The Aegean Sea is not excessively windy, cloudy, or stormy when compared with ocean waters such as the North Atlantic. Gales and storms of Beaufort 8 and higher (winds in excess of 62 kilometers per hour) occur in 5% or fewer observations, while light to moderate squalls are somewhat more frequent at 10% in winter, but only 2% in summer (USNHO 1952: 10). Dead calms are also rare, however.
Summer disturbances differ from those in winter. In summer, low-pressure disturbances tend to pass over the Eurasian continent, well north of the Aegean, or remain to the west of Greece. In frequency and severity these are greatly reduced from winter, rarely interrupting the prevailing northerly winds or local sea and land breezes.
Winter gales may arise from several directions, associated with depressions moving east-northeast past southern Greece from Libya, or east-southeast from Italy to cross the Greek mainland. Winter winds are more variable and unstable because of the greater number of high - and low-pressure systems that move through the Mediterranean, which determine the occurrence and severity of winds and storms. Low-pressure systems (depressions) crossing the Mediterranean from the west are often preceded by strong southerly winds. Once a storm passes over the Aegean, the wind shifts through several directions and brings showers and squalls. At other times, cold polar air from high-pressure systems over the Eurasian continent may pass to the south, pushing against the depression and generating strong winds from the north or northeast, accompanied by showers, sleet, or even snow. These storms are particularly dangerous at night on the windward side of coasts and islands because of low visibility and heavy seas; ships encountering these conditions are well advised to make for southern, lee shores. If the continental high enters the Aegean with no depression to the south, skies will be clear with strong northerly winds. The general winter pattern is that the northern Aegean remains chiefly under the influence of the continental high, and thus northerly winds, while the southern Aegean experiences frequent low-pressure systems and a mix of southerly and northerly winds. The frequency of strong winds varies by island or coastal location, and by windward or leeward position. Temporally, the greater frequency of storms and dangerous sailing conditions in winter defined the nonsailing season, as we know from ancient Greek sources beginning with Hesiod (Works and Days 620—95), but these conditions did not preclude maritime communication completely, as we shall see.
The prevailing winds from the north are most marked during the summer meltemia. Although meltemia are fair-weather winds, when blowing strongly they may kick up “white squalls," so named after the appearance of agitated water in sunlight. Locally, however, these and other winds can vary widely due largely to topography, and in summer to land and sea breezes. While land breezes are always light, sea breezes may be strong enough to disrupt or even eliminate the effects of the meltemi. An example of this phenomenon is the coastal promontory at Gytheion in Laconia. There, the meltemi is dissipated by the Taygetos mountains to the north, which shield the Gytheion area. Instead, sea and land breezes dominate during the day, with gusts off the mountains occurring at night. When forceful, sea and land breezes can be used strategically by navigators to make progress against prevailing winds and currents. By contrast, at Kythera Island off the south coast of the Peloponnese facing Gytheion, the meltemi becomes the prevailing wind in late summer as the sea warms and consequently the sea breeze generated by land/sea temperature differentials diminishes (USNHO 1952: 11). The north-facing anchorages are particularly vulnerable to northerly and westerly winds (Heikell 2007: 144—48).
Cloud cover is light overall, with summer skies seldom overcast, but heavier in winter when most precipitation falls. When clouds do occur, a diurnal pattern of minimal cloudiness in the morning, followed by increasing clouds in the afternoon and dissipation in the evening, is common throughout the Aegean. During winter, cloud cover averages 50%, with little variation from November to April. Great banks of clouds shrouding mountain summits often precede bad weather, especially in the northern Aegean.
Consistent with a characteristic Mediterranean climate, the Aegean region experiences distinct wet and dry seasons, with most rain falling between October and March (Xoplaki 2002: 10—12, figs. 1.1, 1.2). Driven by the great weather engines described above, the precipitation of early winter is often heaviest as warm, moist air forming over the open Mediterranean comes into contact with cold, drier polar air lying over the Eurasian continent.
Rainfall patterns across the Aegean basin are variable; the frequency, timing, and amount of rain a particular locality receives depend on several factors. In the northern Aegean, southerly winds contribute most of the rain, though northerly systems sometimes deposit snow. In the southern and central Aegean, southerly, westerly, and northerly winds can all bring rainfall. Because Mediterranean depressions carry abundant moisture, the islands of the southern Aegean, exposed to eastward-tracking depressions from the central Mediterranean, receive more rain than the Greek mainland, but in lower-frequency, higher-volume events. Rains seldom last for more than a few days at a time. On
4.8 Satellite image of Kapsali Bay, Kythera. Image © 2011 Google Earth, © 2011 European Space Imaging.
The mainland, rain occurs most frequently in the afternoon, while over the sea and islands, rainfall at night or early morning is more common.
Sometimes rain effects are topographic in origin. The northwestern Greek province of Epirus is an area of high rainfall because storm systems crossing the mainland from the west are halted by the Pindos mountain range. There, the clouds release rain (“orographic rainfall": Morton 2001: 64—65), which then drains down the western side of the Pindos to feed large perennial streams and springs. A corresponding “rain shadow" region on the eastern side of the Pindos is much drier. In the mountainous Greek terrain, such rain surplus and deficit relationships are common on both macro - and microregional scales, detectable, for example, even between Athens and its northern suburbs. All areas of the Aegean are also subject to potentially large interannual fluctuations in rainfall, which in drier areas such as the Cycladic Islands can have dire implications for subsistence (Broodbank 2000: 76—78).
World History
