An alternative mechanism explaining the hygropause formation in tropical regions

Radiosonde data obtained during CEPEX and TOGA-COARE experiments show that a very simple mechanism can explain the existence, in tropical regions, of a local hygropause with a very low water vapor mixing ratio, less than 2 pp mv. This mechanism explains also why this hygropause is generally located w ell above the average tropopause in the lower stratosphere, and why it can temporarily coincide with the local tropopause. This interpretation is base d on the existence, during periods of intense convective phenomena, of an u plift of the tropopause inducing a cooling of its temperature. We indeed fi nd in these circumstances, when temperature and water vapor measurements ar e simultaneously available, very low water vapor values at the same level a s the temperature minimum. After the end of the intense convection episode, the minimum temperature level is reestablished at a lower altitude while t he hygropause remains positioned in the lower stratosphere but with a low v alue for the water vapor mixing ratio.