DOCSLIB.ORG

A Generalization of the Thermal Wind Equation to Arbitrary Horizontal Flow CAPT

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
A Generalization of the Thermal Wind Equation to Arbitrary Horizontal Flow CAPT A Generalization of the Thermal Wind Equation to Arbitrary Horizontal Flow CAPT. GEORGE E. FORSYTHE, A.C. Hq., AAF Weather Service, Asheville, N. C. INTRODUCTION N THE COURSE of his European upper-air analysis for the Army Air Forces, Major R. C. I Bundgaard found that the shear of the observed wind field was frequently not parallel to the isotherms, even when allowance was made for errors in measuring the wind and temperature. Deviations of as much as 30 degrees were occasionally found. Since the ther- mal wind relation was found to be very useful on the occasions where it did give the direction and spacing of the isotherms, an attempt was made to give qualitative rules for correcting the observed wind-shear vector, to make it agree more closely with the shear of the geostrophic wind (and hence to make it lie along the isotherms). These rules were only partially correct and could not be made quantitative; no general rules were available. Bellamy, in a recent paper,1 has presented a thermal wind formula for the gradient wind, using for thermodynamic parameters pressure altitude and specific virtual temperature anom- aly. Bellamy's discussion is inadequate, however, in that it fails to demonstrate or account for the difference in direction between the shear of the geostrophic wind and the shear of the gradient wind. The purpose of the present note is to derive a formula for the shear of the actual wind, assuming horizontal flow of the air in the absence of frictional forces, and to show how the direction and spacing of the virtual-temperature isotherms can be obtained from this shear. A method of drawing a sketch (see accompanying figure) is given which can be used qualita- tively to examine all possible cases of gradient wind shear. NOTATION 2 v wind velocity for cyclonic (anticyclonic) cur- v wind speed vature v0 geostrophic wind velocity RH 1 /KH — radius of horizontal curva- Vg geostrophic wind speed ture VH horizontal acceleration « specific volume V dv/dt T* virtual temperature t unit vector along v p pressure k unit vector pointing toward zenith — V//( ) horizontal vector gradient of ( ) n k X t, the horizontal unit vector to — ( )p horizontal isobaric vector gra- left of v dient of ( ). [The variable ( ) <p latitude is plotted on an isobaric sur- <t> geopotential face and the whole plot is pro- angle between v and v0 jected onto a horizontal plane. angular rotation of earth, positive — Vff( )p is then the gradient of (negative) in northern (south- ( ) on the horizontal plane. See ern) hemisphere page 212 of Holmboe, Forsythe, ttz il sin | <p | and Gustin, op. tit.] zp pressure altitude KH horizontal component of curvature S* specific virtual temperature anom- of trajectory, positive (negative) aly (see Bellamy, op. tit.). 1 John C. Bellamy, "The Use of Pressure Altitude and Altimeter Corrections in Meteorology," Journal of Meteorology, vol. 2, no. 1 (1945); section 2. 2 The notation is that of Holmboe, Forsythe, and Gustin, Dynamic Meteorology, John Wiley & Sons, 1945, q. v. for detailed explanation of the symbols used here. Unauthenticated | Downloaded 09/28/21 03:50 PM UTC 372 BULLETIN AMERICAN METEOROLOGICAL SOCIETY [Vol. 26 DERIVATION OF GENERAL EQUATION The horizontal equation of motion of air in the absence of frictional forces may be formed by equating the horizontal acceleration (v#) to the sum of the horizontal Coriolis force per unit mass (— 2£ls Xv) and the horizontal pressure force per unit mass3 (— VH4>P): (1) VH = - 2xv -VH4>P. The acceleration V// can be written as VH = vt + IPKHU-, and the Coriolis force can be written as - 2£lz x v = - 2ttzvn. By substitution from the last two equations into (1), it is seen that vt + vPKnii = — 2Qzvn — VHcf>Pf or (2) vt + (2ttzv + v2KH)n = - Vh4>v- It is convenient to multiply equation (2) vectorially with the unit vector k, thereby rotating all vectors clockwise by 90°, as seen from above: - vn + (2VZV + V2KH)t = - X k. Since vt = v, the last equation can be written in its final form: (3) - vn + (2+ VKH)V = - VHCF>P X k. If I) is set equal to zero, the solution v of equation (3) is the gradient wind; if both V and KH are set equal to zero, v becomes the geostrophic wind. Equation (3) is now ready to be differentiated with respect to geopotential <t>; we obtain (4) - + (2fi2 + vKH) g + 5) v = _ fe) xk. The left-hand side of equation (4) is already in finished form; there remains only to trans- form the right-hand side. Since 8<f> is assumed equal to — adp, — 5(V//<£p)/5<£ is equal to 5(VH4>P) /a8p. Now the operations 8/dp and V#( )p are independent of each other, and may be interchanged. Hence 5(Vh4>p)/a8p is equal to Vh(84>/8p)p/(x, or to — (Vhocp)/<x. By loga- rithmic differentiation of the equation of state, it is seen that — /A equals — (VHTP*)/T*. Thus we have transformed the right-hand side of equation (4) completely: xl VhTp* x 8<j> T* The general thermal wind equation takes the final form 3 The vector — VH<T>P is the equivalent for constant-pressure analysis of the horizontal pressure-force vector — OC^HV considered in constant-level analysis. Strictly speaking, the vectors — VH<T>P and — AXIHV are equal only when the hydrostatic equation 8<j> = — a8p is satisfied—that is, when the air is stationary. Since 8<f> must be assumed equal to — a8p in the derivation of the thermal wind equation proper, it seems reasonable to accept their equality at this point. Unauthenticated | Downloaded 09/28/21 03:50 PM UTC Nov., 1945] ARTICLES 373 In terms of the variables used by Bellamy, op. ext., equation (5) takes the form DISCUSSION When V = KH = 0, equation (5) assumes its usual form (9) for the geostrophic wind, stating that the geostrophic wind shear is parallel to the isotherms of virtual temperature, with a strength directly proportional to the magnitude of the horizontal isobaric virtual temperature gradient and inversely proportional to the virtual temperature itself. When the wind is not geostrophic, the terms VKH8V/8<!>, V8(VKH)/8<f>, and — 8(VN)/8<f) of equation (5) show exactly how much the wind shear must be corrected in magnitude and direction in order to become equal to the right-hand side—that is, equal to the shear of the geostrophic wind. It is to be noted that v, n, v, and KH may all vary with increasing geo- potential, and that all the terms of equation (5) can theoretically be evaluated numerically. The three correction terms can all be of the same general order of magnitude as the shear vector 212z8v/8<F> itself, thus causing the vector — (1 /T*)(^HTP*) Xk sometimes to, deviate markedly from the vector 21225v/5</>. This fact undoubtedly accounts for the lack of success frequently experienced by upper-air analysts in attempting to orient and space isotherms by (in effect) using the actual shear vector 2ttz8v/8<t> as the left-hand side of equation (9). Of the three correction terms on the left-hand side of equation (5), the term — 8(vn)/8<f> is undoubtedly the hardest to estimate in practice. The quantity v is seen from equation (2) to be equal to the component of the pressure-force — Vn<f>P in the direction of the wind v. Let p denote the angle between the wind v and the geostrophic wind direction vg (with p taken positive for a wind blowing toward lower pressure). Then v = \VH<f>P\ sin 0, and the geostrophic wind law states that = 2£lzvg. Hence, from the last two equations, v = 212zVg sin p, and (6) - vn = — 2Qevg(sin p)n. By differentiation of equation (6) with respect to geopotential, it is seen that (7) - = - 202 g (sin p)n - 2Q^(cos P) g n - 2l2^(sin p) g- Now p is very difficult to determine in actual upper-air analysis, and 8p/8<t> is still more diffi- cult. It appears, then, that — 8(vn)/8<j) is next to impossible to estimate accurately. THE CASE OF GRADIENT W^IND Because of the difficulty of evaluating the term — 8(vn)/84> in equation (5), the practical use of that equation is probably limited to the case of gradient wind v (1) = 0): 6V 5V b{vKll) V T (8^ ) 90 si 4+ - nvKK h a 4+ - v = ~ » ** * kV> and to the geostrophic wind VY {V = KH = 0): (9) It will be noted that the quantity VKH and its variation with geopotential comprise the only difference between equation (8) and the ordinary thermal wind formula (9) for the geostrophic wind. Therefore, assuming the wind to be gradient, it is necessary to know values only of v Unauthenticated | Downloaded 09/28/21 03:50 PM UTC and VKH on various isobaric surfaces over a given station, in order to determine the direction and spacing of the virtual-temperature isotherms above the station. As usual, nature com- pensates: The advantage of the more exact equation (8) over the usual equation (9) is paid for justly by the requirement that, in addition to the wind v, the analyst must keep track of the quantity VKH. The price does not seem high. Comparison of equations (8) and (9) reveals the properties of the gradient wind shear. Since it is presumed that the reader is familiar with the use of the geostrophic wind shear for determining the virtual temperature field, the right-hand side will be eliminated between equations (8) and (9): In practice, v is given at various levels from wind observations, and KH can be estimated at various levels from the curvature of the contours and speed of the systems.
Load more

Recommended publications
  • Balanced Flow Natural Coordinates
    Balanced Flow • The pressure and velocity distributions in atmospheric systems are related by relatively simple, approximate force balances. • We can gain a qualitative understanding by considering steady-state conditions, in which the fluid flow does not vary with time, and by assuming there are no vertical motions. • To explore these balanced flow conditions, it is useful to define a new coordinate system, known as natural coordinates. Natural Coordinates • Natural coordinates are defined by a set of mutually orthogonal unit vectors whose orientation depends on the direction of the flow. Unit vector tˆ points along the direction of the flow. ˆ k kˆ Unit vector nˆ is perpendicular to ˆ t the flow, with positive to the left. kˆ nˆ ˆ t nˆ Unit vector k ˆ points upward. ˆ ˆ t nˆ tˆ k nˆ ˆ r k kˆ Horizontal velocity: V = Vtˆ tˆ kˆ nˆ ˆ V is the horizontal speed, t nˆ ˆ which is a nonnegative tˆ tˆ k nˆ scalar defined by V ≡ ds dt , nˆ where s ( x , y , t ) is the curve followed by a fluid parcel moving in the horizontal plane. To determine acceleration following the fluid motion, r dV d = ()Vˆt dt dt r dV dV dˆt = ˆt +V dt dt dt δt δs δtˆ δψ = = = δtˆ t+δt R tˆ δψ δψ R radius of curvature (positive in = R δs positive n direction) t n R > 0 if air parcels turn toward left R < 0 if air parcels turn toward right ˆ dtˆ nˆ k kˆ = (taking limit as δs → 0) tˆ R < 0 ds R kˆ nˆ ˆ ˆ ˆ t nˆ dt dt ds nˆ ˆ ˆ = = V t nˆ tˆ k dt ds dt R R > 0 nˆ r dV dV dˆt = ˆt +V dt dt dt r 2 dV dV V vector form of acceleration following = ˆt + nˆ dt dt R fluid motion in natural coordinates r − fkˆ ×V = − fVnˆ Coriolis (always acts normal to flow) ⎛ˆ ∂Φ ∂Φ ⎞ − ∇ pΦ = −⎜t + nˆ ⎟ pressure gradient ⎝ ∂s ∂n ⎠ dV ∂Φ = − dt ∂s component equations of horizontal V 2 ∂Φ momentum equation (isobaric) in + fV = − natural coordinate system R ∂n dV ∂Φ = − Balance of forces parallel to flow.
    [Show full text]
  • ESSENTIALS of METEOROLOGY (7Th Ed.) GLOSSARY
    ESSENTIALS OF METEOROLOGY (7th ed.) GLOSSARY Chapter 1 Aerosols Tiny suspended solid particles (dust, smoke, etc.) or liquid droplets that enter the atmosphere from either natural or human (anthropogenic) sources, such as the burning of fossil fuels. Sulfur-containing fossil fuels, such as coal, produce sulfate aerosols. Air density The ratio of the mass of a substance to the volume occupied by it. Air density is usually expressed as g/cm3 or kg/m3. Also See Density. Air pressure The pressure exerted by the mass of air above a given point, usually expressed in millibars (mb), inches of (atmospheric mercury (Hg) or in hectopascals (hPa). pressure) Atmosphere The envelope of gases that surround a planet and are held to it by the planet's gravitational attraction. The earth's atmosphere is mainly nitrogen and oxygen. Carbon dioxide (CO2) A colorless, odorless gas whose concentration is about 0.039 percent (390 ppm) in a volume of air near sea level. It is a selective absorber of infrared radiation and, consequently, it is important in the earth's atmospheric greenhouse effect. Solid CO2 is called dry ice. Climate The accumulation of daily and seasonal weather events over a long period of time. Front The transition zone between two distinct air masses. Hurricane A tropical cyclone having winds in excess of 64 knots (74 mi/hr). Ionosphere An electrified region of the upper atmosphere where fairly large concentrations of ions and free electrons exist. Lapse rate The rate at which an atmospheric variable (usually temperature) decreases with height. (See Environmental lapse rate.) Mesosphere The atmospheric layer between the stratosphere and the thermosphere.
    [Show full text]
  • Chapter 7 Balanced Flow
    Chapter 7 Balanced flow In Chapter 6 we derived the equations that govern the evolution of the at- mosphere and ocean, setting our discussion on a sound theoretical footing. However, these equations describe myriad phenomena, many of which are not central to our discussion of the large-scale circulation of the atmosphere and ocean. In this chapter, therefore, we focus on a subset of possible motions known as ‘balanced flows’ which are relevant to the general circulation. We have already seen that large-scale flow in the atmosphere and ocean is hydrostatically balanced in the vertical in the sense that gravitational and pressure gradient forces balance one another, rather than inducing accelera- tions. It turns out that the atmosphere and ocean are also close to balance in the horizontal, in the sense that Coriolis forces are balanced by horizon- tal pressure gradients in what is known as ‘geostrophic motion’ – from the Greek: ‘geo’ for ‘earth’, ‘strophe’ for ‘turning’. In this Chapter we describe how the rather peculiar and counter-intuitive properties of the geostrophic motion of a homogeneous fluid are encapsulated in the ‘Taylor-Proudman theorem’ which expresses in mathematical form the ‘stiffness’ imparted to a fluid by rotation. This stiffness property will be repeatedly applied in later chapters to come to some understanding of the large-scale circulation of the atmosphere and ocean. We go on to discuss how the Taylor-Proudman theo- rem is modified in a fluid in which the density is not homogeneous but varies from place to place, deriving the ‘thermal wind equation’. Finally we dis- cuss so-called ‘ageostrophic flow’ motion, which is not in geostrophic balance but is modified by friction in regions where the atmosphere and ocean rubs against solid boundaries or at the atmosphere-ocean interface.
    [Show full text]
  • Methods for Diagnosing Regions of Conditional Symmetric Instability
    Methods for Diagnosing Regions of Conditional Symmetric Instability James T. Moore Cooperative Institute for Precipitation Systems Saint Louis University Dept. of Earth & Atmospheric Sciences Ted Funk Science and Operations Officer WFO Louisville, KY Spectrum of Instabilities Which Can Result in Enhanced Precipitation • Inertial Instability • Potential Symmetric Instability • Conditional Symmetric Instability • Weak Symmetric Stability • Elevated Convective Instability 1 Inertial Instability Inertial instability is the horizontal analog to gravitational instability; i.e., if a parcel is displaced horizontally from its geostrophically balanced base state, will it return to its original position or will it accelerate further from that position? Inertially unstable regions are diagnosed where: .g + f < 0 ; absolute geostrophic vorticity < 0 OR if we define Mg = vg + fx = absolute geostrophic momentum, then inertially unstable regions are diagnosed where: MMg/ Mx = Mvg/ Mx + f < 0 ; since .g = Mvg/ Mx (NOTE: vg = geostrophic wind normal to the thermal gradient) x = a fixed point; for wind increasing with height, Mg surfaces become more horizontal (i.e., Mg increases with height) Inertial Instability (cont.) Inertial stability is weak or unstable typically in two regions (Blanchard et al. 1998, MWR): .g + f = (V/Rs - MV/ Mn) + f ; in natural coordinates where V/Rs = curvature term and MV/ Mn = shear term • Equatorward of a westerly wind maximum (jet streak) where the anticyclonic relative geostrophic vorticity is large (to offset the Coriolis
    [Show full text]
  • Synoptic Meteorology
    Lecture Notes on Synoptic Meteorology For Integrated Meteorological Training Course By Dr. Prakash Khare Scientist E India Meteorological Department Meteorological Training Institute Pashan,Pune-8 186 IMTC SYLLABUS OF SYNOPTIC METEOROLOGY (FOR DIRECT RECRUITED S.A’S OF IMD) Theory (25 Periods) ❖ Scales of weather systems; Network of Observatories; Surface, upper air; special observations (satellite, radar, aircraft etc.); analysis of fields of meteorological elements on synoptic charts; Vertical time / cross sections and their analysis. ❖ Wind and pressure analysis: Isobars on level surface and contours on constant pressure surface. Isotherms, thickness field; examples of geostrophic, gradient and thermal winds: slope of pressure system, streamline and Isotachs analysis. ❖ Western disturbance and its structure and associated weather, Waves in mid-latitude westerlies. ❖ Thunderstorm and severe local storm, synoptic conditions favourable for thunderstorm, concepts of triggering mechanism, conditional instability; Norwesters, dust storm, hail storm. Squall, tornado, microburst/cloudburst, landslide. ❖ Indian summer monsoon; S.W. Monsoon onset: semi permanent systems, Active and break monsoon, Monsoon depressions: MTC; Offshore troughs/vortices. Influence of extra tropical troughs and typhoons in northwest Pacific; withdrawal of S.W. Monsoon, Northeast monsoon, ❖ Tropical Cyclone: Life cycle, vertical and horizontal structure of TC, Its movement and intensification. Weather associated with TC. Easterly wave and its structure and associated weather. ❖ Jet Streams – WMO definition of Jet stream, different jet streams around the globe, Jet streams and weather ❖ Meso-scale meteorology, sea and land breezes, mountain/valley winds, mountain wave. ❖ Short range weather forecasting (Elementary ideas only); persistence, climatology and steering methods, movement and development of synoptic scale systems; Analogue techniques- prediction of individual weather elements, visibility, surface and upper level winds, convective phenomena.
    [Show full text]
  • ATM 316 - the “Thermal Wind” Fall, 2016 – Fovell
    ATM 316 - The \thermal wind" Fall, 2016 { Fovell Recap and isobaric coordinates We have seen that for the synoptic time and space scales, the three leading terms in the horizontal equations of motion are du 1 @p − fv = − (1) dt ρ @x dv 1 @p + fu = − ; (2) dt ρ @y where f = 2Ω sin φ. The two largest terms are the Coriolis and pressure gradient forces (PGF) which combined represent geostrophic balance. We can define geostrophic winds ug and vg that exactly satisfy geostrophic balance, as 1 @p −fv ≡ − (3) g ρ @x 1 @p fu ≡ − ; (4) g ρ @y and thus we can also write du = f(v − v ) (5) dt g dv = −f(u − u ): (6) dt g In other words, on the synoptic scale, accelerations result from departures from geostrophic balance. z R p z Q δ δx p+δp x Figure 1: Isobaric coordinates. It is convenient to shift into an isobaric coordinate system, replacing height z by pressure p. Remember that pressure gradients on constant height surfaces are height gradients on constant pressure surfaces (such as the 500 mb chart). In Fig. 1, the points Q and R reside on the same isobar p. Ignoring the y direction for simplicity, then p = p(x; z) and the chain rule says @p @p δp = δx + δz: @x @z 1 Here, since the points reside on the same isobar, δp = 0. Therefore, we can rearrange the remainder to find δz @p = − @x : δx @p @z Using the hydrostatic equation on the denominator of the RHS, and cleaning up the notation, we find 1 @p @z − = −g : (7) ρ @x @x In other words, we have related the PGF (per unit mass) on constant height surfaces to a \height gradient force" (again per unit mass) on constant pressure surfaces.
    [Show full text]
  • Wind Power Meteorology. Part I: Climate and Turbulence 3
    WIND ENERGY Wind Energ., 1, 2±22 (1998) Review Wind Power Meteorology. Article Part I: Climate and Turbulence Erik L. Petersen,* Niels G. Mortensen, Lars Landberg, Jùrgen Hùjstrup and Helmut P. Frank, Department of Wind Energy and Atmospheric Physics, Risù National Laboratory, Frederiks- borgvej 399, DK-4000 Roskilde, Denmark Key words: Wind power meteorology has evolved as an applied science ®rmly founded on boundary wind atlas; layer meteorology but with strong links to climatology and geography. It concerns itself resource with three main areas: siting of wind turbines, regional wind resource assessment and assessment; siting; short-term prediction of the wind resource. The history, status and perspectives of wind wind climatology; power meteorology are presented, with emphasis on physical considerations and on its wind power practical application. Following a global view of the wind resource, the elements of meterology; boundary layer meteorology which are most important for wind energy are reviewed: wind pro®les; wind pro®les and shear, turbulence and gust, and extreme winds. *c 1998 John Wiley & turbulence; extreme winds; Sons, Ltd. rotor wakes Preface The kind invitation by John Wiley & Sons to write an overview article on wind power meteorology prompted us to lay down the fundamental principles as well as attempting to reveal the state of the artÐ and also to disclose what we think are the most important issues to stake future research eorts on. Unfortunately, such an eort calls for a lengthy historical, philosophical, physical, mathematical and statistical elucidation, resulting in an exorbitant requirement for writing space. By kind permission of the publisher we are able to present our eort in full, but in two partsÐPart I: Climate and Turbulence and Part II: Siting and Models.
    [Show full text]
  • Thickness and Thermal Wind
    ESCI 241 – Meteorology Lesson 12 – Geopotential, Thickness, and Thermal Wind Dr. DeCaria GEOPOTENTIAL l The acceleration due to gravity is not constant. It varies from place to place, with the largest variation due to latitude. o What we call gravity is actually the combination of the gravitational acceleration and the centrifugal acceleration due to the rotation of the Earth. o Gravity at the North Pole is approximately 9.83 m/s2, while at the Equator it is about 9.78 m/s2. l Though small, the variation in gravity must be accounted for. We do this via the concept of geopotential. l A surface of constant geopotential represents a surface along which all objects of the same mass have the same potential energy (the potential energy is just mF). l If gravity were constant, a geopotential surface would also have the same altitude everywhere. Since gravity is not constant, a geopotential surface will have varying altitude. l Geopotential is defined as z F º ò gdz, (1) 0 or in differential form as dF = gdz. (2) l Geopotential height is defined as F 1 z Z º = ò gdz (3) g0 g0 0 2 where g0 is a constant called standard gravity, and has a value of 9.80665 m/s . l If the change in gravity with height is ignored, geopotential height and geometric height are related via g Z = z. (4) g 0 o If the local gravity is stronger than standard gravity, then Z > z. o If the local gravity is weaker than standard gravity, then Z < z.
    [Show full text]
  • Symmetric Stability/00176
    Encyclopedia of Atmospheric Sciences (2nd Edition) - CONTRIBUTORS’ INSTRUCTIONS PROOFREADING The text content for your contribution is in its final form when you receive your proofs. Read the proofs for accuracy and clarity, as well as for typographical errors, but please DO NOT REWRITE. Titles and headings should be checked carefully for spelling and capitalization. Please be sure that the correct typeface and size have been used to indicate the proper level of heading. Review numbered items for proper order – e.g., tables, figures, footnotes, and lists. Proofread the captions and credit lines of illustrations and tables. Ensure that any material requiring permissions has the required credit line and that we have the relevant permission letters. Your name and affiliation will appear at the beginning of the article and also in a List of Contributors. Your full postal address appears on the non-print items page and will be used to keep our records up-to-date (it will not appear in the published work). Please check that they are both correct. Keywords are shown for indexing purposes ONLY and will not appear in the published work. Any copy editor questions are presented in an accompanying Author Query list at the beginning of the proof document. Please address these questions as necessary. While it is appreciated that some articles will require updating/revising, please try to keep any alterations to a minimum. Excessive alterations may be charged to the contributors. Note that these proofs may not resemble the image quality of the final printed version of the work, and are for content checking only.
    [Show full text]
  • UNIVERSITY of CALIFORNIA SAN DIEGO Mesoscale Dynamics Of
    UNIVERSITY OF CALIFORNIA SAN DIEGO Mesoscale Dynamics of Atmospheric Rivers A dissertation submitted in partial satisfaction of the requirements for the degree Doctor of Philosophy in Oceanography by Reuben Demirdjian Committee in charge: F. Martin Ralph, Chair Joel Norris, Co-Chair Amato Evan Jan Kleissl Richard Rotunno Shang-Ping Xie 2020 Copyright Reuben Demirdjian, 2020 All rights reserved. The Dissertation of Reuben Demirdjian is approved, and it is acceptable in quality and form for publication on microfilm and electronically: _____________________________________________________________ _____________________________________________________________ _____________________________________________________________ _____________________________________________________________ _____________________________________________________________ Co-chair _____________________________________________________________ Chair University of California San Diego 2020 iii DEDICATION For my family (friends included) iv EPIGRAPH “Look again at that dot. That's here. That's home. That's us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives. The aggregate of our joy and suffering, thousands of confident religions, ideologies, and economic doctrines, every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant, every young couple in love, every mother and father, hopeful child, inventor and explorer, every teacher of morals, every
    [Show full text]
  • Lecture 4: Pressure and Wind
    LectureLecture 4:4: PressurePressure andand WindWind Pressure, Measurement, Distribution Forces Affect Wind Geostrophic Balance Winds in Upper Atmosphere Near-Surface Winds Hydrostatic Balance (why the sky isn’t falling!) Thermal Wind Balance ESS55 Prof. Jin-Yi Yu WindWind isis movingmoving air.air. ESS55 Prof. Jin-Yi Yu ForceForce thatthat DeterminesDetermines WindWind Pressure gradient force Coriolis force Friction Centrifugal force ESS55 Prof. Jin-Yi Yu ThermalThermal EnergyEnergy toto KineticKinetic EnergyEnergy Pole cold H (high pressure) pressure gradient force (low pressure) Eq warm L (on a horizontal surface) ESS55 Prof. Jin-Yi Yu GlobalGlobal AtmosphericAtmospheric CirculationCirculation ModelModel ESS55 Prof. Jin-Yi Yu Sea Level Pressure (July) ESS55 Prof. Jin-Yi Yu Sea Level Pressure (January) ESS55 Prof. Jin-Yi Yu MeasurementMeasurement ofof PressurePressure Aneroid barometer (left) and its workings (right) A barograph continually records air pressure through time ESS55 Prof. Jin-Yi Yu PressurePressure GradientGradient ForceForce (from Meteorology Today) PG = (pressure difference) / distance Pressure gradient force force goes from high pressure to low pressure. Closely spaced isobars on a weather map indicate steep pressure gradient. ESS55 Prof. Jin-Yi Yu ThermalThermal EnergyEnergy toto KineticKinetic EnergyEnergy Pole cold H (high pressure) pressure gradient force (low pressure) Eq warm L (on a horizontal surface) ESS55 Prof. Jin-Yi Yu Upper Troposphere (free atmosphere) e c n a l a b c i Surface h --Yi Yu p o r ESS55 t Prof. Jin s o e BalanceBalance ofof ForceForce inin thetheg HorizontalHorizontal ) geostrophic balance plus frictional force Weather & Climate (high pressure)pressure gradient force H (from (low pressure) L Can happen in the tropics where the Coriolis force is small.
    [Show full text]
  • ATM 241, Spring 2020 Lecture 5 the General Circulation
    ATM 241, Spring 2020 Lecture 5 The General Circulation Paul A. Ullrich [email protected] Marshall & PlumB Ch. 5, 8 Paul Ullrich The General Circulation Spring 2020 In this section… Definitions Questions • Geostrophic wind • What are the dominant forms of balance in • Polar cell the atmosphere? • • Ferrel cell What is the primary driver of the meridional structure of the atmosphere? • Hadley cell • What are the four mechanisms for meridional • Intertropical Convergence Zone heat transport? • Jet streams • Where are these mechanisms dominant? • Atmospheric rivers • What are the key features of the Hadley cell? • Thermal wind • What are the key features of the Farrel cell? • Veering winds • How are meridional temperatures and zonal • Backing winds wind speeds connected? Paul Ullrich The General Circulation Spring 2020 Review: Balanced Flow Paul Ullrich The General Circulation Spring 2020 Atmosphere in Balance The atmosphere, to a large degree, is in a state of equilibrated balance. Processes in the atmosphere act to smooth out perturbations from that equilibrium through geostrophic adjustment (adjustment towards geostrophic balance). The two dominant balances in the atmosphere are: • Hydrostatic Balance • Balance between vertical pressure gradient force and gravity • Holds because vertical velocities are small • Geostrophic Balance • Balance between horizontal pressure gradient force and Coriolis force • Holds in the midlatitudes where Coriolis is sufficiently large Paul Ullrich The General Circulation Spring 2020 Atmosphere in Balance
    [Show full text]