Previous studies of the clear sky greenhouse effect and water vapor feedback have focused on subpolar regions. In view of modeled amplification of greenhouse warming in the Arctic we investigate the humidity characteristics, clear sky greenhouse effect and water vapor feedback in the Arctic by using 10 years of radiosonde data obtained from the Russian drifting ice island stations along with a radiative transfer model. By taking advantage of the natural variability associated with seasonal and interannual variations, we can infer the water vapor feedback from the data. Results of this study indicate that waver vapor feedback over the Arctic Ocean is substantially more complex than in other regions because of the relative lack of convective coupling between the surface and the atmosphere and the different thermodynamic and radiative environment in the Arctic. In particular, the effect of water vapor on the net flux of radiation is complicated by low temperatures, low amounts of water vapor, and the presence of temperature and humidity inversions. During winter a ''hyper'' water vapor feedback arises from the control of ice saturation on the lower tropospheric humidity and a water vapor ''window'' in the rotation band at low atmospheric humidities. Implications for global warming are discussed. ¿ American Geophysical Union 1995