Abstract
Abstract. Considering the Mediterranean as a region of high evaporation and low precipitation, evaluations of sinks and sources of moisture and precipitation in the Mediterranean basin have been carried out within the frame of the CIRCE (Climate Change and Impact Research: the Mediterranean Environment) project. Besides these evaluations, residence time and stagnation/ventilation analyses have been carried out to investigate transport to and from the Mediterranean basin and in the basin itself. A Lagrangian moisture diagnosis method calculating budgets of evaporation minus precipitation was applied to a 5.5 year (October 1999–April 2005) trajectory data set and evaluated for eight representative Mediterranean Regions Of Interest (ROI). The Mediterranean basin has been identified as a major source of moisture and precipitation to the surrounding land area and to the basin itself. Main regions of stagnation, i.e. the Po basin, have been defined on a seasonal basis through residence time analysis. Evaluation of the transport to and from the basin shows that the Mediterranean is a crossroad of airstreams where air enters mainly from the northwest and continues in two separate streams, one going southwest over North Africa into the trade wind zone and the other one to the northeast through Central Asia.
Highlights
1.1 MotivationThe Mediterranean region has been identified as one of the “hot spots” for present and future climate change (Giorgi, 2006; Gibelin and Deque, 2003)
We found that in a few rare cases specific humidity suddenly dropped from one time step to the from plausible values to nearly zero specific humidity, probably indicating a bug in the FLEXPART data set
The residence time is defined as the average of the time spent by the simulated particles in the respective evaluation grid cell within the Regions Of Interest (ROI) and within the predefined time windows in this study
Summary
The Mediterranean region has been identified as one of the “hot spots” for present and future climate change (Giorgi, 2006; Gibelin and Deque, 2003). Stagnation and recirculation are common and contribute to accumulation of air pollutants, especially ozone (Millan et al, 1996, 1997). On this background, several large research programmes have been launched, such as MedClivar (Mediterranean CLImate VARiability and Predictability) (Lionello et al, 2006), HyMeX2 (HYdrological cycle in the Mediterranean EXperiment) (Drobinski and Ducrocq, 2008), and CIRCE3 (Climate Change and Impact Research: the Mediterranean Environment). The transport and residence times of air masses are related both to moisture and air pollution budgets; the moisture budgets are considered explicitly here as we have detailed information about them through the ECMWF data
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