INDIA LOCAL WINDS
Towards the end of summer, there are pre-monsoon showers which are a common phenomena in Kerala and coastal areas of Karnataka. Locally, they are known as mango showers since they help in the early ripening of mangoes. (ii) Blossom Shower : With this shower, coffee flowers blossom in Kerala and nearby areas. (iii) Nor Westers : These are dreaded evening thunderstorms in Bengal and Assam. Their notorious nature can be understood from the local nomenclature of ‘Kalbaisakhi’, a calamity of the month of Baisakh. These showers are useful for tea, jute and rice cultivation. In Assam, these storms are known as “Bardoli Chheerha”. Loo : Hot, dry and oppressing winds blowing in the Northern plains from Punjab to Bihar with higher intensity between Delhi and Patna.
WORLD LOCAL WINDS
Bora: North easterly from eastern Europe to north eastern Italy Chinook: Warm dry westerly off the Rocky Mountains Fohn: Warm dry southerly off the northern side of the Alps and Switzerland. Harmattan: Dry northerly wind across central Africa Karaburan: ‘Black storm’ a spring and summer katabatic wind of central Asia Khamsin: South easterly from North Africa to the eastern Mediterranean Loo: Hot and dry wind which blows over plains of India and Pakistan.
Mistral: Cold northerly from central
France and the Alps to Mediterranean. Nor’easter: Strong winds from the northeast in the eastern United States, especially New England Nor’wester: Wind that brings rain to the West Coast, and warm dry winds to the East Coast of New Zealand’s South Island, caused by the moist prevailing winds being uplifted over the Southern Alps, often accompanied by a distinctive arched cloud pattern. Pampero: Argentina, very strong wind which blows in the Pampa. Simoom: Strong, dry, desert wind that blows in the Sahara, Israel, Jordan, Syria, and the desert of Arabia. Sirocco: Southerly from North Africa to southern Europe. Zonda wind: On the eastern slope of the Andes in Argentina. Air Masses When the air remains over a homogenous area for a sufficiently longer time, it acquires the characteristics of the area. The homogenous regions can be the vast ocean surface or vast plains. The air with distinctive characteristics in terms of temperature and humidity is called an airmass. It is defined as a large body of air having little horizontal variation in temperature and moisture. The homogenous surfaces, over which air masses form, are called the source regions. The air masses are classified according to the source regions. There are five major source regions. These are: (i) Warm tropical and subtropical oceans; (ii) The subtropical hot deserts; (iii) The relatively cold high latitude oceans; (iv) The very cold snow covered continents in high latitudes; (v) Permanently ice covered continents in the Arctic and Antarctica. Accordingly, following types of airmasses are recognised:
- Maritime tropical (mT);
- Continental tropical (cT);
- Maritime polar (mP);
- Continental polar (cP);
- Continental arctic (cA).
When two different air masses meet, the boundary zone between them is called a front. The process of formation of the fronts is known as frontogenesis. There are four types of fronts: (a) Cold; (b) Warm; (c) Stationary; (d) Occluded When the front remains stationary, it is called a stationary front. When the cold air moves towards the warm air mass, its contact zone is called the cold front, whereas if the warm air mass moves towards the cold air mass, the contact zone is a warm front. If an air mass is fully lifted above the land surface, it is called the occluded front. The fronts occur in middle latitudes and are characterised by steep gradient in temperature and pressure. They bring abrupt changes in temperature and cause the air to rise to form clouds and cause precipitation.