Dr Jonathan Evans

Micrometeorologist

Background

I have 12 years’ experience in instrument development, installation and application of Water Quality and Micro-Meteorological systems. Major work has included the development of the Mk4 Hydra, a low-power, integrated open-path Carbon Dioxide and Water Vapour eddy-correlation system. I have a BSc in Chemical Physics (Bristol University, 1990), MSc in Scientific Instrumentation (Manchester Metropolitan University, 1993), and am currently working towards a PhD (The University of Reading) in the application of scintillometry.

Projects have included:

• Field support and training for the Carbonsink project, measuring the carbon cycle in the Brazilian rainforest. Measurements of CO2, latent and sensible heat fluxes using the eddy correlation technique and complimentary micrometeorological and hydrological measurements.
• Large-aperture infra-red scintillometer field trial at Sonning Farm.
• Development of an integrated low-power open-path field instrument for the measurement of H2O and CO2 fluxes: The Mk3 Hydra. This included, the design of an infra-red gas analyser, signal processing, data logging and field trials in the UK and Brazil. Development of PC processing software using Visual Basic and analysis of instrument performance.
• Training and field support for the River Basin Management Project, Chile.
• Design and development of automatic water quality monitoring and sampling systems.
• Development of instruments for the measurement of soil moisture content, using a capacitance measurement technique operating at radio frequencies.

Current research

I am currently specialising in Micro-meteorology, particularly the field measurement of the Surface Energy Balance (including evaporation), using the technique of infra-red Large-Aperture Scintillometery (LAS) over complex terrain in the Berkshire Downs (LOCAR research) towards my PhD at Reading University.

There are a number of scientific questions to be investigated:

1) How can scintillometry be best applied to complex terrain (both topographic and land-use type inhomogeneities)?

2) What method should be used to aggregate point and field measurements, over different land-use types, to calculate catchment-scale averages?

3) How is the eddy correlation technique best applied over complex terrain? Field-scale sensible heat flux measurements will be compared with the scintillometer measurements.

4) How can the scintillometer footprint be determined.

5) What is the blending height along the scintillometer path? How does this vary with micrometeorological conditions? What effect does orography have on the blending height? Knowledge of the blending height is important to be able to confidently apply Monin-Obukhov similarity theory, when calculating sensible heat flux from the scintillometer.

Other current research is developing a new design of Millimeter-wave Scintillometer (94 GHz), to be directly sensitive to humidity fluctuations; this will be used with the LAS to measure evaporation directly over a 2.4 Km path length.