DOCSLIB.ORG

Instability, Cyclogenesis, and Anticyclogenesis the Concept of Instability ! When Pressure Systems Intensify, the Increased Pressure Gradient Increases Wind Speeds

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Instability, Cyclogenesis, and Anticyclogenesis the Concept of Instability ! When Pressure Systems Intensify, the Increased Pressure Gradient Increases Wind Speeds Instability, Cyclogenesis, and Anticyclogenesis The concept of instability ! When pressure systems intensify, the increased pressure gradient increases wind speeds ! Two ways this happens in the atmosphere: ! Conversion of available potential energy to kinetic energy through the lifting of warm air and sinking of cold air Baroclinic instability ! Conversion of kinetic energy of the mean flow into the kinetic energy of the growing disturbance Barotropic instability Barotropic instability ! [1.94] ! Discovered by Kuo in the late 1940’s ( . f ..,. C+ I ! A necessary condition for barotropic instability in a zonal current is where the gradient in absolute vorticity vanishes ! This condition is often met near jets where u o nlit ,clonic g . hear s id e of jet and the background flow ! go to zero and y the wave’s ! can grow - . ." Q"hcyclon,c - Sh OOf . ,,'" '--- -. Baroclinic instability ! Consider a simple example of a coin sitting on a table ! Standing on its side, a z coin has available 0 potential energy given by its mass times gravity times the height z0 of the center of mass (above right) minus the potential energy of the coin sitting on its side (below right) Baroclinic instability (continued) ! “Tipping” the coin over will convert available potential energy to kinetic energy ! The coin still has some z0 potential energy, but it is unavailable to the system ! The earth’s atmosphere is more complicated, because it is compressible and the earth rotates Sanders analytic model ! We will use an analytic model developed by Fred Sanders in 1971 to understand the baroclinic instability process on cyclones in the real atmosphere ! To the board! y L 0.0 0.0 4"-'1',---- 0 0 /---...... , / 6' / '°0 0 \ 0 o <D L I ell I '0 10.2 -10.2 0 \ / 0 / 0 "- '-.... ---/' ,,,, ,,,, x L L 0 L L -"2 -4" 4" "2 Figure 1.27 Isopleths of 1000-mb height at intervals of 6 dam in Sanders' analytic 2 model. <1>0 = 1020 m S-2, and A = L/4. The abscissa is the x direction; the ordinate is the y direction. is an infinite checkerboard of warm and cold perturbation centers - [t cos(2.7l'/ L)x cos(2.7l'/ L)y] superimposed upon a field of uniform meridional temperature gradient (-ay). The x direction points toward the east, and the y direction points toward the north. The parameter L is the (isotropic) horizontal wavelength, and A is the phase lag of the lOOO-mb temperature field y .L.... 0 f 0 ci \ 0 N 0 N J L "'4" x L L o L L -"2 "'4" 4" "2 Figure 1.28 Isotherms at 1000 mb in °C (solid lines) in Sanders' analytic model. 5 1 a = 1.0 x 10- °C m- , f = 10°C, and L = 3500 km. The abscissa is the x direction; the ordinate is the y direction. [1.30] y h 4 552. ...r /' 0 H 576. 56". _h 4 X l l 0 l -2 -'4 '4 2 Figure 1.30 500-mb height at intervals of 6 dam (solid lines) in Sanders' analytic model. The value of ll' is 0.722, and «11m (500 mb)/g =5555 m. The abscissa is the x direction; the ordinate is the y direction. 500 hPa height at intervals of 6 dm in Sanders’ analytic model. (" = 0.722, !m/g = 5555 m) ! Derivations on board – see text / / / I. .... .., / L (103 km) Figure 'l.96 Deepening rate (a<l>/at) of the 1000-mb cyclone as a function of wavelength (L) and meridional temperature gradient (ordinate) for selected values of the vorticity-stability parameter and for f = 1°C. The isopleths are labeled in 3 2 units of 10- m S-3. The dashed, solid, and dotted lines are for values of the vorticity-stability parameter as in Fig. 1.39. The longer dashed lines are loci of the wavelength of maximum deepening rate (from Sanders, 1971). (Courtesy of the American Meteorological Society) Sanders’ analytic model: height tendency "# & L ( 2*% $ %, 0, 1000 hPa = (K13P13 $ K14 P14 )sin "t ' 2 ) L ˆ Physical effect: vertical motion accompanying f0RaTL vertical motion due to advection of relative vorticity K13 = 4"T0# by the thermal wind ! Related to L, static stability ", and meridional temperature gradient a ! 2 ˆ 3 Physical effect: vertical motion accompanying f0 T" L advection of the earth’s vorticity (a.k.a. beta effect) K14 = 3 4(2#) T0$ by the thermal wind Related to L3, static stability ", and meridional temperature gradient a. ! Analysis ! If there were no beta effect, troughs of all wavelengths would deepen ! The wavelength that this happens is called the long wave cutoff. ! At short wavelengths, advection of geostrostropic vorticity is dominant – but Q-G assumptions get violated. ! Sanders’ model shows deepening rate going to 0 – short wave cutoff ! The most rapid intensification occurs at wavelengths between 1500 and 3000 km Analysis, cont. ! Since K13 is proportional to a and inversely proportional to ", baroclinic instability increases with meridional temperature gradient, and decreases with static stability ! This makes sense since the thermal wind is proportional to a, and the magnitude of vertical motion predicted by the omega equation is inversely proportional to static stability ! The magnitude of the vertical circulation that lifts/ sinks warm/cold air (converting APE to KE) is proportional to a and 1/"# ! Seasonal effects? Baroclinic instability and the flow pattern ! Sanders’ model is limited for many reasons ! Why? ! Must be careful in interpreting its solution ! It has been noted since the 1930s that the shape of the troughs have something to do with their likelihood to produce a cyclone ! Bjerknes (1954) and Polster (1960) identified that the majority of cyclones intensify under diffluent troughs ! Only a few occur under confluent troughs ! Why? Diffluent Confluent Tilting troughs ! Waves in the westerlies whose axes slope in the direction of the flow with latitude are called positively tilted. ! Associated with poleward fluxes of angular momentum ! Negatively tilted troughs slope against the direction of the flow with latitude in the westerlies. ! Associated with equatorward fluxes of angular momentum, also removing momentum from westerly jet and growing system due to barotropic instability Why do waves tilt? ! Consider the Rossby wave phase dispersion relation: U " # c = 2 % 2$' & L ( ! What happens when ! ! U increases with latitude? ! U decreases with latitude? ! Fractured waves? Fractured trough Cont. Cont. Bombs ! Explosive cyclogenesis occurs most frequently over the ocean during the cold season. Definition: Pressure fall of 1 mb/h for 24 hours (termed a bergeron) Vertical cross section through a bomb Seclusion Polar low/instant occlusion Dryline-front intersection low Thermal low Subtropical high Idealized structures of baroclinic waves in the westerlies ! Based on surface obs in Europe, Bjerknes, Bergeron, and Solberg of the Bergen “Norwegian School” formulated the Polar-Front Theory: cyclones form on fronts ! Now, it is generally accepted that surface cyclones often*** intensify when DPVA downstream of an upper level trough encounters a frontal zone at the surface (Palmen and Newton 1955) ***not always! East coast lows Other types of cyclones ! Colorado lows ! Alps lows ! Flow over topography, subsidence generates cyclonic low level relative vorticity -> not sufficient to generate a propagating cyclone ! Short wave aloft triggers cyclogenesis ! Low initially moves southeasterly (higher terrain to the right combined with warm air advection to the east) ! Low then moves more easterly apart from topography, usually towards Chicago in North America. Homework ! Create a Miller-type Diagram consisting of the key parameters conducive for severe weather for the period 18Z-06Z tomorrow covering the region outlined on the SPC risk map ! Write a SPC-style mesoscale discussion which textually describes the ingredients regarding the potential for severe weather during this period. Use the convective forecasting handbook. ! Submit via COMPASS as a PPT file, due tomorrow at 21Z .
Load more

Recommended publications
  • Soaring Weather
    Chapter 16 SOARING WEATHER While horse racing may be the "Sport of Kings," of the craft depends on the weather and the skill soaring may be considered the "King of Sports." of the pilot. Forward thrust comes from gliding Soaring bears the relationship to flying that sailing downward relative to the air the same as thrust bears to power boating. Soaring has made notable is developed in a power-off glide by a conven­ contributions to meteorology. For example, soar­ tional aircraft. Therefore, to gain or maintain ing pilots have probed thunderstorms and moun­ altitude, the soaring pilot must rely on upward tain waves with findings that have made flying motion of the air. safer for all pilots. However, soaring is primarily To a sailplane pilot, "lift" means the rate of recreational. climb he can achieve in an up-current, while "sink" A sailplane must have auxiliary power to be­ denotes his rate of descent in a downdraft or in come airborne such as a winch, a ground tow, or neutral air. "Zero sink" means that upward cur­ a tow by a powered aircraft. Once the sailcraft is rents are just strong enough to enable him to hold airborne and the tow cable released, performance altitude but not to climb. Sailplanes are highly 171 r efficient machines; a sink rate of a mere 2 feet per second. There is no point in trying to soar until second provides an airspeed of about 40 knots, and weather conditions favor vertical speeds greater a sink rate of 6 feet per second gives an airspeed than the minimum sink rate of the aircraft.
    [Show full text]
  • CALIFORNIA STATE UNIVERSITY, NORTHRIDGE FORECASTING CALIFORNIA THUNDERSTORMS a Thesis Submitted in Partial Fulfillment of the Re
    CALIFORNIA STATE UNIVERSITY, NORTHRIDGE FORECASTING CALIFORNIA THUNDERSTORMS A thesis submitted in partial fulfillment of the requirements For the degree of Master of Arts in Geography By Ilya Neyman May 2013 The thesis of Ilya Neyman is approved: _______________________ _________________ Dr. Steve LaDochy Date _______________________ _________________ Dr. Ron Davidson Date _______________________ _________________ Dr. James Hayes, Chair Date California State University, Northridge ii TABLE OF CONTENTS SIGNATURE PAGE ii ABSTRACT iv INTRODUCTION 1 THESIS STATEMENT 12 IMPORTANT TERMS AND DEFINITIONS 13 LITERATURE REVIEW 17 APPROACH AND METHODOLOGY 24 TRADITIONALLY RECOGNIZED TORNADIC PARAMETERS 28 CASE STUDY 1: SEPTEMBER 10, 2011 33 CASE STUDY 2: JULY 29, 2003 48 CASE STUDY 3: JANUARY 19, 2010 62 CASE STUDY 4: MAY 22, 2008 91 CONCLUSIONS 111 REFERENCES 116 iii ABSTRACT FORECASTING CALIFORNIA THUNDERSTORMS By Ilya Neyman Master of Arts in Geography Thunderstorms are a significant forecasting concern for southern California. Even though convection across this region is less frequent than in many other parts of the country significant thunderstorm events and occasional severe weather does occur. It has been found that a further challenge in convective forecasting across southern California is due to the variety of sub-regions that exist including coastal plains, inland valleys, mountains and deserts, each of which is associated with different weather conditions and sometimes drastically different convective parameters. In this paper four recent thunderstorm case studies were conducted, with each one representative of a different category of seasonal and synoptic patterns that are known to affect southern California. In addition to supporting points made in prior literature there were numerous new and unique findings that were discovered during the scope of this research and these are discussed as they are investigated in their respective case study as applicable.
    [Show full text]
  • The Iberian Peninsula Thermal Low
    Q. J. R. Meteorol. Soc. (2003), 129, pp. 1491–1511 doi: 10.1256/qj.01.189 The Iberian Peninsula thermal low 1 2 By KLAUS P. HOINKA ¤ and MANUEL DE CASTRO 1Institut fur¨ Physik der Atmosph¨are, DLR, Oberpfaffenhofen, Germany 2Dpto. Ciencias Ambientales, Universidad Castilla-La Mancha, Toledo, Spain (Received 9 November 2001; revised 26 September 2002) SUMMARY Statistics of the thermal low above the Iberian Peninsula are presented for the period between 1979 and 1993, based on gridded data from the European Centre for Medium-Range Weather Forecasts reanalysis project. The sample of days with a thermal low above the Iberian Peninsula was selected objectively using criteria applied to mean-sea-level pressure and 925 hPa geopotential elds. The synoptic- and regional-scale horizontal structure is characterized by the climatology of the 500 hPa geopotential and mean-sea-level pressure distributions. The diurnal evolution of the mean-sea-level pressure is portrayed by mean elds at 00, 06, 12 and 18 UTC. The climatological vertical structure of the thermal low is shown by relation to meridional and zonal cross- sections passing through the thermal low’s centre. The diurnal evolution of the divergence, relative vorticity, potential temperature and vertical velocity is investigated. Statistics are presented also for the monthly frequency, geographical location, vertical extent and intensity of the Iberian thermal low. KEYWORDS: ERA data Heated low 1. INTRODUCTION A thermal low is a warm, shallow, non-frontal depression which forms above continental regions, mostly in the subtropics, but also in the lower midlatitudes. They form mostly during summer months because of the intense surface heating over land.
    [Show full text]
  • Waves in the Westerlies
    Operational Weather Analysis … www.wxonline.info Chapter 9 Waves in the Westerlies Operational meteorologists track middle latitude disturbances in the middle to upper troposphere as part of their analysis of the atmosphere. This chapter describes these waves and highlights the importance of these waves to day-to-day weather changes at the Earth’s surface. The Westerlies Atmospheric flow above the Earth’s surface in the middle latitudes is primarily westerly. That is, the winds have a prevailing westerly component with numerous north and south meanders that impose wave-like undulations upon the basic west- to-east flow. This flow extends from the subtropical high pressure belt poleward to around 65 degrees latitude. A glance at any upper level chart from 700 mb upward to 200 mb shows that the westerlies dominate in the middle and upper troposphere. The term westerlies will refer to this layer unless otherwise specified. Upper Level Charts The westerlies are easily identified on charts of constant pressure in the middle to upper troposphere. That is, charts are prepared from upper level data at specified pressure levels (called standard levels). Traditionally, lines are drawn on these charts to represent the height of the pressure surface above mean sea level, temperature, and, on some charts, wind speed. With modern computer workstations, any observed or derived parameter may be drawn on an upper level chart. Standard levels include charts for 925, 850, 700, 500, 300, 250, 200, 150 and 100 mb. For our discussion of the westerlies, only levels from 700 mb upward to 200 mb will be considered.
    [Show full text]
  • An Examination of the Mesoscale Environment of the James Island Memorial Day Tornado
    19.6 AN EXAMINATION OF THE MESOSCALE ENVIRONMENT OF THE JAMES ISLAND MEMORIAL DAY TORNADO STEVEN B. TAYLOR NOAA/NATIONAL WEATHER SERVICE FORECAST OFFICE CHARLESTON, SC 1. INTRODUCTION conditions also induced weak cyclogenesis along the front near the vicinity of KVDI. By 1200 UTC A cluster of severe thunderstorms the surface low was located between KNBC and moved across portions of south coastal South KCHS. This low and its influences on the Carolina during the early morning hours of 30 kinematic environment as well as the eventual May 2006. Around 1135 UTC, a severe position of the surface frontal boundary will prove thunderstorm spawned an F-1 tornado in the to be the main contributing factors leading to the James Island community of Charleston, SC. The development of the James Island tornado. tornado produced wind and structural damage as it moved rapidly NE through several residential neighborhoods. The tornado was on the ground for approximately 0.1 mi before it emerged into the Atlantic Ocean as a large waterspout near the entrance to the Charleston Harbor. Timely tornado warnings were issued by the NOAA/National Weather Service Forecast Office (WFO) in Charleston, SC (CHS), despite the event occurring during a climatologically rare time of day. This study will concentrate on the mesoscale factors that supported the genesis of the tornado and its parent severe thunderstorm. Radar data generated by the KCLX WSR-88D will also be presented. 2. SYNOPTIC ENVIRONMENT The synoptic environment supported the development of scattered convective precipitation Fig 1. Map of eastern SC/GA across much of the coastal areas of the Carolinas and Georgia.
    [Show full text]
  • Dynamical and Synoptic Characteristics of Heavy Rainfall Episodes in Southern Brazil
    598 MONTHLY WEATHER REVIEW VOLUME 135 Dynamical and Synoptic Characteristics of Heavy Rainfall Episodes in Southern Brazil MATEUS DA SILVA TEIXEIRA Instituto Nacional de Pesquisas Espaciais, Sdo Jose dos Campos, Sdo Paulo, Brazil PRAKKI SATYAMURTY Centro de Previsao de Tempo e Estudos Climdticos/INPE,Sio Jose dos Campos, Sdo Paulo, Brazil (Manuscript received 21 December 2005, in final form 19 May 2006) ABSTRACT The dynamical and synoptic characteristics that distinguish heavy rainfall episodes from nonheavy rainfall episodes in southern Brazil are discussed. A heavy rainfall episode is defined here as one in which the 2 50 mm day-' isohyet encloses an area of not less than [0 000 km in the domain of southern Brazil. One hundred and seventy such events are identified in the 11-yr period'of 1991-2001. The mean flow patterns in the period of 1-3 days preceding the episodes show some striking synoptic-scale features that may be considered forerunners of these episodes: (i) a deepening midtropospheric trough in the eastern South Pacific approaches the continent 3 days before, (ii) a surface low,pressure center forms in northern Ar- gentina 1 day before, (iii) a northerly low-level jet develops over Paraguay 2 days before, and (iv) a strong moisture flux convergence over southern Brazil becomes prominent 1 day before the episode. A parameter called rainfall quantity, defined as the product .of the area enclosed by the 50 mm day-' isohyet and the average rainfall intensity, is,correlated with fields of atmospheric variables such as 500-hPa geopotential and 850-hPa meridional winds. Significant lag correlations show that the anomalies of some atmospheric vari- ables could be viewed as precursors of heavy rainfall in southern Brazil that can be explored for use in improving the forecasts.
    [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]
  • The Effects of Diabatic Heating on Upper
    THE EFFECTS OF DIABATIC HEATING ON UPPER- TROPOSPHERIC ANTICYCLOGENESIS by Ross A. Lazear A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science (Atmospheric and Oceanic Sciences) at the UNIVERSITY OF WISCONSIN - MADISON 2007 i Abstract The role of diabatic heating in the development and maintenance of persistent, upper- tropospheric, large-scale anticyclonic anomalies in the subtropics (subtropical gyres) and middle latitudes (blocking highs) is investigated from the perspective of potential vorticity (PV) non-conservation. The low PV within blocking anticyclones is related to condensational heating within strengthening upstream synoptic-scale systems. Additionally, the associated convective outflow from tropical cyclones (TCs) is shown to build upper- tropospheric, subtropical anticyclones. Not only do both of these large-scale flow phenomena have an impact on the structure and dynamics of neighboring weather systems, and consequently the day-to-day weather, the very persistence of these anticyclones means that they have a profound influence on the seasonal climate of the regions in which they exist. A blocking index based on the meridional reversal of potential temperature on the dynamic tropopause is used to identify cases of wintertime blocking in the North Atlantic from 2000-2007. Two specific cases of blocking are analyzed, one event from February 1983, and another identified using the index, from January 2007. Parallel numerical simulations of these blocking events, differing only in one simulation’s neglect of the effects of latent heating of condensation (a “fake dry” run), illustrate the importance of latent heating in the amplification and wave-breaking of both blocking events.
    [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]
  • Chapter 10: Cyclones: East of the Rocky Mountain
    Chapter 10: Cyclones: East of the Rocky Mountain • Environment prior to the development of the Cyclone • Initial Development of the Extratropical Cyclone • Early Weather Along the Fronts • Storm Intensification • Mature Cyclone • Dissipating Cyclone ESS124 1 Prof. Jin-Yi Yu Extratropical Cyclones in North America Cyclones preferentially form in five locations in North America: (1) East of the Rocky Mountains (2) East of Canadian Rockies (3) Gulf Coast of the US (4) East Coast of the US (5) Bering Sea & Gulf of Alaska ESS124 2 Prof. Jin-Yi Yu Extratropical Cyclones • Extratropical cyclones are large swirling storm systems that form along the jetstream between 30 and 70 latitude. • The entire life cycle of an extratropical cyclone can span several days to well over a week. • The storm covers areas ranging from several Visible satellite image of an extratropical cyclone hundred to thousand miles covering the central United States across. ESS124 3 Prof. Jin-Yi Yu Mid-Latitude Cyclones • Mid-latitude cyclones form along a boundary separating polar air from warmer air to the south. • These cyclones are large-scale systems that typically travels eastward over great distance and bring precipitations over wide areas. • Lasting a week or more. ESS124 4 Prof. Jin-Yi Yu Polar Front Theory • Bjerknes, the founder of the Bergen school of meteorology, developed a polar front theory during WWI to describe the formation, growth, and dissipation of mid-latitude cyclones. Vilhelm Bjerknes (1862-1951) ESS124 5 Prof. Jin-Yi Yu Life Cycle of Mid-Latitude Cyclone • Cyclogenesis • Mature Cyclone • Occlusion ESS124 6 (from Weather & Climate) Prof. Jin-Yi Yu Life Cycle of Extratropical Cyclone • Extratropical cyclones form and intensify quickly, typically reaching maximum intensity (lowest central pressure) within 36 to 48 hours of formation.
    [Show full text]
  • Chapter 16 Extratropical Cyclones
    CHAPTER 16 SCHULTZ ET AL. 16.1 Chapter 16 Extratropical Cyclones: A Century of Research on Meteorology’s Centerpiece a b c d DAVID M. SCHULTZ, LANCE F. BOSART, BRIAN A. COLLE, HUW C. DAVIES, e b f g CHRISTOPHER DEARDEN, DANIEL KEYSER, OLIVIA MARTIUS, PAUL J. ROEBBER, h i b W. JAMES STEENBURGH, HANS VOLKERT, AND ANDREW C. WINTERS a Centre for Atmospheric Science, School of Earth and Environmental Sciences, University of Manchester, Manchester, United Kingdom b Department of Atmospheric and Environmental Sciences, University at Albany, State University of New York, Albany, New York c School of Marine and Atmospheric Sciences, Stony Brook University, State University of New York, Stony Brook, New York d Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland e Centre of Excellence for Modelling the Atmosphere and Climate, School of Earth and Environment, University of Leeds, Leeds, United Kingdom f Oeschger Centre for Climate Change Research, Institute of Geography, University of Bern, Bern, Switzerland g Atmospheric Science Group, Department of Mathematical Sciences, University of Wisconsin–Milwaukee, Milwaukee, Wisconsin h Department of Atmospheric Sciences, University of Utah, Salt Lake City, Utah i Deutsches Zentrum fur€ Luft- und Raumfahrt, Institut fur€ Physik der Atmosphare,€ Oberpfaffenhofen, Germany ABSTRACT The year 1919 was important in meteorology, not only because it was the year that the American Meteorological Society was founded, but also for two other reasons. One of the foundational papers in extratropical cyclone structure by Jakob Bjerknes was published in 1919, leading to what is now known as the Norwegian cyclone model. Also that year, a series of meetings was held that led to the formation of organizations that promoted the in- ternational collaboration and scientific exchange required for extratropical cyclone research, which by necessity involves spatial scales spanning national borders.
    [Show full text]
  • Tropical Cyclone: Climatology
    ESCI 344 – Tropical Meteorology Lesson 5 – Tropical Cyclones: Climatology References: A Global View of Tropical Cyclones, Elsberry (ed.) The Hurricane, Pielke Tropical Cyclones: Their evolution, structure, and effects, Anthes Forecasters’ Guide to Tropical Meteorology, Atkinsson Forecasters Guide to Tropical Meteorology (updated), Ramage Global Guide to Tropical Cyclone Forecasting, Holland (ed.) Reading: Introduction to the Meteorology and Climate of the Tropics, Chapter 9 A Global View of Tropical Cyclones, Chapter 3 REQUIREMENTS FOR FORMATION In order for a tropical cyclone to form, the following general conditions must be present: Deep, warm ocean mixed layer. ◼ Sea-surface temperature at least 26.5C. ◼ Mixed layer depth of 45 meters or more. Relative maxima in absolute vorticity in the lower troposphere ◼ Need a preexisting cyclonic disturbance. ◼ Must be more than a few degrees of latitude from the Equator. Small values of vertical wind shear. ◼ Disturbance must be in deep easterly flow, or in a region of light upper- level winds. Mean upward vertical motion with humid mid-levels. GLOBAL CLIMATOLOGY Note: Most of the statistics given in this section are from Gray, W.M., 1985: Tropical Cyclone Global Climatology, WMO Technical Document WMO/TD-72, Vol. I, 1985. About 80 tropical cyclones per year world-wide reach tropical storm strength ( 34 kts). About 50 – 55 each year world-wide reach hurricane/typhoon strength ( 64 kts). The rate of occurrence globally is very steady. Global average annual variation is small (about 7%). Extreme variations are in the range of 16 to 22%. Variability within a particular region is much larger than global variability. Most (87%) form within 20 of the Equator.
    [Show full text]