Some Measurement Issues for Urban Test Beds

1. Some Measurement Issues for Urban Test Beds R. P. Hosker, Jr. NOAA / OAR / ARL Atmospheric Turbulence & Diffusion Division Oak Ridge, TN 37830 USA

2. Urban Test Beds • Who: Atmospheric monitoring and research communities • What: Selected urban areas with permanent instruments to provide data for long-term urban studies, support for urban requirements, and base instrumentation arrays for short-term research studies. • When and Where: U.S. efforts under way in DC, soon in Las Vegas and elsewhere. • Why: cities are where the people are / will be (see U.S. projection from 2001 U of MA study). Need atmospheric data to protect, advise, & assist urban populations.

3. Some Urban Issues Related to the Atmosphere • Extremes of heat and cold • Transportation problems (air, ground, water) • Electric power and water demands • Structural integrity (wind engineering standards) • Flash floods and runoff handling • Transport & dispersion of airborne substances • Air quality • Construction and outdoor work • Urban vegetation impacts • Recreation • Impacts on local economy

4. Scales of Interest in Urban Regions • Individual buildings (probably large ones) • Groups of buildings (a few city blocks) • Entire sections of city (neighborhoods) • Urban core (CBD) • Entire city (CBD + surroundings) • Metropolitan area • Mesoscale Measurements and measurement locations must suit the particular urban problem, and the spatial scale of interest. An urban test bed must cope with multiple problems and scales.

5. What’s Needed in Urban Test Beds? It Depends. Oke (2004) suggests 3 scales. Larger scales require more of “view from above”, and resolution of spatial variability. • Mesoscale requires sensing well above city & across region. • Local scale requires sensing well above rooftops & across whole neighborhoods. • Microscale requires high resolution sensing within a region of great variability.

6. Some Likely Measurement Needs for a Multi-purpose Urban Test Bed • Precip (totals & rates, spatial variability, extremes, snow depth, hail, icing) • Temp & humidity (means, extremes, spatial variability) • Wind speed (means & extremes, gustiness, variability incl. in the vertical) • Wind direction (means & std deviation, variability) • 3-D turbulence components (variability important) • Local energy balances & variability (incl. fluxes) • B-layer data (mixing layer, similarity variables, depth, variability)

7. Classes of Measurement Tools Available for Use in Urban Areas • “Point” systems (ground & tower-based). Problems with representativeness, logistics, siting permissions, vandals. • Sodars. Limited range due to noise. Annoy neighbors. • Radars. Costly, coarse resolution. Siting. • Lidars. Costly. Siting. Some eye safety issues. DIAL for concentrations of some materials. • Aircraft. Costly, limited flight paths and altitudes. • Satellites. Costs, limited periods of observation. • Models (numerical & physical)

8. Inadequacies of Current Tools • Point systems. Depending on scale of interest, may need many sites. May see very strong local influences (heat, aerodynamics). Very limited vertical reach possible. Depend on benevolence of many site owners. Difficulties in mounting, power, comms, repair access, sometimes aesthetics. • Sodars. Signal/noise ratio a big problem in noisy urban areas; limits range. Frequencies that give best range annoy neighbors. Rooftop sites may be operationally useful; access can be an issue. • Radars. Expensive, unless piggybacking on existing installations (profilers, NEXRAD, Terminal Doppler Weather Radar). Require expertise in operating, interpreting data.

9. Inadequacies of Current Tools (continued) • Lidars. Expensive. Need good field of view. Can be eye safety issues. Require expertise in operating, interpreting data. Not always reliable for continuous operations. • Aircraft. Costly to operate special flights; limited flight paths and altitudes over populated areas. Routine data from commercial flights using ACARS, TAMDAR (Tropospheric Airborne Meteorological Data Reporting), but some strings attached. • Satellites. Costs, limited periods of observation, usually need clear skies. Mostly passive sensors. Require expertise in interpreting data.

10. Wish List for New Urban Measurement Systems • Resolve local flows & met variables (street canyons, wakes, rooftop flows), . • Resolve flows & met variables above UCL, within roughness sublayer. Measure representative local energy balances, fluxes. • Systems must be reliable, inexpensive, modest power, compact, continuous operation, fast responding, near-real time reporting, rugged, low-maintenance, inconspicuous… • Need more emphasis on development of remote sensing systems for urban use. Need good resolution (short range gates), modest range, easy-to-interpret outputs. • Need urban data networks to move data from disparate sensors to central repository in near-real time.