CHOCO-JEX: A Research Programme Focused on the CHOCO Low-level Jet

over the Far Eastern Pacific and Western Colombia - Reanalysis Evaluation

IntroductionThe Choco low-level jet (ChocoJet) is a

prominent circulation feature of the Intra-

Americas climate over the far eastern Pacific.

This jet contribute to wet seasons over the

Colombian Pacific coast and southern Central

America (Poveda & Mesa, 1999; 2000). The

structure and dynamics of the ChocoJet have

been studied using reanalysis products, but no

permanent upper-air soundings have been put

in place on the region neither for improving the

understanding of the ChocoJet nor for

evaluating the reanalysis skills in capturing its

dynamical and thermodynamical features. This

work shows a validation assessment of diverse

reanalysis using independent upper-air

soundings off-shore and inland the Colombian

Pacific during the 2016 Choco-JEX field

campaigns.

Results

References

Objective

• Bao, X., & F. Zhang (2012), Evaluation of NCEP/CFSR, NCEP/ NCAR, ERA-Interim, and ERA-40 reanalysis datasets

against independent sounding observations over the Tibetan Plateau. J. Climate, 26, 206–214.

• Poveda, G., & O. J. Mesa (1999), La corriente de chorro superficial del oeste (del Chocó) y otras dos corrientes de

chorro en Colombia: Climatología y variabilidad durante las fases del ENSO. Rev. Acad. Colomb. Cienc, 89: 517–528.

• Poveda, G., & O. J. Mesa (2000), On the existence of Lloró (the rainiest locality on Earth): Enhanced ocean-atmosphere-

land interaction by a low-level jet”. Geoph. Res. Lett., Vol. 27, No. 11, 1675-1678.

Acknowledgments:We thanks to personnel from Colombian Air Force, the Colombian Navy and Universidad Tecnológica

del Chocó (UTCH) involved in the IOPs. The work of J. Yepes was supported by COLCIENCIAS

Doctorate Fellowship Program. The work of G. Poveda has been supported by Universidad Nacional

de Colombia, and the work of J. F. Mejía was supported by Desert Research Institute.

Johanna Yepes1, John F. Mejía2 and Germán Poveda1

1 Department of Geosciences and Environment, Universidad Nacional de Colombia, Sede Medellín, Colombia2 Desert Research Institute, Reno, NV, United States

e-mail: ljyepes@unal.edu.co

To evaluate the skill of different reanalyses on

their ability to characterize the observed upper

atmosphere environment of the ChocoJet over

the far Eastern Pacific.

Mean vertical profiles and STD of T, q, U, V contrasting ChocoJEX observations

against CFSR, Era-Interim, MERRA and NCEP/NCAR reanalysis

FIGURE 1. (Left Panel) Vertical profiles of mean temperature (°C) (first column), specific humidity (g/kg) (second column), zonal (third column)

and meridional wind (m/s) (four column) averaged over each independent IOP1 (first row), IOP2 (second row), IOP3 (third row) and IOP4 (four

row) ChocoJEX soundings and CFSR, Era Interim, MERRA, NCEP-NCAR reanalysis (Right Panel) As in left panel but for the STD.

Bias and RMSE of T, q, U, V contrasting ChocoJEX observations

against CFSR, Era-Interim, MERRA and NCEP/NCAR reanalysis

FIGURE 2. (Left Panel) Vertical profiles of mean biases for each reanalysis compared against the independent IOP1 (first row), IOP2

(second row), IOP3 (third row) and IOP4 (four row) ChocoJEX soundings. Columns show results for temperature (°C) (first column), specific

humidity (g/kg) (second column), zonal wind (third column) and meridional wind (m/s) (four column) (Right Panel) As in left panel for RMSE.

Data and Methodology

CHOCO-JEX Experiment

Discussion

A pioneering interinstitutional partnership

among the National University of Colombia,

the Colombian Air Force, the Colombian

Navy and the Desert Research Institute

(University of NV) involving 4 week-long

Intensive Observing Periods (IOP) in 2016,

using 6-hourly upper-air soundings :

• IOP1: January 15-22 (Off-Shore).

• IOP2: Quibdó, June 25-Jul 1 (Inland).

• IOP3: Quibdó, October 15-22 (Inland).

• IOP4: November 21-28 (Off-Shore)

• Temperature (T), Specific Humidity, Zonal (U)

and Meridional Wind (V) using MW41 Vaisala

system and Radiosonde RS41-SG.

• Same upper-air parametros were retrieved

from CFSR (0.5°grid size), Era-Interim (0.75°),

MERRA(1.25°) and NCEP/NCAR (2.5°).

• Maritime observations were averaged over an

area defined by the vessel track.

• Validation metrics: Vertical Mean Profiles, Bias,

Standard Deviation (STD), and RSME (Bao

and Zhang, 2012).

T q U V T q U V

IOP1

(Off-Shore)

IOP2

(Inland)

IOP3

(Inland)

IOP4

(Off-Shore)

IOP1

(Off-Shore)

IOP2

(Inland)

IOP3

(Inland)

IOP4

(Off-Shore)

T q U V T q U V

• Despite the short duration of the 4 IOPs, all reanalysis show acceptable mean vertical profiles for T, q, U and V.

Maritime mean wind profiles are in better agreement than those over land.

• During IOP4, CFSR, Era-Interim and MERRA show deeper and stronger low-level ChocoJet structure (+1 m/s),

whereas the coarse NCEP/NCAR reanalysis does not capture ChocoJet.

• During IOP1, all reanalysis underestimate the Standard Deviation of all variables. They all failed to capture the

relatively higher mid-level variability exhibited by T (0.6°C) and q (1g/kg).

• CFSR and MERRA show warm systematic bias at 700 hPa (IOP1=1.5 °C, IOP2=0.5 °C, IOP= 0.5°C, IOP4=0.5 °C).

Also, they show wetter (drier) troposphere at mid (superficial) levels in the oceanic IOPs.

• CFSR, Era-Interim and NCEP/NCAR underestimate easterlies in mid-levels (<2 m/s) and overestimate easterlies at

lower levels (<4 m/s) in IOP1. In contrast, same reanalysis overestimate both easterlies in mid-levels (<2 m/s) and

westerlies at superficial levels (<2 m/s) in IOP4.

• Large RMSE are linked to strong changes in synoptic conditions (not shown).