Wave and turbulence structure in a disturbed nocturnal inversion

Abstract

Acoustic sounder and tower data obtained at the Boulder Atmospheric Observatory (BAO) are used to examine several features of the wave and turbulence structure associated with a disturbed nocturnal inversion. General features, including mean fields and Richardson number, for the case selected for this study are presented. Spectral analysis of the tower data reveals a separation of energy into wavelike and turbulent fluctuations. Analysis of the heat flux, however, shows upward counter-gradient fluxes in the vicinity of a low-level jet and near the top of the inversion. Cospectral analysis shows that the major contribution to the upward heat flux occurs at frequencies that would normally be considered characteristic of waves. In some cases, the upward flux is associated with a phase shift between vertical velocity w and fluctuating temperature 0 different from the quadrature relation that would be expected of internal waves. Time series analysis reveals that these unexpected positive fluxes occur in relatively short bursts. Analysis of time series of 0 and w in other cases, as well as inspection of acoustic sounder records, shows that sometimes such upward fluxes can result from a combination of wave motion and horizontal temperature advection. In this case the advection is associated with a shallow cold front.

Influence of stability on the flux-profile relationships for wind speed, <i>Φ</i><sub>m</sub>, and temperature, <i>Φ</i><sub>h</sub>, for the stable atmospheric boundary layer

“…At the higher levels, z=13.5 m and 32 m, there is little evidence of the similarity function following Businger's or Webb's functions. In fact, if a detailed analysis of the structure of the ABL is performed when high φ h values are present with low ζ , a complex structure of the lower atmosphere can be seen which is influenced by the presence of internal waves (Nai-Ping et al, 1983;Rees et al, 2000). These low values of ζ (for the S-period) are not truly neutral points and should not be used to do a fit in this range.…”

Observations of a multi-level turbulence structure in a very stable atmospheric boundary layer

“…From only tower measurements, it is really not possible to tell if fluctuations are due to waves propagating relative to the mean flow. But a number of authors have successfully analysed spectra and co-spectra and manifested the presence of waves in the low-frequency range (Caughey and Readings, 1975;Caughey, 1977;Lu Nai-Ping et al, 1983;Hunt et al, 1985;and De Baas and Driedonks, 1985). As stated before, there is often a clear separation (gap) between the high and low frequency part of the stable spectra at n = 0.01 (see also Olesen et al, 1984, andSmedman, 1987).…”

“…Data from the Cabauw tower have been used to show the existence of unstable gravity waves in the SBL (DeBaas and Driedonks, 1985). Recordings from the extensive measuring program at Boulder have been used by several investigators to map the complicated structure of waves and turbulence in the SBL over non-homogeneous terrain Einaudi and Finnigan, 198 I;Fua et al, 1982;Lu Nai-Ping et al, 1983;Finnigan et al, 1984;and Hunt et al, 1985).…”

On the characteristics of eddies in the stable atmospheric boundary layer

“…Previous work using cross-spectral techniques to study waves and turbulence in the stable ABL includes that of McBean and Miyake (1972), who investigated turbulent fluxes above a grass surface at Ladner, Canada. Nai-Ping et al (1983) and Hunt et al (1985) used cross-spectra to interpret observations of the nocturnal boundary layer made at the Boulder Atmospheric Observatory. Mahrt et al (1979) also presented an observational study of the nocturnal boundary layer.…”