Roquetas Field Days: Environmental Monitoring and Modelling

GEOG2840 Alps Field ClassGlacier mass balance modelling

Ödenwinkelkees Glacier: Glacier Mass Balance Modelling

Field Day Objectives

1. Develop an understanding of the links between snow, ice and climate
2. Understand complexity of earth surface systems and process interactions
3. Understand there are different methods of collecting digital data.
4. Understand how we can devise a sampling strategy to measure and model snow and ice melt.
5. Understand the relationship between meteorology, snow surface properties and melt.
6. Be able to create geomorphological maps and understand their use.
7. Understand the processes that control the rate and timing of surface melting.
8. Understand the limitations of field data collection.

Learning Outcomes

1. Students will be able to use install and record surface lowering using ablation stakes.
2. Students will understand that melt is a response to environmental factors.
3. Students will identify relationships between meteorology, snow surface properties and melt.
4. Students will observe the natural variability in earth surface systems.
5. Students will use a model to simulate observed melt.

Equipment

3m tape (x3)

Windwatch (x3)

Magnetic compass (x3)

Handheld GPS (x3)

Wooden mallet (x2)

Thermometer (for snow) x3

Stakes (20x 1m-2m long dowell or bamboo)

Ice drill

Thick black marker pen (x3)

Hi-visibility survey spray or tape (x2)

Clinometers (x3)

Clipboard, plastic bag (x4)

Soft pencils (x10)

Spring balance (x3) (500g type)

Plastic beaker that can be hung on balance (ie with holes for string to go through)

Snow shovel (lightweight, short handle) (x2)

Pyranometer (x2)

Support material

Geomorphic mapping legends

Data logging tables

Energy balance model instructions

Field Day Plan / Provisional Timetable

Introduction: 9:00 – 10:00

Record weather conditions at hut.

Set altimeter. Walk in, observing landforms and features on route.

Field Orientation – 1ry processes / landforms / any points of interest.

Stop at edge of snowpack discuss:

• Background, rationale and method.
• Concept: Glacier mass balance; difference between input and output (accumulation and ablation).
• Do you think there will be variability in surface ablation?

Morning: 10:30 – 12:30

Data collection:

Hourly temperature, humidity, wind speed and incoming shortwave radiation, ablation stake height. You will also record surface parameters and general meteorological conditions.

Lunch: 12:30 – 1:00

Discussion of concept: Energy balance and hydrological balance

Afternoon:1:00 – 3:30

Field sketch exercise: glacial processes and landforms

Data collection: repeat surveys

Evening: Data processing and interpretation

1. Calculate mean relative surface height changes (mm/hr)
2. Calculate mean relative changes in meteorological parameters (change per hour)
3. Calculate relative changes in surface conditions (change per hour)

Do not write long paragraphs. Rather think first, then write concisely but coherently, using bullet points where possible.

1. Input data to Ben Brock’s model and calculate modelled melt.
2. Compare the predicted vs. measured melt.
3. Comment on any perceived spatial and temporal relationships. For example, between surface changes and situation, between surface changes and meteorological parameters, between situation and meteorological parameters.
4. In your own words interpret what these relationships show.
5. Think about why the modelled and observed melt is different.
6. Discuss what these measurements do not show. For example what might be diurnal changes (i.e. including night-time), seasonal changes?
7. Discuss these measurements and results in the wider context of glacier monitoring. For example mass, energy and hydrological balances, direct and indirect techniques, and spatial and temporal coverage.

Your evening presentation should cover:

1. Your research question or aim

Why is this interesting and important?

1. Sampling method

Briefly, describe the sampling approach you chose.

1. Results

Visual presentation of results in a clear manner, describing important trends and features. Include the results of any statistical tests which prove/disprove each hypothesis.

1. Discussion, reflection and limitations, and Conclusions

What can you conclude about the underlying processes governing any differences that you see?Reflect on the field research methods used. Did they work? Could they be improved? If a hypothesis couldn’t be tested with the data you have, what further information would be needed?

Concepts

Mass balance is the difference between annual snow and ice accumulation, and snow and ice melted (ablated from a glacier). It can be represented as an average thickness (in water equivalent) added to or lost from the glacier for a given year. Mass balance is the most sensitive annual glacier-climate indicator.

The glacier energy balance equation is the sum of all inputs and outputs of energy into a glacier system. That is the sum of net radiation (short wave; from the sun, and long wave; primarily reflected from the glacier surface), and convective fluxes (sensible heat and latent heat). Sensible heat is heat that you can sense, i.e. warming; and latent heat is heat released due to phase changes between ice, water and gas (vapour).

Hydrological balance is a modification whereby total melt (ablation) is measured in proglacial streams

Direct measurements: are very time and resource consuming and thus expensive. The longest continuous record of mass balance for a single glacier is 53yrs, at Storglaciaren, N. Sweden. They require a network of ~50 ablation stakes to be measured once every two weeks, in summer and winter, and for snow density measurements to be taken. Hydrological balance requires near-daily field measurements.

Indirect measurements: Surface elevation changes can be observed from successive aerial photographs or satellite images. Energy balances can be modelled but require field data input and field validation.

Extended Field Material

Use these materials to help you with your group work, they provide you with the ancillary information that you need.

Activity 1: Ablation stakes

Aims:

• To measure hourly surface lowering
• Quantify any spatial heterogeneity in surface lowering
• Look at relationships between surface lowering and landsurface attributes

Equipment:

3m tape (x3)

Windwatch (x3)

Magnetic compass (x3)

Handheld GPS (x3)

Wooden mallet (x2)

Stakes (20x 1m-2m long dowell or bamboo)

Ice drill

Thick black marker pen (x3)

Hi-visibility survey spray or tape (x2)

Clinometers (x3)

Clipboard, plastic bag (x4)

Soft pencils (x10)

Data Logging sheets

Create these, thinking about what measurements / readings / notes you will need to record – see below for a guide.

Methods:

1. Decide on a sampling strategy.
2. Use the ice drill to create holes about 1 m deep.
3. Place the stakes in the holes.
4. Attach high visibility tape to the stakes.
5. Annotate a fieldsketch to show location of stakes
6. Fill in a table like the one shown below, every hour for every stake.

Things to think about:

1. What role does aspect play in controlling observed patterns in melt?
2. What controls the variability in melt?
3. Can you see evidence of this variability in melt rates?

For each stake location record the location in lat and long, altitude, surface albedo, surface gradient, aspect and surface roughness (see attached sheets for values).

GEOG2840 Alps Field ClassGlacier mass balance modelling

Stake number:

Stake number:

Stake number:

Activity2: Snow density and temperature

Aims

• To consider how snow density will change with depth
• To quantify changes in snow temperature and density with depth
• To interpret these changes in density with depth

Equipment:

Thermometer (for snow) x3

Spring balance (x3) (500g type)

Plastic beaker that can be hung on balance (ie with holes for string to go through)

Snow shovel (lightweight, short handle) (x2)

Method

1. Decide on a site and dig a snow pit to a depth of ~ 1m.
2. We are going to measure any changes in snow density and temperature as we move down the snow pit. Hint: you will want to do one near the surface
3. Decide on your sampling interval down the pit
4. Record the snow temperature at your first sampling point
5. Sample a known volume of snow (m3)
6. Measure the weight of this known volume of snow (kg)
7. Divide the weight by the volume of the snow (kgm-3)
8. Repeat measurements down the pit

Activity 3: Surface albedo

Aims

• To understand controls and variability in surface albedo
• To quantify albedo values for different surfaces
• To investigate any variability in surface albedo during the day

Equipment

Pyranometer

Compass

Clinometer

Method

1. Investigate the variability in surface reflectance for different surfaces
2. You will need to perform repeat measurements.
3. You will want to look at variables such as surface roughness, surface aspect, cloud cover, debris cover, topographic shading, snow age, ice cover, time of day.

EB_INFO

Instructions For Using The EB_AUTO Spreadsheet Energy Balance Model

Ben Brock, Dundee

Email:

25 November 1999

Introduction

EB_AUTO is a Microsoft Excel workbook which calculates the hourly, total and daily rates of the melt, net shortwave, net longwave, turbulent sensible and turbulent latent heat fluxes (all in mm water equivalent) at a point on a melting snow or ice surface, from hourly inputs of incoming shortwave radiation, air temperature, air vapour pressure and wind speed.

Before You Start

You will need to obtain a copy of either EB_AUTO5 (for Excel Versions 5.0 and above) or EB_AUTO7 (for Excel Versions 97 and above) from the Earth Surface Processes and Landforms software web site. A sample data file SAMPLMET is also supplied. This file contains meteorological measurements recorded at a site adjacent to the ablation area of Solheimajokull, an outlet glacier in Southern Iceland, at an elevation of 300m above sea level on 26 and 27 June 1997. Wind speed, temperature, humidity and incoming shortwave radiation were recorded at a height of 2 metres.

Format For Input Meteorological Data

Input meteorological data for the model must be contained in a separate file made up of six columns of data in the following order: Julian Day; Time (using the ‘hundred-hour’ clock); incoming shortwave radiation (in Watts per metre-squared); air vapour pressure (in Pascals); air temperature (in degrees Celsius) and wind speed (in metres per second). Each hour of data must be recorded on a separate row. For example, look at the format of the SAMPLMET data file. The only restriction on the length of the data file is that of the Excel worksheet, which for Excel Version 97 is 65534 rows (hours) of data, allowing 2730 days (almost 7.5 years) of data. On Excel Version 5.0 the maximum number or rows (hours) is 16384, allowing 682 days (nearly 2 years) of data.

Instructions For Running The Model

1. Open Microsoft Excel and Open EB_AUTO5 or EB_AUTO7

1. If running on Excel Version 5.0, press ‘Return’ to remove the 'Cannot resolve circular references' message if prompted. If running on Excel Verion 97, click ‘Enable macros’ at the virus warning message box if prompted, and click ‘Cancel’ to the circular reference warning message box if prompted.

1. Enter the site details (numeric values) in Column A:When first opened the site details will be set for the ablation area of Solheimajokull in Southern Iceland, corresponding with the SAMPLMET data file.

• ‘Latitude’, ‘Longitude’ and ‘Slope’ are self-explanatory. Further information concerning the other site details is given below:
• Ref. Longitude (deg) is the longitude of the time zone in which the site is located in degrees, e.g.
• Iceland's reference longitude is 0 (since Iceland is on GMT)
• Summertime hours can be added if there is any daylight saving, otherwise 0
• Aspect is measured in degrees away from due south (positive to the west and negative to the east)
• Elevation (m) is the elevation of the site for which calculations are being made
• Albedo, suggested values are: 0.8 for fresh snow, 0.5 for old dirty snow; 0.4 for clean ice and 0.1 for very dirty ice or moraine.
• Roughness (m), i.e. the aerodynamic roughness, z0, suggested values are: 0.0001m for fresh snow, 0.002m for old snow and ice. Very rough surfaces, e.g. heavily crevassed ice may have a z0 of several cm or more.
• Met. St. Elev. (m) is the elevation of the meteorological station supplying the input data.
• Lapse Rate (deg/m) is the temperature lapse rate with elevation, so the model can work out the temperature difference between the meteorological station and the site for which calculations are being made.

1. Run the energy-balance program by either: clicking on the 'EB' customised tool button (if you can't see it check that Toolbar1 is visible in View>Toolbars); or by pressing CTRL-E

1. Enter the input information as requested. You will be prompted for six pieces of information before the model will run. In order to run the model with the SAMPLMET data file (assuming this is in a directory called h:\ebmodel) enter the following list of input at the six prompts: 2, 0, h:\ebmodel, samplmet.xls, a2:f49, output1.xls

Further specifications for the input information are given below:

• ‘Input Number Of Days’: integers only
• ‘Input Number Of Hours’: integers only

• (e.g. for 30 hours of data, enter 1 for Number of Days and 6 for Number of Hours)
• ‘Input Meteorological Data Directory’: give root and directory, e.g. h:\ebmodel (omitting final backslash)
• ‘Input Meteorological Data Filename’: e.g. samplmet.xls
• ‘InputCellRange’: give the inclusive range of cells in the meteorological data file containing the meteorological data separated by a colon, e.g. a2:f25 (for the first 24 hours of data)
• ‘Input the Output Filename’ - e.g. Output1.xls (no directory can be specified for the output file, i.e. the output will be written to the same directory as the energy balance model. If a different directory is required for the output data the Visual Basic Macro must first be edited to accommodate this)

1. Wait until the 'Calculation Completed' message appears. The total values of the net shortwave radiation (SWR), net longwave radiation (LWR), turbulent sensible heat flux (SHF), turbulent latent heat flux (LHF) and the melt (MLT) fluxes appear in columns A to E of row 3 in the output file, while the mean daily values of these fluxes appear in columns A to E of row 7 of the output file. The energy fluxes are expressed in units of millimetres of water melted equivalent. In addition, the hourly values of each energy flux are given in columns G to N of the output file. A column titled ‘melt total’ is given in addition to ‘MLT’ so that any periods with a negative energy balance, i.e. when energy is lost from the snow/ice surface, can be identified. Periods with negative energy balance are ignored in the final MLT summation.

The output (to the nearest 0.1mm) from the SAMPLMET example data file should be as follows:

Flux Totals

SWRLWRTSHTLHMLT

86.1-7.99.94.693.0

Daily Flux Rates

SWRLWRTSHTLHMLT

43.0-3.95.02.346.5

1. When closing the energy balance worksheet DO NOT save any changes to EB_AUTO

Additional Points

If calculating over long periods (e.g. >7 days) it will be quicker to copy cell formulae manually (using Copy and Paste). This is because most of the running time of the EB macro is taken up with copying cell formulae, although it depends on how fast your computer's processor is. You can work out which formulae to copy and in which order by reading through the program listing. Find this by clicking on the 'Module 1' tab at the bottom of the EB_AUTO5 workbook or selecting 'Macro>Visual Basic Editor' from the 'Tools' menu on EB_AUTO7. The order in which formuale are copied to calculate the turbulent fluxes (Cells AQ-BC) is critical, otherwise the Monin- Obukhov iteration won't work.

Editing The Model

You can edit the model to: accommodate different formats of meteorological data, for example to incorporate an additional column of measured net radiation measurements; to calculate other energy fluxes, for example heat conduction or energy provided by precipitation; or to change the way in which a particular energy flux is calculated. In the latter case the cell formulae relating to a particular energy flux can be edited in the spreadsheet itself, without affecting the overall running of the model. For other changes, the Visual Basic macro, which controls the input and output of data, executes the calculations, etc., must be edited. On Excel Version 5.0 this is accessed via the ‘Module 1’ tab at the bottom of the workbook. On Excel Version 97 it is accessed by selecting ‘Macro>Visual Basic Editor’ from the ‘Tools’ menu. A number of good introductory Visual Basic manuals are available and sufficient competence can be gained in a day or two to make most required changes to the model.