Sleet

                      SLEET

   

    Sleet is made up of a translucent ball of frozen raindrops. Sleet forms when the layer of subfreezing air ( colder than the temperature at which water freezes) in the atmosphere deep enough to freeze.

     

    The difference between freezing rain and sleet is very minimal. When sleet hits the ground (or any surface), it bounces off unlike freezing rain which covers a surface with a sheet of ice. Instead sleet covers a flat surface with millions of tiny ice pellets.

    Both snow and sleet can fall at any temperature below 32 F and when the air beneath the cloud is dry. If this happens, the rain partly evaporates as it falls. Then the evaporation cools the particles enough to keep them frozen all the way to the ground. Sleet is particularly resilient against melting.

Freezing Rain

              FREEZING RAIN

   Freezing Rain forms when snow falls into a band of warmer air, the snow melts to form raindrops. If the air is below freezing, the raindrops cool along with the temperature (below freezing), but they will not freeze until they reach the ground.
   Freezing Rain coats everything in a sheet of ice, causing plants to die or be damaged and roads dangerous.
   

   During an intense freezing rain storm, trees can be painted with a thick coat of ice. The extra weight can sometimes be to much for the branches to bare, damaging the tree badly. 

   Freezing rain is the most common in the North East, the Upper Mid-West, the Columbia River Valley, and along the Mid Atlantic foothills of the Appalachians. The reason for freezing rain to here is because these are areas were cold air sinks or can be trapped at the surface. Meaning, warmer air moves above the cold arir to form the warm layer the snow passes through.

Percipitation

                                         RAIN

      Like snow and hail, rain falls when they grow  to be to heavy to carried by the cloud. From the top of the cloud the start to fall, collecting smaller water droplets on the way down until they reach the cloud base (the bottom of the cloud). Then the rain falls. Smaller rain drops, called drizzle, comes from stratus clouds.
     Smaller raindrops are shaped like a sphere. While larger raindrops make a more spheroid shape, a sphere with a dent at the bottom. The sent is caused by the wind resistance. If they grow larger they open up like a parachute before bursting into smaller raindrops.

    

   If the temperature remains above 32 degrees, precipitation particles melts into liquid drops bigger than 0.5 mm., called "rain".

Snow

                                        Snow

    Snow, like rain drops falls when they grow to heavy for their cloud. Snow forms if the cloud height is below a height of 1000 ft. high so that the ice crystals (snow) do no t melt by the time they reach the ground. 

   Wilson A. Bentley (was a farmer of Vermont, U.S.A), is known for taking the first detailed photograph of a snowflake in 1885. His book 'Snow Crystals' has become a classic and the phrase 'No two snowflakes are alike' came from him. The shape of a snowflake is established by the temperature and the humidity level of the atmosphere. The different forms snowflakes come in are shown below:

    1888 was not a good year for weather, for two famous and tragic blizzards occured in this year.

• The Children's Blizzard (or also known as the 'Schoolhouse Blizzard'). Hit the U.S planes states on January, 12, 1888. The blizzard came unexpectedly on a warm day, causing many people to go unaware of the great blizzard. Especially the children in the one room schoolhouse, giving this blizzard its name, for most of the 235 causalities were children. This storm started on January 12, and ended on January 13.
  
  
  
  
  
  
• 'The Great Blizzard Of 1888' going through March 11, and March 14, 1888. Also known as 'The Great White Hurricane' was one of the worst blizzards in recorded in the U.S.A. Hitting the East Coast from the Chesapeake Bay to Maine as well as th eAtlantic province of Canada. Snowfall was recorded to get as deep as 20-60 inches, and held winds more than 45 miles per hours fast.

 

   Even though it can never be to cold to snow, it can become less likely in below freezing temperatures. This is because cold air carries less water vapor, and heavy and dense making it less likely to expand to condense. 

Hail

                                           Hail

    Hailstorms tend to be most damaging and frequent where thunderstorms most commonly occur and where the topography (the arrangement of the natural and artificial physical features of an area) is elevated. Severe thunderstorms generate wild, gusty winds and can sometimes produce hailstones. Hailstorms are most common in mid latitudes, particularly in spring and summer.
    Hail is formed inside the cumulonimbus cloud. As you know the cumulonimbus have thermals (updrafts), raindrops can get caught in the thermals carrying them up. As they go up in the cloud again the mold with other raindrops, and because its so cold inside the cloud they freeze up together. Growing every time they go up until they become hailstones, this procces keeps happening until the hailstones become grow to be to heavy for the cumulonimbus cloud. they larger the hailstone the faster they fall.
    While most hailstone grow up to the size of peas, some can form as large as golf

balls or even grapefruits. Lobes and asymmetric shaped can occur in rare, extremely large hailstones. The largest hailstone in recorded history fell in Aura Nebraska, U.S.A, it fell on June, 22, 2003. It measured 18.75 in. in circumference.
    The strongest hailstorm in recorded history occurred on November,3,2007, this storm fell over Bogata, Columbia. The storm blanketed the city with ice. Rain followed by hail and cold temperatures buried dozens of cars in up to 59 in. of ice and freezing rain. 

Cumulonimbus cloud

         CUMULONIMBUS CLOUD (CB)

   'Cumulonimbus' (CB) is also called 'thunderstorm clouds'. The name ' Cumulonimbus' means 'Rain Heap'. There are two different types of Cumulonimbus clouds:

•  Calvus meaning 'the bald'. It is called 'The Bald' because it has a rounded fluffy top and no anvil. (Shown below)

•  Capillatus meaning 'hair'. It is called this because unlike the Calvus, the Capillatus gas an anvil. (Shown below)                                            
  
  
  
  
  

    When you see this cloud it looks like a towing almost castle like, with a fluffy cauliflower look, or else with a flat anvil top. This enormous cloud is sometimes refers to as the ' king cloud ', or ' cloud 9'.

  
  

  
  
  

  These cloud extend over the whole height o the Troposphere, there are even some occurrences when they reach up into the lower Stratosphere. The Cumulonimbus cloud can generate thunderstorms that release as much energy as an atomic bomb! Cumulonimbus develops in unstable and moist atmospheric conditions. It continues to rise because it is continually warmed by latent heat. Latent heat: is energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process that is specified in some way. An example is latent heat of fusion for a phase change, melting, at a specified temperature and pressure.

  
  

  When the cloud is over you it is almost impossible to tell whether it is a Nimbustratus or an Cumulonimbus cloud over your head. Some ways to figure if its a Cumulonimbus is if there are:

  
  

  •  Strong Winds
  • Thunder and/or lightning

  Cumulonimbus clouds can produce large quantities of rain, severe weather such as hail, heavy snow, and tornadoes. 
     An Anvil is produced in the highest area of the Troposphere where its coldest. The Anvil is made up of frozen water particles, clumped up in a thin layer of ice on top if the cumulonimbus cloud.
     Cumulonimbus clouds penetrate the atmosphere to great heights and their rapid updraft speeds ans turbulence's, are best avoided by aircraft, but it is the effects closer to the ground that are most evident to us. The downdraft associated with the fall of rain can be great, releasing a strong, cold storm outflow near the ground.
      Powerful thunderstorms often have a line of towering Cumulus Congestus clouds leading up to the main part of the storm. These clouds are called 'Flanking clouds'. They are fed by an outflow of cold air, and may eventually merge into the parent storm.
      
  

  

  
  
    'Fractus Clouds' are shreds of clouds often seen below Cumulonimbus. They are a adornment cloud, having been torn off of a larger cloud by strong winds. Customarily short-lived, and may develop and merge with other clouds, or else they dissipate.
  

  

  
  
  

    'Mammatus clouds' (also called 'breast clouds') are formed on the under side of an anvil top when strong downdrafts push bundles of warm moist air into an area of cooler air. When most people see the Mammatus cloud they think something bad is about to happen, but actually it signifies the ending of a bad storm.

   

  
      'Pileus clouds' are associated with the Cumulonimbus clouds. Pileus clouds form over the tops of the rising cumulonimbus.When rising air pushes up a cold, moist layer sufficiently fast for it to cool, and further saturate and grow ice crystals.
  

  

  
  

                   THUNDERSTORMS

      At any given time, about 2,000 Thunderstorms rage across Earth. Storms can result anywhere in the world, but most generally take place in equilateral reqions. All Thunderstorms have lightning, but other than that storm attributes vary widely. Most Thunderstorms bring brief, intense rainfall, followed by strokes of lightning. A small group of Thunderstorms can bring extreme weather. Less common features are flooding rains, heavy hail, and tornado's. 

       'Lightning' heats the air greatly, causing it to expand violently, which is a great crashing noise called 'thunder'. Lightning is a giant spark created when an enormous imbalance of positive and negative charge transpire. There in fact are four different types of lightning:

  • Intracloud Lightning, is the most common type of lightning. this is an arc between the upper and lower parts of the cloud that have opposite charges.Also called 'Cloud-to-cloud'.
    
    

  • Inter-cloud Lightning, is a less common type of lighting. This type of lightning discharges between adjacent Cumulonimbus clouds, when their areas of opposite charge are located close to each other.
    
  • Cloud-to-ground negative polarity, strikes connect to the negative at the bottom of the Thunderstorm and the positive charge attracted in the ground beneath.
    
  • Cloud- to-ground positive polarity, strikes connect to the positive charge high in the Thunderstorm and a negative charge that is attracted in the ground below.
    
    
    
  
      The power of a Thunderstorm is very strong. So powerful that the amount of energy generated in an average Thunderstorm is 10 times as much as the energy generated by The World's Largest Hydroelectric Dam, which produced 3,427 terawatt-hours in 2010. 
      The energy of the storm is released when the water vapor condenses and rain falls. most of the energy heats up in the atmosphere, but a small amount drives the strong winds that comes along with Cumulonimbus. 
      The three main ingredients for creating Thunderstorms are: 
  • moisture
  • instability
  • lift (turbulence)

     Thunderstorms are generated by convection (convection: in Meteorology and Oceanology, the up and down motion of air or water caused by temperature difference). One way to trigger convection is by heating the bottom of the atmosphere, for example the heat is managed into the air. The heated air becomes light and resilient causing the air to rise, similar to the hot air in a Hot-Air Balloon. 
      

El Nino

                                          El Nino

   El Nino is triggered when -for unknown reasons-the trade winds ( trade winds: a wind blowing steadily toward the equator from the northeast in the northern hemisphere or the southeast in the southern hemisphere, especially at sea. Two belts of trade winds encircle the earth, blowing from the tropical high-pressure belts to the low-pressure zone at the equator) weaken or reverse direction and blow from west to east. This process allows a large majority of water from Indonesia, to move eastward along the equator until i reaches the South American coast.
   The name 'El Nino' or 'Christ Child', was used by the fisher men along the coast of the equator and Peru, but the El Nino warmed their cool nutrient rich waters they depended on. This warming disrupted their marine food chain in the district causing the local economy to suffer from the loss of fish. 
   El Nino is a wide-range warming of the near-surface of the water in the equatorial Pacific Ocean between South America and the international date line. The warming happens in the connection with changes in the atmosphere over the same district, which are known as the 'southern Oscillation'. 'Southern oscillation' means opposing swings of surface atmosphere pressure between the eastern and the western tropical pacific ocean, associated with El Nino and La Nina.
   During El Nino occurrence, there are two distinct changes:
                          (1) Cold coastal waters are replaced by warm waters.
                          (2) The height of the ocean surface drops over Indonesia and rises on the eastern Pacific Ocean, forcing the thermocline ( a zone of the ocean in which the temperature decreases rapidly with depth) lower near south America and preventing upwelling. 
    Meteorologist's use satellites to measure both of these features that comes with El Nino with an active sensor called an 'Altimeter'. (Below shows what they see from the Altimeter).

     El Nino is an example of the interaction between the atmosphere and the ocean, and how these interactions can affect the climate. 
     Waters off the western coast of South America, is a typical area to experience upwelling. Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water towards the ocean surface, replacing the warmer, usually nutrient-depleted surface water. This is because the Southerly winds combined with the Subtropical high causes the water to be moved off shore, to the left of the wind. 'Subtropical': Bordering on the characteristics warm, subtropical waters, also called 'Semitropical'.
     The upwelling waters are cold and rich in nutrients. Every few years, the upwelling slows or sometimes stops in the district, turning the ocean warmer sometimes reaching 7 °F above normal. This warming occurrence usually first appears around Christmas, off the coast of South America. this can last for several months. El Nino warming have occurred systematically every 2-7 years in the past century. (The red shows El Nino, while the blue shows La Nina).

     In normal circumstances the SST's (Sea Surface Temperature) off the coast of Peru are cold because of upwelling, and waters from the Western equilateral Pacific are warm. Off South American's western coast the SST's are 14 degree's cooler that the SST's in the western Pacific. Steady trade of winds from the east, push the water toward Indonesia. This raises the the level of the ocean by about 1/2 meters higher compared to the South American coast. The water flows westward, it warms up . This is a result of hindrance of solar energy and heat exchange with the atmosphere. Over the Pacific ocean, the warm water evaporates and is followed by precipitation.  
     

                  EL NINO'S AFFECT ON GLOBAL WEATHER                                                     PATTERNS

   The western Pacific experiences below- normal precipitation, as heavy rain follows the warm water and more eastward toward South America, during El Nino.
    The shift in the large Tropical Rain Clouds alters the patterns of the Subtropical Jets Streams. Subtropical Jet Streams: a region of strong winds typically found in the upper Troposphere (see 'The Layers Of The Atmoshpere') between 20 and 40 degrees latitude. The are rising in these thunder storms moves north and strengthens the Subtropical Jet Streams over South America. (The picture below shows the connection between El Nino and thunderstorms).