Weather


Elements of Climate


Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elements in a given region over a long period of time. Climate can be contrasted to weather, which is the present condition of these same elements and their variations over shorter time periods.


The main elements of atmosphere which are subject to change and which influence human life on earth are

  • temperature
  • pressure
  • winds
  • humidity
  • clouds
  • precipitation 


The Beaufort scale


The Beaufort Scale  is an empirical measure for describing wind speed based mainly on observed sea conditions.On land it is categorised by the physical effects it has on vegetation and structures. Its full name is the Beaufort Wind Force Scale.

The scale is named after its inventor, Admiral Francis Beaufort (1774–1857).

The initial scale of thirteen classes (zero to twelve) did not reference wind speed numbers but related qualitative wind conditions to effects on the sails of a man-of-war, then the main ship of the Royal Navy

The Beaufort scale was extended in 1946, when Forces 13 to 17 were added.

However, Forces 13 to 17 were intended to apply only to special cases, such as tropical cyclones. Nowadays, the extended scale is only used in Taiwan and mainland China, which are often affected by typhoons.

Wind speed on the 1946 Beaufort scale is based on the empirical formula:
v = 0.836 B3/2 m/s
where v is the equivalent wind speed at 10 metres above the sea surface and B is Beaufort scale number. For example, B = 9.5 is related to 24.5 m/s which is equal to the lower limit of "10 Beaufort". Using this formula the highest winds in hurricanes would be 23 in the scale.






Cloud Layers



The following is a list of cloud classifications:

  • Cumulus—Heaped or piled clouds.
  • Stratus—Formed in layers.
  • Cirrus—Ringlets; fibrous clouds; also high-level clouds above 20,000 feet.
  • Castellanus—Common base with separate vertical development; castle-like.
  • Lenticularus—Lens shaped; formed over mountains in strong winds.
  • Nimbus—Rain bearing clouds.
  • Fracto—Ragged or broken.
  • Alto—Meaning high; also middle-level clouds existing at 5,000 to 20,000 feet.

Clouds are visible indicators and are often indicative of future weather. For clouds to form, there must be adequate water vapor and condensation nuclei, as well as a method by which the air can be cooled. When the air cools and reaches its saturation point, the invisible water vapor changes into a visible state. Through the processes of deposition (also referred to as sublimation) and condensation, moisture condenses or sublimates onto miniscule particles of matter like dust, salt, and smoke known as condensation nuclei. The nuclei are important because they provide a means for the moisture to change from one state to another.

Cloud type is determined by its height, shape, and behavior. They are classified according to the height of their bases as low, middle, or high clouds, as well as clouds with vertical development.

Cumulus and cumulonimbus
The most common cloud shape. Normally it is not a harmful cloud type, but it can easily develop into cumulonimbus and result stormy weather. If you see these kind of clouds in the sky, it is the best time for gliding.

Stratus
Stratus clouds are thin, soft clouds. The thinner ones never bring any rain, but they can evolve into nimbostratuses that shower us with that so called “light rain”. Stratus clouds may appear on lower and higher levels of the athmoshphere.

Cirrus
Cirrus clouds can always be found on higher levels. They are those curtain-like soft clouds that sometimes appear to be nothing else but the gas coming out of airoplanes.  But they are clouds.

Low clouds are those that form near the Earth´s surface and extend up to 6,500 feet AGL. They are made primarily of water droplets, but can include supercooled water droplets that induce hazardous aircraft icing. Typical low clouds are stratus, stratocumulus, and nimbostratus. Fog is also classified as a type of low cloud formation. Clouds in this family create low ceilings, hamper visibility, and can change rapidly. Because of this, they influence flight planning and can make VFR flight impossible.

Middle clouds form around 6,500 feet AGL and extend up to 20,000 feet AGL. They are composed of water, ice crystals, and supercooled water droplets. Typical middle-level clouds include altostratus and altocumulus. These types of clouds may be encountered on cross-country flights at higher altitudes. 

Altostratus clouds can produce turbulence and may contain moderate icing. Altocumulus clouds, which usually form when altostratus clouds are breaking apart, also may contain light turbulence and icing.

High clouds form above 20,000 feet AGL and usually form only in stable air. They are made up of ice crystals and pose no real threat of turbulence or aircraft icing.

Typical high-level clouds are cirrus, cirrostratus, and cirrocumulus.

Clouds with extensive vertical development are cumulus clouds that build vertically into towering cumulus or cumulonimbus clouds. The bases of these clouds form in the low to middle cloud base region but can extend into high altitude cloud levels. Towering cumulus clouds indicate areas of instability in the atmosphere, and the air around and inside them is turbulent. These types of clouds often develop into cumulonimbus clouds or thunderstorms.

Cumulonimbus clouds contain large amounts of moisture and unstable air, and usually produce hazardous weather phenomena such as lightning, hail, tornadoes, gusty winds, and wind shear. These extensive vertical clouds can be obscured by other cloud formations and are not always visible from the ground or while in flight. When this happens, these clouds are said to be embedded, hence the term, embedded thunderstorms.

Cloud classification can be further broken down into specific cloud types according to the outward appearance and cloud composition. Knowing these terms can help identify visible clouds.

To pilots, the cumulonimbus cloud is perhaps the most dangerous cloud type. It appears individually or in groups and is known as either an air mass or orographic thunderstorm. Heating of the air near the Earth´s surface creates an air mass thunderstorm; the upslope motion of air in the mountainous regions causes orographic thunderstorms. Cumulonimbus clouds that form in a continuous line are nonfrontal bands of thunderstorms or squall lines.

Since rising air currents cause cumulonimbus clouds, they are extremely turbulent and pose a significant hazard to flight safety. For example, if an aircraft enters a thunderstorm, the aircraft could experience updrafts and downdrafts that exceed 3,000 feet per minute. In addition, thunderstorms can produce large hailstones, damaging lightning, tornadoes, and large quantities of water, all of which are potentially hazardous to aircraft.

A thunderstorm makes its way through three distinct stages before dissipating. It begins with the cumulus stage, in which lifting action of the air begins. If sufficient moisture and instability are present, the clouds continue to increase in vertical height.

Continuous, strong updrafts prohibit moisture from falling. The updraft region grows larger than the individual thermals feeding the storm. Within approximately 15 minutes, the thunderstorm reaches the mature stage, which is the most violent time period of the thunderstorm´s life cycle. 

At this point, drops of moisture, whether rain or ice, are too heavy for the cloud to support and begin falling in the form of rain or hail. This creates a downward motion of the air. Warm, rising air; cool, precipitation-induced descending air; and violent turbulence all exist within and near the cloud. Below the cloud, the down-rushing air increases surface winds and decreases the temperature. 

Once the vertical motion near the top of the cloud slows down, the top of the cloud spreads out and takes on an anvil-like shape. At this point, the storm enters the dissipating stage. This is when the downdrafts spread out and replace the updrafts needed to sustain the storm.



Share:

0 comments:

Post a Comment

Upsc - Civils Preparation

Exam Strategy
Tips and Tricks
Preparation and Guidance
Optional Subjects - Preparation
Optional Subjects - Guidance
Many more >>

Bank Exams Preparation

Bank, Currency, Money, RBI,
Budget, Planning, Stock Exchange
Insurance, Taxation, International Organizations
Economic Issues, Fiscal Policy, Committee or Commissions
Many more >>

Computer Knowledge

History, Generations, Terminology
Hardware, Software, Internet
Networks, Shortcut Keys
Many more >>

Interview Preparation

General Do's and Don'ts in Interview
Entry and Dressing up
How to prepare?, Qualities judged
Many more >>