The temperatures (black) for the year 2010 (panel a) and the difference from the reference level (panel b) The vertical dashed lines (from left to right) correspond to the dates 15th and 24th January. The grey shade is |$\pm 1 \sigma$| error in the temperature and same as in Fig. 9(c). For comparison, the red curve (panel a,b) shows the temperature estimation (and the artefacts) under the assumption of constant mass index (see the text). All temperatures here represent a three-day running mean.