Chapter 6 ENSO, ATLANTIC CLIMATE VARIABILITY, and the WALKER and HADLEY CIRCULATIONS
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Meteorology Climate
Meteorology: Climate • Climate is the third topic in the B-Division Science Olympiad Meteorology Event. • Topics rotate annually so a middle school participant may receive a comprehensive course of instruction in meteorology during this three-year cycle. • Sequence: 1. Climate (2006) 2. Everyday Weather (2007) 3. Severe Storms (2008) Weather versus Climate Weather occurs in the troposphere from day to day and week to week and even year to year. It is the state of the atmosphere at a particular location and moment in time. http://weathereye.kgan.com/cadet/cl imate/climate_vs.html http://apollo.lsc.vsc.edu/classes/me t130/notes/chapter1/wea_clim.html Weather versus Climate Climate is the sum of weather trends over long periods of time (centuries or even thousands of years). http://calspace.ucsd.edu/virtualmuseum/ climatechange1/07_1.shtml Weather versus Climate The nature of weather and climate are determined by many of the same elements. The most important of these are: 1. Temperature. Daily extremes in temperature and average annual temperatures determine weather over the short term; temperature tendencies determine climate over the long term. 2. Precipitation: including type (snow, rain, ground fog, etc.) and amount 3. Global circulation patterns: both oceanic and atmospheric 4. Continentiality: presence or absence of large land masses 5. Astronomical factors: including precession, axial tilt, eccen- tricity of Earth’s orbit, and variable solar output 6. Human impact: including green house gas emissions, ozone layer degradation, and deforestation http://www.ecn.ac.uk/Education/factors_affecting_climate.htm http://www.necci.sr.unh.edu/necci-report/NERAch3.pdf http://www.bbm.me.uk/portsdown/PH_731_Milank.htm Natural Climatic Variability Natural climatic variability refers to naturally occurring factors that affect global temperatures. -
Tropical Meteorology
Tropical Meteorology Chapter 01B Topics ¾ El Niño – Southern Oscillation (ENSO) ¾ The Madden-Julian Oscillation ¾ Westerly wind bursts 1 The Southern Oscillation ¾ There is considerable interannual variability in the scale and intensity of the Walker Circulation, which is manifest in the so-called Southern Oscillation (SO). ¾ The SO is associated with fluctuations in sea level pressure in the tropics, monsoon rainfall, and wintertime circulation over the Pacific Ocean and also over North America and other parts of the extratropics. ¾ It is the single most prominent signal in year-to-year climate variability in the atmosphere. ¾ It was first described in a series of papers in the 1920s by Sir Gilbert Walker and a review and references are contained in a paper by Julian and Chervin (1978). The Southern Oscillation ¾ Julian and Chervin (1978) use Walker´s own words to summarize the phenomenon. "By the southern oscillation is implied the tendency of (surface) pressure at stations in the Pacific (San Francisco, Tokyo, Honolulu, Samoa and South America), and of rainfall in India and Java... to increase, while pressure in the region of the Indian Ocean (Cairo, N.W. India, Darwin, Mauritius, S.E. Australia and the Cape) decreases...“ and "We can perhaps best sum up the situation by saying that there is a swaying of pressure on a big scale backwards and forwards between the Pacific and Indian Oceans...". 2 Fig 1.17 The Southern Oscillation ¾ Bjerknes (1969) first pointed to an association between the SO and the Walker Circulation, but the seeds for this association were present in the studies by Troup (1965). -
Impacts of the Tropical Pacific/Indian Oceans on the Seasonal Cycle Of
3878 JOURNAL OF CLIMATE VOLUME 24 Impacts of the Tropical Pacific/Indian Oceans on the Seasonal Cycle of the West African Monsoon ,1 #,@ & E. MOHINO,* B. RODRI´GUEZ-FONSECA, C. R. MECHOSO, S. GERVOIS,* 11 P. RUTI,** AND F. CHAUVIN, * LOCEAN/IPSL, Universite´ Pierre et Marie Curie, Paris, France 1 Universidad de Sevilla, Seville, Spain # Universidad Complutense de Madrid, Madrid, Spain @ Instituto de Geosciencias, Consejo Superior de Investigaciones Cientificas and Universidad Complutense de Madrid, Madrid, Spain & Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, Los Angeles, California ** Progetto Speciale Clima Globale, Ente Nazionale per le Nuove Tecnologie, l’Energia e l’Ambiente, Rome, Italy 11 GAME/CNRM, Me´te´o-France/CNRS, Toulouse, France (Manuscript received 9 August 2010, in final form 19 January 2011) ABSTRACT The current consensus is that drought has developed in the Sahel during the second half of the twentieth century as a result of remote effects of oceanic anomalies amplified by local land–atmosphere interactions. This paper focuses on the impacts of oceanic anomalies upon West African climate and specifically aims to identify those from SST anomalies in the Pacific/Indian Oceans during spring and summer seasons, when they were significant. Idealized sensitivity experiments are performed with four atmospheric general circulation models (AGCMs). The prescribed SST patterns used in the AGCMs are based on the leading mode of covariability between SST anomalies over the Pacific/Indian Oceans and summer rainfall over West Africa. The results show that such oceanic anomalies in the Pacific/Indian Ocean lead to a northward shift of an anomalous dry belt from the Gulf of Guinea to the Sahel as the season advances. -
An Observational Study of the Tropical Tropospheric Circulation
An Observational Study of the Tropical Tropospheric Circulation Ioana M. Dima A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy University of Washington 2005 Program Authorized to Offer Degree: Department of Atmospheric Sciences University of Washington Graduate School This is to certify that I have examined this copy of a doctoral dissertation by Ioana M. Dima and have found that it is complete and satisfactory in all respects, and that any and all revisions by the final examining committee have been made. Chair of the Supervisory Committee: ______________________________________________________________________ John M. Wallace Reading Committee: ______________________________________________________________________ John M. Wallace ______________________________________________________________________ Dennis L. Hartmann ______________________________________________________________________ Edward S. Sarachik Date: ______________________ In presenting this dissertation in partial fulfillment of the requirements for the doctoral degree at the University of Washington, I agree that the Library shall make its copies freely available for inspection. I further agree that extensive copying of the dissertation is allowable only for scholarly purposes, consistent with “fair use” as prescribed in the U.S. Copyright Law. Requests for copying or reproduction of this dissertation may be referred to Proquest Information and Learning, 300 North Zeeb Road, Ann Arbor, MI 48106-1346, to whom the -
Impact of the Equatorial Atlantic on the El Ni˜No Southern Oscillation
Noname manuscript No. (will be inserted by the editor) Impact of the Equatorial Atlantic on the El Ni~no Southern Oscillation Hui Ding · Noel S. Keenlyside · Mojib Latif Received: date / Accepted: date Abstract Observations indicate that the Atlantic zonal mode influences El Ni~noSouthern Oscillation (ENSO) in the Pacific, as already suggested in pre- vious studies. Here we demonstrate for the first time using partial coupled ex- periments that the Atlantic zonal mode indeed influences ENSO. The partial coupling experiments are performed by forcing the coupled general circulation model (ECHAM5/MPI-OM) with observed sea surface temperature (SST) in the Tropical Atlantic, but with full air-sea coupling allowed in the Pacific and Indian Ocean. The ensemble mean of five members simulations reproduce the observational results well. Hui Ding IFM-GEOMAR, D¨usternbrooker Weg 20, Kiel 24105, Germany Tel.: +49-431-6004071 Fax: +49-431-6004052 E-mail: [email protected] 2 Hui Ding et al. Analysis of observations, reanalysis, and coupled model simulations all in- dicate the following mechanism: SST anomalies associated with the Atlantic zonal mode affect the Walker Circulation, driving westward wind anomalies over the equatorial Pacific during boreal summer. The wind stress anomalies increase the east-west thermocline slope and enhance the SST gradient across the Pacific; the Bjerknes positive feedback acts to amplify these anomalies favouring the development of a La Ni~na-like anomalies. The same mechanisms act for the cold phase of Atlantic zonal mode, but with opposite sign. In con- trast to previous studies, the model shows that the influence on ENSO exists before 1970. -
Teleconnections of the Tropical Atlantic to the Tropical Indian and Pacific Oceans: a Review of Recent findings
Meteorologische Zeitschrift, Vol. 18, No. 4, 445-454 (August 2009) Article c by Gebr¨uder Borntraeger 2009 Teleconnections of the tropical Atlantic to the tropical Indian and Pacific Oceans: A review of recent findings 1∗ 2 2 3 CHUNZAI WANG ,FRED KUCHARSKI ,RONDROTIANA BARIMALALA and ANNALISA BRACCO 1NOAA Atlantic Oceanographic and Meteorological Laboratory, Miami, Florida U.S.A. 2The Abdus Salam International Centre for Theoretical Physics, Earth System Physics Section Trieste, Italy 3School of Earth and Atmospheric Sciences Georgia Institute of Technology, Atlanta, Georgia, U.S.A. (Manuscript received November 12, 2008; in revised form February 16, 2009; accepted March 18, 2009) Abstract Recent studies found that tropical Atlantic variability may affect the climate in both the tropical Pacific and Indian Ocean basins, possibly modulating the Indian summer monsoon and Pacific ENSO events. A warm tropical Atlantic Ocean forces a Gill-Matsuno-type quadrupole response with a low-level anticyclone located over India that weakens the Indian monsoon circulation, and vice versa for a cold tropical Atlantic Ocean. The tropical Atlantic Ocean can also induce changes in the Indian Ocean sea surface temperatures (SSTs), especially along the coast of Africa and in the western side of the Indian basin. Additionally, it can influence the tropical Pacific Ocean via an atmospheric teleconnection that is associated with the Atlantic Walker circulation. Although the Pacific El Ni˜no does not contemporaneously correlate with the Atlantic Ni˜no, anomalous warming or cooling of the two equatorial oceans can form an inter-basin SST gradient that induces surface zonal wind anomalies over equatorial South America and other regions in both ocean basins. -
EL NIÑO SOUTHERN OSCILLATION GLOBAL CLIMATE INFLUENCER by James Rohman | March 2014
EL NIÑO SOUTHERN OSCILLATION GLOBAL CLIMATE INFLUENCER By James Rohman | March 2014 This El Niño event had a warm Water mass of roughly 4.7 million square miles, or 1.5 times the size of the continental United States Figure 1. Warm water (red/white) spreads out from equatorial South America during a strong El Niño, September 1997. The La Niña phenomenon can Significantly alter flood/drought patterns and tropical/extratropical cyclone genesis on approximately 60% of the earth’s surface Figure 2. Cold water (blue/purple) dominates the equatorial Pacific during a strong La Niña, May 1999. El Niño Southern Oscillation | Global Climate Influencer 1 Introduction In the world’s oceans lay massive repositories of stored energy. The various cold and warm patches of ocean water act to cool or heat the atmosphere, influencing global climate patterns. The heat transfer controls weather over both land and sea. The largest such recurring climate pattern is the El Niño Southern Oscillation (ENSO) in the Pacific Ocean. ENSO is the anomalous and recurring pattern of cold and warm patches of water periodically developing off the western coast of South America. El Niño is the appearance of warm water along western South America, from Chile up to Peru and Ecuador. La Niña is the exact opposite, with anomalously cold water spreading across the equatorial Pacific. In addition to changes in thermal energy in the ocean environment, the relative height of the sea surface also relates to ENSO. As patches of oceans warm, the sea level rises; as water cools, the sea level drops. -
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1JANUARY 2007 KEENLYSIDE AND LATIF 131 Understanding Equatorial Atlantic Interannual Variability NOEL S. KEENLYSIDE AND MOJIB LATIF Leibniz-Institut für Meereswissenschaften, Kiel, Germany (Manuscript received 5 May 2005, in final form 19 May 2006) ABSTRACT An observational-based analysis of coupled variability in the equatorial Atlantic and its seasonality is presented. Regression analysis shows that the three elements of the Bjerknes positive feedback exist in the Atlantic and are spatially similar to those of the Pacific. The cross-correlation functions of the elements of the Bjerknes feedback are also similar and consistent with an ocean–atmosphere coupled mode. However, the growth rate in the Atlantic is up to 50% weaker, and explained variance is significantly lower. The Bjerknes feedback in the Atlantic is strong in boreal spring and summer, and weak in other seasons, which explains why the largest sea surface temperature anomalies (SSTAs) occur in boreal summer. Its seasonality is determined by seasonal variations in both atmospheric sensitivity to SSTA and SSTA sensitivity to subsurface temperature anomalies. 1. Introduction sphere to cross-equatorial SST gradients is recognized (Chiang et al. 2002), but it is not clear if it results in a Studies of tropical Atlantic variability over the past positive ocean–atmosphere feedback (Chang et al. two decades have shown that on interannual time scales 2000; Sutton et al. 2000). coherent SST variability occurs in three main regions: The Atlantic equatorial mode of variability, also re- the north tropical Atlantic (NTA), equatorial Atlantic, ferred to as the equatorial zonal mode or Atlantic Niño and southern subtropical Atlantic (e.g., Enfield and mode, is the focus of this paper. -
Underestimated Responses of Walker Circulation to ENSO-Related SST
Wang et al. Geosci. Lett. (2021) 8:17 https://doi.org/10.1186/s40562-021-00186-8 RESEARCH LETTER Open Access Underestimated responses of Walker circulation to ENSO-related SST anomaly in atmospheric and coupled models Xin‑Yue Wang1,2, Jiang Zhu1,2, Chueh‑Hsin Chang3, Nathaniel C. Johnson4,5, Hailong Liu1,2, Yadi Li1,2, Chentao Song1,2, Meijiao Xin1,2, Yi Zhou1,2 and Xichen Li1,6* Abstract The Pacifc Walker circulation (WC) is a major component of the global climate system. It connects the Pacifc sea surface temperature (SST) variability to the climate variabilities from the other ocean basins to the mid‑ and high latitudes. Previous studies indicated that the ENSO‑related atmospheric feedback, in particular, the surface wind response is largely underestimated in AMIP and CMIP models. In this study, we further investigate the responses in the WC stream function and the sea level pressure (SLP) to the ENSO‑related SST variability by comparing the responses in 45 AMIP and 63 CMIP models and six reanalysis datasets. We reveal a diversity in the performances of simulated SLP and WC between diferent models. While the SLP responses to the El Niño‑related SST variability are well simulated in most of the atmospheric and coupled models, the WC stream function responses are largely underestimated in most of these models. The WC responses in the AMIP5/6 models capture ~ 75% of those in the reanalysis, whereas the CMIP5/6 models capture ~ 58% of the responses. Further analysis indicates that these underestimated circula‑ tion responses could be partially attributed to the biases in the precipitation scheme in both the atmospheric and coupled models, as well as the biases in the simulated ENSO‑related SST patterns in the coupled models. -
Rainfall Variations in Central Indo-Pacific Over the Past 2,700 Y
Rainfall variations in central Indo-Pacific over the past 2,700 y Liangcheng Tana,b,c,d,1, Chuan-Chou Shene,f,1, Ludvig Löwemarke,f, Sakonvan Chawchaig, R. Lawrence Edwardsh, Yanjun Caia,b,c, Sebastian F. M. Breitenbachi, Hai Chengj,h, Yu-Chen Choue, Helmut Duerrastk, Judson W. Partinl, Wenju Caim,n, Akkaneewut Chabangborng, Yongli Gaoo, Ola Kwiecieni, Chung-Che Wue, Zhengguo Shia,b, Huang-Hsiung Hsup, and Barbara Wohlfarthq,r aState Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, 710061 Xi’an, China; bCenter for Excellence in Quaternary Science and Global Change, Chinese Academy of Sciences, 710061 Xi’an, China; cOpen Studio for Oceanic-Continental Climate and Environment Changes, Pilot National Laboratory for Marine Science and Technology (Qingdao), 266061 Qingdao, China; dSchool of Earth Science and Resources, Chang‘an University, 710064 Xi’an, China; eDepartment of Geosciences, National Taiwan University, 10617 Taipei, Taiwan; fResearch Center for Future Earth, National Taiwan University, 10617 Taipei, Taiwan; gDepartment of Geology, Faculty of Science, Chulalongkorn University, 10330 Bangkok, Thailand; hDepartment of Earth Sciences, University of Minnesota, Minneapolis, MN 55455; iInstitute for Geology, Mineralogy & Geophysics, Ruhr- Universität Bochum, D-44801 Bochum, Germany; jInstitute of Global Environmental Change, Xi’an Jiaotong University, 710049 Xi’an, China; kDepartment of Physics, Faculty of Science, Prince of Songkla University, 90112 HatYai, Thailand; lJackson -
Weakened Seasonality of the African Rainforest Precipitation in Boreal
Wang et al. Geosci. Lett. (2021) 8:22 https://doi.org/10.1186/s40562-021-00192-w RESEARCH LETTER Open Access Weakened seasonality of the African rainforest precipitation in boreal winter and spring driven by tropical SST variabilities Xin‑Yue Wang1,2, Jiang Zhu1,2, Meijiao Xin1,2, Chentao Song1,2, Yadi Li1,2, Yi Zhou1,2 and Xichen Li1,3* Abstract Precipitation in the equatorial African rainforest plays an important role in both the regional hydrological cycle and the global climate variability. Previous studies mostly focus on the trends of drought in recent decades or long‑time scales. Using two observational datasets, we reveal a remarkable weakening of the seasonal precipitation cycle over this region from 1979 to 2015, with precipitation signifcantly increased in the boreal winter dry season (~ 0.13 mm/ day/decade) and decreased in the boreal spring wet season (~ 0.21 mm/day/decade), which account for ~ 14% (the precipitation changes from 1979 to 2015) of their respective climatological means. We further use a state‑of‑the‑ art atmospheric model to isolate the impact of sea surface temperature change from diferent ocean basins on the precipitation changes in the dry and wet seasons. Results show that the strengthening precipitation in the dry season is mainly driven by the Atlantic warming, whereas the weakening precipitation in the wet season can be primarily attributed to the Indian Ocean. Warming Atlantic intensifes the zonal circulation over the African rainforest, strength‑ ening moisture convergence and intensifying precipitation in the boreal winter dry season. Warming Indian Ocean contributes more to reducing the zonal circulation and suppressing the convection in the boreal spring wet season, leading to an opposite efect on precipitation. -
Local Energetic Constraints on Walker Circulation Strength
JUNE 2017 W I L L S E T A L . 1907 Local Energetic Constraints on Walker Circulation Strength ROBERT C. WILLS ETH Zurich,€ Zurich, Switzerland, and California Institute of Technology, Pasadena, California XAVIER J. LEVINE Yale University, New Haven, Connecticut TAPIO SCHNEIDER ETH Zurich,€ Zurich, Switzerland, and California Institute of Technology, Pasadena, California (Manuscript received 25 July 2016, in final form 20 January 2017) ABSTRACT The weakening of tropical overturning circulations is a robust response to global warming in climate models and observations. However, there remain open questions on the causes of this change and the extent to which this weakening affects individual circulation features such as the Walker circulation. The study presents idealized GCM simulations of a Walker circulation forced by prescribed ocean heat flux convergence in a slab ocean, where the longwave opacity of the atmosphere is varied to simulate a wide range of climates. The weakening of the Walker circulation with warming results from an increase in gross moist stability (GMS), a measure of the tropospheric moist static energy (MSE) stratification, which provides an effective static sta- bility for tropical circulations. Baroclinic mode theory is used to determine changes in GMS in terms of the tropical-mean profiles of temperature and MSE. The GMS increases with warming, owing primarily to the rise in tropopause height, decreasing the sensitivity of the Walker circulation to zonally anomalous net energy input. In the absence of large changes in net energy input, this results in a rapid weakening of the Walker circulation with global warming. 1. Introduction convective mass fluxes globally in response to increasing near-surface specific humidity with global warming In climate models and observations, convective mass (Betts 1998; Held and Soden 2006; Vecchi and Soden flux and zonally anomalous tropical overturning circu- 2007; Schneider et al.