Types of Winds system,Local Winds,Land & Sea Breezes,Katabatic Winds,Anabatic Winds


Types of Winds system

There are three types of wind systems

  • Permanent Systems   
    • Macro level highs and lows causing Westerlies and Trades
  • Periodic Systems
    • Monsoons caused by during hemispherical summers
  • Local conditions.
    • Land & Sea breeze
    • Katabatic and Anabatic winds
    • Thunderstorms           

Local Winds

  • There are a large number of local winds which blow across various harbours, bays and seas in the world. They are caused due to :-
    • Diurnal heating and cooling of a coast.
      • Sea Breeze & Land Breeze
      • Katabatic & Anabatic Winds
      • Thunderstorm
    • Movement of cold front (Pampero and Southerly Buster.)
    • Tornadoes and waterspouts.

Land & Sea Breezes

  • These are caused by large differences in diurnal range of atmospheric temperature over land and sea which can be as high as 20° on land as against 1° at sea.
  • Land and sea breezes occur when
  • Large expanse and land and sea meet.
  • The coast is high, dry, rocky and desert with no swamps or trees.
  • Coastal regions do not experience extreme hot or cold because of the Land and sea breeze where frequent exchange of heat occurs between two differently heated regions.
  • Effect of such breeze is felt up to a maximum of 20 nm from the coast.
  • Sea breeze is much stronger than the land breeze.

Significance for a Mariner

  • High drift rate towards the land during evening hours.
  • Strong drift towards the jetty depending upon its location.

Land Breeze

  • At night, the land cools rapidly resulting in high atmospheric pressure over it.
  • Sea temperature changes little and atmospheric pressure over the sea also changes little.
  • A pressure gradient builds up between the land and sea with isobars running roughly parallel to the coast.
  • Land breeze lasts from couple of hours after sunset till half an hour after sunrise. (Remember this coincides with the minima of diurnal temperature)

Sea Breeze

  1. During the day, land gets heated up rapidly resulting in low atmospheric pressure over it. 
  2. Sea temperature changes little and atmospheric pressure over the sea also changes little.
  3. A pressure gradient builds up between the sea and land with isobars running roughly parallel to the coast.
  4. Wind blows from sea to land and because of steep gradient, can strong.
  5. Sea breeze sets in by 1000 to 1100 hrs and reaches force of 3 to 4 by 1400 hrs (Coincides with the maxima of the diurnal variation) and dies out after sunset.
  6. Sea breeze blows upto 20 nm but have been detected as far away 100nm from the coast.

Katabatic Winds

  1. Katabatic blow downhill during night and anabatic blow up hill during daytime.
  2. At night land cools and HP develops and the air is denser.
  3. On a slope, this dense air rolls down.
  4. With high hinterland, It picks up speed upto force 7.
  5. It finally blows over the sea.
  6. Common in Adriatic, Norway and Greenland.
  7. Because of unpredictability, it is dangerous and can jeopardisea ships along side by breaking off of the mooring lines.
  8. The Remedial action:-
  9. Read latest sailing directions for up–todate information.
  10. Tighten the moorings and pass additional lines ashore.
  11. Pay out more cable and keep 2nd anchor ready for letting go.
  12. Extra vigilance during night hours.  .

Anabatic Winds

  1. Land gets heated up during the day and LP developed.
  2. If there is a dip in the land (like a valley), the air from higher altitude sinks in the valley.
  3. The air in the valley, gets pushed out and goes up the slope of the valley.
  4. These winds are much weaker than the Katabatic winds.
  5. OF little relevance to a Mariner as they do not blow at sea.