Turbulence spectra of CO2, water vapor, temperature and wind velocity fluctuations over a crop surface

✍ Scribed by Dean E. Anderson; Shashi B. Verma

• Publisher: Springer
• Year: 1985
• Tongue: English
• Weight: 666 KB
• Volume: 33
• Category: Article
• ISSN: 0006-8314
• DOI: 10.1007/bf00137033

✦ Synopsis

A prototype rapid-response CO, sensor was used in conjunction with a Lyman-alpha hygrometer, fine-wire thermocouples and a three-dimensional drag anemometer to measure COz, humidity, temperature and wind velocity fluctuations. Measurements were made over a soybean crop grown on relatively flat terrain near Mead, Nebraska.

Temperature, humidity and CO, spectra measured under near neutral conditions were most similar in shape while longitudinal velocity (U) spectra appeared to be somewhat broader. Peaks occurred around f = 0.02 to 0.06 (where f is the non-dimensional frequency) in all spectra except for vertical velocity which had a peak near f = 0.5. As thermal stability changed from neutral to stable, spectra exhibited lower peaks, were narrower in shape and were shifted towards higher frequencies. Opposite behavior was observed with increasing instability.

Cospectra for momentum, heat, water vapor and CO, measured during neutral conditions had similar peak frequencies (near f = 0.15). Among the cospectra studied, CO, and water vapor cospectra had the greatest similarity in shape.