DOCSLIB.ORG

Analogous Pacific and Atlantic Meridional Modes of Tropical

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Analogous Pacific and Atlantic Meridional Modes of Tropical 1NOVEMBER 2004 CHIANG AND VIMONT 4143 Analogous Paci®c and Atlantic Meridional Modes of Tropical Atmosphere±Ocean Variability* JOHN C. H. CHIANG 1Department of Geography, and Center for Atmospheric Sciences, University of California, Berkeley, Berkeley, California DANIEL J. VIMONT Department of Atmospheric and Oceanic Sciences, University of WisconsinÐMadison, Madison, Wisconsin (Manuscript received 4 December 2003, in ®nal form 28 May 2004) ABSTRACT From observational analysis a Paci®c mode of variability in the intertropical convergence zone (ITCZ)/cold tongue region is identi®ed that possesses characteristics and interpretation similar to the dominant ``meridional'' mode of interannual±decadal variability in the tropical Atlantic. The Paci®c and Atlantic meridional modes are characterized by an anomalous sea surface temperature (SST) gradient across the mean latitude of the ITCZ coupled to an anomalous displacement of the ITCZ toward the warmer hemisphere. Both are forced by trade wind variations in their respective northern subtropical oceans. The Paci®c meridional mode exists independently of ENSO, although ENSO nonlinearity projects strongly on it during the peak anomaly season of boreal spring. It is suggested that the Paci®c and Atlantic modes are analogous, governed by physics intrinsic to the ITCZ/ cold tongue complex. 1. Introduction mode (hereafter the meridional mode, also known as the gradient or interhemispheric mode) arises. Nobre and The dominant statistical mode of tropical Atlantic in- Shukla (1996) argued from observational analysis that terannual±decadal atmosphere±ocean variability is an trade wind variations in the north tropical Atlantic pre- anomalous meridional SST gradient across the mean intertropical convergence zone (ITCZ) latitude and a cede the tropical basinwide anomalies that in turn pro- cross-gradient atmospheric boundary layer ¯ow toward duced SST anomalies there (and hence an anomalous the anomalously warmer hemisphere (Nobre and Shukla SST gradient across the mean ITCZ latitude), implying 1996; Chang et al. 1997). Hastenrath and Greischar that the mode is externally forced. Two sources of ex- (1993) proposed that this boundary layer ¯ow is driven ternal forcing have been identi®ed: ENSO and the North by the anomalous meridional SST gradient through its Atlantic Oscillation (NAO; e.g., Curtis and Hastenrath hydrostatic effect on sea level pressure (Lindzen and 1995; Nobre and Shukla 1996; Xie and Tanimoto 1998; Nigam 1987). The cross-gradient ¯ow implies a shift of Giannini et al. 2000). They directly perturb the boreal the ITCZ and associated convection toward the anom- winter north tropical Atlantic (NTA) trade wind alously warmer hemisphere (e.g., Hastenrath and Heller strength, changing the underlying SST through latent 1977). This basic pictureÐlinking anomalous SST, heat ¯uxes. The resulting NTA SST perturbation peaks winds, and convectionÐhas been supported in subse- in boreal spring, creating the near-equatorial meridional quent observational and modeling studies (e.g., Ruiz- SST gradient. Barradas et al. 1999; Chang et al. 2000; Chiang et al. Chang et al. (1997) proposed an alternative expla- 2002). nation for the origins of the meridional mode, pointing Two interpretations had been proposed for how this to a positive feedback [sometimes known as wind±evap- oration±SST (WES) feedback (e.g., Xie 1999)] between the SST gradient and the cross-gradient ¯ow. The cross- * National Oceanic and Atmospheric Administration Contribution Number 1010. gradient ¯ow reduced the strength of the trade winds in the anomalously warmer hemisphere and increased the trades in the cooler hemisphere, and this reinforced the Corresponding author address: John Chiang, Department of Ge- SST gradient through wind speed impact on anomalous ography, University of California, 547 McCone Hall, Berkeley, Berkeley, CA 94720-4740. evaporation. Idealized modeling studies (e.g., Chang et E-mail: [email protected] al. 1997; Xie 1999) have shown that this feedback can q 2004 American Meteorological Society Unauthenticated | Downloaded 09/30/21 06:48 PM UTC 4144 JOURNAL OF CLIMATE VOLUME 17 qualitatively reproduce the observed behavior, though march lagging by a quarter cycle the seasonal cycle of it was found that under realistic coupling strength the the ITCZ over land (Mitchell and Wallace 1992). An model behavior was not self-sustaining, and that exter- idealized tropical coupled general circulation model nal forcing was required to sustain the variability. Sub- study (Xie and Saito 2001) shows that in the absence sequent modeling and observational studies show this of thermocline±SST feedback central to the ENSO phys- feedback is relatively weak and limited to the deep Trop- ics, interannual variations in the north±south oceanic ics (Chang et al. 2000; Chiang et al. 2002; Czaja et al. ITCZ position are present, suggesting that this vari- 2002), further underlining the need for external forcing. ability is intrinsic to the ITCZ/cold tongue climate. In- A more recent idealized model study by Kushnir et al. deed, a mode in the Paci®c with spatial pattern remi- (2002) incorporating the deep Tropics±limited WES niscent of the Atlantic meridional mode was identi®ed feedback suggests, however, that the feedback is essen- in a recent coupled model study with realistic con®g- tial to the decadal nature of meridional mode variability. uration (Yukimoto et al. 2000). Finally, recent detailed Our current knowledge of the meridional mode physics observational and general circulation model (GCM) thus suggests that it is externally forced through trade analyses by Vimont and collaborators (Vimont et al. wind variations, with limited WES feedback in the deep 2001, 2003b) shows that a leading mode of wintertime Tropics. atmospheric variability in the North Paci®c [the North An outstanding issue with the meridional mode is the Paci®c Oscillation (NPO); Rogers 1981] forces varia- issue of (out of phase) coherence between the SST tions of the north tropical Paci®c (NTP) SST through anomalies on either side of the anomalous SST gradient. its control of the subtropical trades there, a mechanism Houghton and Tourre 1992) showed that the dipolelike similar to the external forcing of the tropical Atlantic nature of the anomalies derived from a straight empirical meridional mode by the NAO. orthogonal function (EOF) analysis of tropical Atlantic These similarities motivate us to search for analogous SST anomalies do not survive under varimax rotation; tropical meridional modes in the two basins. We will instead, the two SST lobes appear to vary independently show that once the ENSO in¯uence is linearly removed of each other, a result supported by subsequent obser- from the SST and wind data we analyze, the dominant vational analysis (Mehta and Delworth 1995; En®eld et mode of atmosphere±ocean variability extracted sepa- al. 1999), and also the modeling study by Dommenget rately from the tropical Paci®c and tropical Atlantic ba- and Latif (2000). On the other hand, Xie and Tanimoto sin resembles each other in spatial and temporal char- (1998) argue using observational and modeling evi- acteristics (section 2). The Atlantic pattern is the me- dence for anticoherence between the two lobes at de- ridional mode pattern, whose interpretation is fairly well cadal time scales and part of a coherent pan-Atlantic established from previous studies. A nonlinear com- decadal oscillation characterized by zonal bands of SST ponent of ENSO does, however, project strongly on the and wind anomalies with alternate polarities from the derived Paci®c mode. We show that by additionally ®l- tropical South Atlantic to Greenland. The ``dipole'' is- tering out the strong ENSO years from our analysis, the sue is intimately tied to the physical interpretation of derived Paci®c mode stays essentially the same, indi- the mode, since independent behavior between the cating that this mode does not depend on ENSO for its northern and southern SST lobes suggests an externally existence (section 3). We then show that the Paci®c and forced mechanism with little to no positive feedback in Atlantic modes share the same physical interpretation, the Tropics, whereas dipole behavior between the north- and on that basis we argue that the Paci®c mode is the ern and southern lobes implies a stronger role for pos- analogue to the Atlantic meridional mode pattern (sec- itive feedback. At present, the prevailing evidence sug- tion 4). We reinforce our interpretation by showing the gests that the SST lobes act essentially independently, similarity between the two basins using a different in agreement with the prevailing physical interpretation; (composite) analysis (section 5). A summary and dis- although we emphasize that this issue is not yet fully cussion of the potential implications of our results is resolved in large part because of inadequate length of given in section 6. data, but also in part because simple models hint at dipolelike anomalous SST structures even with WES 2. Data, method, and results feedback limited to the deep Tropics (Kushnir et al. 2002). We use monthly mean SST and 10-m winds from the A similar tropical Paci®c mode of variability (here- National Centers for Environmental Prediction±Nation- after the meridional mode, following Servain et al. al Center for Atmospheric Research (NCEP±NCAR) re- 1999) has heretofore not been identi®ed, in large part analysis (Kalnay et al. 1996, hereafter simply the re- because the El NinÄo±Southern Oscillation (ENSO) dom- analysis) spanning January 1948±December 2001. For inates the variability there (Wallace et al. 1998). There each ®eld, we spatially averaged over six adjoining (two are, however, compelling reasons for its existence. Each latitude by three longitude) grid points, computed de- basin possesses similar mean states: namely, a cold trended monthly mean anomalies, and applied a 3-month tongue over the equatorial oceans (weighted to the east) running mean. The spatial averaging does not unduly and an ITCZ at its northern edge that follows an annual impact the result, as the extracted dominant mode pos- Unauthenticated | Downloaded 09/30/21 06:48 PM UTC 1NOVEMBER 2004 CHIANG AND VIMONT 4145 FIG.
Load more

Recommended publications
  • Strong Modulation of the Pacific Meridional Mode On
    1OCTOBER 2018 G A O E T A L . 7739 Strong Modulation of the Pacific Meridional Mode on the Occurrence of Intense Tropical Cyclones over the Western North Pacific SI GAO AND LANGFENG ZHU Key Laboratory of Meteorological Disaster of Ministry of Education/Joint International Research Laboratory on Climate and Environment Change/Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, Nanjing University of Information Science and Technology, Nanjing, China WEI ZHANG IIHR-Hydroscience and Engineering, The University of Iowa, Iowa City, Iowa ZHIFAN CHEN Key Laboratory of Meteorological Disaster of Ministry of Education/Joint International Research Laboratory on Climate and Environment Change/Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, Nanjing University of Information Science and Technology, Nanjing, China (Manuscript received 8 December 2017, in final form 21 May 2018) ABSTRACT This study finds a significant positive correlation between the Pacific meridional mode (PMM) index and the frequency of intense tropical cyclones (TCs) over the western North Pacific (WNP) during the peak TC season (June–November). The PMM influences the occurrence of intense TCs mainly by modulating large- scale dynamical conditions over the main development region. During the positive PMM phase, anomalous off-equatorial heating in the eastern Pacific induces anomalous low-level westerlies (and cyclonic flow) and upper-level easterlies (and anticyclonic flow) over a large portion of the main development region through a Matsuno–Gill-type Rossby wave response. The resulting weaker vertical wind shear and larger low-level relative vorticity favor the genesis of intense TCs over the southeastern part of the WNP and their subsequent intensification over the main development region.
    [Show full text]
  • System Identification Techniques for Detection of Teleconnections Within Climate Models
    https://doi.org/10.5194/gmd-2020-228 Preprint. Discussion started: 5 August 2020 c Author(s) 2020. CC BY 4.0 License. System identification techniques for detection of teleconnections within climate models Bethany Sutherland1, Ben Kravitz2,3, Philip J. Rasch3, and Hailong Wang3 1Marine, Earth, and Atmospheric Sciences Department, North Carolina State University, Raleigh, NC, USA 2Department of Earth and Atmospheric Sciences, Indiana University, Bloomington, IN, USA 3Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, Richland, WA, USA Correspondence: Bethany Sutherland, 2800 Faucette Drive, 1125 Jordan Hall, Campus Box 8208, NC State University, Raleigh, NC 27695, USA ([email protected]) Abstract. Quantifying teleconnections and discovering new ones is a complex, difficult process. Using transfer functions, we introduce a new method of identifying teleconnections in climate models on arbitrary timescales. We validate this method by perturbing temperature in the Niño3.4 region in a climate model. Temperature and precipitation responses in the model match known El Niño-Southern Oscillation (ENSO)-like teleconnection features, consistent with modes of tropical variability. Per- 5 turbing the Niño3.4 region results in temperature responses consistent with the Pacific Meridional Mode, the Pacific Decadal Oscillation, and the Indian Ocean Dipole, all of which have strong ties to ENSO. Some precipitation features are also con- sistent with these modes of variability, although because precipitation is noisier than temperature, obtaining robust responses is more difficult. While much work remains to develop this method further, transfer functions show promise in quantifying teleconnections or, perhaps, identifying new ones. 10 1 Introduction Climate system teleconnections are a category of features whereby a forcing in one region of the globe can trigger a response far away through propagation or a cascade of physical mechanisms.
    [Show full text]
  • 2018 Monsoon Outlook Albuquerque for Central & Northern New Mexico WEATHER FORECAST OFFICE
    2018 Monsoon Outlook Albuquerque For Central & Northern New Mexico WEATHER FORECAST OFFICE Figure 1. What brings about an above to well above average North American Monsoon (NAM)? Is it all thermally driven? Does low snowpack in the Southern Rockies make a difference? The answer is quite complex and not fully understood but the common denominator seems to be the Walker Circulation, a pattern in the tropical Pacific of air rising in the west and sinking in the east with westward moving air at the surface. Anomalous ocean warming in the central and eastern Pacific (orange) help to shift the rising branch of the Walker Circulation westward to near 180°, while the compensating (or associated) sinking branches shift to just west of the Maritime continent and far southeastern North America. NOAA Climate.gov drawing by Fiona Martin. 2018 Monsoon Outlook Albuquerque North American Monsoon (NAM) – What is it? WEATHER FORECAST OFFICE Courtesy: Todd Shoemake The North American Monsoon (NAM), like its much stronger cousin the Asian or Indian Monsoon, is the result of the polar jet stream and sub-tropical upper-level highs migrating northward during the warm season. The word “monsoon” comes from the Arabic word mausim, meaning season. Essentially, it describes a seasonal wind shift over a region that is usually accompanied by an increase in moisture and precipitation, accounting for nearly half of annual precipitation for much of New Mexico. Source regions for the moisture include, the Gulf of Mexico, Gulf of California and the eastern Pacific Ocean. Monsoon onset dates in the U.S. Southwest typically begin in mid to late June in northwest Mexico (Sonora, Chihuahua, Sinaloa, and Durango) and early July in New Mexico and Arizona.
    [Show full text]
  • Western North Pacific Tropical Cyclone Activity in 2018
    www.nature.com/scientificreports OPEN Western North Pacifc Tropical Cyclone Activity in 2018: A Season of Extremes Si Gao1,2*, Langfeng Zhu3, Wei Zhang4* & Xinyong Shen2,3 The 2018 tropical cyclone (TC) season over the western North Pacifc (WNP) underwent two extreme situations: 18 TCs observed during June–August (JJA) and ranked the second most active summer in the satellite era; only 5 TCs that occurred during September–October (SO), making it the most inactive period since the late 1970s. Here we attribute the two extreme situations based on observational analyses and numerical experiments. The extremely active TC activity and northward shift of TC genesis during JJA of 2018 can be attributed to the WNP anomalous low-level cyclone, which is due primarily to El Niño Modoki and secondarily to the positive phase of the Pacifc Meridional Mode (PMM). Overall, the extremely inactive TC activity during SO of 2018 is due to the absence of TC formation over the South China Sea and Philippine Sea, which can be attributed to the in-situ anomalous low-level anticyclone associated with the positive phase of the Indian Ocean Dipole, although the positive PMM phase and El Niño Modoki still hold. Te western North Pacifc (WNP) including the South China Sea (SCS) is the most active basin of tropical cyclone (TC) activity. On average, 20 TCs are observed over the WNP during the peak season (June to October, JJASO), with 11 TCs during June–August (JJA) and 9 TCs during September–October (SO). However, the 2018 WNP TC season was featured by a season of extreme cases (Fig.
    [Show full text]
  • The Changing El Niño–Southern Oscillation and Associated Climate Extremes
    1 The Changing El Niño–Southern Oscillation and Associated Climate Extremes Jin‐Yi Yu1, Xin Wang2, Song Yang3,4, Houk Paek1, and Mengyan Chen2 ABSTRACT The El Niño–Southern Oscillation (ENSO) is one of the most powerful climate phenomena that produce p rofound global impacts. Extensive research since the 1970s has resulted in a theoretical framework capable of explaining the observed properties and impacts of the ENSO and predictive models. However, during the most recent two decades there have been significant changes observed in the properties of ENSO that suggest r evisions are required in the existing theoretical framework developed primarily for the canonical ENSO. The observed changes include a shift in the location of maximum sea surface temperature variability, an increased importance in the underlying dynamics of coupled ocean‐atmosphere process in the subtropical Pacific, and different remote atmospheric teleconnection patterns that give rise to distinct climate extremes. The causes of these recent changes in ENSO are still a matter of debate but have been attributed to both global warming and natural climate variability involving interactions between the Pacific and Atlantic oceans. The possible future changes of ENSO properties have also been suggested using climate model projections. 1.1. INTRODUCTION characteristic of ENSO, a tremendous amount of effort has been expended by the research community to describe El Niño–Southern Oscillation (ENSO) is a prominent and understand the complex nature of this phenomenon climate phenomenon in the tropical Pacific that can dis­ and its underlying generation mechanisms. By the 1990s, rupt global atmospheric and oceanic circulation patterns the effort had led to the developments of successful theo­ and exert profound impacts on global climate and socio­ retical frameworks that could explain the major features economic activities.
    [Show full text]
  • A Relay Teleconnection
    Clim Dyn DOI 10.1007/s00382-006-0198-5 Extratropical control of recent tropical Pacific decadal climate variability: a relay teleconnection Lixin Wu Æ Zhengyu Liu Æ Chun Li Æ Yan Sun Received: 1 March 2006 / Accepted: 11 September 2006 Ó Springer-Verlag 2006 Abstract Observations indicate that recent tropical Southern Oscillation (ENSO) dynamics and impacts Pacific decadal climate variability tends to be associ- (e.g., Trenberth et al. 1998; Alexander et al. 2002; ated with the extratropical North Pacific through a Wang and Picaut 2004). In addition to its interannual relay teleconnection of a fast coupled ocean-atmo- ENSO variability, the tropical Pacific climate also re- sphere bridge and a slow oceanic tunnel. A coupled veals substantial decadal fluctuations. The anomalous ocean-atmosphere model, forced by the observed warm conditions over the equatorial Pacific in con- decadal wind in the extratropical North Pacific, junction with the relaxation of the trade winds since explicitly demonstrates that extratropical decadal sea mid-1970s have been noted in many studies, and fre- surface temperature (SST) anomalies may propagate quently described in terms of the Pacific decadal cli- to the tropics through a coupled wind-evaporative-SST mate regime shift (e.g., Mantua et al. 1997; Zhang et al. (WES) feedback. The WES feedback cannot only lead 1997). The persistent tropical climate decadal varia- to a nearly synchronous change of tropical SST, but tions not only have profound impacts on marine eco- also force a delayed adjustment of the meridional systems (Mantua et al. 1997; Chavez et al. 2003; Miller overturning circulation in the upper ocean to further et al.
    [Show full text]
  • Separating the North and South Pacific Meridional Modes
    ADVANICNG J...I ,. •100 EARTHAND j \\.:J\i SPACESCIENCE Geophysical Research Letters RESEARCH LETTER Separating the North and South Pacific Meridional Modes 10.1029/2018GU>80320 Contributions to ENSO and Tropical Decadal Variability Key Poin ts : 1 1 Giovanni Liguori ,2 and Emanuele Di Lorenzo The absence of NPMM variability in E) E) CESM leads to a significant 1 School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA,2 ARC Centre of reduction of the tropical interannual variability (- 35%) Excellence for Climate Extremes, School of Earth, Atmosphere and Environment, Monash University, Melbourne, The absence of the SPMM does not Victoria, Australia impact the ENSOspectrum butleads to a significant reduction of the decadal variability (- 30%) Abstract North and South Pacific Meridional Modes (NPMM and SPMM) are known precursors of El The NPMM and SPMM modes Nino-Sou thern Oscillat ion (ENSO) and Tropical Pacific decadal variability (TPDV). However, the energiz.e the tropical variance independently on interannual and relative importanceof these precursors and the timescale on which they impact the tropics remain decadal timescale respectively unclear. Using a 30-member ensemble of the Community Earth System Model as the control climate, we generate two additional members where the NPMM and SPMM are selectively suppressed. We find Supporting Information: , FigureSl that both meridional modes energize the tropical variance independently on different timescales. The absence of NPMM leads to a significant reduction of the tropical interannual variability (- 35%), wh ile the absence of the SPMM has no appreciable impact on ENSO but significantlyreduces the TPDV Correspondence to: (- 30%). While the relative importanceof the NPMM and SPMM may be model dependent, the stochastic G.
    [Show full text]
  • Separating the North and South Pacific Meridional Modes
    RESEARCH LETTER Separating the North and South Pacific Meridional Modes 10.1029/2018GL080320 Contributions to ENSO and Tropical Decadal Variability Key Points: Giovanni Liguori1,2 and Emanuele Di Lorenzo1 • The absence of NPMM variability in CESM leads to a significant 1School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA, 2ARC Centre of reduction of the tropical interannual variability (~35%) Excellence for Climate Extremes, School of Earth, Atmosphere and Environment, Monash University, Melbourne, • The absence of the SPMM does not Victoria, Australia impact the ENSO spectrum but leads to a significant reduction of the decadal variability (~30%) North and South Pacific Meridional Modes (NPMM and SPMM) are known precursors of El • Abstract The NPMM and SPMM modes – fi energize the tropical variance Niño Southern Oscillation (ENSO) and Tropical Paci c decadal variability (TPDV). However, the independently on interannual and relative importance of these precursors and the timescale on which they impact the tropics remain decadal timescale respectively unclear. Using a 30‐member ensemble of the Community Earth System Model as the control climate, we generate two additional members where the NPMM and SPMM are selectively suppressed. We find Supporting Information: • Figure S1 that both meridional modes energize the tropical variance independently on different timescales. The absence of NPMM leads to a significant reduction of the tropical interannual variability (~35%), while the absence of the SPMM has no appreciable impact on ENSO but significantly reduces the TPDV Correspondence to: (~30%). While the relative importance of the NPMM and SPMM may be model dependent, the stochastic G. Liguori, atmospheric variability in the extratropics that energizes the meridional modes emerges as a key source [email protected] of TPDV.
    [Show full text]
  • The Role of South Pacific Atmospheric Variability in the Development Of
    Geophysical Research Letters RESEARCH LETTER The role of South Pacific atmospheric variability 10.1002/2017GL073475 in the development of different Key Points: types of ENSO • South Pacific atmospheric variability, namely, the South Pacific Oscillation (SPO), plays a key role in the Yujia You1 and Jason C. Furtado1 prediction of ENSO flavors • The sources of variability of the SPO 1 are both intrinsic and also forced by School of Meteorology, University of Oklahoma, Norman, Oklahoma, USA anomalous convection in the central tropical Pacific • The SPO potentially plays a significant Abstract Recent advances in tropical Pacific climate variability have focused on understanding the role in climate variability on multiple development of El Niño–Southern Oscillation (ENSO) events, specifically the types or “flavors” of ENSO timescales: seasonal, interannual, and multidecadal (i.e., central versus eastern Pacific events). While precursors to ENSO events exist, distinguishing the particular flavor of the expected ENSO event remains unresolved. This study offers a new look at ENSO predictability using South Pacific atmospheric variability during austral winter as an indicator. The positive Supporting Information: • Supporting Information S1 phase of the leading mode of South Pacific sea level pressure variability, which we term the South Pacific Oscillation (SPO), exhibits a meridional dipole with with a(n) (anti)cyclonic anomaly dominating the subtropics (extratropics/high latitudes). Once energized, the cyclonic anomalies in the subtropical node Correspondence to: Y. You, of the SPO weaken the southeasterly trade winds and promote the charging of the eastern equatorial [email protected] Pacific Ocean, giving rise to eastern Pacific ENSO events. Indeed, the type of ENSO event can be determined accurately using only the magnitude and phase of the SPO during austral winter as a predictor (17 out of Citation: 23 cases).
    [Show full text]
  • Increased Typhoon Activity in the Pacific Deep Tropics Driven by Little Ice Age Circulation Changes
    ARTICLES https://doi.org/10.1038/s41561-020-00656-2 Increased typhoon activity in the Pacific deep tropics driven by Little Ice Age circulation changes James F. Bramante 1,2 ✉ , Murray R. Ford3, Paul S. Kench4, Andrew D. Ashton 1, Michael R. Toomey5, Richard M. Sullivan 1, Kristopher B. Karnauskas6, Caroline C. Ummenhofer 7 and Jeffrey P. Donnelly1 The instrumental record reveals that tropical cyclone activity is sensitive to oceanic and atmospheric variability on inter-annual and decadal scales. However, our understanding of the influence of climate on tropical cyclone behaviour is restricted by the short historical record and the sparseness of prehistorical reconstructions, particularly in the western North Pacific, where coastal communities suffer loss of life and livelihood from typhoons annually. Here, to explore past regional typhoon dynamics, we reconstruct three millennia of deep tropical North Pacific cyclogenesis. Combined with existing records, our reconstruction demonstrates that low-baseline typhoon activity prior to 1350 CE was followed by an interval of frequent storms during the Little Ice Age. This pattern, concurrent with hydroclimate proxy variability, suggests a centennial-scale link between Pacific hydro- climate and tropical cyclone climatology. An ensemble of global climate models demonstrates a migration of the Pacific Walker circulation and variability in two Pacific climate modes during the Little Ice Age, which probably contributed to enhanced tropi- cal cyclone activity in the tropical western North Pacific. In the next century, projected changes to the Pacific Walker circulation and expansion of the tropics will invert these Little Ice Age hydroclimate trends, potentially reducing typhoon activity in the deep tropical Pacific.
    [Show full text]
  • The Effect of the SST Over the PMM Region and the Eastern Northwestern Pacific on Tropical Cyclone Genesis Over WNP in 2018
    The effect of the SST over the PMM region and the eastern northwestern Pacific on tropical cyclone genesis over WNP in 2018 Takahiro, Ishiyama*1, Masaki Satoh1 1 Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Japan *Correspondence to: [email protected] Typhoons in the northwest Pacific in 2018 exceeded the average for 29 occurrences, the number of landings to Japan to 5, and for the typhoon which became extreme strength it was updated with the most record and the activity was active. In the ENSO phase, during the most active period of the typhoon (from June to November), the ENSO phase was still in a neutral state. Therefore, PMM is focused recently. Previous studies have pointed out that this positive PMM favors TC activities in the northwest Pacific (e.g. Zhang et al. 2016). Looking at the PMM index from 1948 to 2018, there was positive PMM in 2018. The purpose of this research is to focus on the monthly SST variation such as ENSO and PMM and to evaluate the Potential of the 2018 typhoon activity. We also focus on the PMM and the SST over the eastern of northwest Pacific, and investigate how they affect the 2018 typhoon activity. For the above purpose, we conducted perpetual experiments in which boundary conditions were fixed from July to October, respectively, using a non-hydrostatic model NICAM. The horizontal resolution was 56 km. Comparing the experimental result of SLP with JRA-55, although the position of the maximum value of the high pressure in July is misaligned, the position and overhang of the high pressure does not dif9fer greatly in each month, and perpetual experiments also reproduce the reality well.
    [Show full text]
  • Three Evolution Patterns of the Central-Pacific El Niño
    1 2 Relationships between Extratropical Sea Level Pressure Variations and the Central- 3 Pacific and Eastern-Pacific Types of ENSO 4 5 6 7 8 Jin-Yi Yu* and Seon Tae Kim 9 10 Department of Earth System Science 11 University of California 12 Irvine, California, USA 13 14 15 16 17 18 19 20 February, 2010, Submitted 21 August, 2010, Revised 22 In Press, Journal of Climate 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 ________________________ 38 *. Corresponding author address: Dr. Jin-Yi Yu, Department of Earth System Science, 39 University of California, Irvine, CA 92697-3100. E-mail: [email protected] 1 40 41 ABSTRACT 42 This study examines the linkages between leading patterns of interannual sea level 43 pressure (SLP) variability over the extratropical Pacific (20°N-60°N) and the Eastern- 44 Pacific (EP) and Central-Pacific (CP) types of El Niño-Southern Oscillation (ENSO). The 45 first Empirical Orthogonal Function (EOF) mode of the extratropical SLP anomalies 46 represents variations of the Aleutian Low, and the second EOF mode represents the North 47 Pacific Oscillation (NPO) and is characterized by a meridional SLP anomaly dipole with 48 a nodal point near 50°N. It is shown that a fraction of the 1st SLP mode can be excited by 49 both the EP and CP types of ENSO. The SLP response to the EP type is stronger and 50 more immediate. The tropical-extratropical teleconnection appears to act slower for the 51 CP ENSO. During the decay phase of EP events, the associated extratropical SLP 52 anomalies shift from the 1st SLP mode to the 2nd SLP mode.
    [Show full text]