Below I will attempt to explain some of the more typical weather phenomena that happen on the seas of our great planet. Sailors encounter all sorts of storms, seas and temperatures, and with a rudimentary knowledge of the science behind these things, a sailor can take measures to protect himself and ship.
Let’s focus on the big 3: Clouds, Seas, and Poseidon.
First thing’s first. The atmosphere is split into layers. To simplify things, we can look at it as a three layered air bubble surrounding the earth. Air is made up of a few different elements, but generally we can think of it as mostly CO2 and Oxygen. These elements have weight, and the combined weight of the average of all of these elements on the Earth’s surface is equal to 1 Atmospheric pressure (ATM). ATM is also commonly called barometric pressure. Because heat plays a factor in density, some air is more or less dense than other air, which then of course shifts the ATM on any given spot on the Earth’s surface. These differences in pressure on the surface of the Earth are known as high and low pressure systems. Because air acts like other particles, it tries to move from a place of high pressure (very dense – or cold) to areas of low pressures (less dense – warm). So, then we can move further and say that oceans are typically colder than continents (this is true) and then air typically moves (blows/wind) from the oceans to the land! If you look at the dynamics of a low pressure system (think tornadoes if you want to be extreme) air flows in to the middle, spins upwards and is then off set by the highest layer of our three-layered atmosphere, the jet-streams.
So the top layer is the jet-stream, a very windy place that is effected minimally by the Earth below. It is cold and air there tends to be volatile. Large cumulonimbus clouds often move with the jet-streams, avoiding any condition local on the Earth’s surface. While you are out on your boat, in peaceful conditions, and you see large thunderheads in the distant, you should know that these clouds are moving with the forces of jet-stream winds and may be heading for you. Cumulonimbus clouds are associated with thunderstorms, and they create havoc near the surface because of the contrary weather patterns happening in that part of the atmosphere. When a near-surface pressure system passes under a jet-stream system, things will go wrong and you die a horrible death on your pretty little ship.
The lowest level of the atmosphere is commonly known as the marine layer. This is a very shallow area of the atmosphere rising to just 200 meters above the Earth. Mountains mostly break through this layer. This layer is susceptible to temperature changes through heat transfer known as convection. Warm air moving over ice is cooled, and cool air moving over warm surfaces is, well, hopefully it’s obvious, warmed. If there is enough water vapor in this air, it will condense and turn into clouds – fog. This phenomenon is seen at its best on the West Coast of North America. Cool ocean waters come down in currents from the Gulf of Alaska, and rush by the Coast in large ocean trenches. Air, which is flowing in from the Pacific High is rushing in to meet the North American Low (or Central Valley Low if you want to get technical) and moves directly over the chilled currents below. During many times of the year this causes the air temp to drop below the dew point and water vapor condensates – Fog. A similar feature of air flow happens near mountains. If you’ve noticed in your sailing adventures that mountains commonly have clouds hovering at their peaks, you’ve been a good observer. This is a condition of air pressure falling quickly as it rises (like it does as it is blown up hill). The pressure difference in the air changes so drastically, water vapor is squeezed and condenses. If you’ve heard of the term “rain shadow” like you have in the deserts on the lee of most mountains – the Himalayas are the famous ones – then you can now imagine why these shadows exist. Water is actually squeezed out of the air as it rises quickly over mountains.
I digress. The motion of the ocean is not due to the moon or due to the spin of the earth. It is due to wind. Winds spin clockwise in High Pressure systems in the northern hemisphere, and likewise so do the oceans. Winds are created by difference in atmospheric pressures, which are created by differences of temperatures on the Earth’s surface. Water does not hold heat as well as rock, and therefore rock is hotter and wind moves towards land and so do ocean swells. Currents follow pressure systems, and sea swells follow winds. The faster the wind the larger the wave, to a degree. If you are in an ocean with few waves, but large winds, you are probably in the lee of a large land mass (the explorers of the 16th century knew this well). If you are in an area with pointy swells, you are in shallow waters. If there are breakers, you are about to run aground. The longer the trough, the further away the nearby weather system (storm). And, as I mentioned earlier, waves come from the direction of the wind. If large waves are breaking on shore, larger than normal, than there is a storm off the coast in that direction. Currents follow pressure systems, and generally pressure systems are stationary – with the exception of dynamic thunderstorms, trapped in the volatile jet-streams
Remember. If there are big fluffy dark clouds blowing your way, even if the seas are calm, your fucked and you should put your seatbelt on.
Thanks for reading.
