Numerical simulation of a real case of multicell storm over Northeastern Argentina

TORRES BRIZUELA, MARCELA; NICOLINI, MATILDE

Foz do Iguaçu, Brazil

Conferencia; 8th International Conference on Southern Hemisphere Meteorology and Oceanography; 2006

American Meteorological Society

A multicellular storm, developed during the morning of 19 October, 2000 over the area of Resistencia (27¡ã27¡¯S, 59¡ã03¡¯W), Province of Chaco, Argentina. The synoptic environment of this event was studied using satellite images, radiosoundings and surface data provided by the National Weather Service and the NCEP reanalysis data set. Some evidences of typical conditions leading to bow-echo development were present in the environment: a moderate to high CAPE and a vertical wind shear with a high magnitude in the first 2.5km above ground level. Besides, satellite information displayed the evolution of a mesoscale convective system with a pattern and time length similar to the expected for bow-echoes. Unfortunately, this suspicion could not be strictly confirmed as no radar exists in the Chaco area.               In order to explore the possible formation and evolution of a bow-echo in this region given the related phenomena typically produced by these convective systems as severe winds, heavy precipitation and tornadoes, a mesoscale numerical model was used as a tool to simulate  this real storm case. The mesoscale model used was the ARPS, developed at the University of Oklahoma. The ARPS model was initialized in an homogeneous enviroment with a radiosounding at Resistencia (12UTC) and the convection was initiated with a warm bubble placed at the middle of the domain. Since the complicated enviromental wind profile, in terms of multiple changes in the vertical shear vector that makes a complex hodograph, two different numerical experiments have been performed. The first one (E1) was run with a smoothed hodograph in order to approach the evolution from a more idealized wind profile configuration. A second experiment with the real wind profile (E2) was conducted to compare real versus ideal conditions.               The evolution in the experiment E1 exhibited an explosive development with a complete cell splitting below 5km with a stronger intensification of the left flank updraft, coherent with the anticlockwise veering of the wind hodograph in the Southern Hemisphere. Later in the simulation the convective arrangement acquired a typical bow-echo configuration with strong rotational downdrafts in the apex of the convective line (book-end vortex) and a slight intensification of the wind in the rear part of the convective system at low-levels (¡Ö 2km). Experiment E2 displayed similar features to E1 but with a reinforcement of the right updraft instead, although the persistent character of its left cell. This persistence was explained by the merging of new developments at the gust-front in the eastern sector. The significant features of a bow-echo were more evident in the real experiment (E2). Both experiments exhibited extremely cold tops, in agreement with cold temperatures in the infrared satellite images.