^{2}ξ

^{2}); c) ε

_{χ}at 29 m for the period 20 Dec 2006 to 10 Feb 2007. The thin black line in (a) represents the local value of N [Hz] determined from the χpod. The histogram in (d) corresponds to frequencies estimated from 155 unstable modes computed from linear stability analysis. The solid line in (d) is the temperature spectrum (variance-preserving form) for the full period shown in (a). (from Moum et al., 2011)