Abstract
Abstract. Recently, Lovejoy et al. (2009) argued that the steep ~k−3 atmospheric kinetic energy spectrum at synoptic scales (≥1000 km) observed by aircraft is a spurious artefact of aircraft following isobars instead of isoheights. Without taking into account the earth's rotation they hypothesise that the horizontal atmospheric energy spectrum should scale as k−5/3 at all scales. We point out that the approximate k−3-spectrum at synoptic scales has been observed by a number of non-aircraft means since the 1960s and that general circulation models and other current models have successfully produced this spectrum. We also argue that the vertical movements of the aircraft are far too small to cause any strong effect on the measured spectrum at synoptic scales.
Highlights
Aircraft measurements (Nastrom and Gage, 1985) show that the atmospheric kinetic energy wavenumber spectrum has a transition from an approximate k−3-range, at scales from several hundred kilometres to several thousand kilometres, to an approximate k−5/3-range at scales from about five hundred kilometres down to one kilometre
Lovejoy et al (2009) argued that the observed steep spectrum at synoptic scales is an artefact of the vertical motions of the aircraft
Wiin-Nielsen (1967) calculated kinetic energy spectra using meteorological data from six different levels in the troposphere and found that the spectra had power law dependence at the four highest levels, with exponents varying from −2.6 to −3.1
Summary
Aircraft measurements (Nastrom and Gage, 1985) show that the atmospheric kinetic energy wavenumber spectrum has a transition from an approximate k−3-range, at scales from several hundred kilometres to several thousand kilometres (synoptic scales), to an approximate k−5/3-range at scales from about five hundred kilometres down to one kilometre (mesoscales). Structure function analyses from aircraft measurements (e.g. Cho and Lindborg 2001) are consistent with this result.
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