A Climatological Study of Typhoon Formation and Typhoon Visit to Japan

Total Page:16

File Type:pdf, Size:1020Kb

A Climatological Study of Typhoon Formation and Typhoon Visit to Japan 気象砺究所研究報告 第36巷 第2号 61-118頁 昭和60年6月 Papers in Meteorology and Geophysics、ア01. 36,No. 2,PP,61-118.June 1985 A Climatological Study of Typhoon Formation and Typhoon Visit to Japan by Takashi Aoki* ハ4α¢070Jog1αzlノ~2s2α76h lnsオπ㍑彪,ITsz漉%わα,1わα7α勉,305∫‘功αη (Received Feb.28,1985;Revised March28,1985) Abstract The formation of typhoons in the westem North Pacific and typhoon visits to Japan are investigated from a climatological standpoint.The relationship between the frequency of typhoon formation or typhoon visits and the sea surface temperature in the North Pacific is also studied. First,the formation of typhoons for the30.year period from l953to1982is examined. The average number of typhoons formed is27a year. For the amual var量ation of monthly『 frequency of typhoon formation,the maximum frequency occurs in August and the minimum in February。 Typhoons are formed most frequently in the ocean east of the Philippine Islands.The latitude of typhoon formation moves northward in summer and then retreats equatorward. Secular variation in the frequency of typhoon formation is studied by trend analysis and power spectrum analysis。The frequency showed a peak in the middle of the1960ンs.The frequency of typhoon formation increased until the middle of the1960’s an(i then decreased・ There exist two periodicities of3to4years and6to7years in the secular variation of typhoon formation. In the frequent/infrequeht months of typhoon formation the following characteristics are found. The frequency shows a marked increase north of15。N in the case of frequent typhoon formation.The polar vortex is weak/strong.The zonal index is high/low,because the Aleutian low is active/inactive and the subtropical anticyclone and the intertropical con- vergence zone exist north/80uth of their normal positions. The negative/positlve anomalies of sea surface temperature are extensive in the subtropical ocean south of Japan。 Next,typhoon visit to Japan is investigated for the perio(i of 70 years from l913to 1982.When a typhoon apProaches Japan and comes within a distance of apProximately300 km from the coast,it is(iesignated as a typhoon that visits Japan。The average amual number of typhoon visits is9. The maximum monthly frequency occurs in August and there are no typhoons from January tσMarch in Japan。 The area of the most frequent visits is the sea south of the Okinawa Islands。Typhoon visits are the least fre〔1uent in the sea northeast of the Hokkaido District。 The∫requencyr of typhoon visits is high in the open sea and straits and is relatively low near the islands an(1momtains.The typhoon season opens負rst near the Nansei Islands,and then the fre- quency increases also in northern areas。 In the later typhoon season,typhoon visits occur frequently in the sea southeast of the Pacific coast. Secular variation of typhoon visit is examined by trend analysis and power spectrum analysis. The frequency is lower from the latter half of the1920ンs to the1930’s.There exist h三gh frequencies of visit from the latter half of the1940’s to the early1950’s and *Present af五liation Japan Meteorological Agency,Tokyo100,Japan。 62 T.Aoki Vo1.36, No.2 around1960。 The results also show the existence of variations of approximately2to2,5 years and 5to6 years periodicities,in addition to a perio(iicity of40 years. In years of frequent/infrequent typhoon formation,typhoons frequently/infrequently visit the coast from the Tokai District to the Kanto District。 The annual variations of regional typhoon visit to Japan are studied by principal com- ponent analysis. The first four eigenvectors account for97.5% of the total variance and the pro丘1e of the annual variation in frequency of regional typhoon visits is adequately describe(i by the four eigenvectors. AregionaldivisionofJapanisproposedbyusingtheamplitudecoe伍cientscorrespon(1- ing to these four eigenvectors. Ten regions are obtained. Broadly speaking,these regions can be divided into four groups. The Pacific Ocean side and the Japan Sea side form one boundary while the Kinki and Shikoku Districts form another. Finally,the correlations between the frequency of typhoon formation or typhoon visits and sea surface temperature are analyse(L The frequency of typhoon formation shows a minimum during El Ni五〇events and maximum frequency is observed two years Iater.There is simultaneous correlation in the sense that as the sea surface temperature in the eastem Equatorial Pacific rises,the fre- quency of typhoon formation(1ecreases,and vice versa。 There are significant correlations between the number of typhoons formed and the sea surface temperature in the preceding year and two years before. The same relationship hOlds true for typho6n visit. High positive correlations are found for the sea surface tem- perature in the eastem Equatorial Pacific,while there are negative correlations for the northwestem part of the North Paci丘c. For typhoon visit,there are significant positive correlations with the sea surface temperature of the summer of the preceding year in the ocean south an(i southeast of Japan. To predict the frequency of typhoon formation and typhoon visit,.multiple regression equations are develope(i by hsing sea surface temperatures as independent variables.The multiple correlation coefncients for typhoon formation and typhoon visit are O.854and O.825, respectively. These equations may be useful in long-range forecasting. Contents 1 Introduction.。. 63 L L Review of Climatological Studies of Typhoon Formation and Typhoon Visit to Japan...... 63 L2.Purpose of This Study 65 1.3. Data 65 2 Climatology of Typhoon Formation 66 21。Frequency of Typhoon Formation.。.。 66 2.1。1.Distribution of Typhoon Formation 66 2.1.2。Annual Variation of Typhoon Formation..... 69 2.2.Secular Variation of Typhoon Formation 75 2。2.1.Trends in Frequency of Typhoon Formation. 75 2.2.2.Power Spectrum Analysis of Typhoon Formation 76 2.3.Contrastive Study for Frequent and Infrequent Months of Typhoon Formation 77 2.3。L Typhoon Formation in Frequent and Infrequent Months 77 2.3・2・Large-Scale Circulation of the Atmosphere in Frequent and Infrequent Months 79 2.3。3.Cloudiness in Frequent and Infrequent Months.... 80 2.3.4。Sea Surface Temperature in Frequent and Infrequent Months 81 2.4.Summary。 83 3 Climatology of Typhoon Visit to Japan 84 3.1,Frequency of Typhoon Visit to Japan..... 84 3.1。1.Distribution of Typhoon Visit to Japan 84 3.L2。Annual Variation of Typhoon Visit to Japan. 86 3.2.Secular Variation of Typhoon Visit to Japan.... 90 1985 AClimatologica1StudyofTyphoon 63 3.2。1。Characteristics of the Secular Variation of Typhoon Visit to Japan.......... 90 3.2。2,Power Spectrum Analysis of Typhoon Visit to Japan ..,....,......._.., 91 3・2・3・Relationship between Frequency of TyphoQn Formation and Typhoon Visit toJapan_.。99.9..甲......臼...9.....噸.り9.9.-9....響.--.-...曾.........臼...9991 3。3。Regional Division of Japan Based on Typhoon Visit..。................。........ 94 3、3。L Principal Component Analysis of Annual Variations of Regional Typhoon Visit 94 3.3。2,Method of Classi丘cation...............................。....................95 3.3。3.Results of Analysis............。...........。.....。......................... 97 3・4。Summary..9.....乳.曾...9.9..噸....9.....9......曾.......9......り............9...曾 99 4。Relationship between Typho6n and Sea Surface Temperature.......。................100 4・1・Correlation between Frequency of Typoon Formation and Sea Surface Temperature lOO 4.L l.EI Ni五〇Events and Frequency of Typhoon Formation......。...............100 4・L2・Seasonal Variation of Correlation Pattems for Frequency of Typhoon Formation IOl 4・1・3・Distribution of Correlation Coef五cients for Fre(1uency of Typhoon Formation..102 4,2。Correlation between Frequency of Typhoon Visits to Japan an(l Sea Surface Temperature.ロ...9..9.9..99.....D.D......9一.曾.9..............6.}.....9...9.9..!05 4・2・L Seasonal Variation of Correlation Pattems for Frequency of Typhoon Visits 105 4.2,2.Distribution of Correla亡ion Coe伍cients for Frequency『of Typhoon Visits....106 4.3.Multiple Regression Analysis。.....................。.......................。...108 4.3。1。Possible Independent Variables........。...................................。.109 4・3・2・Development of Multiple Regression Equations..............................U1 4。4.Summary.......り....り9.り..9..曾......99....9..9....9.......り.................9.ll2 5. Conclusions......し...............9....9.......9....9..........9..曾................. 113 Acknowledgements..........。.。......。...............。........................。.......115 References.9..9......◎...............雪..............................................99 115 和文概要3.D....9一......9.D.....6臼.い..9C..9..9.99-9...9.9.............9........9..9一...118 1.Introduction Meteoro1ogical activities in Japan have developed greatly since the beginning of this 1.1Rc漉ωofα伽α孟oZo9εcαZS飢αεε80f century,and meteorological stations have been T〃P尭ooπForηεα孟εoπαπδT〃phooπ 1Vεs甜 established on various islands as far away as 加」αPαn! Hachijojima,Chichijima,the Nansei,Islands Atyphoonisoneofthemostviolent and Formosa,as shown in Fig.1.Meteoro- storms in the world.A number of typhoons 10gical data obtained from ships have been are formed in the westem North Paci行c every collected via marine ra(1io since l910.Con- year,some of which strike Japan.Strong sequently,numerous observational data on winds and heavy rainfalls associated with typhoons have become available. typhoons are a major cause of natural disasters Otani (1940) investigate(l the average in Japan.The damage suffered from typhoons monthly tracks of typhoons。He found that
Recommended publications
  • (QBO) Impact on the Boreal Winter Polar Vortex
    https://doi.org/10.5194/acp-2019-1119 Preprint. Discussion started: 14 January 2020 c Author(s) 2020. CC BY 4.0 License. A tropospheric pathway of the stratospheric quasi-biennial oscillation (QBO) impact on the boreal winter polar vortex Koji Yamazaki1, Tetsu Nakamura1, Jinro Ukita2, and Kazuhira Hoshi3 5 1Faculty of Environmental Earth Science, Hokkaido University, Sapporo, 060-0810, Japan 2Faculty of Science, Niigata University, Niigata, 950-2181, Japan 3Graduate School of Science and Technology, Niigata University, Niigata, 950-2181, Japan 10 Correspondence to: Koji Yamazaki ([email protected]) Abstract. The quasi-biennial oscillation (QBO) is quasi-periodic oscillation of the tropical zonal wind in the stratosphere. When the tropical lower stratospheric wind is easterly (westerly), the winter Northern Hemisphere (NH) stratospheric polar vortex tends to be weak (strong). This relation is known as Holton-Tan relationship. Several mechanisms for this relationship have been proposed, especially linking the tropics with high-latitudes through stratospheric pathway. Although QBO impacts 15 on the troposphere have been extensively discussed, a tropospheric pathway of the Holton-Tan relationship has not been explored previously. We here propose a tropospheric pathway of the QBO impact, which may partly account for the Holton- Tan relationship in early winter, especially in the November-December period. The study is based on analyses on observational data and results from a simple linear model and atmospheric general circulation model (AGCM) simulations. The mechanism is summarized as follows: the easterly phase of the QBO is accompanied with colder temperature in the 20 tropical tropopause layer, which enhances convective activity over the tropical western Pacific and suppresses over the Indian Ocean, thus enhancing the Walker circulation.
    [Show full text]
  • Program At-A-Glance
    Sunday, 29 September 2019 Dinner (6:30–8:00 PM) ___________________________________________________________________________________________________ Monday, 30 September 2019 Breakfast (7:00–8:00 AM) Session 1: Extratropical Cyclone Structure and Dynamics: Part I (8:00–10:00 AM) Chair: Michael Riemer Time Author(s) Title 8:00–8:40 Spengler 100th Anniversary of the Bergen School of Meteorology Paper Raveh-Rubin 8:40–9:00 Climatology and Dynamics of the Link Between Dry Intrusions and Cold Fronts and Catto Tochimoto 9:00–9:20 Structures of Extratropical Cyclones Developing in Pacific Storm Track and Niino 9:20–9:40 Sinclair and Dacre Poleward Moisture Transport by Extratropical Cyclones in the Southern Hemisphere 9:40–10:00 Discussion Break (10:00–10:30 AM) Session 2: Jet Dynamics and Diagnostics (10:30 AM–12:10 PM) Chair: Victoria Sinclair Time Author(s) Title Breeden 10:30–10:50 Evidence for Nonlinear Processes in Fostering a North Pacific Jet Retraction and Martin Finocchio How the Jet Stream Controls the Downstream Response to Recurving 10:50–11:10 and Doyle Tropical Cyclones: Insights from Idealized Simulations 11:10–11:30 Madsen and Martin Exploring Characteristic Intraseasonal Transitions of the Wintertime Pacific Jet Stream The Role of Subsidence during the Development of North American 11:30–11:50 Winters et al. Polar/Subtropical Jet Superpositions 11:50–12:10 Discussion Lunch (12:10–1:10 PM) Session 3: Rossby Waves (1:10–3:10 PM) Chair: Annika Oertel Time Author(s) Title Recurrent Synoptic-Scale Rossby Wave Patterns and Their Effect on the Persistence of 1:10–1:30 Röthlisberger et al.
    [Show full text]
  • Reducing Tornado Fatalities Outside Traditional “Tornado
    Reducing Tornado Fatalities Outside Traditional “Tornado Alley” Erin A. Thead May 2016 Introduction Atmospheric scientists have long suspected that climate change produces an increase in weather extremes of all varieties, but tornadoes are an unusually tricky case. A recent publication from the National Academy of Sciences summarizes the state of the art in the new discipline of event attribution, finding that that, although tornadoes are among the most difficult extreme weather events attribute to anthropogenic climate change, improvements in modeling and climate-weather model coupling have made possible some degree of probabilistic attribution.1 At present it seems likely that the influence of climate change on tornadoes is indirect, manifested largely by more direct influences on natural climate cycles such as the amplitude of waves in the jet stream that bounds the polar vortex and the El Niño-Southern Oscillation (ENSO), with which severe tornado seasons and their predominant locations have been loosely linked.2,3 Researchers are not yet in a position to say for sure what if any role climate change has played in the increases in tornado frequency and severity we have seen over the past 50 years.4 However, we need not wait until these issues are sorted out to begin working to protect vulnerable populations. In what follows, I first give some background on the increasingly significant threat posed by tornadoes and then outline some proactive steps governments and other entities can take to keep people safe. A Disturbing Trend A disturbing trend has already developed concerning tornado fatalities. After several decades of decline that can largely be credited to a great increase in forecasting skills and warning lead time, the United States fatality rate for tornadoes has leveled off, although there may have been a slight increase in recent years.
    [Show full text]
  • Observed Cyclone–Anticyclone Tropopause Vortex Asymmetries
    JANUARY 2005 H A K I M A N D CANAVAN 231 Observed Cyclone–Anticyclone Tropopause Vortex Asymmetries GREGORY J. HAKIM AND AMELIA K. CANAVAN University of Washington, Seattle, Washington (Manuscript received 30 September 2003, in final form 28 June 2004) ABSTRACT Relatively little is known about coherent vortices near the extratropical tropopause, even with regard to basic facts about their frequency of occurrence, longevity, and structure. This study addresses these issues through an objective census of observed tropopause vortices. The authors test a hypothesis regarding vortex-merger asymmetry where cyclone pairs are repelled and anticyclone pairs are attracted by divergent flow due to frontogenesis. Emphasis is placed on arctic vortices, where jet stream influences are weaker, in order to facilitate comparisons with earlier idealized numerical simulations. Results show that arctic cyclones are more numerous, persistent, and stronger than arctic anticyclones. An average of 15 cyclonic vortices and 11 anticyclonic vortices are observed per month, with maximum frequency of occurrence for cyclones (anticyclones) during winter (summer). There are are about 47% more cyclones than anticyclones that survive at least 4 days, and for longer lifetimes, 1-day survival probabilities are nearly constant at 65% for cyclones, and 55% for anticyclones. Mean tropopause potential-temperature amplitude is 13 K for cyclones and 11 K for anticyclones, with cyclones exhibiting a greater tail toward larger values. An analysis of close-proximity vortex pairs reveals divergence between cyclones and convergence be- tween anticyclones. This result agrees qualitatively with previous idealized numerical simulations, although it is unclear to what extent the divergent circulations regulate vortex asymmetries.
    [Show full text]
  • Aleutian Islands
    Ecosystem Status Report 2018 Aleutian Islands Edited by: Stephani Zador1 and Ivonne Ortiz2 1Resource Ecology and Fisheries Management Division, Alaska Fisheries Science Center, National Marine Fisheries Service, NOAA 7600 Sand Point Way NE, Seattle, WA 98115 2 JISAO, University of Washington, Seattle, WA With contributions from: Sonia Batten, Jennifer Boldt, Nick Bond, Anne Marie Eich, Ben Fissel, Shannon Fitzgerald, Sarah Gaichas, Jerry Hoff, Steve Kasperski, Carol Ladd, Ned Laman, Geoffrey Lang, Jean Lee, Jennifer Mondragon, John Olson,Ivonne Ortiz, Wayne Palsson, Heather Renner, Nora Rojek, Chris Rooper, Kim Sparks, Michelle St Martin, Jordan Watson, George A. Whitehouse, Sarah Wise, and Stephani Zador Reviewed by: The Plan Teams for the Groundfish Fisheries of the Bering Sea, Aleutian Islands, and Gulf of Alaska November 13, 2018 North Pacific Fishery Management Council 605 W. 4th Avenue, Suite 306 Anchorage, AK 99301 Aleutian Islands 2018 Report Card Region-wide The North Pacific Index (NPI) was strongly positive from fall 2017 into 2018 due to the relatively high sea level pressure in the region of the Aleutian Low, which was displaced to the northwest, over Siberia, and caused persistent warm winds from the southwest. Positive NPI is expected during La Ni~na,but its magnitude was greater than expected. The Aleutians Islands region experienced suppressed storminess through fall and winter 2017/2018 across the region. The Alaska Stream appears to have been relatively diffuse on the south side of the eastern Aleutian Islands. Although the sea surface temperatures cooled in 2018, relative to the 2014{2017 warm period, the overall temperature was still warm due to heat retention throughout the water column.
    [Show full text]
  • Review of the Draft Climate Science Special Report
    THE NATIONAL ACADEMIES PRESS This PDF is available at http://www.nap.edu/24712 SHARE Review of the Draft Climate Science Special Report DETAILS 132 pages | 8.5 x 11 | PAPERBACK ISBN 978-0-309-45664-7 | DOI: 10.17226/24712 CONTRIBUTORS GET THIS BOOK Committee to Review the Draft Climate Science Special Report; Board on Atmospheric Sciences and Climate; Division on Earth and Life Studies; National Academies of Sciences, Engineering, and FIND RELATED TITLES Medicine Visit the National Academies Press at NAP.edu and login or register to get: – Access to free PDF downloads of thousands of scientific reports – 10% off the price of print titles – Email or social media notifications of new titles related to your interests – Special offers and discounts Distribution, posting, or copying of this PDF is strictly prohibited without written permission of the National Academies Press. (Request Permission) Unless otherwise indicated, all materials in this PDF are copyrighted by the National Academy of Sciences. Copyright © National Academy of Sciences. All rights reserved. Review of the Draft Climate Science Special Report Committee to Review the Draft Climatee Science Special Report Board on Atmospheric Sciences and Climate Division on Earth and Life Studies A Report of Copyright © National Academy of Sciences. All rights reserved. Review of the Draft Climate Science Special Report THE NATIONAL ACADEMIES PRESS 500 Fifth Street, NW Washington, DC 20001 This study was supported by the National Aeronautics and Space Administration under award numbers NNH14CK78B and NNH14CK79D. Any opinions, findings, conclusions, or recommendations expressed in this publication do not necessarily reflect the views of any organization or agency that provided support for the project.
    [Show full text]
  • The North Atlantic Variability Structure, Storm Tracks, and Precipitation Depending on the Polar Vortex Strength
    Atmos. Chem. Phys., 5, 239–248, 2005 www.atmos-chem-phys.org/acp/5/239/ Atmospheric SRef-ID: 1680-7324/acp/2005-5-239 Chemistry European Geosciences Union and Physics The North Atlantic variability structure, storm tracks, and precipitation depending on the polar vortex strength K. Walter1 and H.-F. Graf1,2 1Max-Planck-Institute for Meteorology, Bundesstrasse 54, D-20146 Hamburg, Germany 2Centre for Atmospheric Science, University of Cambridge, Dept. Geography, Cambridge, CB2 3EN, UK Received: 10 June 2004 – Published in Atmos. Chem. Phys. Discuss.: 5 October 2004 Revised: 7 December 2004 – Accepted: 27 January 2005 – Published: 1 February 2005 Abstract. Motivated by the strong evidence that the state 1 Introduction of the northern hemisphere vortex in boreal winter influ- ences tropospheric variability, teleconnection patterns over During boreal winter the climate in large parts of the North- the North Atlantic are defined separately for winter episodes ern Hemisphere is under the influence of the North Atlantic where the zonal wind at 50 hPa and 65◦ N is above or below Oscillation (NAO). The latter constitutes the dominant mode the critical velocity for vertical propagation of zonal plane- of tropospheric variability in the North Atlantic region in- tary wave 1. We argue that the teleconnection structure in the cluding the North American East Coast and Europe, with ex- middle and upper troposphere differs considerably between tensions to Siberia and the Eastern Mediterranean. The NAO the two regimes of the polar vortex, while this is not the case is characterised by a meridional oscillation of mass between at sea level. If the polar vortex is strong, there exists one two major centres of action over the subtropical Atlantic and meridional dipole structure of geopotential height in the up- near Iceland: the Azores High and the Iceland Low.
    [Show full text]
  • Interaction of Tropical Cyclones with a Dipole Vortex
    Chapter 2 Interaction of Tropical Cyclones with a Dipole Vortex Ismael Perez‐Garcia, Alejandro Aguilar‐Sierra and Jaime Hernández Additional information is available at the end of the chapter http://dx.doi.org/10.5772/65953 Abstract The purpose of this chapter is to discuss certain disturbances around the pole of a Venus–type planet that result as a response to barotropic instability processes in a zonal flow. We discuss a linear instability of normal modes in a zonal flow through the barotropic vorticity equations (BVEs). By using a simple idealization of a zonal flow, the instability is employed on measurements of the upper atmosphere of Venus. In 1998, the tropical cyclone Mitch gave way to the observational study of a dipole vortex. This dipole vortex might have helped to intensify the cyclone and moved it towards the SW. In order to examine this process of interaction, the nonlinear BVE was integrated in time applied to the 800–200 hPa average layer in the previous moment when it moved towards the SW. The 2-day integrations carried out with the model showed that the geometric structure of the solution can be calculated to a good approximation. The solution HLC moves very fast westwards as observed. On October 27, the HLA headed north-eastward and then became quasi-stationary. It was also observed that HLA and HLC as a coupled system rotates in the clockwise direction. Keywords: polar vortices Venus, barotropic vorticity equation, normal mode instabil- ity, tropical cyclone, American monsoon system. 1. Introduction The air at the equatorial regions rises when heated by the sun and as it does, it cools down and sinks.
    [Show full text]
  • Spring 2014 Volume V-1
    The Coastal Front Spring 2014 Volume V-1 Skywarn Spotter Training Photo by John Jensenius By Chris Kimble, Forecaster Inside This Issue: Over the last several decades, technology has greatly improved our ability to observe and forecast the weather. Tools like satellite and radar provide more insight than ever into what the weather is doing Severe WX: Be Prepared Page 2 right now. Computers have allowed for greater integration of all the Dual Pol Radar Page 3 data, and complex forecast models provide valuable insight into how Winter Weather Review Page 4 weather systems will evolve over the next several days. But, no matter how December Ice Storm Page 5 advanced technol- Polar Vortex Explained Page 6 ogy has become, Staff Profile Page 7 forecasters rely on Note From the Editors Page 9 volunteers to re- port the ground truth of what’s Editor-in-Chief: Chris Kimble really happening in their town. Editors: Stacie Hanes Margaret Curtis While weather Michael Kistner radar is a great Figure 1: A supercell thunderstorm tracks across Nichole Becker tool to view Portland, Maine on June 23, 2013. Photo by Chris thunderstorms and Legro. Meteorologist in Charge (MIC): Hendricus Lulofs other precipitation events above the ground, there are often significant gaps between Warning Coordination what the radar sees above the ground and what is observed at ground Meteorologist (WCM): John Jensenius level where it matters most. Skywarn Storm Spotters provide invaluable information to NWS forecasters during and after severe thunderstorms, tornadoes, flash floods, and snow storms. If you have an interest in weather and want to become a volunteer Skywarn Storm Spotter, attend one of our Skywarn training sessions.
    [Show full text]
  • 5. Analyses and Forecasts of Stratospheric Winter Polar Vortex Break-Up: September 2002 in the Southern Hemisphere and Related Events from ECMWF Operations and ERA-40
    ERA-40 Project Report Series 5. Analyses and forecasts of stratospheric winter polar vortex break-up: September 2002 in the Southern Hemisphere and related events from ECMWF operations and ERA-40 Adrian Simmons, Mariano Hortal, Graeme Kelly, Anthony McNally, Agathe Untch and Sakari Uppala European Centre for Medium-Range Weather Forecasts Europäisches Zentrum für mittelfristige Wettervorhersage Centre européen pour les prévisions météorologiques à moyen terme For additional copies contact: The Library ECMWF Shinfield Park Reading, Berks RG2 9AX [email protected] Series: ERA40 Project Report Series A full list of ECMWF Publications can be found on our web site under: http://www.ecmwf.int/publications/ © Copyright 2003 European Centre for Medium Range Weather Forecasts Shinfield Park, Reading, Berkshire RG2 9AX, England Literary and scientific copyrights belong to ECMWF and are reserved in all countries. This publication is not to be reprinted or translated in whole or in part without the written permission of the Director. Appropriate non- commercial use will normally be granted under the condition that reference is made to ECMWF. The information within this publication is given in good faith and considered to be true, but ECMWF accepts no liability for error, omission and for loss or damage arising from its use. ERA-40 project report series no.5 Analyses and forecasts of stratospheric winter polar vortex break-up: September 2002 in the southern hemisphere and related events from ECMWF operations and ERA-40 Adrian Simmons, Mariano Hortal, Graeme Kelly, Anthony McNally, Agathe Untch and Sakari Uppala Research Department March 2003 Analyses and forecasts of stratospheric winter polar vortex break-up ABSTRACT Break-up of the polar stratospheric vortex in the northern hemisphere is an event that is known to be predictable for up to a week or so ahead.
    [Show full text]
  • Explaining the Trends and Variability in the United States Tornado Records
    www.nature.com/scientificreports OPEN Explaining the trends and variability in the United States tornado records using climate teleconnections and shifts in observational practices Niloufar Nouri1*, Naresh Devineni1,2*, Valerie Were2 & Reza Khanbilvardi1,2 The annual frequency of tornadoes during 1950–2018 across the major tornado-impacted states were examined and modeled using anthropogenic and large-scale climate covariates in a hierarchical Bayesian inference framework. Anthropogenic factors include increases in population density and better detection systems since the mid-1990s. Large-scale climate variables include El Niño Southern Oscillation (ENSO), Southern Oscillation Index (SOI), North Atlantic Oscillation (NAO), Pacifc Decadal Oscillation (PDO), Arctic Oscillation (AO), and Atlantic Multi-decadal Oscillation (AMO). The model provides a robust way of estimating the response coefcients by considering pooling of information across groups of states that belong to Tornado Alley, Dixie Alley, and Other States, thereby reducing their uncertainty. The infuence of the anthropogenic factors and the large-scale climate variables are modeled in a nested framework to unravel secular trend from cyclical variability. Population density explains the long-term trend in Dixie Alley. The step-increase induced due to the installation of the Doppler Radar systems explains the long-term trend in Tornado Alley. NAO and the interplay between NAO and ENSO explained the interannual to multi-decadal variability in Tornado Alley. PDO and AMO are also contributing to this multi-time scale variability. SOI and AO explain the cyclical variability in Dixie Alley. This improved understanding of the variability and trends in tornadoes should be of immense value to public planners, businesses, and insurance-based risk management agencies.
    [Show full text]
  • A Quick Guide to Important Drivers of US Winter Weather Patterns
    A Quick Guide to Important Drivers of US Winter Weather Patterns Web: www.frontierweather.com Email: [email protected] Phone: 918-252-7791 Twitter: @FrontierWeather Facebook: www.facebook.com/frontierweather KEY TERMS NORMAL YEAR PATTERN El Niño: An anomalous warming of the No strong SST anomalies central and eastern equatorial Pacific that occurs every 3-7 years. SST: Sea Surface Temperature Niño 3.4: A region of the Pacific between 5°N – 5°S and 120° – 170°W. SST Trade winds blow from east to west, concentrating the warmest water anomalies in this region are often used to and most of the tropical convection in the western tropical Pacific. define El Niño. Average actual SST pattern, not anomalies wind direction ONI: Oceanic Niño Index, a 3 month warmest average of the Nino 3.4 anomalies. water MEI: Multivariate ENSO Index. A six variable composite index of El Niño. EL NINO YEAR PATTERN Shifts in tropical convection are what drive global weather pattern changes during El Niño. SST anomaly pattern Tropical convection strength and location is directly tied to the location and intensity of the warmest anomalies warmest water temperatures. Warmer peak equatorial water temperatures (not anomalies), tend to produce colder eastern US winters. Trade winds slacken or even reverse, allowing warmer water to flow eastward. This shifts tropical convection eastward as well. Average actual SST pattern, not anomalies wind direction warmest water can flip to west El Niño and US Winter Weather Strong El Niño events have cooler peak water temperatures near the dateline. When warm anomalies are located farther west or when the western tropical Pacific stays warm during El Niño, peak water temperatures are higher, and tropical convection is stronger near and west of the dateline.
    [Show full text]