The summer spatial structure and sub-monthly temporal evolution of one of the key dynamical features of Central American climate, the Caribbean Low-Level Jet (CLLJ), is investigated by means of extended empirical orthogonal functions (EEOFs). The Caribbean 925-hPa zonal wind from the CFSR reanalysis for the period 1979 -2010 is used for the analysis. This approach reveals new insights into the dynamical processes and spatio-temporal evolution of the CLLJ summer intensification, and through lead and lag linear regressions, significant climate links in the broader Caribbean region are identified. The results show that the CLLJ generates significant precipitation and temperature responses with a distinct temporal evolution over the Caribbean-Atlantic domain to that over the tropical Pacific, which hints at different underlying controlling mechanisms over these two large-scale regions. These anomalies are linked with the mid and upper tropospheric circulation, where a vertical cell over the Caribbean (ascending at the jet exit and subsiding at its entrance) varies in phase with large-scale divergence over the Pacific Ocean. Extratropical hemispheric-wide waves and the weakening of a thermal low in northeast Mexico-central US are identified as potential triggering factors for the CLLJ summer intensification. Two leading modes of tropical variability, El Niño Southern Oscillation and the Madden-Julian Oscillation, are found to modulate the CLLJ by intensifying it and prolonging its life cycle. Details of the underlying mechanisms are provided. These results help to advance the understanding of the processes that modulate local climate variations, which is an important issue in view of the rapid climate change the region is undergoing.

Changes in frequency, duration and intensity of three heat wave (HW) types (compound, daytime, and nighttime) over the United States (U.S.) and Mexico during the second half of the 20th-century are investigated using the Community Earth System Model Large Ensemble (CESM-LE). The individual role of anthropogenic aerosols and greenhouse gases (GHGs), as well as the contribution from internal variability (IV), are identified and contrasted by means of the CESM-LE single forcing experiments during two periods: 1950–1975, when North American aerosol emissions peaked, and 1980–2005, when aerosol emissions declined. HW changes are strongly affected by anthropogenic forcing. During 1950–1975, aerosols, via both aerosol-radiation and aerosol-cloud interactions, dominate the decreasing trends in compound HWs over the central U.S., the daytime HWs in large parts of the domain and the nighttime HWs over Mexico. Conversely, all three HW types are considerably more frequent ( > 2 HWs summer−1 decade−1), longer-lasting (with increases of up to 2 days HW−1 decade−1 in some regions) and more intense (e.g., > 3 ∘ C HW−1 decade−1 in compound HWs) across large regions of the domain during the 1980–2005 period. The results show that the decline in aerosol emissions and the continuous rise in GHGs lead to widespread warming and subsequent circulation adjustments, contributing to the positive HW trends. The contribution of IV is large during 1950–1975 (over 60% in most areas), and considerably reduced later on. This study provides a comprehensive picture of the role of anthropogenic forcing and IV on the marked HW changes in the recent decades and their underpinning physical mechanisms.

The effects of increased North American sulphate aerosol emissions on the climate of Mexico and the United States (U.S.) during 1950–1975 are investigated by using two sets of transient coupled experiments with the Community Earth System Model, one with historically evolving emissions, and a second one where North American SO2 emissions are kept at their pre-industrial levels. The 1950–1975 increase in North American sulphate aerosols is found to have regional and remote impact. Over central U.S. and northern Mexico, the strengthening and westward expansion of the North Atlantic Subtropical High and subsequent intensification of the low-level easterlies, along with local aerosol interactions with radiation and clouds, cause a cooling trend and enhance precipitation. The interaction between the enhanced moisture transport across the Gulf of Mexico and the elevated topography of central Mexico favours positive rainfall on the Atlantic side while suppressing it on the Pacific side. These continental anomalies are embedded in a hemispheric-wide upper-tropospheric teleconnection pattern over the mid-latitudes, extending from the Pacific to the Atlantic basin. Details of the underlying mechanisms—in particular the prominent role of dynamical adjustments—are provided. With SO2 emissions considerably reduced in the U.S., and the expectation of a continued global decline throughout the 21st century, this study sheds light upon possible ongoing and future regional climate responses to changes in anthropogenic forcing.

<p align="justify">In autumn and winter, the dynamics and thermodynamics of the anticyclonic eddies detached from the Loop Current in the Gulf of Mexico are strongly influenced by the passage of cold fronts and Northerly winds. In turn, the interaction between the wind and these anticyclonic eddies modulates vertical nutrient fluxes, biomass, and phytoplankton community distribution at mesoscale and sub-mesoscale. In this work, the physical mechanisms of eddy-cold front interactions are analysed based on high-resolution (3 km) numerical simulations of the NEMO (Nucleous for European Modeling of the Ocean) model, contrasting simulations that partially include or not the effect of ocean currents on the wind stress (the so-called current feedback). This analysis is part of a work in progress focused on developing and implementing a high-resolution ocean-atmosphere coupled model for the Gulf of Mexico.</p>