Monday, 11 January 2016
A 21-year climatology of Easterly Wave Disturbances (EWDs) over the Northeast Brazil (NEB) region was constructed in order to obtain a better understanding of the dynamic and synoptic processes during the life cycle of these systems, including genesis, growth / decay, trajectory and dissipation. The identification of EWDs was obtained subjectively through satellite images in infrared channel and fields of streamlines and relative vorticity at the levels 1000, 850, 700, 500 and 200 hPa from ERA-Interim reanalysis. During this period, 518 EWDs were identified, where 97% (3%) of these waves hit (not hit) the NEB region, 64% (36%) were convective (non-convective) and 14% (86%) reached the Amazon region. On average, we observed approximately 25 waves per year, with maximum (minimum) frequency between the months of March to August (September to February) and, with pronounced interannual variability. The life cycle of EWDs was evaluated objectively using an automatic method for the identification and tracking (TracKH). From the 518 events identified in the subjective analysis, TracKH was able to capture 342 waves (~ 66%) using ERA-Interim data. From this detection, an analysis was made at the 850 hPa level to determine the characteristics of their life cycle, which shows a prominent peak around of 35°W-15°W and 20°S-5°N associated with the genesis density. The trajectory and dissipation are concentrated over the east coast of the NEB, between the states of Alagoas and Rio Grande do Norte, but the dissipation decreases once the systems enter the continent. The synoptic patterns associated with EWDs were analyzed by composing the anomalies during the period of maximum (wet) and minimum (dry) frequencies from 3 days before until one day after the EWDs reached the NEB coast. During the wet period, the circulation indicates cyclonic and confluent anomalies, negative vorticity and convergence at all levels except at 200 hPa which only shows a trough characteristic while for the dry season, this feature was only observed at low levels. Negative anomalies of vertical motion and temperature and positive anomalies of humidity are associated with EWDs in both seasons, but reaching higher elevations during the dry period.
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