Physics of Atmosphere in Cyclones, Thunderstorms and Lightning discharges
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An electrical and magnetic approach to understand the physics of severe weather phenomena such as cyclones, thunderstorms and lightning discharges.
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Physics of Atmosphere in Cyclones, Thunderstorms and Lightning discharges
- 1. 04th September 2015 Annual Talk by Adarsh Dube Guided by Dr. Rajesh Singh.
- 2. Outline of the Talk • Atmosphere • Ionosphere • Forcing to the Ionosphere • Causes of forcing • Future work
- 3. Atmosphere • The blanket/envelope of air around earth is termed as its atmosphere. • Air comprises of gases(78% nitrogen, 21% oxygen, 0.9% argon, and 0.03% carbon dioxide with very small percentages of other elements like water vapor, aerosols, smoke, and dust particles, etc ). • The Atmosphere spans from the earth’s surface to a height of 480km after which it becomes thinner until it gradually reaches space.
- 4. Governing Equations of a Sphere • The basic equations for the motion of a dry atmosphere are 1. 𝜌 𝐷𝒖 𝐷𝑡 = −𝛻𝑝 + 𝜌𝑔 − 𝜌𝜴 × 𝒖 + 𝑭…………Conservation of momentum 2. 𝐷𝜌 𝐷𝑡 = −𝜌𝛻. 𝒖…………………Conservation of mass 3. 𝐶 𝑝 𝐷 𝐷𝑡 𝑙𝑛𝜃 = 𝑄 𝑇 ……..Conservation of energy(1st law of thermodynamics) 4. 𝑝 = 𝜌𝑅𝑇…………equation of state. • The variables represent u→3D fluid velocity, p→Total pressure, ρ→ density, T→ Temperature θ→ potential temperature, and Q→ diabatic heating rate F→ viscous and/or turbulent stresses, g→ the effective gravity.
- 5. Geometry of the Earth atmosphere • As far as geometry is concerned the equations of motion can be expressed with sufficient accuracy in a spherical coordinate system (λ, φ, r), the components of which represent longitude, latitude and radial distance from the Centre of the Earth(Smith,2013). • The coordinate system rotates with the earth at an angular rate Ω = |Ω| = 7.292 × 10−5 rad s−1. • An important dynamical requirement in the approximation to a sphere is that the effective gravity appears only in the radial equation of motion, i.e. we regard spherical surfaces as exact geopotentials so that the effective gravity has no equatorial component • The Atmosphere is very shallow compared with its radius (99% of the mass of the atmosphere lies below 30 km, whereas r = 6367 km).
- 6. Measuring the Atmosphere • Our knowledge about the atmosphere has developed based on data from a variety of sources, including direct measurements from balloons and aircraft as well as remote measurements from satellites.
- 7. Pressure in the Atmosphere • Atmospheric pressure can be imagined as the weight of the overlying column of air. • Traces of the atmosphere can be detected as far as 500 km above Earth's surface but 80 percent of the atmosphere's mass is contained within the 18 km closest to the surface. • Atmospheric pressure is generally measured in millibars (mb). • 1 atm=1.013 bar=1013 mb=760 mm Hg F = ma = (104 kg) (9.8 m/s2) = 1 X 105 N P = F / A = 1 X 105 N / 1 m2 =1 X 105 Pa 1 atm = 1.01325 X 105 Pa.
- 8. How does pressure vary with height ? • Consider a single component gas of the Earth’s atmosphere. The most primitive form of the ideal gas law relates the number of molecules N of this gas contained in a volume V to the pressure p and absolute temperature T of the gas. 𝑝𝑉 = 𝑁𝑘𝑇 where k is the Boltzmann constant; it has the value 1.38 x 10-23 J/K. If the molecular mass of this gas is m, the gas law may be rewritten as 𝑝 = 𝑚 𝑁 𝑉 𝑘 𝑚 𝑇 = 𝜌𝑅𝑇 • Consider a column of gas of a specific type acted upon by gravity alone and not subject to vertical accelerations anywhere in the column. Such a gas is said to be in hydrostatic equilibrium: At any level in the column, the pressure (force per unit area exerted by the gas) is determined solely by the weight of the overlying gas in the column. The change in pressure with altitude is given by 𝜕𝑝 𝜕𝑧 = 𝜌𝑔
- 9. where g is the acceleration due to the Earth’s gravity. At the Earth’s surface, g is approximately 9.807 m s-2 . With the help of the ideal gas law, one can rewrite the equation as 1 𝑝 𝜕𝑝 𝜕𝑧 = − 𝑔 𝑅𝑇 This expression can be integrated from sea level (z = 0) to some higher altitude z, or equivalently from the pressure at sea level Po to the pressure P at altitude z. The result is 𝑃 = 𝑃𝑜 exp(− 0 𝑧 𝑔 𝑅𝑇 𝑑𝑧) This expression gives the variation of pressure in atmosphere for a specific gas, R is constant with altitude, g decreases slowly with altitude, and T may increase or decrease.
- 10. Pressure System in the Atmosphere • A pressure system is a region of the Earth's atmosphere where air pressure is a relative peak or lull in the sea level pressure distribution • A low-pressure area, or "low", is a region where the atmospheric pressure at sea level is below that of surrounding locations • Low pressure systems are associated with bad weather • High-pressure systems are frequently associated with light winds at the surface and subsidence through the lower portion of the troposphere. • Generally, high pressure systems are associated with fair weather and clear skies
- 12. • The atmosphere is divided into the thermosphere, mesosphere, stratosphere, and troposphere, and the boundaries between these layers are defined by changes in temperature gradients. • Within the troposphere, temperature decreases with altitude at a rate of about 6.5° C per kilometer, called as ELR. • Temperature reaches its lowest value in Mesosphere at about -126° C. Temperature in the atmosphere
- 13. Controls of the temperature • The variation in the temperature of the atmosphere is regulated by the heat transfer processes namely conduction, convection and radiation, the causes are: 1. Differential heating of land and water (differences in Evaporation, Specific Heat, Movement) 2. Ocean currents 3. Altitude 4. Geographic position 5. Cloud cover and albedo From adiabatic gas law, 𝑝 𝛾−1 𝑇 𝛾 = 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡 on taking logarithms it gives 𝑑𝑝 𝑝 = 𝛾 𝛾 − 1 𝑑𝑇 𝑇 From modified hydrostatic equilibrium equation, we can write, 𝛾 𝛾 − 1 𝑑𝑇 𝑇 = − 𝜇𝑔 𝑅𝑇 𝑑𝑧 Or 𝑑𝑇 𝑑𝑧 = − 𝛾 − 1 𝛾 𝜇𝑔 𝑅 This gives the relation between temperature of the air parcel dT at any height dz in the atmosphere and is known as DALR, DALR = 9.8C/km.
- 14. Mean annual temperature range (◦C) of the air near sea level.
- 15. Ionosphere • The Ionosphere is part of Earth’s upper atmosphere, between 80 and about 600 km • Extreme Ultra Violet (EUV) and x-ray solar radiation ionizes the atoms and molecules thus creating a layer of electrons. • Due to spectral variability of the solar radiation and the density of various constituents in the atmosphere, there are layers are created within the ionosphere, called the D-layer, E-layer, and F-layer.
- 16. Dynamics of Ionosphere • Solar phenomena, such as flares, changes in the solar wind and geomagnetic storms effect the charging of the ionosphere. Since the largest amount of ionization is caused by solar irradiance, the night-side of the earth, and the pole pointed away from the sun (depending on the season) have much less ionization than the day-side of the earth, and the pole pointing towards the sun.
- 17. Ionospheric model • The International Reference Ionosphere (IRI) is an international project sponsored by the Committee on Space Research (COSPAR) and the International Union of Radio Science (URSI). These organizations formed a Working Group in the late sixties to produce an empirical standard model of the ionosphere, based on all available data sources with emphasis on parameters such as Electron density, electron temperature, ion temperature, ion composition (O+, H+, He+, NO+, O+ 2), ion drift, ionopsheric electron content (TEC), F1 and spread-F probability • IRI is updated yearly during special IRI Workshops (e.g., during COSPAR general assembly)
- 18. Persistent anomalies to the idealized model • Winter anomaly- Lower total F2 ionization in the local summer months. It is always present in the northern hemisphere but is usually absent in the southern hemisphere during periods of low solar activity. • Equatorial anomaly- occurrence of a trough in the ionization in the F2 layer at the equator and crests at about 17 degrees in magnetic latitude. • Equatorial electrojet -an enhanced eastward current flow within ± 3 degrees of the magnetic equator. Diurnal Ionospheric Current
- 19. Observing the Ionosphere • Ionosondes (shortwave transmitter)-one of the first techniques to observe ionosphere. radio signal at given frequency transmitted reflects at an altitude where f equal to local electron plasma f • Ionospheric radars- flow speeds, ion composition • Magnetometers- electric currents • Optical instruments- Ionization and Dynamics • Sounding rockets- Various local parameters
- 20. Forcing to the Ionosphere • Forcing from above-Solar zenith angle, variability of solar ionizing radiation with the solar cycle, solar rotation, solar flares, and space weather phenomena mostly of solar origin are responsible for the extraterrestrial control of the ionosphere. • Forcing from below- from lower-lying layers of the atmosphere, basically from troposphere, are summarized for simplicity under the term ‘meteorological processes’. • Forcing from Lithospheric processes- A case study of 26 December 2004 Indian Ocean Tsunami (Liu et al, 2006) reveals the tsunami waves triggered atmospheric disturbances near the sea surface, which then traveled upward with an average velocity of about 730 m/s (2700 km/hr) into the ionosphere and significantly disturbed the electron density within it.
- 21. Forcing from Meteorological processes • Meteorological processes can affect the ionosphere mainly through two channels: 1. electrical and electromagnetic phenomena:- This includes red sprites, blue jets and other lightning upward-induced phenomena, which play a role in the lower ionosphere below 100 km, changes in the global electric circuit, lightning-induced whistlers which can reach the magnetosphere, and a few other phenomena. 2. upward propagating waves in the neutral atmosphere:- upward propagating waves in the neutral atmosphere, are more important from the point of view of energy deposition and atmospheric modification.
- 22. • Thunderstorms • Typhoons/Cyclones • Tsunami • Zonal Winds Examples of Meteorological processes Examples of Solid Earth processes • Volcanic Eruptions • Earth Quakes • Plate Tectonics
- 23. Tropical Cyclones • The name cyclone is derived from a greek word ‘cyclos’ which means ‘serpent’. • They are also named as typhoons (Western North pacific, V> 119 km/h), hurricanes(Caribbean, eastern pacific), storms in Indian region(V> 60 km/h) • Formation- Cyclones are formed when two air masses collide. • Pattern of movement-generally cyclones are accompanied by strong winds in anti-clockwise direction in northern hemisphere.
- 24. Precursor to formation of cyclones • The conditions Necessary but not sufficient for the formation of tropical cyclones (Gray,1986) are: 1. Overlying SST > 26.5C up to 60m depth.(to fuel the heat engine of tropical cyclone) 2. enhanced mid-troposphere (700 hPa) relative humidity (energy liberated by thunderstorms helps) 3. conditional instability 4. enhanced lower troposphere relative vorticity 5. Limited vertical wind shear 6. displacement by at least 5° latitude away from the equator.
- 25. Rossby Radius of deformation • The ability for initial convection to survive for many days depends on its vorticity, stability and depth- defined by its rossby radius of deformation, LR. • LR can be generalized as • 𝐿 𝑅 = 𝑁𝐻 (𝜁+𝑓𝑜) • 𝐿 𝑅 ≈ 1000𝑘𝑚, for a vertical Scale associated with the Height of the tropopause • H → Depth of the system • N → Brunt-Vaisala frequency, 𝑁2 = 𝑔𝑑𝜃 𝜃𝑑𝑧 , N=0.012 𝑠−1 for a period of oscillation of 9min. • 𝜁 → Vertical component of relative vorticity, 𝜁 = ( 𝜕𝑣 𝜕𝑥 − 𝜕𝑢 𝜕𝑦 ) ≈ 10−5 𝑚𝑠−1 • 𝑓𝑜 → Coriolis parameter, 𝑓𝑜 = 2Ω𝑠𝑖𝑛𝜙 ≈ 10−5 𝑟𝑎𝑑𝑠−1
- 26. Effects of cyclones on Ionosphere • Cyclones perturb the geostrophic balance of the atmosphere • Thus, The atmosphere adjusts back into geostrophic balance by generating inertial-gravity waves which propagate energy away from the cyclone. • It is suggested that powerful meteorological disturbances (cyclones, thunderstorms, tornadoes, etc.) must serve as sources of gravity waves of different types, which, under favorable conditions, can penetrate to ionospheric heights and manifest themselves there as traveling ionospheric disturbances (TIDs) (Danilov et al., 1987; Hocke and Shlegel, 1996; Kazimirovsky et al., 2003; Lastovicka(2006).
- 27. • The propagation from the bottom upward of internal atmospheric waves (IAWs) of different scales can serve as the mechanism of interaction of Ionosphere with underlying atmospheric layers (Danilov et al.,1987; Hocke and Shlegel, 1996; Kazimirovsky et al.,2003; Lastovicka, 2006): planetary waves (with periods of several days), tidal waves (with periods of several hours), and gravity waves (with periods of 1–150 min). • The influence of tropospheric structures on the overlying layers can be also exerted through the redistribution of minor constituents (for example, ozone) associated with ejections of charged and neutral particles from the cyclone zone (Vanina Dart et al., 2007a, b; Danilov et al., 1987).
- 28. Thunderstorms • A thunderstorm is the result of convection. • All thunderstorms require three ingredients for their formation: 1. Moisture, 2. Instability, and 3. a lifting mechanism- differential heating, fronts, drylines, etc. Fig: The electric charge structure in a air mass storm : based on balloon soundings of electric field
- 29. Life Cycle of a thunderstorm • The building block of all thunderstorms is the thunderstorm cell. The thunderstorm cell has a distinct life-cycle that lasts about 30 minutes 1. The Towering Cumulus Stage(a)- dominated by updrafts 2. The Mature Cumulus Stage(b)- Strong updrafts and downdrafts coexist 3. The Dissipating Stage(c)- the downdraft cuts off the updraft
- 30. Electrification of a thundercloud • The convective theory proposes that free ions in the atmosphere are captured by cloud droplets and then are moved by the convective currents in the cloud to produce the charged regions. • The gravitational theory assumes that negatively charged particles are heavier and are separated from lighter positively charged particles by gravitational settling.
- 31. Effects of Thunderstorms • Modeling of atmospheric gravity waves (AGWs), originating from thunderstorms, has predicted variations in total electron content (TEC) associated with these AGWs of ±7% [Vadas and Liu, 2009]. • Large thunderstorms are capable of producing the kinds of electrical phenomena called transient luminous events (TLEs) that occur high in the atmosphere. They are rarely observed visually and not well understood. The most common TLEs include red sprites, blue jets, and elves.
- 32. Effects of thunderstorms • Studies on the D layer ionosphere (~65–90 km altitude) have shown that AGWs originating from large mesoscale thunderstorms clearly perturb the electron distribution at the lower boundary of the ionosphere [Lay and Shao, 2011a] • electrical activity within even a small storm affects the D layer above by heating electrons and consequently reducing the density of the free electrons [Shao et al., 2013]
- 33. Lightning • A giant spark of electricity in the atmosphere between clouds, the air, or the ground. • In the early stages of development, air acts as an insulator between the positive and negative charges in the cloud and between the cloud and the ground. • When the opposite charges builds up enough, this insulating capacity of the air breaks down and there is a rapid discharge of electricity that we know as lightning. • The flash of lightning temporarily equalizes the charged regions in the atmosphere until the opposite charges build up again.
- 34. Types of Lightning • The precursor of any lightning strike is the polarization of positive and negative charges within a storm cloud. • Polarization develops by two mechanisms, frictional charging and freezing mechanism. • The excess electrons flow in a stream of current from cloud to ground, to earth surface or to air.
- 35. The process of lightning • The path of a typical cloud-to-ground (CG) flash lowering negative charge to earth is carved by a series of stepped leaders, each moving a bundle of charge a distance on the order of a city block. • Each step takes only 1 microsecond or so, but the pauses between steps are much longer--on the order of 50 microseconds. • At each step, the bolt may shift direction toward a stronger electric field, thus creating its crooked appearance. As a CG flash approaches several regions of opposite charge on the ground, it often branches into several parts. Step 1 Step 2 Step 3
- 36. • Just before it reaches ground, the step leader induces a huge electric potential (some 10 million volts), enough to bring up surges of positive charge from sharp objects or irregularities near the ground. • Once the impulses meet--a few tens of meters above earth--the connection is established and the return stroke zips upward at a rate much faster than the stepped leader's descent. It is this return stroke that produces the visible flash as it heats surrounding air to 30,000 degrees C (54,000 degrees F), which in turn creates the shock wave we hear as thunder. Step 4 Step 5
- 37. Effects of Lightning • Lightning is one of the oldest observed natural phenomena on earth. It can be seen in volcanic eruptions, extremely intense forest fires, surface nuclear detonations, heavy snowstorms, in large hurricanes, and obviously, thunderstorms. • A statistical study by Davis and Johnson,2005 found a correlation between intensification in the sporadic E layer and lightning activity. • Statistics reveal that the period of most frequent whistler occurrence does not correspond to the maximum in lightning activity in the conjugate region but is strongly influenced by ionospheric illumination in a study by Collier et al., 2006.
- 38. Future Work • I wish to study the severe weather phenomena and its impact on upper atmosphere e.g.. 1. Ionospheric perturbations due to cyclones, and mesoscale thunderstorms 2. Cloud bursts and related impacts 3. Upward electric discharges- TLE
- 39. Present work • Details of lightning on 11-10-2013 • Total no. of lightning- 61217 • No. of positive polarity lightning- 18980 • Max Peak Current- 535kA • Peak current events>200kA-54 • No. of negative polarity lightning- 42237 • Max –ve peak current- 624kA • -ve Peak current events >200kA-331
Editor's Notes
- Atmosphere can be of sun, moon , and planets. Earth’s atmosphere is composed mainly of nitrogen but Sun’s atmosphere is composed of hydrogen. The Earth's atmosphere is more than just the air we breathe. It's also a buffer that keeps us from being peppered by meteorites, a screen against deadly radiation, and the reason radio waves can be bounced for long distances around the planet. - National Geographic Although both nitrogen and oxygen are essential to human life on the planet, they have little effect on weather and other atmospheric processes. The variable components, which make up far less than 1 percent of the atmosphere, have a much greater influence on both short-term weather and long-term climate. For example, variations in water vapor in the atmosphere are familiar to us as relative humidity. Water vapor, CO2, CH4, N2O, and SO2 all have an important property: They absorb heat emitted by Earth and thus warm the atmosphere, creating what we call the "greenhouse effect." Without these so-called greenhouse gases, the Earth's surface would be about 30 degrees Celsius cooler – too cold for life to exist as we know it. Though the greenhouse effect is sometimes portrayed as a bad thing, trace amounts of gases like CO2 warm our planet's atmosphere enough to sustain life. Global warming, on the other hand, is a separate process that can be caused by increased amounts of greenhouse gases in the atmosphere. In addition to gases, the atmosphere also contains particulate matter such as dust, volcanic ash, rain, and snow. These are, of course, highly variable and are generally less persistent than gas concentrations, but they can sometimes remain in the atmosphere for relatively long periods of time. Volcanic ash from the 1991 eruption of Mt. Pinatubo in the Philippines, for example, darkened skies around the globe for over a year. Though the major components of the atmosphere vary little today, they have changed dramatically over Earth's history, about 4.6 billion years. The early atmosphere was hardly the life-sustaining blanket of air that it is today; most geologists believe that the main constituents then were nitrogen gas and carbon dioxide, but no free oxygen. In fact, there is no evidence for free oxygen in the atmosphere until about 2 billion years ago, when photosynthesizing bacteria evolved and began taking in atmospheric carbon dioxide and releasing oxygen. The amount of oxygen in the atmosphere has risen steadily from 0 percent 2 billion years ago to about 21 percent today. Reference:- http://www.visionlearning.com/en/library/Earth-Science/6/The-Composition-of-Earths-Atmosphere/107 air parcel (plural air parcels) (physics, meteorology) An imaginary body of air to which may be assigned any or all of the basic dynamic and thermodynamic properties of atmospheric air. A parcel is large enough to contain a very great number of molecules, but small enough so that the properties assigned to it are approximately uniform within it and so that its motions with respect to the surrounding atmosphere do not induce markedcompensatory movements. It cannot be given precise numerical definition, but a cubic foot of air might fit well into most contexts where air parcels are discussed, particularly those related to static stability. Source-Wikipedia
- The first three represent the conservation of momentum, the conservation of mass and the conservation of energy (first law of thermodynamics), respectively; the last is the equation of state. The variables u, p, ρ, T and θ and Q represent the (three-dimensional) fluid velocity, total pressure, density, temperature, potential temperature, and diabatic heating rate, respectively; F represents viscous and or turbulent stresses, and g is the effective gravity. The potential temperature is related to the temperature and pressure by the formula θ = T(p∗/p)κ, where p∗ = 1000 mb and κ = 0.2865. The shape of the earths surface is approximately an oblate spheroid with an equatorial radius of 6378 km and a polar radius of 6357 km. The surface is close to a geopotential surface, i.e. a surface which is perpendicular to the effective gravity (see DM, Chapter 3). As far as geometry is concerned the equations of motion can be expressed with sufficient accuracy in a spherical coordinate system (λ, φ, r), the components of which represent longitude, latitude and radial distance from the centre of the earth (see Fig. 2.1). The coordinate system rotates with the earth at an angular rate Ω = |Ω| = 7.292 × 10−5 rad s−1. An important dynamical requirement in the approximation to a sphere is that the effective gravity appears only in the radial equation of motion, i.e. we regard spherical surfaces as exact geopotentials so that the effective gravity has no equatorial component.
- We now have continuous satellite monitoring of the atmosphere and Doppler radar to tell us whether or not we will experience rain anytime soon; however, atmospheric measurements used to be few and far between. Today, measurements such as temperature and pressure not only help us predict the weather, but also help us look at long-term changes in global climate (see our Temperature module). The first atmospheric scientists were less concerned with weather prediction, however, and more interested in the composition and structure of the atmosphere. The two most important instruments for taking measurements in Earth's atmosphere were developed hundreds of years ago: Galileo is credited with inventing the thermometer in 1593, andEvangelista Torricelli invented the barometer in 1643. With these two instruments, temperature and pressure could be recorded at any time and at any place. Of course, the earliest pressure and temperature measurements were taken at Earth's surface. It was a hundred years before the thermometer and barometer went aloft. While many people are familiar with Ben Franklin's kite and key experiment that tested lightning for the presence of electricity, few realize that kites were the main vehicle for obtaining atmospheric measurements above Earth's surface. Throughout the 18th and 19th centuries, kite-mounted instruments collected pressure, temperature, and humidity readings; unfortunately, scientists could only reach up to an altitude of about 3 km with this technique. Unmanned balloons were able to take measurements at higher altitudes than kites, but because they were simply released with no passengers and no strings attached, they had to be retrieved in order to obtain the data that had been collected. This changed with the development of the radiosonde, an unmanned balloon capable of achieving high altitudes, in the early 1930s. The radiosonde included a radio transmitter among its many instruments, allowing data to be transmitted as it was being collected so that the balloons no longer needed to be retrieved. A radiosonde network was developed in the United States in 1937, and continues to this day under the auspices of the National Weather Service.
- Atmospheric pressure can be imagined as the weight of the overlying column of air. Unlike temperature, pressure decreases exponentially with altitude. Traces of the atmosphere can be detected as far as 500 km above Earth's surface, but 80 percent of the atmosphere's mass is contained within the 18 km closest to the surface. Atmospheric pressure is generally measured in millibars (mb); this unit of measurement is equivalent to 1 gram per centimeter squared (1 g/cm2). Other units are occasionally used, such as bars, atmospheres, or millimeters of mercury. The correspondence between these units is shown here:- 1.013 bar=1013 mb=1 atm=760 mm Hg At sea level, pressure ranges from about 960 to 1,050 mb, with an average of 1,013 mb. At the top of Mt. Everest, pressure is as low as 300 mb. Because gas pressure is related to density, this low pressuremeans that there are approximately one-third as many gas molecules inhaled per breath on top of Mt. Everest as at sea level – which is why climbers experience ever more severe shortness of breath the higher they go, as less oxygen is inhaled with every breath. Though other planets host atmospheres, the presence of free oxygen and water vapor makes our atmosphere unique as far as we know. These components both encouraged and protected life on Earth as it developed, not only by providing oxygen for respiration, but by shielding organisms from harmful UV rays and by incinerating small meteors before they hit the surface. Additionally, the composition and structure of this unique resource are important keys to understanding circulation in the atmosphere,biogeochemical cycling of nutrients, short-term local weather patterns, and long-term global climate changes. U can tell about pressure differences of lows and highs in the atmosphere
- Net upward force = Net downward force Consider a thin vertical slice of the atmosphere of cross-sectional area A which starts at height above ground level z and extends to height z+dz. The upwards force exerted on this slice from the gas below is p(z)A, where p(z) is the pressure at height z . Likewise, the downward force exerted by the gas above the slice is (p(z+dz)A). The net upward force is clearly (p(z)-p(z+dz))A. In equilibrium, this upward force must be balanced by the downward force due to the weight of the slice: this is Adzg , where is the density of the gas, and g is the acceleration due to gravity. In follows that the force balance condition can be written (p(z)-p(z+dz))A = Adzg which reduces to dp/dz = g This is the hydrostatic equilibrium.
- Up to this point, discussion has centered on a specific gas, but the atmosphere is a mixture of gases, to be discussed specifically in section 4. Dalton’s Law of Partial Pressures states that each component gas in a mixture exerts its own pressure as if it were alone in the volume containing the mixture at temperature T. The total pressure p exerted by all gases in a mixture is just the sum of the partial pressures pi. The case then is modified with combination of dry air and moist air(water vapor). Standard atmospheres assume dry air . The main reason is that the concentration of water vapor, the third most abundant atmospheric gas, is highly variable, mainly because the maximum possible vapor pressure is a strong function of temperature. Once the air is saturated with water vapor, any reduction in temperature will cause condensation. No other constituent gas changes phase under normal atmospheric conditions. Water vapor is responsible for most of the weather people experience. Condensed into clouds and precipitation, water in liquid or ice phases can pose serious hazards to aircraft, but that is discussed in a companion article on meteorology in this volume.
- Reference- livescience.com, met.uk, Wikipedia
- through examination of measurements collected by radiosonde and aircraft (and later by rockets), scientists became aware that the atmosphere is not uniform. Many people had long recognized that temperature decreased with altitude – if you've ever hiked up a tall mountain, you might learn to bring a jacket to wear at the top even when it is warm at the base – but it wasn't until the early 1900s that radiosondes revealed a layer, about 18 km above the surface, where temperature abruptly changed and began to increase with altitude. The discovery of this reversal led to division of the atmosphere into layers based on their thermal properties. The lowermost 12 to 18 km of the atmosphere, called the troposphere, is where all weather occurs – clouds form and precipitation falls, wind blows, humidity varies from place to place, and the atmosphere interacts with the surface below. Within the troposphere, temperature decreases with altitude at a rate of about 6.5° C per kilometer. At 8,856 m high, Mt. Everest still reaches less than halfway through the troposphere. Assuming a sea level temperature of 26° C (80° F), that means the temperature on the summit of Everest would be around -31° C (-24° F)! In fact, temperature at Everest's summit averages -36° C, whereas temperatures in New Delhi (in nearby India), at an elevation of 233 m, average about 28° C (82.4° F). At the uppermost boundary of the troposphere, air temperature reaches about -100° C and then begins to increase with altitude. This layer of increasing temperature is called the stratosphere. The cause of the temperature reversal is a layer of concentrated ozone. Ozone's ability to absorb incoming ultraviolet (UV) radiation from the sun had been recognized in 1881, but the existence of the ozone layer at an altitude of 20 to 50 km was not postulated until the 1920s. By absorbing UV rays, the ozone layer both warms the air around it and protects us on the surface from the harmful short-wavelength radiation that can cause skin cancer. It is important to recognize the difference between the ozone layer in the stratosphere and ozone present in trace amounts in the troposphere. Stratospheric ozone is produced when energy from the sun breaks apart O2 gas molecules into O atoms; these O atoms then bond with other O2 molecules to form O3, ozone. This process was first described in 1930 by Sydney Chapman, a geophysicist who synthesized many of the known facts about the ozone layer. Tropospheric ozone, on the other hand, is a pollutant produced when emissions from fossil-fuel burning interact with sunlight. Above the stratosphere, temperature begins to drop again in the next layer of the atmosphere called the mesosphere, as seen in the previous figure. This temperature decrease results from the rapidly decreasing density of the air at this altitude. Finally, at the outer reaches of Earth's atmosphere, the intense, unfiltered radiation from the sun causes molecules like O2 and N2 to break apart into ions. The release of energy from these reactions actually causes the temperature to rise again in the thermosphere, the outermost layer. The thermosphere extends to about 500 km above Earth's surface, still a few hundred kilometers below the altitude of most orbiting satellites.
- It depends on three important properties of air : Air is transparent to all but by no means to electromagnetic spectrum (Air ). Atmosphere is transparent to Longwave radiation but Opaque to Shortwave radiation. Air is constantly in motion (should get thoroughly mixed but then it do not mixes, because of 3rd property) Air is a poor conductor of heat. Imagine a packet of air which is being swirled around in the atmosphere. We would expect it to always remain at the same pressure as its surroundings, otherwise it would be mechanically unstable. It is also plausible that the packet moves around too quickly to effectively exchange heat with its surroundings, since air is very a poor heat conductor, and heat flow is consequently quite a slow process. So, to a first approximation, the air in the packet is adiabatic. In a steady-state atmosphere, we expect that as the packet moves upwards, expands due to the reduced pressure, and cools adiabatically, its temperature always remains the same as that of its immediate surroundings. This means that we can use the adiabatic gas law to characterize the cooling of the atmosphere with increasing altitude. In this particular case, the most useful manifestation of the adiabatic law is 1st equation in the slide. Suppose that the lapse rate of the atmosphere differs from the adiabatic value. Let us ignore the complication of water vapour and assume that the atmosphere is dry. Consider a packet of air which moves slightly upwards from its equilibrium height. The temperature of the packet will decrease with altitude according to the adiabatic lapse rate, because its expansion is adiabatic. We assume that the packet always maintains pressure balance with its surroundings. It follows that since , according to the ideal gas law, then (333) If the atmospheric lapse rate is less than the adiabatic value then implying that . So, the packet will be denser than its immediate surroundings, and will, therefore, tend to fall back to its original height. Clearly, an atmosphere whose lapse rate is less than the adiabatic value is stable. On the other hand, if the atmospheric lapse rate exceeds the adiabatic value then, after rising a little way, the packet will be less dense than its immediate surroundings, and will, therefore, continue to rise due to buoyancy effects. Clearly, an atmosphere whose lapse rate is greater than the adiabatic value is unstable. This effect is of great importance in Meteorology. The normal stable state of the atmosphere is for the lapse rate to be slightly less than the adiabatic value. Occasionally, however, the lapse rate exceeds the adiabatic value, and this is always associated with extremely disturbed weather patterns.
- The Ionosphere is part of Earth’s upper atmosphere, between 80 and about 600 km where Extreme UltraViolet (EUV) and x-ray solar radiation ionizes the atoms and molecules thus creating a layer of electrons. the ionosphere is important because it reflects and modifies radio waves used for communication and navigation. Other phenomena such as energetic charged particles and cosmic rays also have an ionizing effect and can contribute to the ionosphere. Above 100 km, cosmic radiation, Solar X-rays and Ultraviolet radiation increasingly affect the atmosphere, which cause ionization, or electrical charging, by separating negatively charged electrons from neutral oxygen atoms and nitrogen molecules, leaving the atom or molecule with a net positive charge (ion). We can define the ionosphere as the height region of the earth’s atmosphere where the concentration of free electrons is so large that it affects radio waves. The ionosphere was discovered when it was observed that radio waves can propagate over large distances, and one therefore had to assume the existence of an electrical conductive layer in the upper atmosphere which could reflect the waves. the concentration of electrons ne varies from 107 particles per m3 at 50km to a maximum of 1012 particles per m3 at 250-300km.
- The atmospheric atoms and molecules are impacted by the high energy the EUV and X-ray photons from the sun. The amount of energy (photon flux) at EUV and x-ray wavelengths varies by nearly a factor of ten over the 11 year solar cycle. The density of the ionosphere changes accordingly. Due to spectral variability of the solar radiation and the density of various constituents in the atmosphere, there are layers are created within the ionosphere, called the D, E, and F-layers. Other solar phenomena, such as flares, and changes in the solar wind and geomagnetic storms also effect the charging of the ionosphere. Since the largest amount of ionization is caused by solar irradiance, the night-side of the earth, and the pole pointed away from the sun (depending on the season) have much less ionization than the day-side of the earth, and the pole pointing towards the sun.
- For given location, time and date, IRI describes the electron density, electron temperature, ion temperature, and ion composition in the altitude range from about 50 km to about 2000 km; and also the electron content. It provides monthly averages in the non-auroral ionosphere for magnetically quiet conditions. The major data sources are the worldwide network of ionosondes, the powerful incoherent scatter radars (Jicamarca, Arecibo, Millstone Hill, Malvern, St. Santin), the ISIS and Alouette topside sounders, and in situ instruments on several satellites and rockets. IRI is updated yearly during special IRI Workshops (e.g., during COSPAR general assembly). More information can be found in the workshop reports. Several extensions are planned, including models for the ion drift, description of the auroral and polar ionosphere, and consideration of magnetic storm effects. An IRI Newsletter is published quarterly. Please contact the Newsletter editor K. Oyama if you would like to be included on the distribution list. There is also an electronic mailer with uptodate IRI-relevant information. The IRI master copy is held at the National Space Science Data Center (NSSDC) and updated according to the decisions of the Working Group. The software package distributed by NSSDC includes the FORTRAN subroutines, model coefficients (CCIR and URSI), and documentation files. The IRI build-up and formulas described in detail in a 158-page NSSDC report (Bilitza, 1990). Reference- http://iri.gsfc.nasa.gov/
- Winter Anomaly- At mid-latitudes, the F2 layer daytime ion production is higher in the summer, as expected, since the Sun shines more directly on the Earth. However, there are seasonal changes in the molecular-to-atomic ratio of the neutral atmosphere that cause the summer ion loss rate to be even higher. The result is that the increase in the summertime loss overwhelms the increase in summertime production, and total F2 ionization is actually lower in the local summer months. This effect is known as the winter anomaly. The anomaly is always present in the northern hemisphere, but is usually absent in the southern hemisphere during periods of low solar activity. Equatorial Anomaly- Within approximately ± 20 degrees of the magnetic equator, is the equatorial anomaly. It is the occurrence of a trough in the ionization in the F2 layer at the equator and crests at about 17 degrees in magnetic latitude. The Earth's magnetic field lines are horizontal at the magnetic equator. Solar heating and tidal oscillations in the lower ionosphere move plasma up and across the magnetic field lines. This sets up a sheet of electric current in the E region which, with the horizontal magnetic field, forces ionization up into the F layer, concentrating at ± 20 degrees from the magnetic equator. This phenomenon is known as the equatorial fountain. Equatorial electrojet- The worldwide solar-driven wind results in the so-called Sq (solar quiet) current system in the E region of the Earth's ionosphere (ionospheric dynamo region) (100 km (62 mi) – 130 km (81 mi) altitude). Resulting from this current is an electrostatic field directed E-W (dawn-dusk) in the equatorial day side of the ionosphere. At the magnetic dip equator, where the geomagnetic field is horizontal, this electric field results in an enhanced eastward current flow within ± 3 degrees of the magnetic equator, known as the equatorial electrojet. The equatorial electrojet (EEJ) is a narrow ribbon of current flowing eastward in the day time equatorial region of the Earth's ionosphere. Reference- Wikipedia
- The generic name "tropical cyclones" may be used anywhere in the world for tropical storms with peak wind speeds (1-minute mean, 10-minute mean or gust wind speed are used in different regions) exceeding 17 m s-1. In the western North Pacific, the strongest of these storms (peak wind speeds exceeding 33 m s-1) are called "typhoons In the Caribbean—and, more recently, in the eastern Pacific—the strongest of these storms are also referred to as "hurricanes" after the Carib god of evil, Hurican Accurate observational records are not always available after the passage of a tropical cyclone. The instruments may have been blown or washed away – or the instruments may not be located in the path of the storm. Thus, in the late 1960s Herb Saffir and Robert Simpson5,6 devised a classification convention to relate the observed damage due to a North Atlantic tropical cyclone with the peak surface winds or minimum surface pressure (two measures of the "intensity" of a tropical cyclone) and storm surge in vulnerable coastal locations. The classification system became known as the "Saffir–Simpson Scale" and has become shorthand for describing the destructive power expected from tropical cyclones around the world. The Saffir–Simpson scale was updated by the National Hurricane Center (NHC) in early 2010 Based on the wind speeds and
- Image ref- Wikipedia
- The Rossby radius, LR, is the critical scale at which rotation becomes as important as buoyancy. When the disturbance size is wider than LR, it persists; systems that are smaller than LR will disperse (Fig. above ). LR is inversely proportional to latitude so it is very large in the tropics. However, the high vorticity in tropical cyclones reduces the Rossby radius and enables tropical cyclones to last for many days and even weeks. Reference- NOAA textbook, Introduction to Tropical Meteorology, 2nd edition (http://www.goes-r.gov/) Vorticity is the microscopic measure of spin and rotation in a fluid. For large scale circulations, a typical magnitude for vorticity is 𝜁≈ 𝑈 𝐿 = 10 −5 𝑚𝑠 −1 . For Brunt Vaisala frequency, theta is potential temperature, g is the local acceleration of gravity, and z is geometric height. A typical value in the atmosphere is 0.012 per second and the period of oscillation is 9min. The potential temperature 𝜃, is defined as the temperature a parcel of air would have if brought adiabatically to a pressure of 1000 mb
- An unstable air mass is characterized by warm moist air near the surface and cold dry air aloft. Lifting mechanism involves, differential heating of the earth surface, fronts, Drylines and Outflow boundaries. Fronts are the boundary between two air masses of different temperatures and therefore different air densities. The colder, more dense air behind the front lift warmer, less dense air abruptly. If the air is moist thunderstorms will often form along the cold front. Drylines are the boundary between two air masses of different moisture content and separates warm, moist air from hot, dry air. Moist air is less dense then dry air. Drylines therefore, act similar to fronts in that a boundary exists between the two air masses of different densities. The air temperature behind a dryline is often much higher due to the lack of moisture. That alone will make the air less dense but the moist air ahead of the dryline has an even lower density making it more buoyant. The end result is air lifted along the dryline forming thunderstorms. This is common over the plains in the spring and early summer. Outflow boundaries are a result of the rush of cold air as a thunderstorm moves overhead. The rain-cooled, more dense, air acts as a "mini cold front", called an outflow boundary. Like fronts, this boundary lifts warm moist air and can cause new thunderstorms to form.
- For the gravitational theory to work, there must be some charge exchange process between particles of different sizes. Charge can be exchanged between particles in various states by inductive and non-inductive processes. The most promising is the non inductive exchange between ice crystals and hailstones, referred to as the ice-ice process. The effectiveness of the ice-ice process lies in the thermo-electric properties of ice. The mobility of the (OH3)+ defect in ice is greater than the (OH)- defect and the number of defects increase with temperature. When warm and cold ice particles come in contact, the positive defect flows faster from the warmer to the colder particles than the converse, giving the colder particles a net positive charge. Therefore in the typical scenario, a warm hailstone or snow pellet will acquire a net negative charge as it falls through a region of cold ice crystals.