Joint modes of climate variability across the inter‐Americas

Abstract

Surface temperature (Ts), sea-level pressure (SLP), and zonal wind (U) fields from NCEP/NCAR reanalysis spanning the period 1949-2006 have been jointly analysed by means of principal component analysis to assess the dominant modes of climate variability in the inter-American region, including the eastern Pacific and Atlantic Oceans. Two aspects of these time-series were analysed: the annual cycle and its residual. Seasonal modes 1 and 2 take the form of north-south dipoles of Ts over oceanic and terrestrial environments. Seasonal mode 3 derives from SLP changes over the Amazon with a Caribbean wind response. Temporal fluctuations in the residual (ANOM) fields are resolved by six modes. ANOM1-3 is dominated by SLP and Ts changes across the equator in the Atlantic and east Pacific. The ANOM4 pattern is an isolated wind mode in the NE Atlantic. ANOM5 and 6 are dominated by sea temperature patterns in the South Atlantic and in the path of African easterly waves crossing the tropical Atlantic. The residual time scores are marked by significant warming (Ts) trends and co-located lower pressure. Cycles in the anomaly time scores tend to occur at 2-to 5-year periods. Modes dominated by atmospheric variables exhibit greater high-frequency 'noise' than oceanic modes. Predictability is assessed through development of multivariate regression models trained on Caribbean rainfall and related target time-series. The seasonal dipole between North and South America is found to modulate Pacific El Niño-Southern Oscillation and tropical Atlantic influence on Caribbean rainfall.

Improved seasonal prediction skill of rainfall for the Primera season in Central America

“…Outlooks of the Primera season are important because wetter (drier) MJ seasons tend to be associated with early (late) onsets of the rainy season (Alfaro et al, ; Maldonado et al, ). The early summer rainfall tends to be spatially heterogeneous across the Caribbean (Alfaro, ; Jury and Malmgren, ). So having a late start of the rains, like in 2015 (Amador et al, ), followed by a significantly drier‐than‐normal season in MJ with a deep MSD in July and August (Alfaro, ; Hernández and Fernández, ; Solano, ; Maldonado et al, ), could significantly affect key socio‐economic sectors in Central America, as most cities in the isthmus are located on the Pacific slope.…”

Variability of the Caribbean low-level jet during boreal winter: large-scale forcings

“…The variability of the CLLJ during each season is reportedly associated with different forcings, the fluctuations of the jet during winter being related to large‐scale features such as SST anomalies over the Niño 3.4 region (−5° to 5°N, 120° to 170°W), whereas the CLLJ perturbations in summer are associated with regional‐scale forcings such as the difference in the SSTs of the tropical North Atlantic (TNA) and El Niño regions (Amador et al , ). Jury and Malmgren () found evidence that the variability of the CLLJ is associated with SLP anomalies over the Amazons and the Atlantic ITCZ, rather than the North Atlantic anticyclone. Recently, Hidalgo et al () presented evidence that the CLLJ during summer is modulated by a pattern of divergence between lower and higher levels of the troposphere over the Intra‐Americas Sea region.…”