DOCSLIB.ORG

Prmet Ch11 General Circulation

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Prmet Ch11 General Circulation This work is made available under the Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-nd/3.0/ or send a letter to Creative Commons, 444 Castro Street, Suite 900, Mountain View, California, 94041, USA. Additional permissions: Individuals may print this work for their own use. Instructors may have printed cop- ies made for their students. This work is available at http://www.eos.ubc.ca/books/Practical_Meteorology/ Copyright © 2015 by Roland Stull. Practical Meteorology: An Algebra-based Survey of Atmospheric Science. “Practical Meteorology: An Algebra-based Survey of Atmospheric Science” by Roland Stull is licensed under a Creative Commons At- tribution-NonCommercial-ShareAlike 4.0 International License. View this license at http://creativecommons.org/licenses/by-nc-sa/4.0/ . This work is available at http://www.eos.ubc.ca/books/Practical_Meteorology/ . 11 GENERAL CIRCULATION Contents A spatial imbalance between radiative inputs and outputs exists for the earth-ocean-atmosphere Key Terms 330 system. The earth loses energy at all latitudes due A Simplified Description of the Global Circulation 330 to outgoing infrared (IR) radiation. Near the trop- Near the Surface 330 ics, more solar radiation enters than IR leaves, hence Upper-troposphere 331 there is a net input of radiative energy. Near Earth’s Vertical Circulations 332 poles, incoming solar radiation is too weak to totally Monsoonal Circulations 333 offset the IR cooling. The net result is differential Radiative Differential Heating 334 heating, creating warm equatorial air and cold po- North-South Temperature Gradient 335 lar air (Fig. 11.1a). Global Radiation Budgets 336 This imbalance drives the global-scale general Radiative Forcing by Latitude Belt 338 circulation of winds. Such a circulation is a fluid- General Circulation Heat Transport 338 dynamical analogy to Le Chatelier’s Principle of Pressure Profiles 340 chemistry. Namely, an imbalanced system reacts Non-hydrostatic Pressure Couplets 340 in a way to partially counteract the imbalance. The Hydrostatic Thermal Circulations 341 continued destabilization by radiation causes a gen- Geostrophic Wind & Geostrophic Adjustment 343 eral circulation of winds that is unceasing. Ageostrophic Winds at the Equator 343 You might first guess that buoyancy causes air Definitions 343 in the warm regions to rise, while cold air near Geostrophic Adjustment - Part 1 344 the poles sink (Fig. 11.1b). Instead, the real general Thermal Wind Effect 345 circulation has three bands of circulations in the Definition of Thickness 346 Northern Hemisphere (Fig. 11.1c), and three in the Thermal-wind Components 346 Case Study 348 Southern. In this chapter, we will identify charac- Thermal Wind & Geostrophic Adjust. - Part 2 349 teristics of the general circulation, explain why they exist, and learn how they work. Explaining the General Circulation 350 Low Latitudes 350 High Latitudes 352 B DPPM C DPPM Mid-latitudes 352 Monsoon 356 Jet Streams 357 XBSN XBSN Baroclinicity & the Polar Jet 359 Angular Momentum & Subtropical Jet 360 XBSN XBSN Types of Vorticity 362 Relative-vorticity Definition 362 Absolute-vorticity Definition 363 DPPM DPPM Potential-vorticity Definition 363 Isentropic Potential Vorticity Definition 364 D DPPM 1PMBSDFMM Horizontal Circulation 365 3PTTCZXBWFT Extratropical Ridges & Troughs 367 Barotropic Instability 367 )BEMFZDFMM Baroclinic Instability 371 XBSN XBSN Meridional Transport by Rossby Waves 374 )BEMFZDFMM Three-band Global Circulation 376 3PTTCZXBWFT A Metric for Vertical Circulation 377 1PMBSDFMM Effective Vertical Circulation 377 DPPM Earth image Ekman Spiral of Ocean Currents 378 Figure 11.1 credit: NASA Review 379 Radiative imbalances create (a) warm tropics and cold poles, in- Homework Exercises 380 ducing (b) buoyant circulations. Add Earth’s rotation, and (c) three circulation bands form in each hemisphere. 329 330 cHAPTER 11 • General CIRCULATION OPSUIQPMF / Key Terms QPMBS IJHIMBUJUVEFT Lines of constant latitude are called parallels, MBUJUVEF X TVCQPMBS and winds parallel to the parallels are identified as MP G / O zonal flows (Fig. 11.2). Lines of constant longitude M JB B E NJE J O FYUSBUSPQJDBM are called meridians, and winds parallel to the me- S P MBUJUVEFT F J E ridians are known as meridional flows. N J S F TVCUSPQJDBM Between latitudes of 30° and 60° are the mid- / N MPXMBUJUVEFT latitudes. High latitudes are 60° to 90°, and low USPQJDBMPS latitudes are 0° to 30°. Each 1° of latitude = 111 km. FRVBUPS FRVJUPSJBM Tropics, subtropics, subpolar, and polar re- [POBMGMPX MPXMBUJUVEFT gions are as shown in Fig. 11.2. Regions not in the TVCUSPQJDBM tropics are called extratropical; namely, poleward UIQBSBMMFM 8 of about 30°N and about 30°S. M 4 8 P NJE O FYUSBUSPQJDBM For example, tropical cyclones such as hur- H MBUJUVEFT J UV ricanes are in the tropics. Low-pressure centers 4 E F (lows, as indicated by L on weather maps) outside TVCQPMBS IJHIMBUJUVEFT of the tropics are called extratropical cyclones. QPMBS In many climate studies, data from the months of June, July, and August (JJA) are used to repre- 4 sent conditions in N. Hemisphere summer (and S. TPVUIQPMF Hemisphere winter). Similarly, December, January, February (DJF) data are used to represent N. Hemi- Figure 11.2 sphere winter (and S. Hemisphere summer). Global key terms. A SCIENTIFIC PERSPECTiVe • idealiza- tions of nature A simplified descripTion of The Natural atmospheric phenomena often involve the GlobAl circulation superposition of many different physical processes and scales of motion. Large-scale average conditions Consider a hypothetical rotating planet with are said to be caused by zeroth-order processes. no contrast between continents and oceans. The Dominant variations about the mean are controlled climatological average (average over 30 years; by first-order processes. Finer details are caused see the Climate chapter) winds in such a simpli- by higher-order processes. Sometimes insight is possible by stripping away fied planet would have characteristics as sketched the higher-order processes and focusing on one or in Figs. 11.3. Actual winds on any day could dif- two lower orders. Equations that describe such sim- fer from this climatological average due to transient plified physics are known as toy models. With the weather systems that perturb the average flow. Also, right simplifications, some toy models admit analyti- monthly-average conditions tend to shift toward the cal solutions. Compare this to the unsimplified phys- summer hemisphere (e.g., the circulation bands shift ics, which might be too complicated to solve analyti- northward during April through September). cally (although numerical solutions are possible). A rotating spherical Earth with no oceans and with uniform temperature is one example of a zeroth- near the surface order toy model. A first-order toy model might add Near-surface average winds are sketched in Fig. the north-south temperature variation, while neglect- 11.3a. At low latitudes are broad bands of persistent ing east-west and continent-ocean variations. With easterly winds (U ≈ –7 m s–1) called trade winds, even more sophistication, seasonal or monthly varia- named because the easterlies allowed sailing ships tions might be explained. We will take the approach to conduct transoceanic trade in the old days. in this chapter to start with zeroth-order models to These trade winds also blow toward the equa- focus on basic climate concepts, and then gradually tor from both hemispheres, and the equatorial belt add more realism. John Harte (1988) wrote a book demonstrating the of convergence is called the intertropical conver- utility of such toy models. It is “Consider a Spherical gence zone (ITCZ). On average, the air at the ITCZ Cow”, by University Science Books. 283 pages. is hot and humid, with low pressure, strong upward R. STULL • PraCTICAL METEOROLOGY 331 air motion, heavy convective (thunderstorm) pre- B /FBS4VSGBDF cipitation, and light to calm winds except in thun- 1PMBS)JHI derstorms. This equatorial trough (low-pressure ) belt) was called the doldrums by sailors whose - 4VCQPMBS-PXT - - / sailing ships were becalmed there for many days. At 30° latitude are belts of high surface pressure called subtropical highs (Fig. 11.3a). In these belts ) - 8FTUFSMJFT are hot, dry, cloud-free air descending from higher in the troposphere. Surface winds in these belts are ) ) 4VCUSPQJDBM)JHIT ) ) / also calm on average. In the old days, becalmed sail- 5SBEF8JOET ing ships would often run short of drinking water, /PSUI&BTUFSMJFT causing horses on board to die and be thrown over- board. Hence, sailors called these miserable places - EPMESVNT - *5$; - DBMN - the horse latitudes. On land, many of the world’s 4PVUI&BTUFSMJFT deserts are near these latitudes. 5SBEF8JOET In mid-latitudes are transient centers of low pres- sure (mid-latitude cyclones, L) and high pressure ) ) 4VCUSPQJDBM)JHIT ) ) 4 (anticyclones, H). Winds around lows converge 8FTUFSMJFT (come together) and circulate cyclonically — coun- ) - terclockwise in the N. Hemisphere, and clockwise in the S. Hemisphere. Winds around highs diverge - 4VCQPMBS-PXT - - 4 (spread out) and rotate anticyclonically — clock- ) wise in the N. Hemisphere, and counterclockwise in 1PMBS)JHI the S. Hemisphere. The cyclones are regions of bad weather (clouds, rain, high humidity, strong winds) and fronts. The anticyclones are regions of good weather (clear skies or fair-weather clouds, no pre- C /FBS5SPQPQBVTF cipitation, dry air, and light winds). 1PMBS-PX The high- and low-pressure centers move on av- - erage from west to east, driven by large-scale winds / from the west. Although these westerlies dominate the general circulation at mid-latitudes, the surface USPVHI winds are quite variable in time and space due to the 1PMBS+FU sum of the westerlies plus the transient circulations SJEHF around the highs and lows. )) )) 4VCUSPQJDBM+FU )) )) / Near 60° latitude are belts of low surface pres- sure called subpolar lows. Along these belts are light to calm winds, upward air motion, clouds, cool temperatures, and precipitation (as snow in winter).
Load more

Recommended publications
  • Responses of the Hydrological Cycle to Solar Forcings
    1 Responses of the hydrological cycle to solar forcings Jane Smyth Advised by Dr. Trude Storelvmo Second Reader Dr. William Boos May 6, 2016 A Senior Thesis presented to the faculty of the Department of Geology and Geophysics, Yale University, in partial fulfillment of the Bachelor’s Degree. In presenting this thesis in partial fulfillment of the Bachelor’s Degree from the Department of Geology and Geophysics, Yale University, I agree that the department may make copies or post it on the departmental website so that others may better understand the undergraduate research of the de- partment. I further agree that extensive copying of this thesis is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this thesis for commercial purposes or financial gain is not allowed without my written consent. Jane Elizabeth Smyth, 6 May, 2016 RESPONSESOFTHE HYDROLOGICALCYCLETOjane smyth SOLARFORCINGS Senior Thesis advised by dr. trude storelvmo 1 Chapter I: Solar Geoengineering 4 contents1.1 Abstract . 4 1.2 Introduction . 5 1.2.1 Solar Geoengineering . 5 1.2.2 The Hydrological Cycle . 5 1.3 Models & Methods . 7 1.4 Results and Discussion . 9 1.4.1 Thermodynamic Scaling of Net Precipitation . 9 1.4.2 Dynamically Driven Precipitation . 12 1.4.3 Relative Humidity . 12 1.5 Conclusions . 14 1.6 Appendix . 16 2 Chapter II: Orbital Precession 22 2.1 Abstract . 22 2.2 Introduction . 23 2.3 Experimental Design & Methods . 24 2.3.1 Atmospheric Heat Transport . 25 2.3.2 Hadley Circulation . 25 2.3.3 Gross Moist Stability .
    [Show full text]
  • Hadley Cell and the Trade Winds of Hawai'i: Nā Makani
    November 19, 2012 Hadley Cell and the Trade Winds of Hawai'i Hadley Cell and the Trade Winds of Hawai‘i: Nā Makani Mau Steven Businger & Sara da Silva [email protected], [email protected] Iasona Ellinwood, [email protected] Pauline W. U. Chinn, [email protected] University of Hawai‘i at Mānoa Figure 1. Schematic of global circulation Grades: 6-8, modifiable for 9-12 Time: 2 - 10 hours Nā Honua Mauli Ola, Guidelines for Educators, No Nā Kumu: Educators are able to sustain respect for the integrity of one’s own cultural knowledge and provide meaningful opportunities to make new connections among other knowledge systems (p. 37). Standard: Earth and Space Science 2.D ESS2D: Weather and Climate Weather varies day to day and seasonally; it is the condition of the atmosphere at a given place and time. Climate is the range of a region’s weather over one to many years. Both are shaped by complex interactions involving sunlight, ocean, atmosphere, latitude, altitude, ice, living things, and geography that can drive changes over multiple time scales—days, weeks, and months for weather to years, decades, centuries, and beyond for climate. The ocean absorbs and stores large amounts of energy from the sun and releases it slowly, moderating and stabilizing global climates. Sunlight heats the land more rapidly. Heat energy is redistributed through ocean currents and atmospheric circulation, winds. Greenhouse gases absorb and retain the energy radiated from land and ocean surfaces, regulating temperatures and keep Earth habitable. (A Framework for K-12 Science Education, NRC, 2012) Hawai‘i Content and Performance Standards (HCPS) III http://standardstoolkit.k12.hi.us/index.html 1 November 19, 2012 Hadley Cell and the Trade Winds of Hawai'i STRAND THE SCIENTIFIC PROCESS Standard 1: The Scientific Process: SCIENTIFIC INVESTIGATION: Discover, invent, and investigate using the skills necessary to engage in the scientific process Benchmarks: SC.8.1.1 Determine the link(s) between evidence and the Topic: Scientific Inquiry conclusion(s) of an investigation.
    [Show full text]
  • Change of the Tropical Hadley Cell Since 1950
    Change of the Tropical Hadley Cell Since 1950 Xiao-Wei Quan, Henry F. Diaz, and Martin P. Hoerling NOAA-CIRES Climate Diagnostic Center, Boulder, Colorado, USA last revision: March 24, 2004 Abstract The change in the tropical Hadley cell since 1950 is examined within the context of the long-term warming in the global surface temperatures. The study involves analyses of observations, including various metrics of Hadley cell, and ensemble 50-year simulations by an atmospheric general circulation model forced with the observed evolution of global sea surface temperature since 1950. Consistent evidence is found for an intensification of the Northern Hemisphere winter Hadley cell since 1950. This is shown to be an atmospheric response to the observed tropical ocean warming trend, together with an intensification in El Niño’s interannual fluctuations including larger amplitude and increased frequency after 1976. The intensification of the winter Hadley cell is shown to be associated with an intensified hydrological cycle consisting of increased equatorial oceanic rainfall, and a general drying of tropical/subtropical landmasses. This Hadley cell change is consistent with previously documented dynamic changes in the extratropics, including a strengthening of westerly atmospheric flow and an intensification of midlatitude cyclones. 1. Introduction The tropical Hadley cell, by definition, is the zonal mean meridional mass circulation in the atmosphere bounded roughly by 30ºS and 30ºN. It is characterized by equatorward mass transport by the prevailing trade wind flow in the lower troposphere, and poleward mass transport in the upper troposphere. This lateral mass circulation links the mean ascending motion in the equatorial zone with subsidence in the subtropics, and represents a major part of the large-scale meridional overturning between tropics and subtropics.
    [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]
  • Hadley's Principle: Understanding and Misunderstanding the Trade
    History of Meteorology 3 (2006) 17 Hadley’s Principle: Understanding and Misunderstanding the Trade Winds Anders O. Persson Department for research and development Swedish Meteorological and Hydrological Institute SE 601 71 Norrköping, Sweden [email protected] Old knowledge will often be rediscovered and presented under new labels, causing much confusion and impeding progress—Tor Bergeron.1 Introduction In May 1735 a fairly unknown Englishman, George Hadley, published a groundbreaking paper, “On the Cause of the General Trade Winds,” in the Philosophical Transactions of the Royal Society. His path to fame was long and it took 100 years to have his ideas accepted by the scientific community. But today there is a “Hadley Crater” on the moon, the convectively overturning in the tropics is called “The Hadley Cell,” and the climatological centre of the UK Meteorological Office “The Hadley Centre.” By profession a lawyer, born in London, George Hadley (1685-1768) had in 1735 just became a member of the Royal Society. He was in charge of the Society’s meteorological work which consisted of providing instruments to foreign correspondents and of supervising, collecting and scrutinizing the continental network of meteorological observations2. This made him think about the variations in time and geographical location of the surface pressure and its relation to the winds3. Already in a paper, possibly written before 1735, Hadley carried out an interesting and far-sighted discussion on the winds, which he found “of so uncertain and variable nature”: Hadley’s Principle 18 …concerning the Cause of the Trade-Winds, that for the same Cause the Motion of the Air will not be naturally in a great Circle, for any great Space upon the surface of the Earth anywhere, unless in the Equator itself, but in some other Line, and, in general, all Winds, as they come nearer the Equator will become more easterly, and as they recede from it, more and more westerly, unless some other Cause intervene4.
    [Show full text]
  • Atmospheric Circulation
    Atmospheric circulation Trade winds http://science.nasa.gov/science-news/science-at-nasa/2002/10apr_hawaii/ Atmosphere (noun) the envelope of gases (air) surrounding the earth or another planet Dry air: Argon, 0.98% O2, 21% N2, 78% CO2, >400ppm & rising Water vapor can be up to 4% 50% below 5.6 km (18,000 ft) 90% below 16 km (52,000 ft) http://mychinaviews.com/2011/06/into-thin-air.html Drivers of atmospheric circulation Uneven solar heating At poles sun’s energy is spread over a larger region Uneven solar heating At poles sun’s energy is spread over a larger region Uneven solar heating At poles sun’s energy is spread over a larger region Ways to transfer heat Conduction: Transfer of heat by direct contact. Heat goes from warmer areas to colder areas. Ways to transfer heat Radiation: Any object radiates heat as electromagnetic radiation (light, infrared) based on temperature of the object. Ways to transfer heat Convection: Heat carried by a fluid (air, water, etc) from a region of high temperature to a region of lower temperature. Convection cell Warm air rises, then as it cools it sinks back down Thermal (heat) balance Heat in = Heat out, for earth as a whole ! Heat in = Heat out, for latitude bands " Heat out t r o p s n a r Heat in t t a e h t e N RedistributionIncreasing heat of heat drive atmospheric circulation So, might expect Cool air sinking near the poles Warm air rising at equator Lutgens and Tarbuk, 2001 http://www.ux1.eiu.edu/~cfjps/1400/circulation.html Turns out a 3 cell modelis better Polar cell Ferrel cell (Mid-latitude
    [Show full text]
  • ESCI 344 – Tropical Meteorology Lesson 3 – General Circulation of the Tropics
    ESCI 344 – Tropical Meteorology Lesson 3 – General Circulation of the Tropics References: Forecaster’s Guide to Tropical Meteorology (updated), Ramage Climate Dynamics of the Tropics, Hastenrath Tropical Climatology (2nd ed), McGregor and Nieuwolt Tropical Meteorology, Tarakanov Climate and Weather in the Tropics, Riehl General Circulation of the Tropical Atmosphere, Vol II, Newell et al. “The South Pacific Convergence Zone (SPCZ): A Review”, Vincent, Mon.Wea. Rev., 122, 1949-1970, 1994 “The Central Pacific Near-Equatorial Convergence Zone”, Ramage, J. Geophys. Res., 86, 6580-6598 Reading: Introduction to the Meteorology and Climate of the Tropics, Chapter 3 Vincent, “The SPCZ: A Review” Lau and Yang, “Walker Circulation” James, “Hadley Circulation” Waliser, “Intertropical Convergence Zones” Hastenrath, “Tropical Climates” Madden, “Intraseasonal Oscillation (MJO)” TERMINOLOGY Boreal refers to the Northern Hemisphere Austral refers to the Southern Hemisphere LATITUDINAL HEAT IMBALANCE Net radiation flux is defined as the difference in incoming radiation flux and outgoing radiation flux. A positive net radiation flux indicates a surplus of energy, while a negative net radiation flux indicates a deficit. This figure shows the longitudinally-averaged, annual-mean radiation fluxes at the top of the atmosphere. Outgoing shortwave is due to scattering and reflection. Net shortwave is the difference between the incoming and outgoing shortwave radiation. When the earth-atmosphere system is considered as a whole, there is a positive net radiation flux between about 40N and 40S, while there is a negative net radiation flux poleward of 40 in both hemispheres. In order for a steady-state temperature to be achieved, there must be transport of heat from the earth’s surface to the atmosphere, and from the tropics to the polar regions.
    [Show full text]
  • Hadley Cell Expansion in CMIP6 Models Kevin M
    https://doi.org/10.5194/acp-2019-1206 Preprint. Discussion started: 22 January 2020 c Author(s) 2020. CC BY 4.0 License. Hadley cell expansion in CMIP6 models Kevin M. Grise1, Sean M. Davis2 1Department of Environmental Sciences, University of Virginia, Charlottesville, VA 22904, USA 2NOAA Earth System Research Laboratory Chemical Sciences Division, Boulder, CO 80305 USA 5 Correspondence to: Kevin M. Grise ([email protected]) Abstract. In response to increasing greenhouse gases, the subtropical edges of Earth’s Hadley circulation shift poleWard in global climate models. Recent studies have found that reanalysis trends in the Hadley cell edge over the past 30–40 years are Within the range of trends simulated by Coupled Model Intercomparison Project Phase 5 (CMIP5) models, and have documented seasonal and hemispheric asymmetries in these trends. In this study, We evaluate Whether these conclusions 10 hold for the newest generation of models (CMIP6). Overall, We find similar characteristics of Hadley cell expansion in CMIP5 and CMIP6 models. In both CMIP5 and CMIP6 models, the poleward shift of the Hadley cell edge in response to increasing greenhouse gases is 2–3 times larger in the Southern Hemisphere (SH), except during September–November. The trends from CMIP5 and CMIP6 models agree Well With reanalyses, although prescribing observed coupled atmosphere- ocean variability allows the models to better capture reanalysis trends in the Northern Hemisphere (NH). We find tWo 15 notable differences betWeen CMIP5 and CMIP6 models. First, both CMIP5 and CMIP6 models contract the NH summertime Hadley circulation equatorward (particularly over the Pacific sector), but this contraction is larger in CMIP6 models due to their higher average climate sensitivity.
    [Show full text]
  • The Coriolis Effect, Geostrophy, Winds and the General Circulation of The
    VII. the Coriolis effect, winds, storms and the general circulation of the atmosphere clicker question absorbed solar emitted IR (OLR) The local imbalances of received and emitted radiation (above) mean that: a) the poles will cool forever, b) the tropics will heat up forever, c) both a & b, d) there must be a poleward transport of heat, e) there must be an equatorward transport of heat clicker question heating at the surface leads to: a) expansion of air, b) buoyancy, c) convection, d) gradients of pressure, e) all of the above review (from last week) northern limb Hadley cell 500 mb high low 500 mb 950 mb low high 1050 mb tropics extra (30 °N) tropics the horizontal movements of air can be satisfied by buoyancy driven vertical movements, comprising a circulation cell, such as the Hadley cell review (from last week) • differential heating leads to gradients of pressure • air moves from areas of high pressure to areas of low pressure • but does air always move in a straight line? surface pressure mbar surface pressure “belts” high low high low high low another high down under pressure-force-only winds is this the observed pattern? the Coriolis effect • Newton says pushed objects will move in a straight line, but....... • the coriolis force describes the apparent tendency of a fluid (air or water) moving across the surface of the Earth to be deflected from its straight line path • this is not a real force, but apparent only from the w/in of the rotating Earth system (an observer in space would not note deflection) • let’s see a simple experiment platter is stationary Newton was right! a simple experiment platter now rotates! what happened ??????? how would it look from above? the Coriolis effect • Newton says pushed objects will move in a straight line, but......
    [Show full text]
  • The Response of Subtropical Highs to Climate Change
    Current Climate Change Reports https://doi.org/10.1007/s40641-018-0114-1 CLIMATE CHANGE AND ATMOSPHERIC CIRCULATION (R CHADWICK, SECTION EDITOR) The Response of Subtropical Highs to Climate Change Annalisa Cherchi1 & Tercio Ambrizzi2 & Swadhin Behera3 & Ana Carolina Vasques Freitas4 & Yushi Morioka3 & Tianjun Zhou5 # Springer Nature Switzerland AG 2018 Abstract Purpose of Review Subtropical highs are an important component of the climate system with clear implications on the local climate regimes of the subtropical regions. In a climate change perspective, understanding and predicting subtropical highs and related climate is crucial to local societies for climate mitigation and adaptation strategies. We review the current understanding of the subtropical highs in the framework of climate change. Recent Findings Projected changes of subtropical highs are not uniform. Intensification, weakening, and shifts may largely differ in the two hemispheres but may also change across different ocean basins. For some regions, large inter-model spread represen- tation of subtropical highs and related dynamics is largely responsible for the uncertainties in the projections. The understanding and evaluation of the projected changes may also depend on the metrics considered and may require investigations separating thermodynamical and dynamical processes. Summary The dynamics of subtropical highs has a well-established theoretical background but the understanding of its vari- ability and change is still affected by large uncertainties. Climate model systematic errors, low-frequency chaotic variability, coupled ocean-atmosphere processes, and sensitivity to climate forcing are all sources of uncertainty that reduce the confidence in atmospheric circulation aspects of climate change, including the subtropical highs. Compensating signals, coming from a tug-of- war between components associated with direct carbon dioxide radiative forcing and indirect sea surface temperature warming, impose limits that must be considered.
    [Show full text]
  • The Longitudinally-Dependent Hadley Circulation: Seasonality and Interannual Variability
    The longitudinally-dependent Hadley circulation: seasonality and interannual variability Eli Galanti1, Dana Raiter1, Yohai Kaspi1, and Eli Tziperman2 submitted to Journal of Climate January 1, 2019 1Department of Earth and Planetary Sciences, moisture transport from the equatorial region to the sub- Weizmann Institute of Science, Rehovot, Israel. tropics [e.g., Trenberth and Stepaniak, 2003]. The cir- 2Department of Earth and Planetary Sciences, Harvard culation is commonly defined as the zonally-averaged University, Cambridge, MA, USA meridional circulation in the tropical region [Hartmann, 2016], and is usually calculated as an annual mean or as an average over specific months or seasons. The large longitudinal variations in the different el- Abstract ements involved in the Hadley circulation, such as the strength of the Inter Tropical Convergence Zone (ITCZ) The Hadley circulation is commonly defined as the and the location of the subtropical jets that mark the meridional circulation of the zonally averaged flow in edge of the Hadley circulation, led to the need to calcu- the tropics. In recent years, several studies looked at late the contributions to the Hadley circulation at differ- the longitudinal decomposition of the three-dimensional ent longitudes. A method for calculating localized 2D cir- atmospheric flow into local meridional and zonal flows. culations from the 3D wind field was first introduced by These studies gave useful analysis on the regionality and Keyser et al. [1989]. Decomposing the wind field into a variability of the meridional circulation, yet their spatial rotational and divergent components (Helmholtz decom- analysis remained essentially three-dimensional, and the position), the longitudinally-dependent circulation can temporal variability was strongly dependent on assump- be derived from the divergent part of the flow.
    [Show full text]
  • Interannual Variability of the Atlantic Hadley Circulation in Boreal Summer and Its Impacts on Tropical Cyclone Activity
    1NOVEMBER 2013 Z H A N G A N D W A N G 8529 Interannual Variability of the Atlantic Hadley Circulation in Boreal Summer and Its Impacts on Tropical Cyclone Activity GAN ZHANG AND ZHUO WANG Department of Atmospheric Sciences, University of Illinois at Urbana–Champaign, Urbana, Illinois (Manuscript received 16 November 2012, in final form 22 May 2013) ABSTRACT A novel method was developed to define the regional Hadley circulation (HC) in terms of the meridional streamfunction. The interannual variability of the Atlantic HC in boreal summer was examined using EOF analysis. The leading mode (M1), explaining more than 45% of the variances, is associated with the intensity change of the ITCZ. M1 is significantly correlated to multiple climate factors and has strong impacts on Atlantic tropical cyclone (TC) activity. In the positive (negative) phase of M1, the ITCZ is stronger (weaker) than normal, and more (fewer) TCs form over the main development region (MDR) with a larger (smaller) fraction of storms intensifying into major hurricanes. Analyses showed that the large-scale dynamic and thermodynamic conditions associated with a stronger ITCZ are more favorable for TC activity. The roles of tropical easterly waves in modulating the Atlantic TC activity are highlighted. In the positive phase of M1, the wave activity is significantly enhanced over the MDR and the Caribbean Sea, which can be attributed to stronger coastal convection and mean flow structure changes. In the context of the recently proposed marsupial paradigm, the frequency and structure of wave pouches were examined. In the positive phase of M1, the pouch frequency increases, and the number of pouches with a vertically coherent structure also rises significantly.
    [Show full text]