Left column: Distribution of the decay index in the FPIL-aligned planes. The blue and red curves indicate where n exceeds 1.5 and 0.8, respectively. Dotted gray lines indicate the correspondingly estimated critical height of the TI. Shaded areas mark the corresponding uncertainties. Right column: Profile of $\stackrel{\sim }{n}$ vs. height. The horizontal blue (red) lines indicate where $\stackrel{\sim }{n}$ = 1.5 (0.8), respectively. Vertical solid (dotted) blue lines mark the heights at which $\stackrel{\sim }{n}$ ± 1 MAD = 1.5. Vertical solid (dotted) red lines mark the heights at which $\stackrel{\sim }{n}$ ± 1 MAD = 0.8.