The Variability of the Wind Resource in the Caribbean and Associated Teleconnections

Long term temporal and spatial variability of wind speeds at 80 meters in the Caribbean was explored using wind speed reanalysis data for the period 1950 to 2015. The wind resource across the Caribbean is vast and diversified. It peaks in two distinct zones: the southwest Caribbean and the Eastern Caribbean with long term annual mean wind speeds ranging from 8 to 13 ms^-1 and 7 to 11 ms^-1 respectively, with corresponding wind power densities of 400 to 800 Wm^-2 and 200 to 500 Wm^-2. The minimum wind resource is observed over the Guianas, with annual mean wind speeds of 5.11 ms^-1, with a corresponding wind power density of up to 150 Wm^-2.

Marked seasonality was observed in the wind resource when the data was stratified across seasons. The pattern across the Caribbean exhibits changes in intensity and spatial location in response to the north-south oscillation of the Equatorial Trough and the North Atlantic High Pressure System. A remarkable drop of almost 2 ms^-1 in the seasonal mean wind speeds is seen across the entire Caribbean during the September-October-November (SON) period. The corresponding drop in wind power density is approximately 50 to 250 Wm^-2. Most of the Caribbean displayed a similar monthly pattern, with two peaks (maxima) in January-February and June-July, and two minima in September-October and April-May, respectively. In contrast, the Guianas, experienced one broad peak in February and a single minimum in July.

EOF analysis was also performed on the dataset to investigate temporal and spatial patterns in the wind resource. The first mode showed in phase variability across the Caribbean and accounted for 82.7%, 80.6%, 78.1% and 79.7% of the total variance for December-January-February (DJF), March-April-May (MAM), June-July-August (JJA), and SON respectively, an indication that the patterns are governed by well-defined physical processes. The principal components for all four seasonal patterns for the first modes show an increase in the wind speed amplitude from the year 2000 onwards, compared to previous years. The total variance explained by the second modes is small (~3%) and changed very little across seasons. Unlike the first modes that showed in-phase oscillation, the second modes depicted out-of-phase oscillation (opposite sign). For JJA and SON, between the Caribbean south of 24⁰ N and the Atlantic north of 24⁰ N; between the Atlantic north of 30⁰ N and south of 30⁰ N for MAM; between the Caribbean Sea and Atlantic between 15⁰ N and 30⁰ N for DJF.

Correlation analysis was carried out to characterize the nature of the relationships between the EOF spatial patterns of the wind resource and the major large-scale climate controls. The analysis suggested that the wind resource across the Caribbean is modulated by three major controls: El Nino and La Nina, the North Atlantic Oscillation (NAO) and a newly identified Tropical North Atlantic Oscillation. The results indicate that significant correlations with the NAO have very little spatial spread and therefore a meaningful conclusion about the validity of this teleconnection could not be established. The teleconnection signal associated with El Nino and La Nina was also not strong, with the exception of the MAM season which showed significant spatial spread. The strongest teleconnection signal is associated with the oscillation of Sea Level Pressure (SLP). An oscillation index was created using the difference between standardized SLP anomalies between the North Atlantic High Pressure and the Equatorial Trough. The amplitude of the oscillation varies between +2.5 and -2.75. These correlation results suggest that the wind resource across the Caribbean is largely modulated by the variability in SLP oscillations across the seasons. A dipole pattern was observed during the DJF season. The patterns exhibited for MAM and JJA were opposite to the pattern in SON.