Category Weather & Climate

            Satellites serve two purposes in weather forecasting. Communications satellites are used to send weather data around the world, while dedicated weather satellites monitor the movement of weather systems and the patterns of cloud cover: There are two types of weather satellite. Geostationary satellites are fixed in one position, observing a certain area from their orbit high above the Equator. Polar-orbiting satellites circle the Earth from pole to pole. The planet’s rotation means that each orbit takes in a different part of the Earth.

            In order to predict the weather accurately for the hours and days ahead weather forecasters must analyze the information they receive from number of sources – including local weather observes, weather balloons, weather stations, and satellites.

           Speaking of satellites – NASA has a train of satellites called the Afternoons Constellation, nicknamed the “A”-Train, which are orbiting the Earth and are collecting all sorts of data. This includes data that will help predict weather and climate change.

            For example NASA has the Cloudsat satellite for studding the aspect of clouds, and Caplipso for studding the climate change, and how aerosols and particles affect the Earth’s atmosphere.

            Many businesses and people rely on accurate weather conditions for different purposes – farmers need to know the best time to plant they crops; airplane takeoffs, landings, and flight paths are scheduled according to local weather conditions. Weather forecast alert people for severe storms that can be danger to personal property. Most people want to know what the weather will be like as they go to and from work, school, or plan outdoor activities.

           The atmosphere is constantly changing and even though the scientist receive weather data from variety of sources – stations, satellites, observers, and balloons – it is still impossible to predict the weather correctly 100% of the time.

            One of the ways of improving weather prediction and climate is to develop new technologies that helps scientists understand how the atmosphere works.

            One such tech is the NASA’s Cloudsat satellite. This instrument provides a vertical cloud profiling from space improving weather and climate forecast.

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            Computers are used to collect weather information and also to help meteorologists predict the weather. Special software uses the data to develop a “model” of the expected weather.

            Throughout history, numerous techniques and experiments were performed by meteorologists to predict the weather with greater efficacy over time. Due to substantial advances in technology, it is now possible to forecast the weather days and even months in advance—which was not truly possible before the mid-20th century. The use of computer models became widespread mainly throughout the 1960s, as the first weather satellites were launched. The types of computer models that are used in forecasts depend mostly on the type of climate and weather conditions.

            Climate models are primarily used to forecast substantial changes in the earth’s climate. Climate is the average weather conditions in an area for a prolonged period of time. Therefore, climate models use a combination of statistical and current data to provide a reasonable forecast. The CFS is one of the primary climate models used for forecasting planetary scale weather conditions such as: El Nino, Madden Julian Oscillations (MJO), and monsoons.

            Statistical models are primarily used to help meteorologist provide accurate analog forecasts. Statistical models use data from previous storms and weather conditions to help meteorologists get a better idea of how to track current weather systems. Statistical models are commonly used to track tropical and mid latitude cyclones. If the dynamical model consensus is not reasonable, meteorologists often use statistical models to provide better forecasts.

            Although atmospheric computer models are effective tools for weather forecasting, they are not impeccably accurate. Computer models are usually less efficient during the preliminary runs. For instance during the first stages of tropical cyclogenesis (tropical cyclone formation), computer models are usually not initialized enough to provide a reasonable forecast. Long range forecasts (beyond a week) are usually less accurate, because there are many atmospheric factors that can come into play beyond that time. Dynamic models are most accurate for three- to five-day forecasts.

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            Weather data in remote areas is collected by automated weather stations. Equipped with a wide range of instruments and computers, the stations record and transmit information via satellite every hour. Individual observers with a small number of simple instruments also play an important part in all levels of weather forecasting.

            A weather station is a facility, either on land or sea, with instruments and equipment for measuring atmospheric conditions to provide information for weather forecasts and to study the weather and climate. The measurements taken include temperature, atmospheric pressure, humidity, wind speed, wind direction, and precipitation amounts. Wind measurements are taken with as few other obstructions as possible, while temperature and humidity measurements are kept free from direct solar radiation, or insolation. Manual observations are taken at least once daily, while automated measurements are taken at least once an hour. Weather conditions out at sea are taken by ships and buoys, which measure slightly different meteorological quantities such as sea surface temperature (SST), wave height, and wave period. Drifting weather buoys outnumber their moored versions by a significant amount.

Typical weather stations have the following instruments:

• Thermometer for measuring air and sea surface temperature
• Barometer for measuring atmospheric pressure
• Hygrometer for measuring humidity
• Anemometer for measuring wind speed
• Pyranometer for measuring solar radiation
• Rain gauge for measuring liquid precipitation over a set period of time.
• Wind sock for measuring general wind speed and wind direction
• Wind vane, also called a weather vane or a weathercock: it shows whence the wind is blowing.

In addition, at certain automated airport weather stations, additional instruments may be employed, including:

• Present Weather/Precipitation Identification Sensor for identifying falling precipitation
• Disdrometer for measuring drop size distribution
• Transmissometer for measuring visibility
• Ceilometer for measuring cloud ceiling

More sophisticated stations may also measure the ultraviolet index, leaf wetness, soil moisture, soil temperature, water temperature in ponds, lakes, creeks, or rivers, and occasionally other data.

Exposure

           Except for those instruments requiring direct exposure to the elements (anemometer, rain gauge), the instruments should be sheltered in a vented box, usually a Stevenson screen, to keep direct sunlight off the thermometer and wind off the hygrometer. The instrumentation may be specialized to allow for periodic recording otherwise significant manual labour is required for record keeping. Automatic transmission of data, in a format such as METAR, is also desirable as many weather station’s data is required for weather forecasting.

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            Research Aircraft are used to obtain detailed information about the atmosphere. They carry very sophisticated radar and laser equipment that records a three-dimensional picture of clouds at various levels in the atmosphere. Some planes are dedicated to monitoring hurricanes, often flying into the centre of the storm itself. The information collected by aircraft is much more detailed than that collected by weather balloons.

            A recent example of unexpected utility is the meteorological application of transponders developed for air-traffic management. Accurate wind information for the upper atmosphere is a key requirement for weather prediction. Currently, most wind data comes from weather balloons, wind profilers, Doppler radars and satellites. Mode-S EHS, a novel source of wind data from aircraft flight levels, is helping us to make more accurate weather forecasts.

            Under European regulations, all large aircraft must carry Mode-S EHS- enhanced surveillance navigation apparatus. Aircraft equipped with EHS transponders are interrogated every four seconds by ground-based radar and, in response, send information on position, flight level, magnetic heading, air speed and ground speed. Air-traffic control monitors this data to ensure efficient and safe operations.

            Suppose a plane is heading eastwards at 200m per second. Its position is known accurately by the satellite-based global positioning system or GPS. Four seconds later, it should be 800m east of its initial position. But suppose there is a wind of 50m per second from the southeast. This will slow the plane and cause it to drift to the north.

            The GPS location shows precisely where the plane has gone in four seconds and determines the ground speed. Since ground speed (G) is the vector sum of air speed (A) and wind speed (W), a simple vector calculation gives us the wind. What a delightfully simple application of vectors; what a shame that vectors have been dropped from Leaving Cert maths.

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            Weather balloons are used to take measurements of humidity, pressure and temperature at altitudes of up to 20km (12 miles). The readings are taken by instruments called radiosondes carried beneath the balloon. These transmit the information to processing stations on the ground. Wind strength and direction is monitored by tracking the movement of the balloon.

            A weather or sounding balloon is a balloon (specifically a type of high-altitude balloon) that carries instruments aloft to send back information on atmospheric pressure, temperature, humidity and wind speed by means of a small, expendable measuring device called a radiosonde. To obtain wind data, they can be tracked by radar, radio direction finding, or navigation systems (such as the satellite-based Global Positioning System, GPS). Balloons meant to stay at a constant altitude for long periods of time are known as transosondes. Weather balloons that do not carry an instrument pack are used to determine upper-level winds and the height of cloud layers. For such balloons, a theodolite or total station is used to track the balloon’s azimuth and elevation, which are then converted to estimated wind speed and direction and/or cloud height, as applicable.

            One of the first persons to use weather balloons was Léon Teisserenc de Bort, the French meteorologist. Starting in 1896 he launched hundreds of weather balloons from his observatory in Trappes, France. These experiments led to his discovery of the tropopause and stratosphere. Transosondes, weather balloons with instrumentation meant to stay at a constant altitude for long periods of time to help diagnose radioactive debris from atomic fallout, were experimented with in 1958.

            Weather balloons are launched around the world for observations used to diagnose current conditions as well as by human forecasters and computer models for weather forecasting. About 800 locations around the globe do routine releases, twice daily, usually at 0000 UTC and 1200 UTC. Some facilities will also do occasional supplementary “special” releases when meteorologists determine there is a need for additional data between the 12-hour routine launches in which time much can change in the atmosphere. Military and civilian government meteorological agencies such as the National Weather Service in the US typically launch balloons, and by international agreements almost all the data are shared with all nations.

            Specialized uses also exist, such as for aviation interests, pollution monitoring, photography or videography and research. Examples include pilot balloons (Pibal). Field research programs often use mobile launchers from land vehicles as well as ships and aircraft (usually dropsondes in this case). In recent years weather balloons have also been used for scattering human ashes at high-altitude. The weather balloon was also used to create the fictional entity ‘Rover’ during production of the 1960s TV series The Prisoner in Portmeirion, Gwynedd, North Wales, UK in September 1966. This was retained in further scenes shot at MGM Borehamwood UK during 1966-67.

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            Meteorologists forecast the weather based on information gathered from a huge variety of sources. To get the clearest picture about the weather, both people and technology are employed around the world to continuously take weather measurements. Instruments on land, at sea, in the air and in space feed the information into a global network, where it is accessed and analyzed by the world’s weather experts.

            Meteorologists use a variety of tools to help them gather information about weather and climate. Some more familiar ones are thermometers which measure air temperature, anemometers which gauge wind speeds, and barometers which provide information on air pressure. These instruments allow meteorologists to gather data about what is happening near Earth’s surface. Collecting data from other sources—and other parts of the atmosphere—helps to create a more descriptive picture of weather.

            Meteorological phenomena are observable weather events that are explained by the science of meteorology. Meteorological phenomena are described and quantified by the variables of Earth’s atmosphere: temperature, air pressure, water vapour, mass flow, and the variations and interactions of those variables, and how they change over time. Different spatial scales are used to describe and predict weather on local, regional, and global levels.

           Meteorology, climatology, atmospheric physics, and atmospheric chemistry are sub-disciplines of the atmospheric sciences. Meteorology and hydrology compose the interdisciplinary field of hydrometeorology. The interactions between Earth’s atmosphere and its oceans are part of a coupled ocean-atmosphere system. Meteorology has application in many diverse fields such as the military, energy production, transport, agriculture, and construction.

            The ability to predict rains and floods based on annual cycles was evidently used by humans at least from the time of agricultural settlement if not earlier. Early approaches to predicting weather were based on astrology and were practiced by priests. Cuneiform inscriptions on Babylonian tablets included associations between thunder and rain. The Chaldeans differentiated the 22° and 46° halos.

            Ancient Indian Upanishads contain mentions of clouds and seasons. The Samaveda mentions sacrifices to be performed when certain phenomena were noticed. Var?hamihira’s classical work Brihatsamhita, written about 500 AD, provides evidence of weather observation.

            In 350 BC, Aristotle wrote Meteorology. Aristotle is considered the founder of meteorology. One of the most impressive achievements described in the Meteorology is the description of what is now known as the hydrologic cycle.

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