Comparative analysis of humidity characteristics for open-sea and coastal areas in the Mediterranean

In this study we use observational data to examine the characteristics of open-sea areas over the Mediterranean Sea with respect to the water vapour variability. Datasets of vertical water vapour distribution available from coastal radiosoundings and satellite-derived products are analyzed with respect to the seasonal variability of four variables: relative humidity at three reference pressure levels (surface, 850 hPa, 500 hPa), precipitable water for three layers between surface and pressure levels of 850 hPa, 500 hPa and 200 hPa, as well as for mean lower and upper tropospheric relative humidity. It is found that the eastern basin presents a distinct and well marked regional characteristic, namely a stronger seasonal cycle of relative humidity and dryer upper troposphere during summer. Differences in the seasonal variability of relative humidity between the maritime and coastal environments are also documented. The direct comparison is complemented by the performance analysis of a linear regression model relating surface water vapour mixing ratio to integrated and mean measures of humidity. The results show that in general, coastal profiles describe reasonably well the open-sea conditions for winter months, characterized by low synoptic variability.