendix in Brown (2005), I have used measured air pressure, air temperature, relative humidity, wind speed, and net radiation to estimate reference ET using equations: A16, A1, A11, A17 and an equation like #2 that we have introduced in class plus a few other intermediate variables. The worksheet introduces each of these factors and provides a step-by-step guide on how to perform the calculation.

  • Calculating Reference ET (15 pts)
  • Graphs should be evaluated using the Graph Grading Rubric (Microsoft Word 2007 (.docx) 17kB Dec23 16) (15 pts)

References and Resources

Sources of Data

  • Critical Zone Observatory National Database,

Background References

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These materials are part of a collection of classroom-tested modules and courses developed by InTeGrate. The materials engage students in understanding the earth system as it intertwines with key societal issues. The collection is freely available and ready to be adapted by undergraduate educators across a range of courses including: general education or majors courses in Earth-focused disciplines such as geoscience or environmental science, social science, engineering, and other sciences, as well as courses for interdisciplinary programs.
Explore the Collection »