Distúrbios ondulatórios de leste no nordeste brasileiro: climatologia e modelagem numérica

Abstract

A 21-year climatology of Easterly Wave Disturbances (EWDs) over NEB region was conducted in order to obtain a better understanding of dynamic and synoptic processes life cycle of these systems, including genesis, growth/decay, trajectory, and dissipation. Moreover, we evaluated the efficiency of WRF mesoscale model to simulate this type of system. The identification of DOLs 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. The main systems that gave rise to DOLs were: Intertropical Convergence Zone (ITCZ), Upper-Tropospheric Cyclonic Vortex (UTCV), Cold Fronts (FF), and convective clusters from the west coast of Africa (AF). In addition, the interaction between systems AF/FF, AF/ITCZ, AF/UTCV and ITCV/FF were associated with their formation. On average, we observed approximately 25 waves per year, with maximum (minimum) frequency between the months of March and August (September to February), and with pronounced interannual variability. The life cycle of EWDs was evaluated objectively using an automatic method for theidentification and tracking (TracKH). From the 518 events identified in the subjective analysis, TracKH was able to capture 342 waves (~66%). From this detection, an analysis was made at 850 hPa level to determine the characteristics of their life cycle, which shows a prominent peak around of 35ºW-15ºW and 20ºS-5ºN associated with density genesis. The trajectory and dissipation have concentrated over east coast of NEB, between the states of Alagoas and Rio Grande do Norte, but the dissipation decreased once the systems enter the continent. The synoptic patterns associated with EWDs were analyzed by composing anomaly during periods of maximum (wet) and minimum (dry) frequency from 3 days before until one day after the EWDs reaching the NEB coast. During the wet period, presented cyclonic and the confluent anomaly, negative vorticity, and convergence at all levels except at 200 hPa which only showed a trough characteristics while for the dry season, this feature was only observed at low levels. Negative anomalies of vertical movements and temperature and positive humidity associated with EWDs were observed in both seasons, but reaching higher ELEVATIONS during the dry period. Thr precipitation composition indicated that the EWDs are responsible for an increase of 16% (4%) during the wet season (dry). Typical characteristics of these waves were: mean period of 8 (73) days, wavelength of about 4500 (5500) km and phase velocity of about 6.5 (0.9) m.s-1, for the wet period (dry). The WRF model simulated the synoptic patterns, precipitation and the typical features associated with EWDs in a coherently manner, when compared to the results of the Climate Forecast System Reanalysis (CFSR), but with greater intensity, to the events of 11 and 17 June, 2006.