Plot of the “integrated-averaged” T-P profile (diamonds) obtained in Sect. 4.3. The vertical error bars show the pressure domain of the corresponding temperature estimates. The thin triple-dot-dashed line shows the altitude of the sodium abundance drop measured by Sing et al. (2008a,b). At pressure between 10^-3 and 10^-5 bar, the low temperature (T < 800 K) favors the sodium condensation scenario to explain the sodium abundance drop. Our T-P profile is consistent with the T-P profile obtained by Sing et al. (2008b) using a parametric fit of the same data set (dotted line) without the addition of the latest observations at higher altitude levels from Snellen et al. (2008). For comparison several theoretical T-P profiles are over plotted. At higher pressures (P > 1 mbar), models of Barman et al. (2005; dash-triple-dotted line), Showman et al. (2008; long dashed line) and Guillot (2010; two solid lines, one for μ = 0 at the terminator limb and the other at μ = 0.1 close to the terminator limb) are shown. At lower pressure levels, the Yelle (2004) theoretical T-P profile is also shown for comparison (dashed line). The dot-dashed line shows the vertical velocity of the hydrodynamic outflow in the Yelle (2004) model (in m/s). This velocity is negligible at pressure above a few 10^-8 bar where the hydrostatic assumption is therefore justified.