The western Colombia low-level jet and its simulation by CMIP5 models

The western Colombia low-level jet (a.k.a. Choco jet) is the result of a combination of several land-ocean-atmohsphere interactions (e.g., sea level pressure and surface temperature gradients, orographic lifting on the Andes, relationships with other jets). This low-level jet plays an important role in moisture transport from the Eastern Pacific Ocean to northwestern South America (mainly during boreal Fall) and its strengthening (weakening) during the cold (warm) ENSO phase partially explain the anomalies observed in streamflows and rainfall over the western and central Colombian regions. In addition, its interaction with the easterly trade winds from the Atlantic is a key element to trigger convection in this region. These processes help to explain the high precipitation values experienced over the Colombian Pacific coast (between 8.000 to 13.000 mm per year). In order to build confidence on model simulations and projections of future climat e in northern South America, we assess the ability of 26 Global Climate Models (GCM's) participating in the Coupled Model Intercomparison Project phase 5 (CMIP5) to simulate the general features of this jet (e.g., seasonal cycle, spatial distribution and location, vertical structure and intensity) and the processes involved in its dynamics. We also analyze the representation of the relationship between the El Niño Southern Oscillation and the strength of this jet. We use the historical experiment for both coupled and uncoupled GCMs from the CMIP and AMIP (Atmosphere Model Intercomparison Project) projects included in the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5). Although there are several previous studies about the representation of other low-level jets in America by GCMs (e.g., Caribbean low-level jet, Great Plains low-level jet), the representation of the Choco low-level jet has not been widely evaluated. A coherent representation of this low-level jet in northern South America by current GCMs generation could provide stronger reliability on climate change projections over the region.