Horizontal spectra of atmospheric tracers measured during the Global Atmospheric Sampling Program

Variance power spectra of potential temperature, ozone, carbon monoxide, and water vapor at airliner cruise altitudes are presented. These results are based on data collected aboard commercial airlines at cruise altitudes during the Global Atmospheric Sampling Program (GASP). The horizontal scales (wavelengths) resolved by these data extend from 2.6–2400 km for temperature, 10–2400 km for ozone, 150–3000 km for water vapor, and 300–2500 km for carbon monoxide. The results divide into two distinct regimes in most cases, with the transition found at 500- to 800-km wavelength. The long wavelength regime of temperature behaves as predicted by geostrophic turbulence theory, but only some of the chemical tracer results fit this model. At scales less than 500–800 km, spectral shapes of all tracers follow an approximately −5/3 power law dependence on wave number. At scales less than about 100 km, tropospheric ozone spectra follow a −1 power law. Spectral amplitudes of potential temperature and ozone are larger in the stratosphere than in the troposphere, while spectral amplitudes of carbon monoxide and water vapor are larger in the troposphere. The horizontal fluctuations giving rise to these spectra apparently result from that component of a spectrum of quasi-horizontal displacements which acts orthogonal to the background gradient of each tracer. Numerical checks support this hypothesis for each of the chemical tracers, assuming the tracers are horizontally stratified. Finally, it is found that the frequency distribution of ozone spectral magnitude at a given wave number is approximately lognormal.