The Combined and Individual Effects of the North Atlantic Oscillation
and the Atlantic Meridional Mode on Early Rainfall Season Precipitation
in the Insular Caribbean
Abstract
The insular Caribbean is a region influenced by Atlantic Ocean climate
variability. Effects of low-frequency atmospheric circulation patterns
on the precipitation of the Caribbean have been well documented.
However, individual modes of variability are usually only considered in
isolation. Here we analyse the combined and individual effects of the
North Atlantic Oscillation (NAO) and the Atlantic Meridional Mode (AMM)
on insular Caribbean precipitation. This work focuses on the Early
Rainfall Season (ERS, April-July), which explains much of the
interannual variability in precipitation for this region, from
1960-2016. Correlation analysis compare monthly NAO and AMM indices from
the National Oceanic and Atmospheric Administration (NOAA) against
monthly Caribbean precipitation from the Climate Research Unit (CRU)
year-by-year climate variables by country. Sea surface temperature (SST)
and sea level pressure (SLP) composites using NOAA data were also
created to analyse regional patterns. Analysis of the results show that
the NAO and AMM presented a correlation of opposite signs and affected
the Eastern Caribbean (from Dominican Republic to Grenada) during ERS,
resulting in precipitation anomalies above/below ± 10%. The combined
and individual effects of NAO and AMM indicate that Feb-Mar NAO and AMM
are significant correlated to May-Jun Eastern Caribbean precipitation
anomalies. More frequent and consistent regional effects on
precipitation anomalies, and more regionally spread and persistent SLP
and SST were registered when both NAO and AMM occurred together in the
previous winter. These results could be helpful in seasonal forecasting,
by indicating whether a wetter or drier ERS would be expected based on
the previous season NAO and AMM activity.