Abstract ID: 473

Squall Lines moving over Santarem

We document the large-scale atmospheric basic states in which different categories of eastern Amazon squall lines develop. Over five years we found 212 Squall Lines propagating inland from Amazon Atlantic Coast, but only 56% moved over Santarem (2o26’S, 54o43’W) with convective activity. Using the precipitation from CMORPH, during the period that the squall lines across Santarem (00 to 09 UTC), we verified that the squall lines moving over Santarem have more convective activity than do squall lines in other categories. The precipitation associated the squall line exibited a minimum at confluence of Tapajos and Amazon river. The precipitation in branch north squall lines is larger than south, perhaps because the north branch is located in a region where the topography is around 400 meters. Therefore, the precipitation observed during early morning by Fitzjarrald et al (2008) probably is associated these squall lines. For squall lines that reached Santarém, the sea breeze along the coast was stronger than it was for squall lines that dissipated closer to the coast. We note the presence of a relatively more intense low-level northerly jet for squall lines that reached Santarem. Simulation of a squall line that reached Santarem was performed using an atmospheric model in high resolution ('Control') calibrated with data available. We evaluated the influence of topography on development during this case study removing the topography of control experiment. Less precipitation associated the squall line occurred in the experiment without topography. This convective system propagated more slowly than did the one in the control experiment. A vertical cross-section across of the squall line shows structure comparable to that observed in tropical squall lines, with downdrafts bringing cold and dry air from high levels to near the surface.

Session:  Feedbacks to Climate - Land cover, surface hydrology, and atmospheric feedbacks. (A)

Presentation Type:  Oral