With the foundation of HRCT, drainage passage and ostium of the frontal sinus were identified and opened through the landmark of agger nasi cells, the superior attachment of the uncinate process and the anterosupterior basal lamella of the bulla.
The frontalpassage in cold-front process usually led to a dramatic decrease of relative humidity. The air is relatively dry in the south side of the cyclone in Mongolia cyclone process which usually results in server sandstorm.