The role of the meridional sea surface temperature gradient in controlling the Caribbean low‐level jet

Abstract

The Caribbean low‐level jet (CLLJ) is an important modulator of regional climate, especially precipitation, in the Caribbean and Central America. Previous work has inferred, due to their semiannual cycle, an association between CLLJ strength and meridional sea surface temperature (SST) gradients in the Caribbean Sea, suggesting that the SST gradients may control the intensity and vertical shear of the CLLJ. In addition, both the horizontal and vertical structure of the jet have been related to topographic effects via interaction with the mountains in Northern South America (NSA), including funneling effects and changes in the meridional geopotential gradient. Here we test these hypotheses, using an atmospheric general circulation model to perform a set of sensitivity experiments to examine the impact of both SST gradients and topography on the CLLJ. In one sensitivity experiment, we remove the meridional SST gradient over the Caribbean Sea and in the other, we flatten the mountains over NSA. Our results show that the SST gradient and topography have little or no impact on the jet intensity, vertical, and horizontal wind shears, contrary to previous works. However, our findings do not discount a possible one‐way coupling between the SST and the wind over the Caribbean Sea through friction force. We also examined an alternative approach based on barotropic instability to understand the CLLJ intensity, vertical, and horizontal wind shears. Our results show that the current hypothesis about the CLLJ must be reviewed in order to fully understand the atmospheric dynamics governing the Caribbean region.

Caribbean Low‐Level Jet future projections using a multiparameter ensemble of RegCM4 configurations

“…In all cases, the HadG shows the poorest results in term of correlation and standard deviation because of an underestimation of the annual mean SST over the region (Martin and Schumacher, 2011), which can affect the structure of the zonal wind patterns, or because the cumulus parameterization affects the low‐level circulation. In addition, land‐sea thermal contrast is better represented in a high‐resolution model and this can also contribute to the RCM's better results (Cook and Vizy, 2010; Maldonado et al ., 2017).…”

WWLLN Hot and Cold-Spots of Lightning Activity and Their Relation to Climate in an Extended Central America Region 2012–2020

“…The convective inhibition is mainly due to the climatology wind shear distribution. This shear as pointed out by [67] is not explained by the observed meridional sea surface temperature gradient, so baroclinicity can be ruled out as opposed to the African Easterly Jet [68] showed that the CLLJ is barotropically unstable in that region [22], so energy could be exchanged between mean flow and disturbances. The CLLJ entrance is observed in the easternmost part of the CS, where descending motion dominates and precipitation is a regional minimum [23,44].…”

Sub-monthly evolution of the Caribbean Low-Level Jet and its relationship with regional precipitation and atmospheric circulation

“…However, the possible summer connections between the CLLJ and the MJO, and their dynamical mechanisms at sub-monthly timescale are yet to be explored. Fluctuations in the intensity of the CLLJ have been suggested to be modulated by the SST gradient between the tropical Pacific and the Caribbean Sea-Atlantic domain (Enfield and Alfaro 1999;Small et al 2007;Wang 2007;Martinez-Sanchez and Cavazos 2014;Fuentes-Franco et al 2015), although this is a current debate (e.g., Maldonado et al 2017). The CLLJ has been observed to strengthen when the inter-basin SST gradient increases (with a warmer-Pacific and cooler-Atlantic configuration), however, Whyte et al 2008 found out that the spatial pattern of the CLLJ intensification depends on which specific basin is primarily modulating the temperature gradient.…”