Area Climatology — Page 433, Lesson 404

I want to walk you through the area climatology of the Mediterranean region, starting with the surface winds that have specific local names and characteristics. First, we have the Levanter. This is a summer outflow from the Mediterranean that occurs at Gibraltar. The name comes from the fact that it blows from the east — from the Levant — and it occurs during July through October, and also in March. It can reach gale force. Now, the Rock of Gibraltar has its axis oriented north/south, and when this easterly wind hits the east side of the Rock, it gets forced upward — that's orographic uplift — through about 1100 feet. This uplift can produce a banner of stratocumulus or stratus — ST/SC — which then streams westward from the top of the Rock. In stable air, standing waves can occur over the Rock. There can be considerable turbulence up to 5000 feet above the adjacent airfield, so that's a significant operational concern for aircraft operating in that area. Next is the Etesian wind. This is a moderate, persistent wind that blows from the north across the Greek Islands of the Aegean Sea, towards the island of Rhodes, and then continues southwards. It's caused by the pressure gradient between the Azores ridge — which extends across the western and central Mediterranean — and heat-induced low pressure overland to the east. So you have high pressure to the west and low pressure to the east, and that pressure difference drives this northerly flow. The Etesian wind is dry and brings clear skies and good visibility. However, strong Etesians can bring gales and affect the area from western Greece to western Turkey, and as far south as the North African coast. When that happens, cumulus — CU — may develop after the long sea track, because the air picks up moisture over the sea. Then we have sea breezes. These can be strong at this time of the year and will locally modify the surface wind direction. So even if the general wind pattern is from a certain direction, a sea breeze can change it near the coast. Now let's move to the upper winds. In the western part of the region, we have light westerly winds. In the eastern part, the westerly wind averages 40 to 50 knots. Both jet streams are out of the region to the north — so the jet streams don't directly affect the Mediterranean in summer. For icing, the freezing level is high in summer, so icing is not normally a problem. That's a welcome fact for pilots operating in the region during this season. Let's look at the average tropopause heights. In the south region, the tropopause is at about 53,000 feet. In the north region, it's lower at about 40,000 feet. That's a significant difference — about 13,000 feet — which reflects the different air masses and temperatures. Finally, the average freezing levels. In winter, the freezing level is at about 6000 feet. In summer, it rises to about 14,000 feet. That's why icing is not normally a problem in summer — the freezing level is high enough that most flight levels stay well below it in the warm air.