Dive Atlas of the World. Jack Jackson

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      Monsoon winds are primarily caused by the difference between temperatures over large landmasses and adjacent large oceans, notably Arabia, Asia, Australia, and the Indian subcontinent. Seasonal changes in temperature are large over land, but small over oceans. A monsoon wind blows from cold to warm regions and, in summer, from the sea towards land carrying humid air from the ocean. In winter it blows from the land toward the sea. As a consequence, where monsoons occur, one side of a landmass may get heavy rain and not be divable at one time of year and the opposite side of that landmass at another.

      Some regions are known for consistently bad tropical cyclones or monsoons at certain times of year and the resorts shut down for that period. Regions where these events only occasionally cause problems, tend to stay open during the bad weather season, while offering cheaper rates. Divers who book resorts in these regions at this cheaper time of year should be aware that their holiday could be ruined.

      Although not necessarily of tropical cyclone strength, bad weather can occur anywhere at any time of year. However, diving can be quite pleasant during inclement weather, if divers jump into the water and quickly descend below the swell. The real problems are in getting the boat out to the site and, worse, getting out of the water into a boat in a heavy swell.

      MAJOR CURRENTS

      Although local currents vary during the day due to winds, upwellings, downwellings and the heat of the sun, there are more consistent current patterns in the world’s oceans that affect the climate, conditions for diving and which migratory species can be found at a given time in a normal year.

      Ocean currents are horizontal and vertical circulation systems of ocean waters that are produced by the earth’s rotation, gravity, wind friction, and the variations in water density that result from differences in temperature and salinity.

      For instance, the currents that form the Gulf Stream bring warm waters northward, affecting the climates and waters of the Bahamas, Bermuda, eastern North America, the British Isles and the Atlantic coast of Norway. This leads to tropical species off Bermuda and some surprising species such as Ocean Sunfish and Leatherback Turtles visiting the west coast of the UK. Similarly, part of the South Equatorial Current that flows towards East Africa joins the Agulhas Current and relatively warm water flows southward at high speed along the east coast of South Africa. However, when this current is reversed, cold water flows north, bringing with it huge quantities of sardines, which in turn attract large predators.

      The Lionfish (Pterois miles) is the Indian Ocean relative of the Pacific’s Pterois volitans. They are often treated as a single species.

       Tube worms burrow into sediment or live coral. They retract instantly into their tubes if a shadow passes over them.

      The Red Sea Bannerfish (Heniochus intermedius) is endemic to the Red Sea. Juveniles form shoals, but adults are solitary or in pairs.

      TIDES

      Tides are primarily caused by the combined effects of the centrifugal force of the spinning earth and gravitational attraction between the moon and the earth. The sun, despite its huge size, is so far away that its effect on the tides is only about half that of the moon. The cycle of one tide, to go from high water to low water and back to high water again, usually takes roughly 12 hours (semidiurnal). In some parts of the world it may take roughly 24 hours (diurnal), depending on whether the sun or the moon is dominant. Some areas experience a mixture of both diurnal and semidiurnal tides. The normal tidal day is 24 hours and 50 minutes. Around some islands and reefs you may, effectively, get four tides per day if the flow along one side of the obstacle is longer than along the other.

      Spring tides, those of maximum range СКАЧАТЬ