Obviously meteorology is a far more complex subject than the thumbnail I’m giving again. I’m just covering some of the major influencing factors for Ireland and the North East Atlantic.
So last time we saw some of the prevailing winds ran opposite those across Ireland.
To explain these difference we need a few further scientific names.
The first is Circulation Cells.
These were originally used to describe the circulating patterns of air. Hadley Cell is the movement in the equatorial region, Ferrell Cell is the mid-latitudes and Polar Cell is Latitude above 60 deg. North.
In the Hadley Cell, warm air rises at the equator, flows north (and south) and DROPS when colder and denser at about the sub-tropical (30 deg. Latitude) point to flow south again.
In the Ferrel Cell the air flows along the surface and RISES when warmer at around the 60 deg latitude point.
In the Polar Cell cold air flows along the surface south (or north in the souther hemisphere), until about the 60 deg latitude line, where, warmer, it rises again and flow back toward the pole.
So the upshot of all this for Ireland is:
- South of us is a semi-permanent High Pressure region.
- North of us is a semi-permanent low pressure region.
So low pressure systems will be blocked on the south and flow north eastwards generally. This , you will recognise as the prevailing pattern in Ireland. Bad weather (cyclones) come in from the west, and move up toward Scandanavia.
Of course other factors are required also for this to happen. For one thing, the theoretical model in the attached picture is affected by different land and water geography.
Given our position on the edge of the Atlantic we are subject to something most the rest of Europe isn’t, namely the edge of the Marine Polar air mass.
The world is also covered in Air Masses. The North Atlantic is covered by the mP, i.e. marine Polar, i.e. cold, Air Mass. Whereas continental Europe isn’t covered by a stable air mass.
Around the Azores is the differentiation to the mT, marine Temperate, zone. This acts as a block to low pressures more northerly than the 30 deg N, Ferrel Cell boundary.
And there you have some broad outlines.
An offshoot of this for Ireland is you can understand a low pressure system better. Due to the Coriolis Effect, low pressure systems (anti-cyclones) in the northern hemisphere circulate anti-clockwise. Think about an anti cyclone off the west or north west coast. The air will flow southward and swing around through westerly until it is again flowing northwards (a southerly wind). These are our prevailing local wind conditions, onshore southerly winds on the south coast which are offshore on the north coast.
IANAM (I am not a meteorologist)