Atlantic Warm Pool Research Articles

Rapid Laurentide Ice Sheet growth preceding the Last Glacial Maximum due to summer snowfall

There has been extensive research into the nonlinear responses of the Earth system to astronomical forcing during the last glacial cycle. However, the speed and spatial geometry of ice sheet expansion to its largest extent at the Last Glacial Maximum 21 thousand years ago remains uncertain. Here we use an Earth system model with interactive ice sheets to show that distinct initial North American (Laurentide) ice sheets at 38 thousand years ago converge towards a configuration consistent with the Last Glacial Maximum due to feedbacks between atmospheric circulation and ice sheet geometry. Notably, ice advance speed and spatial pattern in our model are controlled by the amount of summer snowfall, which is dependent on moisture transport pathways from the North Atlantic warm pool linked to ice sheet geometry. The consequence of increased summer snowfall on the surface mass balance of the ice sheet is not only the direct increase in accumulation but the indirect reduction in melt through the snow/ice–albedo feedback. These feedbacks provide an effective mechanism for ice growth for a range of initial ice sheet states and may explain the rapid North American ice volume increase during the last ice age and potentially driving growth during previous glacial periods.

Unprecedented cross-equatorial southerly wind anomalies during the 2020–2023 triple-dip La Niña: Impacts and mechanisms

The 2020–2023 La Niña event, the third triple-dip occurrence since 1950, stands out for its unique characteristics when compared to the preceding events in 1973–1976 and 1998–2001. Unlike its predecessors, the latest event emerged without a preceding strong El Niño episode, starting from a state of weak discharge. Moreover, the resurgence of cold sea surface temperature (SST) anomalies during 2020–2023 showed a loose link to ocean-atmosphere variability in the northern subtropical Pacific. The spatial pattern of anomalous conditions in this recent event featured persistent SST cooling in the southeast tropical Pacific, accompanied by pronounced meridional southerly wind anomalies. Our comprehensive investigation indicates a minimal role of subsurface ocean dynamics, underscoring the exceptional strength of cross-equatorial meridional southerly wind anomalies as a primary driver of sustained negative sea surface temperature anomalies. By considering the influences of intra-basin and inter-basin factors, we propose that the observed patterns may be the combined outcome of interannual variability within the tropical Pacific and decadal variations beyond the tropics. Noteworthy contributions from the low-frequency components of the South Pacific Meridional Mode and the Atlantic Warm Pool further shape the dynamics of this event. Our findings underline the increasing importance of meridional winds in shaping the evolution of ENSO in recent decades.

Changes to Sea Surface Temperatures and Vertical Wind Shear and Their Influence on Tropical Cyclone Activity in the Caribbean and the Main Developing Region

Sea surface temperatures and vertical wind shear are essential to tropical cyclone formation. TCs need warm SSTs and low shear for genesis. Increasing SSTs and decreasing VWS influences storm development. This work analyzes SST and VWS trends for the Caribbean, surrounding region, and the Atlantic hurricane main developing region from 1982–2020. Storm intensity increases significantly during this period. Annual and seasonal trends show that regional SSTs in the MDR are warming annually at 0.0219 °C yr−1 and, per season, 0.0280 °C yr−1. Simultaneously, VWS decreases during the late rainfall season, at 0.056 m/s yr−1 in the MDR and 0.0167 m/s yr−1 in the Caribbean and surrounding area. The Atlantic Warm Pool is expanding at 0.51 km2 per decade, increasing upper atmospheric winds and driving VWS changes. Correlations of large-area averages do not show significant relationships between TC intensity, frequency, and SSTs/VWS during the LRS. The observed changes appear to be associated with regional warming SSTs impacting TC changes. Plain Language Abstract: Tropical cyclone (TC) formation requires warm ocean waters and low wind shear. Changes to sea surface anomalies and wind shear influences are essential to understanding storm development and intensification. The ability to forecast storm changes is vital to human lives and livelihoods. This work analyzes sea surface temperatures (SSTs) and vertical wind shear (VWS) trends in the Caribbean, surrounding areas, and the Atlantic main developing region (MDR). We found increasing SSTs, decreasing wind shears, an expanding Atlantic Warm Pool (AWP), and increased storm intensity during the Atlantic hurricane season.

Reading the sediment archive of the Eastern Campeche Bank (southern Gulf of Mexico): from the aftermath of the Chicxulub impact to Loop Current variability

This is the first high-resolution seismic study showing how the Chicxulub impact shaped the eastern slope of the Campeche Bank in the south-eastern Gulf of Mexico. The induced shock wave fractured Cretaceous strata causing the collapse of the upper slope and shelf over a length of ca. 200 km. Failed material was either transported downslope or remained in parts on the accommodation space created by the collapsed. In the Cenozoic, the East Campeche Plastered Drift developed within the created accommodation space, controlled by the inflowing surface current from the Caribbean, which forms the Loop Current. The internal reflection configuration of the drift shows that the closure of the Suwannee Strait in the Late Oligocene and the closure of the CAS in the Mid to Late Miocene controlled the variability of the southern Loop Current in time. Since the Loop Current transports heat and moisture from the western Atlantic warm water pool into the North Atlantic and further to NW Europe by the Gulf Stream, the drift represents an archive for controlling factors that influenced climate of the northern hemisphere. This first high-resolution seismic reflection study from the eastern Campeche Bank expands the understanding of destructive processes that a meteorite impact induces into the earth system. Furthermore, these data document that the East Campeche Plastered Drift bears the potential to understand the link between the climate variability of the northern hemisphere and oceanic processes in the equatorial western Atlantic.

Influence of the North American dipole on the Atlantic warm pool

Using the observational data, the Coupled Model Intercomparison Project phase 6 (CMIP6) models and the numerical experiment, this study examines the influence of the North American dipole (NAD) on the Atlantic warm pool (AWP). The results show that a strong positive (negative) phase of the winter NAD tends to inhibit (favor) the development of AWP in its area and depth in subsequent months. As opposed to the North Atlantic Oscillation (NAO), the NAD plays a more pivotal role in influencing the AWP due to its effectiveness in forcing the tropical North Atlantic (TNA) SST variability, which means that AWP variability may be more of a lagging response to NAD atmospheric forcing than a lagging response to NAO atmospheric forcing. Additional analysis indicates that the winter NAD-like atmospheric signal may be stored in the following AWP, thus markedly influencing the TNA precipitation and air temperature in summer. It is speculated that the AWP may act as a bridge linking winter NAD to the following summer precipitation and air temperature in the TNA region.

Climate-modulated range expansion of reef-building coral communities off southeast Florida during the late Holocene

The Holocene reefs off southeast Florida provide unique insights into the biogeographical and ecological response of western Atlantic coral reefs to past climate change that can be used to evaluate future climate impacts. However, previous studies have focused on millennial-scale change during the stable mid-Holocene, making it difficult to make inferences about the impact of shorter-term variability that is relevant to modern climate warming. Using uranium-series dating of newly discovered subfossil coral rubble deposits, we establish a new high-resolution record of coral community development off southeast Florida during a period of variable climate in the late Holocene. Our results indicate that coral communities dominated by reef-building Acropora palmata and Orbicella spp. persisted in the nearshore environments off southeast Florida ~75 km north of their primary historical ranges between ~3500 and 1800 years before present. This timing coincides with regional warming at the northern extent of the Atlantic Warm Pool, suggesting a likely link between regional oceanographic climate and the expansion of cold-sensitive reef-building coral communities to the high-latitude reefs off southeast Florida. These findings not only extend the record of coral-reef development in southeast Florida into the late Holocene, but they also have important implications for future range expansions of reef-building coral communities in response to modern climate change.

Modulation of North American Heat Waves by the Tropical Atlantic Warm Pool

AbstractHeat waves are among the deadliest natural hazards affecting the United States (US). Therefore, understanding the physical mechanisms modulating their occurrence is essential for improving their predictions and future projections. Using observational data and model simulations, this study finds that the interannual variability of the tropical Atlantic warm pool (AWP, measured as the area enclosed by the 28.5°C sea surface temperature isotherm) modulates heat wave occurrence over the US Great Plains during boreal summer. For example, a larger than normal AWP enhances atmospheric convection over the Caribbean Sea, driving an upper tropospheric anticyclonic anomaly over the Gulf of Mexico and Great Plains, which strengthens subsidence, reduces cloud cover, and increases surface warming. This circulation anomaly thus weakens the Great Plains low‐level jet and associated moisture transport into the Great Plains, leading to drought conditions and increased heat wave occurrence for most of the US east of the Rockies.

Critical Role of Tropical North Atlantic SSTA in Boreal Summer in Affecting Subsequent ENSO Evolution

AbstractThe season‐dependent impacts of the tropical North Atlantic (TNA) sea surface temperature anomaly (SSTA) on subsequent El Niño‐Southern Oscillation (ENSO) evolution were investigated through observational and modeling studies. The results indicate that, although the maximum amplitude of the TNA SSTA occurs during boreal spring, the TNA SSTA in boreal summer generates a stronger rainfall response in situ, which can further induce a significantly stronger zonal wind anomaly over the equatorial western Pacific via Kelvin and Rossby wave processes. The cause of a stronger precipitation response in boreal summer is attributed to the northward migration of the climatological Atlantic warm pool and the Inter‐Tropical Convergence Zone. Idealized Coupled General Circulation Model experiments further demonstrate that a persisting TNA SSTA forcing up to boreal summer is critical in conveying the TNA impact to subsequent ENSO evolutions in the Pacific.

A Hyperactive End to the Atlantic Hurricane Season October–November 2020

Abstract The active 2020 Atlantic hurricane season produced 30 named storms, 14 hurricanes, and 7 major hurricanes (category 3+ on the Saffir–Simpson hurricane wind scale). Though the season was active overall, the final two months (October–November) raised 2020 into the upper echelon of Atlantic hurricane activity for integrated metrics such as accumulated cyclone energy (ACE). This study focuses on October–November 2020, when 7 named storms, 6 hurricanes, and 5 major hurricanes formed and produced ACE of 74 × 104 kt2 (1 kt ≈ 0.51 m s−1). Since 1950, October–November 2020 ranks tied for third for named storms, first for hurricanes and major hurricanes, and second for ACE. Six named storms also underwent rapid intensification (≥30 kt intensification in ≤24 h) in October–November 2020—the most on record. This manuscript includes a climatological analysis of October–November tropical cyclones (TCs) and their primary formation regions. In 2020, anomalously low wind shear in the western Caribbean and Gulf of Mexico, likely driven by a moderate-intensity La Niña event and anomalously high sea surface temperatures (SSTs) in the Caribbean, provided dynamic and thermodynamic conditions that were much more conducive than normal for late-season TC formation and rapid intensification. This study also highlights October–November 2020 landfalls, including Hurricanes Delta and Zeta in Louisiana and in Mexico and Hurricanes Eta and Iota in Nicaragua. The active late season in the Caribbean would have been anticipated by a statistical model using the July–September-averaged ENSO longitude index and Atlantic warm pool SSTs as predictors.

A Climatological Study of the Mechanisms Controlling the Seasonal Meridional Migration of the Atlantic Warm Pool in an OGCM

The tropical Atlantic Warm Pool is one of the main drivers of the marine intertropical convergence zone and the associated coastal Northeast Brazilian and West-African monsoons. Its meridional displacement is driven by the solar cycle, modulated by the atmosphere and ocean interactions, whose nature and respective proportions are still poorly understood. This paper presents a climatological study of the upper ocean and lower atmosphere contributions to the warm pool seasonal migration, using an Ocean General Circulation Model (OGCM). First, we provide quantitative, albeit simple, pieces of evidence on how the large amplitude of migration in the west, compared to the east, is mainly due to the strong east–west contrast of the background meridional SST gradient intensities, which is maintained by equatorial and eastern tropical upwellings. Our main results consist first in identifying a diagnostic equation for the migration speed of the two meridional boundary isotherms of the Warm Pool, expressed in terms of the various mixed-layer heat fluxes. We then evidence and quantify how, in general, the migration is forced by air–sea fluxes, and damped by ocean circulation. However, remarkable controls by the ocean are identified in some specific regions. In particular, in the northwestern part of the Warm Pool, characterized by a large temperature inversion area, the boreal spring northward movement speed depends on the restitution of the solar heating by the thermocline. Additionally, over the southern part of the Warm Pool, our study quantifies the key role of the equatorial upwelling, which, depending on the longitude, significantly accelerates or slows down the summer poleward migration.

The North Pacific Blob acts to increase the predictability of the Atlantic warm pool

The Atlantic warm pool (AWP) has profound impacts on extreme weather events and climate variability. Factors influencing the AWP and its predictability are still not fully understood. Other than local ocean–atmosphere feedbacks and El Niño Southern Oscillation, we find an extratropical precursor from the Northeast Pacific (known as the Blob), which leads the AWP by 1 year with a robust correlation (r = 0.68). A suite of Northeast Pacific pacemaker experiments successfully reproduces the leading influence of the Blob on the AWP. The preceding summer Blob-related sea surface temperature (SST) warming signal can be transmitted towards the lower latitudes through the seasonal footprint mechanism, leading to the central Pacific warming in the winter and following spring. Such a strong tropical Pacific SST heating excites an anomalous atmospheric wave train that resembles the Pacific/North American (PNA) teleconnection pattern. At the downstream portion of the PNA, the low sea surface pressure anomalies can be found over the AWP region during the following spring. The anomalous low initiates the AWP SST warming, and the AWP warmer SST can persist into summer and is further amplified due to ocean–atmosphere feedbacks. Our results show that the North Pacific Blob may act as a useful predictor of the AWP 1 year in advance through trans-basin interactions. A Blob-based prediction model shows considerable hindcast skill for the observed AWP SST anomaly.

Impacts of the Atlantic warm pool on North American precipitation and global sea surface temperature in a coupled general circulation model

The responses of North American precipitation to the Atlantic warm pool (AWP) are investigated by using observational data and the NCAR Community Earth System Model. We show that the responses are controlled by different physical mechanisms in different seasons. In the warm season, a large AWP reduces the North Atlantic subtropical high, consistent with Gill’s physics. The corresponding influence over North America is northerly wind anomalies in the lower atmosphere, which leads to a precipitation suppression in the central United States. However, in the cold season the AWP’s impact on North American precipitation is operated via the teleconnection of cold SST anomalies in the tropical Pacific which are induced by the AWP. A large AWP enhances the local Hadley circulation that moves across the equator to the tropical southeastern Pacific in the boreal summer. This inter-hemispheric process strengthens the atmospheric sinking and then increases the South Pacific subtropical high, resulting in the enhancement of the surface easterly trade wind and thus cold SST anomalies in tropical southeastern Pacific. The wind-evaporation-SST and Bjerknes feedbacks further lead tropical central Pacific SST to a La Nina-like pattern, which is consistent with that the significant and negative correlation between ENSO and the AWP is observed after the 1990s when the AWP leads by 6–9 months. The AWP-induced La Nina-like SST anomalies in the tropical central Pacific further prompts a negative phase of the Pacific North American teleconnection, resulting in decreased precipitation over the southern United States; and vice versa. In addition to the AWP-induced central Pacific-type of ENSO events, the paper also shows the influences of the AWP on SSTs in the North Pacific and Indian Oceans.

The Role of Tropical Cyclones on the Total Precipitation in Cuba during the Hurricane Season from 1980 to 2016

This study quantifies the amount of rainfall supplied by tropical cyclones (TCs) to Cuba. It uses the long–term global gridded Multi–Source Weighted–Ensemble Precipitation (MSWEP) v2 data set, with a resolution of 0.1° in latitude and longitude, and a temporal resolution of 3 h during the hurricane seasons from 1980–2016. During this study period, 146 TCs were identified within a 500–km radius of Cuba. The contribution of TCs to the total precipitation over Cuba during the cyclonic season was ~11%. The maximum contribution occurs in October and November, representing 18% and 28% of the total precipitation, respectively. The interannual precipitation contribution shows a positive correlation (~0.74) with the number of TCs, but without a significant trend for the period. A climatological spatial analysis of the rainfall associated with TCs revealed great heterogeneity, although the major contribution was observed along the southern coast of the eastern and central provinces of Cuba, and in the western province of Pinar del Río. No significant difference was observed between the number of TCs that affected Cuba and their rainfall contribution under the positive and negative phases of the El Niño Southern Oscillation. However, the negative phase of the NAO led to an increase in the genesis of TCs that later affected Cuba, which led to a greater contribution to precipitation compared to that obtained from TCs during the positive phase of this oscillation. Our results also confirm that anomalous warmth of the tropical Atlantic Ocean, revealed through the Atlantic Meridional Mode, and enlargement of the Atlantic Warm Pool, enhances the genesis in the North Atlantic Basin of the TCs that affect Cuba, which was associated with an increase of the rainfall contribution to the total precipitation compared to that calculated for TCs formed during the opposite phases.

The temperature increase in Greenland has accelerated in the past five years

Abstract Understanding the changes in Greenland's temperature is important for assessing and predicting the mass of the Greenland ice sheet, which plays an important role in sea level rise. In this study, we analyzed the annual and seasonal coastal Greenland's temperatures during the period 1952–2017 (focusing on the period 2013–2017) based on a dataset obtained from the Danish Meteorological Institute (DMI). Overall, the annual coastal Greenland's temperature increased during 1952–2017 at a rate of 0.23 °C decade−1, especially in the southeastern (0.70 °C decade−1) and northern (0.42 °C decade−1) regions of the island. From the changes in the seasonal coastal Greenland's composite temperature (CT), winter exhibited the largest change rate (0.28 °C decade−1), and the summer CT increased by 0.25 °C decade−1, while the spring CT increased by 0.17 °C decade−1 with less variation. The temperature increase accelerated during 2013–2017 according to Mann-Kendall (M-K) tests, especially in the northeastern and northern regions of the island. The seasonal temperature change of the whole island decreased in the following order: annual > autumn > summer > winter > spring. We also analyzed the annual inland temperature change during the period 1997–2017 based on a dataset obtained from the Greenland Climate Network; the results indicated that the inland temperature increased by 0.13 °C decade−1. Pearson correlation analysis was used to determine the teleconnection relationship between the coastal temperatures and large-scale atmosphere-ocean climate indexes, and we found that the Greenland Blocking Index (GBI), Atlantic Multidecadal Oscillation (AMO), Tropical Northern Atlantic Index (TNA), North Tropical Atlantic Index (NTA), Caribbean Index (CAR), Atlantic Meridional Mode (AMM), East Atlantic (EA) and Western Hemisphere warm pool (WHWP) have significant positive correlations with the coastal temperature in most months, except in February and May. However, the North Atlantic Oscillation (NAO), Arctic Oscillation (AO) and Eastern Asia/Western Russia (EAWR) show significant negative correlations with temperature. Overall, there exists a time lag effect between the climate indexes (except for the GBI, AO and NAO) and temperature. From the application of the random forest model, we found that the GBI, NAO, CO2, AMO, N2O, SF6, CH4, and Northern Oscillation Index (NOI) are the most important variables that influenced the CT changes during 1979–2017. Finally, we calculated the contribution rates of the most important variables to temperature change during the period 1979–2017 and showed that the contribution rates of the GBI, CO2 and NOI to temperature change were 47.30%, 35.68%, and 17.02%, respectively.

Last interglacial (MIS 5e) and Holocene paleohydrology and paleovegetation of midcontinental North America from Gulf of Mexico sediments

Marine Isotope Stage (MIS) 5e experienced slightly higher insolation and lower global ice volume compared to the pre-industrial climate, however, how climate and vegetation differ regionally during MIS 5e is poorly known. Here, we examined MIS 5e hydrologic and vegetation conditions in the Mississippi River Basin (MRB) in North America (NA) and compared this to the Holocene. To do this, we reconstructed paleohydrology and paleovegetation conditions during the last 150 kyr using plant waxes (n-alkanes) and their carbon (δ13Calk) and hydrogen (δ2Halk) isotopic compositions preserved in ODP 625B core from the northwestern Gulf of Mexico (GOM) near the MRB discharge area. In the early MIS 5e, the jet stream may have been located in its northern most position over the last 150 kyr indicated by the highest δ2Halk values resulting in high warm and moist air mass contribution from the GOM and tropical Atlantic to the MRB. This is likely caused by northern expansion of the Atlantic Warm Pool and a northward shift of the ITCZ with increased warming. The climate may have become drier towards late MIS 5e with precipitation concentrated in summer expanding the C4 grassland distribution, which persisted through the MIS 5b. We speculate that this may be due to prolonged warming and drying from early to mid MIS 5. There were notable increases in plant wax export from western dry grasslands during deglaciation (13.5 ka) and the mid-Holocene (5.3 ka). In contrast, plant wax delivery was low during the MIS 5e without significant source changes. Such contrast between the two interglacials is due to the earlier completion of the LIS retreat in late MIS 6 and an onset of a full interglacial climate during the MIS 5e compared to the Last Glacial and Holocene transition. This study presents timing and mechanisms of precipitation source and vegetation composition changes over the NA as a result of slight changes in insolation and rates of deglaciation. These results provide a baseline for understanding the sensitivity of regional hydrologic and vegetation conditions to slight changes in global climate.

Insights into sea surface temperatures from the Cayman Islands from corals over the last ~540 years

Seven large corals (Orbicella annularis and Montastrea cavernosa) from Grand Cayman and Cayman Brac, which grew between ~1474 to 1512 CE and ~1815 to 2014 CE, are characterized by growth banding that reflects bi-annual growth periods. Some of these growth bands, however, include micro-scale bands that reflect sub-annual growth phases. Paleotemperatures derived from the oxygen isotope composition of these corals indicate that Sea Surface Temperature (SST) between ~1474 to 1512 CE and ~1815 to 2014 CE ranged from 18 to 34 °C and included four main periods of temperature change with smaller-scale warm or cool intervals superimposed on these periods. Cool Period 1 (~1474 to 1512 CE) coincided with decreased temperatures that existed in the northern hemisphere during the Little Ice Age (LIA. ca 1450–1850 CE). Cool Period 2 (~1815 to 1924 CE) coincided with a Caribbean wide reduction in temperatures that was probably related to the final phase of the LIA. Warm Period 1 (~1924 to 2006 CE), is characterized by an overall increase in SST consistent with the pronounced global warming since the 1970's. Modern Period 1 (~2006–2014 CE), is characterized by temperatures that fluctuate around 28.5 °C, the current average water temperature for Grand Cayman. The overall ~3 °C ± 0.96 °C increase in SST since ~1815 CE, derived from the Cayman corals, is consistent with the Caribbean and global temperature increases since the 1850's. Smaller scale deviations in the Cayman temperature profiles from the general Caribbean/global temperature trends probably reflect local factors such as increased storm and/or cold-air front frequencies, a reduction in the size and/or intensity of the Atlantic Warm Pool, shifts in the phase of the Atlantic Multidecadal Oscillation, and/or weakening of the Cayman Basin current.

SST Indexes in the Tropical South Atlantic for Forecasting Rainy Seasons in Northeast Brazil

May-to-July and February-to-April represent peak rainy seasons in two sub-regions of Northeast Brazil (NEB): Eastern NEB and Northern NEB respectively. In this paper, we identify key oceanic indexes in the tropical South Atlantic for driving these two rainy seasons. In Eastern NEB, the May-to-July rainfall anomalies present a positive relationship with the previous boreal winter sea surface temperature anomalies (SSTA) in the southeast tropical Atlantic (20°–10° S; 10° W–5° E). This positive relationship, which spread westward along the southern branch of the South Equatorial Current, is associated with northwesterly surface wind anomalies. A warmer sea surface temperature in the southwestern Atlantic warm pool increases the moisture flux convergence, as well as its ascending motion and, hence, the rainfall along the adjacent coastal region. For the Northern NEB, another positive relationship is observed between the February-to-April rainfall anomalies and the SSTA of the previous boreal summer in the Atlantic Niño region (3° S–3° N; 20° W–0°). The negative remote relationship noticeable between the Northern NEB rainfall and the concomitant Pacific Niño/Niña follows cold/warm events occurring during the previous boreal summer in the eastern equatorial Atlantic. The southeastern tropical Atlantic and Atlantic Niño SSTA indexes may, then, be useful to predict seasonal rainfall over the Eastern and Northern NEB, respectively, for about a 6 month leading period. The ability of both southeastern tropical Atlantic and Atlantic Niño SSTA indexes to forecast the Eastern and Northern NEB rainfall, with about a 6 month lead time, is improved when these indexes are respectively combined with the Niño3 (5° S–5° N; 150°–90° W) and the northeast subtropical Atlantic (20° N–35° N, 45° W–20° W), mainly from the 1970’s climate shift.

Role of the western hemisphere warm pool in climate variability over the western North Pacific

The climate variability in the Western North Pacific (WNP), which is surrounded by densely populated countries, is closely tied to the lives of the people in the East Asia in terms of climate and socioeconomics. Along with global warming, remarkable interannual and interdecadal variations in sea surface temperature (SST) and sea surface height have been observed in the WNP. Here we demonstrated that boreal summer SST variability in the western hemisphere warm pool (WHWP, a.k.a. Atlantic Warm Pool) near the Intra-Americas Sea, which is known as the second largest warm pool on the planet, has considerably contributed to the climate variability in the WNP in subsequent winter. This is possible due to westward propagation of Rossby waves associated with a WHWP-SST warming (cooling) in mid-summer to early fall season, which induces northerly (southerly) wind anomalies over the North Pacific. In the presence of northeasterly mean trade winds, the anomalous meridional winds interact with SST and precipitation anomalies. Such air-sea coupling processes gradually move equatorward and westward along the climatological migration of the Pacific Intertropical Convergence Zone, and it has finally an effect on the climate variability over the WNP in winter. Further diagnosis verifies that WHWP-WNP connection exists not only on interannual time scale but also on decadal time scale. The analysis using state-of-the-art climate models reasonably supports this argument. A better understanding of the WHWP influence is expected to improve forecasts for the WNP climate and assist socioeconomic development in the East Asia.

Seasonal climatology and dynamical mechanisms of rainfall in the Caribbean

The Caribbean is a complex region that heavily relies on its rainfall cycle for its economic and societal needs. This makes the Caribbean especially susceptible to hydro-meteorological disasters (i.e. droughts and floods). Previous studies have investigated the seasonal cycle of rainfall in the Caribbean with monthly or longer resolutions that often mask the seasonal transitions and regional differences of rainfall. This has resulted in inconsistent findings on the seasonal cycle. In addition, the mechanisms that shape the climatological rainfall cycle in the region are not fully understood. To address these problems, this study conducts: (i) a principal component analysis of the annual cycle of precipitation across 38 Caribbean stations using daily observed precipitation data; and, (ii) a moisture budget analysis for the Caribbean, using the ERA-Interim Reanalysis. This study finds that the seasonal cycle of rainfall in the Caribbean hinges on three main facilitators of moisture convergence: the Eastern Pacific ITCZ, the Atlantic ITCZ, and the western flank of the North Atlantic Subtropical High (NASH). The Atlantic Warm Pool and Caribbean Low-Level Jet modify the extent of moisture provided by these main facilitators. The expansion and contraction of the western flank of NASH generate the bimodal pattern of the precipitation annual cycle in the northwestern Caribbean, central Caribbean, and with the Eastern Pacific ITCZ the western Caribbean. This study identifies the Atlantic ITCZ as the major source of precipitation for the central and southern Lesser Antilles, which is responsible for their unimodal rainfall pattern. Convergence by sub-monthly transients contributes little to Caribbean rainfall.

Effect of recent Atlantic warming in strengthening Atlantic–Pacific teleconnection on interannual timescale via enhanced connection with the pacific meridional mode

The Atlantic warm pool (AWP), which features the highest sea surface temperature (SST) in the western Hemisphere in boreal summer to early fall, has been known to have a significant influence on the climate in its surrounding regions. It is reported that the AWP has become warmer and warmer, so that AWP–SST during a couple of recent decades has been higher than any other period since the twentieth century. Under the increased mean AWP–SST, atmospheric responses to the anomalous AWP–SST are intensified, which corresponds to a higher possibility of deep convection formation. Through Rossby wave propagation induced by the deep convection, AWP signals are able to reach further west toward the central North Pacific. At this moment, anomalous northerly winds are introduced over the North Pacific, which advects negative moist static energy (MSE) into the subtropics and simultaneously contributes to a SST cooling by interacting with northerly mean trade winds. Owing to the Gill-type response to a negative heating anomaly associated with the anomalous SST cooling and the negative MSE, the anomalous northerly winds are further developed over the North Pacific. Such air–sea coupling persists throughout fall to winter, leading to Pacific meridional mode development in the following spring. Subsequently, the PMM acts to boost El Nino and Southern Oscillation events. Coupled model experiments were carried out to investigate the extent to which the mean AWP–SST warming strengthens the Atlantic–Pacific interbasin teleconnection on interannual timescales, and it is proven to support observational analysis.