China-Brazil Joint Laboratory for Space Weather
; Chinese Academy of Science
; Programa de Nucleos de Excelencia-PRONEX [76.97.1079.00]
英文摘要:
Na lidar temperature measurements were taken successfully from 2007 to 2009 in the mesopause region over SAo Jose dos Campos (23.1 degrees S, 45.9 degrees W). Strong gradients on these vertical temperature profiles are often observed. A simple theoretical study has shown that temperature gradient of at least -8 K/km is required concurrently with the typical tidal wind shear in order to generate dynamical instability in the MLT region. We have studied vertical shear in horizontal wind related to atmospheric tides, inferred by meteor radar, with the aim of analyzing instability occurrence. These wind measurements were taken from an all-sky meteor radar at Cachoeira Paulista (22.7 degrees S, 45 degrees W). Two years of simultaneous data, wind and temperature, were used in this analysis which represent 79days, totalizing 589h of simultaneous observations. We realize that the condition for the local Richardson number (Ri) dropping below the critical value of instability (Ri<0.25) is often reached in 98% of the analyzed cases. The mean probabilities for occurrence of convective and dynamical instabilities, in the altitude region between 82 and 98km, were observed to be about 3% and 17.5%, respectively. Additionally, vertical distribution of these probabilities has revealed a weak occurrence of dynamical instability around 90km, and this fact can be related to the double mesopause typically observed in this site.
