Low Level Jet Effects Upon the Surface Atmospheric Boundary-layer Wind Field Above Caxiuana Forest Reserve During Dry Season
Leonardo
Deane de Abreu
Sá, CPTEC-INPE/MPEG, ldsa@museu-goeldi.br
(Presenting)
Daniele
Santos
Nogueira, DM-UFPA, holywod@interconect.com.br
Julia Clarinda
Paiva
Cohen, DM-UFPA, jcpcohen@ufpa.br
In this work we investigate the occurrence of low-level jet (LLJ) events during the dry season in the nocturnal boundary-layer above the Caxiuana Forest Reserve. As LLJ we define a region of the wind velocity vertical profile located below 1 km height in which the strength of the wind is greater than 5 m/s and where there is a relative maximum value in such way that the wind velocity values decay at least 2 m/s just above and below the jet region. We use data collected during the CIMELA (Eastern Amazonia Mesoscale Circulations) Experiment, which took place in several eastern Amazonia sites during October-November 2003: i) radiossonde data to obtain vertical profiles of wind velocity to detect LLJs and to determine some mixing characteristics induced by them; ii) four "Vektor" cup anemometer (30 s sampling rate) located in a 54 m height meteorological tower installed in forest environment to obtain wind velocity profiles, both above and below the forest canopy. LLJs occurred in three different nocturnal profiles. Its mean height was approximately 550 m and its mean velocity value was often greater than 10 m/s. Some very strong wind events, lasting no more than 3 min, were been observed near 22 LT (local time), probably associated with LLJ mixing. Our interpretation is that "top-down" mixing induced by LLJ reaches the surface during these strong wind events. They have obvious consequences for forest-atmosphere exchange processes.