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• Cloud


  A large collection of very tiny droplets of water or ice crystals that can float in the air
• Cloud formation


  1. Water vapor in the air condenses into visible water droplets or ice crystals

  2. Adiabatic cooling - air rises, expands and cools, causing water vapor to condense

  3. Frontal lifting - warm, moist air mass meets cold, dry air mass, causing warm air to rise and cool, condensing water vapor
• Clouds


  • White because light from the sun is dispersed by water droplets
  • Thicker clouds appear darker as less light makes it through

  
• Clouds are formed when water vapor in the air condenses into visible water droplets or ice crystals
• Adiabatic cooling - as air rises, it expands and cools, causing water vapor to condense into clouds
• Frontal lifting - warm, moist air mass meets cold, dry air mass, causing warm air to rise and cool, condensing water vapor into clouds
• Warmer air can hold more water vapor than colder air, so clouds are more likely to form in warm air
• Humid air already contains a lot of water vapor, so it is more likely to form clouds than dry air
• Determining cloud coverage by visual observation

  1. Choose a good observation site

  2. Divide the sky into oktas (eighths)

  3. Estimate the cloud cover in each okta

  4. Sum the cloud cover in each okta to get the total cloud cover

  
• Oktas


  Eighths of the sky, used to measure total cloud or sky cover

  
• Cloud cover by oktas

  • Clear sky (0 oktas)
  • Mostly clear (1-2 oktas)
  • Partly cloudy (3-4 oktas)
  • Mostly cloudy (5-6 oktas)
  • Overcast (7-8 oktas)

  
• Determining cloud coverage by hand

  1. Hold hand out at arm's length, palm facing up - amount of sky covered is approximately 1 okta

  2. Observe above a 14-degree angle with the horizon

  3. Make observations at the same time each day

  4. Be aware of time of day and direction of sun

  
• Visibility


  The greatest distance at which an object can be seen and identified by an unaided eye in daylight
• Visibility is reduced by the suspension of liquid or solid particles in the atmosphere

  
• Fog


  Visibility reduced to less than 1km due to water droplets suspended in the air

  
• Mist


  Visibility 1km or greater due to water droplets suspended in the air

  
• Restricted visibility due to fog, heavy rain or dust storm is one of the most dangerous conditions for navigating a ship
• Fog


  A visible aerosol consisting of tiny water droplets or ice crystals suspended in the air at or near the Earth's surface
• Causes of fog


  1. Water vapor condenses when the atmosphere cannot make the rising vapors rise higher and they become suspended in the air

  2. Fog is also a type of precipitation, being a type of stratus cloud that is precipitating inside the cloud
• Radiation fog


  Land-based fog formed by cooling of the land surface after sunset by infrared thermal radiation in calm conditions with a clear sky

  
• Advection fog


  Formed by the slow passage of relatively warm, moist, stable air over a colder wet surface, common at sea where cold and warm ocean currents meet
• Fog stays there until the atmosphere loses its ability to evaporate it due to relatively low temperatures, thus saturating it and condensing on the surface
• Causes of Fog


  01/03/2024
• Fog is also a type of precipitation being this is also a type of stratus cloud and it is precipitating inside the cloud
• As the vessel passes the fog it will wet its deck like there is a drizzle that passed
• Radiation Fog


  1. Formed by cooling of the land surface after sunset by infrared thermal radiation in calm conditions with a clear sky

  2. Most suitable conditions: clear sky, high relative humidity, very low wind speeds, and a relatively long period during which the air can cool

  
• Advection Fog


  1. Formed by the slow passage of relatively warm, moist, stable air over a colder wet surface

  2. Unlike radiation fog, may form under cloudy skies and with moderate to strong winds

  3. Once formed, may move across the landscape, pushed by low level winds

  4. Can last for several days and is most common in the U.S. on the West Coast

  
• Difference between Radiation Fog and Advection Fog

  • Radiation fog forms over the land only, while advection fog can form over the sea too
  • Advection fog needs a surface that is already cool
  • Radiation fog disappears some time after sunrise, but advection fog can resist for days
  • Radiation fog needs a high pressure area, while advection fog is favorable for light wind
• Mist


  A suspension in the air of water droplets or wet hygroscopic particles that reduces the visibility at the earth's surface to less than 10 km but not more 1 km

  
• Mist is a phenomenon caused by small droplets of water suspended in air. Physically, it is an example of a dispersion. It is most commonly seen where warm, moist air meets sudden cooling, such as in exhaled air in the winter, or when throwing water onto the hot stove of a sauna
• Haze


  A suspension in the air of extremely small dry particles that are invisible to the naked eye but numerous enough to give the sky an opalescent appearance

  
• Haze is traditionally an atmospheric phenomenon in which dust, smoke, and other dry particulates obscure the clarity of the sky. Sources for haze particles include farming (ploughing in dry weather), traffic, industry, and wildfires
• Smog


  Air pollution that reduces visibility, a mixture of smoke and fog
• Smog was common in industrial areas and remains a familiar sight in cities today. When the smog crawls down to the sea surface from nearby factories it will affect the visibility and it will mix with the moisture from the sea and will worsen the visibility as it will add to the thickness of the fog
• Frost


  A thin layer of ice on a solid surface, which forms from water vapor in an above freezing atmosphere coming in contact with a solid surface whose temperature is below freezing and resulting in a phase change from water vapor to ice as the water vapor reaches the freezing point
• When these water vapors went stagnant on the windows of the navigating bridge and a super cooled air interacts with the vapors it will obscure the view from inside the bridge. To counter this ships are installed with window heaters
• Sea Smoke


  Fog which is formed when very cold air moves over warmer water. It forms when a light wind of very cold air mixes with a shallow layer of saturated warm air immediately above the warmer water and because this type of fog requires very low air temperatures, it is uncommon in temperate climates, but is common in the Arctic and Antarctic
• Why Humidity Makes You Feel Hotter?
• What is Humidity?
• Humidity


  The amount of water vapour in the air. It is the most variable characteristic of the atmosphere and constitutes a major factor in climate and weather