We developed a time-dependent radiative model for the atmosphere of HD209458b to investigate its thermal structure and chemical composition .
Time-dependent temperature profiles were calculated , using a uniform zonal wind modelled as a solid body rotation .
We predict day/night temperature variations of 600K around 0.1 bar , for a 1 km/s wind velocity , in good agreement with the predictions by Showman & Guillot ( 2002 ) .
On the night side , the low temperature allows the sodium to condense .
Depletion of sodium in the morning limb may explain the lower than expected abundance found by Charbonneau et al ( 2002 ) .