DOCSLIB.ORG

Jet Stream Dynamics

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Jet Stream Dynamics ATMS 310 Jet Streams Jet Streams A jet stream is an intense (30+ m/s in upper troposphere, 15+ m/s lower troposphere), narrow (width at least ½ order magnitude less than the length) horizontal current of air associated with strong (at least 5-10 ms-1km-1) vertical wind shear. A Jet Streak is an isotach maximum embedded within a jet stream. Jet streams are mesoscale in the cross-flow direction and synoptic-scale in the along-flow direction. They were discovered in the 1940s at the University of Chicago. Polar Jet A jet stream found at about 200-300 mb at the transition from tropical (or mid-latitude) to polar air. Occurs in the vicinity of the surface polar front. The relationship between the jet location and temperature gradient is a consequence of the thermal wind relation. The polar jet for the most part does not show up on mean wind maps, mostly because it meanders so much. However, there are two climatological polar jets that do show up on mean maps: There is a big difference in the zonal wind along about 30° latitude. For example, the jet core over the western Pacific has wind speeds about 50 m/s higher than similar latitudes off the west coast of California. It is believed that the land/sea contrasts off the east coasts of Asia and North America, particularly during the winter season, enhance the pressure gradients and thus the jetstreams as well. Subtropical Jet Located near 200 mb in winter at latitudes between 20° and 35°. In winter it is hard to distinguish between the polar and subtropical jets as the polar jet penetrates far south toward the equator. In summer, the subtropical jet disappears. Low-level Jet This is a jet stream found typically below 850 mb, usually in the southern plains of the U.S. east of the Rocky mountains. It may extend eastward to the Mississippi valley. Also occurs east of a low-level cyclone or south/southwest of a low-level cyclone. See the figure below, which highlight low-level jets. Jet streams are important source regions for storm development. To see how, examine the zonal component of the momentum equation (Eq. 10.70 in Holton): D u g g =f() v − v ≡ f v (1) Dt o g o a (a) (b) where a) is the total rate of change of the geostrophic zonal wind with time, which is a function of b), the Coriolis parameter multiplied by the ageostrophic component of the meridional wind ( va = v − vg ). In the entrance region of the jet stream (upstream from the core) the zonal wind is accelerating. In order for that to happen, va > 0 (poleward Dg u g wind). Conversely, in the exit region (downstream from the core) < 0 and thus va Dt < 0 (equatorward wind). The figure below illustrates these effects: The secondary circulation induced by the jet stream creates two different environments, depending on where one is in relation to the jet core. If you are north of the jet core in the entrance region, where there is a poleward flow at upper levels, high pressure is created as the upper level flow sinks at higher latitudes, and the return flow is relatively weak. If you are located downstream and north of the jet core, you will encounter strong westerly winds and low-level convergence (stormy weather). There is a strong eddy heat flux (warm air advection) in that region as well. See the figure below (Fig. 10.16 in Holton): Note that the convergence on the poleward side of the jet is thermally indirect – that is, cool air is rising and warm air is sinking. Typical synoptic-scale disturbances develop under the jet in the entrance region, grow as the move under the jet core, and then decay in the jet exit region. Jet Stream Development/Propagation The change in kinetic energy of a parcel of air can be found by dot multiplying the horizontal equation of motion in isobaric coordinates by the 3-dimensional wind to yield: dk v = −gV • ∇ z (2) dt a p v v 2 2 V• V u+ v v 2 where k = kinetic energy = ≡ ≡ V 2/ and Va is the ageostrophic wind. If 2 2 the ageostrophic component of the flow flows toward lower heights (∇z < 0 ), then the RHS of (2) is positive and the kinetic energy increases with time. Qualitatively, acceleration will occur as the air parcel tries to restore geostrophic balance. Thus, jet streams are formed or intensified by mechanisms that increase the pressure (or height) gradient in a concentrated area. There are four processes that can do this: 1) Differential heating 2) Differential temperature advection 3) Differential adiabatic cooling 4) Differential vorticity advection For example, the following scenario would intensify this jet: since the processes north of the jet core will lower the heights there and processes south of the jet core will raise the heights. This will increase the height gradient and thus through (2) increase the kinetic energy of the jet. Alternatively, you can think of the process in terms of the thermal wind. The geostrophic wind must increase with height if the temperature gradient increases on a pressure level. The same process works to propagate the jet stream. If the forcing mechanisms occur ahead of the jet, the jet will move in that direction. Coupled Jets If two jet streaks are sufficiently close to one another and placed such that the right entrance region of one is superimposed on the left exit region of the other, their interaction will enhance the upward vertical motion in that area. These are called coupled jets (see Uccellini and Kocin, Weather and Forecasting, 1987, 289-308). The figure below is from the Uccellini and Kocin paper – note the location of the jets and the enhanced secondary circulation. This situation may contribute to “bomb” development. .
Load more

Recommended publications
  • Extratropical Cyclones and Anticyclones
    © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION Courtesy of Jeff Schmaltz, the MODIS Rapid Response Team at NASA GSFC/NASA Extratropical Cyclones 10 and Anticyclones CHAPTER OUTLINE INTRODUCTION A TIME AND PLACE OF TRAGEDY A LiFE CYCLE OF GROWTH AND DEATH DAY 1: BIRTH OF AN EXTRATROPICAL CYCLONE ■■ Typical Extratropical Cyclone Paths DaY 2: WiTH THE FI TZ ■■ Portrait of the Cyclone as a Young Adult ■■ Cyclones and Fronts: On the Ground ■■ Cyclones and Fronts: In the Sky ■■ Back with the Fitz: A Fateful Course Correction ■■ Cyclones and Jet Streams 298 9781284027372_CH10_0298.indd 298 8/10/13 5:00 PM © Jones & Bartlett Learning, LLC. NOT FOR SALE OR DISTRIBUTION Introduction 299 DaY 3: THE MaTURE CYCLONE ■■ Bittersweet Badge of Adulthood: The Occlusion Process ■■ Hurricane West Wind ■■ One of the Worst . ■■ “Nosedive” DaY 4 (AND BEYOND): DEATH ■■ The Cyclone ■■ The Fitzgerald ■■ The Sailors THE EXTRATROPICAL ANTICYCLONE HIGH PRESSURE, HiGH HEAT: THE DEADLY EUROPEAN HEAT WaVE OF 2003 PUTTING IT ALL TOGETHER ■■ Summary ■■ Key Terms ■■ Review Questions ■■ Observation Activities AFTER COMPLETING THIS CHAPTER, YOU SHOULD BE ABLE TO: • Describe the different life-cycle stages in the Norwegian model of the extratropical cyclone, identifying the stages when the cyclone possesses cold, warm, and occluded fronts and life-threatening conditions • Explain the relationship between a surface cyclone and winds at the jet-stream level and how the two interact to intensify the cyclone • Differentiate between extratropical cyclones and anticyclones in terms of their birthplaces, life cycles, relationships to air masses and jet-stream winds, threats to life and property, and their appearance on satellite images INTRODUCTION What do you see in the diagram to the right: a vase or two faces? This classic psychology experiment exploits our amazing ability to recognize visual patterns.
    [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]
  • Ozone: Good up High, Bad Nearby
    actions you can take High-Altitude “Good” Ozone Ground-Level “Bad” Ozone •Protect yourself against sunburn. When the UV Index is •Check the air quality forecast in your area. At times when the Air “high” or “very high”: Limit outdoor activities between 10 Quality Index (AQI) is forecast to be unhealthy, limit physical exertion am and 4 pm, when the sun is most intense. Twenty minutes outdoors. In many places, ozone peaks in mid-afternoon to early before going outside, liberally apply a broad-spectrum evening. Change the time of day of strenuous outdoor activity to avoid sunscreen with a Sun Protection Factor (SPF) of at least 15. these hours, or reduce the intensity of the activity. For AQI forecasts, Reapply every two hours or after swimming or sweating. For check your local media reports or visit: www.epa.gov/airnow UV Index forecasts, check local media reports or visit: www.epa.gov/sunwise/uvindex.html •Help your local electric utilities reduce ozone air pollution by conserving energy at home and the office. Consider setting your •Use approved refrigerants in air conditioning and thermostat a little higher in the summer. Participate in your local refrigeration equipment. Make sure technicians that work on utilities’ load-sharing and energy conservation programs. your car or home air conditioners or refrigerator are certified to recover the refrigerant. Repair leaky air conditioning units •Reduce air pollution from cars, trucks, gas-powered lawn and garden before refilling them. equipment, boats and other engines by keeping equipment properly tuned and maintained. During the summer, fill your gas tank during the cooler evening hours and be careful not to spill gasoline.
    [Show full text]
  • Migration and Climate Change
    Migration and Climate Change No. 31 The opinions expressed in the report are those of the authors and do not necessarily reflect the views of the International Organization for Migration (IOM). The designations employed and the presentation of material throughout the report do not imply the expression of any opinion whatsoever on the part of IOM concerning the legal status of any country, territory, city or area, or of its authorities, or concerning its frontiers or boundaries. _______________ IOM is committed to the principle that humane and orderly migration benefits migrants and society. As an intergovernmental organization, IOM acts with its partners in the international community to: assist in meeting the operational challenges of migration; advance understanding of migration issues; encourage social and economic development through migration; and uphold the human dignity and well-being of migrants. _______________ Publisher: International Organization for Migration 17 route des Morillons 1211 Geneva 19 Switzerland Tel: +41.22.717 91 11 Fax: +41.22.798 61 50 E-mail: [email protected] Internet: http://www.iom.int Copy Editor: Ilse Pinto-Dobernig _______________ ISSN 1607-338X © 2008 International Organization for Migration (IOM) _______________ All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise without the prior written permission of the publisher. 11_08 Migration and Climate Change1 Prepared for IOM by Oli Brown2 International Organization for Migration Geneva CONTENTS Abbreviations 5 Acknowledgements 7 Executive Summary 9 1. Introduction 11 A growing crisis 11 200 million climate migrants by 2050? 11 A complex, unpredictable relationship 12 Refugee or migrant? 1 2.
    [Show full text]
  • Thunderstorm Analysis in the Northern Rocky Mountains
    This file was created by scanning the printed publication. ^1 / Errors identified by the software have been corrected; ^n/' however, some errors may remain. 4* * THUNDERSTORM ANALYSTS c' Tn the NORTHERN ROCKY MOUNTATNS DeVerColson ENTERMOUNTAEN FOREST AND RANGE EXPEREMENT STATEON FOREST SERVECE UNETED STATES DEPARTMENT OF AGRECULTURE Ogden, Utah Reed W. Bailey, Director RESEARCH PAPER NO. 49 1957 Research Paper No. 49 l957 THUNDERSTORM ANALYSIS IN THE NORTHERN ROCKY MOUNTAINS By DeVer Colson Meteorologist INTERMOUNTAIN FOREST AND RANGE EXPERIMENT STATION Forest Service U.S. Department of Agriculture Ogden, Utah Reed W. Bailey, Director THUNDERSTORM ANALYSIS IN THE NORTHERN ROCKY MOUNTAINS DeVer Col son!' U.S. Weather Bureau Washington, D.C. INTRODUCTION Lightning-caused fires are a continuing serious threat to forests in the northern Rocky Mountain area. More than 70 percent of all forest fires in this area are caused by lightning. In one l0-day period in July l940 the all-time record of l,488 lightning fires started on the national forests in Region l of the U.S. Forest Service.—' Project Skyfire was planned and organized to study the causes and char acteristics of lightning storms and to see what steps could be taken to decrease the great losses caused by lightning fires. One important phase of Project Skyfire is the study and analysis of the weather phenomena associated with the formation and growth of lightning storms. A better understanding of these factors is valuable to both the forester and the meteorologist. In the Project Skyfire research program,analyses are being made of the specific characteristics of individual lightning storms and the general characteristics of storms during an entire fire season.
    [Show full text]
  • Dynamics of Jupiter's Atmosphere
    6 Dynamics of Jupiter's Atmosphere Andrew P. Ingersoll California Institute of Technology Timothy E. Dowling University of Louisville P eter J. Gierasch Cornell University GlennS. Orton J et P ropulsion Laboratory, California Institute of Technology Peter L. Read Oxford. University Agustin Sanchez-Lavega Universidad del P ais Vasco, Spain Adam P. Showman University of A rizona Amy A. Simon-Miller NASA Goddard. Space Flight Center Ashwin R . V asavada J et Propulsion Laboratory, California Institute of Technology 6.1 INTRODUCTION occurs on both planets. On Earth, electrical charge separa­ tion is associated with falling ice and rain. On Jupiter, t he Giant planet atmospheres provided many of the surprises separation mechanism is still to be determined. and remarkable discoveries of planetary exploration during The winds of Jupiter are only 1/ 3 as strong as t hose t he past few decades. Studying Jupiter's atmosphere and of aturn and Neptune, and yet the other giant planets comparing it with Earth's gives us critical insight and a have less sunlight and less internal heat than Jupiter. Earth broad understanding of how atmospheres work that could probably has the weakest winds of any planet, although its not be obtained by studying Earth alone. absorbed solar power per unit area is largest. All the gi­ ant planets are banded. Even Uranus, whose rotation axis Jupiter has half a dozen eastward jet streams in each is tipped 98° relative to its orbit axis. exhibits banded hemisphere. On average, Earth has only one in each hemi­ cloud patterns and east- west (zonal) jets.
    [Show full text]
  • The Jet Stream and Climate Change Martin Stendel1, Jennifer Francis2, Rachel White3, Paul D
    CHAPTER 15 The jet stream and climate change Martin Stendel1, Jennifer Francis2, Rachel White3, Paul D. Williams4, Tim Woollings5 1Department of Climate and Arctic Research, Danish Meteorological Institute, Copenhagen, Denmark; 2Woodwell Climate Research Center, Falmouth, MA, United States; 3Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, BC, Canada; 4Department of Meteorology, University of Reading, Reading, United Kingdom; 5Department of Physics, University of Oxford, Oxford, United Kingdom 1. Introduction 1.1 Jet streams The jet streams are powerful, relatively narrow currents of air that encircle the globe from west to east in both the northern and southern hemispheres. While the strongest winds are found at heights of 10e15 km, typical of cruising aircraft, jet streams, particularly in temperate latitudes, “steer” the movement of frontal zones and air masses, thus affecting sur- face weather and contributing to the prevailing westerly winds familiar to many in the mid- latitude regions. The jet streams rose to prominence in meteorology following World War II, when high- altitude air campaigns had on several occasions been adversely affected by unexpectedly strong winds [1]. The establishment of hemispheric-scale networks of radiosonde observa- tions by Carl-Gustav Rossby and collaborators in the 1940s and 1950s identified for the first time the global nature of the jet streams and the waves that propagate along them [2]. Since then, the jets have been central to our understanding of weather patterns and climate variability. Although not observed or measured until relatively recently, the existence of jet streams was theorized by George Hadley in the 18th century in his groundbreaking discussion on the cause of the tropical trade winds [3].
    [Show full text]
  • U.S. Violent Tornadoes Relative to the Position of the 850-Mb
    U.S. VIOLENT TORNADOES RELATIVE TO THE POSITION OF THE 850 MB JET Chris Broyles1, Corey K. Potvin 2, Casey Crosbie3, Robert M. Rabin4, Patrick Skinner5 1 NOAA/NWS/NCEP/Storm Prediction Center, Norman, Oklahoma 2 Cooperative Institute for Mesoscale Meteorological Studies, and School of Meteorology, University of Oklahoma, and NOAA/OAR National Severe Storms Laboratory, Norman, Oklahoma 3 NOAA/NWS/CWSU, Indianapolis, Indiana 4 National Severe Storms Laboratory, Norman, Oklahoma 5 Cooperative Institute for Mesoscale Meteorological Studies, and NOAA/OAR National Severe Storms Laboratory, Norman, Oklahoma Abstract The Violent Tornado Webpage from the Storm Prediction Center has been used to obtain data for 182 events (404 violent tornadoes) in which an F4-F5 or EF4-EF5 tornado occurred in the United States from 1950 to 2014. The position of each violent tornado was recorded on a gridded plot compared to the 850 mb jet center within 90 minutes of the violent tornado. The position of each 850 mb jet was determined using the North American Regional Reanalysis (NARR) from 1979 to 2014 and NCEP/NCAR Reanalysis from 1950 to 1978. Plots are shown of the position of each violent tornado relative to the center of the 850 mb low-level jet. The United States was divided into four parts and the plots are available for the southern Plains, northern Plains, northeastern U.S. and southeastern U.S with a division between east and west at the Mississippi River. Great Plains violent tornadoes clustered around a center about 130 statute miles to the left and slightly ahead of the low-level jet center while eastern U.S.
    [Show full text]
  • ESCI 107 – the Atmosphere Lesson 16 – Tropical Cyclones Reading
    ESCI 107 – The Atmosphere Lesson 16 – Tropical Cyclones Reading: Meteorology Today, Chapter 15 TROPICAL CYCLONES l A tropical cyclone is a large, low-pressure system that forms over the tropical oceans. l Tropical cyclones are classified by sustained wind speed as o Tropical disturbance – wind less than 25 knots o Tropical Depression (TD) – wind 25 to 34 knots o Tropical storm (TS) – wind 35 to 64 knots o Hurricane (or Typhoon) – wind 65 knots or greater l Sustained winds means winds averaged over a 1-minute period (in U.S.). o It is the sustained wind that is used to classify tropical cyclones, not the gusts. l A typhoon and a hurricane are the exact same thing. They just have different names in different parts of the world. Global numbers ¡ About 80 tropical cyclones per year world-wide reach tropical storm strength ¡ About 50 – 55 each year world-wide reach hurricane/typhoon strength Safir-Simpson Intensity Scale (used in U.S.) Category Max Sustained Wind knots mph 1 64 - 82 74 - 95 2 83 - 95 96 - 110 3 96 - 113 111 - 130 4 114 - 134 131 - 155 5 135 + 156 + ¡ A major hurricane is a Category III or higher. FORMATION l The energy that drives hurricanes is the latent heat of condensation from the thunderstorms that comprise the hurricane. l Therefore, hurricanes can only form over very warm water, where there is plenty of evaporation to feed moisture to the thunderstorms. o Water temperatures must be at least 26.5°C (about 80°F). o The upper ‘mixed layer’ of the ocean must also be relatively deep (at least 45 meters) so that the waves do not mix away the warm water at the surface.
    [Show full text]
  • Variability of the North Atlantic Eddy-Driven Jet Stream
    CORE Metadata, citation and similar papers at core.ac.uk Provided by Central Archive at the University of Reading QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY Q. J. R. Meteorol. Soc. 00: 1–?? (2009) Published online in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/qj.000 Variability of the North Atlantic eddy-driven jet stream Tim Woollings, Abdel Hannachi and Brian Hoskins Department of Meteorology, University of Reading, Earley Gate, PO Box 243, Reading, RG6 6BB, UK. [email protected] Abstract: Much of the atmospheric variability in the North Atlantic sector is associated with variations in the eddy-driven component of the zonal flow. Here we present a simple method to specifically diagnose this component of the flow using the low-level wind field (925-700 hPa). We focus on the North Atlantic winter season in the ERA-40 reanalysis. Diagnostics of the latitude and speed of the eddy-driven jet stream are compared with conventional diagnostics of the North Atlantic Oscillation (NAO) and the East Atlantic (EA) pattern. This shows that the NAO and the EA both describe combined changes in the latitude and speed of the jet stream. It is therefore necessary, but not always sufficient, to consider both the NAO and the EA in identifying changes in the jet stream. The jet stream analysis suggests that there are three preferred latitudinal positions of the North Atlantic eddy-driven jet stream in winter. This result is in very good agreement with the application of a statistical mixture model to the two-dimensional state space defined by the NAO and the EA.
    [Show full text]
  • Jetstream and Rainfall Distribution in the Mediterranean Region
    Nat. Hazards Earth Syst. Sci., 11, 2469–2481, 2011 www.nat-hazards-earth-syst-sci.net/11/2469/2011/ Natural Hazards doi:10.5194/nhess-11-2469-2011 and Earth © Author(s) 2011. CC Attribution 3.0 License. System Sciences Jetstream and rainfall distribution in the Mediterranean region M. Gaetani, M. Baldi, G. A. Dalu, and G. Maracchi Institute of Biometeorology, IBIMET, CNR, Rome, Italy Received: 5 September 2010 – Revised: 13 May 2011 – Accepted: 19 May 2011 – Published: 19 September 2011 Abstract. This is a study on the impact of the jetstream in of the Atlantic jet produces rainfall anomalies in the western the Euro-Atlantic region on the rainfall distribution in the and central Mediterranean, with 45 % explained covariance. Mediterranean region; the study, based on data analysis, is re- In spring, the latitudinal displacement of the African jet pro- stricted to the Mediterranean rainy season, which lasts from duces rainfall anomalies, with 38 % explained covariance. September to May. During this season, most of the weather systems originate over the Atlantic, and are carried towards the Mediterranean region by the westerly flow. In the up- 1 Introduction per troposphere of the Euro-Atlantic region this flow is char- acterized by two jets: the Atlantic jet, which crosses the The rainfall distribution in the Mediterranean region is im- ocean with a northeasterly tilt, and the African jet, which portant, because this region is at risk of water shortage flows above the coast of North Africa. This study shows that (Hulme et al., 1999). In fact, an elaboration of the data the cross-jet circulation of the Atlantic jet favors storm ac- reported by Marshall et al.
    [Show full text]
  • Lecture 14. Extratropical Cyclones • in Mid-Latitudes, Much of Our Weather
    Lecture 14. Extratropical Cyclones • In mid-latitudes, much of our weather is associated with a particular kind of storm, the extratropical cyclone Cyclone: circulation around low pressure center Some midwesterners call tornadoes cyclones Tropical cyclone = hurricane • Extratropical cyclones derive their energy from horizontal temperature con- trasts. • They typically form on a boundary between a warm and a cold air mass associated with an upper tropospheric jet stream • Their circulations affect the entire troposphere over a region 1000 km or more across. • Extratropical cyclones tend to develop with a particular lifecycle . • The low pressure center moves roughly with the speed of the 500 mb wind above it. • An extratropical cyclone tends to focus the temperature contrasts into ‘fron- tal zones’ of particularly rapid horizontal temperature change. The Norwegian Cyclone Model In 1922, well before routine upper air observations began, Bjerknes and Sol- berg in Bergen, Norway, codified experience from analyzing surface weather maps over Europe into the Norwegian Cyclone Model, a conceptual picture of the evolution of an ET cyclone and associated frontal zones at ground They noted that the strongest temperature gradients usually occur at the warm edge of the frontal zone, which they called the front. They classified fronts into four types, each with its own symbol: Cold front - Cold air advancing into warm air Warm front - Warm air advancing into cold air Stationary front - Neither airmass advances Occluded front - Looks like a cold front
    [Show full text]