اتجاه محور الأخدود و الانبعاج فوق البحر المتوسط عند مستوى ضغط 500 ملليبار لسنوات الجفاف في الأردن

Abstract EN

Trough and Ridge Axes Orientation over Mediterranian Sea at 500 mb.

Level for Dry Years in Jordan.

The study aims at understanding the weather effects of varied situations which constitute the upper trough and ridge axes orientation at 500 millibar level.

The role of these situations in forming climatic dry years was revealed through connecting these situations with surface atmospheric regime, the steering and trajectories of which are determined by upper atmospheric regime, as well as a clear perception of the behavior of climatic drought phenomena.

The methodology followed the analysis of 1200 successive daily upper synoptic charts at 500 millibar level of the five drought years being studied which are equivalent to 40 rainy months.

The data related to the situations of the study variables were computerized for obtaining cross—tabulation to interpret the percentage of the crossing of upper trough axe with ridge axe orientation over the Mediterranian sea.

It was found that each situation of any one of the two variables has its effect on surface weather conditions.

The study revealed that the type of association between ridge axe orientation and the position of trough axe at 500 millibar level has its active role in determining the type of flowing air mass which it may be dry polar or marine polar; and the speed of air on the axe length and its ability to penetrate tropical area towards the south.

Therefore, throughout 87,5% of the cases which represent 35 rainy months out of 40 months, the associations were in their prefect situations from north-east to south-west and north-south with the oblique of trough axe to the left or right “according to map reader”.

This means providing the ridge with polar dry air, since most of the situations of trough axe are left or right oblique which weakened their ability to move or stimulate surface atmospheric regime, and characterizing surface low atmospheric depressions with being slow in motion towards east and being shallow up till vanishing.

This means that morphological characteristics of the study variables led to the damping of surface frontal systems, whereas the active associations were in 12.5% of the cases, which represent only five rainy months, during which the ridge axe orientation was north-west to south-east, associated with a verticle trough position.