The mobile EC platform consists of a telescoping tower that extends to a height of 15 m, however in this study EC measurements were taken at 7.0, 8.0, and 9.0 m. High-frequency turbulent fluxes were measured using an open-path infrared gas analyzer and a three-dimensional sonic anemometer and aligned to the dominant wind direction for each deployment, as determined from wind rose diagrams from nearby stations. Site conditions were inspected to select the measurement height for each case to obtain sensible and latent heat fluxes above the height of the urban land cover of interest (i.e., xeric trees, pavement, turf grass), while maintaining a relatively small EC footprint. Measurements were sampled at frequencies of 10 or 20 Hz, recorded with a datalogger (CR3000 or CR5000, Campbell Scientific) and processed at 30 min intervals using the EdiRE software program (Clement, 1999) (http://www.geos.ed.ac.uk/homes/jbm/micromet/EdiRe/). EC processing was performed consistently for all sites and included correcting for fluctuations in stability (Foken et al., 2006: ) and density (Webb et al., 1980), using the sonic temperature to calculate sensible heat flux (Paw U et al., 2000), rotating the coordinate frame to set the mean vertical wind speed to zero during each 30 min interval (Wilczak et al., 2001) and removing the signal lag in the gas concentrations (Massman, 2001). Flux data was also filtered to exclude periods with precipitation (> 0.2 mm/30 min), when the wind direction was 180° ± 10° from the direction at which instruments were mounted and for outliers greater than 3 standard deviations from mean values. Additional sensors recorded radiation, meteorological and soil conditions as 30 min averages, including standard weather observations of pressure, air temperature, relative humidity and precipitation. A four component net radiometer installed at 5 m measured incoming and outgoing shortwave and longwave radiation over a footprint of ~1100 m2, while a pyranometer was used to verify the incoming shortwave radiation. Ground heat flux was measured using a heat flux plate at 5 cm depth and two thermocouples at 2 and 4 cm depths to account for shallow soil heat storage at all sites except the pavement surface at PL. Soil moisture was measured at 5 and 50 cm depths at PV, and 5, 15 and 50 cm depths at TG to quantify soil responses to precipitation and irrigation.

Setup and instruments details:

Tower details:

instrument, manufacturer, measurements

3D sonic anemometer/CSAT3 (1), Campbell Scientific, Three-dimensional wind velocities, virtual sonic temperature

Infrared gas analyzer/LI-7500A (1), Li-Cor Biosciences, Water vapor and carbon dioxide concentrations

Temperature and relative humidity sensor/HMP155A (3), Vaisala, Air temperature and relative humidity

Four component net radiometer/CNR4 (1), Kipp & Zonen, Incoming and outgoing shortwave and longwave radiation

Pyranometer/SP-110 (1), Apogee Instruments, Total shortwave radiation

Barometer/CS100 (1), Setra Systems, Barometric pressure

Near ground level:

instrument, manufacturer, measurements

Rain gauge/TE525MM (1), Texas Electronics, Precipitation

Infrared radiometer/SI-111 (1), Apogee Instruments, Surface temperature

Below ground level:

instrument, manufacturer, measurements

Soil heat flux plate/HFP01SC (1), Hukseflux, Ground heat flux

Soil averaging thermocouple/TCAV (2), Campbell Scientific, Soil temperature

Water content reflectometer/CS616 (3), Campbell Scientific, Soil volumetric water content

References:

Foken, T., Wimmer, F., Mauder, M., Thomas, C., & Liebethal, C. (2006). Some aspects of the energy balance closure problem. Atmospheric Chemistry and Physics, 6(12), 4395–4402. doi:10.5194/acp-6-4395-2006

Massman, W. J. (2000). A simple method for estimating frequency response corrections for eddy covariance systems. Agricultural and Forest Meteorology, 104(3), 185–198. doi:10.1016/s0168-1923(00)00164-7

Paw U, K. T., Baldocchi, D. D., Meyers, T. P., & Wilson, K. B. (2000). Boundary-Layer Meteorology, 97(3), 487–511. doi:10.1023/a:1002786702909

Webb, E. K., Pearman, G. I., & Leuning, R. (1980). Correction of flux measurements for density effects due to heat and water vapour transfer. Quarterly Journal of the Royal Meteorological Society, 106(447), 85–100. doi:10.1002/qj.49710644707

Wilczak, J. M., Oncley, S. P., & Stage, S. A. (2001). Boundary-Layer Meteorology, 99(1), 127–150. doi:10.1023/a:1018966204465