The idealised model of climate zones , pressure patterns and global wind belts that can be sketched however, is complicated by the position of continents and oceans.
Land surfaces react quickly to heat gain and loss, becoming warm in summer, cold in winter.
The oceans react far more slowly and during the summer they are cooler than the adjoining land, whilst in winter they are warmer. High atmospheric pressure usually develops over cold areas were air is descending, whilst low pressure forms over warmer regions where air is rising. C. A weaker winter anticyclone develops over North America. In contrast, low-pressure centres known as depressions continue to develop in the warmer North Atlantic and North Pacific Oceans, centred respectively on Iceland and the Aleutian Islands. These are the Icelandic and Aleutian Lows.