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This investigative team has deployed a Radiation and Energy Balance Systems, Inc (REBS) Bowen Ratio system (Figure 1a) in August, 2003, on the western side of the bunny fence at one of the agricultural research stations in the Merredin Dryland Research Institute The REBS Bowen ratio system determines the surface energy balance components using the Bowen Ratio Energy Balance Method.  This system calculates the available energy at the surface, which is the sum of net radiation and soil heat flow, and separates it into latent heat and sensible heat fluxes.  The Bowen ration is a ratio of sensible heat flux to latent heat flux, and this ratio is computed from measured near surface gradients of temperature and humidity and using transport equations for heat and moisture.  The REBS Bowen ratio system uses a double-sided total hemispherical radiometer and a double-sided pyranometer to measure upwelling and downwelling longwave and shortwave fluxes at the surface.  A soil sensor cluster in this system measures soil moisture, soil temperature and ground heat flux.  Temperature and humidity sensors measure vertical temperature and vapor pressure gradients needed for determining the Bowen Ratio.  A unique feature of this system is the automatic exchange of humidity and temperature sensor location every fifteen minutes.  This feature is essential for accurate measurements of surface energy fluxes when using a Bowen ratio system.  The system also has a tipping bucket rain gauge for measuring rainfall, as well as a barometer and an anemometer.  The system is powered using a deep cycle marine battery that is charged by a solar panel during the daytime.  The data collected by the system is logged using in a Campbell Scientific CR10X datalogger.  This system, which is valued at $22,000, will be made available to this project for the minimal cost of shipping it to Australia and associated personnel travel funds.  Funds for shipping and travel are requested since the current deployment of the system in Australia is expected to last only for a period of six month after which it will be used elsewhere.

A 25m flux tower for studying carbon fluxes, has been erected on the eastern side of the bunny fence in the native vegetation area at Sturt Meadows by a Japanese research team led by Prof. Koichi Yamada.  This system also provides similar measurements of energy fluxes, soil moisture and other precipitation (Figure 1b).  This flux tower is expected to be operational during the proposed period of the study and Prof. Yamada has agreed to provide the data from this tower for the proposed study.

radiosonde images

Figure 1.  Instrumentation for measuring surface energy budget and soil moisture. a) The REBS Bowen Ratio Station ; b) the 25 m flux tower at Sturt Meadows, southwest Australia

Using the data acquired from these two surface energy flux measurement sites, along with radiosonde, aircraft and satellite observations, the investigative team will assess the role of land use in boundary layer development and cloud formation.  The surface energy fluxes will also be used along with perturbation analysis of radiosonde wind observations to aid in the identification of mesoscale circulation patterns.  The intensity of mesoscale circulations is expected to be proportional to differences in surface energy fluxes between native areas of contrasting land use and atmospheric stability.  Correlations between patterns observed in the perturbation wind analysis and surface energy fluxes thus aid in identifying the mesoscale circulations using radiosonde observations.  The surface energy flux measurements will also be used for verifying the performance of numerical model simulations.


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