DOCSLIB.ORG

Simulation of a Serial Upstream-Propagating Mesoscale Convective System Event Over Southeastern South America Using Composite Initial Conditions

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Simulation of a Serial Upstream-Propagating Mesoscale Convective System Event Over Southeastern South America Using Composite Initial Conditions 2144 MONTHLY WEATHER REVIEW VOLUME 137 Simulation of a Serial Upstream-Propagating Mesoscale Convective System Event over Southeastern South America Using Composite Initial Conditions VAGNER ANABOR Laborato´rio de Fı´sica da Atmosfera, Departamento de Fı´sica, Universidade Federal de Santa Maria, Santa Maria, Brazil DAVID J. STENSRUD NOAA/National Severe Storms Laboratory, Norman, Oklahoma OSVALDO L. L. DE MORAES Laborato´rio de Fı´sica da Atmosfera, Departamento de Fı´sica, Universidade Federal de Santa Maria, Santa Maria, Brazil (Manuscript received 10 April 2008, in final form 29 November 2008) ABSTRACT Serial upstream-propagating mesoscale convective system (MCS) events over southeastern South America are important contributors to the local hydrologic cycle as they can provide roughly half of the total monthly summer precipitation. However, the mechanisms of upstream propagation for these events have not been explored. To remedy this situation, a numerical simulation of the composite environmental conditions from 10 observed serial MCS events is conducted. Results indicate that the 3-day simulation from the composite yields a reasonable evolution of the large-scale environment and produces a large region of organized convection in the warm sector over an extended period as seen in observations. Upstream propagation of the convective region is produced and is tied initially to the development and evolution of untrapped internal gravity waves. However, as convective downdrafts develop and begin to merge and form a surface cold pool in the simulation, the cold pool and its interaction with the environmental low-level flow also begins to play a role in convective evolution. While the internal gravity waves and cold pool interact over a several hour period to control the convective development, the cold pool eventually dominates and determines the propagation of the convective region by the end of the simulation. This upstream propagation of a South American convective region resembles the southward burst convective events described over the United States and highlights the complex interactions and feedbacks that challenge accurate forecasts of convective system evolution. 1. Introduction Fritsch 1997). Over South America, a high incidence of MCCs occurs in southeastern South America (SESA) Mesoscale convective complexes (MCCs) are char- during the warm season (Velasco and Fritsch 1987). acterized by both their long lifetimes (.6 h) and the Zipser et al. (2006) further suggest that SESA has the large quasi-circular cloud shields they produce when most intense thunderstorms in South America, making observed at infrared wavelengths by satellite (2328C this area an important region for the study of deep contiguous area .104 km2; Maddox 1980). These com- convection. plexes commonly occur over land in the lee of major It is well known that North American MCCs develop mountain ranges and in association with low-level jets within conditionally unstable environments in asso- (LLJs; Stensrud 1996a), and make significant contribu- ciation with strong low-level warm advection, a LLJ, a tions to local and global hydrologic budgets (Laing and weak midlevel short-wave trough, and a quasi-stationary frontal boundary (Maddox 1983). Over SESA, the Andes Mountains play a large role in producing the mean low- Corresponding author address: Vagner Anabor, Laborato´ rio de Fı´sica da Atmosfera, Departamento de Fı´sica, Universidade level northerly flow that is observed throughout much of Federal de Santa Maria, 97119.900 Santa Maria, RS, Brazil. the year (Byerle and Paegle 2002; Campetella and Vera E-mail: [email protected] 2002). Often embedded in this northerly flow is a LLJ DOI: 10.1175/2008MWR2617.1 Ó 2009 American Meteorological Society Unauthenticated | Downloaded 09/29/21 12:42 PM UTC JULY 2009 A N A B O R E T A L . 2145 (Marengo et al. 2004). This South American low-level of the event. The MCSs develop on the anticyclonic jet (SALLJ) is characterized by a poleward penetration side of the entrance region to an upper-level jet as also of the northerly wind, promoting moisture and heat seen in South American MCS environments by Salio transport from the Amazon region into SESA (Saulo et al. (2007). Unfortunately, the use of the low-resolution et al. 2004). Numerous studies show that the SALLJ is NCEP–NCAR reanalysis data to document the envi- important to the hydrologic cycle in the La Plata basin ronments for the upstream-propagating MCS events in of SESA (James and Anderson 1984; Rasmusson and Anabor et al. (2008) does not allow for the investigation Mo 1996; Marengo et al. 2004). Owing to this favorable of the physical mechanisms that produce the upstream mean low-level flow and advection pattern, it is not propagation of the convective region. surprising that MCCs are a common occurrence in this The upstream propagation of convective regions over region. the United States is shown to be a fairly regular occur- A more common type of organized convective region, rence by Porter et al. (1955). An examination of a single containing a contiguous precipitation region of at least long-lived upstream-propagating convective event by 100 km in horizontal extent, is the mesoscale convective Stensrud and Fritsch (1993, 1994) shows that these system (MCS) of which the larger MCC is a subset. southward burst systems propagate upstream with re- Over SESA, Nicolini et al. (2002) find a high correlation spect to the flow at all levels of the atmosphere as also between the presence of MCSs and the SALLJ, with documented over South America by Anabor et al. 81% of the 27 precipitating MCSs investigated occur- (2008). This upstream propagation occurs via a combi- ring during SALLJ events. Salio et al. (2007) further nation of cold pool propagation and internal gravity find that 81% of the spring MCSs and 67% of the waves that move ahead of the convective line and initiate summer MCSs develop during SALLJ events. Using new convective development. Thus, while the individual regional modeling experiments, Saulo et al. (2007) ex- MCSs move downstream, the convective region as a plore the linkages between LLJs and organized con- whole propagates upstream (Stensrud and Fritsch 1993). vection. Their results show that the LLJ generates The importance of MCSs in SESA is emphasized by moisture convergence and warm advection, thereby noting that the rainfall from MCSs contributes nearly providing a favorable environment for the triggering of 90% of the total rainfall in the La Plata basin (Nesbitt deep convection. The subsequent latent heat release et al. 2006). This result strongly suggests that these from the convection reinforces the convergence, help- systems are very important to both the local climate and ing to extend the life of the MCS. Using satellite, radar, human populations. Berbery and Barros (2002) indicate radiosonde, and surface observations in combination that ;80% of the total precipitation in the La Plata with selected regional modeling experiments over the river basin occurs in the austral warm season (October– southwest Amazon basin, Silva Dias et al. (2002) show April) when the main concentration of MCSs is ob- that only a few deep and intense tropical convective served over SESA (Velasco and Fritsch 1987; Laing and cells are necessary to explain the overall convective line Fritsch 2000; Zipser et al. 2006). The SESA region also formation and that the production of multiple convec- produces about 70% of the total combined gross na- tive lines may be related to discrete cell propagation and tional product of Brazil, Uruguay, Argentina, Paraguay, their coupling with upper-atmosphere circulations. and Bolivia, and houses about half of their combined Examining an important subset of all MCSs over population. Thus, the SESA region has a large impact SESA, Anabor et al. (2008) document 10 long-lived on energy production, water resources, agriculture, and serial MCS events (lifetimes .18 h) over South America livestock in South America (Vera et al. 2006), suggest- using satellite data and National Centers for Environ- ing that the accurate prediction of MCS activity in this mental Prediction–National Center for Atmospheric region would be very beneficial to a number of users of Research (NCEP–NCAR) reanalysis data. They show weather information. that a series of individual MCSs in the prefrontal region The aim of this study is to investigate the relationship develop upstream relative to the flow at all levels of the between the SALLJ and the upstream-propagating troposphere and move away from the frontal boundary convective region as documented by Anabor et al. to produce these long-lived events. These serial MCSs (2008) and to analyze the physical mechanisms for up- form within an environment of strong low-level warm stream propagation. Section 2 contains a description of advection and strong moisture advection from the Am- the numerical model, while the methods used to create azon region southward, a situation very reminiscent of the initial and boundary conditions are discussed in the environments of North American MCCs (Maddox section 3. Results are presented in section 4 followed by 1983). A strong surface anticyclone off the Brazilian an examination of the mechanisms of upstream propa- coast influences the low-level flow during the early stages gation. A final discussion is found in section 6. Unauthenticated | Downloaded 09/29/21 12:42 PM UTC 2146 MONTHLY WEATHER REVIEW VOLUME 137 the most reasonable evolution of the convective activity in comparison with the available observations. 3. Composite initial and boundary conditions Inspired by Coniglio and Stensrud (2001), realistic horizontally nonhomogeneous initial and boundary con- ditions are created using a simple composite approach on the 10 serial upstream-propagating MCS events docu- mented by Anabor et al. (2008). This approach is selected to capture the features that are common to the environ- ments of these serial MCS events, while removing fea- tures that are unique to individual cases.
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]
  • 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]
  • Chapter 7 – Atmospheric Circulations (Pp
    Chapter 7 - Title Chapter 7 – Atmospheric Circulations (pp. 165-195) Contents • scales of motion and turbulence • local winds • the General Circulation of the atmosphere • ocean currents Wind Examples Fig. 7.1: Scales of atmospheric motion. Microscale → mesoscale → synoptic scale. Scales of Motion • Microscale – e.g. chimney – Short lived ‘eddies’, chaotic motion – Timescale: minutes • Mesoscale – e.g. local winds, thunderstorms – Timescale mins/hr/days • Synoptic scale – e.g. weather maps – Timescale: days to weeks • Planetary scale – Entire earth Scales of Motion Table 7.1: Scales of atmospheric motion Turbulence • Eddies : internal friction generated as laminar (smooth, steady) flow becomes irregular and turbulent • Most weather disturbances involve turbulence • 3 kinds: – Mechanical turbulence – you, buildings, etc. – Thermal turbulence – due to warm air rising and cold air sinking caused by surface heating – Clear Air Turbulence (CAT) - due to wind shear, i.e. change in wind speed and/or direction Mechanical Turbulence • Mechanical turbulence – due to flow over or around objects (mountains, buildings, etc.) Mechanical Turbulence: Wave Clouds • Flow over a mountain, generating: – Wave clouds – Rotors, bad for planes and gliders! Fig. 7.2: Mechanical turbulence - Air flowing past a mountain range creates eddies hazardous to flying. Thermal Turbulence • Thermal turbulence - essentially rising thermals of air generated by surface heating • Thermal turbulence is maximum during max surface heating - mid afternoon Questions 1. A pilot enters the weather service office and wants to know what time of the day she can expect to encounter the least turbulent winds at 760 m above central Kansas. If you were the weather forecaster, what would you tell her? 2.
    [Show full text]
  • ERTH 365 - Lecture 8 Notes
    1 Yoon Chang Kimberly Le ERTH 365 - Lecture 8 Notes Topics Discussed - Further processes for warming and cooling the atmosphere - Cold and warm core low pressure systems; - Hurricanes in depth - Hurricane Harvey review for Homework 2 (suppl. Notes) Warming & Cooling the atmosphere - other processes ● Another way of WARMING air ​ ​ ○ Physicists tell us that when water vapor condenses, a certain amount of thermal energy is “given” to the atmosphere. In short, condensation is a ​ warming process. ​ ○ The amount of heating is proportional to the amount of water that condenses. At sea-level temperatures and pressures, the warming is about 590 calories for each gram of water that condenses. The 590 calories is known as “latent heat.” ​ ○ Since air with 100% relative humidity at lower dewpoint temperatures holds less water vapor than air with 100% relative humidity at higher dewpoint temperatures, much more heat is liberated in cases for which ​ cloud development is occurring in high dewpoint environments. ​ ● Another way of COOLING air ​ ​ ○ Conductional Cooling ■ Air flows over a cold surface and is cooled by conduction. (this process is termed “advective cooling”) If the cooling is sufficient to take the air parcel’s temperature to the dew point, the resulting condensation will produce a layered cloud on the ground. ■ Air “sits” on a surface that gets cold overnight. (radiation cooling) if the cooling is sufficient to take the air parcel’s temperature to the 2 dew point, the resulting condensation will produce a layered cloud on the ground. ○ Expansion cooling ■ Air expands, molecules get “further apart”, do not strike each other as often, do not “vibrate” as much.
    [Show full text]
  • An Analysis of the 28Th August 1999 Tornadic Event in Eastern Spain
    Atmospheric Research 67–68 (2003) 301–317 www.elsevier.com/locate/atmos Tornadoes over complex terrain: an analysis of the 28th August 1999 tornadic event in eastern Spain V. Homara,*, M. Gaya` b, R. Romeroa, C. Ramisa, S. Alonsoa,c a Meteorology Group, Departament de Fı´sica, Universitat de les Illes Balears, Palma de Mallorca 07071, Spain b Instituto Nacional de Meteorologı´a, Centre Meteorolo`gic a les Illes Balears, Palma de Mallorca, Spain c IMEDEA, UIB-CSIC, Palma de Mallorca, Spain Accepted 28 March 2003 Abstract On 28 August 1999, a tornadic storm developed during the afternoon over the Gudar range, near the border between Teruel and Castello´n provinces (Sistema Ibe´rico, eastern Spain). The area has a characteristic complex terrain with peaks up to 2000 m. At least one tornado developed, which attained F3 intensity, producing severe damage in the forest that covers the mountains. The region is well known as a summer convective storm nest and, not surprisingly, a range in the Sistema Iberico is called Sierra del Rayo (lightning range). The meteorological situation on 28 August 1999 shows the presence of a thermal low over the Iberian peninsula, producing warm and moist air advection towards inland Castellon at low levels. Meanwhile, a cold trough crossed the Iberian Peninsula from west to east at upper levels. Deep convection is identified on the Meteosat images during the afternoon, when the upper level trough reached the area where warm and humid Mediterranean air was concentrated. The radar images reveal signals indicating the supercellular character of the tornado-producing storm.
    [Show full text]
  • The Carr Fire Vortex: a Case of Pyrotornadogenesis? 10.1029/2018GL080667 N
    Geophysical Research Letters RESEARCH LETTER The Carr Fire Vortex: A Case of Pyrotornadogenesis? 10.1029/2018GL080667 N. P. Lareau1 , N. J. Nauslar2, and J. T. Abatzoglou3 Key Points: 1Department of Physics, University of Nevada, Reno, Reno, NV, USA, 2Storm Prediction Center, NCEP, NWS, NOAA, Norman, • fi A re-generated vortex produced 3 tornado-strength winds, extreme fire OK, USA, Department of Geography, University of Idaho, Moscow, ID, USA behavior, and devastated parts of Redding, California • The vortex exhibited tornado-like Abstract Radar and satellite observations document the evolution of a destructive fire-generated vortex dynamics, emerging from a shear during the Carr fire on 26 July 2018 near Redding, California. The National Weather Service estimated that zone during the rapid development of a pyrocumulonimbus surface wind speeds in the vortex were in excess of 64 m/s, equivalent to an EF-3 tornado. Radar data show that the vortex formed within an antecedent region of cyclonic wind shear along the fire perimeter and immediately following rapid vertical development of the convective plume, which grew from 6 to 12 km aloft Supporting Information: • Supporting Information S1 in just 15 min. The rapid plume development was linked to the release of moist instability in a • Movie S1 pyrocumulonimbus (pyroCb). As the cloud grew, the vortex intensified and ascended, eventually reaching an • Movie S2 altitude of 5,200 m. The role of the pyroCb in concentrating near-surface vorticity distinguishes this event from other fire-generated vortices and suggests dynamical similarities to nonmesocyclonic tornadoes. Correspondence to: N. P. Lareau, Plain Language Summary A tornado-strength fire-generated vortex devastated portions of [email protected] Redding, California, during the Carr fire on 26 July 2018.
    [Show full text]
  • Regional Weather
    Chapter 09 Appendices REV3 :Layout 1 10/6/08 9:59 PM Page 191 Regional Weather 001 The following are descriptions of typical weather more often in the spring season. patterns in major boating regions of the United States. 007 Gales. Gale force winds may occur in any season but are most frequent in winter. Nor’ easters are common and sometimes are of near hurricane New England, force in winter. They are rare in summer. Mid-Atlantic 008 Hurricanes. West Indies hurricanes are a poten- tial threat until they either move over land well 002 This area is frequently a meeting place for cP to the south (when they may still re-curve and and mT air masses. When cP prevails, the bring flooding rainfall as they move back out to weather is dry. When mT prevails, temperature sea) or until they re-curve at sea and pass south and humidity are comparatively high. Storms and east of 40° N, 70° W. While the official pass along the boundary between the two air Atlantic Hurricane season is 1 June to 30 masses and are frequent, especially from November the season is very peaked with most autumn through spring. tropical storms and hurricanes occurring from 003 Most warm fronts move into an area between August through October. south and west; most cold fronts between west and north. East of the Appalachians, however, a 009 Visibility. There is a great deal of advection fog cold front sometimes moves down from the along the Atlantic coast in spring and summer, northeast. This is known as a back-door front.
    [Show 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 /---.....
    [Show full text]
  • Observations of PAN and Its Confinement in The
    Atmos. Chem. Phys., 16, 8389–8403, 2016 www.atmos-chem-phys.net/16/8389/2016/ doi:10.5194/acp-16-8389-2016 © Author(s) 2016. CC Attribution 3.0 License. Observations of PAN and its confinement in the Asian summer monsoon anticyclone in high spatial resolution Jörn Ungermann, Mandfred Ern, Martin Kaufmann, Rolf Müller, Reinhold Spang, Felix Ploeger, Bärbel Vogel, and Martin Riese Institut für Energie- und Klimaforschung – Stratosphäre (IEK-7), Forschungszentrum Jülich GmbH, Jülich, Germany Correspondence to: Jörn Ungermann ([email protected]) Received: 14 January 2016 – Published in Atmos. Chem. Phys. Discuss.: 1 February 2016 Revised: 30 May 2016 – Accepted: 15 June 2016 – Published: 12 July 2016 Abstract. This paper presents an analysis of trace gases in 1 Introduction the Asian summer monsoon (ASM) region on the basis of observations by the CRISTA infrared limb sounder taken The Asian summer monsoon (ASM) anticyclone is the dom- in low-earth orbit in August 1997. The spatially highly re- inant circulation pattern in the summertime Northern Hemi- solved measurements of peroxyacetyl nitrate (PAN) and O3 sphere in the upper troposphere/lower stratosphere (UTLS). allow a detailed analysis of an eddy-shedding event of the It has a major impact on stratosphere–troposphere exchange ASM anticyclone. We identify enhanced PAN volume mix- (STE) and thus on the trace gas composition of the north- ing ratios (VMRs) within the main anticyclone and within ern lowermost stratosphere and tropical upper troposphere. It the eddy, which are suitable as a tracer for polluted air origi- is caused by persistent thermal heating during summer with nating in India and China.
    [Show full text]
  • Baroclinic Instability and Cyclogenesis (Based on Dr
    Ch. 8 Baroclinic Instability and Cyclogenesis (Based on Dr. Matt Eastin’s Lecture Notes) Baroclinic Instability and Cyclogenesis • Basic Idea • Evidence of Initiation from the Flow Patterns Special Types of Cyclogenesis • The “Bomb” • Polar Low • “Zipper” Low • Dryline Low • Thermal Low Advanced Synoptic M. D. Eastin Baroclinic Instability The Basic Idea: “Coin Model” • Consider a coin resting on its edge Center of (an “unstable” situation) Gravity • Its center of gravity (or mass) is located h some distance (h) above the surface • As long as h > 0, the coin has some “available potential energy” . If the coin is given a small push to one side, it will fall over and come to rest on its side (a “stable” situation) . The instability was “released” and “removed” • Its center of gravity was lowered and thus its potential energy was decreased • The coin’s motion represents kinetic energy that was converted from the available h ≈ 0 potential energy Advanced Synoptic M. D. Eastin Baroclinic Instability The Basic Idea: “Simple Atmosphere” Tropopause Light • Consider a stratified four-layer atmosphere with the most dense air near the surface at the pole and the P least dense near the tropopause above the equator (an “unstable” situation) • Each layer has a center of gravity ( ) located some distance above the surface Surface Heavy • Each layer has some available potential energy • The entire atmosphere also has a center of gravity ( ) Equator T Pole and some available potential energy . If the atmosphere is given a small “push” (e.g. a weak Light cyclone) then the layers will move until they have adjusted their centers of gravity to the configuration that provides lowest possible center of gravity for the atmosphere (the most “stable” situation) .
    [Show full text]