Observational study of the South American low‐level jet during the SALLJEX

YABRA, MELINA SOL; NICOLINI, MATILDE; BORQUE, PALOMA; SKABAR, YANINA GARCIA; SALIO, PAOLA

INTERNATIONAL JOURNAL OF CLIMATOLOGY

JOHN WILEY & SONS LTD

Año: 2022

0899-8418

The South American low-level jet (SALLJ) is a narrow northerly wind speed maximumpresent just above the boundary layer. It is an important component of thetropical–extratropical heat and moisture exchange in South America and canfavour deep moist convection in southeastern South America. The main objectiveof this study is to analyse the SALLJ characteristics at 21 upper-air stationsdeployed between the Tropics and the subtropics from just east of the Andes tothe eastern plains during the SALLJ Experiment (SALLJEX). The greatest windspeed occurs between 300 and 2,000 m AGL between 0300 and 1200 UTC, mainlyin connection with greater northerly winds during an anticlockwise rotation ofthe wind from sunset to sunrise, thus suggesting the important role of the inertialoscillation in the wind's diurnal cycle. The spatial variation of the LLJ throughoutthe SALLJEX network shows a weakening of the maximum wind speed from stationsnear the Andes towards the Plains suggesting the presence of the LLJ corejust east of the Andes around Santa Cruz de la Sierra's latitude (17480S). Weak,moderate, and strong SALLJ categories defined from a local maximum northerlywind speed threshold at each station are defined to analyse the relationshipbetween the SALLJ intensity and the thermodynamic properties of the lowerlayers of the atmosphere. Strong SALLJs are frequently observed at night-time,while weak SALLJs are likely to occur at any time of the day. Strong cases havedeeper and less stable nocturnal boundary layers, which could be due to theSALLJ warm advection near the time of wind speed maximum (0600 UTC). Deeperconvective boundary layers and higher low-level temperatures observed at1800 UTC prior to strong nocturnal SALLJs can potentially lead to larger amplitudesof inertial oscillation and contribute to generating stronger SALLJs.