Climatic simulations of the eastern Andes low-level jet and its dependency on convective parameterizations

• Published in: Meteorology and atmospheric physics Vol. 108; no. 1-2; pp. 9 - 27
• Main Authors: da Silva, Maria Cristina Lemos, da Rocha, Rosmeri Porfírio, Ynoue, Rita Yuri
• Format: Journal Article
• Language: English
• Published: Vienna Vienna : Springer Vienna 01-09-2010; Springer Vienna; Springer; Springer Nature B.V
• Subjects: Aquatic Pollution; Atmospheric circulation; Atmospheric models; Atmospheric physics; Atmospheric Sciences; Climate; Climate models; Computer simulation; Criteria; Earth and Environmental Science; Earth Sciences; Earth, ocean, space; Exact sciences and technology; External geophysics; Horizontal; Low level; Math. Appl. in Environmental Science; Meteorology; Original Paper; Oscillations; Parametrization; Rainfall; Rainfall intensity; Simulation; Terrestrial Pollution; Tropical environments; Waste Water Technology; Water Management; Water Pollution Control; Wind; South America; Andes; Trinidad; Antilles; West Indies; Trinidad and Tobago; Lesser Antilles; Caribbean region; Andes Mountains; ASW, South America; ASW, Caribbean Sea, Trinidad and Tobago, Trinidad; South America, Andes Mts; Maximum Wind Speed; Meridional Wind; Wind Profile; Diurnal Cycle; Zonal Wind; Wind field; atmospheric precipitation; Regional scope; tropical zone; Summer; Climate models; Low level jet; subtropical zone; anomalies; Rainfall rate; diurnal variations; parametrization; Spatial distribution; winds; Composite analysis; Altitudinal distribution
• ISSN: 0177-7971; 1436-5065
• DOI: 10.1007/s00703-010-0077-9

The South American low level jet (SALLJ) of the Eastern Andes is investigated with Regional Climate Model version 3 (RegCM3) simulations during the 2002-2003 austral summer using two convective parameterizations (Grell and Emanuel). The simulated SALLJ is compared with the special observations of SALLJEX (SALLJ Experiment). Both the Grell and Emanuel schemes adequately simulate the low level flow over South America. However, there are some intensity differences. Due to the larger (smaller) convective activity, the Emanuel (Grell) scheme simulates more intense (weaker) low level wind than analysis in the tropics and subtropics. The objectives criteria of Sugahara (SJ) and Bonner (BJ) were used for LLJ identification. When applied to the observations, both criteria suggest a larger frequency of the SALLJ in Santa Cruz, followed by Mariscal, Trinidad and Asunción. In Mariscal and Asunción, the diurnal cycle indicates that SJ occurs mainly at 12 UTCs (morning), while the BJ criterion presents the SALLJ as more homogenously distributed. The concentration into two of the four-times-a-day observations does not allow conclusions about the diurnal cycle in Santa Cruz and Trinidad. The simulated wind profiles result in a lower than observed frequency of SALLJ using both the SJ and BJ criteria, with fewer events obtained with the BJ. Due to the stronger simulated winds, the Emanuel scheme produces an equal or greater relative frequency of SALLJ than the Grell scheme. However, the Grell scheme using the SJ criterion simulates the SALLJ diurnal cycle closer to the observed one. Although some discrepancies between observed and simulated mean vertical profiles of the horizontal wind are noted, there is large agreement between the composites of the vertical structure of the SALLJ, especially when the SJ criterion is used with the Grell scheme. On an intraseasonal scale, a larger southward displacement of SALLJ in February and December when compared with January has been noted. The Grell and Emanuel schemes simulated this observed oscillation in the low-level flow. However, the spatial pattern and intensity of rainfall and circulation anomalies simulated by the Grell scheme are closer to the analyses than those obtained with the Emanuel scheme.