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Role of Caribbean low-level jet and Choco jet in the transport of moisture patterns towards Central America
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1  Escuela Ambiental, Facultad de Ingeniería, Universidad de Antioquia.


Central America (CAM) is a thin strip of land, whose climate is influenced by the presence of low-level jets, by transporting atmospheric moisture from the surrounding oceanic masses (Pacific and Atlantic Oceans). In this study, we analyzed the seasonal patterns of water vapor transport to this region and their interannual variability, with special emphasis on the role of the Caribbean low-level jet (CLLJ) and the Choco jet (CJ). The semi-lagrangian 2D model Dynamic Recycling Model (DRM) is implemented, using information from ERA-Interim reanalysis during the period 1980-2012. Our results suggest that approximately 72% of mean annual atmospheric moisture transported to Central America comes from the Atlantic Ocean, with a contribution of 35% from the Caribbean Sea, and 23 and 14% from the North Atlantic and the Tropical North Atlantic, respectively. This transport is closely related to the CLLJ, showing that a strong (weak) jet induces a greater (smaller) transport from the Atlantic to CAM. On the other hand, transport from the Pacific exhibits a very marked seasonality, responding to the intensity of the CJ, which during high intensity episodes stimulates an increase in transport of water vapor. Finally, at the interannual time scale, it is found that during the positive phase of the El Niño–Southern Oscillation (ENSO) more moisture from the Caribbean reaches CAM during boreal Spring and Autumn, in contrast to a marked decrease from the Pacific during Autumn. A comparison of our results with the work by Durán-Quesada et al. (2017) using the 3D FLEXPART model, suggests that the DRM has a bias in estimating the mean annual cycle of water vapor transport associated with the CLLJ wind shear. However, the DRM is able to capture the interannual variability of the moisture transport and its response to ENSO and anomalies in the low-level jets.

Comments on this paper
Teddy Allen
tangential questions
Thank you for sharing your work. I have just a few questions.
1) The summer peak in CLLJ intensity coincides with a cold SST tongue induced by upwelling. How does moisture transport via the CLLJ during the mid-summer (July) vary since the CLLJ and the local SST are indirectly related (high CLLJ, cooler SST)?

2) Do you know how ENSO impacts the Choco Jet? Do you know what are the origins of the Choco Jet?

3) Are you aware of any interactions between the Choco Jet and the CLLJ? I've often wondered if there is a relationship between these two patterns and the formation of the Panama Low during May-June.

Thank you!
José Morales
Hi Teddy
We didn’t have in account the SST on the analysis, we focused our analysis on the dynamic patterns of low-level jet through indexes. But, I think the moisture transport vary indirectly related to SST. Since, studies like developed by Wang (2007) and Amador (2008) suggest that when SST in the Caribbean is anomalously cold, the easterly CLLJ is anomalously strong, as suggest physical mechanism for the SST-SLP-CLLJ relationship. In our case, we found that when the CLLJ is anomalously strong, induce a largest transport from Atlantic to Central America and Tropical North Pacific (see Fig. 4 of the paper) (during mid-summer, when there is cooler SST).

yes, I know. The impacts of ENSO in the Choco jet (CJ) are different for each phase of this phenomena. During La Niña (El Niño), the CJ gets weak (strong) by affecting the contrast of temperature between the region Niño 1+2 and Pacific coast of Colombia. The origin of this structure is associated to the gradient of temperature between the region Niño 1+2 and Pacific coast of Colombia that induce a bending of the trade winds southeasterly and northeasterly. For more information you can see Poveda and Mesa (1998).

We aren’t aware of the interaction of this structure. But we found that the transport between the Pacific and Atlantic associated to these jets are contrasting. When the CJ is anomalously strong during August the transport from Pacific to Central America is anomalously strong, while the transport from Caribbean Sea is anomalously weak (see Fig. 4 of the paper). Additionally, we made some composite of wind at 925 hPa for anomalously strong CLLJ during August, and found that when this event is presented the CJ is anomalously weak, and vice versa.

Thank you for your interest!