Caribbean Low-level Jet Research Articles

Precipitation variability and environmental change across late Quaternary glacial-interglacial cycles in lowland Central America: Insights from Lake Petén Itzá (Guatemala) sediments

Lowland Central America, a biodiversity hotspot in the northern Neotropics, is a region where the climate is influenced by the location and expansion-contraction of the Intertropical Convergence Zone (ITCZ) on seasonal to millennial timescales. Paleo-records from the Caribbean Sea and the eastern equatorial and subtropical Pacific Ocean illustrate the response of regional precipitation to fluctuations in global temperature, driven by glacial-interglacial cyclicity over the past 500 kyr. Here, we present a paleoclimate and paleoenvironment record from Lake Petén Itzá, lowland Guatemala, which spans the last ∼413 kyr. Sediment in the lake recorded lacustrine and terrestrial ecosystem responses to large-scale climate variability. Precipitation patterns during MIS11-9 (∼413-304 ka BP) align with the latitudinal position of the ITCZ, with superimposed effects from the strength of the Caribbean Low-Level Jet (CLLJ). A sediment hiatus, likely attributable to mass removal processes in the lake's shallower areas, spans the period from MIS8 (starting at 304 ka BP) to the end of MIS6 (at 149 ka BP). MIS6 was characterized by humid conditions, perhaps ascribable to a more southerly extension of cold fronts and intensification of the CLLJ. During MIS5, pronounced fluctuations among all sediment variables, accompanied by an abrupt decline in precipitation, may correspond with cold events inferred from North Atlantic Ocean sediment cores. Although discontinuous, the Lake Petén Itzá sediment record provides a window into late Quaternary climate and environmental change in lowland Central America.

The emission, transport, and impacts of the extreme Saharan dust storm of 2015

Abstract. ​​​​​​​Each summer, the Saharan Air Layer (SAL) transports massive amounts of mineral dust across the Atlantic Ocean, affecting weather, climate, and public health over large areas. Despite the considerable impacts of African dust, the causes and impacts of extreme trans-Atlantic African dust events are not fully understood. The “Godzilla” trans-Atlantic dust event of 2020 has been extensively studied, but little is known about other similar events. Here, we examine the June 2015 event, the second strongest trans-Atlantic African dust event that occurred during the summers from 2003–2022. This event was characterized by moderately high dust emissions over western North Africa and an extremely high aerosol optical depth (AOD) over the tropical North Atlantic. The high dust loading over the Atlantic is associated with atmospheric circulation extremes similar to the Godzilla event. Both the African easterly jet (AEJ) and Caribbean low-level jet (CLLJ) have greatly intensified, along with a westward extension of the North Atlantic subtropical high (NASH), all of which favor the westward transport of African dust. The enhanced dust emissions are related to anomalously strong surface winds in dust source regions and reduced vegetation density and soil moisture across the northern Sahel. The dust plume reduced net surface shortwave radiation over the eastern tropical North Atlantic by about 25 W m−2 but increased net longwave flux by about 3 W m−2. In contrast to the Godzilla event, the 2015 event had minor air quality impacts on the US, partially due to the extremely intensified CLLJ that dispersed the dust plume towards the Pacific.

An analysis of surface waves in the Caribbean Sea based on a high-resolution numerical wave model

Surface waves are extremely important in a large variety of oceanographic applications and thus, the study of their spatiotemporal characteristics remains crucial. This study analyzes waves in the Caribbean Sea (CS) and western Atlantic Ocean (AO) using a high-resolution (HR) Simulating WAves Nearshore model validated with buoy observations and paired with a HR bathymetric dataset from 2010 – 2019. Island sheltering effects are examined but special attention is given to these effects under Hurricane Dorian in The Bahamas using observations from the China-France Oceanographic Satellite. Results illustrate that wave heights within the CS fluctuated with Caribbean Low-Level Jet activity, but a different wave regime exists within the AO. While wind waves overwhelmingly dominate the wave field and this is true even in the AO, surprisingly, the contribution of swell in the central CS was equal to one site in the AO. Possibly, due to interaction with the shallow Nicaraguan Rise, wave heights were strongly (depth-induced) refracted nearly 45°, a feature unseen in previous research using coarse bathymetric datasets. Island sheltering effects were pervasive and were naturally most pronounced under hurricane conditions. Crucially, New Providence in The Bahamas is vulnerable to hurricane-forced waves funneled through the Grand Bahama and Northeastern Providence Channels.

Upwelling-induced inflow pulses in a tropical bay during mid-summer drought

Bahía Santa Elena is a tropical bay located in the northern Pacific region of Costa Rica. This region experiences a period of reduced precipitation from July to August, known as mid-summer drought, induced by the intensification of northeastern winds from the Caribbean Low-Level Jet. Intensification of upwelling-favorable winds can cool surface waters adjacent to the bay, leading to a reduction in water temperatures within the bay, that alters the biological dynamics of coastal habitats. This study aims to analyze upwelling-induced inflow pulses in Bahía Santa Elena during mid-summer drought, focusing on the cooling effect of intensified upwelling-favorable winds and the subsequent warm water inflows following wind relaxation. We conducted two measuring campaigns from June to July in 2021 and in 2022. The first campaign consisted of a single acoustic Doppler current profiler (ADCP) moored inside the bay. The second campaign consisted of two mooring deployments: an ADCP with a thermistor chain inside the bay and an ADCP installed at the inlet. Each campaign presented five distinct events of upwelled water inflows into the bay promoted by an offshore Ekman transport. Upwelling-favorable wind peaks were followed by a decrease in temperature of the water column. When the upwelling-favorable wind relaxed, a warm water pulse entered the bay. These events are expected to play an important role in biological processes within tropical bays adjacent to upwelling zones during mid-summer drought.

Extreme waves in the Caribbean Sea: spatial regionalization and long-term analysis

The extreme wave height distribution in the Caribbean Sea is studied using a new method based on the maximum basin-wide aggregate of significant wave height, Hs, values per month. Besides, by means of the Self-Organizing Maps (SOM) technique, we identify coherent geographical regions with similar extreme wave height variability in the Caribbean Sea. Our findings revealed three primary regions: the eastern side with comparatively lower values, the central region with intermediate values, and the western side with the highest extreme wave heights. The study also examines the wind forcing conditions driving the spatial and temporal variability of the extreme waves, highlighting the influence of the low-pressure belt dynamics as well as the role played by the Caribbean Low-Level Jet (CLLJ) index, and the impact of cold fronts and hurricanes on extreme wave heights. Additionally, we explore the relationship between the extreme wave height distribution and climatic indices, such as the Atlantic Multidecadal Oscillation (AMO), the Atlantic Meridional Mode (AMM), the North Atlantic Oscillation (NAO) and the Oceanic Niño (ONI). The results reveal that the spatial distribution of extreme wave heights in the Caribbean Sea is mostly ruled by the influence of the CLLJ, with correlations close to 80%. In addition, significant correlations were observed between the extreme wave heights and the ENSO in the central Caribbean, as well as positive correlations between the extreme wave heights and NAO in the eastern part of the basin, and significant values of correlation with the negative phases of AMO and AMM in the whole basin. We show that, unlike conventional (or broadly used) methods deployed to identify extreme wave height, such as percentile 99th, Hs99, our methodology allows a further assessment of the wind and climate forcing conditions associated with the extreme wave events. Although, we acknowledge that the method here presented has limitations to capture extreme wave height outliers, it has the advantage of being used concomitant with the wind forcing to develop multivariate wave climate analysis at basin scale, and could be extended to a more local scale when studying coastal processes.

An objective procedure for rainy season onset and withdrawal dates over the Mexico Valley Basin

This work aims to define a procedure to declare rainy season onset and withdrawal dates for the Mexico Valley Basin, located in central Mexico. The onset/withdrawal is obtained using only precipitation for the study period 1981–2020. The onset is defined as the first day, between May 1st and July 15th, of the first 20 consecutive days having a 20-day average precipitation over the Basin of at least 2.5 mm/day. The withdrawal is defined as the last day, between September 1st and November 15th, of the last 20 consecutive days having a 20-day average precipitation of at least 1.7 mm/day. The mean onset is June 6th, with a standard deviation of 14.3 days; the mean withdrawal date is October 15th, with a standard deviation of 16.1 days; and the average length of the rainy season is 131 days, with a standard deviation of 22.7 days. These criteria maximize the precipitation change slope during onset/withdrawal. We categorized pre- and post-onset/withdrawal periods to investigate mean circulation characteristic changes. Besides a stark increase (decrease) in rainfall over the Basin during onset (withdrawal), we found that vertically integrated moisture transport over the Caribbean Low-Level Jet core region increases (decreases). The onset/withdrawal dates derived show interannual trends, while a late (early) withdrawal is associated with a positive (negative) ENSO Index, and a strong (weak) Caribbean Low Level Jet (CLLJ) is associated with a late (early) onset.

A spatio-temporal analysis of the role of climatic drivers influencing extreme precipitation events in a Costa Rican basin

Regional patterns of rainfall are changing around the world, putting pressure on social, economic, and environmental systems, and changing the outlook for food, water, and health security. This is the case in the Tempisque-Bebedero River Basin (TBRB), located on the Pacific slope of northwest Costa Rica, which relies heavily on water resources for tourism, agriculture, ranching, and fish farming. In this study, we use non-stationary extreme value analysis to characterize the climatic drivers of extreme precipitation in the TBRB. Daily extreme precipitation events at stations across the TBRB are selected using a peak-above-threshold approach, and interannual climate variability is included as time-varying covariates in a non-stationary point process model, using three regional climate indices: the Caribbean Low-Level Jet (CLLJ) index, the Oceanic Niño Index (ONI), representative of the El Niño Southern Oscillation (ENSO), and the Atlantic Multidecadal Oscillation (AMO) index. We find that the magnitude and frequency of precipitation extremes in the basin are driven by the CLLJ and the AMO. The ONI is only a significant driver of extreme precipitation in the northwestern region of the basin. This is likely because ENSO controls the strength of the CLLJ, thus the dominant impact of ENSO on precipitation in the TBRB may be incorporated within the CLLJ component of our model.

Easterly wave activity in the Intra Americas Seas region analyzed with vertically integrated moisture fluxes

Introduction: Easterly waves (EWs) are a dominant atmospheric phenomenon in the tropics. EWs in Mexico, Central America and the Caribbean region produce intense precipitation and significantly contribute to the summer rainy season, but some climatologies indicate their activity is weak or even null over the Intra-Americas Seas (IAS). As it is shown in the present study, EW activity over the IAS is not negligible but its variability is less than that off the western coast of Africa.Method: Given the well-known coupling of wind and atmospheric moisture in EWs, their characteristics may be described using vertically integrated moisture fluxes (VIMF) and their divergence. By means of Hovmöller diagrams, lagged correlations and composite analyses, the propagation and the meteorological effects of these waves across the Caribbean Sea and the Gulf of Mexico, particularly on moisture and rains, are examined.Results: It is observed that as EWs propagate, the VIMF convergence increases the level of precipitable water which frequently results in intense precipitation events. High frequency variability of the meridional component of the VIMF is used to estimate EW activity. Over the Caribbean Sea, EWs are less energetic than in the eastern tropical Atlantic even while the number of waves over these regions is comparable.Discussion: When the Caribbean Low-Level Jet (CLLJ) is strong, EW activity tends to diminish due to a decrease in precipitable water (PW), sea surface temperature (SST) over the Caribbean, and possibly to an intensified vertical wind shear. Therefore, years of a stronger than normal CLLJ tend to result in summer precipitation below normal over most of the IAS and southern Mexico.

Investigation of Multi-Timescale Sea Level Variability near Jamaica in the Caribbean Using Satellite Altimetry Records

There is a dearth of studies characterizing historical sea level variability at the local scale for the islands in the Caribbean. This is due to the lack of reliable long term tide gauge data. There is, however, a significant need for such studies given that small islands are under increasing threat from rising sea levels, storm surges, and coastal flooding due to global warming. The growing length of satellite altimetry records provides a useful alternative to undertake sea level analyses. Altimetry data, spanning 1993–2019, are used herein to explore multi-timescale sea level variability near the south coast of Jamaica, in the northwest Caribbean. Caribbean basin dynamics and largescale forcing mechanisms, which could account for the variability, are also investigated. The results show that the average annual amplitude off the south coast of Jamaica is approximately 10 cm with a seasonal peak during the summer (July–August). The highest annual sea levels occur within the Caribbean storm season, adding to the annual risk. The annual trend over the 27 years is 3.3 ± 0.4 mm/yr when adjusted for Glacial Isostatic Adjustment (GIA), instrumental drift, and accounting for uncertainties. This is comparable to mean global sea level rise, but almost twice the prior estimates for the Caribbean which used altimetry data up to 2010. This suggests an accelerated rate of rise in the Caribbean over the last decade. Empirical Orthogonal Function (EOF) and correlation analyses show the long-term trend to be a basin-wide characteristic and linked to warming Caribbean sea surface temperatures (SSTs) over the period. When the altimetry data are detrended and deseasoned, the leading EOF mode has maximum loadings over the northwest Caribbean, including Jamaica, and exhibits interannual variability which correlates significantly with a tropical Pacific-tropical Atlantic SST gradient index, local wind strength, and the Caribbean Low Level Jet (CLLJ). Correlations with the El Niño Southern Oscillation (ENSO) in summer, seen in this and other studies, likely arise through the contribution of the ENSO to the SST gradient index and the ENSO’s modulation of the CLLJ peak strength in July. The results demonstrate the usefulness of altimetry data for characterizing sea level risk on various timescales for small islands. They also suggest the potential for developing predictive models geared towards reducing those risks.

Millennial hydrological variability in the continental northern Neotropics during Marine Isotope Stages (MISs) 3–2 (59–15 cal ka BP) inferred from sediments of Lake Petén Itzá, Guatemala

Abstract. Lake Petén Itzá (Guatemala) possesses one of the longest lacustrine sediment records in the northern Neotropics, which enabled study of paleoclimate variability in the region during the last ∼400 000 years. We used geochemical (Ti, Ca/(Ti+Fe) and Mn/Fe) and mineralogical (carbonates, gypsum, quartz, clay) data from sediment core PI-2 to infer past changes in runoff, lake evaporation, organic matter sources and redox conditions in the water column, caused by hydrological changes in the northern Neotropics during Marine Isotope Stages (MISs) 3–2. From 59 to 39 cal ka BP climate conditions were relatively wet, and the lake was marked by higher primary productivity and anoxic bottom waters. This wet environment was interrupted for two periods of possible low water level at 52 and 46 cal ka BP, when our data suggest higher evaporation, high terrestrial organic matter input and persistent oxic conditions. Between 39 and 23 cal ka BP, evaporation and input of terrestrial organic matter increased considerably, lake level declined, and lake bottom waters generally became oxic. These conditions reversed during the Last Glacial Maximum (23.5–18.0 cal ka BP), when runoff and lake productivity increased, and rising lake level caused bottom waters to again become anoxic. Comparison of our hydrologic proxy data with sea surface temperature anomalies between the eastern Pacific and the Caribbean suggests that changes in the intensity of the Caribbean Low-Level Jet (CLLJ) may have influenced long-term changes in runoff during MISs 3–2. Higher intensity of the CLLJ during the onset of MIS 3 and the LGM might have led to greater runoff into the lake, whereas the MIS 3–2 transition experienced a weaker CLLJ and consequently less runoff. A refined, high-resolution age–depth model for the PI-2 sediment core enabled us to identify millennial-scale Greenland interstadials (GIs) 14–2, Greenland stadials (GSs) 14–2 and Heinrich stadials (HSs) 5–1. In general, HSs and GSs were characterized by drier conditions. In contrast to GSs and HSs, GIs were characterized by greater runoff and overall wetter conditions, with the most pronounced GI peaks between 40 and 30 cal ka BP. Whereas GSs 9, 8, 7 and 6 began with abrupt increases in evaporation and ended with gradual increases in humidity, GSs 11 and 10 showed reversed patterns. The Lake Petén Itzá paleohydrology record, along with other regional paleoclimate records, led us to conclude that shifts in the position of the Intertropical Convergence Zone (ITCZ) altered moisture delivery to the lake on millennial timescales. During GSs and HSs, high evaporation from Petén Itzá (dry climate conditions) was associated with a more southerly position of the ITCZ, whereas wetter GIs prevailed during a more northerly ITCZ position. Although abrupt millennial-scale shifts in ITCZ and hydroclimate between GSs/HSs and GIs can be linked to instabilities in the Atlantic Meridional Overturning Circulation (AMOC), longer-term changes were additionally influenced by changes in atmospheric convection linked to modulations of the CLLJ in response to ΔSST between the equatorial Pacific and tropical Atlantic.

Inter ocean basin moisture fluxes and the onset of the summer rainy season over southern Mexico

The onset of the rainy season in monsoonal climates is a key element for the development of water related activities. In southern Mexico, it starts in late May or early June, while in western and northwestern part of the country in begins between early and mid-July. Previous studies indicate that it depends on the meridional position of the eastern Pacific Inter Tropical Convergence Zone (ITCZ). By mean of analyses of the Vertically Integrated Moisture Flux, the low level atmospheric dynamics in the tropical Americas is analyzed to establish the temporal evolution of inter ocean moisture fluxes that lead to the onset of the summer rainy season in southern Mexico. The onset of the rainy season depends on the longitudinal position of the center of maximum convective activity in the ITCZ, which induces a quasi-stationary low-level cyclonic circulation that results in moisture fluxes to the Mexican Pacific coast and rains. The Caribbean Low-Level Jet (CLLJ) is a mechanism that modulates inter ocean basin moisture fluxes into the eastern Pacific ITCZ and the location of the maximum convective activity in this system. We propose that the sequence of events that leads to the onset of the rainy season in southern Mexico is: (i) an episode of strong moisture flux from the Caribbean Sea into the eastern Pacific ITCZ, (ii) a region of intense convective activity in the ITCZ that triggers a quasi-stationary low-level cyclonic circulation which in turn, induces moisture flux into southern Mexico, and (iii) the development of convective activity in southern Mexico that determines the onset of the rainy season. The intensification of the CLLJ from June to July also results in a westward displacement of the region of maximum convection within the ITCZ that leads to changes in the atmospheric circulations and moisture fluxes that determine the onset of the rainy season at higher latitudes in the Mexican Pacific coast.

Multiscale Interactions of Climate Variability and Rainfall in the Sogamoso River Basin: Implications for the 1998–2000 and 2010–2012 Multiyear La Niña Events

In this research, we explored rainfall variability in the Sogamoso River Basin (SRB), its relationship with multiple scales of variability associated with El Niño–Southern Oscillation (ENSO), and the implications for rainfall prolongation during multiyear La Niña events. First, we examined time-frequency rainfall variations in the SRB based on the standardized precipitation index (SPI) from 1982 to 2019, using wavelet transform and principal component analysis (PCA). In addition, we applied wavelet analysis to investigate the links at different time scales between ENSO and the main mode of rainfall variability in the SRB. Finally, we explored the role that each scale of variability played in the prolongation and intensity of rainfall in the SRB during the 1998–2000 and 2010–2012 multiyear La Niña events. The results of the wavelet analyses revealed significant ENSO relationships affecting SRB rainfall at three different scales: quasi-biennial (2–3-years) between 1994 and 2002, as well as from 2008 to 2015; interannual (5–7 years) from 1995 to 2011; and quasi-decadal (9–12 years) from 1994 to 2012. This indicates that multiyear events are a consequence of the interaction of several scales of variability rather than a unique scale. During the 1998–2000 event, El Niño conditions were observed during the first half of 1998; subsequently, a cooling of the central and eastern tropical Pacific (western tropical Pacific) on the quasi-biennial (interannual) scale was observed during 1999; in 2000, only La Niña conditions were observed on the interannual scale. Therefore, during this event, the quasi-biennial (interannual) scale promoted wet conditions in the Caribbean, the Andes, and the Colombian Pacific from June–August (JJA) 1998 to JJA 1999 (during 1999–2000). During the 2010–2012 La Niña event, the interbasin sea surface temperature gradient between the tropical Pacific and tropical North Atlantic contributed to strengthening (weakening) of the Choco jet (Caribbean low-level jet) on the quasi-biennial scale during 2010, and the interannual scale prolonged its intensification (weakening) during 2011–2012, acting to extend the rainy periods over most of the Colombian territory. Variations on quasi-decadal scales were modulated by the Pacific decadal oscillation (PDO), resulting in a further intensification of the 2010–2012 La Niña event, which developed under conditions of the cold PDO (CPDO) phase, whereas the 1998–2000 La Niña occurred during the transition from warm (WPDO, 1977–1998) to cold (CPDO, 2001–2015) conditions. These results indicate that the interaction of quasi-biennial to quasi-decadal scales of variability could play a differential role in the configuration and prolongation of rainfall events in the SRB.

Variability of Precipitation Recycling and Moisture Sources over the Colombian Pacific Region: A Precipitationshed Approach

This study assessed the precipitation recycling and moisture sources in the Colombian Pacific region between 1980–2017, based on the monitoring of moisture in the atmosphere through the Eulerian Water Accounting Model-2 layer (WAM2 layer) and the delimitation of the area contributing to terrestrial and oceanic moisture in the region is performed using the “precipitationshed” approach. The results indicate a unimodal precipitation recycling ratio for the North and Central Pacific and Patía-Mira regions, with the highest percentages between March and April, reaching 30% and 34%, respectively, and the lowest between September and October (between 19% and 21%). Moreover, monthly changes in the circulation of the region promote a remarkable variability of the sources that contribute to the precipitation of the study area and the spatial dynamics of the precipitationshed. From December to April, the main contributions come from continental sources in eastern Colombia and Venezuela, the tropical North Atlantic, and the Caribbean Sea, a period of high activity of the Orinoco Low-Level jet. In September, the moisture source region is located over the Pacific Ocean, where a southwesterly cross-equatorial circulation predominates, converging in western Colombia, known as the Choco Jet (CJ), decreasing the continental contribution. An intensified Caribbean Low-Level Jet inhibits moisture sources from the north between June and August, strengthening a southerly cross-equatorial flow from the Amazon River basin and the southeastern tropical Pacific. The March–April (September–October) season of higher (lower) recycling of continental precipitation is related to the weakening (strengthening) of the CJ in the first (second) half of the year, which decreases (increases) the contribution of moisture from the Pacific Ocean to the region, increasing (decreasing) the influence of land-based sources in the study area.

Revisiting mechanisms of the Mesoamerican Midsummer drought

Observations show that the seasonal cycle of precipitation in parts of southern Mexico and Central America exhibits a bimodal signal, known as the Midsummer drought (MSD), but there is no consensus on which processes are most relevant for the two-peak structure of the rainy season. This paper evaluates three hypotheses that could explain the MSD: the SST cloud-radiative feedback, the solar declination angle and the Caribbean Low-Level Jet (CLLJ) moisture transport hypotheses. Model experiments produced by the Met Office Hadley Centre (MOHC) for CMIP6 as well as ERA5 reanalysis data are used to critically assess the predictions of each hypothesis. The simulations capture the double peak signal of precipitation well and reasonably simulate the spatial and temporal variations of the MSD and other relevant climate features such as the CLLJ. Evidence from our analysis suggests that the Eastern Pacific SSTs do not increase in late summer in ERA5 data and only slightly increase in the simulations. More importantly, the Eastern Pacific SST variability in ERA5 and in the model experiments cannot explain the differences in the seasonality of precipitation. The net shortwave radiation at the surface shows a two-peak seasonal cycle; however, this behaviour appears to result from a strong anti-correlation of the incoming shortwave and convective activity due to cloud radiative-effects. There was no evidence found by this study of a causal link in which absorption of shortwave energy forces precipitation variations, as suggested by the solar declination angle hypothesis. The moisture convergence, CLLJ and the precipitable water vapor variations best explain the characteristics of the observed and simulated MSD, particularly for the onset of the MSD. The diagnosed variations of moisture convergence, which are synchronous with the timing of the MSD, point to a dynamic mechanism in which the low-level inflow from the Caribbean is more important for the MSD than other radiative mechanisms.

WWLLN Hot and Cold-Spots of Lightning Activity and Their Relation to Climate in an Extended Central America Region 2012–2020

Lightning activity has been recognized to have, historically, social and environmental consequences around the globe. This work analyzes the space-time distribution of lightning-densities (D) in an extended Central America region (ECA). World Wide Lightning Location Network data was analyzed to link D with dominant climate patterns over the ECA for 2012–2020. D associated with cold surges entering the tropics dominate during boreal winter. The highest D (hot-spots) was found to agree well with previously known sites, such as the “Catatumbo” in Venezuela; however, D was lower here due to different detection efficiencies. Previously reported hot-spots showed strong continental signals in CA; however, in this work, they were over the oceans near to coastlines, especially in the eastern tropical Pacific (ETP). Most cold-spots, implying a minimum of vulnerability to human impacts and to some industries, were situated in the Caribbean Sea side of Central America. The Mid-Summer-Drought and the Caribbean-Low-Level-Jet (CLLJ) markedly reduced the D during July-August. The CLLJ in the central CS and across the Yucatan and the southern Gulf of Mexico acts as a lid inhibiting convection due to its strong vertical shear during the boreal summer. The CLLJ vertical wind-shear and its extension to the Gulf of Papagayo also diminished convection and considerably decreased the D over a region extending westward into the ETP for at least 400–450 km. A simple physical mechanism to account for the coupling between the CLLJ, the MSD, and lightning activity is proposed for the latter region.

Sensitivity of precipitation and atmospheric low-level circulation patterns to domain size and choice of parameterization schemes in RegCM4.4 over Central America

The sensitivity of regional climate model simulations to domain size and position is becoming increasingly important for generating reliable climate scenarios. In this study, the Central America CORDEX domain (CCA) at 50 km horizontal resolution with a relaxation zone of 10° around the boundaries (CCA+) was taken as the basis to increase domain size in the RegCM4.4 model. The low-level circulation and precipitation patterns over Central America, the western Caribbean Sea, and the eastern tropical Pacific do not show strong sensitivity to domain size changes for an area increment of 18, 32, and 52% with respect to the size of CCA+. The physical configuration in RegCM4.4 has a greater impact on the representation of relevant climate characteristics and atmospheric processes. Simulated 925 hPa winds over the Caribbean low-level jet (CLLJ) region show unrealistic winter and summer intensities, especially in July. Similar issues were found in other studies for the CCA domain, using different models and physical configurations. A reduction of the critical Richardson number in the selected planetary boundary layer scheme resulted in little change in the strength of the summer component of the CLLJ. The model simulations do not completely capture key regional precipitation patterns such as the mid-summer drought, due to limitations in adequately representing low-level circulation. However, simulations using the Grell cumulus parameterization perform relatively better than those using a mixed scheme (Grell over land-Emanuel over ocean).

Joint Offshore Wind and Wave Energy Resources in the Caribbean Sea

Complementarities between wind and wave energies have many significant advantages that are unavailable with the sole deployment of either. Using all available wind speed, significant wave height, and wave period buoy observations over a 10-year period (i.e., 2009–2019), colocated wind and wave energy resources are estimated. Although buoy records are imperfect, results show that the inner Caribbean Sea (CS) under the influence of the Caribbean low-level jet has the highest wind energy resource at ~ 1500 W/m2, followed by the outer CS at ~ 600 W/m2 and Atlantic Ocean (AO) at ~ 550–600 W/m2 at a 100 m height. Wave energy was most abundant in the AO at 14 kW/m, followed by the inner CS at 13 kW/m and outer CS at 5 kW/m. The average and dominant wave energies can reach a maximum of 10 and 14 kW/m, respectively. Asymmetry between wind and wave energy resources is observed in the AO, where wave energy is higher than the low wind speed/energy would suggest. Swell is responsible for this discrepancy; thus, it must be considered not only for wave energy extraction but also for wind turbine fatigue, stability, and power extraction efficiency.

Seasonal-To-Interannual Variability of Sea-Surface Temperatures in The Inter-Americas Seas: Pattern-Dependent Biases in The Regional Ocean Modeling System

The Inter-Americas Seas (IAS), involving the Gulf of Mexico, the Caribbean and a section of the eastern tropical Pacific Ocean bordering Central America, Colombia and Ecuador, exhibits very active ocean-land-atmosphere interactions that impact socio-economic activities within and beyond the region, and that are still not well understood or represented in state-of-the-art models. On seasonal-to-interannual timescales, the main source of variability of this geographical area is related to interactions between the Pacific and the Atlantic oceans, involving to anomalous sea-surface temperature (SST) patterns like El Niño-Southern Oscillation (ENSO), and regional features in the Caribbean linked to the bi-modal seasonality of the Caribbean Low-Level Jet. This study investigates seasonal-to-interannual IAS surface-temperature anomalies in observations, and their representation in am eddy-permitting, 1/9o-resolution simulation using the Regional Ocean Modeling System (ROMS), interannually-forced by the Climate Forecast System Reanalysis. Here, rather than analyzing model biases locally (i.e., gridbox-by-gridbox), a non-local SST pattern-based diagnostic was conducted via a principal component analysis. The approach allowed to identify magnitude, variance and spatial systematic errors in SST patterns related to the Western Hemisphere Warm Pool, ENSO, the Inter-American Seas Dipole, and several other variability modes. These biases are mainly related to errors in surface heat fluxes, misrepresentation of air-sea interactions impacting surface latent cooling in the Caribbean, and too strong sub-surface thermal stratification, mostly off the coast of Ecuador and northern Peru.

Forcing of cool and warm subsurface water events in Bahía Salinas, Costa Rica

Introduction: Bahía Salinas, on the north Pacific coast of Costa Rica, is a seasonal upwelling area. Sea temperature in Bahía Salinas could be modulated by synoptic and other large-scale systems. This region belongs to the Central American Dry Corridor (CADC), a sub-region in the isthmus that is relatively drier than the rest of the territory, which extends along the Pacific littoral from western Guatemala through northern Costa Rica.
 Objective: To study the warm and cold events that could be inferred by studying the sea subsurface temperature in Bahía Salinas, and also analyzing the large-scale conditions and synoptic systems of the historical sources when they occurred in order to identify the atmospheric mechanisms that favored their appearance.
 Methods: A Sea Subsurface Temperature Index was calculated using hourly data from seven stations located at three different points in Bahía Salinas. Records range from June 19, 2003 to December 5, 2017. Additionally, six meteorological stations, with hourly wind records, were used to create two wind indices. The Sea Subsurface Temperature Index was used to identify the warmest and coldest events in the bay. Wind indices and monthly meteorological bulletins were used to analyze the large-scale conditions and synoptic systems in which cold and warm events occurred in Bahía Salinas.
 Results: Mean sea temperature in Bahía Salinas is 25.2°C. Colder temperatures were observed in February-March, below 21°C. There were two maxima in May-June and August-October with temperatures above 27°C. In four of the five cold events studied, Northeasterly wind anomalies were observed in the Costa Rican North Pacific, associated with trade wind reinforcements; meanwhile westerly anomalies were observed in all the warm events, associated with weaker trade wind conditions.
 Conclusions: The main seasonal climate driver in Bahía Salinas is the North Atlantic Subtropical High because its latitudinal migration is associated with the strength of the trade winds over Central America. Seasonal upwelling is modulated also by two synoptic scale climate features, the boreal winter arrival of cold front outbreaks and the winter maximum of the easterly Caribbean Low-Level Jet. El Niño-Southern Oscillation is also an important modulator of the sea temperature variability, since warm and cool events are related with positive and negative sea temperature anomalies.

Pacific and Atlantic Multidecadal Variability Relations with the Choco and Caribbean Low-Level Jets during the 1900–2015 Period

This study analyzes the variability of the Choco jet (CJ) and Caribbean low-level jet (CLLJ) with consideration of the simultaneous Pacific interdecadal oscillation (PDO) and Atlantic multidecadal oscillation (AMO) low-frequency mean states and their effects on the atmospheric circulation and rainfall in northwestern South America and Central America for the 1900–2015 period, during the seasons with the highest intensities of the CJ (September–November (SON)) and the CLLJ (June–August). Variations in the sea surface temperature (SST) anomaly positioning in the eastern Pacific, tropical North Atlantic (TNA)/Caribbean Sea during different mean states restrict the anomalous circulation, and, consequently, the intensity of the CJ and CLLJ. During the warm AMO (WAMO)/cold PDO (CPDO), the SST gradient from the tropical Pacific into the TNA, accompanied by a cyclonic circulation near the east coast of the Americas, intensifies the west–east circulation in the region, strengthening the CJ and weakening the CLLJ during SON such that rainfall increases over Colombia, Central America and in adjacent oceans. During the cold AMO (CAMO)/warm PDO (WPDO) phase, a relative east/west SST gradient occurs in TNA, consistent with a cyclonic circulation in western TNA, establishing an anomalous southwest–northwestward circulation from the eastern Pacific into the Caribbean basin, forming a well-configured CJ, increasing precipitation over Central America and its adjacent oceans. For the CLLJ, during CAMO phases, the anticyclonic circulations extended over most of the TNA favor its intensification from 30° W to the Caribbean Sea. In contrast, during WAMO, the cyclonic circulation near the east coast of the United States restricts its intensification to the Caribbean Sea region. To the best of our knowledge, the results presented here are new and might be useful in atmospheric modeling and extreme event studies.