EB_AUTO: A Microsoft Excel^TM based point surface energy balance melt model for glacier and snow melt studies

Introduction

'EB_AUTO' is a Microsoft Excel^TM Workbook containing a point surface energy balance model for a snow or ice surface. EB_AUTO incorporates a large amount of previous research on the surface energy balance of snow and ice and presents it in an easy to use form. The model contains a visual basic macro which calculates the fluxes of net shortwave and net longwave radiation, turbulent sensible and latent heat and melt at a point on a melting snow or ice surface, using hourly inputs of incoming shortwave radiation (W m^-2), air temperature (°C), air vapour pressure (Pa) and wind speed (m s^-1). The latitude, longitude, slope angle, slope aspect, elevation, local temperature lapse rate, albedo and aerodynamic roughness of the study site, and elevation of the meteorological station can be specified at the start of the model run, making the model easily transferable and suitable for inter-site comparisons and modelling experiments. An output file containing the hourly and daily rates, and totals, of each energy flux in units of mm water equivalent melt is generated. The advantages of the model are:

it requires only a laptop or PC running standards Microsoft Windows software, enabling it to be used at a desktop or in the field;
it can be quickly adapted to different sites or meteorological data formats and it is well suited to modelling experiments;
its simplicity and flexibility make it ideal as a teaching tool

Downloads

EB_AUTO Workbook: Microsoft Excel Workbook containing the energy balance model
Printable Instructions: a 'read me' PDF Document contain information about running the model.
Sample Excel meteorological file : from a glacier in southern Iceland, showing the format required for the input data.

Reference

Reference should be given to the following paper in any reports or papers using EB_AUTO:

Brock, B.W. and N.S. Arnold. 2000. A spreadsheet-based (Microsoft Excel) point surface energy balance model for glacier and snow melt studies. Earth Surface Processes and Landforms. 25, 649-658.

Further information

EB_AUTO is a modified version of the model described in detail in Brock and Arnold (2000). The input meteorological data need to be arranged in a Microsoft Excel Worksheet/book in six columns: day of year; hour; incoming shortwave radiation; air vapour pressure; air temperature and wind speed and recorded at an hourly interval. The model uses an astronomical calculation to locate the position of the sun relative to the target at an hourly resolution. Comparison of measured and theoretical incoming shortwave radiation enables an estimate of cloud cover and the ratio of direct and diffuse shortwave radiation. Direct shortwave radiation is corrected for the site slope and aspect; both direct and diffuse incoming shortwave radiation are converted to net shortwave radiation using the surface albedo. Outgoing longwave radiation is assumed to be a constant for a black body at 0°C. Incoming longwave radiation is calculated from air temperature and estimated cloud cover using the Stefan-Bolzmann relationship. The turbulent fluxes assume air vapour pressure, humidity and wind speed are measured at 2 m above the surface. Air vapour pressure can be calculated from air temperature and relative humidity using standard formulae. The turbulent fluxes are calculated from gradients of wind speed, temperature and vapour pressure between the surface and the measurement height, using the Monin-Obukhov similarity equations to account for atmospheric stability above melting snow and ice surfaces. The model uses an iterative procedure to optimise the value of the Monin-Obukhov length scale.

The energy fluxes and surface melt rate are strongly influenced by the surface albedo and aerodynamic roughness length specified for the study site. See papers by Brock and others (2000 and 2006) for discussion of these surface variables and their parameterisation.

Two modifications to the original 2000 version of EB_AUTO have been made:

Daytime cloud cover is estimated by comparing the measured and potential incoming shortwave radiation flux. This method does not work in hours of darkness and cloud cover is set to 0.5 between sunset and sunrise. To use a different night time cloud cover (between 0.0 for clear sky to 1.0 for overcast) change the final value in the Cell X2 formula.
The decrease in air density with increasing elevation above mean sea level is now incorporated into the calculation of the turbulent fluxes.

References

Brock, B.W. and N.S. Arnold. 2000. A spreadsheet-based (Microsoft Excel) point surface energy balance model for glacier and snow melt studies. Earth Surface Processes and Landforms. 25, 649-658.

Brock, B.W., I.C. Willis and M.J. Sharp. 2000. Measurement and parameterisation of albedo variations at Haut Glacier d'Arolla, Switzerland. Journal of Glaciology, 46(155), 675-688.

Brock, B.W., I.C. Willis, and M.J. Sharp. 2006. Measurement and parameterisation of surface roughness variations at Haut Glacier d'Arolla, Switzerland. Journal of Glaciology, 2(177), 281-297.