A Climatological Relationship between MJO/ENSO Phases and Tropical Cyclone Interactions with Saharan Dust Storms across the Tropical Atlantic Basin
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Atlantic hurricane
Madden–Julian oscillation
Tropical cyclogenesis
Tropical Atlantic
Tropical cyclone scales
African easterly jet
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Abstract Statistically coupled patterns of South Asian Summer Monsoon ( SASM ) interannual variability in the tropical oceans have been explored. Maximum covariance analysis ( MCA ) performed between global tropical sea surface temperature ( SST ) and SASM precipitation shows that El‐Niño southern oscillation ( ENSO ) is the leading mode in the tropics, whereas the eastern pole of the Indian Ocean Dipole contributes to the second global mode and is the leading mode in the Indian Ocean. South tropical Atlantic SST variability is contributing to the second and third mode in the tropics and is the leading mode in the tropical Atlantic MCA coupled with SASM .
Tropical Atlantic
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The El Niño-Southern Oscillation (ENSO) in the preceding winter (December-January-February) is one of the key factors affecting subsequent East Asian summer (June-July-August) rainfall (EASR). However, current models face great challenges in reproducing ENSO’s impact on the EASR. This study attempts to reveal the factors that determine whether a model in phase 6 of the Coupled Model Intercomparison Project (CMIP6) can successfully reproduce this relationship by analyzing the outputs of historical climate simulation in 20 CMIP6 models. The results show that most of the models that overestimated ENSO interannual variability reproduced significant ENSO-EASR relationships, whereas all models that underestimated ENSO variability failed to reproduce this relationship. Further analyses show that models with stronger ENSO variability tended to simulate more realistic physical processes linking ENSO and EASR, i.e. the connections between ENSO and the tropical Indian Ocean (TIO) sea surface temperature (SST), between TIO SST and the Philippine Sea convection (PSC), and between PSC and EASR. Moreover, among the models that overestimated ENSO variability, only those that successfully captured significant TIO SST-PSC connections reproduced the observed ENSO-EASR relationship, although all these models captured ENSO-TIO SST and PSC-EASR teleconnections well. Therefore, simulating stronger ENSO interannual variability is the first necessary precondition for a CMIP6 model to capture the delayed effect of ENSO on EASR; reproducing a realistic TIO SST-PSC teleconnection is the second necessary precondition. This study will help models to improve their skills in simulation and prediction of EASR.
Teleconnection
Multivariate ENSO index
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Tropical cyclogenesis
Teleconnection
Cyclogenesis
Atlantic hurricane
Jet stream
Extratropical cyclone
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Abstract Two distinct roles of the Atlantic sea surface temperatures (SSTs), namely, the North Tropical Atlantic (NTA) SST and the Atlantic Niño, on the El Niño–Southern Oscillation (ENSO) variability are investigated using the observational data from 1980 to 2010 and coupled model experiments. It appears that the NTA SST and the Atlantic Niño can be used as two independent predictors for predicting the development of ENSO events in the following season. Furthermore, they are likely to be linked to different types of El Niño events. Specifically, the NTA SST cooling during February, March, and April contributes to the central Pacific warming at the subsequent winter season, while the negative Atlantic Niño event during June, July, and August contributes to enhancing the eastern Pacific warming. The coupled model experiments support these results. With the aid of a lagged inverse relationship, the statistical forecast using two Atlantic indices can successfully predict various ENSO indices.
Tropical Atlantic
Atlantic Equatorial mode
Atlantic hurricane
Multivariate ENSO index
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Abstract Southern African tropical lows are synoptic‐scale cyclonic vortices that propagate westward across southern Africa in the Austral summer. They strongly influence local rainfall and aggregate in the climatological December, January, and February mean to form the Angola Low. In this study, tropical lows are identified and tracked using an objective feature tracking method. The statistics of tropical low tracks over southern Africa are presented and compared across three reanalysis products. Findings are compared to the literature of tropical low‐pressure areas elsewhere in the world, where it is found that most tracking statistics compare well but that the tendency of tropical lows to become semistationary over Angola is unique to southern Africa. The hypothesis that tropical lows in Angola have a causal relationship with Tropical Temperate Troughs is tested, and a correlation between occurrence frequencies is found at interannual but not daily time scales. Precipitation is attributed to the tropical lows, and it is found that tropical lows are associated with 31% of rainfall across tropical southern Africa, based on gridded precipitation products. The interannual variability of the number of tropical lows that form per year ( σ =6 events/year) is linked to El Niño–Southern Oscillation (ENSO) and the tropical easterly jet. The mean latitude of tropical lows is shifted northward during El Niño and southward during La Niña. Much of the interannual precipitation variability maximum in Angola is attributed to rainfall associated with tropical lows. These results provide insights into the southern African response to ENSO and into the mechanisms of rainfall in the southern African tropical edge.
African easterly jet
Tropical Atlantic
Anomaly (physics)
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A new research study shows that overall global tropical cyclone activity has decreased to historically low levels during the past 5 years. Maue analyzed global tropical cyclone data from 1970 through May 2011 to examine the considerable interannual variability of the accumulated cyclone energy (ACE) metric. Since 2006, global and Northern Hemisphere ACE have decreased significantly, reaching their lowest levels since the late 1970s. Also, during 2010–2011, the overall global frequency of tropical cyclones reached a historic low. The author demonstrated that much of the variability in tropical cyclone energy during the past 40 years is clearly associated with natural large‐scale climate oscillations such as the El Niño—Southern Oscillation and the Pacific Decadal Oscillation. ( Geophysical Research Letters , doi:10.1029/2011GL047711, 2011)
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Abstract Easterly waves (EWs) are important moisture carriers and their variability can impact the total May–November rainfall, defined as seasonal precipitation, over the Tropical Americas. The contribution of EWs to the seasonal precipitation is explored over the tropical Americas using rain gauge stations, reanalysis data and a regional model ensemble during the 1980–2013 period. In the present study, EWs are found to produce up to 50% of seasonal rainfall mainly over the north of South America and contribute substantially to interannual regional rainfall variability. An observational analysis shows that the El Niño Southern Oscillation (ENSO) affects EW frequency and therefore, their contribution to seasonal rainfall. In recent years, tropical cyclone (TC) activity over the Main Development Region (MDR) of the tropical North Atlantic has a negative impact on regional seasonal precipitation over northern South America. High TC activity over MDR corresponds to below-normal precipitation because it reduces the EW activity reaching northern South America through the recurving of TC tracks. Recurving TC tracks redirect moisture away from the tropical belt and into the mid-latitudes. However, this relationship only holds under neutral ENSO conditions and the positive phase of the Atlantic Multidecadal Oscillation. A 10-member regional model multi-physics ensemble simulation for the period 1990–2000 was analyzed to show the relationships are robust to different representations of physical processes. This new understanding of seasonal rainfall over the tropical Americas may support improved regional seasonal and climate outlooks.
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Forcing (mathematics)
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Abstract In this study, we compared the performance of two potential predicators, that is, El Niño–Southern Oscillation (ENSO) index (Niño‐3.4) and mega‐ENSO index, in the seasonal forecast of tropical cyclone (TC) activity and its spatial distribution over the western North Pacific (WNP) during the extended TC season, which is of public concern. Our results clearly show that, although both mega‐ENSO and Niño‐3.4 indices in the preceding May are important predictors for the seasonal predication, the relative‐sea surface temperature (SST)‐dependent mega‐ENSO exhibits a higher skill in the seasonal forecasting compared with the absolute‐SST‐dependent ENSO. Further results show that, despite of stronger destructiveness of TCs in high mega‐ENSO (El Niño) years than in low mega‐ENSO (La Niña) years, more attention should be paid to the TCs in low mega‐ENSO years, which are more likely to occur in coastal areas compared with the TCs in high mega‐ENSO years. Due to the responses of TC genesis, TC potential intensity, and large‐scale flow to the SST change in low mega‐ENSO years, the WNP TCs tend to originate in the northwestern quadrant and intensify at high latitudes and then turn northwestward over the TC prevailing region, which contributes to the northwestward migration of the WNP TC exposure in terms of track density and destructiveness density and thus imposes more risks in the coastal areas in low mega‐ENSO years. In addition, despite the significant predication skill in forecasting TC activity when using mega‐ENSO/Niño‐3.4 as a single predicator, it is still far to predict reliable WNP activity, especially its spatial distribution, without considering other predictors.
Multivariate ENSO index
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Examined are statistical aspects of the 715 tropical cyclones that formed in the North Atlantic basin during the interval 1945-2010. These 715 tropical cyclones include 306 storms that attained only tropical storm strength, 409 hurricanes, 179 major or intense hurricanes, and 108 storms that struck the US coastline as hurricanes. Comparisons made using 10-year moving average (10-yma) values between tropical cyclone parametric values and surface air and ENSO-related parametric values indicate strong correlations to exist, in particular, against the Armagh Observatory (Northern Ireland) surface air temperature, the Atlantic Multi-decadal Oscillation (AMO) index, the Atlantic Meridional Mode (AMM) index, and the North Atlantic Oscillation (NAO) index, in addition to the Oceanic Ni o index (ONI) and Quasi-Biennial Oscillation (QBO) indices. Also examined are the decadal variations of the tropical cyclone parametric values and a look ahead towards the 2012 hurricane season and beyond.
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Tropical cyclogenesis
Tropical Atlantic
Extratropical cyclone
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CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 22:141-146 (2002) - doi:10.3354/cr022141 Interannual variability of the bimodal distribution of summertime rainfall over Central America and tropical storm activity in the far-eastern Pacific Scott Curtis* Joint Center for Earth Systems Technology, University of Maryland, Baltimore County, Department of Geography, NASA/Goddard Space Flight Center, Code 912, Greenbelt, Maryland 20771, USA *E-mail: curtis@agnes.gsfc.nasa.gov ABSTRACT: The summer climate of southern Mexico and Central America is characterized by a mid-summer drought (MSD), where rainfall is reduced by 40% in July as compared to June and September. A mid-summer reduction in the climatological number of eastern Pacific tropical cyclones has also been noted. Little is understood about the climatology and interannual variability of these minima. The present study uses a novel approach to quantify the bimodal distribution of summertime rainfall for the globe and finds that this feature of the annual cycle is most extreme over Pan America and adjacent oceans. One dominant interannual signal in this region occurs the summer before a strong winter El Niño/Southern Oscillation (ENSO). Before El Niño events the region is dry, the MSD is strong and centered over the ocean, and the mid-summer minimum in tropical cyclone frequency is most pronounced. This is significantly different from Neutral cases (non-El Niño and non-La Niña), when the MSD is weak and positioned over the land bridge. The MSD is highly variable for La Niña years, and there is not an obvious mid-summer minimum in the number of tropical cyclones. KEY WORDS: Rainfall · Tropical storms · Summer · Central America · ENSO Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 22, No. 2. Online publication date: September 06, 2002 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2002 Inter-Research.
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