Example of observation and models of the water line at 67.09 μm at the centre of the beacon in July 2011, at the relative pointing coordinates RA=−5.90″, Dec=4.16″ (corresponding to the x-marker position in Fig. 8). The spectrum is expressed in terms of continuum-substracted line-to-continuum (1/c-1). The observed spectrum is in dashed grey lines. It is obtained after the calibration and baseline removal steps presented in Section 2.2. The dashed-dotted green line corresponds to a model in which only the temperature increase in the beacon is accounted for (Step 1 – see Section 4.1). The solid blue line and dotted cyan line represent the rescaled photochemical models (Step 2 – see Section 4.2) in which we consider only the haze sublimation (rescaled by a factor of 0.39), then we add the downward winds to the sublimation (rescaled by a factor of 0.13), respectively. The red line depicts a model in which the water mole fraction is fitted in the beacon as a single free parameter (Step 3 – see Section 4.3). The black point with error bars corresponds to the 1σ line amplitude uncertainty of about 15–20%, mostly caused by the baseline removal. This value is different from the line area uncertainty (see 2Section 2.2).