Evolution of the Planetary Boundary Layer on the northern coast of Brazil during the CHUVA campaign

• Published in: Atmospheric research Vol. 203; pp. 298 - 310
• Main Authors: Ramos, Diogo Nunes da Silva, Fernandez, Julio Pablo Reyes, Fisch, Gilberto
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.05.2018
• Subjects: Atmospheric stability; Lapse rate; Nighttime precipitation; Tropical planetary boundary layer; Wind profile; Wind profile; Nighttime precipitation; Tropical planetary boundary layer; Lapse rate; Atmospheric stability
• ISSN: 0169-8095; 1873-2895
• DOI: 10.1016/j.atmosres.2017.12.016

This study aims to characterize the wind and thermodynamic structure of the Planetary Boundary Layer (PBL) on the northern coast of Brazil (NCB) via the CHUVA datasets. Three synoptic conditions were present in the NCB region between March 1 and 25, 2010: a dry period, the Upper Tropospheric Cyclonic Vortex (UTCV) and the Intertropical Convergence Zone (ITCZ). Nighttime precipitation accounted for 78% of the total precipitation observed in the month, mainly during the ITCZ. In general, the surface meteorological fields were few changed by intense weather events due to proximity to the ocean and the predominant contribution of the northeasterly trade winds. There was also a weak sea breeze signal that maintained the horizontal moisture flow in the studied area. On dry days, the PBL depth was higher, drier, and warmer, resulting in stronger winds below 500m. Moreover, trends throughout the period suggest that PBLs are near-neutral below 500m. However, the wind variability was intensified by up to 20% due to downdrafts and higher wind shears during the deep convection mechanisms derived by UTCV. Furthermore, ITCZ mixed rainfall cooled the PBL at approximately 2K, making it very stable according to the Richardson number classification adopted. The observed temporal and spatial scale represent challenges to the physical parameterizations used to improve numerical weather prediction models over tropical coastal areas. [Display omitted] •Nighttime precipitation was predominant with 78% of the total of the March 2010.•PBL evolution was favored by low thermal and moisture amplitude due to the coastal area.•Atmospheric stability near-surface is quasi-neutral, mainly on dry days.•UTCV modified the dynamic forcing of PBL by increasing wind shear.•ITCZ affected the PBL through strong cooling below 500m height.