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Meteorology is the interdisciplinary scientific study of the atmosphere that focuses on weather processes and forecasting (in contrast with climatology). Studies in the field stretch back millennia, though significant progress in meteorology did not occur until the eighteenth century. The nineteenth century saw breakthroughs occur after observing networks developed across several countries. Breakthroughs in weather forecasting were achieved in the latter half of the twentieth century, after the development of the computer.
Meteorological phenomena are observable weather events which illuminate and are explained by the science of meteorology. Those events are bound by the variables that exist in Earth's atmosphere: They are temperature, air pressure, water vapor, and the gradients and interactions of each variable, and how they change in time. The majority of Earth's observed weather is located in the troposphere. Different spatial scales are studied to determine how systems on local, region, and global levels impact weather and climatology. Meteorology, climatology, atmospheric physics, and atmospheric chemistry are sub-disciplines of the atmospheric sciences. Meteorology and hydrology compose the interdisciplinary field of hydrometeorology. Interactions between Earth's atmosphere and the oceans are part of coupled ocean-atmosphere studies. Meteorology has application in many diverse fields such as the military, energy production, transport, agriculture and construction.
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. The Greek scientist Theophrastus compiled a book on weather forecasting, called the Book of Signs. The work of Theophrastus remained a dominant influence in the study of weather and in weather forecasting for nearly 2,000 years. In 25 AD, Pomponius Mela, a geographer for the Roman Empire, formalized the climatic zone system. Around the 9th century, Al-Kindi (Alkindus), an Arab naturalist, wrote a treatise on meteorology entitled Risala fi l-Illa al-Failali l-Madd wa l-Fazr (Treatise on the Efficient Cause of the Flow and Ebb), in which he presents an argument on tides which "depends on the changes which take place in bodies owing to the rise and fall of temperature." Also in the 9th century, Al-Dinawari, a Kurdish naturalist, writes the Kitab al-Nabat (Book of Plants), in which he deals with the application of meteorology to agriculture during the Muslim Agricultural Revolution. He describes the meteorological character of the sky, the planets and constellations, the sun and moon, the lunar phases indicating seasons and rain, the anwa (heavenly bodies of rain), and atmospheric phenomena such as winds, thunder, lightning, snow, floods, valleys, rivers, lakes, wells and other sources of water.
In 1021, Ibn al-Haytham (Alhazen) wrote on the atmospheric refraction of light. He showed that the twilight is due to atmospheric refraction and only begins when the Sun is 19 degrees below the horizon, and uses a complex geometric demonstration to measure the height of the Earth's atmosphere as 52,000 passuum (49 miles (79 km)), which is very close to the modern measurement of 50 miles (80 km). He also realized that the atmosphere also reflects light, from his observations of the sky brightening even before the Sun rises. In 1121, Al-Khazini, a Muslim scientist of Byzantine Greek descent, publishes the The Book of the Balance of Wisdom, the first study on the hydrostatic balance. In the late 13th century and early 14th century, Qutb al-Din al-Shirazi and his student Kamāl al-Dīn al-Fārisī continued the work of Ibn al-Haytham, and they were the first to give the correct explanations for the rainbow phenomenon. In 1716, Edmund Halley suggests that aurorae are caused by "magnetic effluvia" moving along the Earth's magnetic field lines.
In 1441, King Sejongs son, Prince Munjong, invented the first standardized rain gauge. These were sent throughout the Joseon Dynasty of Korea as an official tool to assess land taxes based upon a farmer's potential harvest. In 1450, Leone Battista Alberti developed a swinging-plate anemometer, and is known as the first anemometer. In 1607, Galileo Galilei constructs a thermoscope. In 1611, Johannes Kepler writes the first scientific treatise on snow crystals: "Strena Seu de Nive Sexangula (A New Year's Gift of Hexagonal Snow)". In 1643, Evangelista Torricelli invents the mercury barometer. In 1662, Sir Christopher Wren invented the mechanical, self-emptying, tipping bucket rain gauge. In 1714, Gabriel Fahrenheit creates a reliable scale for measuring temperature with a mercury-type thermometer. In 1742, Anders Celsius, a Swedish astronomer, proposed the 'centigrade' temperature scale, the predecessor of the current Celsius scale. In 1783, the first hair hygrometer is demonstrated by Horace-Bénédict de Saussure. In 1802-1803, Luke Howard writes On the Modification of Clouds in which he assigns cloud types Latin names. In 1806, Francis Beaufort introduced his system for classifying wind speeds. Near the end of the 19th century the first cloud atlases were published, including the International Cloud Atlas, which has remained in print ever since. The April 1960 launch of the first successful weather satellite, TIROS-1, marked the beginning of the age where weather information became available globally.
In 1648, Blaise Pascal rediscovers that atmospheric pressure decreases with height, and deduces that there is a vacuum above the atmosphere. In 1738, Daniel Bernoulli publishes Hydrodynamics, initiating the kinetic theory of gases and established the basic laws for the theory of gases. In 1761, Joseph Black discovers that ice absorbs heat without changing its temperature when melting. In 1772, Black's student Daniel Rutherford discovers nitrogen, which he calls phlogisticated air, and together they developed the phlogiston theory. In 1777, Antoine Lavoisier discovers oxygen and develops an explanation for combustion. In 1783, in Lavoisier's book Reflexions sur le phlogistique, he deprecates the phlogiston theory and proposes a caloric theory. In 1804, Sir John Leslie observes that a matte black surface radiates heat more effectively than a polished surface, suggesting the importance of black body radiation. In 1808, John Dalton defends caloric theory in A New System of Chemistry and describes how it combines with matter, especially gases; he proposes that the heat capacity of gases varies inversely with atomic weight. In 1824, Sadi Carnot analyzes the efficiency of steam engines using caloric theory; he develops the notion of a reversible process and, in postulating that no such thing exists in nature, lays the foundation for the second law of thermodynamics.
In 1494, Christopher Columbus experiences a tropical cyclone, leads to the first written European account of a hurricane. In 1686, Edmund Halley presents a systematic study of the trade winds and monsoons and identifies solar heating as the cause of atmospheric motions. In 1735, an ideal explanation of global circulation through study of the Trade winds was written by George Hadley. In 1743, when Benjamin Franklin is prevented from seeing a lunar eclipse by a hurricane, he decides that cyclones move in a contrary manner to the winds at their periphery. Understanding the kinematics of how exactly the rotation of the Earth affects airflow was partial at first. Gaspard-Gustave Coriolis published a paper in 1835 on the energy yield of machines with rotating parts, such as waterwheels. In 1856, William Ferrel proposed the existence of a circulation cell in the mid-latitudes with air being deflected by the Coriolis force to create the prevailing westerly winds. Late in the 19th century the full extent of the large scale interaction of pressure gradient force and deflecting force that in the end causes air masses to move along isobars was understood. By 1912, this deflecting force was named the Coriolis effect. Just after World War II, a group of meteorologists in Norway led by Vilhelm Bjerknes developed the Norwegian cyclone model that explains the generation, intensification and ultimate decay (the life cycle) of mid-latitude cyclones, introducing the idea of fronts, that is, sharply defined boundaries between air masses. The group included Carl-Gustaf Rossby (who was the first to explain the large scale atmospheric flow in terms of fluid dynamics), Tor Bergeron (who first determined the mechanism by which rain forms) and Jacob Bjerknes.
In 1654, Ferdinando II de Medici establishes the first weather observing network, that consisted of meteorological stations in Florence, Cutigliano, Vallombrosa, Bologna, Parma, Milan, Innsbruck, Osnabruck, Paris and Warsaw. Collected data was centrally sent to Florence at regular time intervals. In 1832, an electromagnetic telegraph was created by Baron Schilling. The arrival of the electrical telegraph in 1837 afforded, for the first time, a practical method for quickly gathering surface weather observations from a wide area. This data could be used to produce maps of the state of the atmosphere for a region near the Earth's surface and to study how these states evolved through time. To make frequent weather forecasts based on these data required a reliable network of observations, but it was not until 1849 that the Smithsonian Institution began to establish an observation network across the United States under the leadership of Joseph Henry. Similar observation networks were established in Europe at this time. In 1854, the United Kingdom government appointed Robert FitzRoy to the new office of Meteorological Statist to the Board of Trade with the role of gathering weather observations at sea. FitzRoy's office became the United Kingdom Meteorological Office in 1854, the first national meteorological service in the world. The first daily weather forecasts made by FitzRoy's Office were published in The Times newspaper in 1860. The following year a system was introduced of hoisting storm warning cones at principal ports when a gale was expected.
Over the next 50 years many countries established national meteorological services. The India Meteorological Department (1875) was established following tropical cyclone and monsoon related famines in the previous decades. The Finnish Meteorological Central Office (1881) was formed from part of Magnetic Observatory of Helsinki University. Japan's Tokyo Meteorological Observatory, the forerunner of the Japan Meteorological Agency, began constructing surface weather maps in 1883. The United States Weather Bureau (1890) was established under the United States Department of Agriculture. The Australian Bureau of Meteorology (1906) was established by a Meteorology Act to unify existing state meteorological services.
In 1904, Norwegian scientist Vilhelm Bjerknes first argued in his paper Weather Forecasting as a Problem in Mechanics and Physics that it should be possible to forecast weather from calculations based upon natural laws.
It was not until later in the 20th century that advances in the understanding of atmospheric physics led to the foundation of modern numerical weather prediction. In 1922, Lewis Fry Richardson published "Weather Prediction By Numerical Process," after finding notes and derivations he worked on as an ambulance driver in World War I. He described therein how small terms in the prognostic fluid dynamics equations governing atmospheric flow could be neglected, and a finite differencing scheme in time and space could be devised, to allow numerical prediction solutions to be found. Richardson envisioned a large auditorium of thousands of people performing the calculations and passing them to others. However, the sheer number of calculations required was too large to be completed without the use of computers, and the size of the grid and time steps led to unrealistic results in deepening systems. It was later found, through numerical analysis, that this was due to numerical instability.
Starting in the 1950s, numerical forecasts with computers became feasible. The first weather forecasts derived this way used barotropic (that means, single-vertical-level) models, and could successfully predict the large-scale movement of midlatitude Rossby waves, that is, the pattern of atmospheric lows and highs.
In the 1960s, the chaotic nature of the atmosphere was first observed and understood by Edward Lorenz, founding the field of chaos theory. These advances have led to the current use of ensemble forecasting in most major forecasting centers, to take into account uncertainty arising from the chaotic nature of the atmosphere. In recent years, climate models have been developed that feature a resolution comparable to older weather prediction models. These climate models are used to investigate long-term climate shifts, such as what effects might be caused by human emission of greenhouse gases.
Meteorologists are scientists who study meteorology. Meteorologists work in government agencies, private consulting and research services, industrial enterprises, utilities, radio and television stations, and in education. In the United States, meteorologists held about 8,800 jobs in 2006.
Meteorologists are best-known for forecasting the weather. Many radio and television weather forecasters are professional meteorologists, while others are merely reporters with no formal meteorological training. The American Meteorological Society and National Weather Association issue "Seals of Approval" to weather broadcasters who meet certain requirements.
Each science has its own unique sets of laboratory equipment. In the atmosphere, there are many things or qualities of the atmosphere that can be measured. Rain, which can be observed, or seen anywhere and anytime was one of the first ones to be measured historically. Also, two other accurately measured qualities are wind and humidity. Neither of these can be seen but can be felt. The devices to measure these three sprang up in the mid-15th century and were respectively the rain gauge, the anemometer, and the hygrometer.
Sets of surface measurements are important data to meteorologists. They give a snapshot of a variety of weather conditions at one single location and are usually at a weather station, a ship or a weather buoy. The measurements taken at a weather station can include any number of atmospheric observables. Usually, temperature, pressure, wind measurements, and humidity are the variables that are measured by a thermometer, barometer, anemometer, and hygrometer, respectively. Upper air data are of crucial importance for weather forecasting. The most widely used technique is launches of radiosondes. Supplementing the radiosondes a network of aircraft collection is organized by the World Meteorological Organization.
Remote sensing, as used in meteorology, is the concept of collecting data from remote weather events and subsequently producing weather information. The common types of remote sensing are Radar, Lidar, and satellites (or photogrammetry). Each collects data about the atmosphere from a remote location and, usually, stores the data where the instrument is located. RADAR and LIDAR are not passive because both use EM radiation to illuminate a specific portion of the atmosphere. Weather satellites along with more general-purpose Earth-observing satellites circling the earth at various altitudes have become an indispensable tool for studying a wide range of phenomena from forest fires to El Niño.
In the study of the atmosphere, meteorology can be divided into distinct areas of emphasis depending on the temporal scope and spatial scope of interest. At one extreme of this scale is climatology. In the timescales of hours to days, meteorology separates into micro-, meso-, and synoptic scale meteorology. Respectively, the geospatial size of each of these three scales relates directly with the appropriate timescale.
Other subclassifications are available based on the need by or by the unique, local or broad effects that are studied within that sub-class.
Microscale meteorology is the study of atmospheric phenomena of about 1 km or less. Individual thunderstorms, clouds, and local turbulence caused by buildings and other obstacles, such as individual hills fall within this category.
Mesoscale meteorology is the study of atmospheric phenomena that has horizontal scales ranging from microscale limits to synoptic scale limits and a vertical scale that starts at the Earth's surface and includes the atmospheric boundary layer, troposphere, tropopause, and the lower section of the stratosphere. Mesoscale timescales last from less than a day to the lifetime of the event, which in some cases can be weeks. The events typically of interest are thunderstorms, squall lines, fronts, precipitation bands in tropical and extratropical cyclones, and topographically generated weather systems such as mountain waves and sea and land breezes.
Synoptic scale meteorology is generally large area dynamics referred to in horizontal coordinates and with respect to time. The phenomena typically described by synoptic meteorology include events like extratropical cyclones, baroclinic troughs and ridges, frontal zones, and to some extent jet streams. All of these are typically given on weather maps for a specific time. The minimum horizontal scale of synoptic phenomena are limited to the spacing between surface observation stations.
Global scale meteorology is study of weather patterns related to the transport of heat from the tropics to the poles. Also, very large scale oscillations are of importance. Those oscillations have time periods typically longer than a full annual seasonal cycle, such as ENSO, PDO, MJO, etc. Global scale pushes the thresholds of the perception of meteorology into climatology. The traditional definition of climate is pushed in to larger timescales with the further understanding of how the global oscillations cause both climate and weather disturbances in the synoptic and mesoscale timescales.
Numerical Weather Prediction is a main focus in understanding air-sea interaction, tropical meteorology, atmospheric predictability, and tropospheric/stratospheric processes.. Currently (2007) Naval Research Laboratory in Monterey produces the atmospheric model called NOGAPS, a global scale atmospheric model, this model is run operationally at Fleet Numerical Meteorology and Oceanography Center. There are several other global atmospheric models.
Boundary layer meteorology is the study of processes in the air layer directly above Earth's surface, known as the atmospheric boundary layer (ABL). The effects of the surface – heating, cooling, and friction – cause turbulent mixing within the air layer. Significant fluxes of heat, matter, or momentum on time scales of less than a day are advected by turbulent motions. Boundary layer meteorology includes the study of all types of surface-atmosphere boundary, including ocean, lake, urban land and non-urban land.
Dynamic meteorology generally focuses on the fluid dynamics of the atmosphere. The idea of air parcel is used to define the smallest element of the atmosphere, while ignoring the discrete molecular and chemical nature of the atmosphere. An air parcel is defined as a point in the fluid continuum of the atmosphere. The fundamental laws of fluid dynamics, thermodynamics, and motion are used to study the atmosphere. The physical quantities that characterize the state of the atmosphere are temperature, density, pressure, etc. These variables have unique values in the continuum.
Weather forecasting is the application of science and technology to predict the state of the atmosphere for a future time and a given location. Human beings have attempted to predict the weather informally for millennia, and formally since at least the nineteenth century. Weather forecasts are made by collecting quantitative data about the current state of the atmosphere and using scientific understanding of atmospheric processes to project how the atmosphere will evolve.
Once an all human endeavor based mainly upon changes in barometric pressure, current weather conditions, and sky condition, forecast models are now used to determine future conditions. Human input is still required to pick the best possible forecast model to base the forecast upon, which involves pattern recognition skills, teleconnections, knowledge of model performance, and knowledge of model biases. The chaotic nature of the atmosphere, the massive computational power required to solve the equations that describe the atmosphere, error involved in measuring the initial conditions, and an incomplete understanding of atmospheric processes mean that forecasts become less accurate as the difference in current time and the time for which the forecast is being made (the range of the forecast) increases. The use of ensembles and model consensus help narrow the error and pick the most likely outcome.
There are a variety of end users to weather forecasts. Weather warnings are important forecasts because they are used to protect life and property. Forecasts based on temperature and precipitation are important to agriculture, and therefore to commodity traders within stock markets. Temperature forecasts are used by utility companies to estimate demand over coming days. On an everyday basis, people use weather forecasts to determine what to wear on a given day. Since outdoor activities are severely curtailed by heavy rain, snow and the wind chill, forecasts can be used to plan activities around these events, and to plan ahead and survive them.
Aviation meteorology deals with the impact of weather on air traffic management. It is important for air crews to understand the implications of weather on their flight plan as well as their aircraft, as noted by the Aeronautical Information Manual:
The effects of ice on aircraft are cumulative-thrust is reduced, drag increases, lift lessens, and weight increases. The results are an increase in stall speed and a deterioration of aircraft performance. In extreme cases, 2 to 3 inches of ice can form on the leading edge of the airfoil in less than 5 minutes. It takes but 1/2 inch of ice to reduce the lifting power of some aircraft by 50 percent and increases the frictional drag by an equal percentage.
Meteorologists, soil scientists, agricultural hydrologists, and agronomists are persons concerned with studying the effects of weather and climate on plant distribution, crop yield, water-use efficiency, phenology of plant and animal development, and the energy balance of managed and natural ecosystems. Conversely, they are interested in the role of vegetation on climate and weather.
Hydrometeorology is the branch of meteorology that deals with the hydrologic cycle, the water budget, and the rainfall statistics of storms. A hydrometeorologist prepares and issues forecasts of accumulating (quantitative) precipitation, heavy rain, heavy snow, and highlights areas with the potential for flash flooding. Typically the range of knowledge that is required overlaps with climatology, mesoscale and synoptic meteorology, and other geosciences.
Maritime meteorology deals with air and wave forecasts for ships operating at sea. Organizations such as the Ocean Prediction Center, Honolulu National Weather Service forecast office, United Kingdom Met Office, and JMA prepare high seas forecasts for the world's oceans.
Please see weather forecasting for weather forecast sites.
|Links to other keywords in meteorology||
Atmospheric conditions: Absolute stable air | Temperature inversion | Dine's compensation | precipitation | Cyclone | anticyclone | Thermal | Tropical cyclone (hurricane or typhoon) | Vertical draft | Extratropical cyclone
Climatic or Atmospheric Patterns: Alberta clipper | El Niño | Derecho | Gulf Stream | La Niña | Jet stream | North Atlantic Oscillation | Madden-Julian oscillation | Pacific decadal oscillation | Pineapple Express | Sirocco | Siberian Express | Walker circulation
State the composition of the Atmosphere.
Explain the presence and importance of water vapour in the atmosphere.
Explain the relationship between water vapour content and atmospheric temperature.
Describe the effect of:
(a) latitude and altitude on water vapour presence;
(b) changes to the state of water on the weather.
Explain the manner in which water vapour is added to, and subtracted from the atmosphere.
(a) the process of formation, and characteristics of carbon dioxide;
(b) how oceans and plant life add and subtract carbon dioxide to and from the atmosphere.
Explain: (a) how and where atmospheric ozone is generally formed and where it most commonly accumulates;
(b) the effect of the ozone layer on solar radiation.
Describe the importance and effects of salt, dust and other solid particles in the atmosphere.
Interpret a graph of temperature versus altitude from the earth’s surface to the stratopause, and explain why the shape of the curve is different in the troposphere compared to the stratosphere.
Describe the following features of the troposphere:
(a) approximate vertical extent at low, middle and high latitudes;
(b) average temperature lapse rate;
(c) pressure lapse rate;
(d) molecular mass compared to the total in the atmosphere;
(e) weather and turbulence.
Explain how the temperature/pressure lapse rates generally determine the temperature and altitude of the tropopause.
Describe the relationship between tropopause height and tropopause temperature at various latitudes.
Explain why different angles of insolation produce differences in air density, and variations in tropopause height.
Explain the processes of:
(a) insolation and warming of the atmosphere;
(b) absence of insulation and cooling of the atmosphere.
Describe the following features of the stratosphere:
(a) vertical extent;
(b) predominant means of heating;
Explain why the stratosphere is generally devoid of cloud and weather.
Define ‘atmospheric pressure’.
(a) the unit of pressure;
(b) the unit of pressure commonly use in meteorology.
Describe the principles of operation:
(a) of the mercury barometer;
(b) of the aneroid barometer.
Define ‘pressure lapse rate’.
Explain the relationship between air temperature and pressure lapse rate.
State the average pressure lapse rate in the lower troposphere and explain how this rate changes at higher altitudes.
Define ‘wind velocity’.
State the basic rules that apply to isobars, and explain their use.
(a) anticyclone (or ‘high’);
(b) depression (or ‘low’);
(c) ridge of high pressure;
(d) trough of low pressure;
With respect to pressure systems, describe:
(a) high and low level convergence;
(b) high and low level divergence.
Explain how subsidence and ascent of air influence the type of weather commonly associated with pressure systems.
Describe the circulation and speed of the wind commonly associated with:
(a) anticyclones and ridges of high pressure;
(b) depressions and troughs of low pressure;
Identify the general direction of movement of pressure systems in the mid latitudes of both hemispheres.
Define 'diurnal' and 'semi-diurnal' variations, and
(a) describe the semi-diurnal variation of pressure;
(b) state the latitudes where the semi-diurnal variation of pressure has significance;
(c) explain the phenomena often associated with a departure from the semi- diurnal variation of pressure in those latitudes.
Define ‘pressure gradient’.
(a) causes of pressure gradient;
(b) relationship between isobars and pressure gradient.
Describe the meaning and consequences of ‘steep’ and shallow’ pressure gradients.
List the assumed conditions on which the International Standard Atmosphere (ISA) is based.
Explain the need for, and application of, the ISA for aviation.
Determine the temperature and pressure lapse rates in the ISA.
Given an ISA related temperature at an altitude, convert this to °C ambient, and given an ambient temperature °C at an altitude, convert this to ISA temperature.
Explain why an altimeter requires a subscale adjustment.
Define and apply:
Determine altimeter indications, and/or altitude of aircraft, when subscale settings are incorrect.
Identify the effect of changes in temperature on volume, density, state of matter, and gasses.
State the units of measurement of temperature.
State the usual height at which the surface air temperature is measured.
Define ‘radiation’ (as this applies to meteorology).
Explain the effect of emitting or receiving radiation on the temperature of a body or gas.
Explain the relationship between the temperature of an emitting substance and the:
(a) associated electromagnetic energy wavelength/frequency;
(b) type of radiation (spectrum).
Describe the characteristics of solar radiation.
State the atmospheric constituents that absorb, reflect or scatter all, or part of, solar radiation.
(a) sky radiation;
(b) global solar radiation.
List and explain the three main factors that influence the amount of solar energy received by the earth.
Describe the characteristics of terrestrial radiation.
Explain the relationship between solar radiation, terrestrial radiation and warming/cooling of the atmosphere.
List the substances that absorb terrestrial radiation, and explain the consequence of this absorption on global air temperature.
Define ‘atmospheric window’.
Define ‘energy budget’.
Describe the process of conduction.
Describe the process of convection.
Define ‘sensible heat’.
Define ‘latent heat’.
Describe ‘diurnal variation of surface air temperature’.
Explain the effects of the following factors on the diurnal variation of surface air temperature:
(a) type of surface;
(b) oceans and other large water areas;
(c) water vapour;
(e) the wind.
Define ‘specific heat’.
Interpret the curves of the diurnal variation of surface air temperature over a 24 hour period which reflects the factors listed in 20.6.44.
Describe the basic principles and methods through which heat transfer takes place globally.
Describe the main characteristics of the following climates:
(h) adiabatic process;
(i) super saturation.
Describe and explain the condensation process and the main methods through which condensation occurs.
Describe the function of condensation nuclei in the condensation process.
Describe the deposition process.
Describe the evaporation process.
Explain what is meant by ‘partial pressure’ of a gas.
Explain what is meant by ‘saturation vapour pressure of moist air’.
Describe the effect of ice surfaces, and high atmospheric temperatures, on the saturation vapour pressure of moist air.
Explain the function of latent heat in the condensation and evaporation processes.
Describe how temperature, water content of air, the wind, and atmospheric pressure influence the rate of evaporation.
State six processes through which water can alter its state and explain whether
Explain the relationship between density of water, temperature and volume.
Explain what is meant by the terms:
(a) absolute humidity;
(b) humidity mixing ratio;
(c) saturation content;
(d) relative humidity.
Describe the relationship between absolute humidity, air temperature, and relative humidity.
Describe the diurnal variation of relative humidity.
Define ‘dew point’.
Explain how water content and altitude influence the value of the dew point.
Describe the relationship between absolute humidity, air temperature, relative humidity and dew point.
Explain the method of operation of the:
(a) wet bulb/dry bulb hygrometer;
(b) hair hygrometer;
(c) lithium chloride element.
Describe the effect of moisture content on the density of air.
State the four forces that have a fundamental influence on the wind velocity.
Explain the principle of Coriolis force on moving air.
(a) variation of the magnitude of Coriolis force with latitude;
(b) direction of Coriolis force relative to the flow of air.
Explain the effect of Coriolis force and pressure gradient on the movement of air relative to the isobars.
Describe the inter-relation between pressure gradient, Coriolis force and centrifugal (cyclostrophic) force on the curvature of the isobars around high and low pressure systems in the Southern Hemisphere.
(a) gradient wind;
(b) geostrophic wind.
Explain how stability, wind strength and surface roughness affect the friction layer near the earth's surface.
Describe the vertical variation of wind speed and direction in the friction layer.
Describe the diurnal variation of the surface wind in the Southern Hemisphere.
(a) backing of the wind;
(b) veering of the wind.
Describe the change in wind velocity when climbing out of, or descending into, the friction layer.
With regard to the rotating cup anemometer:
(a) describe the principle of operation;
(b) state the function it performs;
(c) state the usual height at which the surface wind is measured.
State the approximate wind strength indicated by a 25-knot windsock when at 30°, 45°, 75°, and 90 degrees from the vertical.
Describe how an approximate wind direction can be determined from:
(a) ripples on water;
(b) wind lanes on water;
(c) wind shadow.
State Buys Ballot’s law.
Describe the application of Buys Ballot’s law on determining areas of high and low pressure, and on establishing possible errors in altimeter reading.
Define ‘wind shear’.
Describe the effect of vertical and horizontal wind shear on aircraft operations.
Explain how the adiabatic process affects the temperature of rising and descending parcels of air.
Define: (a) stable air;
(b) unstable air;
(c) neutrally stable/unstable air.
Describe the weather characteristics of:
(a) stable air;
(b) unstable air.
Describe how stable and unstable air affect flying conditions.
State the two main factors that determine whether air will be stable or unstable.
Describe what is meant by ‘environment lapse rate (ELR)’.
(a) describe steep and shallow ELRs;
(b) define and describe ‘inversion’ and ‘isothermal layer’.
Define ‘adiabatic process’.
Define ‘dry adiabatic lapse rate’ (DALR).
State the value of the average DALR.
Interpret graphs comparing the DALR against altitude and temperature, and identify the temperature changes in rising and descending parcels of unsaturated air.
Comparing ELR against DALR, explain how the stability or instability of rising and descending 'dry' air can be determined.
Define ‘saturated adiabatic lapse rate’ (SALR).
State the value of the average SALR.
Explain why the SALR steepens with altitude.
Comparing ELR against SALR, explain how the stability or instability of rising and descending saturated air can be determined.
Explain what is meant by:
(a) ‘absolute stability’;
(b) ‘absolute instability’;
(c) ‘conditional stability (or instability)’.
Explain what is meant by ‘super adiabatic lapse rate’.
Define ‘rising condensation level’.
Given environment temperatures, dew points and mountain crest elevation:
(a) calculate the lifting condensation level or dew point;
(b) determine the stability of air;
(c) determine the type of cloud, if formed;
(d) determine the cloud top, if possible.
Define ‘convective condensation level’.
Given an ELR and dew point:
(a) determine the convective condensation level;
(b) calculate the required surface temperature to produce cumuliform cloud;
(c) determine, if possible, cloud top height.
NOTE: The given factors and the required answers in 20.12.40 and 20.12.44 may be interchanged to present similar problem solving exercises.
Describe: (a) convective stability; (b) diurnal variation of stability. 20.14 Local winds 20.14.2 Describe the sea breeze process, and describe typical: (a) timing of the occurrence; (b) average strength of the wind; (c) horizontal and vertical extent; (d) associated cloud development; (e) associated precipitation; (f) effect on air temperature over the land; (g) effect on the pressure gradient; (h) associated wind shear problems; (i) associated turbulence. 20.14.4 Describe the pseudo sea breeze. 20.14.6 Describe the land breeze process. Page 59 Advisory Circular AC 61-1.5 Revision 13 15 December 2006 CAA of NZ 58 Sub Topic Syllabus Item 20.14.8 With regard to the land breeze process, explain the: (a) timing of the occurrence; (b) average strength of the wind; (c) most likely season for the occurrence. 20.14.10 Describe the katabatic and anabatic wind processes. 20.14.12 With regard to katabatic and anabatic winds, explain the: (a) timing of each occurrence; (b) effect of the force of gravity; (c) strength of the winds; (d) effect of adiabatic warming and cooling; (e) effect of moist valley air on cloud/fog formation. 20.14.14 Define: (a) gusts (or gustiness); (b) squalls. 20.14.16 Describe the fohn wind process. 20.14.18 With regard to the fohn wind, given environment temperatures, dew points and mountain crest elevations: (a) determine the cloud base on the windward side; (b) determine the cloud base on the lee side; (c) determine the temperature at a stated lee side datum. NOTE: The given factors and the required answers in 20.14.18 may be interchanged to present similar problem solving. 20.14.20 Describe the flight conditions associated with the fohn wind. 20.14.22 Describe the mountain wave (standing or lee wave) process. 20.14.24 Explain the factors that affect wavelength of mountain waves. 20.14.26 Explain the factors that affect amplitude of mountain waves. 20.14.28 Describe: (a) the action of rotor zones with mountain waves; (b) the cloud formations often associated with mountain waves; Page 60 Advisory Circular AC 61-1.5 Revision 13 15 December 2006 CAA of NZ 59 Sub Topic Syllabus Item (c) the flight conditions associated with mountain waves. 20.14.30 Explain the rotor streaming process. 20.14.32 Describe the flight conditions associated with rotor streaming. 20.16 Inversions 20.16.2 Define ‘inversion’. 20.16.4 Explain the effect of inversions on: (a) formation and development of cloud; (b) visibility; (c) turbulence; (d) relative humidity and dew point; (e) stability of air. 20.16.6 Describe flight conditions in the presence of inversions. 20.16.8 Explain the factors involved with a: (a) radiation inversion; (b) turbulence inversion; (c) subsidence inversion; (d) frontal inversion. 20.18 Cloud 20.18.2 Describe the basic cloud formation process. 20.18.4 Describe: (a) the main causes which can produce rising air, and formation of cloud; (b) the relationship between stability of air and cloud type. 20.18.6 List two processes that can provide/enhance buoyancy of air. 20.18.8 List the factors that determine the rate at which falling waterdrops evaporate below cloud, and describe the variants of each factor. 20.18.10 Describe the relationship between air temperature, relative humidity, dew point, water content of cloud, and cloud base. 20.18.12 List the vertical dimensions of the three main cloud layers: Page 61 Advisory Circular AC 61-1.5 Revision 13 15 December 2006 CAA of NZ 60 Sub Topic Syllabus Item (a) in mid latitudes; (b) in tropical latitudes. 20.18.14 Name, and describe the appearance and characteristics of: (a) high cloud; (b) middle cloud; (c) low cloud. 20.18.16 Describe conditions to be expected with each type of cloud with respect to: (a) turbulence; (b) icing; (c) precipitation. 20.18.18 Explain the formation and development of artificial cloud. 20.18.20 Explain what is meant by ‘okta’. 20.18.22 In terms of cloud amount, explain the meaning of: (a) SKC; (b) FEW; (c) SCT; (d) BKN; (e) OVC; (f) fracto. 20.18.24 Describe how cloud and cloud base are reported. 20.18.26 Describe the principle of operation, and operational effectiveness of the: (a) cloud searchlight; (b) laser ceilometer. 20.18.28 Explain the main processes that contribute to cloud dispersal. 20.20 Precipitation 20.20.2 Describe the basic principles of water drop growth through: (a) the Bergeron process; (b) coalescence (or fusion). Page 62 Advisory Circular AC 61-1.5 Revision 13 15 December 2006 CAA of NZ 61 Sub Topic Syllabus Item 20.20.4 Identify the factors that affect the rate of fall of water drops. 20.20.6 Describe the following types of precipitation: (a) rain; (b) drizzle; (c) snow; (d) sleet; (e) hail. 20.20.8 Describe the character of precipitation: (a) continuous; (b) intermittent; (c) showers. 20.20.10 Describe the rate of precipitation: (a) light; (b) moderate; (c) heavy. 20.22 Visibility 20.22.2 Define (meteorological) ‘visibility’. 20.22.4 Explain what is meant by ‘transparency of air’. 20.22.6 Explain whether illumination from the sun or moon have an effect on visibility. 20.22.8 Describe the effects of the following on visibility distance: (a) precipitation; (b) fog or mist; (c) haze; (d) smoke; (e) sea spray. 20.22.10 Describe the following factors affecting visibility range: (a) colour background; (b) white-out; Page 63 Advisory Circular AC 61-1.5 Revision 13 15 December 2006 CAA of NZ 62 Sub Topic Syllabus Item (c) sunlight and moonlight. 20.22.12 Explain the factors involved in ‘slant range’. 20.22.14 Define ‘Runway Visual Range (RVR). 20.22.16 Explain the effect of altitude on visibility. 20.22.18 Describe the principle of operation of the Handar visibility sensor. 20.24 Fog 20.24.2 Define ‘fog’. 20.24.4 Describe the principle of formation, required meteorological conditions, factors affecting extent of, timing, and dispersal of: (a) radiation fog; (b) advection fog; (c) valley fog; (d) upslope fog; (e) cold and warm stream fog; (f) steaming fog; (g) frontal fog. 20.26 Fronts and depressions 20.26.2 Define ‘synoptic observation’. 20.26.4 Describe the Polar Front theory. 20.26.6 Define ‘airmass’. 20.26.8 List the airmass categories. 20.26.10 Describe each type of airmass and explain the likely weather conditions in New Zealand during warm and cold airstream advection. 20.26.12 Describe the concept of vorticity & associated convergence/divergence relating to weather systems. 20.26.14 Explain the characteristics of: (a) mid latitude depressions; (b) polar depressions. 20.26.16 Identify the manner in which fronts are shown on weather maps. Page 64 Advisory Circular AC 61-1.5 Revision 13 15 December 2006 CAA of NZ 63 Sub Topic Syllabus Item 20.26.18 Describe the: (a) cold, warm, stationary, occluded front; (b) wind and weather sequence associated with each type of front; (c) movement of fronts and pressure systems. 20.26.20 Describe the factors associated with: (a) orographic depressions; (b) the heat (or thermal) low. 20.28 Thunderstorms 20.28.2 Explain the conditions to be met for the development of thunderstorms. 20.28.4 Describe the: (a) three stages of thunderstorms; (b) regeneration of thunderstorms. 20.28.6 List the types of thunderstorm, and describe the: (a) characteristics and development of each type; (b) hazards associated with thunderstorms; (c) precautions that can be taken by pilots to avoid or lessen the effects of thunderstorms. 20.28.8 Describe the processes involved in the formation of hail. 20.28.10 Explain the origin and development of tornadoes, and state the main hazards. 20.30 Icing 20.30.2 Explain the process of freezing and melting. 20.30.4 Define latent heat of fusion. 20.30.6 Describe the process involved in the formation of: (a) clear (translucent or glaze) ice; (b) rime (opaque) ice; (c) hoar frost; (d) freezing rain. 20.30.8 Explain the dangers (to aircraft) from ice accretion associated with the processes in 20.30.6 (a) - (d). Page 65 Advisory Circular AC 61-1.5 Revision 13 15 December 2006 CAA of NZ 64 Sub Topic Syllabus Item 20.30.10 Explain the factors, which influence the rate of ice accretion. 20.30.12 Describe the following de-icing/anti-icing methods: (a) mechanical; (b) fluid; (c) thermal. 20.30.14 Explain the process of carburetor icing. 20.30.16 State the maximum temperature range in which carburetor ice can form. 20.30.18 Explain how the accretion rate of carburetor icing is governed by: (a) moisture content of air; (b) throttle setting. 20.30.19 Describe the method commonly used in light aircraft to combat carburetor ice. 20.30.20 Explain: (a) the process of engine intake icing for piston and turbine engine aircraft; (b) the methods commonly used to combat intake icing. 20.30.22 Explain the: (a) likelihood of ice accretion in the 10 main cloud types; (b) type of ice to be expected in these cloud types; (c) altitudes relative to the freezing level where rime or clear ice can be expected in the cloud types. 20.30.24 List the three classifications of icing and describe their effect on aircraft. 20.32 Turbulence 20.32.2 Define ‘turbulence’. 20.32.4 Describe the cause(s), factors involved and techniques commonly used to avoid or minimise: (a) thermal turbulence; (b) mechanical turbulence, small-scale and large-scale; (c) wind shear turbulence; (d) wake turbulence. 20.32.6 Explain the characteristics of: Page 66 Advisory Circular AC 61-1.5 Revision 13 15 December 2006 CAA of NZ 65 Sub Topic Syllabus Item (a) light turbulence; (b) moderate turbulence; (c) severe turbulence. 20.34 Tropical meteorology 20.34.2 State the approximate latitude limits applicable to tropical meteorology. 20.34.4 In broad terms, describe the tropical Hadley cell. 20.34.6 Explain what is meant by: (a) horse latitudes; (b) doldrums. 20.34.8 Differentiate between the equatorial trough and the inter-tropical convergence zone (ITCZ). 20.34.10 Describe the: (a) seasonal location of the equatorial trough and ITCZ; (b) typical weather in an active and inactive ITCZ. 20.34.12 Explain the origin, common location and associated weather of the South Pacific Convergence Zone (SPCZ). 20.34.14 With regard to the trade winds, describe the: (a) origin and mechanics (of the trade winds); (b) approximate latitudinal and vertical limits; (c) seasonal location and direction; (d) commonly associated weather; (e) winds and weather usually experienced above the trade winds; (f) topographical influences (on the trade winds). 20.34.16 Define ‘monsoon’. 20.34.18 With regard to wet monsoons, describe the mechanics involved. 20.34.20 State the: (a) major global monsoon regions; (b) season during which the Australian monsoon is generally present. 20.34.22 List the requirements for the formation and development of tropical cyclones. Page 67 Advisory Circular AC 61-1.5 Revision 13 15 December 2006 CAA of NZ 66 Sub Topic Syllabus Item 20.34.24 Explain the requirement for thermal energy in the development of tropical cyclones, and state the two main sources of this energy. 20.34.26 With regard to tropical cyclones, describe the horizontal and vertical extents, pressure and wind velocity tendencies, and other associated factors during the: (a) formative stage; (b) immature stage; (c) mature stage; (d) decaying stage. 20.34.28 Describe the weather conditions associated with tropical cyclones. 20.34.30 With regard to the Southern Oscillation, describe the principles of the Walker Circulation. 20.34.32 Explain the factors involved when the ENSO index results in the: (a) El Nino events; (b) La Nina events. 20.34.34 Describe how the El Nino and La Nina events influence the weather in New Zealand. 20.34.36 Describe what is meant by ‘streamline analysis’. 20.34.38 Explain how isotachs and streamlines can be used to determine wind velocity. 20.34.40 Describe how areas of high and low pressure, convergence/divergence, and cols are depicted on streamline analysis charts. 20.36 The General Circulation 20.36.2 Explain what is meant by “The General Circulation”. 20.36.4 Describe what is meant by “high zonal index” and “low zonal index” and explain their effects on the movement of weather systems in the troposphere. 20.36.6 State the common locations in the southwest Pacific Ocean where ‘blocking anticyclones’ tend to form. 20.36.8 Describe the characteristics of a blocking anticyclone. 20.36.10 Describe the weather in the east and west of New Zealand when a blocking anticyclone has formed to the immediate east of the country. 20.38 Hazardous meteorological conditions 20.38.2 Describe the effects on climbing and descending flight paths when low-level wind shear is experienced. Page 68 Advisory Circular AC 61-1.5 Revision 13 15 December 2006 CAA of NZ 67 Sub Topic Syllabus Item 20.38.4 Explain the mechanics of a downburst. 20.38.6 Explain the mechanics of a microburst. 20.38.8 Explain the effects of downbursts and microbursts on aircraft operations. 20.38.10 Explain the effect of ice accretion on aircraft performance. 20.38.12 Differentiate between anti-icing and de-icing. 20.38.14 With regard to the rate of ice accretion, explain the effect of: (a) airspeed (including helicopter rotor rpm); (b) shape of aircraft components. 20.38.16 Explain why it is not advisable to operate aircraft in areas affected by volcanic ash. 20.38.18 Describe the adverse effects of reduced visibility during VFR flight. 20.38.20 Identify four actions that could be taken by a pilot to reduce or avoid the effects of turbulence. 20.38.22 Identify the three main types of aquaplaning. 20.38.24 Describe the effects of aquaplaning during landing. 20.40 New Zealand climatology 20.40.2 Describe the effects of latitude, oceanic surroundings and topography on the climate of New Zealand. 20.40.4 Describe the effect of latitude and topography on cold fronts traveling over New Zealand. 20.40.6 In general terms, describe cloudiness, gustiness and turbulence at various parts of New Zealand during typical: (a) northwest wind regimes; (b) northeast wind regimes; (c) southwest wind regimes; (d) southeast wind regimes. 20.42 Meteorological services, reports and forecasts 20.42.2 Assess and interpret information presented on mean sea level analysis and prognosis weather charts covering the Southwest Pacific region. 20.42.4 Describe the general principles of operation of automatic weather stations and associated equipment including the modern visibility sensor and laser ceilometer Page 69 Advisory Circular AC 61-1.5 Revision 13 15 Dece
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Most people assume meteorology to be weather, or vise versa. Most people think that you can easily look at some pictures and say what the weather will most likely be. Both of these statements are wrong. When you want to understand meteorology, you have to understand the atmosphere, some physics, and a lot of charts. In this book, I will try and open people's world to meteorology, but that does mean learning a lot of other topics that may seem to have nothing to do with weather or climate. If you stick with me, I will do my best to make sure it stays on topic and doesn't go in depth on other topics without actually needing to. For example, I will not throw handfuls of physics formulas at you, but instead simply cover what you need to know and go from there.
The book was originally a small set of articles talking about random points of meteorology. Of course, you can not talk about one thing without talking about another, this made the articles hard to read and understand. Hopefully, in time and with the help of others, this book will become useful for anyone looking for a piece of information they forgot a long time ago or are just curious.
Meteorology is a branch of atmospheric physics that focuses on air pressure, the climate, temperature and weather prediction. People who practice meteorology are called meteorologists. It is also a major branch of earth science.frr:Wääderkunde