MODELING THE TRANS-ATLANTIC TRANSPORTATION OF SAHARAN DUST

In the present study we are simulating the trans-Atlantic transport of dust from Sahara to the South-Central America, using the regional climate model RegCM4 and its online dust scheme, for the year 2007. The simulated horizontal and vertical distributions of the mineral dust optical properties were evaluated against the LIVAS CALIPSO satellite dust product. The Trans-Atlantic dust transport is simulated adequately with RegCM4, but there are some spatial discrepancies. Dust optical thickness is overestimated in the eastern Sahara throughout the year by 0.1-0.2, while near the gulf of Guinea is underestimated during winter and spring. Although RegCM4 dust plume is located southern on winter and spring, it doesn't spatially match the dust optical thickness of LIVAS. In summer and autumn the vertical distribution of dust between 3-4km during the Trans-Atlantic transport is simulated by the model adequately up to 30ºW 40ºW longitude. However, during winter-spring RegCM4 misplaces dust loading into higher altitude. Finally, we discuss some possible reasons and mechanisms that might be responsible for the differences between the model and the observations

Fog characteristics at the airport of Thessaloniki, Greece

A statistical approach in order to study fog event characteristics occuring at the airport of Thessaloniki, Northern Greece is presented in this work. To achieve this, the seasonal and diurnal characteristics of fog are investigated using 35 years (1971–2005) of observations of meteorological parameters such as: visibility, air temperature, dew point temperature, air relative humidity, wind vector, precipitation, and cloud base height and coverage. Hourly surface observations of fifteen (15) years (1991–2005) are used to identify fog events induced by various physical mechanisms. Fog events are classified into fog types through the application of objective criteria that are derived upon fog formation processes and under the influence of various physiographic features. The temporal variability of different fog type occurrences are examined and the events are characterized according to their duration and intensity. <br><br> The results are somehow affected by regional and local factors. Fog is mainly formed in winter time (~64%) with an enhanced likelihood to appear also in late autumn (19%). The highest frequency of the fog events occurs around sunrise or 1 to 2 h before of it. The mean duration of the events is about 4.5 h. Most of them (75%) are dense (visibility <400 m). The overall fog phenomenon is a combination of various types, such as: advection fog, radiation fog, cloud-base lowering fog and precipitation fog. Advection fog (30%) and radiation fog (29%), which are the most common types, occur predominantly in winter and early spring time. With respect to the former type, it seems that, in many cases, already formed fog is advected from the nearby <i>Anthemountas</i> valley. Moreover, a considerable number of fog events (22%) result from cloud-base lowering, and they frequently occur in late autumn and mid winter