Abstract/Summary

This thesis examines the variability of the Hadley Circulation in the north-west Atlantic (NWAHC) and links with precipitation over Trinidad and the Tropical North-West Atlantic (TNWA), and representation by climate model simulations. Variability of the NWAHC is investigated in the ERA-Interim reanalysis dataset and the HadGEM2 climate modeL Precipitation is assessed using satellite and gauge-based observations, including the Trinidad gauge network, the ERA-Interim reanalysis and HadGEM2 climate model. Analyses of the recent variability of the NWAHC in the HadGEM2 simulations indicate an overestimation of intensity by up to -10x1010 kg/so There is anomalous southward displacement of the equatorward edge with concomitant anomalous widths in the model, by up to -12°. The reanalysis precipitation is excessive, simulating around twice as much precipitation as the observations during both the wet season Gune to December) and dry season Ganuary to May), throughout the Tl\.'WA. Interannual precipitation variability is influenced by SST anomalies in the tropical Atlantic (TA) and Equatorial Eastern Pacific (EEP), which produce changes in the atmospheric circulation. In the EEP positive SST anomalies result in precipitation decreases during both seasons in the TNWA. Positive SST anomalies in the west TA and the north TA result in precipitation increases in the CAR and SCA region. A relationship, consistent across all the datasets, was found between the location of the March-April-May (MAM) West-Atlantic Intertropical Convergence Zone (WAlTCZ) and precipitation patterns during the dry season in the CAR and SCA regions, where northward movement of the WAITCZ results in precipitation increases. In comparison to observations, the HadGEM2 model simulates excessive precipitation in the CAR region by up to 80% and underestimates precipitation by up to 50% in the SCA region. For Trinidad, dry season precipitation in the model is underestimated by up to 90% in comparison to gauge observations, however, interannual variability has a correlation of 0.6, whereas during the wet season interannual variability has a low correlation of 0.2. For HadGEM2 projections of the NWAHC over the period 2070-2099, there is a weakening in December to August by -5x1010 kg/s and a strengthening in September to November by -10x1010 kg/s. This is associated with a projected decline in precipitation for the SCA, CAR and over Trinidad by 8%, 23%, 18% during the wet season and 10%,22% 33% during the dry season.